A new decohesion element with the capability of dealing with crack propagation under mixed-mode loading is proposed and demonstrated. The element is used at the interface between solid finite elements to model the initiation and non-self-similar growth of delaminations in composite materials. A single relative displacement-based damage parameter is applied in a softening law to track the damage state of the interface and to prevent the restoration of the cohesive state during unloading. The softening law is applied in the three-parameter Benzeggagh-Kenane mode interaction criterion to predict mixed-mode delamination propagation. To demonstrate the accuracy of the predictions, steady-state delamination growth is simulated for quasi-static loading of various single mode and mixed-mode delamination test specimens and the results are compared with experimental data.

Numerical simulation of mixed-mode progressive delamination in composite materials

A new decohesion element with mixed-mode capability is proposed and demonstrated. The element is used at the interface between solid finite elements to model the initiation and non-self-similar growth of delaminations. A single relative displacement-based damage parameter is applied in a softening law to track the damage state of the interface and to prevent the restoration of the cohesive state during unloading. The softening law for mixed-mode delamination propagation can be applied to any mode interaction criterion such as the two-parameter power law or the three-parameter Benzeggagh-Kenane criterion. To demonstrate the accuracy of the predictions and the irreversibility capability of the constitutive law, steady-state delamination growth is simulated for quasistatic loading-unloading cycles of various single mode and mixed-mode delamination test specimens.

/pdf/mixed-mode-decohesion-finite-elements-for-the-simulation-of-58v2hnt70u.pdf

Mixed-Mode Decohesion Finite Elements for the Simulation of Delamination in Composite Materials

https://ntrs.nasa.gov/api/citations/20080014292/downloads/20080014292.pdf

A damage model for the simulation of delamination in advanced composites under variable-mode loading

One of the fundamental aspects in cohesive zone modeling is the definition of the traction-separation relationship across fracture surfaces, which approximates the nonlinear fracture process. Cohesive traction-separation relationships may be classified as either nonpotential-based models or potential-based models. Potential-based models are of special interest in the present review article. Several potential-based models display limitations, especially for mixed-mode problems, because of the boundary conditions associated with cohesive fracture. In addition, this paper shows that most effective displacement-based models can be formulated under a single framework. These models lead to positive stiffness under certain separation paths, contrary to general cohesive fracture phenomena wherein the increase of separation generally results in the decrease of failure resistance across the fracture surface (i.e., negative stiffness). To this end, the constitutive relationship of mixed-mode cohesive fracture should be selected with great caution.

Cohesive Zone Models: A Critical Review of Traction-Separation Relationships Across Fracture Surfaces

Accurate simulation of delamination growth under mixed-mode loading using cohesive elements: Definition of interlaminar strengths and elastic stiffness

http://forum.cad.de/foren/ubb/uploads/emad.sdp/Benzeggagh2.pdf

Measurement of mixed-mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed-mode bending apparatus

Initiation and growth of delamination in glass/epoxy composites subjected to static and dynamic loading by acoustic emission monitoring

The aim of this study was to develop a semi-empirical criterion capable of predicting the fatigue threshold delamination under varying mixed-mode ratio. To validate this criterion, a series of fatigue delamination tests in a unidirectional glass/epoxy composite were carried out at pure mode I, pure mode II, and different mixed modes. These tests were conducted using DCB (mode I), ENF (mode II), and MMB (mixed mode (I + II)) specimens. The experimental results have been expressed in terms of the total strain energy release rate thresholds GTth which correspond to no delamination growth after 106 cycles. They were correlated with the semi-empirical fatigue criterion through the plot of the total strain release rate thresholds ΔGTth versus the G II G T modal ratio.

Experimental development of fatigue delamination threshold criterion

Interlaminar fracture is the dominant failure mechanism in most advanced composite materials. The delaminating behaviour of materials is quantified in terms of the strain energy release rate G. In this paper, the experimental measurements of the fatigue delaminating growth for some combinations of energy release rate mode ratio have been carried out on unidirectional glass/epoxy laminates. On this base the constants in the Paris equation have been determined for each G II /G T considered modal ratio. The fatigue threshold strain energy release rate Δ G Tth , below which delaminating doesn't occur, were measured. Three type specimens were tested, namely: double cantilever beam (DCB), end-loaded split (ELS) and mixed-mode bending (MMB) under mode I, mode II and mixed-mode (I + II) loading, respectively. Scanning electron microscopy techniques were used to identify the fatigue delamination growth mechanisms and to define the differences between the various modes of fracture.

M. Kenane

Papers

Measurement of mixed-mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed-mode bending apparatus

Initiation and growth of delamination in glass/epoxy composites subjected to static and dynamic loading by acoustic emission monitoring

Experimental development of fatigue delamination threshold criterion

Fracture and fatigue study of unidirectional glass/epoxy laminate under different mode of loading