Comprehensive Investigation of Quasibrittle Fracture of IM7/977-3 Laminates via Size Effect Analysis

Abstract

This thesis investigates the non-linear size effect of fracture of IM7/977-3 laminates with different sizes in multiple modes including the matrix-dominated Mode I intralaminar fracture, the fiber-dominated Mode I intralaminar fracture, the Mode I interlaminar fracture, and the Mode II interlaminar fracture.The IM7/977-3 laminates, which are composed of HexTow® IM7 carbon fibers and CYCOM® 977-3 epoxy resin, are fabricated in-house using vacuum-bagged autoclave curing. Four types of tests, including Single-Edge Notched Tension (SENT), Double-Edge Notched Tension (DENT), Double Cantilever Beam (DCB), and End-Notched Flexure (ENF), are conducted to examine the fracture in the above-mentioned modes. In addition, Digital Image Correlation (DIC) is used to visualize the stain localization near the crack tip of DCB and ENF coupons. The load-displacement curve of each is recorded to obtain its fracture load. Based on the test results, with the assistance of the finite element method and Baˇzant’s size effect law, key parameters, including the fracture energy, the effective Fracture Processing Zone (FPZ) size, the pseudo-plastic limit, and the characteristic size are determined. Significant non-linearity is observed for the matrix-dominated Mode I intralaminar fracture, the fiber-dominated Mode I intralaminar fracture, and the Mode II interlaminar fracture. Therefore, compared to the conventional Linear Elastic Fracture Mechanics (LEFM), this study provides a more accurate prediction of fracture load of IM7/977-3 laminates in these modes at any size. The outcome of this study can be utilized to further optimize the structures made of IM7/977-3 laminates to get better performance.