An assessment of mechanical behavior and fractography study of glass/epoxy composites at different temperatures and loading speeds

• Loading rate has a significant effect on the fiber/polymer composites.
• We studied the mechanical behavior and fractography with loading rates.
• Interlaminar shear strength (ILSS) is influenced by loading rate and temperature.
• ILSS value, high at low loading speed and becomes low at high loading speed.
• Localized plastic deformation process plays dominating role at low loading speed.

Effect of loading rate on fracture and mechanical behavior of autoclave cured glass fiber/epoxy prepreg composite has been studied at various loading (striking) rates (0.01-103 mm/min). The maximum load carrying capacity and strain at yield continuously increases with increasing loading speed. The interlaminar shear strength (ILSS) value is high at low loading speed and becomes low at high loading speed with the transition of loading rate at approximately 300 mm/min. The formation of steps, welt interfacial failure and cleavage formation on matrix resin i.e. localized plastic deformation processes were dominating mechanisms for specimens tested at low loading rates, while brittle fracture of fiber, fiber pull-out and impregnation were dominating mechanisms for specimens tested at loading rates of 800 mm/min or higher.

Fracture starts to occur preferentially at fiber/matrix interface region. Heat capacity at matrix is less, thus an appreciable temperature rise occurred in front of the crack tip even small value of inelastic energy at low temperature. It is anticipated as by existing of adiabatic heating i.e. unstable crack propagation. In this state, rate of heat generation is lower than for its removal (thermally active zone to passive zone). Thus shear strength values decrease at higher cross head speed which shown in figure. This may also be hypothesized of preexisting microcracks, notches, debris i.e. with a stable element (low-energy crack growth). This fracture may be arrested and then reinitiated, or may lead to initiation and growth of secondary mode of failure.Figure optionsDownload as PowerPoint slide