مقاومت در برابر فرسودگی آلومینیوم
Abstract
Conclusions
References
Abstract
The aim of this study is to evaluate a full integrated modelling strategy to evaluate the influence of casting defects on the fatigue life directly from process simulation. We have shown that defects characterized by their size and the microstructure characterized by the SDAS, are the main parameters that control the fatigue limit. A fatigue criterion that already takes into account for the effect of the defect on the fatigue limit was modified to introduce the effect of SDAS. This improved criterion has been employed to predict the Kitagawa diagram for multiaxial loading for different loading cases. The simulation of the modified criterion showed that the reduction of the fatigue limit with the defect size and SDAS is well described. In the last part a numerical model was developed to perform a simulation of the fatigue limit starting from the simulation of the casting process. Using this numerical model, we simulated the defect size and SDAS depending on the solidification time, the fatigue limit is simulated using the improved criterion. We proposed in this part a mold which let to obtain samples with two different microstructures. In this study, a second fatigue tests was carried out on these samples to validate the numerical simulation on the proposed mold. It turns out that the numerical model provides reasonably well the obtained experimental results.
HCF studies on cast aluminum alloys have shown [1, 2] that the effect of defect size is in competition with other microstructural features such as SDAS/DAS to limit fatigue life. It has been clearly observed that casting defects have a detrimental effect on fatigue limit above a critical size [3, 4]. In addition, the influence of microstructure defined by DAS or SDAS on the fatigue behaviour of cast aluminum alloy cannot be neglected [5-7]. It has been demonstrated [6] that the eutectic phase can cause micro-cracking due to strain accumulation in proximity to Siparticles. As reported in [1], for small defect sizes, there is a prominent interaction between defects and microstructure on the fatigue limit of cast A356-T6 aluminum alloy. Therefore, the simulation of defect size and microstructure distributions within a cast aluminum alloy component are critical inputs for fatigue design. In this context, several studies [8-12] have proposed models to simulate the solidification process and the formation of porosity. A number of models combine the shrinkage pressure and hydrogen concentration to describe porosity formation. In these models the defects were explicitly assumed to be spherical [13-15]. Atwood et al [11] assumed that during solidification, due to solid-liquid balance, pore shapes become complex as they grow between grains or between dendrite arms. Several studies [8, 13] have suggested that it is more appropriate to consider an equivalent pore size rather than trying to characterize the complex 3D shape. This assumption is useful in simplifying the fatigue design for casting aluminum alloy components. In some studies [8, 10-12], the effects of pressure, cooling rate and the distribution of hydrogen in the casting on the formation of pores has been studied.