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Holmberg, Anders
Publications (3 of 3) Show all publications
Holmberg, A., Andersson, M. & Kassman Rudolphi, Å. (2019). Rolling fatigue life of PM steel with different porosity and surface finish. Paper presented at 22nd International Conference on Wear of Materials (WOM), APR 14-18, 2019, Miami, FL. Wear, 426-427(Part A), 454-461
Open this publication in new window or tab >>Rolling fatigue life of PM steel with different porosity and surface finish
2019 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 426-427, no Part A, p. 454-461Article in journal (Refereed) Published
Abstract [en]

Gears made of PM steel are of interest for the automotive industry because they can be produced to near net shape with only a few processing steps. Automotive gears experience a complex contact situation with rolling as well as combined rolling and sliding. They also have to be able to withstand high loads and fairly high temperature variations. Earlier work show that the main limiting parameter of the contact fatigue life of PM steel is the porosity. A higher porosity/lower density will decrease the fatigue life of the PM component. In the present study, the pure rolling contact fatigue life of PM steel with different density and surface finish has been investigated. A rolling contact fatigue test rig, where rods of the tested material are mounted between two rolling wheels, was used. Two densities of PM steel, 6.8 and 7.15 g/cm(3) and a full density reference steel with two different surface finishes, centerless grinded and superfinished, were tested. The tests were run for a given number of load cycles or until failure (fatigue life). SEM was used to study the surfaces and cross-sections to reveal the mechanisms of crack initiation and propagation. The higher density PM steel (7.15 g/cm(3)) outperformed the lower density steel (6.18 g/cm(3)) by a factor of around 4 in fatigue life at the same surface pressure, regardless of surface finish. Cracks are initiated at a depth of around 100 mu m. These cracks propagate and eventually they reach the surface, causing surface damage and failure. For the low density PM steel, both sub surface crack initiation and failure occurred earlier (at a lower number of load cycles) than for the higher density PM steel. Severe surface damage or wear were not found until failure occurred. Still, some initial alteration of the surfaces was seen already after 0.5 million load cycles, in the form of removal of the highest asperity peaks on the centerless grinded surfaces, and opening of the surface pores on the superfinished surface. No effect of surface finish was found on the fatigue life. The difference in surface roughness could induce a difference in local stress concentrations at the surface, but in this test the cracks causing fatigue failure are initiated at a depth where the stress distribution is not affected by local surface stress concentrations. This means that for fairly smooth surfaces roughness, the surface of PM steel is not important when it comes to pure rolling fatigue life.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Rolling contact fatigue, Porosity, PM steel, Gears
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:uu:diva-382823 (URN)10.1016/j.wear.2019.01.006 (DOI)000464583700049 ()
Conference
22nd International Conference on Wear of Materials (WOM), APR 14-18, 2019, Miami, FL
Funder
Swedish Foundation for Strategic Research , GMT14-0045
Available from: 2019-05-06 Created: 2019-05-06 Last updated: 2019-05-06Bibliographically approved
Ajaxon, I., Holmberg, A., Öhman, C. & Persson, C. (2018). Fatigue performance of a high-strength, degradable calcium phosphate bone cement. Journal of The Mechanical Behavior of Biomedical Materials, 79, 46-52
Open this publication in new window or tab >>Fatigue performance of a high-strength, degradable calcium phosphate bone cement
2018 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 79, p. 46-52Article in journal (Refereed) Published
Abstract [en]

Calcium phosphate cements (CPCs) are clinically used as injectable materials to fill bone voids and to improve hardware fixation in fracture surgery. In vivo they are dynamically loaded; nonetheless little is known about their fatigue properties. The aim of this study was to, for the first time, investigate the fatigue performance of a high strength, degradable (brushitic) CPC, and also evaluate the effect of cement porosity (by varying the liquid to powder ratio, L/P) and the environment (air at room temperature or in a phosphate buffered saline solution, PBS, at 37 degrees C) on the fatigue life. At a maximum compressive stress level of 15 MPa, the cements prepared with an L/P-ratio of 0.22 and 0.28 ml/g, corresponding to porosities of approximately 12% and 20%, had a 100% probability of survival until run-out of 5 million cycles, in air. When the maximum stress level, or the L/P-ratio, was increased, the probability of survival decreased. Testing in PBS at 37 degrees C led to more rapid failure of the specimens. However, the high-strength cement had a 100% probability of survival up to approximately 2.5 million cycles at a maximum compressive stress level of 10 MPa in PBS, which is substantially higher than some in vivo stress levels, e.g., those found in the spine. At 5 MPa in PBS, all specimens survived to run-out. The results found herein are important if clinical use of the material is to increase, as characterisation of the fatigue performance of CPCs is largely lacking from the literature.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Bone cement, Calcium phosphate, Brushite, Fatigue, Compression, Porosity, Mechanical properties
National Category
Medical Materials
Identifiers
urn:nbn:se:uu:diva-347539 (URN)10.1016/j.jmbbm.2017.12.005 (DOI)000425072300006 ()29272812 (PubMedID)
Funder
Swedish Research Council, 621-2011-6258
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-09Bibliographically approved
Toller-Nordström, L., Gee, M., Holmberg, A., Mingard, K., Lilja, M. & Norgren, S. Abrasive wear of hardmetals with a binder phase forming deformation induced martensite.
Open this publication in new window or tab >>Abrasive wear of hardmetals with a binder phase forming deformation induced martensite
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Hardmetals with alternative binder phases with compositions tailored for specific applications may be used to achieve improved performance of tools. In this paper an iron based binder phase that has previously been found to undergo a phase transformation from austenite to martensite as a response to plastic deformation is tested in three different tests: Micro scratch tests, micro abrasion and rock turning. All three tests show characteristic wear of the tungsten carbide and removal of binder phase from the surface.

Keywords
hardmetal, alternative binders, cemented carbides, rock drilling, microscale abrasion, micro scratch testing
National Category
Engineering and Technology Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-395618 (URN)
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-11-06
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