차체사이드부재의 충격 흡수 능력에 관한 연구

Abstract

In modern society, drivers and engineers take carefully into account the safety capacity as well as the main function of the vehicles that is to transport passengers or goods as they purchase and produce them. The top-hat cross-section is the most commonly used side member in vehicles. In order to help automakers design the optimum devices and develop the production technologies for such structures, it is very important to look into their collapse properties and histories. In this study, the valid physical meanings such as absorbed energy and mean crushing load of specimens containing spot-welds are experimentally studied. Static and dynamic normal crushing tests have been respectively conducted on the materials which have different configurations; top-triangle, double-triangle, and double-hat thin-walled sections. Same tests have been also carried out on different cross-sectional area ratios in TH. Each of the post-test results including load-displacement curves is compared and the superior energy absorption capacity is determined. Objects including vehicles, aircrafts, and ships consist of a number of components and they perform their own roles in each part. Although a car is one of the preferred means of transportation, with the increment of car accidents pessengers’ interest in safety gets increasing day after day. As a result of that, skilled engineers are trying to advance the existing items and develop the new efficient materials. In order to conduct static and dynamic axial crushing tests on four kinds of specimens(top-triangle-hat, top-hat, double-triangle-hat, and double-hat) which were manufactured by welding the top and bottom part. There are six spot-welds per sample, the diameter is 6mm and distance between spot-welds is 22mm. The static tests were carried out on the Universal Testing Machine at a continuous speed of 10mm/min and test specimens were crushed by controlling the displacement up to 70mm out of total length at ambient temperature. To acquire important results of impact tests, the crosshead of 40kg has been vertically shot into a substance on the load cell at a speed of 7.19m/s repeatedly. The computer controlled optical displacement transducer 100F, ZIMMER, supplied the amount of axial deformation and impact load was measured using strain gauges attached to the load cell. Energy absorption of the specimens on both static and dynamic tests could be computed by obtaining the area of load-deformation curves. It also means that the energy absorption is equal to the mean crush load times the total deformation. In experiments on the impact axial crushing, we assumed that materials on the load cell entirely absorb EI(Impact energy) that is a theoretical value. However, post-test results were approximately 4% less than expectation .It may be thought that friction taking place between the cross head and vertical axis deprived specimens of the energy. The DH has the highest amount of energy absorption in static tests and absorbs the similar energy in spite of less deformation than others in impact tests. That is to say, it means that DH members have the highest strength among tested ones. However, they did not show the regular progressive collapse mode such as TH which is widely used for frontal-crash protection of vehicles. DH structures will be very helpful for side member providing that they have stable lobes and make an effective deformation configuration barring deteriorating strength.