Natesan Elanghovan, Ahlström Johan, Eriksson Stefan, Persson Christer
Department of Industrial and Materials Science, Chalmers University of Technology, 41296 Gothenburg, Sweden.
Volvo Car Corporation, Analysis and Verification, 40531 Gothenburg, Sweden.
Materials (Basel). 2021 Dec 20;14(24):7898. doi: 10.3390/ma14247898.
As the electrification of vehicle powertrains takes prominence to meet stringent emission norms, parts of internal combustion engines like cylinder heads are subjected to an increased number of thermal load cycles. The cost-effective design of such structures subjected to cyclic thermo-mechanical loads relies on the development of accurate material models capable of describing the continuum deformation behaviour of the material. This study investigates the effect of temperature on the evolution of flow stress under cyclic loading in A356-T7 + 0.5% Cu cast aluminium alloy commonly used in modern internal combustion engine cylinder heads. The material exhibits peak stress and flow stress asymmetry with the stress response and flow stress of the material under compressive loading higher than under tension. This peak and flow stress asymmetry decrease with an increase in temperature. To compare this stress asymmetry against conventional steel, cyclic strain-controlled fatigue tests are run on fully pearlitic R260 railway steel material. To study the effect of mean strain on the cyclic mean stress evolution and fatigue behaviour of the alloy, tests with tensile and compressive mean strains of +0.2% and -0.2% are compared against fully reversed (R = -1) strain-controlled tests. The material exhibits greater stress asymmetry between the peak tensile and peak compressive stresses for the strain-controlled tests with a compressive mean strain than the tests with an identical magnitude tensile mean strain. The material exhibits mean stress relaxation at all temperatures. Reduced durability of the material is observed for the tests with tensile mean strains at lower test temperatures of up to 150 °C. The tensile mean strains at elevated temperatures do not exhibit such a detrimental effect on the endurance limit of the material.
随着车辆动力系统的电气化日益突出以满足严格的排放规范，内燃机的部件如气缸盖承受的热负荷循环次数增加。这种承受循环热机械载荷的结构的经济高效设计依赖于能够描述材料连续变形行为的精确材料模型的开发。本研究调查了温度对现代内燃机气缸盖常用的A356-T7 + 0.5% Cu铸造铝合金在循环加载下流动应力演变的影响。该材料表现出峰值应力和流动应力不对称，材料在压缩加载下的应力响应和流动应力高于拉伸加载下的。这种峰值和流动应力不对称随着温度升高而减小。为了将这种应力不对称与传统钢进行比较，对全珠光体R260铁路钢材料进行了循环应变控制疲劳试验。为了研究平均应变对合金循环平均应力演变和疲劳行为的影响，将拉伸和压缩平均应变分别为+0.2%和-0.2%的试验与完全反向（R = -1）应变控制试验进行了比较。对于具有压缩平均应变的应变控制试验，材料在峰值拉伸应力和峰值压缩应力之间表现出比具有相同大小拉伸平均应变的试验更大的应力不对称。该材料在所有温度下均表现出平均应力松弛。在高达150°C的较低试验温度下，对于具有拉伸平均应变的试验，观察到材料的耐久性降低。在高温下的拉伸平均应变对材料的 endurance limit没有这种有害影响。 （注：原文中“endurance limit”未明确中文释义，保留英文）
