1,721,021 research outputs found
A feasibility study on additive manufactured hybrid metal/composite shock absorbers
No full textCommonly adopted shock absorbers and, in general, crashworthy structural components, based on sandwich structural concepts and/or complex dumping mechanisms, are, generally, characterized by high volumes and significant additional mass. This research activity is focused on the investigation of the feasibility and effectiveness of novel thin additive manufactured hybrid metal/composite lattice structures as lightweight shock absorbing devices for application to structural key components in impact events. These hybrid structures would represent a real step beyond the state of the art of shock absorbers being characterized by an additive manufactured metal lattice core, able to maximize the absorbed energy by plastic deformations and, at the same time, by a composite skin/cohesive coating, fully integrated with the internal metal lattice structure, able to lower the global weight and increase the stiffness and strength of the shock absorber. First, an extensive explicit numerical activity has been performed finalised to the assessment of the mechanical behaviour of basic lattice Unit Cells configurations under impact conditions in shock-absorbing panels. The variation of the geometrical characteristics of the lattice cells have been taken into account by adopting a parametric Python routine in ABAQUS with a simplified FEM formulation based on beam and shell elements. Once identified the key features maximizing the energy absorption capabilities of the metallic core, several complex models with 3d solid element formulation have been developed. A final comparison between the hybrid configurations and the state of the art shock absorbing panels, demonstrated the effectiveness of the proposed lightweight hybrid configuration based on additive manufacturing techniques in terms of mass reduction, mechanical and energy absorption performances
Component-Wise measure of elastic energy contributions in laminated composite beams
No full textThis paper investigates the energy distribution in fibre-reinforced composites at the macro-, meso-, and micro-scales. Specifically, the energy contained within the laminate (macro-scale), the layers (meso-scale), and the fibres and matrix (micro-scale) is evaluated. To develop cost-efficient and reliable mathematical models capable of addressing the different scales of the composite structure, one-dimensional (1D) refined finite elements are adopted using the Carrera Unified Formulation (CUF). CUF facilitates the straightforward development of mathematical models at various scales through the use of flexible expansion polynomials, resulting in a three-dimensional (3D) description of the problem using 1D finite elements. The Component-Wise (CW) approach is employed to construct the models at these different scales. Through numerical analysis and comparison with solid finite element models, this study demonstrates that, while the total energy absorbed by a structure under specific loading conditions remains constant, modeling the structure at different scales provides valuable insights into the energy distribution across various components. Additionally, an alternative approach combining the micro- and meso-scales is proposed, in which only one fibre is treated as kinematically independent from the surrounding domains. The results emphasize the accuracy of the different models in capturing the energy distribution, when compared to those obtained from Abaqus analysis using 3D solid elements. Moreover, the proposed technique demonstrates its capability to accurately describe the energy distribution within the composite structure, offering insights into how the structure can withstand external loads and informing design strategies
A user defined material model for the simulation of impact induced damage in composite
No full textLow velocity impacts induce concurring failure phenomena in unidirectional fiber reinforced composites. Hence a refined methodology able to predict the different failure modes and their interaction is mandatory to correctly predict the damage onset and evolution. Indeed, intralaminar damage and inter-laminar damage often take place concurrently, causing a significant strength reduction up to composite structure collapse. In this paper, a numerical study is proposed which, by means of non-linear explicit FEM analysis, aims to completely characterize the composite reinforced laminates damage under low velocity impacts by introducing a user defined material model in the FEM code ABAQUS. The proposed 3-D numerical investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the damage formation and evolution
Numerical-Experimental Correlation of Interlaminar Damage Growth in Composite Structures: Setting Cohesive Zone Model Parameters
Full text linkComposite laminates are characterized by high mechanical in-plane properties while experiencing, on the contrary, a poor out-of-plane response. The composite laminates, indeed, are often highly vulnerable to interlaminar damages, also called "delaminations." One of the main techniques used for the numerical prediction of interlaminar damage onset and growth is the cohesive zone model (CZM). However, this approach is characterised by uncertainties in the definition of the parameters needed for the implementation of the cohesive behaviour in the numerical software. To overcome this issue, in the present paper, a numerical-experimental procedure for the calibration of material parameters governing the mechanical behaviour of CZM based on cohesive surface and cohesive element approaches is presented. Indeed, by comparing the results obtained from the double cantilever beam (DCB) and end-notched flexure (ENF) experimental tests with the corresponding numerical results, it has been possible to accurately calibrate the parameters of the numerical models needed to simulate the delamination growth phenomenon at coupon level
