Investigating the Effect of Adding Natural Fibers on Interlaminar Fracture Toughness of Glass/Epoxy Composites Under Mode Ⅰ Loading Using Acoustic Emission Test

In recent years, with the increase in the price of non-renewable petroleum products and strict environmental laws, the application of natural fibers as reinforcement in composite materials has been increased. In the current study, the effect of adding natural fibers on the resilience to delamination, which is the most common type of failure in laminated composites, is investigated in mode Ⅰ loading using features extracted and evaluated from acoustic emission non-destructive method. The samples were made using the hand lay-up method. The double edge cantilever beam test was used to test the samples. Using the methods provided in the ASTM D5528 standard, the occurrence of initiation of delamination is determined in the samples. The results show that only the use of the mechanical methods provided in the mentioned standard is not enough to determine the initiation of delamination, and for an easier and more accurate determination of the initiation of delamination. Thus, the assessment of delamination defect initiation and fracture toughness by means of features measured by acoustic emission test should be applied. Then, using the energy method, cumulative energy, count and cumulative count are used to determine the initiation of delamination in the samples. Then, using the critical load and critical displacement determined by different mechanical and acoustic emission methods, the interlaminar fracture toughness values of the samples are calculated. At the end, the results of the present study are compared with previous studies. According to the obtained results, the usage of kenaf fibers does not show a significant increase in the interlaminar fracture toughness of glass/epoxy composites, but application of cotton fibers causes a significant increase in the interlaminar fracture toughness. Among the different acoustic emission methods, the count method shows the lowest error of 1.8 percent regarding the method proposed in the standard, nonlinear method, among the other acoustic emission methods.