Behavior of Woven Fabric Reinforced Epoxy Composites Under Bending and Compressive Loads

Abstract

The mechanical behavior of epoxy reinforced by three different types of woven fibers was studied under compressive and bending loads. The reinforcements used were: woven glass fibers (volume fractions: 9.2%, 18.4%, 27.6%, and 36.8%), woven carbon fibers, and woven hybrid (carbon/glass) fibers at 36.8 vol.%, each. The composites were manufactured using the hand lay-up technique. Pure (unreinforced) epoxy specimens were tested as a reference material. The fracture behavior of the investigated specimens was studied both macroscopically, and using scanning electron microscopy (SEM). It was found that under compressive loads, elastic deformation is nonlinear for pure epoxy as well as epoxy reinforced by low volume fractions of glass woven fibers. At high volume fractions of glass fibers, carbon fibers, or hybrid ones, this non linearity diminished significantly. The modulus of elasticity of epoxy-reinforced by glass fibers (GF) continued to increase as a function of fiber volume fraction. At 9.2 vol.% the modulus of elasticity showed an increase of 65% compared to pure epoxy, while at 36.8 vol.% GF the improvement reached 117%. At the same volume fraction of 36.8% hybrid, and carbon reinforcements the improvements were 160%, and 178%, respectively. Similar trend of improvements were observed for the other mechanical properties under compressive loads. Under bending loads, both the flexure modulus, and flexure strength showed significant improvement as a function of glass fiber volume fraction. At the same reinforcement volume fraction, carbon fiber composites gave the highest mechanical properties, followed by hybrid composites, while glass fiber composites showed lowest improvement (about 348% improvement in flexure strength compared to pure epoxy). Fiber pull-out and debonding are the main fracture mechanisms for glass fiber reinforced epoxy, while interlaminar shearing is the main mechanism for carbon fiber composites. Hybrid (C/G) composites showed a mixed mode mechanism. The fracture process in bending proceeded in stages from the tension side inwards towards the compression side. Each stage is associated with a load drop and audible sound waves.

Hybridization Effects on Bending and Interlaminar Shear Strength of Composite Laminates

“…The Kevlar/epoxy composite has the lowest bending stress and stiffness but the highest strain, evidencing the ductile nature of the fibers that are classified as high-elongation fibers [27,28]. Finally, the results described above are supported by several studies that evoked similar conclusions [12][13][14][23][24][25][26][27][28] and are a consequence of the different damage mechanisms.…”

“…Wonderly et al [11] also reported that the ratio of compressive strength over tensile strength is different for carbon and glass fiber composites, with values around 0.34 and 0.73, respectively. In fact, Santos et al [12] and Ghafaar et al [13] reported that full-carbon composites have the maximum bending stress and stiffness, while fullglass fiber laminates have the lowest value, reaching a difference in bending strength of about four times [14]. Therefore, by adding carbon fibers on the tensile side of glass fiber composites, the flexural strength will increase, while on the compression side the strength will decrease [14,15].…”

“…For example, in carbon/epoxy composites, a void content around 10% by volume reduces the ILSS by around 25% [21]. In the same context, the fiber type and its orientation have a strong influence on the interlaminar shear strength [13,20]. According to Madhavi et al [14], the ILSS values for carbon-reinforced composites are about five times higher than those observed for glass fiber-reinforced composites.…”

Mode I fracture toughness of Carbon/glass hybrid comopsite

“…The glass fiber composites exhibited maximum fracture toughness was 131.90 MPa.mm 1/2 . Abdel Ghafaar et al [17] established three different types of woven fibers in the epoxy resin and prepared by hand lay-up method to evaluate the mechanical properties under the effect of bending loads and observed that the maximum values of the flexural strength and modulus at CFRP compared to the hybrid composites and GFRP were 360 MPa, 17.11 MPa, respectively. In addition, Chinta et al [18] carried out the single edge notch bending (SENB) to study the mode-I fracture toughness for non-hybrid woven carbon/epoxy (C20), and hybrid carbon core composite (G5C10G5), experimentally and finite element modeling (ANSYS).…”

Evaluating the Multifunctional Performance of Structural Composites for Thermal Energy Storage

“…The mechanical properties of these laminates were investigated through quasi-static tensile and 3-point bending tests, short-beam shear tests, and mode I interlaminar fracture toughness tests. The bending load–displacement curves of all laminates ( Figure 3 A) show an initial linear region, but for the neat EP-CFu laminate, the load drops to zero immediately after the maximum value, indicating a sudden and catastrophic failure, which was reported as a sign of good interlaminar adhesion [ 52 , 53 ]. On the other hand, MCs change the failure mode and make the load decreasing stepwise after the maximum, indicating energy dissipation also during damage propagation.…”