T-T cyclic response of Open-Hole Quasi-Isotropic CFRP laminates containing Ultra-Thin Plies
Topic(s) : Special Sessions
Co-authors :
Carlos SANDINO (SPAIN), Roberto PRIETO-GARCÍA (SPAIN), Serafín SÁNCHEZ-CARMONA (SPAIN), Elena CORREA (SPAIN)Abstract :
The “scale effect” is a phenomenon within composite materials which is characterised by a less significant damage onset associated with a decrease in ply thickness. This effect has been revisited in recent years following the introduction of low-grammage prepregs. The physically based explanation proposed for this phenomenon [1] has also spurred research into employing ultra-thin plies for the manufacturing of composite laminates.
To this aim, some studies have revealed the effects of the use of ultra-thin plies in the case of cross-ply laminates subjected to cyclic tensile loads [2]. In this context, the authors propose an experimental study of the application of ultra-thin plies in quasi-isotropic composite laminates. More specifically, the integration of these plies in carbon fibre open-hole quasi-isotropic laminates is explored, in order to analyse damage evolution under cyclic tensile loads. For this purpose, the performance of quasi-isotropic laminates consisting of conventional thickness plies is compared with laminates with 90º ultra-thin plies, while maintaining the same stacking sequence. Furthermore, this study is conducted for two different stacking sequences, which include the same number of 45º, -45º, 0º, and 90º plies. The aim is to analyse the use of 90º ultra-thin plies and their position throughout the thickness, in terms of damage progression, in order to detect a possible improvement in the laminate behaviour.
After the quasi-static tensile characterisation of the laminates, the open-hole specimens are subjected to tension-tension fatigue loading. The fatigue stress ratio is R=0.1, and the maximum load is a fraction of the corresponding ultimate load. Concerning the damage assessment, the evolution of the damage extent over the course of cycles is conducted through ultrasonic inspection. In cases with identical loading levels, laminates containing ultra-thin plies exhibit a diminished progression in damage evolution, delayed failure, and a reduced influence of the presence of the open-hole. The results also reveal that the reorganization of the stacking sequence plays a significant role in the damage mechanism, especially concerning the appearance of free-edge damage. This fact gives significant prominence to the use of 90º ultra-thin plies. All these observations suggest an enhanced performance of quasi-isotropic laminates with ultra-thin plies under cyclic tensile load and, therefore, endorse the potential implementation of this strategy at an industrial scale.
To this aim, some studies have revealed the effects of the use of ultra-thin plies in the case of cross-ply laminates subjected to cyclic tensile loads [2]. In this context, the authors propose an experimental study of the application of ultra-thin plies in quasi-isotropic composite laminates. More specifically, the integration of these plies in carbon fibre open-hole quasi-isotropic laminates is explored, in order to analyse damage evolution under cyclic tensile loads. For this purpose, the performance of quasi-isotropic laminates consisting of conventional thickness plies is compared with laminates with 90º ultra-thin plies, while maintaining the same stacking sequence. Furthermore, this study is conducted for two different stacking sequences, which include the same number of 45º, -45º, 0º, and 90º plies. The aim is to analyse the use of 90º ultra-thin plies and their position throughout the thickness, in terms of damage progression, in order to detect a possible improvement in the laminate behaviour.
After the quasi-static tensile characterisation of the laminates, the open-hole specimens are subjected to tension-tension fatigue loading. The fatigue stress ratio is R=0.1, and the maximum load is a fraction of the corresponding ultimate load. Concerning the damage assessment, the evolution of the damage extent over the course of cycles is conducted through ultrasonic inspection. In cases with identical loading levels, laminates containing ultra-thin plies exhibit a diminished progression in damage evolution, delayed failure, and a reduced influence of the presence of the open-hole. The results also reveal that the reorganization of the stacking sequence plays a significant role in the damage mechanism, especially concerning the appearance of free-edge damage. This fact gives significant prominence to the use of 90º ultra-thin plies. All these observations suggest an enhanced performance of quasi-isotropic laminates with ultra-thin plies under cyclic tensile load and, therefore, endorse the potential implementation of this strategy at an industrial scale.