Cross-Influence between Intra-Laminar Damages and Fibre Bridging at the Skin–Stringer Interface in Stiffened Composite Panels under Compression (original) (raw)
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Materials Today: Proceedings, 2020
In this paper, the debonding behavior of a fiber reinforced composite panel, under flexural loading conditions, is numerically studied. Two material systems, respectively insensitive and sensitive to the fiber bridging phenomenon, are considered. The toughening effect of the fiber bridging phenomenon, on the debonding propagation, is analyzed. An innovative numerical procedure, able to consider G Ic variations with the crack length, is proposed. The results of numerical models are compared to evaluate the fiber bridging sensitivity effects on the maximum attained load and on the delaminated area.
Polymers, 2020
Increasing the Mode I inter-laminar fracture toughness of composite laminates can contribute to slowing down delamination growth phenomena, which can be considered one of the most critical damage mechanisms in composite structures. Actually, the Mode I interlaminar fracture toughness (GIc) in fibre-reinforced composite materials has been found to considerably increase with the crack length when the fibre bridging phenomenon takes place. Hence, in this paper, the fibre bridging phenomenon has been considered as a natural toughening mechanism able to replace embedded metallic or composite reinforcements, currently used to increase tolerance to inter-laminar damage. An experimental/numerical study on the influence of delamination growth on the compressive behaviour of fibre-reinforced composites characterised by high sensitivity to the fibre bridging phenomenon has been performed. Coupons, made of material systems characterised by a variable toughness related to a high sensitivity to t...
Applied Composite Materials, 2010
This paper addresses the prediction of intralaminar and interlaminar damage onset and evolution in composite structures through the use of a finite element based procedure. This procedure joins methodologies whose credibility has been already assessed in literature such as the Virtual Crack Closure Technique (for delamination) and the ply discount approach (for matrix/fiber failures). In order to establish the reliability of the procedure developed, comparisons with literature experimental results on a stiffened panel with an embedded delamination are illustrated. The methodology proposed, implemented in ANSYS © as post-processing routines, is combined with a finite element model of the panel, built by adopting both shell and solid elements within the frame of an embedded global/local approach to connect differently modelled substructures.
Analysis of composite skin/stiffener debounding and failure under uniaxial loading
Composite Structures, 2006
In this paper, damage mechanisms in the composite bounded skin/stiffener constructions under monotonic tension loading are investigated. The approach uses experiments to detect the failure mechanisms, two and three-dimensional stress analysis to determine the location of first matrix cracking and computational fracture mechanics to investigate the potential for cracks and delamination growth. The laminates strength and damage mechanisms obtained from both experimental and finite elements analysis are presented for several laminates lay-up configurations. Observations on the performed experiments show matrix crack initiation and propagation in the skin and near the flange tip, causing the flange to almost fully debounded from the skin in some cases, interlaminar debounding and fiber breakage up to the failure of the components. The finite elements analysis is also show that the matrix cracks are initiated in the first skin layer for most of the cases. With increasing the applied load the matrix cracks are propagated through the thickness to reach the next layer and causes delamination between the two layers. With increasing the applied load this delamination is propagated up to the occurrence of unstable delamination growth or the first fiber breakage known as the final failure of the component. The obtained experimental failure loads are compared with those calculated by the finite elements analysis.
Composite Stiffened Panel Impact Damage Simulations And Parametric Studies
A finite element (FE) based analytical tool, Composite Damage Tolerance Analysis Code (Codac), has been developed at the German Aerospace Center (DLR), Institute of Structural Mechanics, over the past few years. It is a fast tool that can determine impact response, damage and residual strength of flat or curved, stiffened composite panels. The tool features Windows based, graphical user interface (GUI) forms for various modelling and analysis steps. A simplified 2-D modelling approach has been adopted by using eight-node, isoparametric, plate-bending elements and three-node, isoparametric, beam elements for skin and stringer modelling, respectively. Various failure criteria have been implemented for fibre breakage, matrix cracking and delamination. The tool is capable of showing the ply-by-ply progressive damage for different damage modes and performing delamination growth analysis in the postbuckling regime under quasi-static loading. Calculating the strain energy release rate at each in-plane strain increment and comparing this with the critical values determine the delamination growth. Comparisons of the simulation results against the available test data showed that Codac is capable of assessing impact damage rapidly with reasonable accuracy, although further improvement to the tool is necessary as not all predictions agreed closely with the test data. Parametric studies were performed to evaluate the tool's capability and to determine its critical parameters. It was found that impact damage prediction with Codac is sensitive to the meshing, lateral boundary conditions (free, simply supported or clamped), panel size and the impact energy. In the event of impact, delaminations typically occurred in plies located at the mid-plane or away from the impact face. Additionally, the first few plies at the impact side were dominated by fibre breakage at higher impact energies. This has been established as the phenomenon of low velocity impact in composite materials.
