This article presents an approach for modelling fracture and delamination, based on the partition of finite elements and on the energy release rate due to crack propagation in cross-ply laminates. The energy release rate is implemented within an Extended Finite Element Method (XFEM) framework. This approach is enabling the prediction of delamination propagation without pre-allocating damage zones. No element deletion techniques were used either. Mesh refinement was not needed for the propagation of cracks. Virtual testing of transverse cracks-eventually triggering delamination in cross-ply laminates-is presented to show the technique efficiency. Thus, a maximum energy release rate of 0.9 kJ/m 2 is found for a transverse crack within [0 0 , 90 0 ] s laminate. When maximum energy release rate is reached, delamination in the {0 0 /90 0 } interface is triggered. Furthermore, delamination in a composite double cantilever beam is simulated and presented in some detail. The results were compared with experimental outputs and/or by other numerical means showing an excellent correlation.
The proximity of un-melted particles within Selective Laser Sintered (SLS) printed engineering parts made of nylon-12 is found as a major triggering effect for cracking and ultimately failure. The numerical investigation, by means of the eXtended Finite Element Method (XFEM), was performed over samples with different arrangements of un-melted particles obtained experimentally . The onset and propagation of microcracks was simulated. This included inherently how the degree of particle melt (DPM) in SLS parts affects and controls both crack initiation and propagation. The results evidenced that a microcrack started invariably between the two closest un-melted particles in all numerical tests performed considering different arrangements of un-melted particles.
To characterise a transversal crack evolution in a cross-ply [0/90] s fibre reinforced composite laminate, the associated energy release rate (ERR) was calculated by means of the J-integral embedded into the Finite Element Method (FEM). The ERR values computed for the propagation of the transversal crack were correlated to the ones obtained by using the Virtual Crack Closure Technique (VCCT) embedded within the Boundary Element Method (BEM). In addition, the results were compared with analytical values. The results correlated well except when the crack length was approximately 80% of the ply thickness. In such case, ERR values showed some discrepancies between FEM and BEM. The reason stems from the fact that in the VCCT used not all components of the stresses are considered, resulting in smaller ERR values. In addition, the results proved that transversal cracks can influence each other only in a limited distance.
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