An experimental study on low velocity impact performance of bolted composite joints-part 2: Influence of long-term seawater aging

In the first part of this two-part paper (Part 1), the low-velocity impact (LVI) response of bolted fiber-reinforced polymer joints was investigated considering with two scenarios based on the localized impact damage as the impactor hit on the top of the bolt (ToB) and the side of the washer (SoW). Moreover, the influence of halloysite nanotubes (HNTs) reinforcement of the epoxy matrix on the impact performance was also evaluated. As the second part of the research, this paper represents the effects of seawater aging on the LVI response of FRPs. For this, the composite joints were submerged in an artificial seawater environment for six months to accelerate aging. Afterward, as following the systematic experimental path exhibited in Part 1, LVI tests were conducted by dropping the impactor on ToB and SoW regions. The test results showed that the seawater aging impaired almost 30% of the composite joints' impact resistance, where HNTs reinforced multi-scale composite joints exhibited a 13% higher impact loading performance. The ToB impact scenario was considered as visually and quantitatively more detrimental than the SoW tests. The detrimental impact of seawater aging was validated by tracking the elemental evolution in the seawater environment. Based on the mechanical, morphological, and structural analyses, a novel damage mechanism was introduced to address seawater aging's progress, including the role of nanoreinforcements.

Automated summary

This paper investigates the low-velocity impact response of bolted fiber-reinforced polymer joints in two scenarios, and evaluates the impact of halloysite nanotubes (HNTs) reinforcement of the epoxy matrix. The effects of seawater aging on the impact performance of the joints are also studied, with results showing a decrease in impact resistance after aging, but an improvement when using HNTs reinforced joints. The ToB impact scenario is considered more detrimental than the SoW tests, and a novel damage mechanism is introduced to address the impact of seawater aging.