Interlaminar stresses occur at the free edge and notch to cause composite laminates to delaminate. Actually, delamination is an important failure mode and affected, for example, by fiber orientation and stacking sequence as discussed. In analysis, our de veloped mathematical model yields the interlaminar edge stresses and singularities around the hole to predict the onset of delamination. Furthermore, our work mainly aims to inves tigate experimentally the initiation and propagation of delamination subjected to tension and cyclic tension-tension (T-T) tests in centrally notched T300/5208 graphite/epoxy com posite laminates, including four layups: (a) orthotropic [=±45]4s, [90/0] 4s and (b) quasi- isotropic [0/90/±45]2s, [90/0/±45]2s. Experimental result and observation associated with the obtained maximum stresses and the adopted failure criterion are in good agree ment with our predicted delamination onset. Other important findings are highlighted as follows. The failure mode of each layup recorded by X-ray radiograph can be closely cor related to the prediction of our model. The delamination growth rate has also been mea sured. An approximately linear relationship between delamination area and stiffness re duction for the centrally notched quasi-isotropic lammates is established. The critical load for delamination can be estimated by the Hashin-Rotem failure criterion satisfactorily. As a benefit of nondestructive testing, we finally find that the residual strength of the laminate first increases as applied cycles increase and then decreases during fatigue tests. However, residual stiffness always decreases monotonically with the increase of applied cycles.

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The aim of this research is first to model the degradation of the elastic modulus of quasi-isotropic [0/90/ ±45] 2 s graphite/epoxy centrally notched composite laminates subjected to tension-tension ( T-T ) fatigue tests. Then we can predict the fatigue life in terms of elastic modulus as a non-destructive parameter of failure criterion and express the residual strength by using the elastic modulus degradation model. Extensively, the concept of cumulative damage is adopted to expand these models for wide applications to any sequence of loading spectrum instead of the constant stress amplitudes. These models have been modified from the existing models, they possess the features of accuracy, simplicity and applicability. Basically, part of them are verified satisfactorily in comparison with the experimental data. They still have sound theoretical bases and simply applicable to engineering problems.

We fabricate a SiOC comb structure capacitor device, and apply mechanical stress into samples by bending. From I-V fitting, we obtain the energy barrier lowering β, and conclude that the electron transport in single damascene capacitor is due to Poole-Frenkel emission. Tension yields a decrease of energy barrier in the single damascene dielectric layer and an increase of leakage current compared to the unstressed sample. In contrast, compression stress yields the energy barrier increase and the leakage current decrease. The variation of leakage current is originated from the energy barrier change induced by mechanical stress.

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