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Beside prosthesis loosening, wear is the mechanical factor that most significantly influences the lifetime of total knee replacements (TKRs), which can only be described by a number of interrelated parameters. The examination of the wear occurring in TKRs is mostly carried out as a combination of experiments and mathematical modeling. The experiment can provide the real magnitude of wear, while the model is intended to mathematically describe the relationship between wear and the wear-inducing parameters. On the one hand, this study focuses on the mathematical description of wear as a natural-technical phenomenon, presenting the most important analytical and numerical models, while also providing an open view on exciting questions that still await answers. [ABSTRACT FROM AUTHOR]

Introduction: Due to the more resilient biomaterials, problems related to wear in total knee replacements (TKRs) have decreased but not disappeared. In the design-related factors, wear is still the second most important mechanical factor that limits the lifetime of TKRs and it is also highly influenced by the local kinematics of the knee. During wear experiments, constant load and slide-roll ratio is frequently applied in tribo-tests beside other important parameters. Nevertheless, numerous studies demonstrated that constant slide-roll ratio is not accurate approach if TKR wear is modelled, while instead of a constant load, a flexion-angle dependent tibiofemoral force should be involved into the wear model to obtain realistic results. Methods: A new analytical wear model, based upon Archard's law, is introduced, which can determine the effect of the tibiofemoral force and the varying slide-roll on wear between the tibiofemoral connection under standard and non-standard squat movement. Results: The calculated total wear with constant slide-roll during standard squat was 5.5 times higher compared to the reference value, while if total wear includes varying slide-roll during standard squat, the calculated wear was approximately 6.25 times higher. With regard to non-standard squat, total wear with constant slide-roll during standard squat was 4.16 times higher than the reference value. If total wear included varying slide-roll, the calculated wear was approximately 4.75 times higher. Conclusions: It was demonstrated that the augmented force parameter solely caused 65% higher wear volume while the slide-roll ratio itself increased wear volume by 15% higher compared to the reference value. These results state that the force component has the major effect on wear propagation while non-standard squat should be proposed for TKR patients as rehabilitation exercise. Edizioni Internazionali [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA)-made machine elements exhibit easy machining, biodegradability, and excellent mechanical properties. However, enhancing their wear resistance is still a crucial engineering point, which may be achieved by altering (lowering) their coefficient of friction (CoF). Therefore, the first aim of this paper is to analyze how wear is affected by the alteration of CoF. The second aim is connected to the fact that PLA is sensitive to heat, which also limits its applicability. Accordingly, the next goal is to explore the effect of temperature on wear propagation. This study answers these questions by means of multibody dynamics simulations of a PLA-made spur gear pair. Simulations were carried out under constant torque, while the CoF and the temperature were varied in a normal operation domain (CoF: 0.1–0.05, T = 20–30 °C). The results showed that the wear volume gradually began to decline at approximately 0.085 CoF, whilst convergence to steady-state wear could be observed at 0.05 CoF. In conclusion, alteration of the CoF can lower wear by 35%, in this specific domain, while even a 5 °C rise in temperature causes 40% wear progression. The feasibility of the numerical procedure was validated by comparing numerically and experimentally obtained wear–torque results. [ABSTRACT FROM AUTHOR]