Experimental Research And Theoretical Model Of Nonlinear Viscoelastic Crack Growth

Along with the wide application of nonlinear viscoelastic materials,the fracture in these materials has become a very important problemin industry field and scholarship studies. How to calculate the velocityof crack growth and how to get the life time of a structure with anonlinear viscoelastic crack are attractive problems. Because of thecomplexity of these problems, experiments are often introduced.The aim of this research is to find a test program to observe thewhole growth processions of nonlinear viscoelastic cracks with ouravailable experiment facilities.The main results of this research are the proposal of a new testprogram and a model for calculating nonlinear viscoelastic crackgrowth velocity. The new test program is raised by referencing theexisting test programs and by our trial and error. In the new testprogram, facilities involved in the nonlinear viscoelastic cracks testare relatively fewer, the test process is not very explicate and the dataobtained from the experiments is credible. By a model which is basedon the constitutive relation of the material and energy release rate,expressions are developed. And by the expressions the results ofexperiments have been explained roughly.Concrete achievements include: 1) The advantages of doublecantilever beams specimens in nonlinear viscoelastic crack growthtest is proved. Using these specimens, the relatively long time ofcrack growth process is obtained, calculating energy release rate isrelatively simple and the modeling of these specimens is easy. 2) Thetwo useful shapes of modified polypropylene specimen and theirdimensions in nonlinear viscoelastic crack growth test is proposed.And a simple loading system which can reduce lateral instability wasused. 3) After more than four months continuous test, useful datahave been obtained. 4) A model for calculating the velocity ofnonlinear viscoelastic crack growth has been proposed. 5) Havingroughly proved the validity of the model by comparing toexperiments data, and analyzed the limitation of this model. All theseachievements can provide methods and experiences for the nonlinearviscoelastic crack growth test in the future and provide a model thatcan be selected.