Papers by Author: Juan Pablo Casas-Rodriguez

Abstract: The use of structural adhesive joints to join carbon fibre reinforced polymer (CFRP) adherends is now well established in the aerospace industry. These joints are subjected to varied load spectra, of which one of the most damaging forms of loading is fatigue with intermittent low energy impacts, which is termed combined standard and impact fatigue (CISF) in this paper. It is seen that the rate of crack growth in impact fatigue is greater than that in standard fatigue for a given value of the strain energy release rate, moreover, it is seen that the fatigue crack growth rate (FCGR) in standard fatigue (SF) increases after a block of impact fatigue. In this paper a model is proposed to predict crack growth in bonded joints subjected to CISF. The model is based on numerical crack growth integration (NCGI) with a method of accounting for the accelerated crack growth in SF following IF. The model was seen to provide a good prediction of the fatigue crack growth in CISF.

Abstract: The paper presents results of studies into the effect of repetitive low-energy impacting (known as impact fatigue) on reliability and crack growth in adhesively bonded joints. This type of loading is compared to the standard tensile fatigue in order to assess severity of such loading regime. Another loading type studied is a combination of a small portion of repetitive impacts with tensile fatigue. Crack propagation in a joint exposed to these types of loading is studied experimentally and numerically (with finite elements). This analysis is accompanied by microstructural studies of various damage processes, active at different stages of the crack growth process.

Abstract: In recent decades the use of structural adhesive joints in the aerospace industry has increased considerably thanks to their high strength-to-weight ratio, low stress concentration and capacity to join different adherends. There is increasing interest in damage due to low-velocity impacts produced in adhesively bonded components and structures by vibrating loads. This type of loading is known as impact fatigue. The main aim of this paper is to investigate damage evolution in adhesive joints subjected to impact-fatigue and to compare this with damage evolution in standard fatigue (i.e. non-impacting, constant amplitude, sinusoidal fatigue). In this work, adhesively bonded lap joints were subjected to multiple tensile impacts tensile and it was seen that this type of loading was extremely damaging compared to standard fatigue. A number of methods of studying damage evolution in bonded joints subjected to fatigue and impact fatigue loading have been investigated and various parameters have been used to characterise these processes. Two modifications of the accumulated time-stress model [1-4] are proposed and it is shown that both models provide a suitable characterization of impact-fatigue in bonded joints.