Inhibition Mechanism Of Sma Assembly Reinforcement On Fatigue Cracking Of Longitudinal Rib Butt Welds

Due to the complex structure,the number of welds and the outstanding stress concentration of orthotropic steel bridge deck(OSD),the fatigue cracking problem is prominent under the coupling of vehicle load and initial manufacturing defects.The rib-to-rib welded joints is a typical fatigue vulnerable part of OSDs.The fatigue deterioration of the part seriously reduces the rigidity and bearing capacity of OSDs and deteriorates the safety and durability for structural systems of OSDs.This paper takes the structural detail as the research object.On the basis of in-depth study of its fatigue crack propagation characteristics,based on the iron-based shape memory alloy(Fe-SMA),a new method for positive reinforcement of the original structure with micro-damage is proposed,and a corresponding reinforcement system is developed.The effectiveness of using the method to reinforce the non-penetrating and penetrating fatigue cracks of the rib-to-rib welded joints is verified.On this basis,a systematic study of the key influencing parameters of the reinforcement effect is conducted,and the reasonable design parameters of the reinforcement system are determined.The main research contents and conclusions are as follows:(1)Based on the finite element software ABAQUS,the propagation processes of the nonpenetrating and penetrating fatigue cracks in the rib-to-rib welded joints of OSDs are numerically simulated.By analyzing the change regulation of the stress intensity factor at the crack front concerns,it is concluded that the fatigue crack propagation of the structural detail is dominated by Type-I cracking,and the contribution of Type-II and Type-III stress intensity factor amplitudes to the fatigue crack propagation is almost negligible.(2)Based on the fatigue cracking characteristics of the rib-to-rib welded joints,a new intelligent material Fe-SMA is introduced as a reinforcement.A new method for positive reinforcement of the original structure with micro-damage is proposed,and a corresponding assembly reinforcement system is developed.And the reliability and design of the reinforcement system are studied in-depth.The reinforcement method and system uses the shape memory effect of the material to realize the automatic application of prestress and the positive reinforcement of fatigue cracking.The reinforcement method has high material utilization rate,can automatically generate prestress to achieve positive reinforcement,and the reinforcement itself has high fatigue resistance.It belongs to a cold maintenance method with slight damage to the original structure.It provides a new idea for the development of fatigue cracking reinforcement technology for the rib-to-rib welded joints of OSDs.(3)For the non-penetrating fatigue cracks of the rib-to-rib welded joints,the effectiveness of the proposed positive reinforcement method is verified by linear elastic fracture mechanics.On this basis,a systematic study is conducted on the key influencing parameters of the reinforcement effect,and the suitable reinforcement schemes for non-penetrating fatigue cracks of different scales are determined.(4)Long penetration cracks are more common and difficult to reinforce in the rib-to-rib welded joints.In view of the penetrating long fatigue cracks of this structural detail,the reinforcement effects of the three positive reinforcement schemes are compared and the fatigue crack scale intervals applicable to each reinforcement scheme are determined.On the basis of systematic research on the key influencing parameters of each reinforcement scheme,the suitable reinforcement schemes of penetrating fatigue cracks under the condition of typical fatigue cracking scale are determined.