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  • 1.
    Axen, N
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Abrasive wear in intermediate mode of multiphase materials1995In: TRIBOLOGY INTERNATIONAL, ISSN 0301-679X, Vol. 28, no 8, p. 523-529Article in journal (Refereed)
    Abstract [en]

    This article introduces the concept and a model of wear in intermediate (I) mode. Intermediate mode wear proceeds between two wear modes which correspond to upper and lower limits for the wear resistance which can be expected for a multiphase material. Th

  • 2.
    Beccu, R
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Wu, CM
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Reflection and transmission of the energy of transient elastic extensional waves in a bent bar1996In: JOURNAL OF SOUND AND VIBRATION, ISSN 0022-460X, Vol. 191, no 2, p. 261-272Article in journal (Refereed)
    Abstract [en]

    Reflection and transmission of the energy of a transient elastic extensional wave at a sharp or smooth bend of a bar are studied theoretically and experimentally, with the principal aim being to validate the model used by Wu and Lundberg in a parallel stu

  • 3.
    Berzi, P
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Beccu, R
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Identification of a percussive drill rod joint from its response to stress wave loading1996In: INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, ISSN 0734-743X, Vol. 18, no 3, p. 281-290Article in journal (Refereed)
    Abstract [en]

    In percussive drilling of rock, elastic stress waves are generated in a drill string through repeated axial impacts by the hammer of a rock drill. For holes deeper than a few meters, several drill rods are commonly joined by means of cylindrical coupling

  • 4. Bussac, Marie-Noёl
    et al.
    Collet, Pierre
    Gary, G.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Mousavi, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Viscoelastic impact between a cylindrical striker and a long cylindrical bar2008In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 35, no 4, p. 226-239Article in journal (Refereed)
    Abstract [en]

    Axial impact between a cylindrical striker of finite length and a long cylindrical bar, both of linearly viscoelastic materials, is considered. General results are derived for the impact force, the particle velocity and the strain in the bar in terms of closed-contour integrals. Such results are derived also for the transfer of momentum and energy from the striker to the bar. Numerical results for a striker and a bar made of the same material but with different cross-sectional areas are compared. In viscoelastic impact, unlike elastic impact, the duration of contact may be finite and larger than two transit times for a wave front through the striker due to the formation of a tail of finite length after the main pulse. Furthermore, multiple contacts and separations of the striker and the bar may occur within a range of striker-to-bar characteristic impedance ratios. In the case of viscoelastic impact studied numerically, the duration of contact is at least as long and the momentum and energy transferred are at most as large as in elastic impact. Strains measured at three locations of a polymethyl methacrylate (PMMA) bar impacted by strikers of the same material as the bar agree well with the theoretical results.

  • 5. Collet, Pierre
    et al.
    Gary, Gérard
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Noise-corrected Estimation of Complex Modulus in Accord With Causality and Thermodynamics: Application to an Impact test2013In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 80, no 1, p. 011018-Article in journal (Refereed)
    Abstract [en]

    Methods for estimation of the complex modulus generally produce data from which discrete results can be obtained for a set of frequencies. As these results are normally afflicted by noise, they are not necessarily consistent with the principle of causality and requirements of thermodynamics. A method is established for noise-corrected estimation of the complex modulus, subject to the constraints of causality, positivity of dissipation rate and reality of relaxation function, given a finite set of angular frequencies and corresponding complex moduli obtained experimentally. Noise reduction is achieved by requiring that two self-adjoint matrices formed from the experimental data should be positive semidefinite. The method provides a rheological model that corresponds to a specific configuration of springs and dashpots. The poles of the complex modulus on the positive imaginary frequency axis are determined by a subset of parameters obtained as the common positive zeros of certain rational functions, while the remaining parameters are obtained from a least squares fit. If the set of experimental data is sufficiently large, the level of refinement of the rheological model is in accordance with the material behavior and the quality of the experimental data. The method was applied to an impact test with a Nylon bar specimen. In this case, data at the 29 lowest resonance frequencies resulted in a rheological model with 14 parameters. The method has added improvements to the identification of rheological models as follows: (1) Noise reduction is fully integrated. (2) A rheological model is provided with a number of elements in accordance with the complexity of the material behavior and the quality of the experimental data. (3) Parameters determining poles of the complex modulus are obtained without use of a least squares fit.

