Effect of curing temperature on the fundamental properties of laminated composites fabricated using plain weave and non crimp fiber and epoxy resin

During the past decade, the use of textile composites for aerospace and automotive applications has increased exponentially. Although textile composites are attractive from the manufacturing point of view, they have few drawbacks. Some of these drawbacks include the presence of resin rich pocket areas and undulation of weaves, to name a few. Recently, the next generation of reinforcements, namely non-crimp fabric (NCF) is being explored for various structural applications. NCF can exploit low angle plies and can also be stacked as non-symmetric plies about the midplane. NCF provides excellent laminate strength, and the cost of fabrication is usually substantially more economical than traditional composite manufacturing. In the present work, the laminates were manufactured using plain weave carbon fibers and NCF in conjunction with epoxy resin. Traditionally, epoxy resins are challenging to work in manufacturing processes at room temperature because they are more viscous due to their higher glass transition temperatures. In the present research, the laminates were fabricated using HVARTM (Heated vacuum assisted resin transfer molding) technique. This technique uses special heating pads to increase the operating temperature of both resin and fabric to the desired level. As a result, the resin is less viscous and can flow smoothly through the fabric. Once the laminates were fabricated, they were cured at three different temperatures. Since curing, temperatures can play a key role in the fundamental properties of composites such as tensile strength, modulus, etc. These values can vary significantly if the curing time and curing temperatures are different. Therefore, it is important to control the curing temperature and curing time to achieve the optimum fundamental properties of the fabricated composites. The higher the curing temperature, the faster the composite will cure, or in other words, there is an accelerated degree of cure. In the present work, 12 plies of plain weave carbon fiber (CF) and 24 plies of NCF were stacked and infused with epoxy resin to obtain laminates about 2.54 mm (0.1”) thick. These laminates were then cured at three different temperatures 121o C, 149o C, and 177o C (250o F, 300o F, and 350o F). The fabricated laminates were cut into tensile coupons using a water jet machine. The coupons were tested to determine the strength and stiffness of the laminate, and the results are then compared as a function of curing temperature and time. This study will help designers to determine the appropriate curing temperature that may be used during the fabrication of plain weave CF or NCF, depending upon whether the strength or stiffness properties are of importance in composite design.