Study On The Shredding Mechanism Of Metal Sheet Of Discarded Vehicle

With the development of the economy, motor vehicles are greatly used. And they are mainly made up of metal sheet, and their recovery treatment problem after abandoned is one of the major issues that the word people are facing. At present, the most way to deal with the metal sheet of discard motor vehicles is shredding, so this thesis also mainly researches the shredding mechanism of metal sheet.The pendulum impact test for the metal sheet of discard motor vehicle is taken in this thesis, and the analysis shows that:in the shredding process of metal sheet, original cracks and defects show high stress concentration, and then breakdown under the action of transient load of breaking hammer; continued load makes the fragments torn off from the metal scrap. So there are two periods during the shredding process, breakdown and tearing, meaning that it is necessary to study the tearing behavior for further research of crushing of metal sheet.Because this thesis takes metal sheet of the discard motor vehicles as research object, whose brand is difficult to verify and the mechanical property parameters of materials are unknown. So the tension test for the selected material is carried out to obtain the he property parameters, and the material mechanical constitutive relation was simplified as a bilinear model.The analysis makes sure that tearing behavior in the shredding process is essentially a mode Ⅲ crack extension problem. It shows that three-leg trousers tear form is more accordance with this study by comparison two-leg trousers and three-leg trousers tearing test. So the three-leg trousers tearing test are used to study the tearing acts of metal sheet in this thesis. The legs of the metal sheet comes through two opposing elastic-plastic bending deformation in the process of three-leg trousers tearing test, and energy is consumed. From the view of conservation of energy, the amount work done by external force is divided into two parts:the first part is the tearing work of crack propagation, which includes the local deformation work consumed by local elastic plastic deformation of crack tip. The second part is the bending elastic-plastic deformation work which is done when the legs are undergoing bending deformation region. For the tearing process, the tearing work is more significance for tearing research, but it is not easy to calculate directly. Hence, by means of knocking the amount of energy expended in bending deformation off the total energy,the paper obtains the pure tearing work produced by the material, namely the tearing work, further the specific tearing work is gained for per unit new area of crack, which is made as the property parameters of material, and provides the basis for the latter study of shredding.In this dissertation, the non linear finite element analysis software LS-DYNA is successfully applied to simulate the tearing process of metal sheet. By the curves for the distance between two nodes which is on the same straight line originally, and the circumradius for three nodes varied with time, the fact that model has produced bending deformation twice is verified and it accords with the experiment. Further more, the model is reliable to a certain degree is demonstrated, and it paves a way for further study.