  • 6.
    Edqvist, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Hedlund, Emma
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Quasi-static and dynamic electromechanical response of piezoelectric multilayer cantilever beams2010In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 157, no 2, p. 198-209Article in journal (Refereed)
    Abstract [en]

    Piezoelectric multilayer cantilever beams were considered with the aim to establish a simple but general theoretical model, fabricate such beams by a procedure suitable for devices on millimetre scale such as actuators, and study their quasi-static and dynamic electro-mechanical responses. In addition to Euler-Bernoulli assumptions, the beams were assumed to be lossless and have linear piezoelectric response. Four types of beams of nominal length 10 mm, width 2 mm and thickness either 55 or 86 µm, and with two asymmetric configurations of 14 or 15 layers, were fabricated. From top to bottom, each beam consisted of six aluminium electrode layers alternating with five active P(VDF-TrFE) layers, of one passive such layer, and of one polyimide and one copper layer, or vice versa. The thicknesses of the layers and of the beam were determined by use of focused ion beam, scanning electron microscope, light microscope, and Heidenhain probe. Both theoretical and experimental results for resonance frequencies and transverse tip displacement per unit driving voltage showed fair overall agreement from quasi-static conditions to frequencies above the second resonance frequency. Deviations observed are mainly due to variations resulting from the manufacturing process, to nonlinear piezoelectricity and to the presence of losses.

  • 7.
    Hillstrom, L
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Mathematics and Computer Science, Department of Information Technology, Automatic control. Hållfasthetslära.
    Mossberg, M
    Department of Engineering Sciences, Solid Mecanics. Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Mathematics and Computer Science, Department of Information Technology, Automatic control. Hållfasthetslära.
    Identification of complex modulus from measured strains on an axially impacted bar using least squares2000In: JOURNAL OF SOUND AND VIBRATION, ISSN 0022-460X, Vol. 230, no 3, p. 689-707Article in journal (Refereed)
    Abstract [en]

    The complex modulus of a material with linearly viscoelastic behaviour is identified on the basis of strains which are known, from measurements and sometimes from a free end boundary condition, at three or more sections of an axially impacted bar specimen

  • 8.
    Hillström, L
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Valdek, U
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Estimation of the state vector and identification of the complex modulus of a beam2003In: Journal of Sound and Vibration, Vol. 261, p. 653-673Article in journal (Refereed)
  • 9. Holmgren, S. -E.
    et al.
    Svensson, B. A.
    Gradin, P. A.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    An encapsulated split Hopkinson pressure bar for testing of wood at elevated strain rate, temperature, and pressure2008In: Experimental techniques (Westport, Conn.), ISSN 0732-8818, E-ISSN 1747-1567, Vol. 32, no 5, p. 44-50Article in journal (Refereed)
  • 10.
    Jansson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Damping of elastic strain waves by means of a piezoelectric bar element feeding an external RL circuit2008In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 314, no 1-2, p. 70-82Article in journal (Refereed)
    Abstract [en]

    Damping of elastic strain waves in an aluminum bar by means of a pair of piezoelectric members bonded to the bar and loaded by an external RL circuit is studied. Experimental results are compared with theoretical results based on a three-port impedance model for the laminated piezoelectric bar element (PBE). According to this model, the PBE is viewed as a linear system with one electrical and two mechanical ports at which interactions with external devices, e.g., the external parts of the aluminum bar, can take place. The two constitutive equations of the piezoelectric material, the dynamics of the piezoelectric members and the bar, and the dynamics of the resistive-inductive load are taken into account. The experimental results are below the theoretical ones by a few percent for the reflected and transmitted strain waves, by 6-11% for the voltage and current generated, and by 12-19% for the power and energy delivered to the load. This indicates that there are energy losses in the PBE and the external parts of the bars that have not been accounted for in the model. Such losses may be due to, e.g., viscoelastic shear, dielectric losses and generation of bending waves.

  • 11.
    Jansson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Piezoelectric generation of extensional waves in a viscoelastic bar by use of a linear power amplifier: Theoretical basis2007In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 306, no 1-2, p. 318-332Article in journal (Refereed)
    Abstract [en]

    A system consisting of a linear power amplifier driving a piezoelectric actuator pair attached to a long viscoelastic bar is analysed. Coupled piezoelectric theory is used, and allowance is made for the dynamics of the amplifier and of the actuators. Formulae are derived for the relation between the input voltage to the amplifier and the normal force associated with extensional waves generated in the bar and for the load impedance constituted by the actuator-bar assembly. It is established that the mechanical work performed on the external parts of the bar at the actuator/bar interfaces is at most equal to the electrical energy supplied by the amplifier. The results are applied to a three-parameter viscoelastic bar and to an elastic bar, and the effects of the cut-off frequency, without load, and the output impedance of the amplifier are examined. For the elastic bar, sharp response minima occur at frequencies that are integral multiples of the inverse transit time through the actuator region. For the viscoelastic bar, the corresponding minima are less sharp and deep. The input voltage to the amplifier required to produce a desired output wave at the actuator/bar interfaces can be determined provided that the spectrum of this wave is not too broad.

