To assess the life of a new diesel aluminium alloy piston under thermal shock loads, thermo‐mechanical fatigue (TMF) testing was conducted to characterise the TMF properties of the piston alloy, and an empirical model based on the constraint ratio concept was proposed to predict the TMF life of the piston. Considering that the empirical model required expensive experimental support, a platform with high‐frequency induction heating was established to simulate the force on the piston under thermal shock loads to calculate the piston life using the thermal shock test. Additionally, a finite element method was developed to compute the distributions of temperature, strain, and stress during this process. The characteristics of crack initiation and propagation in TMF test rods and piston mock‐ups were also investigated. The results showed that the TMF test rod suffered brittle fracture with brittle quasi‐cleavage features. The microcracks mainly occurred in primary Si particles due to stress concentration around the primary Si particles induced by the difference between the thermal expansion coefficients of Si and Al. From a macro perspective, the piston initially cracked at the rim above the pinhole, where the stress is larger than that along other directions. From a micro perspective, the protrusions of various sizes on the piston rim were induced by the compression stresses at high temperature. The piston cracks usually initiate around primary Si particles, propagate along the edge of primary Si in a straight line, bifurcate and then stop at a certain depth. If the piston was only heated, cracks or plastic deformations were not produced. The piston life can be assessed using the proposed empirical model based on the constraint ratio concept or thermal shock testing based on the developed platform. The difference between the predicted and experimental life was not greater than 7%.

中文翻译：

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铝合金活塞热机械疲劳寿命的实验与计算研究

为了评估新型柴油铝合金活塞在热冲击载荷下的寿命，进行了热机械疲劳（TMF）测试以表征活塞合金的TMF特性，并提出了一种基于约束比概念的经验模型来预测活塞的TMF寿命。考虑到经验模型需要昂贵的实验支持，因此建立了一个带有高频感应加热的平台，以模拟在热冲击载荷下作用在活塞上的力，从而使用热冲击试验计算活塞的寿命。此外，还开发了一种有限元方法来计算此过程中温度，应变和应力的分布。还研究了TMF测试棒和活塞模型中裂纹的萌生和扩展特征。结果表明，TMF测试棒遭受脆性断裂，具有脆性准断裂特征。由于Si和Al的热膨胀系数之差引起的应力集中在初级Si颗粒周围，微裂纹主要发生在初级Si颗粒中。从宏观角度看，活塞最初在针孔上方的边缘处破裂，此处的应力大于沿其他方向的应力。从微观的角度来看，高温下的压缩应力会引起活塞轮缘上各种尺寸的突起。活塞裂纹通常始于原始硅颗粒周围，沿原始硅的边缘沿直线传播，分叉，然后在一定深度处停止。如果仅加热活塞，则不会产生裂纹或塑性变形。可以使用基于约束比概念的建议经验模型或基于已开发平台的热冲击测试来评估活塞寿命。预期寿命与实验寿命之间的差异不大于7％。