Effect of cure pressure on microstructure and interlaminar shear strength properties of carbon fiber–reinforced plastics with microwave curing

Under a given microwave curing process, different curing pressures were applied to the carbon fiber–reinforced epoxy resin pre-impregnated laminates. Nondestructive testing and microscopic analysis were used to assess the effect of curing pressure on the interlaminar shear strength (ILSS) of the carbon fiber–reinforced plastic (CFRP) laminates. Results showed that in the low curing pressure stage (below 0.4 MPa), the porosity and ILSS of the components were reduced substantially as the curing pressure increased. In the high curing pressure stage (above 0.4 MPa), the ILSS only increased by 2.2% or so and the porosity and ILSS were no longer sensitive to the pressure, which indicated there was a threshold value (0.4 MPa) of mechanical property for forming the CFRP by the microwave curing. Above the threshold value, the curing pressure should be sufficient to allow the volatile gases to dissolve in the resin, thereby eliminating the generation of voids fundamentally, and the effect of curing pressure on the quality of composites was becoming small. These results could give process engineers some basic references for eliminating the voids in the CFRP component, so that they could reach a balance between preserving the mechanical properties and reducing the curing pressure in a cost-effective way.