  • 12.
    Jansson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Three-port impedance model of a piezoelectric bar element: Application to generation and damping of extensional waves2008In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 315, no 4-5, p. 985-1002Article in journal (Refereed)
    Abstract [en]

    A straight bar element containing piezoelectric members is viewed as a linear system with one electrical and two mechanical ports where it can interact with external electrical and mechanical devices through voltage, current, forces and velocities. A generalized force vector, with one voltage and two forces as elements, is expressed as the product of an impedance matrix and a generalized velocity vector, with one current and two velocities, as elements. Due to symmetry and reciprocity, this matrix is defined by four of its nine elements. Two applications are considered for a piezoelectric bar element (PBE) that constitutes a part of a long elastic or viscoelastic bar, viz. generation and damping of extensional waves in the bar. In the first, the PBE is driven by a given input voltage or by the output voltage from a linear power amplifier. In the second, the PBE supplies an output voltage to an external load. In numerical simulations carried out for a specific laminated PBE, an elastic bar, a serial RL load and a bell-shaped incident wave, the highest fraction of wave energy dissipated was 8.1%. This is much less than the 50% achievable for a harmonic wave under condition of electrical impedance matching.

  • 13.
    Jansson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Valdek, Urmas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Generation of prescribed strain waves in an elastic bar by use of piezoelectric actuators driven by a linear power amplifier2007In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 306, no 3-5, p. 751-765Article in journal (Refereed)
    Abstract [en]

    The problem of generating prescribed strain waves in an elastic bar by means of a pair of piezoelectric actuators driven in phase by a linear power amplifier was considered theoretically and experimentally. The power amplifier was characterized by its DC voltage gain and 3 dB cut-off frequency unloaded, and by its output resistance and inductance. With the assumption of one-dimensional (1D) wave propagation in the bar, including the actuator region, a linear difference equation was derived for the required input voltage to the power amplifier in terms of the strain associated with the prescribed wave. This difference equation was solved numerically for a bell-shaped strain wave and for a single-period sine strain wave. After identification of the linear power amplifier, two tests were carried out with the aim to generate the two strain waves in an aluminium bar instrumented with semi-conductor strain gauges. Very good agreement was obtained between the implemented and required input voltages, output voltages and output currents of the power amplifier, and good agreement was achieved between the implemented and prescribed strain waves.

  • 14. Jansson, T.
    et al.
    Lundberg, BengtUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Dissipation and transmission of stress wave energy ata percussive drill rod joint2012Conference proceedings (editor) (Refereed)
  • 15. Lidén, Ewa
    et al.
    Andersson, Olof
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Deformation and fracture of a long-rod projectile induced by an oblique moving plate: Experimental test2011In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 38, no 12, p. 989-1000Article in journal (Refereed)
    Abstract [en]

    The influence of projectile length to diameter ratio (15, 30 and 45), plate thickness (0.5, 1 and 2 projectile diameters), projectile velocity (1500, 2000 and 2500 m/s) and plate velocity (−300 to 300 m/s) on the interaction between long-rod tungsten projectiles and oblique steel plates (obliquity 60°) was studied experimentally in small-scale reverse impact tests. The residual projectiles and their motions were characterised in terms of changes in length, velocity, angular momentum, linear momentum and kinetic energy. The parameters found to have the largest influence on the disturbance of the projectile were the plate velocity, in particular its direction, and the thickness of the plate. In the ranges studied, the influence of length to diameter ratio and of projectile velocity were found to be less important.

  • 16.
    Lidén, Ewa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mecanics.
    Johansson, B
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mecanics.
    Effect of thin oblique moving plates on long rod projectiles: a reverse impact study2006In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 32, no 10, p. 1696-1720Article in journal (Refereed)
    Abstract [en]

    The geometry and motion of long rod projectiles after penetrating thin obliquely oriented and moving armour plates were studied. Plates moving in their normal directions towards as well as away from the projectile (scalar product of velocities negative and positive, respectively) were considered. The influences of plate velocity and obliquity (angle between the normal of the plate and the axis of the projectile) were investigated through small-scale reverse impact tests with tungsten projectiles of length 30 mm and diameter 2 mm, and with 2 mm-thick steel plates. The obliquity (30°, 60° and 70°) and the plate velocity (300 to −300 m/s) were varied systematically for a projectile velocity of 2000 m/s. The disturbing effect of the plate on the projectile was characterised in terms of changes in length, velocity, angular momentum, linear momentum and kinetic energy. Plates with obliquity 60–70° moving away from the projectiles with velocity 200–300 m/s were found to cause extensive fragmentation of the projectile and to have large disturbing effects in terms of all measures used.

