COB封装中芯片在基板不同位置的残余应力

利用硅压阻力学芯片传感器作为原位监测的载体，研究了直接贴芯片的封装方式中，芯片在基板上的不同位置对于封装后残余应力的影响以及在热处理过程中残余应力的变化，发现粘贴在基板靠近边的位置和中心位置时应力水平接近，但是靠近基板一角的位置应力较大，而且在热处理过程中应力出现“突跳”和“尖点”。     

残余应力对包装机械腐蚀开裂的影响及对策研究

包装机械零，部件在制造过程，内部都会产生残余应力，通过实验阐述了残余应力对包装机械腐蚀开裂性能的影响，以及防止腐蚀开裂的措施。     

残余应力对轴心压杆稳定的影响及对策

近年来,就残余应力对轴心压杆稳定的影响的研究有了很大的进展.相比较,20年前颁布的<起重机设计规范>中一些相关内容就显得落伍了.文章对此问题进行分析和探讨.     

仪器化压入测试材料表面残余应力的研究进展

仪器化压入是一种新兴的力学测试技术,具有无损、微区、自动等优点,已用于残余应力测试的研究。首先介绍仪器化压入测试残余应力的基本原理;然后针对锥形压入和球形压入测试,分别介绍仪器化压入测试残余应力的主要分析方法,并比较各自的优缺点,提出改进措施;最后总结仪器化压入测试残余应力的研究现状,展望未来的研究工作。     

工程结构表面涂层残余应力的测量

在工程结构中广泛采用表面涂层技术，由于涂层材料与基体材料的热膨胀系数等特性不同，涂层存在一定的残余应力，易使涂层爆裂甚至剥落，造成涂层失效，结构报废，本文研究电测盲孔法测量涂层的残余应力，用来分析产生残余应力的各种影响因素。     

焊接过程对焊接残余应力及残余变形的影响

采用热弹塑性有限元法，对直通焊和多人同时分段焊两种焊接过程的平板对接焊时焊接应力变形和圆柱壳板环缝的焊接变形进行比较，认为多人同时分段焊直通焊无论在降低焊接残余应力还是焊接残余变形都具有非常显著的效果。     

残余应力对金属疲劳强度的影响

残余应力对光滑试样高周疲劳极限的影响可以用Goodman关系来描述，但必须要得到残余应力作用系数m、合理地提取残余应力的表征值和区分开其它因素的影响。残余应力对缺口疲劳极限的作用大于对光滑试样的作用，是由于残余应力也存在应力集中现象，而且不易衰减。残余应力的应力集中系数不仅与缺口几何因素有关，还与材料特性有关。试验研究还表明，表层残余压应力对于承受轴向载荷且疲劳残纹萌生于表面的零件也十分有益。     

表面冶金复合材料残余应力产生及对热疲劳性能影响

本文通过对基体及焊层材料线膨胀系数及焊层表面应力的测试，阐述了热喷焊层残余应力产生的原因主要与第一、二次冷却过程有关，表面冷却速度是影响焊层表面应力的关键因素，分析了表面应力对焊层热疲劳性能的影响，焊层表面残余压应力对焊层抗热疲劳性有利。     

机械应力消除法对焊接残余应力的影响

焊后残留在结构中的焊接应力是影响整个结构寿命的关键,因此,控制和消除焊接应力成了焊接领域的热点议题。本文介绍了机械应力消除法对焊接残余应力的影响,通过两者之间的联系,总结提出有效控制残余应力的指导方法,以详实机械原理消除法与焊接残余应力的联动影响,进一步为焊接领域提供新的总结性方法论     

纤维缠绕复合材料固化过程残余应力/应变的三维数值模拟

采用有限元分析软件ABAQUS,对具有金属内衬的纤维缠绕复合材料圆筒在固化过程中残余应力及应变的变化规律进行了模拟计算。采用FORTRAN语言编制了用以分析固化过程中残余应力的子程序,该子程序考虑了固化过程中复合材料力学性质的变化和由于树脂固化收缩产生的化学收缩应变。算例结果表明：复合材料和金属内衬的残余应力在初始阶段均接近于零,当固化到一定阶段,残余应力迅速增加并且很快达到最大值,在降温阶段释放了部分的残余应力;在整个固化过程中,金属内衬受到压应力,而纤维缠绕层受到拉应力。本文中的三维有限元模型可以得到任意时刻复合材料的温度及固化度分布,通过数值模拟可以有效地优化复合材料固化工艺参数,提高制件的质量。     

表面粗糙度对喷丸残余应力场的影响

为定性研究表面粗糙度对喷丸残余应力场的影响,采用余弦曲线模拟靶材粗糙表面,建立喷丸二维有限元模型,采用ABAQUS/EXPLICIT求解器对喷丸过程进行数值模拟,研究了表面粗糙度喷丸残余应力场的影响规律,分析了同一粗糙度下弹丸尺寸和喷射速度对喷丸残余应力场的影响规律,并与表面理想光滑时的情况进行了对比.结果表明,表面粗糙度的增加使残余压应力区变浅变薄,甚至使靶材表面产生残余拉应力,不利于喷丸强化件抗疲劳性能的提高,喷丸件表面应尽可能光滑以改善喷丸效果.     

