| Accident Reconstruction is an important means to judge responsibility or grasp the character of accident, which displayes the occurring process of accident in the form of dynamic simulation or description by on-looking person. The veracity of traffic reconstruction main depends on the evidence's investigation at the scene of traffic accident, including all kinds of trace and evidence. Debris, as one of the most important evidence at the scene of traffic accident, contains much important information of accident. Then, debris is the key evidence for accident reconstruction.Early, the study on accident reconstruction using debris mostly focus on the analysis of kinetics in collision and the test of distributing fields based on statistics, etc. Being not considering the effect of different material nature, geometrical scale, and thrown condition of debris on the dynamic behavior, the early model's application is limited in real accident case. In this paper, the influence on the rule of dynamic and rebound character of material nature, geometry parameters, thrown condition (altitude, speed and angle), of small-scale debris is analyzed deeply by combining crash simulated experiment and computer simulation with the friction of air and ground, which make up the shortcoming of practical collision. Based on the analysis of dynamic character, the dynamic behavior model is established using collision theory. To some extent, the model established in this paper is benefit for perfecting the dynamic model further. The practical value of using debris to perform accident reconstruction is improved. The main performance is studied as followed:(1) The status quo using debris to perform accident reconstruction at home and abroad is studied in detail. According to the actual needs of reconstruction, take the relativity between material nature, thrown condition and dynamic behavior of debris as the researching cut-in point to study the dynamic behavior theoretical model. Based on the debris meaning of evidence investigation and validation, and the needs of researching, debris is classified generally according to the material nature and geometrical scale respectively. Then, the technical project is proposed. Take the plastic and elastic-plastic small-scale debris as studying object, which can offer foundation for further studying on dynamic behavior rule of middle-scale or large-scale debris.(2) Based on Ansys/Ls-Dyna, the single kinetic simulation model of small-scale debris is set up to study the effect of material nature, geometry parameters, thrown condition, on dynamic behavior and rule with air drag and ground friction. According to the data obtained from simulation, the relation curves are given between thrown distance and the parameters like thrown condition, material nature, and the shape of debris respectively. The connect degrees between thrown distance and the factors of thrown condition just like height, angle, velocity are analyzed deeply by Deng's grey connection analysis. The effect degree of factors on thrown distance is determined by connection order calculated by the method of grey connection analysis.(3) The dynamic rule of different material nature's rebound parameters varies with thrown condition obtained from the kinetic simulation analysis by Ansys/Ls-Dyna. The rebound parameters indexes are vertical rebound coefficient, horizontal rebound coefficient, angle lost coefficient. The effect of rebound character on dynamic behavior after collision is discovered. Based on the meaning of rebound parameters, the nonlinear trend curve of different material nature varying with rebound parameters is given by combing qualitative analysis with quantitative calculation. The abnormal phenomena of debris's motion just like breaking rebound, is expounded.(4) According to the two-phase kinetic model of debris, the dynamic states of different material nature (elastic, elastic-plastic, plastic), different shape (sphere, rectangle, abnormity) after impact are analyzed by referencing the theory of tangent dynamics. Then, the distinguish condition of glide and bounce is established when the debris collision with ground. When distinguish condition is satisfied, the nonlinear multi-factors model is established, applying different material nature, shape, crash velocity, and thrown distance, for accident reconstruction. The practical root can be solved by Matlab.(5) In accordance with the motion mechanism of debris in vehicle collision, the ejecting device is developed for satisfying the need of investigation. The effect degree and the dynamic rule of different material nature, geometry parameters of debris are analyzed and validated by the ejecting test device. The validity of behavior model is verified by comparing the results of simulation with test.The results of this paper enrich the application value of using debris, and offer a new method to calculate and analyze crash velocity for accident reconstruction in real case, which is significant on theory guidance for the department of police and judiciary.
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