Assessment of damage tolerance of bolted composite structures via bearing-after-impact tests

Abstract

Although bolted composite joints are mainly designed to resist bearing loading, dynamic loading such as low-velocity impact can also be a severe threat because of its potential to reduce joint reliability. Surprisingly, it is still unclear how bolted composite joints perform after the dynamic loading, and its effect on the damage tolerance is unknown likewise. This study aims to evaluate experimentally the bearing-after-impact (BAI) damage tolerance of bolted glass-fiber (GF) reinforced epoxy composite joints. For this, the GF/epoxy composite laminates were assembled in single-lap shear joints firstly, and the bolted composite joints were subjected to low-velocity impact tests at various energy levels from 3 to 10 J. Following that, standardized bearing tests were carried out to determine the damage tolerance of the laminated composites following the impact. Nanoclay fillers were also added to the epoxy matrix to improve damage tolerance. After the low-velocity impact loading, the bearing strength diminishes by almost 22% for the bolted composite joints, while the reduction in damage tolerance is effectively limited with the nanoclay addition. However, as the impact energy increases, the efficiency of the nanofiller declines. Increased impact energy results in changes in failure modes, and nanofillers improve damage tolerance with additional nano-scale toughness-increasing mechanisms.