1,721,052 research outputs found
A linear numerical approach to simulate the delamination growth initiation in stiffened composite panels
No full textIn this article, a simplified linear analysis-based approach to simulate the delamination growth initiation in stiffened composite panels, suitable as preliminary design and optimization tool implemented into a finite element code, is presented. The proposed approach is based on the determination of the delamination buckling and on the evaluation of the energy released during the delamination propagation by means of eigenvalue and linear static analyses. Stiffened composite panels with circular embedded bay delaminations, under compression loads, were adopted as a benchmark to test the simulation capabilities of the method. Obtained results, in terms of delamination growth initiation load and energy release rate distributions along the delamination front, have been compared to nonlinear results obtained by the virtual crack closure technique and experimental data for preliminary validation purposes. Comments and considerations upon the applicability of this methodology are, finally, provided with particular focus on delamination sizes and locations within the considered structural elements
Experimental and numerical assessment of the impact behaviour of a composite sandwich panel with a polymeric honeycomb core
No full textThe capability to guarantee passenger safety is a core feature of any transportation system. For this reason, a considerable effort is being committed, by researchers, to the study of innovative shock-absorbing devices able to increase the safety performance. According to this topic of great interest, this paper presents a numerical/experimental study on a new effective shock absorber concept achievable by means of the Additive Manufacturing technology. Indeed, additive technologies exhibit some fundamental advantages, such as the possibility to produce complex microstructures, with superior impact energy absorption capabilities, which cannot be made with standard manufacturing processes. Hence, this manufacturing technique could be preferred for the development of high-efficiency shock absorbers cores. In the present work, to achieve shock absorbers high mechanical efficiency while limiting mass and volume, an innovative sandwich shock absorber concept is introduced, which uses additive manufactured solutions for the core by combining the advantages offered by thermoplastics (polypropylene), such as their ability to absorb energy through plasticisation and their recyclability, to those offered by fibre-reinforced thermoset composites (Carbon Fibre Reinforced Polymers), i.e. high stiffness/mass and strength/mass factors. First, numerical low-velocity impact analyses have been carried out to compare the mechanical response of several shock absorber configurations, Designed for Additive Manufacturing (DfAM), characterised by a polypropylene (PP) honeycomb core and CFRP composite external skins. These PP-CFRP sandwich configurations have been compared to full polypropylene configurations (with polypropylene skins and core PP-PP). Comparisons have shown that the PP-CFRP configurations are characterised by better overall crashworthiness performances (energy absorption and peak-force smoothing). Finally, an experimental activity, including ASTM D7136 based impact tests, have been carried out on the best performing investigated PP-CFRP configuration, to preliminary validate the numerical results
Delamination Growth and Fibre/Matrix Progressive Damage in Composite Plates Under Compression
No full textThe behaviour of delaminated composite plates under compressive load has been investigated by means of a numerical procedure implemented in the B2000 FEM code. In this work the widely studied delamination growth phenomena in composite plates under compression has been investigated by taking into account also the matrix and fibres breakages until the structural collapse condition is reached.
The delamination growth has been simulated by means of interface elements based on the modified virtual crack closure technique (MVCCT) to evaluate the Strain energy Release Rate. Furthermore, an iterative numerical procedure has been introduced to simulate the progressive matrix and fibre breakage by adopting respectively the Hashin’s failure criteria to check the stress state and instantaneous degradation rules for the reduction of the damaged material properties. The penalty method approach has been used for the formulation of the contact phenomena whose introduction in the model is demonstrated to be mandatory when a compressive load is applied to the structure.
The developed procedure has been applied for analysing the mechanical behaviour under compression of a delaminated composite plate. The obtained buckling and post-buckling responses have been compared with experimental data on composite coupons with embedded delaminations
A 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
Simulating the Response of Composite Plates to Fire
No full textThe present paper introduces a numerical study on the fire behavior of composites during exposure to a heating source at high incident power. A novel numerical model is proposed which is able to simulate the behavior of composite materials in fire environment providing the composites mass loss rate and heat release rate during heating source application. Two commercial software have been selected as platforms for the implementation of the proposed numerical model COMSOL and ANSYS. In COMSOL the model has been implemented by introducing proper field equations, while a macro, written in Ansys Parametric Design Language, has been used to allow the ANSYS FEM code to numerically simulate, by an incremental procedure, all the relevant physical phenomena related to fire.
