Objective: In 2020, the world's first crash compatibility rating test will be introduced in the European mobile progressive deformable barrier (MPDB) test. In this research, the quantitative change in partner protection performance of large vehicles in car-to-car (C2C) impacts was studied if these large vehicles were designed in future based on MPDB tests addressing crash compatibility ratings. Methods: Representative vehicles of the European fleet were selected and a Computer Aided Engineering (CAE) parameter study was conducted. In particular, by changing an indicator of structural interaction performance (SD; i.e., the degree of uniformity of barrier deformation)/mass/stiffness of large vehicles systematically in a step-by-step approach, the compatibility evaluation results of large vehicles in MPDB and the occupant injury score of small vehicles in C2C impacts were compared. The CAE result was evaluated compared to that of C2C physical impact tests. Results: The CAE parameter study showed that in the C2C impact condition, the effects on occupant injury in a small vehicle due to changes in the large vehicle were as follows: (1) SD change: The effect was minor except for small overlap condition. (2) Mass and stiffness change: The effect was relatively major. On the other hand, compatibility evaluation in the MPDB showed a tendency to overestimate the effect of SD change in comparison with the above-mentioned C2C impact condition. In addition, physical impact tests showed that, based on SD evaluation, the large vehicle with a relatively inferior compatibility rating compared to those with superior compatibility ratings showed a contradicting trend of better compatibility performance in the C2C test. Conclusions: The currently proposed compatibility evaluation method of the MPDB test showed some tendency to overestimate the effect of SD change and resulted in quantitatively inconsistent outcomes regarding occupant injury in the partner car in C2C impact conditions.
Bending tests using a silicon nitride and an alumina were carried out under 4-point bending to clarify the relation between the strength and the size of flaw observed at a fracture origin. When the fracture originated from a smaller flaw, the strength was confirmed to be lower than that expected from the fracture toughness criterion. A convenient procedure using the mean strength and the fracture toughness was proposed to estimate the strength degradation depending on flaw size. A new model was also developed assuming the stable cracking caused by the separation per one grain ahead of a flaw prior to the final unstable fracture. A Monte Carlo simulation based on the proposed model was made to explain the anomalous behavior of small flaw. The relation of strength vs. crack length simulated by taking account of grain-size distribution showed good agreement with the experimental result. The lower bound in scatter of strength depending on flaw-size was suggested to be estimated by using the size of the largest grain expected in a material.
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