  • 17.
    Lidén, Ewa
    et al.
    FOI, Stockholm.
    Mousawi, Saed
    FOI, Stockholm.
    Helte, Andreas
    FOI, Stockholm.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Deformation and fracture of a long-rod projectile induced by an oblique moving plate: Numerical simulations2012In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 40-41, p. 35-45Article in journal (Refereed)
    Abstract [en]

    Simulations have been performed to evaluate the possibility of reproducing the fragmentation of a long-rod projectile impacted by a moving oblique plate. When the moving plate slides along the projectile, fractures due to shear loading may occur in the projectile. Therefore, a fracture model suggested by Xue–Wierzbicki was used for the projectile together with the Johnson–Cook strength model. This fracture model is based on an equivalent plastic strain of fracture which depends on a stress triaxiality and a deviatoric stress parameter. The results of the simulations were compared with experimental results of a preceding study in which the impact conditions were varied in such a way that the projectile fractured in some but not all tests. The comparisons show that the simulations reproduced the fractures in the projectile well. Also, the transition from a deformed non-fractured to a severely fractured projectile was captured. The benefit of including the deviatoric stress parameter and the mechanisms leading to fragmentation of the projectile are discussed.

  • 18.
    Lundberg, B
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Okrouhlik, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Approximate transmission-equivalence of elastic bar transitions under 3D conditions2002In: Journal of Sound and Vibration, Vol. 256, no 5, p. 941-954Article in journal (Refereed)
  • 19.
    Lundberg, B
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Hållfasthetslära.
    Okrouhlik, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Hållfasthetslära.
    Efficiency of a percussive rock drilling process with consideration of wave energy radiation into the rock2005In: Int.J.Impact EngngArticle in journal (Refereed)
  • 20.
    Lundberg, B
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Okrouhlik, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Influence of 3D effects on the efficiency of percussive rock drilling2001In: Int. J. Impact Engng, Vol. 25, p. 345-360Article in journal (Refereed)
  • 21.
    Lundberg, B
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Ödeen, S
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    In situ determination of the complex modulus from strain measurements on an impacted structure1993In: Journal of Sound and Vibration, Vol. 167, p. 413-419Article in journal (Refereed)
  • 22.
    Lundberg, Bengt
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Collet, P.
    Centre de Physique Theorique.
    Optimal wave shape with respect to efficiency in percussive drilling with detachable drill bit2015In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 86, p. 179-187Article in journal (Refereed)
    Abstract [en]

    Abstract The problem of finding the optimal incident wave of given duration that maximizes the efficiency of conversion of wave energy into work in percussive drilling with detachable drill bit is considered. The drill rod is modelled as 1D linearly elastic and the drill bit as a rigid mass. The bit/rock interaction is described by a history-dependent force versus penetration relation with different constant slopes for primary loading and unloading/reloading. A functional expressing the dependence of the efficiency on the shape of an arbitrary incident wave of given duration is derived and maximized. For short incident waves, there is a weak influence of the bit mass on the optimal wave shape which is nearly rectangular. For longer incident waves, there is a strong influence of the bit mass on the optimal wave shape which significantly differs from rectangular. The efficiencies for optimal waves approach those for rectangular waves for short waves. For long waves they approach or assume values which are independent of wave duration but decrease with increasing bit mass. Relative to commonly-used rectangular waves significant increase in efficiency can be achieved through optimization of the wave shape if the wave is not too short. Optimal incident waves can be realized accurately, e.g., by piezoelectric means.

  • 23.
    Lundberg, Bengt
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Collet, P.
    Optimal wave with respect to efficiency in percussive drilling with integral drill steel2010In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 37, no 8, p. 901-906Article in journal (Refereed)
    Abstract [en]

    The problem considered is that of finding the optimum wave of given finite duration that maximizes the efficiency of conversion of wave energy into work in percussive drilling with integral drill steel (drill rod with integrated bit). A 10 model is used for the drill rod, and the bit-rock interaction is represented by a piecewise linear force versus penetration relation with different penetration resistances for primary loading and for unloading/reloading. A functional expressing the dependence of the efficiency on the incident wave is derived and maximized. The optimal incident wave has exponential shape with time constant for the growth rate equal to the characteristic response time of the percussive drill system, including the rock. The maximal efficiency increases monotonously with the duration of the optimal wave. It approaches zero for very short waves and unity for very long waves. Optimal waves of short duration are close to rectangular while those of long duration approach the semi-infinite exponential wave derived by Long in the 1960s. Optimal waves of medium or longer duration give significantly higher efficiencies than commonly used rectangular waves of the same duration.

