Zubair Sajid

In this study, the role of carbon‐basalt hybridization in improving the impact resistance and damage tolerance of bonded single lap joint has been evaluated. Therefore, four configurations of unidirectional plies stacked in cross ply sequence have been experimentally evaluated under low‐velocity impact and tensile‐after‐impact (TAI) loading. The configurations consist of two pure laminates (CCCC and BBBB) and two inter‐ply hybrids (CBBC and BCCB). Impact testing was performed using a drop‐weight apparatus, and residual strengths were measured through tensile testing on pre‐impacted samples. Results at 2.5 J impact show that (CCCC) laminates exhibit the highest peak impact forces, i.e., (1968.9 N) and residual strengths (3371.2 N), while (BBBB) and BCCB demonstrate lower stiffness but greater damage diffusion and energy absorption. The CBBC hybrid achieved the most effective balance, retaining tensile capacity close to (CCCC) joint configurations, (3360 N) at low energies and exhibiting enhanced impact resistance (2503.3 N, 27.14% increase), due to synergistic stress redistribution between carbon and basalt layers. SEM images further support these results by showing that the sandwiched basalt layers diffuse and spread damage, preventing cracks from directly reaching the adhesive layer, as occurs in (CCCC) joints, and thereby shifting the failure mode toward adhesive‐dominated behavior under tensile loading.

The flexure response of novel thermoplastic (Elium^®) 3D fibre-reinforced composites (FRC) was evaluated and compared with a conventional thermoset (Epolam^®)-based 3D-FRC. Ten different types of sample 3D-FRC were prepared by varying fibre orientations, i.e., 0°, 30°, 45°, 60° and 90°, and resin system, i.e., thermoplastic and thermoset. The bending characteristics and failure mechanisms were determined by conducting a three-point bend test. Results elucidate that the on-axis specimens show linear response and brittle failure; in contrast, the off-axis specimens depicted highly nonlinear response and ductile failure. The thermoplastic on-axis specimen exhibited almost similar flexure strength; in comparison, the off-axis specimens show ~17% lower flexure strength compared to thermoset 3D-FRC. Thermoplastic 3D-FRC shows ~40% higher energy absorption, ~23% lower flexure modulus and ~27% higher flexure strains as compared to its thermoset counterpart.

The effect of tightening torque and washer size on the performance of basalt natural fiber composite joints was investigated experimentally. It was found that washer size is the main design driver in controlling the out-of-plane behavior of the joint. Specifically, there was a 36.5% increase in the 0.2% offset strength when the torque was increased for small washer configurations, whereas a 42% increase was observed when the torque was increased for large washer configurations. Moreover, the ultimate bearing strength also showed an improvement under the combined effect of washer size and tightening torque. Additionally, damage onset and failure mechanisms of the bolted joint were investigated using optical microscopy. The morphological observations indicated excessive crushing for large washer configurations. It is postulated that bearing performance could be improved by choosing appropriate washer size and tightening torque.