1,721,032 research outputs found
A B2000 BASED NUMERICAL TOOL FOR THE SIMULATION OF NON-CRIMP FABRIC COMPOSITES: MECHANICAL PERFORMANCES AND DELAMINATION GROWTH
No full textIn this paper, a novel finite element tool, for the simulation of delamination growth in Non-Crimp fabric (NCF) composite materials, is presented. The proposed finite element tool is based on the implementation of the Stiffness Averaging Method, the Modified Virtual Crack Closure Technique and the Penalty Method in the research oriented B2000 FEM code. The Stiffness Averaging Method allows taking into account the effects of the processing variables, characterizing the Representative Volume Element (RVE) of the NCFs, on their mechanical performances. The Modified Virtual Crack Closure Technique is used to determine the Energy Release Rate for the delamination growth simulation.
Double Cantilever Beam (DCB) tests, used to determine the Mode I fracture toughness, have been considered for validation purposes. DCB tests have been simulated by means of non-linear analyses and compared in terms of deformed shapes and load-displacement curves with relevant experimental data. Moreover, the ability of the developed tool to take into account the NCF performances variability with processing parameters together with the delamination growth has been assessed and critically discussed
Development and Application of a Progressive Damage Approach to a Grid Structure Representative Volume Element
No full textGrid structures configurations prove to be inherently strong and resilient arrangements for composite materials, without material mismatches (different layer orientations) associated with laminated structures. The absence of material mismatch implies that the grid structures possess inherent resistance to impact damage, delamination and crack propagation. The introduction of grid structures into industry has been hampered by a lack of understanding of their behavior, especially in failure mechanics. In order to improve the knowledge about mechanical behavior including failure of such structures, Finite Element model, of a repetitive volume element (RVE) of grid structure has been defined. Geometrically non-linear structural analyses have been carried out by adopting the research oriented FEM code B2000 in order to simulate the mechanical behavior of the structure. Furthermore, within the B2000 FEM code, a damage progression approach has been implemented in order to simulate the damage on-set and propagation in the selected RVE
Development of a numerical FEM model for Non-Crimp Fabric composite materials”, presentato alla conferenza internazionale
No full textThis paper presents a novel finite element based approach able to take into account the complex architecture of the Non-Crimp fabric (NCF) composite materials. By means of the Stiffness Averaging Method, implemented in the research oriented B2000 FEM code, the developed model is able to take into account the effect of the processing variables characterising the Representative Volume Element (RVE) of the NCFs on their mechanical performances. Applications to simple coupons loaded in tension are presented in order to demonstrate the capability and the effectiveness of the presented approach. First, a parametric study has been carried out to investigate the influence of the bundle waviness on the longitudinal stiffness. Then, the numerical results have been compared with experimental results available from literature obtaining a very good agreement. Finally, the presence of the stitching and the influence of the processing variables on the degradation of the in-plane mechanical properties, have been investigated
Damage Propagation in composite structures using an embedded global-local Approach
No full textSince most composite materials are characterised by brittle failure, with low margin of safety through ductility, the failure mechanisms in composites must be investigated and suitable prediction analysis tools need to be developed. In many structural applications a three-dimensional progressive damage approach, able to take into account all the physical phenomena characterising the damage on-set and propagation until the final failure, needs to be adopted.
In the present paper a three-dimensional progressive damage approach for laminated composites will be presented. This approach is based on the use of a progressive damage finite element with the geometrically non-linear finite element formulation for stress calculation. The FEM element has been integrated with Hashin’s failure criteria to split fibre and matrix failure modes and with the ply discount method to simulate the stiffness degradation in each ply. The FEM tool was tested together with an embedded global-local approach in order to prove its effectiveness when dealing with complex structures that need to be modelled by using different mesh densities and different element types.
As an application, the structural behaviour of a notched panel under tensile load has been investigated and the obtained numerical results have been compared with numerical and experimental data from literature. Finally, a comparison between a full 3D model and a global-local model has been performed in order to evaluate the effectiveness of the developed progressive damage approach in global-local analyses
Influence of Loading Conditions on the Impact Damage Resistance of Composite Panels
No full textIn this paper the onset of impact induced delaminations in stiffened composite panels is analysed by using an approach based on a threshold critical impact force. This approach is adopted in combination with geometrically non-linear finite element analyses in order to investigate the influence of the in-service loading conditions on the impact damage resistance of the composite panels. An application to a stiffened composite panel under compression is presented in order to point out the sensitivity of the impact damage resistance to the level of load. Finally, indications on a novel approach, able to take into account the non-linearity of the composite stiffened panels' response, are given
A Novel FEM Model For biaxial Non-Crimp Fabric Composite Materials under tension
No full textThis paper presents a novel finite element based approach able to represent the complex architecture of the non-crimp fabric (NCF) composite materials. By means of the stiffness averaging method, implemented in the research oriented FEM (finite element method) code B2000, the developed model is able to simulate the NCFs mechanical performances. Applications to simple coupons loaded in tension are presented in order to demonstrate the capability and the effectiveness of the presented approach. Nevertheless, the proposed methodology can be applied and extended to all NCF geometries. First, for validation purposes the numerical results detained for a specific configuration have been compared with experimental results available from literature. Then, a parametric study has been carried out to investigate the influence of the bundle waviness on the tension stiffness. Finally, due to the degradation of the in-plane mechanical properties, the presence of the stitching has been investigated
Influence of Loading Conditions on Impact Induced Delaminations in Stiffened Composite Panels
No full textIn this paper the onset of impact induced delaminations in stiffened composite panels is analysed. The adopted approach is based on the determination of the threshold critical impact force for the impact induced delamination onset. This approach, already used to calculate the damage resistance of composite panels for optimisation purposes by means of linear FEM analyses, is applied to a geometrically non-linear Finite Element Analysis in order to investigate the influence of the loading conditions on the impact damage resistance of the composite panels. An application to a stiffened composite panel is presented in order to underline the sensitivity of the impact damage resistance to the level of load and to the impact location. Finally, indications on a novel approach able to take into account the non-linearities of the structural response of composite stiffened panels to a low velocity impact are given
Transient Numerical Analysis of Heat Conduction in Anisotropic Solids Heated by Gaussian Thermal Sources
No full textIntra-laminar damage evolution in a composite grid structure Representative Volume Element under compression load
No full textA Numerical Model for Delamination Growth Simulation in Non-Crimp Fabric Composites
No full textIn this paper, a novel finite-element tool, for the simulation of delamination growth in non-crimp fabric (NCF) composite materials, is presented. The proposed finite-element tool is based on the stiffness averaging method (SAM), on the modified virtual crack closure technique (MVCCT) and on the penalty method (PM); all these methods have been implemented in the research oriented B2000 finite-element code. The stiffness averaging method allows taking into account the effects of the processing variables, which characterize the representative volume element (RVE) of the non-crimp fiber composites (NCF) on their mechanical performances; while the modified virtual crack closure technique is used to determine the strain energy release rate (SERR) for the delamination growth. Already available experimental data on Mode I fracture toughness, obtained by using double cantilever beam (DCB) tests have been employed for validation purpose of numerical procedure. The modeling of DCB tests, considering different geometrical cases, has been performed by means of non-linear analyses. Excellent results in terms of deformed shapes and load-displacement curve, compared with experimental data, are reported to support the validity and the accuracy of the presented computational procedure. Moreover, the ability of the developed tool to take account for the NCF performances variability with processing parameters along with the delamination growth has been assessed and critically discussed
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