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This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fa- tigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respec- tively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.  相似文献   
2.
任淮辉  王习术  陈应龙  李旭东 《中国物理 B》2012,21(3):34501-034501
In this paper, the natural structures of a dragonfly wing, including the corrugation of the chordwise cross-section, the sandwich microstructure veins, and the junctions between the vein and the membrane, have been investigated with experimental observations, and the morphological parameters of these structural features are measured. The experimental result indicates that the corrugated angle among the longitudinal veins ranges from 80° to 150°, and the sandwiched microstructure vein mainly consists of chitin and protein layers. Meanwhile, different finite element models, which include models I and I* for the planar forewings, models II and II* for the corrugated forewings, and a submodel with solid veins and membranes, are created to investigate the effects of these structural features on the natural frequency/modal, the dynamical behaviors of the flapping flight, and the deformation mechanism of the forewings. The numerical results indicate that the corrugated forewing has a more reasonable natural frequency/modal, and the first order up-down flapping frequency of the corrugated wing is closer to the experimental result (about 27.00 Hz), which is significantly larger than that of the planar forewing (10.94 Hz). For the dynamical responses, the corrugated forewing has a larger torsional angle than the planar forewing, but a lower flapping angle. In addition, the sandwich microstructure veins can induce larger amplitudes of torsion deformation, because of the decreasing stiffness of the whole forewing. For the submodel of the forewing, the average stress of the chitin layer is much larger than that of the protein layer in the longitudinal veins. These simulative methods assist us to explain the flapping flight mechanism of the dragonfly and to design a micro aerial vehicle by automatically adjusting the corrugated behavior of the wing.  相似文献   
3.
激发大学生材料力学实验动手与分析的能动性   总被引:3,自引:2,他引:1  
 通过材料力学实验教学的理解和体会,介绍了如何激发学生自 主动手和主观能动地寻找、分析实验中出现的科学问题的教学理念和教学方式. 以典型 的材料力学性能参数检测试验课为例,实现教学中师生互动,启发学生在试验中``听其声, 观其形'寻找科学问题并领悟关键内容与寻找答案的方法.  相似文献   
4.
FGHxx系列结构材料是我国近年来成功开发的损伤容限型粉末高温合金,由FGH95到FGH99系列,主要是通过材料的化学成分、制粉工艺及后续的热处理工艺参数等优化措施,达到提高在役温度下的强度、韧性性能,改善疲劳裂纹扩展阻力等目的。相比于材料工艺力学的现有研究成果,该系列材料在固体力学相关的疲劳损伤表征、寿命评价、微结构对疲劳裂纹萌生行为的研究存在显著滞后,尤其在损伤容限相关的关键科学问题以及工程关注的安全评估手段等有待深入探究。本文基于作者们对现有的FGHxx系列粉末高温合金疲劳损伤研究现状和关键科学问题的掌握和理解以及对应的部分实验研究结果,从材料微结构特征、疲劳数据分散特点、宏微观疲劳裂纹扩展行为、SEM原位测试、疲劳寿命预测模型、疲劳损伤安全区(三维K-T关系图)的建立等进行了评述和展望。  相似文献   
5.
多孔金属抗拉强度公式中的指数项取值   总被引:4,自引:0,他引:4  
高孔率材料抗拉强度公式中的指数项,对强度的计算结果具有重要影响。运用相关实验数据对有关公式中指数项的取值进行了验证。结果表明,对于中塑性的高孔率金属材料,该指数项取1.25比取1.5(即3/2)更适宜。  相似文献   
6.
高温下岩石SEM实时实验研究   总被引:3,自引:0,他引:3  
首次利用带扫描电镜的高温疲劳试验机等目前最先进的实验手段,高温下实时观测了温度变化对石灰岩微结构的影响,有效地避免了由于岩石的热膨胀是不可逆的,它会受加温历史的影响,加热时的特性和冷却后的特性差异较大的影响.发现试样在升温过程很少发现热裂纹,但在冷却过程中反而易出现较多的微裂纹,认为是石灰岩在冷却过程中产生的残余应力所致.  相似文献   
7.
提出一种扫描电镜(SEM)扫描云纹法的相移新技术,通过SEM系统控制电镜电子束扫描线移动,对获取的云纹图像实现0-2π范围内的四步相移,从而获得了更高的位移测量灵敏度。同时对SEM扫描云纹法的测量原理以及相移实验技术的原理进行了详细的阐述。并将该技术应用到电子封装试件栅的相移分析中。实验结果证明了该方法的可行性,该方法为微米云纹法的条纹处理提供了一种新途径。  相似文献   
8.
为了提高扑翼飞行器的飞行性能,借鉴大型鸟类的飞行运动特征,设计了一种以凸轮摇杆为扑动机构的新型扑翼飞行器,建立了扑动机构的运动学和气动力学模型。结果表明:通过大型鸟类翅翼扑动规律对凸轮机构进行优化设计,得到了扑翼下扑占据整个扑动行程的60%左右;而提出的凸轮摇杆扑动机构的运动学模型,能够求解扑翼飞行器的相关运动参数。基于条带理论和扑翼飞行器的气动力模型,分别对凸轮摇杆扑翼飞行器、传统的双曲柄双摇杆机构扑翼飞行器的气动力进行计算比较,前者的平均升力为后者的1.382倍,前者平均推力为后者1.224倍,凸轮摇杆扑翼飞行结构具有更好的气动特性。  相似文献   
9.
In this paper,the natural structures of a dragonfly wing,including the corrugation of the chordwise cross-section,the sandwich microstructure veins,and the junctions between the vein and the membrane,have been investigated with experimental observations,and the morphological parameters of these structural features are measured.The experimental result indicates that the corrugated angle among the longitudinal veins ranges from 80 to 150,and the sandwiched microstructure vein mainly consists of chitin and protein layers.Meanwhile,different finite element models,which include models I and I for the planar forewings,models II and II for the corrugated forewings,and a submodel with solid veins and membranes,are created to investigate the effects of these structural features on the natural frequency/modal,the dynamical behaviors of the flapping flight,and the deformation mechanism of the forewings.The numerical results indicate that the corrugated forewing has a more reasonable natural frequency/modal,and the first order up-down flapping frequency of the corrugated wing is closer to the experimental result(about 27.00 Hz),which is significantly larger than that of the planar forewing(10.94 Hz).For the dynamical responses,the corrugated forewing has a larger torsional angle than the planar forewing,but a lower flapping angle.In addition,the sandwich microstructure veins can induce larger amplitudes of torsion deformation,because of the decreasing stiffness of the whole forewing.For the submodel of the forewing,the average stress of the chitin layer is much larger than that of the protein layer in the longitudinal veins.These simulative methods assist us to explain the flapping flight mechanism of the dragonfly and to design a micro aerial vehicle by automatically adjusting the corrugated behavior of the wing.  相似文献   
10.
本文采用磁致伸缩逆效应(应力对磁化的影响)的磁测技术对常见无缝输油钢管的受力变形进行了两种模拟加载方式的实验研究,给出了适合一定曲率管道"四系数"磁测钢管变形计算方法,并用有限元法对相应的受力状态进行了模拟计算,同时讨论了影响磁测精度的原因和解决方法.有限元计算结果与磁测实验结果基本一致.  相似文献   
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