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.

Low‐velocity impact response of halloysite nanotube reinforced glass/epoxy multi‐scale composite. Part 1: Dynamic loading performance

“…Previous works have indicated that the reinforcement of HNT in multi‐scale composite specimens restricts matrix cracks, delamination, and fiber breakage damages created under impact loads. [ 20,35,36,39 ] Impact damage formations are constrained by toughening mechanisms of HNTs such as crack pinning and deflection, particle debonding and bridging. [ 35 ] In nanoclay addition to epoxy, the widely used reinforcing element of the clay family, improvements were also obtained for impact load performance of glass fiber composites.…”

“…In addition, the intensity of oscillations is related closely to the type of impact damage. [ 20,41 ] Moreover, the slope from the initial point to the peak point on curves is demonstrated the flexural rigidity of specimens. Accordingly, the multi‐scale composite laminates have higher flexural rigidity than GFRP specimens.…”

“…In recent years, nano‐scale reinforcements have become essential to enhance the fiber–matrix interface. [ 15 ] The reinforcements such as carbon nanotube (CNT), [ 16,17 ] SiO 2 , [ 18 ] nanoclay, [ 19,20 ] graphene, [ 21–23 ] CaCO 3 , [ 24 ] and Al 2 O 3 [ 25 ] represented enhancements on the mechanical, thermal and chemical properties of composite materials. On the other hand, halloysite nanotubes (HNTs) are abundant nano particles with tubular 1D structure, large aspect ratio, natural existence, prosperous functionality, good biocompatibility, and high mechanical properties.…”

Tensile behavior of the bolt‐jointed GFRP after low‐velocity impact

“…[ 1–3 ] The laminated construction of fiber‐reinforced composites and the characteristics of their constituent properties (fiber and matrix) often make their structural performance sensitive to even transverse impact loading. [ 4–7 ]…”

Effects of meso‐ and micro‐scale defects on hygrothermal aging behavior of glass fiber reinforced composites

“…Fiber‐reinforced polymers (FRPs) have been extensively used in strategic industries, including aeronautical, marine, transportation, and renewable energy. [ 1–6 ] During their service life, FRPs are subjected to severe environmental conditions such as moisture and elevated temperatures, reducing their performance. [ 1,7–10 ] “Aging” is referred to as the process of degrading the properties of materials over time due to environmental conditions.…”