  • 24.
    Lundberg, Bengt
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Huo, J.
    Sandvik Min & Rock Technol, R&D Dept Min Tools, SE-81181 Sandviken, Sweden..
    Biconvex versus bilinear force-penetration relationship in percussive drilling of rock2017In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 100, p. 7-12Article in journal (Refereed)
    Abstract [en]

    Because of variability of the force vs. penetration relationship (FPR) from one blow to another in percussive drilling, and difficulty to predict FPRs under such conditions, use is commonly made of simple FPR models, such as the bilinear one defined by its loading/unloading slopes. Here a biconvex model with an added parameter representing convexity is considered. One aim is to study the effect of convexity on maximal penetration, maximal force and efficiency. Another is to assess, with the biconvex FPR as an example, how well a bilinear FPR can be used to approximate one that is nonlinear. A simple percussive top-hammer drill model is considered, comprising a hammer, a drill rod and a bit with the same characteristic impedance. The maximal penetration is found to decrease and the maximal force to increase with increasing convexity. The efficiency has a maximum for a finite hammer length (incident wave duration), and the highest maximal efficiency is obtained for a linear FPR With increasing convexity, the maximal efficiency decreases and occurs for shorter hammers (incident waves). The bilinear approximation of a biconvex FPR accurately predicts the position of the maximum in efficiency, even for large convexity, but somewhat overestimates its height and width.

  • 25.
    Lundberg, Bengt
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics. Hållfasthetslära.
    Okrouhlik, M
    Efficiency of a percussive rock drilling process with consideration of wave energy radiation into the rock2006In: Int. J. Impact Engng, Vol. 32, p. 1573-1583Article in journal (Refereed)
  • 26.
    Lundberg, Patrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Transition between interface defeat and penetration for tungsten projectiles and four silicon carbide materials2005In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 31, no 7, p. 781-792Article in journal (Refereed)
    Abstract [en]

    Armour systems containing high-quality ceramics may be capable of defeating armour-piercing projectiles on the surfaces of these hard materials. This capability, named interface defeat, has been studied for four different silicon carbide ceramic materials, viz., SiC–B, SiC–N, SiC–SC–1RN and SiC–HPN by use of a light-gas gun and a small-scale reverse impact technique. The velocities of a tungsten projectile marking the transition between interface defeat and penetration have been determined and compared with the Vickers hardness and fracture toughness of the ceramic materials. It is found that the transition velocity increases with the fracture toughness but not with the Vickers hardness. This indicates that, under the prevailing conditions, fracture may have had more influence than plastic flow on the transition. As a consequence, the observed transition velocities may not be the maximum ones achievable, at least not for SiC–B, SiC–N and SiC–SC–1RN. By suppression of the initiation and propagation of cracks through increase of the confining pressure, it may be possible to increase the transition velocities.

  • 27.
    Lundberg, Patrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Renström, René
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Impact of conical tungsten projectiles on flat silicon carbide targets: Transition from interface defeat to penetration2006In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 32, no 11, p. 1842-1856Article in journal (Refereed)
    Abstract [en]

    Normal impact of conical tungsten projectiles on flat silicon carbide targets was studied experimentally and numerically for half apex angles 5° and 5–15°, respectively, and comparisons were made with cylindrical projectiles. A 30 mm powder gun and two 150 kV and four 450 kV X-ray flashes were used in the impact tests. The numerical simulations were run with the Autodyn code in two steps. In the first, the surface loads were determined for different impact velocities under assumed condition of interface defeat. In the second, these surface loads were applied to the targets in order to obtain critical states of damage and failure related to the transition between interface defeat and penetration, and the corresponding critical velocities. In the impact tests, interface defeat occurred below a transition velocity, which was significantly lower for the conical than for the cylindrical projectiles. Above the transition velocity, the initial penetration of conical projectiles differed markedly from that usually observed for cylindrical projectiles. It occurred along a cone-shaped surface crack, qualitatively corresponding to surface failure observed in the simulations. The transition velocity for the conical projectile was found to be close to the critical velocity associated with this surface failure.

  • 28.
    Lundberg, Patrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Westerling, Lars
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Influence of scale on the penetration of tungsten rods into steel-backed alumina targets1996In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 18, no 4, p. 403-416Article in journal (Refereed)
    Abstract [en]

    As ballistic tests are often performed in reduced geometrical scale, the scaling laws are important for the interpretation of the results. In this study, we tested the validity of replica scaling, by which we mean that all geometrical dimensions are scaled uniformly, while the materials and the impact velocity are kept the same. Long tungsten projectiles with length-to-diameter ratio 15 were fired against unconfined alumina targets with steel backing. The tests were carried out with impact velocities 1500 m s−1 and 2500 m s−1, and in three different scales with projectile lengths 30, 75 and 150 mm (diameters 2, 5 and 10 mm). The alumina targets were photographed by means of a high-speed camera, and the tungsten projectiles were photographed inside the alumina targets by means of flash radiography. Also, the residual penetrations in the steel backings were measured. The Johnson-Holmquist model for ceramic materials was implemented into the AUTODYN code, which was used for simulation of the experiments. The agreement between results of experiment and simulation was fair, and over the tested interval of scales replica scaling was found to be valid with reasonable accuracy.

