Mechanical behaviors and fracture mechanisms of CFRP sandwich composite structures with bio-inspired thin-walled corrugated cores

Abstract

This paper investigates mechanical behaviors and fracture mechanisms of bio-inspired thin-walled corrugated-core sandwich composite structures made of carbon fiber-reinforced polymer (CFRP) under four-point bending and flatwise compression. Biomimetic thin-walled corrugated cores, inspired by nature's structures, were proposed and manufactured using the hot vacuum molding method. Quasi-static bending and compression tests were conducted to characterize the load capacity, compressive strengths, and failure progressions with the assist of the digital image correlation and thermography method. Measured full-field strains revealed critical bending/compression strains of the samples while a temperature increase was observed in full-field thermal maps, which was a sign of crack initiation. We concluded that the fracture mechanisms of specimens in bending tests depend on the fiber orientations of the core. The sandwich structure with a core angle of ±45 degrees exhibited a larger load capacity and bending stiffness than the structure with a core angle of 0/90 degrees. The cracks were mostly initiated at the core (0/90 degrees) and the facesheet (±45 degrees) with a core crushing and facesheet fracture, respectively, and propagated in the core with shear cracks due to fiber fractures. In addition, the failure of the thin-walled corrugated cores in flatwise compressions arose first by buckling and was followed by the subsequent collapse of the cores. The theoretical calculation provided a useful understanding of the different failure mechanisms of the sandwich structure. The proposed sandwich structures achieved prominent mechanical performances that were 26.5 MPa/gcm−3 in bending and 11.8 MPa/gcm−3 in compression and the experimental technique can depict the successive events that lead to the complex fracture of thin-walled corrugated core sandwich composites.