Failure Prediction and Surface Characterization of GFRP Laminates: A Study of Stepwise Loading.

The present study explores the failure and surface characteristics of Glass Fiber-Reinforced Polymers (GFRP). Stepwise loading was applied in this study to understand the multi-static loading effect on the laminates before final failure. The loading was set three times to reach 10 kN with loading-unloading movement before final load until failure. The results showed that the angle of the GFRP UD laminates' position significantly impacts the system's failure. The results were analyzed using theoretical calculation experiment analysis, and then the failure sample was identified using ASTM D3039 standard failure. The laminates with 0° layer on edge ([0/90] laminates) underwent preliminary failure before final failure. The mechanism of stepwise loading can be used to detect the effect of preliminary failure on the laminates. The [0/90] laminates are subjected to stress concentration on the edge due to fiber alignment and discontinued fibers in the 0-degree direction. This fiber then fails due to debonding between the fiber and the matrix. The laminates' strength showed that [90/0] specimens have an average higher strength with 334.45 MPa than the [0/90] laminates with 227.8 MPa. For surface roughness, the value of Ra increases more than six times in the 0° direction and three times in the 90° direction. Moreover, shore D hardness showed that the hardness was decreased from 85.6 SD then decreased to 70.4 SD for [0/90] and 65.9 SD for [90/0]. The matrix debonding, layer delamination and fiber breakage were reported as the failure mode behavior of the laminates.