The Stress And Strain Softening Of HGM/ER Composites Under Cyclic Loading

As a new type of filled composites,hollow glass microbead(HGM)/epoxy resin(ER)composites are widely used in aerospace and biomimetic design industry,due to the superior characteristic of low density,high specific strength,versatility etc..In this paper,lots of experiments were carried out to study the degradation of mechanical property of HGM/ER composites under cyclic loading,and analyse the softening phenomenon and discuss the softening effect under different factors.Firstly,epoxy resin matrix composites filled with five volume fractions and three particle size ranges of hollow glass bead were prepared.The quasi-static compression tests were carried out to obtain stress-strain curves and calculate the elastic modulus and yield strength,and the elastic modulus and yield strength have different variation trend.Then,a cyclic load was designed and the stress softening experiment was performed.The stress softening curve can be divided into three stages: fast softening,stable softening and softening ground to a halt.The stress softening rate is inversely proportional to elastic modulus and different in different volume fraction and particle size.The aggregation effect of small particle size,the reinforcing effect of large size and the initial defect rate of interface between HGM and ER are the main reasons for stress softening.Finally,the strain softening experiment under the control strength of cyclic loading is designed and conducted.The typical strain softening curve is divided into two stages: fast softening and stable softening.As parameters to characterize the strain softening,the peak strain increasing coefficient and strain softening rate are inversely proportional to the elastic modulus of composites.By analyzing the curves of cycle cumulative numbers,it is found that the strain increasing coefficient and strain softening rate with different volume fraction and particle size are different,and take a larger value in smaller size and volume fraction and larger size and volume fraction.