Modeling Evolution of Cutting Force in Ultrasonically Assisted Drilling of Carbon Fiber Reinforced Plastics.

In this study, the effects of process parameters (feed rate, spindle speed, and ultrasonic power level) on the cutting force and delamination in the ultrasonic vibration-assisted drilling of carbon fiber-reinforced plastics (CFRPs) have been investigated. A series of drilling tests under various conditions defined by the design of experiment technique were conducted. The evolution of the cutting force during drilling cycles was measured and analyzed. Experimental analysis results based on the Taguchi method and analysis of variance show that the spindle speed is an influential factor affecting the cutting force with a contribution of 75.36%, and the feed rate significantly affects the delamination damage with a contribution of 46.57%. In addition, the cutting force was found to increase with drilling cycles at different rates, which depends on the process parameters used in drilling. The evolution behavior of cutting force was well fitted based on the process parameters by proposed regression models. Experimental validation indicates that the predicted forces show reasonable agreement with measured values under different conditions and reveal good prediction performances, with a root mean square error of 5.6 and a mean absolute percentage error of 5.8%. In drilling tests with variable cutting conditions, the evolution of the cutting forces predicted based on the selected parameters was successfully verified when compared with the measured results, with RMSE and MAPE values of 7.55 and 5.61%, respectively. As a conclusion, this predictive model provides an effective basis for selecting appropriate drilling parameters to suppress the cutting force on CFRP composites.

Computer simulation on fatigue behavior of cemented hip prostheses: a physiological model.

This paper is concerned with the investigation on the fatigue failure of implant fixation by numerical approaches. A computer algorithm based on finite element analysis and continuum damage mechanics was proposed to quantify the fatigue damage rate of cement mantle under physiological conditions. In examining the interfacial debonding effect, the interface elements were introduced at cement-stem interfaces and calibrated with the increase of loading cycles. Current results reveal that the major sites for failure initiation are in the proximal anterior-medial regions and at the distal prosthesis tip, which clearly demonstrate the same failure scenario as observed in clinical studies. Such fatigue failures not only result in the corruption of cement-stem interfaces, but also greatly affect the cement stress distribution and the damage rate in subsequent loading cycles. Another significant result is that the predicted damage rate increases steadily with gait cycles. This trend in damage development is consistent with the findings obtained from fatigue tests available in literature. It is anticipated that presented methodology can serve as a pre-clinical validation of cemented hip prostheses.

The computer simulation of wear behavior appearing in total hip prosthesis.

Computer algorithms are proposed for the estimation of wear appearing in artificial hip joints using finite element analysis based on the modified Archard's wear law, contact features and an analogue wear process. A pin-on-disk plate experiment is reconstructed to assess the efficiency and validity of the algorithms proposed here. Through the successful verification of wear depth and volume loss of the pin-on-disk plate as well as the artificial hip joint, the current algorithms provide significant agreement with experiments, clinical measurements and numerical calculations and are shown to be both valid and feasible. Further investigation into the effect of femoral heads with various sizes suggests that the larger femoral head may induce larger wear volume but gives a smaller wear depth and that wear depth and volume loss are apparently nonlinearly related to the femoral head diameter. It is shown that the current algorithms are useful and helpful in understanding wear behavior for alternative or new designs of artificial hip joints and even for other analogous structures.