Delamination is an inter-ply damage mechanism in composite laminates, driven by out-of-plane stress components that act in the resin rich layers, with poor mechanical properties, between adjacent plies. Finite elements approaches based on cohesive zone models are a well assessed method to model the non-linear response of the interlaminar layers. For several reasons it is important to capture the strain field in composite laminates during interlaminar crack propagation phenomena. Such an aspect plays a key role in the design of a structural health monitoring system and the numerical experimental correlations at the level of the local strain fields can represent a valuable methodology for the validation of the adopted cohesive zone models. A further important aspect, in the analyses of interlaminar fractures, is the distinction between damages that develop in stable or unstable regimes and the evaluation of strain rates during crack propagation. The paper presents experimental evaluations of strain fields during interlaminar crack propagation in unidirectional glass fibre reinforced laminates, measured by using FBG sensors embedded in the laminate. Mode I propagation in the presence of fibre bridging phenomenon, as well as stable and unstable mode II propagations in three- and four-point ENF tests are considered. An efficient approach to model interlaminar damage by means of quasi-static explicit analyses is presented and applied to model structural response, propagation regimes and the evolution of local strain fields. Results validate the approach in all the considered conditions and assess the accuracy of numerical models at different levels of mesh refinement and computational costs. Finally the approach is applied to model the response of an originally undamaged curved composite laminate subjected to a tensile load condition.

Methods for design and health monitoring of damage tolerant helicopter structures in fiber-reinforced polymer composites

FANTERIA, DANIELE;LAZZERI, LUIGI;
2013-01-01

Abstract

Delamination is an inter-ply damage mechanism in composite laminates, driven by out-of-plane stress components that act in the resin rich layers, with poor mechanical properties, between adjacent plies. Finite elements approaches based on cohesive zone models are a well assessed method to model the non-linear response of the interlaminar layers. For several reasons it is important to capture the strain field in composite laminates during interlaminar crack propagation phenomena. Such an aspect plays a key role in the design of a structural health monitoring system and the numerical experimental correlations at the level of the local strain fields can represent a valuable methodology for the validation of the adopted cohesive zone models. A further important aspect, in the analyses of interlaminar fractures, is the distinction between damages that develop in stable or unstable regimes and the evaluation of strain rates during crack propagation. The paper presents experimental evaluations of strain fields during interlaminar crack propagation in unidirectional glass fibre reinforced laminates, measured by using FBG sensors embedded in the laminate. Mode I propagation in the presence of fibre bridging phenomenon, as well as stable and unstable mode II propagations in three- and four-point ENF tests are considered. An efficient approach to model interlaminar damage by means of quasi-static explicit analyses is presented and applied to model structural response, propagation regimes and the evolution of local strain fields. Results validate the approach in all the considered conditions and assess the accuracy of numerical models at different levels of mesh refinement and computational costs. Finally the approach is applied to model the response of an originally undamaged curved composite laminate subjected to a tensile load condition.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/534872
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