Interlaminar fracture toughness of carbon/epoxy composites under mode I and II

Polymeric composites having high specific strength and stiffness compared to the traditional material are weak in outof-plane mechanical properties. More than above, these kinds of structures in some industrial applications are undergoing cyclic temperatures. In this manuscript, the effect of 200 thermal cycles in the range of -30 to +65 degrees Celsius on the fracture toughness of the carbon/epoxy composites is evaluated. Carbon/epoxy composite laminates are fabricated using carbon fabrics and epoxy resin in the form of the double cantilever beam (DCB), and end notched flexure (ENF) specimens. Samples are exposed to the 200 thermal cycles, and fracture tests are carried out in modes I and II. Test results revealed that the initiation fracture toughness of the samples in mode I (DCB) and mode II (ENF) are reduced 5.7 and 15.5 percent, respectively, compared to those are tested at room temperatures. Also, crack surfaces are investigated using an optical microscope and scanning electron microscope (SEM) in the specimens exposed to the thermal cycles.