| Based on the requirements of energy saving and environmental protection, lightweight design has become a trend in the field of vehicle. Generally, substituting the conventional steel material with low-density materials is one of the most efficient ways to reach the goal of structure lightweight. Within a short term, light materials can’t form a complete vehicle without the use of steel. There will be co-appearing of dissimilar materials in car body, which leads to the problem of dissimilar materials connection. Adhesively bonded joints are widely used in jointing dissimilar materials because of a series of advantages over conventional jointing technologies, which includes better sealing, better fatigue resistance and relatively even stress distribution.Compared with conventional jointing methods, research on the serving performance of adhesively joints is far from enough, which limits its application in automobile industry. Within vehicle’s operating periods, fatigue damage of bonded joints is one of the major causes of failure with dynamic excitation from road surface. Meanwhile, precise prediction on fatigue life of vehicle’s key locations could guarantee fatigue requirement in the process of lightweight design. Till now, while fatigue performance of metal/metal bonded joints is widely studied, there’s still a shortage of research on metal/composite adhesively joints’.The current thesis focused on composites’mechanics properties and Steel-CFRP bonded joints’fatigue damage performance and the research work was carried out in the following aspects:(1) Experimental methods and theoretical models were employed to study the macroscopic mechanics properties of a specific type of composites and CFRP-made substrates, respectively. By designing its corresponding fixtures, quasi-static mechanics test of a specific type of composites were conducted, which obtained its tensile, compression and shearing parameters; Rule of Mixture and Halpin/Tsai model were employed to acquire CFRP-made substrates’ material mechanics parameters which would be used in ABAQUS8 CAE to simulate CFRP substrates’quasi-static tensile process.(2) Based on a total life approach, Steel-CFRP bonded joints’fatigue performance was investigated under a specific constant amplitude loading. Backface Strain method was applied to record strain variation of joints’lap area. Using residual strength and frequency variation as evaluation indicators, effects of different loading periods on joints’static and dynamic performance were studied experimentally. |
