Analysis of Delamination Propagation in Quasi-isotropic Laminated Composites for different loadings
Topic(s) : Special Sessions
Co-authors :
Valentin BEGIN (FRANCE), Christian HOCHARD (FRANCE), Aurélien MAUREL-PANTEL (FRANCE), Guilherme MACHADO (FRANCE)Abstract :
The use of composite materials has seen a significant increase in various industries, specifically in the aviation industry,. The failure of these laminated composite structures can be attributed to a multitude of mechanisms that occur on different scales [1-2]. Often, a primary cause of failure is delamination (edge effects). While models exist to forecast the initiation and propagation of delamination at the edges for static loads, they are less developed for predicting under fatigue or other types of loading. Delamination is a process that occurs within the matrix among the plies. This presentation concerns the analysis of delamination for different loadings in the particular case of quasi-isotropic laminates.
A first study was conducted on an unbalanced glass/epoxy woven material whose intra-ply damage model parameters have been determined in a previous work [3]. After the test samples were prepared using an autoclave, they were tested under different loadings : first, static tensile tests confirmed the maximum stress values, then creep type tests until failure (maintaining a constant stress up to a percentage of the maximal static stress) and, finally, fatigue tests were conducted. The transverse strain was measured using a 3D DIC system since its value depends on the Poisson’s Ratio which varies from ply to ply (Fig. 1). This measurement allows the observation of delamination propagation throughout the test.
Fatigue tests were then conducted on the same material at different percentages of the maximal stress and a constant frequency allowing to compare them to the creep type tests using Stress/Time Curves (Fig. 2).
The test results show that failure can appear prematurely for creep type loading (24 hours at 70% of static loading) and that failure appears quicker for fatigue loading (less than 2 minutes at 10Hz at 70% of static loading). Therefore, there is an effect of time which is added to the effect of cycles. Concerning the fatigue tests conducted at 0.1 Hz, for high loadings the major effect is time whereas for lighter loadings, the effect of fatigue/cycling adds up and leads to quicker failure.
The same tests are currently being carried out on a Carbon/PEEK woven material, this time with a thermoplastic matrix, to discuss the influence of the matrix on the observed results. 3D simulations on the Abaqus software are also conducted using the Cohesive Zone Model (CZM) [4] between plies of the material to model delamination and to compare with the obtained experimental results.
A first study was conducted on an unbalanced glass/epoxy woven material whose intra-ply damage model parameters have been determined in a previous work [3]. After the test samples were prepared using an autoclave, they were tested under different loadings : first, static tensile tests confirmed the maximum stress values, then creep type tests until failure (maintaining a constant stress up to a percentage of the maximal static stress) and, finally, fatigue tests were conducted. The transverse strain was measured using a 3D DIC system since its value depends on the Poisson’s Ratio which varies from ply to ply (Fig. 1). This measurement allows the observation of delamination propagation throughout the test.
Fatigue tests were then conducted on the same material at different percentages of the maximal stress and a constant frequency allowing to compare them to the creep type tests using Stress/Time Curves (Fig. 2).
The test results show that failure can appear prematurely for creep type loading (24 hours at 70% of static loading) and that failure appears quicker for fatigue loading (less than 2 minutes at 10Hz at 70% of static loading). Therefore, there is an effect of time which is added to the effect of cycles. Concerning the fatigue tests conducted at 0.1 Hz, for high loadings the major effect is time whereas for lighter loadings, the effect of fatigue/cycling adds up and leads to quicker failure.
The same tests are currently being carried out on a Carbon/PEEK woven material, this time with a thermoplastic matrix, to discuss the influence of the matrix on the observed results. 3D simulations on the Abaqus software are also conducted using the Cohesive Zone Model (CZM) [4] between plies of the material to model delamination and to compare with the obtained experimental results.