Experimental Investigation on Bending Properties of DP780 Dual-Phase Steel Strengthened by Hybrid Polymer Composite with Aramid and Carbon Fibers

Lowering passenger vehicle weight is a major contributor to improving fuel consumption and reducing greenhouse gas emissions. One fundamental method to achieving lighter cars is to replace heavy materials with lighter ones while still ensuring the required strength, durability, and ride comfort. Currently, there is increasing interest in hybrid structures obtained through adhesive bonding of high-performance fiber-reinforced polymers (FRPs) to high-strength steel sheets. The high weight reduction potential of steel/FRP hybrid structures is obtained by the thickness reduction of the steel sheet with the use of a lightweight FRP. The result is a lighter structure, but it is challenging to retain the stiffness and load-carrying capacity of an unreduced-thickness steel sheet. This work investigates the bending properties of a non-reinforced DP780 steel sheet that has a thickness of 1.45 mm (S1.45) and a hybrid structure (S1.15/ACFRP), and its mechanical properties are examined. The proposed hybrid structure is composed of a DP780 steel sheet with a thickness of 1.15 mm (S1.15) and a hybrid composite (ACFRP) made from two plies of woven hybrid fabric of aramid and carbon fibers and an epoxy resin matrix. The hybridization effect of S1.15 with ACFRP is investigated, and the results are compared with those available in the literature. S1.15/ACFRP is only 5.71% heavier than S1.15, but its bending properties, including bending stiffness, maximum bending load capacity, and absorbed energy, are higher by 29.7, 49.8, and 41.2%, respectively. The results show that debonding at the interface between S1.15 and ACFRP is the primary mode of fracture in S1.15/ACFRP. Importantly, S1.15 is permanently deformed because it reaches its peak plastic strain. It is found that the reinforcement layers of ACFRP remain undamaged during the entire loading process. In the case of S1.45, typical ductile behavior and a two-stage bending response are observed. S1.15/ACFRP and S1.45 are also compared in terms of their weight and bending properties. It is observed that S1.15/ACFRP is 16.47% lighter than S1.45. However, the bending stiffness, maximum bending load capacity, and absorbed energy of S1.15/ACFRP remain 34.4, 11.5, and 21.1% lower compared to S1.45, respectively. Therefore, several modifications to the hybrid structure are suggested to improve its mechanical properties. The results of this study provide valuable conclusions and useful data to continue further research on the application of S1.15/ACFRP in the design of lightweight and durable thin-walled structures.