SUMMARYThe initiation and evolution of transverse matrix cracks and delaminations are predicted within a meshindependent cracking (MIC) framework. MIC is a regularized extended finite element method (x-FEM) that allows the insertion of cracks in directions that are independent of the mesh orientation. The Heaviside step function that is typically used to introduce a displacement discontinuity across a crack surface is replaced by a continuous function approximated by using the original displacement shape functions. Such regularization allows the preservation of the Gaussian integration schema regardless of the enrichment required to model cracking in an arbitrary direction. The interaction between plies is anchored on the integration point distribution, which remains constant through the entire simulation. Initiation and propagation of delaminations between plies as well as intra-ply MIC opening is implemented by using a mixed-mode cohesive formulation in a fully three-dimensional model that includes residual thermal stresses. The validity of the proposed methodology was tested against a variety of problems ranging from simple evolution of delamination from existing transverse cracks to strength predictions of complex laminates without a priori knowledge of damage location or initiation. Good agreement with conventional

This research focuses on developing an embedded sensor system to monitor the health of a composite rotor component. To support this objective, simulations were developed to investigate the impact of sensor insertions on local structural micro-mechanics and sensor responses. In particular, the potential side-effects (e.g., delamination onset and growth) of imbedding lead zirconate titanate (PZT) piezoelectric sensors in composite structures were studied. A modeling approach for evaluating interlaminar damage under the influence of embedded PZT sensors is proposed. The approach uses finite element cohesive zone models to describe interlaminar damage between plies or at ply ends. In addition, an embedded multi-ply PZT model was developed and integrated with the damage models. The approach presented in this paper analyzes the propagation of interlaminar damage in the vicinity of sensors and quantifies the effect of sensor presence on damage growth. A parametric study was performed to understand how damage zones, the size and geometry of resin pockets, and the locations and properties of PZT sensors affected interfacial strength. Damage behavior, under the influence of an embedded PZT sensor, was examined in specimens having a configuration similar to that of a selected rotating rotorcraft component. Finally, optimal locations of embedded PZT transducers were determined for the specimen under consideration.

No abstract

No abstract

No abstract