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Cobalt Chrome is used extensively within the biomedical industry for hip, knee and shoulder prostheses. These components are manufactured using a range of different processes which includes machining. In order to develop Finite Element Models of machining processes, it is necessary to develop the constitutive model of the workpiece material at high strain rates over different temperatures. During this research, Split Hopkinson Pressure Bar tests were conducted over a wide processing domain of temperatures (298-873 K) and strain-rates (600-1400s-1) to predict the constitutive model of biomedical grade Cobalt Chrome based on modified Zerilli-Armstrong, modified Johnson-Cook and strain compensated Arrhenius-type models. The prediction capability of these models was evaluated in terms of average absolute relative error and correlation coefficient between predicted and experimental flow stress values. Results demonstrated that the modified Zerilli-Armstrong model can track the deformational behaviour more accurately throughout the entire processing domain investigated compared to the other models. The model recorded an average absolute relative error of 2.71% and a correlational coefficient of 0.98.

Selective Laser Melting is an additive manufacturing practice that permits the production of metal alloy-based parts. While facilitating the design of complex geometry, SLM leads to the fabrication of a unique material structure that showcases distinct behavioural characteristics relative to their traditional methods of material manufacture. Defects that are innate to SLM inspire the presence of a compositional outlook that is inhomogeneous in nature and only serves to hinder part efficiency. Thus, the Theory of Critical Distances offers a refreshed proposal to evaluating notched Ti-6Al-4V material produced by additive manufacturing processes. Key principles of the theory’s working mechanisms are outlined. Subsequently, symmetrical notches of contrasting size are assessed. Findings reveal that the Theory of Critical Distances is adequately compatible with accurate fatigue prediction of SLM Ti-6Al-4V in its as-built state. Additionally, fracture surface analysis reveals that crack initiation is predominantly a surface-based phenomenon. Hereby, increased focus must be given to the quality of processed material that is located at the externalities of additively manufactured components, in order to enhance their service life capabilities. This will induce an increasingly uniform material structure that will allow for more predictable behavioural characteristics.

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