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61.
A simple energy balance analysis is presented for the tearing of ductile sheet metals using the trousers test. It is shown that the specific essential work of fracture (w
e
) for tearing can be estimated by extrapolating the straight line relationship between the tearing force per unit thickness and the trousers leg width to zero leg width. There are two contributions to the specific essential work of fracture: one is due to the localised plastic shearing work in a zone contiguous with the torn edges (w
e1
) and the other is the final out-of-plane tearing work (w
e2
).
Résumé En utilisant le Trousers Test, on présente une analyse simple d'équilibre énergétique dans le cas du déchirement de feuilles métalliques ductiles. On montre qu'il est possible d'estimer le travail spécifique de rupture en déchirement w e en extrapolant la relation linéaire qui lie la force de déchirement par unité d'épaisseur et la largeur de l'échantillon caractéristique entre une valeur 0 et une valeur donnée. Deux éléments contribuent au travail spécifique essentiel de rupture, l'un est dû au travail de cisaillement plastique local dans une zone contigue aux bords de l'arrachement (w e1 ) et l'autre est le travail de déchirement final hors du plan de la feuille (w e2 ).相似文献
62.
Yujiao Mai Jianping Hu Zheng Yan Shuangju Zhen Shujun Wang Wei Zhang 《Computers in human behavior》2012
This study empirically investigated the structure and function of maladaptive cognitions related to Pathological Internet Use (PIU) among Chinese adolescents. To explore the structure of maladaptive cognitions, this study validated a Chinese Adolescents’ Maladaptive Cognitions Scale (CAMCS) with two samples of adolescents (n1 = 293 and n2 = 609). The results of the exploratory factor analysis and confirmatory factor analysis revealed that CAMCS included three distinct factors, namely, “social comfort,” “distraction,” and “self-realization.” To examine the function of maladaptive cognitions, this study tested an updated cognitive-behavioral model in the third sample of 1059 adolescents. The results of structural equation model analyses verified both the direct effect of maladaptive cognitions on PIU and their mediating role in the relationships between distal factors (social anxiety and stressful life events) and PIU among Chinese adolescents. Theoretical and practical implications of these findings were discussed. 相似文献
63.
The paper reports the results of an experimental investigation on the essential work of fracture of a strain-aged low carbon (0.1% C) temper-rolled 16-gauge sheet steel which has been subjected to pre-strain levels of 2 to 12% and ageing temperatures of 80 and 100C. Deep edge-notched tension specimens were used to determine the specific essential work by extrapolating the straight-line relationship between the specific work of fracture (W
f) and ligament length (I) to zero ligament length. The strain-aged steels at 80 and 100 give approximately the same specific essential fracture work of 0.18 to 0.20 J mm–2 which is independent of the amount of prestrain. Advancing crack opening displacements (C.O.D.) have also been analysed, which give 0.60 to 0.63 mm for the strain-aged steels. For comparison, the prestrained but unaged steels have a higher essential work of fracture of 0.275 J mm–2 and a larger C.O.D. of 0.73 mm. It is concluded, therefore, that the causes of strain-ageing embrittlement are primarily due to the reduction of both the essential work of fracture and the advancing C.O.D. at the crack tip end region. 相似文献
64.
65.
Y. W. Mai 《Journal of Materials Science》1975,10(6):943-954
Crack propagation of PMMA in some liquid environments is described for various testing conditions, such as fixed load, fixed displacement and monotonically increasing displacement. Fracture mechanics concepts have been used successfully in analysing the results. When continuous stable cracking is achieved, values of fracture toughness (R) for PMMA under these loading conditions are obtained as a function of crack velocity () using the method of Gurney and Hunt [11]. For crack velocities greater than 10–2 mm sec–1, the fracture toughness values in the environments are increased when compared with the corresponding air results. Unique relationships betweenR and have been shown to exist for cracking in ethanol and carbon tetrachloride. 相似文献
66.
