Fracture Behavior of a 3-D Braid Graphite/Epoxy Composite

Abstract

An exploratory study of the fracture behavior and notch sensitivity of a 4-step, 3-D braid-reinforced graphite/epoxy composite has been made. Test methods based on the Mode I compact tension specimen were developed and lower bounds for the damage initiating force and the work of fracture were determined for certain notch-to-braid axis orientations. These values are higher than for laminate composites but showed severe anisotropy. Complementary in-situ and post-mortem optical and scanning electron microscopy were used to identify microstructural failure controlling features and to develop a volume-to-surface structural mapping strategy useful in accounting for some of the observed features of the failure process.

Fracture Propagation in Composites with Biaxial Fiber Reinforcement

“…Work of fracture can be evaluated by many methods such as average fracture energy, strain energy release rate, and fracture toughness. In this paper, the energy per unit area of fracture surface consumed in fracture progression [14] is used to define the work of fracture, which is defined by a simple reduction method of critical energy release rate. The fracture characterizing parameter W is defined as:…”

“…The structural examples of this simulation, for which experimental results are available from the published literature by Filatovs et al [14], consist of several biaxial braidreinforced Graphite-Epoxy C(T) specimens. The composite preforms are braided from tows containing 12 K (12000 individual fibers), 7 mm diameter Ceylon G30-500 graphite fibers and braided by the 4-step process in 3 Â 14 patterns.…”

“…To compare with the test results shown in Figure 4, the fracture stages were selected when fiber fracture occurred at a load of 618.3 N (139 lb) and before the ultimate structural failure. Taking into account of the micro-cracks during the compact tension tests, the crack areas were modified by the correction factor n that is identified [14] as 3.2 and 6.0 for these two stages since the fracture propagation stage causes more damaged nodes as Filatovs et al [14] indicated. Table 4 compares computed W values from simulation results with those obtained from the experimental load-displacement relationship using Equation (4).…”

Mode I fracture toughness of fiber-reinforced polymer composites: A review

“…An initial crack can be formed using non-adhesive film [8,115,120,158] or mechanical cutting using saw [13,71]. Screw-driven machines [117], servo-hydraulic [8,159] or tensile testing machines [115,158,160] can be used to perform quasi-static test at constant cross-head displacements [161]. According to the aim of investigation, the test materials and test conditions can be changed.…”

“…According to the aim of investigation, the test materials and test conditions can be changed. During test, crack length can be found visually or by using travelling microscope that help to see crack growth path [117]. Fracture process can be recorded using camera to analysis crack initiation and propagation.…”