parametric finite elements model of slm additive manufacturing process

Abstract An obstacle to the diffusion of additive technology is the difficulty of predicting the residual stresses introduced during the fabrication process. This problem has a considerable practical interest as evidenced by the abundant literature on residual stresses and distortion induced by the SLM (Selective Laser Melting) and EBAM (Electron Beam Additive Manufacturing). The purpose of this paper is to evaluate the effect of different process parameters on the heat distribution and residual stresses in components made with SLM technique. Three aspects are developed and illustrated: a) thermomechanical modeling of the growth process, based on Finite Elements (FE), which considers changes in the behavior of the material (powder→liquid→solid) through the finite element "birth" and "death" technique that enables the progressive activation of the elements as the component grows; b) sensitivity analysis of the model to the physical characteristics of the material (conductivity, specific heat capacity, Young's modulus). This is an important aspect allowing to focus on the most significant parameters to be determined experimentally with high reliability; c) evaluation of the effects of different process parameters (laser power, scan speed, overlap between adjacent paths) on the process. The article illustrates the theoretical thermal model and the detail of the strategy used in the FE analysis. The most influential characteristics of the material are highlighted and, finally, general criteria for choosing the optimal combination of process parameters to limit the residual stresses are provided

Improvement of heart rate recovery after exercise training in older people.

Twenty-four subjects aged 70 and older were retrospectively selected from our archives and screened for symptoms of cardiovascular disease. Baseline exercise test was negative for myocardial ischemia in all subjects. All subjects had completed an 8-week program, performed for a variety of indications and consisting of an aerobic physical training program including 30 minutes of cycling three times per week at 65% to 75% of maximum heart rate achieved at peak exercise test performed at enrollment, an educational intervention, dietary advice, and psychological support. All subjects underwent a cardiopulmonary exercise test (CPX) before and at the end of exercise training. At the end of each CPX, peak oxygen uptake (VO2peak), the rate of increase of ventilation per unit of increase of carbon dioxide production (VE/VCO2slope), and HRR were recorded. Twenty-five healthy subjects younger than 60 with no evidence of exercise-induced myocardial ischemia and not enrolled in any exercise training program were also retrospectively selected from our archives and used as a control group for analyzing HRR. These patients performed two exercise tests several weeks apart. Several studies have shown that changes in vagal tone can be used as an outcome tool that helps identify patients or subjects with or without cardiovascular disease at risk for a cardiovascular event, although the evidence of a prognostic value of HRR in older subjects without cardiovascular disease is rather poor. In this study, exercise training resulted in HRR improvement in healthy elderly subjects, suggesting that exercise training improves vagal/sympathetic balance in older subjects without cardiovascular disease as well. Whether the observed improvement in HRR may have long-term beneficial prognostic effects was not the aim of the study, although a beneficial effect might be postulated, in light of the Framingham dat