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- Composite Materials (1) (entfernen)
The debonding of a fiber in a glass fiber / epoxy composite under transverse loading is studied. The stress field in the interface as well as the energy release rate are analysed for two fiber volume fractions.
The circumferential propagation of an Interface crack starting at the center of a fiber which is located within a hexagonal fiber array is studied. The analysis is performed by a finite element Simulation under plane stress conditions. Two fiber volume fractions are considered, this is 30% and 70%. The stress distribution before and during crack propagation is calculated for different stages of the
crack. The crack opens by dominating tensile stresses in the first phase while it closes when propagating along the interface. The total energy release rate as well as the mode I and mode II parts are calculated. In the first phase the crack is driven by an increasing mode I energy release rate, indicating an unstable crack propagation. Then the mode II energy release rate increases rapidly and dominates the debonding process while the mode I part decreases and finally vanishes. Subsequently also the mode II part decreases, indicating stable crack propagation. In the last phase the crack becomes unstable again due to a strongly increasing mode I energy release rate. During the debonding process a remarkable change the mode ratio takes place.
The main features of the debonding process are similar for low and high fiber volume fraction. In case of the high fiber content, however, the mode I part is more pronounced and the maximum of the total energy release rate is shifted to lower crack angles.