摘要 :
In this work, a survey on the closed form solutions for the prediction of interfacial shear and peeling stresses of bonded structures is first given. And then, comparisons between the closed form solutions, elastic finite element ...
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In this work, a survey on the closed form solutions for the prediction of interfacial shear and peeling stresses of bonded structures is first given. And then, comparisons between the closed form solutions, elastic finite element analysis (FEA) and elastic-creep FE results are performed for the bonded structures subjected to thermal loading. To elucidate the creep effects on interfacial stresses, at last, creep damage FE analysis is carried out referring to the K-R damage creep law. Results indicated that both creep and creep-damage analysis will lead to interfacial stress redistribution and thus reduce the shear stress and peeling stress at interface. Creep damage analysis yields the lowest stresses among the linear elastic and elastic creep analysis results. The maximum damage is produced at the edge of the interface where the failure often occurs and is proportional to the modulus ratio of substrate to film. On the other hand, the damage distribution along the interface is very similar to the trend of peeling stress distribution. Compared to the FE results, the existing closed solutions from Mirman et al. [B.A. Mirman, S. Knecht, IEEE Comp. Pack. Manufact. Technol. 13 (1990) 914] and Zhang et al. [X.C. Zhang, B.S. Xu, H.D.Wang, Y.X.Wu, J. Appl. Phys. 100 (2006) 113524]can only give an accurate prediction of the interfacial shear stress but give a rough estimation to the interfacial peeling stress. As far as effects of creep are concerned, the existing closed form solutions based on elastic analysis are inapplicable anymore.
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摘要 :
Nanocrystalline materials offer very high strength but are typically limited in their strain to failure, and efforts to improve deformability in these materials are usually found to be at the expense of strength. Using a combinati...
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Nanocrystalline materials offer very high strength but are typically limited in their strain to failure, and efforts to improve deformability in these materials are usually found to be at the expense of strength. Using a combination of quantitative in situ compression in a transmission electron microscope and finite-element analysis, we show that the mechanical properties of nanoparticles can be directly measured and interpreted on an individual basis. We find that nanocrystalline CdS synthesized into a spherical shell geometry is capable of withstanding extreme stresses (approaching the ideal shear strength of CdS). This unusual strength enables the spherical shells to exhibit considerable deformation to failure (up to 20% of the sphere's diameter). By taking into account the structural hierarchy intrinsic to novel nanocrystalline materials such as this, we show it is possible to achieve and characterize the ultrahigh stresses and strains that exist within a single nanoparticle during deformation.
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摘要 :
We studied the photoluminescence (PL) in CuInSe_2 thin films grown by metal organic chemical vapor deposition (MOCVD) using a Cu precursor and two gases. By X-ray diffraction (XRD) and PL analysis, we found that the best quality o...
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We studied the photoluminescence (PL) in CuInSe_2 thin films grown by metal organic chemical vapor deposition (MOCVD) using a Cu precursor and two gases. By X-ray diffraction (XRD) and PL analysis, we found that the best quality of CuInSe_2 thin films can be obtained when the deposition time of the trimethylindium (TMI) gas is 30 min. The improvement of the quality of CuInSe_2 thin films after rapid thermal annealing (RTA) is evident from the full width at half maximum (FWHM) of PL. The FWHM of the PL peak is minimum when the RTA temperature is 500℃. It is found the binding energy of the impurity level in CuInSe_2 thin films increases after RTA, revealing that the thermal stability of CuInSe_2 thin films is improved after RTA.
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