Evaluation of plastic deformation and prediction of thermal mechanical fatigue life of an Al–Si alloy piston for diesel engines
Evaluation of plastic deformation and prediction of thermal mechanical fatigue life of an Al–Si alloy piston for diesel engines
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DOI：
10.1111/ffe.13553
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发表时间：
2021-08
影响因子：
3.7
通讯作者：
Ziliang Li;Jianxing Li;Ye Zhu;J. Guo;Meng Li;Yuejian Luo
中科院分区：
文献类型：
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作者：
Ziliang Li;Jianxing Li;Ye Zhu;J. Guo;Meng Li;Yuejian Luo
在本研究中，开发了一种三步预测方法来预测铝硅合金活塞的热机械疲劳（TMF）寿命：（1）通过对铝合金试样进行一系列TMF测试，建立100-350°C温度循环下塑性变形与疲劳寿命之间的关系； (2)通过数值模拟计算活塞在感兴趣的热冲击条件下的危险塑性变形； (3)通过将计算出的塑性变形代入所建立的关系来估算活塞的寿命。通过活塞热震试验验证了所提预测方法的有效性，预测误差不大于25%。活塞开裂的机理可概括为：不均匀的塑性变形在初生硅颗粒和轮缘突出物周围引起较高的拉应力，然后在危险的拉应力作用下，在突出物处产生微裂纹，最后产生宏观裂纹。据推测，在热冲击载荷和燃烧压力下活塞的寿命比在热冲击载荷下的寿命短。考虑到应力松弛对塑性变形的影响，发动机长时间满负荷运行有助于活塞T方向的开裂，而长时间空转则降低了活塞T方向的开裂倾向，增加了活塞F、R方向的开裂倾向。
In this study, a three‐step prediction method was developed to predict the thermal mechanical fatigue (TMF) life of an Al–Si alloy piston: (1) establishing a relation between the plastic deformation and fatigue life under the temperature cycle of 100–350°C via a series of TMF tests of the aluminum alloy specimens; (2) computing the dangerous plastic deformation of the piston under the thermal shock condition of interest by numerical simulation; (3) estimating the life of the piston through taking the computed plastic deformation into the established relation. The effectiveness of the proposed prediction method was verified by thermal shock tests of the piston, and the prediction error is no more than 25%. The mechanism of piston cracking can be summarized as follows: the inhomogeneous plastic deformation induced higher tensile stress around primary Si particles and protrusions at the rim and then microcracks were produced at the protrusions under the dangerous tensile stress, and finally, macrocracks occurred. The life of the piston under the thermal shock load and combustion pressure is speculated to be shorter than that under the thermal shock load. Considering the effect of stress relaxation on plastic deformation, the long full‐load operation of the engine contributes to the piston cracking in T direction, while the long idling operation reduces the piston cracking tendency in T direction and increases the piston cracking tendency in F and R directions.