退火对溅射ZnO薄膜的形貌和内应力的影响

用超高真空射频磁控溅射技术制备了高C轴取向的ZnO薄膜,用扫描电镜和X射线衍射仪分别研究了退火对ZnO薄膜形貌和内应力的影响.结果表明:适当温度退火后薄膜的形貌和内应力得到改善,通过增氧、缺陷原子的热激活和晶粒融合等可以有效地降低薄膜中由热效应、缺陷效应和粒子注入效应等引起的张应力,薄膜组织致密化并且柱状晶粒取向趋于一致.450℃退火的ZnO薄膜具有最低的张应力和最佳的结晶质量.     

A portable electrochemical machining surface preparation system for use in the field of residual stress measurement

Strain gauge residual stress measuring techniques require a smooth site surface for optimum bond performance. Mechanical metal removal techniques are generally used for surface preparation, although these may induce operator dependent residual stress which distorts the original stress distribution. The problem becomes more significant if subsurface conditions are to be evaluated by removing material, especially when hard, tough or strongly work-hardening alloys are being investigated. To avoid the errors caused by surface preparation, the operator independent metal removal alternatives adopted have been electrolytic polishing and chemical etching. However, these methods have slow removal rates and can be hazardous to health, factors which limit their general use for residual stress measurement surveys.     

Local residual stress mitigation after curing process by spread fiber tow in carbon fiber-reinforced plastic

The application of the tow spreading technique to wound filaments or woven composites seems promising because of its advantageous strength enhancement mechanism. The effects of tow spreading on the curing progress and the residual stress of the resin were investigated in this study. We hypothesized that the homogeneous distribution of fibers realized by the tow spreading technique suppresses the stress concentration of the resin in the vicinity of close-packed fibers. This hypothesis was examined through finite element simulation using a micro-scale model with the definite separation of fiber and resin. The residual stress and strain after the curing process were investigated using a newly developed simulation system.     

On the impact of deep rolling at different temperatures on the near surface microstructure and residual stress state of steel AISI 304

The consequences of deep rolling at cryogenic temperature, room temperature and high temperature were investigated for steel X5CrNi18‐10 (AISI 304). Near surface microstructures, martensite content and residual stresses were analyzed. It is shown that, applying different deep rolling temperatures, the near surface states of the processed specimen are altered in a characteristic way. Particularly important is that different depth distributions of strain hardening, martensite volume fraction and residual stresses can be created.     

Crack aspect development curves and fatigue life prediction for surface cracks at weld toes in the presence of residual stress

An engineering procedure is proposed for estimating the crack growth behaviour and fatigue lives of semi-elliptical surface cracks at weld toes, based on a database of stress intensity factors. Some examples of crack aspect development curves (CADC) are given for some typical cracked welded joints subjected to service loading and residual stress conditions. The significance for predicting fatigue life according to the natural crack growth path, namely along the CADC, is emphasized through examples.     

Evaluating the fatigue limit of metals having surface compressive residual stress and exhibiting shakedown

The objective of the study described in this article is to evaluate the effect of shakedown of surface compressive residual stresses introduced by shot peening on fatigue limit of stainless steel. First, the tension‐compression fatigue tests were conducted on ASTM CA6NM specimens under controlled load and displacement conditions to acquire a fatigue limit diagram under various compressive mean stress. The results showed that shakedown of negative mean stress occurs under controlled displacement. We then carried out in‐plane–bending fatigue tests under controlled load conditions on welded ASTM 309 stainless steel specimens with surface compressive residual stress introduced by ultrasonic shot peening. The results provide a fatigue limit of 415 MPa, which agrees with the value of 404 MPa calculated based on a modified Goodman line considering shakedown. Therefore, it is suggested that the surface layer is restricted by the internal bulk that creates controlled displacement conditions and the shakedown of surface compressive residual stress occurs.     

残余应力和粗糙度对叶片振动疲劳性能的影响

为了研究叶片表面完整性对其振动疲劳性能的影响,本文模拟分析了某型高温合金叶片在振动疲劳实验过程中的动力学应力响应,获得叶片共振时应力幅值随时间的变化规律,分析了残余应力和粗糙度对叶片振动疲劳寿命和疲劳极限的影响规律.结果表明:叶片共振过程中的应力响应幅值先增大后减小呈周期性变化,属于"拍"现象,满足关系σ=1 046sin(242.83t)sin(5 828t);叶片的振动疲劳极限和疲劳寿命均随残余应力和粗糙度的增大而减小,振动疲劳极限和残余应力之间的关系满足σfat=510.9-0.31-70.93σrest;而疲劳极限和粗糙度之间的关系则满足σfat=9.67R2roughness-70.93Rroughness+713.23.