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题名	金属基复合材料 SiC_p/Al 中的残余应力及其力学性能
作者	孙正明
学位类别	博士
答辩日期	1992
授予单位	中国科学院金属研究所
授予地点	中国科学院金属研究所
导师	师昌绪
中文摘要	本文研究了碳化硅颗粒增强铝合金复合材料中的残余应力，形变行为以及疲劳性能。研究了用X－射线衍射技术测定复合材料中残余应力的方法。由于复合材料中两相的热膨胀特性的差别，材料中引入了残余应力，证明了这类材料中的残余应力是三维应力。推导了由X－射线衍射测量数据计算三维应力各个应力分量的数学表达式，并指出了测量三维应力的合理步骤。这些公式的导出给试验数据处理及试验结果的评价代来了方便。从理论和实验两方面论证了测量复合材料中残余应力的可行性，并据此证实了具有平行光束衍射光路的X－射线应力仪测定这种金属基复合材料中三维残余应力的可能性，这对方便测量过程具有实际意义。另外还从理论分析和有限元分析入手研究了在样品自由表面测量三维应力的可靠性，结果表明残余应力在样品自由表面的弛豫对应力测量的影响不大。这是因为SiC/Al复合材料对X－射线的吸收不大，射线在材料中有较大的穿透深度。在对测量方法进行了深入研究和了解的基础上，研究了一些金属基复合材料中的残余应力及其受温度变化处理的影响。结果表明，在复合材料中基体承受余拉应力，而增强相承受压应力。液氮温度的低温处理可以有效的降低材料中的残余应力，这是由于基体材料在温度变化过程中发生的塑性形变所致。还研究了残余应力对材料的力学性能的影响。实验表明，在一纯铝基复合材料中，350 ℃和室温间的热循环及低温处理均降低材料中的残余应力。Bauschinger效应的试验结果可以用材料中的残余应力测量结果加以解释。基体中的残余拉应力加强了材料的Bauschinger效应，如果试验过程中先进行压缩然后拉伸，与先拉伸后压缩的顺序相比，其Bauschinger效应更为明显。为了更好地了解金属基复合材料，我们用粉末冶金法制备了含有不同碳化硅体积分数和颗粒尺寸的铝基复合材料。用高频疲劳试验研究了材料的疲劳裂纹扩展及其门槛值，并以应变计法分析了其裂纹闭合效应。还研究并讨论了一种新的裂纹闭合评价方法－－激光干涉局部闭合测量法。结果表明，复合材料在挤压／轧制方向具有较高的裂纹扩展阻力，而横向材料中的裂纹扩展具有较高的闭合效应。对复合材料中的疲劳短裂纹研究表明，材料中的疲劳裂纹更易于在铝合金基体中萌生，这被认为与材料中的残余应力有关。Residual stresses, Bauschinger effect and fatigue crack growth behaviour in silicon carbide particulate reinforced aluminium alloy composites were studied in this thesis. Residual stresses were introduced due to thermal mismatch. Methods for measuring residual stresses with x-ray diffraction technique was studied. Residual stresses in the composite system were proved to be triaxial. Equations for the calculation of triaxial residual stresses from the x-ray diffraction data were derived, which makes more convenient the data processing and evaluation. Feasibility of the method to assess residual stresses in composite was demonstrated from both experimental and theoretical considerations. Based on these studies it was proved possible to measure the triaxial residual stresses in these metal matrix composites with the parallel beam x-ray diffraction technique, as in the usual x-ray stress analyser, which eases the residual stresses evaluation. On the other hand, the reliability of the measurement of triaxial stresses on the free surface of the sample was studied with an analytical approach and a finite element calculation process, both affirmed the method. This could be interpreted with the large penetration depth of the x-ray beam into the material. After large effort was dedicated to the method of measurement, the residual stresses in some composite were measured and an attempt to change the residual stresses in the constituent phases of the material was made. Results showed that the residual stresses in the matrix of the composite are in tension while those in the reinforcement are in compression. A coincidence between the results from the measurement and the FEM calculation was found. A low temperature treatment in liquid nitrogen induced a substantial decrease in the residual stresses. This was interpreted by means of plastic deformation in the matrix during the temperature change process. The influence of residual stresses on the mechanical properties of the material were studied. In a pure aluminium matrix composite, it was found that both thermal cycling between room temperature and 350℃ and low temperature treatment reduces the residual stresses. The experimental results of strength differential effect and Bauschinger effect were consistent with the residual stress interpretation. The existence of tensile residual stresses in the matrix enhanced the strength differential effect. The magnitude of Bauschinger effect is greater for the test initially started in compression than for a test initially started in tension. In order to get more knowledge about the metal matrix composite materials, composites with various volume fractions and different sizes of reinforcing particle were produced with powder metallurgy technique. Fatigue crack closure behavior was studied with strain gauge method. A new closure evaluation technique, laser interferomtry, was discussed. Results indicate a higher fatigue growth resistance for the composite in the longitudinal direction. Higher closure effect was found in the transverse direction compared with longitudinal. Small fatigue crack behaviour in metal matrix composites was also investigated. Results show that fatigue cracks initiate preferentially in the aluminium alloy matrix instead of at particle cracking or by interface decohesion. Small fatigue cracks grow in an anomalous way as compared with the conventional long crack.
语种	中文
公开日期	2012-04-10
页码	181
内容类型	学位论文
源URL	[http://ir.imr.ac.cn/handle/321006/17567]
专题	金属研究所_中国科学院金属研究所
推荐引用方式 GB/T 7714	孙正明. 金属基复合材料 SiC_p/Al 中的残余应力及其力学性能[D]. 中国科学院金属研究所. 中国科学院金属研究所. 1992.

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