2 research outputs found
Investigation of failure mechanisms in GFRP sandwich structures with face sheet wrinkle defects used for wind turbine blades
No full textWrinkle defects can be formed during the production of wind turbine blades consisting of composite monolithic and sandwich laminates. Earlier studies have shown that the in-plane compressive strength of a sandwich panel with wrinkle defects may decrease dramatically. This study focuses on the failure modes of sandwich specimens consisting of thick GFRP face sheets with a wrinkle defect and a balsa wood core subjected to in-plane compression loading. Three distinct modes of failure were found, and the strain distributions leading up to these failures were established by use of digital image correlation (DIC). Finite element analyses were subsequently conducted to model the response of the test specimens prior to failure, and generally a very good agreement was found with the DIC measurements, although slight differences between the predicted and measured strain fields were observed in the local strain values around the wrinkle defect. The Northwestern University (NU) failure criterion was applied to predict failure initiation, and a good correlation with the experimental observations was achieved
A model for the mixed mode crack propagation in composite laminates under cyclic loadings
No full textComposite laminates under fatigue loadings undergo a stiffness degradation due to the initiation and propagation of off-axis cracks. Therefore, predicting the initiation and propagation of such cracks is a matter of extreme importance in the design of composite structures. Recently, Carraro and Quaresimin proposed a criterion for ply crack initiation. In this work, a model for the off-axis crack propagation in laminated composites subjected to multiaxial fatigue loadings is presented. On the basis of several observations reported in the literature, the crack propagation phenomenon can be seen as the result of a series of micro-scale events occurring ahead of the crack tip within a process zone. It is also clear that a change in the damage mode occurs when moving from mode I to mode II conditions. Based on these evidences and by means of a multiscale approach to determine the micro-scale stress fields in the matrix, two simple parameters are defined to be used for predicting the crack growth rate through a Paris-like law. The application to several experimental data from the literature shows the capability of the proposed parameters to summarise all the crack propagation data into two scatter bands covering the whole mode mixity range. © CCM 2020 - 18th European Conference on Composite Materials.Composite laminates under fatigue loadings undergo a stiffness degradation due to the initiation and propagation of off-axis cracks. Therefore, predicting the initiation and propagation of such cracks is a matter of extreme importance in the design of composite structures. Recently, Carraro and Quaresimin proposed a criterion for ply crack initiation. In this work, a model for the off-axis crack propagation in laminated composites subjected to multiaxial fatigue loadings is presented. On the basis of several observations reported in the literature, the crack propagation phenomenon can be seen as the result of a series of micro-scale events occurring ahead of the crack tip within a process zone. It is also clear that a change in the damage mode occurs when moving from mode I to mode II conditions. Based on these evidences and by means of a multiscale approach to determine the micro-scale stress fields in the matrix, two simple parameters are defined to be used for predicting the crack growth rate through a Paris-like law. The application to several experimental data from the literature shows the capability of the proposed parameters to summarise all the crack propagation data into two scatter bands covering the whole mode mixity range.</p
