Hybrid composites such as made of carbon fiber composite and glass fiber composite have many advantages such as high specific stiffness, high specific strength, high impact energy, cost reduction, good corrosion resistance and easy fabrication. These materials have been widely used in automotive and aerospace such as rotor blade, propeller shaft, leaf spring, and fly wheel. Although hybrid composites have excellent mechanical properties for the structure, the joints for the composite materials often reduce the efficiency of the composite structures because the joints are often the weakest areas in composite structures.
In this work, the bolted joints for the hybrid composite materials with glass/epoxy and carbon/epoxy composites under tensile loading were investigate to determine the optimum conditions for the hybrid composite materials. The geometry of the bolted joint specimen was designed to induce bearing failure because the bearing failure was desirable in the view of the design of the bolted joint. The design parameters were the ply angle, the stacking sequence, the ply-number ratio of glass/epoxy to carbon/epoxy, clamping pressure, and the outer diameter of the washer.
From the static tests of the bolted joints for carbon/epoxy composite and glass/epoxy composite with respect to the ply angle, the optimum ply angle for hybrid composites was determined. Then the joint specimens with seven or fourteen different stacking sequences and three different ply-number ratios of glass/epoxy composite to carbon/epoxy composite were tested under tensile loading. The effects of the outer diameter of the washer and the clamping pressure of the bolt on the bearing strength were also investigated.
Inspecting the fracture surfaces of the specimens, the delamination of the hybrid composite specimen on the loaded side of the holes and the extensive damage at the washer edge outside the constrained region were found. The delamination in the vicinity of the loaded hole was investigated by ultrasonic C-scan.
From the test of the bolted joints for hybrid composite materials, the optimum conditions of the hybrid composite materials for the bolted joint under tensile loads were determined. The test results of the bolted joints for hybrid composite materials were compared with those of the bolted joints for carbon/epoxy composite and glass/epoxy composite.
