Mesomechanics Analysis On Damage Mechanism Of Basalt Fibre Reinforced Concrete Under Fatigue Loading

Concrete is a typical heterogeneous composite material.The heterogeneity of meso components makes the material show nonlinear mechanical behavior.The damage and failure of composite materials are often multi-scale mechanical problems across structures and materials.Therefore,in order to reveal the failure mechanism and macro mechanical characteristics of concrete composite materials from the source,it is necessary to study the macro mechanical response of concrete materials caused by the changes of meso mechanical characteristics and structural forms of each component from the meso level,so as to realize the interaction between meso and macro.Basalt fibre reinforced concrete(BFRC)is a new type of composite material.It is of great theoretical significance to study the mechanical properties and damage evolution of BFRC for its application and popularization.Macroscopic test is the most direct method to reveal the material properties,but it is difficult to explain the damage evolution process and failure mechanism of fibre reinforced concrete from the essence,and the test is difficult to repeat.In this paper,the influence of meso components on macro mechanical properties is considered.By establishing a reasonable micro model of basalt fibre reinforced concrete,the close relationship between meso components and macro mechanical properties of BFRC is realized.Based on the meso model,the mechanical properties and fatigue properties of BFRC are analyzed.There are many factors affecting the mechanical properties of BFRC.The main factors considered in this paper are fibre content,fibre length and fibre agglomeration.The main work and research results are as follows:(1)Mori Tanaka homogenization method and meso finite element method were used to predict the elastic modulus of BFRC,and compared with the experimental verification.The results show that: basalt fibre can slightly improve the elastic modulus of concrete,the greater the amount of basalt fibre,the greater the elastic modulus of concrete.The errors of meso finite element method and M-T homogenization method are within the acceptable range,and the M-T method is faster,and the maximum error is only 3.45%.(2)The model of random aggregate is established,and the zero thickness cohesive element is embedded,and the law of traction separation is given to form BFRC meso finite element model.The uniaxial tension-compression and bending resistance(three-point/four-point bending)were analyzed respectively.On the basis of ensuring the reliability,the influence of fibre content,fibre length and fibre aggregates on the static performance of concrete was further analyzed,and the evolution law and failure mechanism of BFRC crack were revealed.The results show that the fibre content has the greatest influence on the static performance of concrete,and 0.2%-0.3% is the optimal content;The effect of fibre agglomeration is the second,which can reduce the flexural strength by 11.98%-17.55%;The influence of fibre length is the weakest,and the optimal length is 18 mm.(3)Based on the reliable static calculation,the three-point and four point bending fatigue properties of BFRC are analyzed from fatigue life and fatigue strength by stress method.The four point bending fatigue properties are compared with the test results,and the influence of content,fibre length and agglomeration on fatigue properties is still analyzed.The results of fatigue test are similar to those of static test,and the content is still the first influencing factor.The larger the content is,the better the fatigue performance is.The increase of 0.2% content is the most obvious;Agglomeration can significantly reduce the fatigue life and strength of concrete;Length has the weakest effect,and 18 mm is still the best length.