  • 29.
    Mohr, Dirk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gary, Gerard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Evaluation of stress-strain curve estimates in dynamic experiments2010In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 37, no 2, p. 161-169Article in journal (Refereed)
    Abstract [en]

    Accurate measurements of the forces and velocities at the boundaries of a dynamically loaded specimen may be obtained using split Hopkinson pressure bars (SHPB) or other experimental devices. However, the determination of a representative stress-strain curve based on these measurements can be challenging. Due to transient effects, the stress and strain fields are not uniform within the specimen. Several formulas have been proposed in the past to estimate the stress-strain curve from dynamic experiments. Here, we make use of the theoretical solution for the waves in an elastic specimen to evaluate the accuracy of these estimates. it is found that it is important to avoid an artificial time shift in the processing of the experimental data. Moreover, it is concluded that the combination of the output force based stress estimate and the average strain provides the best of the commonly used stress-strain curve estimates in standard SHPB experiments.

  • 30.
    Mousavi, S
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Identification of complex moduli and Poisson's ratio from measured strains on an impacted bar2003In: 5thEuromech Solid Mechanics Conference ESMC-5, 2003, p. 424-Conference paper (Other scientific)
  • 31.
    Mousavi, S
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Nicolas, D F
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Identification of complex moduli and Poisson's ratio from measured strains on an impacted bar.2004In: Journal of Sound and Vibration, Vol. 277, p. 971-989Article in journal (Refereed)
  • 32.
    Mousavi, Saed
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Hillström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Identification of complex shear modulus from measured shear strains on a circular disc subjected to transient torsion at its centre2008In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 313, no 3-5, p. 567-580Article in journal (Refereed)
    Abstract [en]

    A method for identification of complex shear modulus from measured shear strains on a circular disc subjected to a transient torque at its centre has been established. It is based on the evolution of an outgoing shear wave between two radial positions at which the associated shear strains are measured. The two-dimensional shear wave solutions used are exact in the sense of three-dimensional theory. Therefore, in principle, there is no frequency beyond which they are not valid. The method requires a minimum disc size, which is related to the duration of the load. The non-parametric results become inaccurate at frequencies near zero and at certain problematic frequencies where the excitation of the disc is weak or non-existent. These frequencies may be moved outside the frequency range of interest by sufficiently decreasing the duration of the load. If there are problematic frequencies within this range, the results of parametric identification become more accurate than those of non-parametric identification. Parametric results from experimental tests with loads having different amplitudes and durations agree well with each other in accord with the assumed linearity of the tested polypropylene material.

  • 33.
    Mousavi, Saed
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Valdek, Urmas
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Welch, Ken
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Lundberg, Bengt
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    SHPB technique for identification of complex modulus under condition of non-uniform stress2004In: ICTAM04 Abstracts and CD-ROM Proceedings, 2004, p. 446-Conference paper (Other academic)
  • 34.
    Nauclér, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    A mechanical wave diode: Using feedforward control for one-way transmission of elastic extensional waves2007In: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865, Vol. 15, no 4, p. 715-724Article in journal (Refereed)
  • 35.
    Norlander, Hans
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Valdek, Urmas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Parameter estimation from wave propagation tests on a tube perforated by helical slots2013In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 40, no 1, p. 385-399Article in journal (Refereed)
    Abstract [en]

    For a tube with doubly symmetric cross section and perforations by helical slots there is a coupling between extension and torsion. In this paper a one dimensional (1D) model structure for a tube with such a helical slot segment (HSS) is established, and parameters accounting for the coupling between extension and torsion are estimated from wave propagation experiments. In these experiments incident extensional waves were generated through axial impact by strikers of different lengths, causing reflected and transmitted waves of extensional and torsional type which were measured in terms of surface strains on either side of the HSS part of the tube. A statistical test on the experimental data shows that the output residuals (the difference between modeled and experimental output) cannot be explained by measurement noise alone. This is not surprising since the 1D model structure is based on some simplifying assumptions concerning the geometry of the HSS. Parameters for two different geometries of the HSS are estimated, and the models are assessed in terms of model fa, simulations and wave energy distribution. It turns out that for one case, where the geometrical assumptions are valid, the 1D model is adequate, while for another case, where the validity of the assumptions is questionable, it is not. It is concluded that the 1D model structure provides a simple and efficient description of the HSS if the geometrical assumptions are valid.

