Thermal shock on interfacial adhesion of thermally conditioned Glass fiber/epoxy
The fiber/matrix adhesion is most likely to control the overall mechanical behavior of fiber-reinforced composites. An interfacial reaction may result in various morphological modifications to polymer matrix microstructure in proximity to the fiber surface. The interactions between fiber and polymer matrix during thermal conditioning and thermal shock are important phenomena.
Thermal stresses were built-up in glass fiber reinforced epoxy composites by up-thermal shock cycles (negative to positive temperature exposure) for different durations and also by down-thermal shock cycles (positive to negative temperature exposure). The concentration of thermal stresses often results in weaker fiber/matrix interface. A degradative effect was observed in both modes for short shock cycles and thereafter, an improvement in shear strength was measured. The effects were shown in two different crosshead speeds during short-beam shear test.
Differential thermal expansion is a prime cause of thermal shock in composite materials. Thermal expansion differences between fiber and matrix can contribute to stresses at the interface [1-5]. A very large thermal expansion mismatch may result in debonding at the fiber/matrix interface and/or a possible matrix cracking due to thermal stress [6-8]. The fiber/matrix interface is likely to affect the overall mechanical behavior of fiber-reinforced composites.
The performance of fiber reinforced composite is often controlled by the adhesion chemistry at the fiber/matrix interface. Thermal expansion coefficients of polymers are substantially greater compared to metals or ceramics. That is why failure of the bond between fiber and resin occurs under the influence of temperature gradient. The common reinforcement for polymer matrix is glass fiber. One of the disadvantages of glass fiber is poor adhesion to matrix resin.
The short beam shear (SBS) test results may reflect the tendency of the bond strength where only the bonding level is a variable . A large number of techniques have been reported for measuring interfacial adhesion in fiber reinforced polymer composites [10-16]. A need probably exists for an assessment of mechanical performance of such composite under the influence of thermal shock.
Thermal stresses caused by temperature gradient should be given special attention in many application areas. A better understanding of interfacial properties and characterization of interfacial adhesion strength can help in evaluating the mechanical behavior of fiber reinforced composite materials.