Delamination tolerance studies in laminated composite panels
Sadhana, 2000
Determination of levels of tolerance in delaminated composite panels is an important issue in composite structures technology. The primary intention is to analyse delaminated composite panels and estimate Strain Energy Release Rate (SERR) parameters at the delamination front to feed into acceptability criteria. Large deformation analysis is necessary to cater for excessive rotational deformations in the delaminated sublaminate. Modified Virtual Crack Closure Integral (MVCCI) is used to estimate all the three SERR components at the delamination front from the finite element output containing displacements, strains and stresses. The applied loading conditions are particularly critical and compressive loading on the panel could lead to buckling of the delaminated sublaminate and consequent growth of delamination. Numerical results are presented for circular delamination of various sizes and delamination at various interfaces (varying depth-wise location) between the base-and the sub-laminates. Numerical data are also presented on the effect of bi-axial loading and in particular on compressive loading in both directions. The results can be used to estimate delamination tolerance at various depths (or at various interfaces) in the laminate.
2015
Analysing the collapse of skin-stiffened structures requires capturing the critical phenomenon of skin-stiffener separation, which can be considered analogous to interlaminar cracking. This paper presents the develop-ment of a numerical approach for simulating the propagation of interlaminar cracks in composite structures. A degradation methodology was introduced in MSC.Marc, which involved the modelling of a structure with shell layers connected by user-defined multiple-point constraints (MPCs). User subroutines were written that employ the virtual crack closure technique (VCCT) to determine the onset of crack growth and modify the properties of the user-defined MPCs to simulate crack propagation. Methodologies for the release of failing MPCs are presented and are discussed with reference to the VCCT assumption of self-similar crack growth. The numerical results obtained by using the release methodologies are then compared with experimental data for a double-cantilever beam specime...
Fracture Toughness Computational Simulation of General Delaminations in Fiber Composites
Journal of Reinforced Plastics and Composites, 1989
A procedure is described to computationally simulate composite laminate fracture toughness in terms of strain energy release rate (SERR). It is also used to evaluate the degradation in laminate structural integrity in terms of displacements, loss in stiffness, loss in vibration frequencies and loss in buckling resistance. Specific laminates are selected for detail studies in order to demonstrate the generality of the procedure. These laminates had center delaminations, off-center delaminations, and pocket delaminations (center and off-center) at the free-edge and center delaminations at the interior. The lami nates had two different thicknesses and were made from three different materials. The results obtained are presented in graphical form to illustrate the effects of delamination on the laminate structural integrity and on the laminate strain energy release rate (composite fracture toughness).
Modelling the damage evolution in notched omega stiffened composite panels under compression
Composites Part B-engineering, 2017
In this paper, the compressive behaviour of an omega stiffened composite panel with a large notch damage has been investigated. The influence of intra-laminar and inter-laminar damage onset and evolution on the compressive behaviour of a stiffened panel, characterised by a cutout located in the middle bay and oriented at 45° with respect to the load direction, has been studied. A numerical model, taking into account delamination and fibre-matrix damage evolution, respectively, by means of cohesive elements and Hashin's failure criteria together with material degradation rules, has been adopted. By comparing the performed numerical analyses, taking into account intra-laminar and inter-laminar damages, the effects of the interaction between delaminations and fibre-matrix damage in the large notch area on the global compressive behaviour of the omega stiffened composite panel have been assessed and critically discussed.