A computational study of the influence of surface roughness on material strength
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In machine component stress analysis, it usually assumed that the geometry specified in CAD provides a fair representation of the geometry of the real component. While in particular circumstances, tolerance information, such as minimum thickness of a highly stressed region, might be taken into consideration, there is no standard practice for the representation of surface quality. It is known that surface roughness significantly influences fatigue life, but for this to be useful in the context of life prediction, there is a need to examine the nature of surface roughness and determine how best to characterise it. Non-smooth geometry can be represented in mathematics by fractals or other methods, but for a representation to have a practical value for a manufactured component, it is necessary to accept that there is a lower limit to surface profile measurement resolution. Resolution and mesh refinement also play a part in any computational analysis undertaken to assess surface profile effects: in the analyses presented, a nominal axi-symmetric geometry has been taken, with a finite non-smooth region on the boundary. Various surface roughness representations are modelled, and the significance of the characterized surface roughness type is investigated. It is shown that the applied load gives rise to a nominally uni-axial stress state of 90% of the yield, although surface roughness features have the effect of modifying the load path, and give rise to localized regions of plasticity near to the surface. The material of the test model is assumed to be elasto-plastic, and the development and evolution of plastic zones formed within the geometry are shown for multiple load cycles.
KeywordsFEA Surface roughness Residual stress Fatigue strength Fractal Geometry
Alison McMillan would like to acknowledge Wrexham Glyndwr University for the release from undergraduate teaching responsibilities, which has provided the time to write this work up. She would also like to acknowledge Chris Rodopoulos for his suggestions and numerous discussions around this topic. The contribution to this paper by GAC was partially supported by the Russian Foundation of Basic Researches (project 15-01-07920). No other external funding was received.
Compliance with ethical standards
Conflict of Interest Statement
The authors declare that they have no conflict of interest.
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