| Abstract [eng] |
In the literature analysis part of the final master‘s project, the target is to get to know about vehicle passive safety elements, construction types and vehicle deformation zones. The main types of car structures are presented, as well as ways to assess their safety and strength properties. The main types and shapes of vehicle longitudinal member, the principles of production and used materials are described. At the end of literature review, the vehicle crash boxes are overlooked. In the research part of the final master‘s project analyses deformation properties of the front side longitudinal members of the selected vehicles. After carrying out tensile tests in the laboratory, the materials of the longitudinal members and their main mechanical characteristics are determined. It was found that both members are made of aluminum alloys. The yield strength of the first longitudinal member is 210 MPa, and the yield strength of the second longitudinal member is 270 MPa. Using „SolidWorks“ software 3D models of selected crash boxes are created and transferred to „Ansys LS-Dyna“ software for finite element analysis. During the analysis, vehicle crash boxes are buckling by applied different analysis conditions. It was determined that first crash box deformed at 10 m/s velocity fails when a force of 132 kN is reached. The second crash box is stronger, deformed at the same speed, it fails at 346 kN reached force. After determined the maximum reaction forces and the amount of absorbed energy, the influence of the inner crash box wall is evaluated. It was found that the first crash box with an additional wall bends harder and at the same time is able to absorb a higher amount of energy, which increases from 6,55 kJ to 9,58 kJ at the 0,1 m displacement point. After removing the inner wall of the second crash box, it was found that crash box bends easier ant the absorbed energy decreases from 15,19 kJ to 8,97 kJ. In the part of determining the influence of the using material, the crash box materials are changed and the amount of absorbed energy is calculated. There are three materials used – two aluminum alloys and structural steel. Using structural steel for crash boxes the results shown that amount of absorbed energy is increased. However, compered to aluminum alloys, the use of steel significantly increases stress of crash boxes. In the last part of the work, the investigation of the crash box shapes is carried out. It was found that the most optimal shapes are the hexagonal shape with one inner wall and the rectangular shape with two inner walls. It was also found that replacing the usual rectangular shape with hexagonal or circular shapes the amount of absorbed energy increases. |
