Study On Mechanical Behavior Of New Cementitious Composites Based On Shape Memory Alloy Fibers

Shape Memory Alloys(SMA)are a new type of intelligent material that has attracted widespread attention from civil engineers in the 21 st century due to its outstanding shape memory effect and super elasticity,and the use of SMA in engineering can improve the deformation recovery and energy dissipation capacity of structures.Therefore,in this paper,the bonding performance of superelastic Shape Memory Alloys Fiber(SMAF)and Fiber Reinforced Cementitious Composite(FRCC)was first investigated,and based on the results of the bonding performance,SMAF was added to FRCC to make a new cementitious composite(SMAF-FRCC)based on Shape Memory Alloys Fiber.The mechanical properties of SMAF-FRCC composites were investigated by flexural,compressive,and cyclic loading tests,and the major research results are as follows:(1)Uniaxial tensile tests showed that FRCC made of modified polypropylene fibers(PP)with a length of 20 mm had the best tensile performance,showing a ductile damage mode with multiple seam cracking and strain hardening phenomenon.(2)The mechanical property indexes such as ultimate tensile strength,ultimate strain,residual strain,and deformation recovery rate of superelastic Ni Ti SMA wire were obtained by uniaxial tensile test and cyclic tensile test,and the effect of diameter on the mechanical properties of SMA wire was analyzed.The results show that SMA wire with a 0.6 mm diameter has the highest ultimate tensile strength and SMA wire with 1.0 mm has the highest ultimate strain and exhibits the best superelastic recovery under cyclic loading.(3)The effects of SMAF diameter,end geometry,and bond length on the bonding performance of SMAF to FRCC substrate were investigated by single fiber pullout tests,and the pullout load-displacement curves of each group of specimens were obtained,and the specimens were evaluated by bond strength and pullout energy.The results of the combined tests showed that increasing the SMAF diameter and changing the SMAF end geometry(L-shaped and N-shaped)could improve the bonding performance between SMAF and FRCC.(4)By orthogonal test method,three levels of variation of four influencing factors of SMAF diameter,quantity,end geometry,and length were selected,and the order of significance of the effects of the interaction of the four factors on the cracking strength,flexural strength,and mean self-centering ratio of SMAF-FRCC pre-opened beam specimens were analyzed,and the results of the orthogonal test were analyzed by ANOVA to arrive at the optimal solution under the four factors.(5)Randomly distributed SMAF-FRCC composite beam specimens were subjected to flexural,compressive,and cyclic loading tests to describe the different failure modes of SMAF-FRCC composite specimens,and to analyze the effects of SMAF volume fraction,diameter,and length on the flexural and compressive strengths,self-centering properties and energy dissipation capacity of composite beam specimens.The results show that the addition of SMAF can significantly improve the performance indexes of composite beam specimens and enhance the ductility and toughness of the material.