Application of multiple residual stress determination methods to coarse-grained biomedical implant castings

Abstract

ASTM F75 femoral knee implant components distort during manufacture due to residual stress redistribution or inducement. X-ray diffraction, neutron diffraction, centre-hole drilling and the contour method residual stress determination techniques were applied to ascast and/or shot-blasted components. The centre-hole drilling and contour methods can only be considered qualitative as a result of uncertainty associated with the elastic anisotropy of gauge volumes. Additionally, neutron diffraction experimentation returned unfeasible results. However, it was qualitatively identified that a shot-blasting shell-removal process has the ability to significantly alter the bulk residual stress state of the implants and induce a stress state which would cause distortion by redistribution following material removal during manufacturing processes.

Residual stress prediction in shot blasted cobalt–chromium biomedical cast components

“…The investment casting process can induce residual stress magnitudes as well as the post-processing procedures, including: Mould removal; Casting cut off; Heat treatments; and Shot blasting [3]. As discussed in section 'Residual stress-induced shape changes' and observed in Figure 5, the shot blasting process used to remove the investment casting shell forms a compressive residual stress layer on the surface of the femoral [1]. During subsequent machining, the stress will rebalance, leading to distortion.…”

“…In a significant amount of conducted studies, the shot is considered to be a rigid body. However, for shot peening ASTM F75 castings, the shot used is typically SUS304 (250-350 Hv) which has a similar hardness to ASTM F75 (310-350 Hv) [1]. This must be accounted for in the simulation as the shot will also deform during the process.…”

“…ASTM F75 femoral knee implants tend to distort unpredictably due to the release of residual stresses after being removed from investment casting, with one of the causes qualitatively assessed as a shot blasting process [1]. In a recent study, two rectilinear ASTM F75 parts measuring approximately 80 × 24 × 2.3 mm 3 were bolted together and put through the same shot blasting process as the ASTM F75 femoral knee implants [2].…”

Residual Stress in Engineering Materials: A Review

“…Moreover, neutron diffraction is not a feasible method to determine residual stresses in implant castings. [ 294 ] Tung et al implemented XRD to quantitatively determine the influence of hydration and X‐ray radiation dose on the residual stress states of the cortical bone constituents. It was clarified that water content would considerably affect the residual stress of the collagen structure in bone.…”

X‐Ray Diffraction Technique for Residual Stress Measurement in NiCrMo Alloy Weld Metal

“…However, there are some difficulties in stress measuring both for neutron and X-ray diffraction methods in weld metals characterised with preferential orientated and coarse grain microstructure. In the case of nonferrous metals and its alloys, especially nickel alloys, such microstructure features can make difficult the analysis of XRD weld metal stress state [11,12].…”