Experimental Study On Fatigue Performance Of PVA-ECC Under Uniaxial Compression

Roads,bridges,water conservancy and other engineering structures are often subjected to fatigue loading,such as vehicles,wind and waves during service,resulting in fatigue failure of the structure at lower than static load strength,which seriously affects the safety and durability of the project.Therefore,it is of great engineering significance to study the fatigue performance of concrete materials.The poor ductility of concrete materials,which are prone to brittle damage under load,leads to their poor fatigue resistance.Engineered fiber reinforced Cementitious Composite（ECC）has received wide attention from scholars at home and abroad,because of its super toughness,quasi-strain hardening and multi-joint cracking characteristics,and its excellent deformation ability can better improve the fatigue performance of concrete materials.However,the current research on the fatigue performance of PVA-ECC is mainly focused on tensile and flexural aspects,and the research on its uniaxial compression fatigue performance is not yet comprehensive.In this paper,the effect of different stress levels(S_max),different cyclic stress ratios(r=S_min/S_max)and different loading frequencies（f）on the compression fatigue performance of PVA-ECC specimens were investigated by uniaxial compression fatigue tests on PVA-ECC cylindrical（d=70mm,h=140mm）specimens.The conclusions are as follows.The final damage morphology of PVA-ECC specimens under uniaxial compression fatigue loading is basically the same as that under direct compression static loading,with shear damage predominating.Due to the toughening and crack resistance of PVA fibers,the specimens have better integrity after damage.The larger the stress level and the smaller the stress ratio,the larger the crack width and the more severe the damage of the specimen after damage,while the loading frequency between 5 and 10 Hz has little effect on the damage morphology of the specimen.The fatigue life of PVA-ECC specimens obeyed the two-parameter Weibull distribution well,and the fatigue life equation under different failure probabilities was established.With the increase of stress ratio,the fatigue life and fatigue strength of PVA-ECC specimens significantly increased,and the smaller the stress level,the more significant the fatigue life of specimens improved with the increase of stress ratio;the larger the loading frequency,the larger the fatigue life of PVA-ECC specimens,and the smaller the stress level,the fatigue life of specimens improved insignificantly with the increase of loading frequency,and the fatigue strength remained unchanged.The fatigue damage process of PVA-ECC specimens under different stress levels,different stress ratios and different loading frequencies all went through three stages of development.the damage development rate of PVA-ECC specimens accelerated with increasing stress levels,and the larger the stress ratio,the faster the damage development of the specimens,while the damage development rate of the specimens slowed down when the loading frequency increased.The residual strain of PVA-ECC specimens was used as the damage variable to calculate the cumulative damage,and the fatigue damage evolution equation of PVA-ECC was established based on the continuous medium damage mechanics theory,and the experimental values were in good agreement with the calculated values.There are 43 figures,32 tables and 135 references in this paper.