Experimental Study On Dynamic Compression Performance Of Engineering Fiber Reinforced Cementitious Composites

Buildings not only have to bear static loads during their service lives but also inevitably suffer from impact loads.For example,the design of building structures in strong earthquake areas should consider earthquake effects.The design of protective structures in national defense projects should consider shock and explosion resistance.Concrete materials are more susceptible to brittle failure under dynamic loads,which limits their engineering application and promotion in related fields.The appearance of engineered fiber reinforced cementitious composite?ECC?has solved the shortcomings of low tensile strength and crack resistance of concrete materials,and ECC also has advantages such as strong energy dissipation capacity,large ultimate tensile strain,and good toughness,which makes it become the hotspot of research in recent years.At present,domestic and foreign scholars have relatively little research on the dynamic performance of PVA-ECC.The existing researches mainly focus on the influence of strain rate on the mechanical properties of materials at normal temperature,and there is still a lack of systematic and comprehensive research.The main work of this paper is to use the Split Hopkinson Pressure bar?SHPB?device to study the dynamic property of PVA-ECC under normal temperature and high temperature.The main jobs and conclusion are as follows:Due to needs of sensitivity analysis of the strain rate of materials,static compression tests were carried out on PVA-ECC under normal temperature and high temperature.Firstly,at normal temperature and high temperature-immersed in water to cool,the cube compressive strength f_cu,axial compressive strength f_c and peak strain?_o of the specimens were measured.Secondly,the mass loss rate of specimens were measured after high temperature-immersed in water to cool.Lastly,the relationship between f_cu and f_c was obtained through regression analysis.PVA-ECC material was dynamically compressed at normal temperature?25??,and the dynamic stress-strain curve was obtained.The sensitivity of the strain rate,failure mode,dynamic peak stress,peak strain,elasticity modulus and toughness index of the specimen were analyzed.With the increase of strain rate,the dynamic peak stress,peak strain and toughness of ECC material are obviously improved,which has a strong strain rate effect.With the increase of fiber volume content,the dynamic peak stress,peak strain and toughness of PVA-ECC increase obviously,and the PVA fiber has the most obvious increase of post-peak toughness of ECC.With the increase of matrix strength,the dynamic peak stress of ECC increases obviously,but the dynamic peak strain did not increase obviously.Moreover,the post-peak toughness of ECC specimens with high matrix strength decreased obviously,and the brittleness was more obvious.PVA-ECC specimens were dynamically compressed after high temperature-immersion cooling,and the dynamic stress-strain curves of the specimens at different fire temperatures were obtained.The sensitivity of the strain rate,failure mode,dynamic peak stress and peak strain of the specimens were analyzed.At three different temperatures,with the increase of the strain rate,the dynamic peak stress and peak strain of the specimens were significantly improved,showing a strong strain rate effect.The dynamic peak strain of the specimen increased with the increase of temperature,while the dynamic peak stress of the material increased only slightly at the high temperature of 150?,and decreased obviously at the fire temperatures of 250?and 350?.Under three different fire temperatures,the dynamic peak strain of the specimen increased with the increase of fiber volume content.The dynamic peak stress of the specimen only increased with the increase of fiber volume content after high temperature-water cooling at 150?,and decreased with the increase of fiber volume content at 250?and 350?.With the increase of the ECC matrix strength,the dynamic peak stress of specimen increases obviously,while the dynamic peak strain of the specimen increases slightly with a small increase.