Failure analysis of adhesively-bonded metal-skin-to-composite-stiffener: Effect of temperature and cyclic loading

Abstract

The aim of this research is to analyse the failure of a Fiber Metal Laminate (FML) skin adhesively bonded to a Carbon Fiber Reinforced Polymer (CFRP) stiffener, under quasi-static loading at different environmental temperatures (−55 °C, Room Temperature RT and +100 °C) and under fatigue loading at RT. This bonded joint was tested using stiffener pull-off tests, which is a typical setup used to simulate full-scale components subject to out-of-plane loading. The failure sequence for all test conditions consist of: (1) damage initiation at the noodle of the CFRP stiffener; (2) damage propagation by delamination from the noodle to the stiffener foot; (3) detachment of the stiffener from the skin. Increasing the temperature, decreases the joint stiffness (40% when compared to RT) and decreasing the temperature decreases the maximum load (50% when compared to RT). The fatigue life initiation of the joint presents a very large scatter but the fatigue life propagation presents more stable results. The fatigue threshold (no damage) is reached at approximately 30% of the maximum load level. The fracture surfaces indicate a predominant inter and intra-laminar failure of the composite under mixed mode I/II. The CFRP stiffener is the weakest link of the bonded FML-skin-to-CFRP-stiffener both for static and fatigue loading.

Sofia Teixeira de Freitas

Principal Investigator

Sofia Teixeira de Freitas researches the structural integrity of bonded and layered materials to enable durable, sustainable structures. She is also an accredited group facilitator, committed to building academic environments grounded in cooperation and inclusion—key to overcoming technological limits and addressing the challenges of a truly sustainable society.