Research On Materail Constitution Models Of TA15 And TC11 Titanium Alloys In Hot Deformation Processes

During hot deformation process, material constitutive model describes the dependence of flow stress on deformation temperature, strain rate and microcosmic structure transformation, and plays an irreplaceable role in the research and development of advanced plastic forming theories and technologies. TA15 and TC11 titanium alloys have found an increasingly wide application in aerospace industry because of its excellent properties. How to construct logical and reliable material constitutive models of these two materials has become an important problem urgently to be solved in frontier fieldes of advanced plastic forming. So, the establishment of TA15 and TC11 constitutive models using BP neural network and stepwise regression method respectively have been studied systematically in this dissertation. A brief introduction to the project and its main achievements are as follows:Based on the hot compression experimental study at isothermal constant strain rate, the influence of deformation temperature,strain rate and strain on flow stress has acquired in hot deformation process of TA15 and TC11 titanium alloys. It is found that deformation temperature and strain rate have an notable influence on the flow stress of TA15 and TC11, and they are materials sensitive to hot and strain rate.Based on MATLAB software, a method has been put forward for reasonably selecting layers and nodes of hidden layer, and TA15 and TC11 constitutive models have been constructed by using an improved trainbr algorithm. The results show that the constitutive models obtained are high in precision and prediction capacity, and they can be used to predict some data, which are hard to be obtained using experiment method, or to decrease some experiments to acquire material characteristic.The "optimum" independent variable subsets of macro-variables testable (deformation temperature,strain rate and strain) influencing the flow stress have been determined by using stepwise regression method. Then, based on experiment data and some ANN prediction data, TA15 and TC11 constitutive models have been constructed using stepwise regression method, the regression coefficients of which had been calculated using Least Squares method. The comparison between...