  • 36.
    Nygren, T
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Andersson, LE
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Optimization of elastic junctions with regard to transmission of wave energy1999In: WAVE MOTION, ISSN 0165-2125, Vol. 29, no 3, p. 223-244Article in journal (Refereed)
    Abstract [en]

    Transmission of the energy of an incident extensional wave through an elastic junction between two uniform and collinear bars is considered. The junction consists of a finite number of uniform segments with equal transit times. We seek the optimum junctio

  • 37.
    Nygren, T
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Andersson, L-E
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Optimum transmission of waves through a non-uniform viscoelastic junction between elastic bars1996In: Eur. J. Mech., A/Solids, Vol. 15, no 1, p. 29-49Article in journal (Refereed)
  • 38.
    Nygren, T
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Andersson, LE
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Synthesis of elastic junctions with wave transmission properties of a given junction1999In: WAVE MOTION, ISSN 0165-2125, Vol. 30, no 2, p. 143-158Article in journal (Refereed)
    Abstract [en]

    Transmission of extensional waves through elastic junctions between two uniform and collinear elastic bars with given characteristic impedances was studied with the aim to synthesize all junctions with the transmission properties of a given junction. For

  • 39.
    Nygren, T
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Andersson, L-E
    Dissipation of wave energy in a viscoelastic junction between elastic bars: Dependence on transmission direction1997In: Journal of Sound and Vibration, Vol. 199, p. 323-336Article in journal (Refereed)
  • 40.
    Nygren, T
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Andersson, L.-E
    Optimisation of viscoelastic junctions with regard to transmission of wave energy2001In: Journal of Sound and Vibration, Vol. 240, no 3, p. 467-481Article in journal (Refereed)
  • 41. Okrouhlik, M.
    et al.
    Ptak, S.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Valdek, Urmas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    FE assessment of an experiment employed for analysis of the transient stress energy flux through spiral slots in axially impacted cylindrical tube2009In: Strojnicky Casopis, ISSN 0039-2472, Vol. 60, no 4, p. 181-209Article in journal (Refereed)
    Abstract [en]

    The temporal and spatial distribution of the stress wave energy flux in an axially impacted cylindrical tube, whose middle part contains four spiral slots, is studied experimentally and numerically. The high-speed recording of transient surface strains was used in the experiment, while the 3D finite element treatment was employed for the numerical analysis. The aim of the paper is to ascertain how reliable is the energy assessment based on transient recordings of surface strains and on subsequent 1D wave theory reasoning. The presented paper quantitatively determines how much of the impact energy, which is predominantly of axial (longitudinal) nature, is transferred into torsional (or shear) energy mode as well as to other energy modes not seen by the experiment.

  • 42.
    Ravasoo, A
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Nonlinear interaction of longitudinal waves in an inhomogeneously predeformed elastic medium2001In: Wave Motion, Vol. 34, no 2, p. 225-237Article in journal (Refereed)
  • 43.
    Renström, René
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Patrik
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Self-similar flow of a conical projectile on a flat target surface under conditions of dwell2009In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 36, no 2, p. 352-362Article in journal (Refereed)
    Abstract [en]

    In order to investigate the state of stress in a target material under conditions of interface defeat or dwell it is necessary to determine the load intensity at the interface of the flowing projectile material and the target. Previous studies for a cylindrical projectile geometry at normal impact under stationary conditions show that the load can be considered to be composed of three components, viz., those of inertia, compressibility and yield strength of the projectile material. In order to determine the influence of projectile shape, a conical projectile in axi-symmetric impact on a ridged, friction-free surface is studied by use of an analytical model for self-similar flow and numerical Autodyn simulations. It is shown how the maximum load intensity, and the position of the maximum, depends on the apex angle. Both the self-similar model and the Autodyn simulations show that the contribution to the load intensity from compressibility is positive below and negative above apex angles 80°. The influence of yield strength on the load intensity depends only weakly on the apex angle and therefore corresponds to that for a cylindrical projectile.

  • 44.
    Renström, René
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Lundberg, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Stationary contact between a cylindrical metallic projectile and a flat target surface under conditions of dwell2004In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 30, no 6, p. 1265-1282Article in journal (Refereed)
    Abstract [en]

    Armour systems capable of defeating an incoming projectile on the surface of a ceramic target have been reported. This capability, called interface defeat or dwell, signifies that the projectile material is forced to flow radially on the surface of the target without penetrating significantly. Under such flow conditions, the hydrodynamic pressure is normally the most important part of the normal load on the target surface. Therefore, projectile properties such as yield strength and compressibility are commonly ignored or assumed to contribute only marginally. In order to investigate the effects of these properties, an analytical expression was derived for the normal load from a cylindrical metallic projectile impacting on a flat, rigid and friction-free surface, which includes the contributions from yield strength and compressibility in addition to that of inertia. At an impact velocity representative of today's ordinance velocities, the contributions to load intensity on the axis from yield strength and compressibility were found to be 15% and 3.4%, respectively, of that of inertia. The analytical results and Autodyn-2D numerical simulations show good agreement within a projectile radius from the axis.

