| Thin films have been increasingly utilized in a vast range of technologically importantapplications. However due to the poor mechanical properties such as strength and interfaceadhesion of thin films, it may lead to crack, delamination even completely failure of thin films.Obviously, the mechanical properties of thin films are the key to design and improve thereliability and service life of film materials. Accordingly, study of the test model indetermining the mechanical properties of film materials is of great significance.Bulge/blister test is currently one of the techniques that have the advantage of being ableto characterize the elastic modulus, residual stress, Poisson ratio and other importantparameters such as interface adhesion and facture toughness. While the existing test models ofthis technique for measuring the mechanical properties of thin films are not perfect. In thisstudy, finite element method simulations are used to define virtual experiments, and thebulge/blister test models in determining the mechanical properties of elastic-plastic thin filmswere studied. The main contents and results of the research are summed up as follows:(1) The existing bulge test model of the bulge/blister test in determining the mechanicalproperties of thin films were compared and concluded, and the advantages and disadvantagesof the existing bulge equation and blister equation were pointed out. Through analyzing andconcluding these test models, a simple generalized bulge equation which can accuratelyreflects the mechanical response of pressurized film was obtained.(2) The corrected bulge test models for circular, square and rectangular window wereestablished in the light of our finite element results. The effect of the elastic constants andresidual stress on the test models was scrutinized by performing the finite element analysis,the results indicate that although the determination of residual stress with the bulge test forcircular films is fairly accurate, the calculation of the biaxial modulus is not as satisfied asexpected, while it shows the opposite tendency in the bulge test for noncircular films. It isobvious that the elastic constants and residual stress have a large effect on the accuracy of thetest models, hence the corrected bulge test models were proposed for improving the accuracyof this technique in measuring the elastic modulus and residual stress. At last, thecorresponding corrected test model was verified by conducting bulge experiments for squarefilm with our self-developed apparatus.(3) The empirical expression for characterization of the interface adhesion energy of theelastic-plastic thin film/substrate was proposed. Firstly, by using the cohesive element to simulate the interfacial debonding of thin films, the blister test of elastic thin film/elasticsubstrate material system was modeled to study the effects of the change of radius on the testmodel of interface adhesion energy. On this basis, the validity of the test model of blister testwas verified in terms of our finite element results. Then the finite element models forelastic-plastic thin film/rigid substrate was established, and with the large-scale computationalsimulation and the data analysis, an empirical expression for characterization of the interfaceadhesion energy of the elastic-plastic thin film/substrate is obtained. The result indicates thatthis expression is simple and the corresponding parameters are also easy to measure.The bulge/blister test models for characterization of the mechanical properties ofelastic-plastic thin film/substrate were studied in this thesis. The accuracy of the existingbulge test models were analyzed, at the same time, the blister test model in determining theinterface adhesion energy of the elastic-plastic thin film/substrate was established. The resultof this study will improve the accuracy and reliability of the bulge/blister test technique tosome extent and provide valuable guidance for characterization of the interface adhesionenergy of the elastic-plastic thin film. |
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