Effect of thermal cycling on composites reinforced with two differently sized silica-glass fibers

ObjectivesTo evaluate the effects of thermal cycling on the flexural properties of composites reinforced with two differently sized fibers.MethodsAcid-washed, woven, fused silica-glass fibers, were heat-treated at 500 °C, silanized and sized with one of two sizing resins (linear poly(butyl methacrylate)) (PBMA), cross-linked poly(methyl methacrylate) (PMMA). Subsequently the fibers were incorporated into a polymer matrix. Two test groups with fibers and one control group without fibers were prepared.The flexural properties of the composite reinforced with linear PBMA-sized fibers were evaluated by 3-point bend testing before thermal cycling. The specimens from all three groups were thermally cycled in water (12,000 cycles, 5/55 °C, dwell time 30 s), and afterwards tested by 3-point bending. SEM micrographs were taken of the fibers and of the fractured fiber reinforced composites (FRC).ResultsThe reduction of ultimate flexural strength after thermal cycling was less than 20% of that prior to thermal cycling for composites reinforced with linear PBMA-sized silica-glass fibers. The flexural strength of the composite reinforced with cross-linked PMMA-sized fibers was reduced to less than half of the initial value.SignificanceThis study demonstrated that thermal cycling differently influences the flexural properties of composites reinforced with different sized silica-glass fibers. The interfacial linear PBMA-sizing polymer acts as a stress-bearing component for the high interfacial stresses during thermal cycling due to the flexible structure of the linear PBMA above Tg. The cross-linked PMMA-sizing, however, acts as a rigid component and therefore causes adhesive fracture between the fibers and matrix after the fatigue process of thermal cycling and flexural fracture.