This paper develops a closed-form solution for anti-plane mechanical and in plane electric and magnetic fields in a magnetoelectroelastic
layer of finite thickness. Explicit expressions for the stresses, electric fields, and magnetic fields, together with their
intensity factors are obtained for the extreme cases for impermeable and permeable cracks. Solutions for some special cases,
such as a magnetoelectroelastic layer with infinite thickness, are also obtained. Applicability of the crack face electromagnetic
boundary conditions is discussed. It is found that the crack profile is important in obtaining the correct electromagnetic
fields and their intensity factors. The stress intensity factor, however, does not depend on the crack face electromagnetic
boundary condition assumptions. 相似文献
67.
Aravind Dasari Zhong-Zhen Yu Mingshu Yang Qing-Xin Zhang Xiao-Lin Xie Yiu-Wing Mai 《Composites Science and Technology》2006,66(16):3097-3114
The primary aim of this paper is to provide an insight on the effect of the location of organoclay on the micro- and nano-scale deformation processes in melt-compounded nylon 66/organoclay/SEBS-g-MA ternary nanocomposites prepared by different blending sequences. In addition, the deformation processes of the ternary nanocomposites were compared to the binary nanocomposites (nylon 66/organoclay and nylon 66/SEBS-g-MA) and neat nylon 66. The incorporation of SEBS-g-MA particles toughened nylon 66 markedly; but the flexural modulus and strength were both reduced. Conversely, the use of organoclay increased the modulus but decreased the fracture toughness of nylon 66. Nylon 66/SEBS-g-MA/organoclay ternary nanocomposites exhibited balanced elastic stiffness and toughness. Stress-whitening studies of the fracture surfaces in terms of gray level were also performed and an attempt was made to correlate the optical reflectivity characteristics with fracture toughness. It was concluded that the capability of SEBS-g-MA particles to cavitate was decreased by the presence of organoclay in the SEBS-g-MA phase, resulting in reduced toughening efficiency. The best micro-structure for toughness and other mechanical properties is thus to maximize the amount of exfoliated organoclay in the nylon 66 matrix rather than to have it embedded in the finely dispersed SEBS-g-MA particles. 相似文献
68.
Wong E. H. Koh S. W. Lee K. H. Lim K.-M. Lim T. B. Mai Y.-W. 《Advanced Packaging, IEEE Transactions on》2006,29(4):751-759
Two advanced techniques have been developed for modeling vapor pressure within the plastic IC packages during solder reflow. The first involves the extension of the "wetness" technique to delamination along multimaterial interface and during dynamic solder reflow. Despite its simplicity, this technique is capable of offering reliable and accurate prediction for packages with high flexural rigidity. For packages with low flexural rigidity, the new "decoupling" technique that integrates thermodynamics, moisture diffusion, and structural analysis into a unified procedure has been shown to be more useful. The rigorous technique has been validated on both leadframe-based as well as laminate-based packages. With high accuracy and computational efficiency, these dynamic modeling tools will be valuable for optimization of package construction, materials, and solder reflow profile against popcorn cracking for both SnPb and Pb-free solders 相似文献
69.
70.
非化学计量一氧化钛的颜色研究 总被引:1,自引:0,他引:1
在确定非化学计量一氧化钛氧指数范围的基础上,研究了其颜色及其随氧指数的变化规律,并比较了其颜色与现用仿金材料之间的优劣。结果表明,在整个氧指数范围内一氧化钛均呈金黄色;随着氧指数的增大,在可见光作用下,对波长350.550nm范围内的紫、蓝和绿光反射逐渐减弱,对波长650-780nm范围内的红、橙光反射逐渐增强,其颜色从浅金黄色稍带白青色至纯正金黄色,最后至金黄色偏红;氧指数在1.14-1.16范围内其颜色最接近金黄,TiO1.15与24KAu色度差仅为0.0044,较仿金铜、TiN的颜色与24K黄金更为接近。 相似文献