# Fatigue Design of Tubular Carbon–Aluminium Bonded Joints Under Constant- and Variable-Amplitude Fatigue

## TL;DR

This study examines how carbon fiber and aluminum bonded joints behave under different types of fatigue loading, showing that a specific stress parameter improves fatigue life predictions.

## Contribution

The study demonstrates the effectiveness of using the Generalised Stress Intensity Factor (H0) for fatigue life estimation in bonded joints under variable-amplitude loading.

## Key findings

- Using H0 reduced the scatter index of fatigue data by a factor of 1.46 compared to nominal stress.
- Miner’s rule confirmed the suitability of H0-based models for variable-amplitude fatigue conditions.
- H0 is shown to be an effective parameter for predicting the fatigue performance of bonded joints.

## Abstract

This study investigates the fatigue behaviour of carbon fibre–aluminium adhesively bonded tubular joints, representative of the suspension arm of a Formula SAE racing car, under both constant- and variable-amplitude fatigue loading. A linear elastic stress analysis was conducted using two-dimensional axisymmetric finite element models to determine the singular stress field parameters—specifically the Generalised Stress Intensity Factor (H0) and the stress singularity exponent (s)—at critical adhesive–adherend interfaces. Experimental tests under quasi-static loading and constant amplitude, as well as variable-amplitude fatigue conditions, were performed. The constant-amplitude fatigue data were reanalysed in terms of both nominal maximum shear stress and H0. The results show that the scatter index of the fatigue data was reduced by a factor of 1.46 when H0 was used as the fatigue-driving parameter, indicating an improved correlation of the experimental results. Variable-amplitude fatigue tests were interpreted using Miner’s cumulative damage rule, confirming the suitability of H0-based life estimation models even under realistic, variable-amplitude loading conditions. The results demonstrate that H0 is an effective parameter for rationalising fatigue performance of tubular bonded joints and highlight its potential for fatigue design in composite–metal structural applications.