  • 45.
    Trendafilova, I
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Ödeen, S
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Identification of viscoelastic materials from electro-optical displacement measurements at two sections of an impacted rod specimen1994Other (Other scientific)
  • 46.
    Welch, Ken
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Mousavi, Saed
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strømme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mecanics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Viscoelastic characterization of compacted pharmaceutical excipient materials by analysis of frequency-dependent mechanical relaxation processes2005In: The European Physical Journal E Soft matter, ISSN 1292-8941, E-ISSN 1292-895X, Vol. 18, no 1, p. 105-112Article in journal (Refereed)
    Abstract [en]

    A newly developed method for determining the frequency-dependent complex Young's modulus was employed to analyze the mechanical response of compacted microcrystalline cellulose, sorbitol, ethyl cellulose and starch for frequencies up to 20 kHz. A Debye-like relaxation was observed in all the studied pharmaceutical excipient materials and a comparison with corresponding dielectric spectroscopy data was made. The location in frequency of the relaxation peak was shown to correlate to the measured tensile strength of the tablets, and the relaxation was interpreted as the vibrational response of the interparticle hydrogen and van der Waals bindings in the tablets. Further, the measured relaxation strength, holding information about the energy loss involved in the relaxation processes, showed that the weakest material in terms of tensile strength, starch, is the material among the four tested ones that is able to absorb the most energy within its structure when exposed to external perturbations inducing vibrations in the studied frequency range. The results indicate that mechanical relaxation analysis performed over relatively broad frequency ranges should be useful for predicting material properties of importance for the functionality of a material in applications such as, e.g., drug delivery, drug storage and handling, and also for clarifying the origin of hitherto unexplained molecular processes.

  • 47.
    Westerling, L
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Lundberg, P
    Holmberg, L
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    High velocity penetration of homogeneous, segmented and telescopic projectiles into alumina targets1997In: Int. J. Impact Engng, Vol. 20, p. 817-827Article in journal (Refereed)
  • 48.
    Westerling, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Stresses in a long cylindrical conductor moving axially through a pair of electrode plates under stationary conditions2013In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 80, no 2, p. 021013-Article in journal (Refereed)
    Abstract [en]

    In a conductor carrying electric current, the Lorentz force gives rise to mechanical stresses. Here, we study a long elastic cylindrical conductor that moves axially with constant velocity through two electrode plates. The aims are to explore how the stresses in the conductor depend on the velocity in the stationary case of constant current and to assess the validity of the analytic method used. The diffusion equation for the magnetic flux density is solved by use of Fourier transform, and the current density is determined. The stresses, due to the Lorentz force, are found by use of an analytic method combining the solutions of a quasi-static radial problem of plane deformation and a dynamic axial problem of uniaxial stress. They are also determined through FE analysis. Radial field profiles between the plates indicate a velocity skin effect signifying that the current and the magnetic field are concentrated near the cylindrical surface up-stream and are more uniformly distributed downstream. The radial and hoop stresses are compressive, while the axial stress is tensile. The von Mises effective stress increases towards the symmetry axis, in the downstream direction, and with velocity. There are circumstances under which a large current can produce an effective stress in a copper conductor of the order of the yield stress without causing a significant temperature rise. The stresses obtained with the two methods agree well, even relatively near the electrode plates. The analytical method should be useful in similar cases as well as for the provision of test cases for more general simulation tools.

  • 49.
    Westerling, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Lundberg, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Lundberg, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
    Tungsten long-rod penetration into confined cylinders of boron carbide at and above ordnance velocities2001In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 25, no 7, p. 703-714Article in journal (Refereed)
    Abstract [en]

    The purpose was to investigate the influence of impact velocity and confinement on the resistance of boron carbide targets to the penetration of tungsten long-rod projectiles. Experimental tests with impact velocities from 1400 to 2600 m/s were performed using a two-stage light-gas gun and a reverse impact technique. The targets consisted of boron carbide cylinders confined by steel tubes of various thicknesses. Simulations were carried out using the AUTODYN-2D code and Johnson–Holmquist's constitutive model with and without damage evolution. The experimental results show that the penetration process had different character in three different regions. At low-impact velocities, no significant penetration occurred. At high-impact velocities, the relation between penetration velocity and impact velocity was approximately linear, and the penetration was steady and symmetrical. In between, there was a narrow transition region of impact velocities with intermittent and strongly variable penetration velocity. In the lower part of this region, extended lateral flow of the projectile took place on the surface of the target. The influence of confinement on penetration velocity was found to be small, especially at high-impact velocities. The simulated results for penetration velocity versus impact velocity agreed fairly well with the experimental results provided damage evolution was suspended below the transition region.

  • 50.
    Widehammar, S
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Gradin, P A
    Lundberg, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of Engineering Sciences, Solid Mecanics. Hållfasthetslära.
    Approximate determination of phase velocities and displacement fields associated with elastic waves in bars: method based on matrix formulation of Hamilton’s principle2001In: Journal of Sound and Vibration, Vol. 246, no 5, p. 853-876Article in journal (Refereed)
12 1 - 50 of 53
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