As an application, an experiment on thermal degradation over a laminated composite plate has been numerically simulated and the numerical model has been validated by comparing the COMSOL and Ansys numerical results to experimental literature data in terms of temperature profile over the panel thickness, Mass Loss Rate and Heat Release Rate. An excellent agreement has been found between the obtained numerical results and the experimental test data for both the adopted numerical platforms. However the ANSYS implementation, which showed to be the most effective in terms of accuracy of results and perspectives of applications to complex numerical models, led to the definition of a powerful tool able to assesses the fire performance of composite structures
Experimental investigation on 3D printed lightweight sandwich structures for energy absorption aerospace applications
No full textOne of the ongoing challenges in aeronautics is the development of increasingly lighter structures. This has become a crucial goal because structural lightening means improving aircraft performance in terms of speed, manoeuvrability, fuel efficiency, and at the same time reducing manufacturing and service costs. The aerospace industry continues to focus more and more on this goal and every improvement in technology and materials can bring significant advantages in performance, efficiency, and safety of aircraft. The present work is part of this framework, as it analyses the feasibility of achieving very high weight reduction in sandwich panels using a new manufacturing approach. It introduces an experimental limited sensitivity analysis on the mechanical responses of composite sandwich structures for shock-absorption applications lightened by appropriately setting a specific additive manufacturing process parameter: the infill value. The investigated sandwich structures are characterised by a core Designed for Additive Manufacturing (DfAM) in order to maximise their performance in terms of energy-to-weight ratio and damping of impact loads. The material chosen for the inner part of the sandwich structure (core and internal face sheets) is polypropylene (PP) while the external face sheets are in Carbon Fibre Reinforced Polymers (CFRP). By comparing the post-impact responses at 20 J impact of three sandwich configurations with the same external shape but different material layer densities related to different setting of the infill parameter in the frame of the printing process, the work proves that this approach leads to lightening of this specific sandwich structures by up to 28% and at the same time improves their structural effectiveness in terms of energy absorption characteristics. The comparison was made by relating specific absorption indices, force-time and force-displacement graphs and CT scans
Fire condition effects on the mechanical behaviour of composite structures
No full textThe fire behaviour of Polymeric composite structures is one of the most critical aerospace research topics. Indeed, the exposure of Polymeric composite structures to high temperatures leads to material decomposition, associated to thermal and mechanical properties degradation. This degradation causes a reduction of the mechanical performances, which can be of main concern for safety reasons. In this paper, the tensile behaviour of Carbon Fibre Composite Polymer specimens, subjected to fire, has been experimentally and numerically investigated. The material properties degradation has been estimated according to an Arrhenius shape function, which relates the mechanical properties of the composite to the temperature. At first, static structural analyses have been carried out to assess the mechanical behaviour of the investigated specimen without fire effects. Then, a coupled thermo-structural analysis allowed evaluating the fire effect on the specimens’ mechanical and the thermal behaviour. In order to preliminary validate the proposed degradation model, the numerical results, in terms of Load versus Displacements curves, have been compared against data obtained from an ad-hoc experimental campaign where fire condition have been suitably replicated during the mechanical tests
A Numerical Study on the Influence of Nanosilica-Reinforced Epoxy Resin on the Delamination Behavior of Composite Laminates
No full textThe use of nanomodified epoxy resins can potentially increase composites application to aeronautical structural components, thanks to the potential enhancement, in terms of physical and mechanical properties, when compared to the neat epoxy matrix. In this work, the effects of silica nanoparticles (NPs) on the fracture toughness and, consequently, the crack growth resistance of fiber-reinforced polymers (FRPs) have been numerically investigated. The skin-stringer debonding initiation and growth have been studied by a tailored innovative numerical procedure considering an aeronautical panel reinforced with a single T-shape stringer, made of carbon fibers/epoxy resin material, and subjected to compressive load. An analytical model has been used to evaluate the Mode I fracture toughness value of the nanomodified resin, and the Virtual Crack Closure Technique methodology has been employed to assess the delamination growth in the frame of a Finite Elements (FE) analysis performed in the Ansys FE environment. Numerical results presenting the comparison between charged and neat configurations have been assessed to provide a first understanding of the influence of nanoparticles on the static delamination growth in geometrically complex composite structures
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