2D higher-order theories for progressive damage model of composite structures based on Hashin and Puck failure criteria
No full textThis paper proposes a high-order 2D finite element model for the progressive damage model of composite structures. The model is based on Carrera Unified Formulation (CUF), which allows to automatically implement different kinematics by using an opportune recursive notation. A Newton-Raphson algorithm and the explicit integration scheme is used to find the converged solution. A single element and an open-hole specimen under tensile and compression loads are investigated using a damage model based on Hashin and Puck failure criteria. The proposed model is compared with literature and ABAQUS continuum shell results
A Numerical Study on the Bird Strike of a Crashworthy composite wing by a Coupled Eulerian-Lagrangian (CEL) approach
No full textCrashworthiness is defined as the capability of a structure to guarantee its occupants safety during a crash event. In the present work, the crashworthiness of a composite wing section, subjected to a bird strike event, has been investigated. Indeed, the mechanical behaviour of the impacted wing section has been investigated by means of the FE code ABAQUS/Explicit. The bird mass has been provided by the certification agencies, and recommended to be limited to 1.82 kg for an impact located on the wings. The impact phenomenon has been numerically simulated by means of a Coupled Eulerian-Lagrangian (CEL) approach. Indeed, the impacted structure has been modelled considering a Lagrangian formulation, while a Eulerian formulation has been used to model the bird. Moreover, Eulerian-Lagrangian contacts are used for transfer the loads arising from the impact event to the Lagrangian structure. The proposed numerical model, capable to take into account the matrix and fibre traction and compression damages, uses a 3D Finite Element formulation to better predict the deformations and the damages onset and propagation during the impact event. The numerical results, in terms of structural deformation, energy absorption, and damage onset and propagation have been obtained by considering different impact locations and different impact angle
Crashworthiness of a general aviation fuselage section: 3D FEM numerical modelling and validation
No full textCrashworthiness is defined as the capability of a structure to guarantee its occupants safety during a crash event. In the present work, the crashworthiness of a composite fuselage section has been preliminary investigated. Indeed, the mechanical behavior of the investigated fuselage section has been assessed by means of the FE code ABAQUS/Explicit, considering an impact event on a rigid surface. The proposed numerical model, capable to take into account the matrix and fiber traction and compression damages, uses a 3D Finite Element formulation to better predict the deformations and the damages onset and propagation during the impact event. Two numerical models have been introduced to study the effect of the passenger floor stiffening on the mechanical response to impact of the entire investigated fuselage barrel. The results in terms of displacements and qualitative deformations of the fuselage, for the analyzed numerical models, have been compared
A numerical study on multi-terrain impacts of an aeronautical fuselage section
No full textThis paper investigates the crashworthiness of a metallic fuselage section. Crashworthiness can be generally described as the ability of a structure to protect its occupants during an impact event. In this paper, the mechanical behaviour of metallic fuselage structures during the crash is simulated by means of the FE code ABAQUS/Explicit. Two different impact terrains have been considered: impact on a rigid surface and ditching on water. The numerical results, in terms of deformation, energy absorption, equivalent stress evolution, and damage onset and propagation have been assessed and compared
Mixed-mode delamination growth prediction in stiffened CFRP panels by means of a novel fast procedure
Full text linkCarbon fiber reinforced plastic (CFRP) structures are highly sensitive to delaminations, resulting from low energy impacts or manufacturing defects. Non-linear numerical algorithms are mandatory to investigate the complex mechanisms governing the delamination growth phenomena. Although the high computational costs associated to the non-linear algorithms are acceptable in a detail verification design stage, less expensive procedures are desired in a preliminary design stage or during optimization procedure. In this work, a fast numerical procedure, able to determine the delamination growth initiation in composite structures in the framework of a damage tolerant design approach when mixed mode I and II growth is expected, is introduced. The state of the art of the fast delamination growth procedures is critically discussed and improvements to the existing approaches are proposed to extend their applicability and to increase their accuracy. Comparisons with the standard non-linear delamination growth approaches are presented to assess the effectiveness of the proposed novel Fast approach. The results of the proposed fast approach are comparable with the ones obtained by means of standard numerical non-linear technique, allowing up to 95% computational cost saving
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