【作者】 卞凯；

【导师】 姜传海；

【作者基本信息】 上海交通大学 ， 材料学， 2010， 硕士

【摘要】 本文主要研究了SiC_w/Al复合材料在不同喷丸工艺处理后材料内应力分布及组织结构的变化,以及残余应力在高温下的应力松弛行为。此外,本文还利用有限元分析软件模拟了喷丸过程,通过建立均质模型分析了喷丸工艺中不同参数对残余应力场的影响;通过建立非均质模型分析了喷丸塑性变形区内微区残余应力的分布状态,分析纤维增强体的形态及分布对基体残余应力场的作用。对SiC_w/Al复合材料表面的传统喷丸处理结果表明,提高喷丸强度可以有效提高残余应力场中各特征参数,但最大残余应力受到材料自身力学性能影响,存在一定的强化极限。而通过改进的变温热喷丸、应力喷丸及复合喷丸则可以进一步提高材料内残余应力的各项特征参数,优化喷丸强化效果,对工业生产领域具有重要的意义。对经喷丸处理的SiC_w/Al复合材料进行等温加热,实验结果表明,当加热温度高于200℃时,材料内出现回复和再结晶行为,SiC_w/Al复合材料中残余应力随加热时间按幂指数方式松弛;加热温度较低时,材料内发生部分蠕变,残余应力发生部分松弛。通过测量喷丸前后材料内的织构成分以及ODF函数研究发现,在喷丸处理后,SiC_w/Al复合材料中表层的原始织构基本被消除。次表层的织构并没有消失,而是织构成分发生了变化,由原始织构{1 10} 112逐渐转变为{1 12} 110。这表明,在晶须增强复合材料中,基体的塑性变形受到晶须增强体在复合材料中分布取向的限制,与增强体的取向趋于一致。利用有限元分析软件建立均质有限元模型并模拟了喷丸处理,得到了符合实际实验结果的应力随层深分布曲线。利用该模型对喷丸工艺中各项参数进行分析,结果表明:喷丸覆盖率、喷丸速度、弹丸种类及大小均对喷丸残余应力场有着不同的作用。提高喷丸覆盖率可以提高材料内的最大残余压应力和压应力层深,并降低材料的表面粗糙度。不同材料弹丸对残余应力场的影响与弹丸的密度有重要的关系,高密度的弹丸意味着较高的动能,其影响的残余压应力层更深,残余压应力也越大。残余应力层深与弹丸尺寸之间具有一定的线性相关性,小直径弹丸喷丸后残余压应力较高,但是残余压应力层深较浅,压应力值随深度下降很快;弹丸直径较大时,表面压应力值和最大压应力值较低,而压应力层加深,压应力随深度下降缓慢。较高的弹丸速度喷丸可以获得更深的残余压应力场,而且可以降低材料内残余拉应力。对SiC_w/Al复合材料非均质模型的数值模拟实验结果表明,在塑性变形区内,由于增强体和基体材料的力学性能差异,经喷丸处理后,增强体内存在较大的残余拉应力,而基体材料内为残余压应力。基体材料在喷丸作用下的塑性变形受到增强体取向的限制,其残余应力场的分布与增强体的分布具有相似的规律。更多还原

【Abstract】 This article mainly studied on how the residual stresses and microstructures of SiC_w/Al MMC are affected by different shot peening treatments, and stress relaxation of SiC_w/Al MMC under heat. Additionally, a finite element analysis method (FEA) is used to simulate shot peening process. Some parameters such shots’material, size, speed and overlay ratios are studied to learn how these parameters affect the distribution of residual stress inside SiC_w/Al MMC. With some simplified methods, a heterogeneous model of shot peening on SiC_w/Al MMC is built. With this model, the micro region distribution of residual stress in plastic deformation area is observed. We also learnt how the size and distribution of whisker reinforcements affect the deformation and stresses of metal matrix.The results of traditional shot peening treatments reveal that the characteristic parameters of residual stress field can be improved by increasing of peening intensity, while the maximum residual stress is limited by SiC_w/Al MMC properties itself. With improved peening methods such as warm peening, stress peening and compound peening, the characteristic parameters of residual stress field can be improved further which has an important meaning to industrial production field.After shot peening, we did some heating treatment to study stress relaxation of SiC_w/Al MMC, the results show that when the heating temperature goes up to 200℃, residual stress in SiC_w/Al MMC relaxed sharply within 10minutes, and residual stress even changed from compressive to tensile. When the heating temperature is about 100℃, residual stress just relaxed partly.ODF function results show that after shot peening, original texture inside SiC_w/Al MMC didn’t disappear or decrease as other materials did. The original texture on surface layer disappeared, while beneath surface, shot peening treatment changed the components of texture from {1 10} 112 to{1 12} 110 , the intensity of texture didn’t reduce so much. This result means that in SiC_w/Al MMC, the plastic deformation of metal matrix is constrained by whisker reinforcements and tends to be uniform of whisker reinforcements’orientation.With a FEA shot peening homogeneous model, we studied how some peening parameters such shots’material, size, speed and overlay ratios affect the distribution of residual stress inside SiC_w/Al MMC. Numerical simulation results show that these parameters take different effects in shot peening treatment. Overlay ratios can improve the maximum residual stress, compressive stress depth and reduce roughness of surface. Different shot material means different density, higher density shots can affects deeper and the value of residual stress is larger. The size of shots is directly related to the depth of compressive stress. With smaller shots, the maximum residual stress is bigger while compressive stress reduces faster in the depth direction. Large shots are easier to generate a deep compressive stress field but maximum stress value is smaller. Shots’speed is highly related to the value of tensile stress beneath compress stress field. Higher speed shot peening can affect deeper and the maximum tensile stress falls sharply.An inhomogeneous peening model is built to study residual stress distribution in micro region of plastic deformation area. Since the mechanical properties between reinforcements and metal matrix are quite different, the stress field in these two materials is discontinuous. In reinforcements, tensile stress is generated after shot peening, while in matrix, residual stress is mostly compressive. Plastic deformation of metal matrix is obviously constrained by whisker reinforcements because the stress field in matrix is similar to the distribution and orientation of whisker reinforcements. Between whiskers, high compressive stresses are obtained, but on two top side area of whisker, compressive stresses are smaller and even some tensile stresses are observed.更多还原