Investigations of Environmental Strength of Metal Matrix Composites under Multiaxial Loading Conditions

金属基复合材料（MMCs）是未来技术领域中具有吸引力和前景的材料之一，在这些技术领域中，要求高强度和高刚度以及良好的疲劳性能与高温和低比重下的性能保持相结合。在这项调查中，连续氧化铝纤维增强铝和SiC晶须增强铝合金的机械性能，包括疲劳在室温和高温下的多轴载荷条件下进行了评估。一些测试也在真空中在室温下进行。研究了温度和拉扭比对复合材料静强度和疲劳强度的影响。特别注意断裂过程：通过扫描电子显微镜（SEM）仔细检查断裂表面，并在SEM中进行一些测试。即使在多轴载荷条件下，复合材料的强度和弹性模量以及疲劳强度也从基体数据增加。讨论了复合材料在多轴加载条件下裂纹萌生和扩展的断裂过程以及温度、应力比和真空度对复合材料强度的影响。

Metal matrix composites (MMCs) are one of the attractive and promising materials for future technological areas, where high strength and high stiffness as well as good fatigue properties combined with retention of properties at high temperatures and low specific gravity are required. In this investigation, mechanical properties including fatigue of continuous alumina fiber reinforced aluminums and SiC whisker reinforced aluminum alloys were evaluated under multiaxial loading conditions at room and elevated temperatures. Some tests were also conducted in vacuum at room temperature. The influence of temperature and applied loading ratio of tension to torsion on static and fatigue strength of the composites were investigated. Special attention was paid to fracture processes: fracture surfaces were closely examined by a scanning electron microscope (SEM), and some tests were conducted in the SEM. Strength and elastic modulus as well as fatigue strength of the composites increased from the matrix data even under multiaxial loading conditions. Fracture processes of crack initiation and propagation of the composites under multiaxial loading conditions as well as the influence of temperature, stress ratio and vacuum on composite strength were discussed.