Papers by Keyword: Cumulative Damage Model

Abstract: Double Crossed Step-Down-Stress Accelerated Life Testing (DCSDS-ALT) discussed in this paper was implemented by switch down the double stresses alternately. Compared to constant stress test, step-stress test decreased specimen numbers, time and cost, and eventually well improve the accelerated testing efficiency. For pneumatic cylinder, the step-down-stress testing failure physics can be described as cumulative degradation model. By use of cumulative damage General Log-Linear relationship and Weibull assumption, the failure data obtained were equivalently converted to failure data under constant stress testing. Then the reliability specifications can be derived with better accuracy. The 5% of average lifetime estimation error and 1.85% of the characteristic lifetime error are very satisfying for pneumatic industrial lifetime prediction.

Abstract: The cumulative damage of the reinforced concrete (RC) crane girders occurred by overload, fatigue and other reasons in service may deteriorate the safety of RC crane girders seriously, so it is necessary to analyze the damage mechanism and rationally reinforce them in good time. In this paper, RC crane girder strengthened with CFRP strips is taken as a target, and the mechanical performance degradation under fatigue load is studied. According to the basic theory of continuum damage mechanics, a damage variable is defined by flexural rigidity, and fatigue- cumulative damage model, which describes the process of damage and fracture, is established. The variation law of cumulative damage of RC crane girders strengthened with FRP strips under crane load is discussed, and the failure patterns such as concrete cracking, debonding between CFRP strips and concrete, yield of steel bars etc., are studied. The criterion which can be used to estimate the cumulative damage degree of strengthened RC crane girders is proposed. Finally, the evolution of the fatigue damage in the RC crane girders strengthened with CFRP strips is numerically simulated, and the results show that the proposed model can correctly describe the damage and failure process of strengthened RC crane girders. The research will provide a reference for the damage analysis and reinforcement of RC crane girders strengthened with CFRP strips.

Abstract: Externally bonded carbon fiber reinforced polymer (CFRP) materials are well suited to the rehabilitation and reinforcement of civil engineering structures due to their high specific strength, specific stiffness and corrosion resistance. To probe the fatigue behavior of CFRP strengthened concrete structures, three point bending experiments of reinforced concrete (RC) beams strengthened with carbon fibre laminate (CFL) under constant amplitude loading were performed. The histories of midspan flexibility and bending stiffness of strengthened beams were recorded automatically. And the linear curve between fatigue strength and the logarithm of fatigue life was obtained. The failure modes go through concrete cracking, CFL debonding from concrete and steel bars yielding and fracture with increasing cycles of fatigue loading. Bonded CFL increases the ductility of strengthened RC beam and results in dense distribution of cracks compared with normal RC beam, and it’s bending stiffness at damage state as well. The fatigue damage evolvement shows three stages of nucleation, steady expansion and failure. Then the failure mechanism was studied and a cumulative damage model was proposed to describe the fatigue damage and fracture process of CFL strengthened RC beams under constant amplitude loading.