Theoretical Research On Crack Monitoring And Self-repairing Mechanism For SMA Intelligent Concrete Materials

Concrete is a kind of widely used engineering material,its unavoidable crack generation and expansion has always been a difficult problem to be solved in the field of civil engineering.In this dissertation,shape memory alloy(SMA)is decided to be embedded in concrete and the crack monitoring and self-repairing mechanism for SMA intelligent concrete materials are researched theoretically as follows:Firstly,the mechanical properties and constitutive model of SMA materials are introduced.Then three unique mechanical behaviors(shape memory effect,partial superelasticity and complete superelasticity)of SMA materials are analyzed in detail.Secondly,the material design and model hypothesis of SMA intelligent concrete illustrated by the case of airport pavement are proposed.By combining the definition of cylindrical conductor resistance in physical principle,constitutive model of SMA and the definition of strain in material mechanics,relationships between crack size and the relative change of SMA resistance are obtained,which is the theoretical model of crack monitoring.The numerical results of the model at different temperatures are compared with the experimental results,and the correctness of the model is verified.Finally,the expressions of the recovery stress at any temperature in the process of electronic heating for SMA with different initial states are obtained by applying the constitutive model to the reserch on reverse phase transformation of constrained SMA materials.The relationship between recovery stress and temperature under a given prestrain is calculated and compared with experimental result to verify the correctness of the model.Then the effects of prestrain and initial state on recovery stress are discussed.In summary,the theoretical models of crack monitoring and self-repairing for SMA intelligent concrete materials are presented in this dissertation,which can provide theoretical guidance for further research and application of SMA materials in the field of civil engineering.