The combination of numerical simulations and experiments in dynamic material research

摘要

In civil engineering structures quasi brittle materials, such as concrete and some composites, are often used. In most applications these materials are loaded dynamically. Consequently, the study of the dynamic behaviour of quasi brittle materials is of major importance. Based on a series of experiments, a material model to describe the dynamic tensile behaviour of quasi brittle materials was developed within the framework of damage mechanics. The constitutive equations describing the dynamic material behaviour have been implemented in a finite element program. The equations contain some material parameters. These material parameters are determined by means of a combined experimental-numerical technique. The necessary experimental results are obtained by means of split Hopkinson bar tests. Although, the test technique has some limitations, certainly when testing quasi brittle materials, Hopkinson tests are used very often in high strain rate material testing, because practical test execution is rather simple, and because Hopkinson type tests give rise to relatively easy interpretation of test results. An automatic procedure has been worked out. With guess-values of the parameters a numerical simulation of a Hopkinson experiment is performed. Well-chosen results of the simulation are compared with experimental signals, a new set of parameters is proposed, a new simulation performed, the results are again compared with the experiment. The parameters are adapted just until sufficient agreement between the experiment and the simulation is obtained. It has been found that the combination of experiments and numerical simulations of the complex stress states and time histories involved in Hopkinson tests is an adequate and essential tool for material modelling.