Effect of silicone rubber mandrels on the pressure distribution and forming quality of composite hat joints by co-curing processing

In this work, composite hat joints were fabricated using silicone rubber mandrel with different proportions of the trapezoidal hole. The co-curing process was selected to form the composite hat joints. The pressure distribution during the co-curing process of composite hat joints was monitored by a capillary pressure test system. The external forming accuracies and internal microstructures of composite hat joints were measured using micrometer, caliper and optical digital microscopy, respectively. The thermal deformation of the silicone rubber mandrels was simulated through the thermo-mechanical coupled model. The results indicated that the internal pressure fluctuated obviously and unevenly without the opening of the trapezoidal hole. With the increase of X-S value of the trapezoidal hole, the internal pressure was uniform and stable at the required pressure of 0.6 MPa at X-S = 0.069. Meanwhile, the average differences for thickness and cavity height were only 0.033 mm and 0.36 mm, respectively, and microstructure was improved. Through the deformation simulation results and comparing with the specific tests, the optimum process windows for trapezoidal hole were recommended at X-S values of 0.06 to 0.08. This work would be helpful to optimize the design of the silicone rubber mandrels and ultimately improve the forming quality of the composite hat joints. [GRAPHICS]