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Título:DYNAMICAL MECHANICAL PROPERTIES MEASUREMENT METHODOLOGY INFLUENCE ON THE PREDICTION OF THE BEHAVIOR OF STRUCTURES SUBMITTED TO ELASTIC-PLASTIC IMPACTS Instituição:PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO - PUC-RIO Autor(es):MARCELO DE JESUS RODRIGUES DA NOBREGA
The strain rate effects in the mechanical properties can be significant in the simulation of the dynamic behavior in plastic deformed structures, this work has the objective to evaluate these effects through two complementary tasks: (i) to develop and qualify an appropriate methodology for the measurement of dynamic mechanical properties, including the requirements necessary to measure and to adjust of the best possible way the experimental data, quantifying the uncertainty they associated; and (ii) to verify the influence of the strategy of measurement of the mechanical properties in the prediction of the behavior of structures submitted to impacts.The models that describe the dynamic mechanical behavior are based on the strain rate de/dt, but usually its parameters are measured in controlled tests by the speed of loading. However, the rate de/dt does not remain constant in the tests realized with fixed speed, which it increases the uncertainty of the predictions based on the measured parameters. For a quantitative evaluation of the influence of the control strategies in the mechanical properties, was first established a appropriated statistical procedure to determine the number of specimens necessary to measure dynamic properties with a acceptable level of reliability. All the data were measured twice, controlling the strain rate or the loading speed imposed in the specimens, in a wide range, 10(-4) less than or equal de/dt less than or equal 10/s, in tests particularly realized with care. The acquisition and data processing were made through a program developed in Labview. A program developed in Mathcad was used to optimize the parameters of the diverse models studied to the data set measured by a Levenberg-Marquardt algorithm. From this study is proposed a new model that describes the yieldind adequately, and minimizes the errors of fitting in the region of transition elasto-plastic, that plays a great role in the structural analysis.A simple porch was chosen to verify the effect of the dynamic properties in the numerical simulations made in program LS-DYNA, used traditionally to simulate elasto-plastics impacts. Several of these porches had been submitted to impacts in a machine of free fall (drop-weight), to induce variable plastic strains in function of the impact speeds. The measured strains were compared with the predicted ones using the properties obtained with the two strategies of control, and adjusted by the diverse studied models. In such way the influence of measurement methodology of the dynamic mechanical properties in the prediction of the behavior of structures submitted to elasto-plastics impacts can be quantified.