# Effects of Aging on Mode I Fatigue Crack Growth Characterization of Double Cantilever Beam Specimens with Thick Adhesive Bondline for Marine Applications

## TL;DR

This study examines how aging affects the fatigue crack growth in adhesive joints used in naval applications, showing significant reductions in performance due to environmental factors.

## Contribution

The paper introduces Bayesian linear regression to account for scatter in fatigue data caused by manufacturing imperfections in adhesive joints.

## Key findings

- Salt-spray-aged specimens show a 16.5% lower crack growth rate compared to unaged specimens.
- Immersion-aged specimens exhibit a 66.1% lower crack growth rate and significant differences in fatigue properties.
- Bayesian regression helps address scatter in data due to voids and discontinuities in adhesive bondlines.

## Abstract

The use of adhesive joints in naval applications requires a thorough understanding of their fatigue performance. This paper reports on the fatigue experiments performed on double cantilever beam specimens with thick adhesive bondline manufactured under shipyard conditions. The specimens have an initial crack at the steel–adhesive interface and are tested in unaged, salt-spray-aged and immersion-aged conditions to determine the interface mode I fatigue properties. The strain energy release rate is calculated using the Kanninen–Penado model, and the fatigue crack growth curve is determined using a power law model. The crack growth rate slope for salt-spray-aged specimens is 16.5% lower than for unaged specimens, while that for immersion-aged specimens is 66.1% lower and is shown to be significantly different. The fracture surfaces are analyzed to identify the failure mechanisms and the influence of the aging process on the interface properties. Since the specimens are manufactured under shipyard conditions, the presence of voids and discontinuities in the adhesive bondline is observed and as a result leads to scatter. Hence, Bayesian linear regression is performed in addition to the ordinary least squares regression to account for the scatter and provide a distribution of plausible values for the power law coefficients. The results highlight the impact of aging on the fatigue property, underscoring the importance of considering environmental effects in the qualification of such joints for marine applications.