1,720,967 research outputs found
Finite element analysis of the stability (buckling and post-buckling) of composite laminated structures: well established procedures and challenges
No full textFinite element procedures for the analysis of composite structures under compressive loads (buckling and post-buckling) generally are not deployed in books because they are still considered object of research whereas they are deemed as assessed by researchers that focus their papers on restricted audience topics. Therefore, regarding these procedures, a gap exists in literature between what researchers consider as well established and what has been already published. The aim of this paper is to contribute to close this gap by providing an insight in linear and non-linear buckling analyses and in their use with composite structures. Both modelling and analysis considerations are presented and discussed, focusing on what can be considered as best practice when dealing with this kind of problems. Applications (to a stiffened panel and to a wing box) are provided for demonstrating the effectiveness of the procedures presented
A Global/Local Finite Element Approach for Predicting Interlaminar and Intralaminar Damage Evolution in Composite Stiffened Panels Under Compressive Load
No full textThis 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
Virtual Crack Closure Technique and fail release approach: an effective finite element implementation for delamination growth phenomena
No full textWithin the frame of the MAAXIMUS project, an interlaminar damage of known dimension and
position has been considered as a pre-existing defect within a stiffened panel (embedded bay
delamination). Its evolution, induced by a static compressive load, has been simulated in ANSYS by
implementing a user subroutine based on the combined use of the Virtual Crack Closure Technique
and of a fail release approach.
It has been observed that, even thought the procedure defined was very effective in predicting the
delamination growth initiation, a strong dependency of the results on the load step and element size
was introduced during the growth phase.
Aim at reducing computational efforts required for delamination growth analyses and at achieving
realistic predictions in terms of growth whatever the mesh density may be, the cause of the
dependency of the results on load step size and mesh density has been investigated.
Then, a convergence check has been introduced into the non linear iterative flow in order to allow
an automatic adjustment of the load step size to be obtained on the basis of the overbalance existing at
each iteration between the energy level computed at the delamination front and the threshold level
fixed by the growth criterion adopted.
Furthermore the presence of peaks of Energy Release Rate where corner were induced in the
delamination front has been identified and mitigated through the introduction of weight factors into
VCCT formulae to take into account the presence of a delaminated area of complex shape.
The results obtained with the novel approach proposed have been validated against literature data
and have been found to be in good agreement with them in terms of both delamination growth rate and
debonded area, showing the effectiveness of the enhancements introduced when dealing with growth
phenomena
Modeling Damage Propagation in Composite Plates with Embedded Delamination under Compressive Load
No full textA numerical procedure aimed at simulating the structural behavior of delaminated composite plates under compressive load, is developed and presented in this article. Although delamination buckling and growth have been widely studied in the literature, in this article the effect of fiber-matrix failure on the buckling behavior of a delaminated structure up to final failure is investigated in detail. A geometrically non linear finite element (FE) approach is adopted for elastic instability simulation, the modified virtual crack closure technique (MVCCT) is used for the energy release rate (ERR) evaluation at the delamination front and fracture mechanics based progressive damage approach is introduced for the simulation of fiber-matrix damage onset and evolution. Comparisons of numerical results with existing experimental data on composite panels with an embedded circular delamination under compressive load, are presented for preliminary validation purposes. Furthermore, the influence of the different failure mechanisms on the compressive behavior of delaminated composite plates is assessed, by comparing numerical results obtained with models characterized by different degrees of complexity. Finally, results of a limited sensitivity analysis are shown, pointing out the influence of some key parameters characteristics of the adopted numerical approach on the accuracy of numerical simulations
On the robustness of finite element procedures based on Virtual Crack Closure Technique and fail release approach for delamination growth phenomena. Definition and assessment of a novel methodology
No full textNumerical procedures based on the combined use of the Virtual Crack Closure Technique and of a fail release approach have been widely used to simulate delamination growth phenomena of composite material structures. This paper starts explaining why this kind of methodologies might not be robust due to mesh and load step size dependency and introduces a novel approach able to cope with the problems identified. Finally the effectiveness and robustness of the proposed procedure, implemented into a commercial finite element software by means of user subroutines, are assessed by comparing the obtained numerical results for a delamination growth phenomenon against literature experimental data on a stiffened panel with a circular embedded delamination under compressive load
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
Analysis of the Effectiveness of Different Finite Element Modelization for the simmulation of Composite Plates Behaviour in Presence of Delaminations: An Essential Step Towards a Fully Damage Tolerant Design Approach
No full textWith the aim to develop a damage tolerant design approach, a numerical tool for the prediction of the mechanical
behaviour of a composite laminated structure in presence of an embedded delamination, which could grow
under the application of a certain load level, has been developed and validated within the Task 2.3 of the CESAR
project. Fracture mechanics concepts have been adopted and used in conjunction with the finite element method
to characterise the delamination status: Energy Release Rate distributions at the delamination front have been
computed by using the Modified Virtual Crack Closure technique and a linear growth criterion has been adopted
to establish critical conditions which lead to the delamination propagation. As the effectiveness of the energy
based approach proposed strongly dependends on the accuracy of the computation of forces and displacements
at nodes on the delamination front, two delamination modelizations have been proposed and their results compared
in terms of Energy Release Rate distributions.
The modelization more suitable to simulate the growth phenomenon has been selected and used to analyze the mechanical
behaviour of a composite plate with an embedded circular delamination starting from the local buckling of the
debonded area up to the global-buckling of the panel taking into account the delamination growth phenomenon. The
results obtained have been validated against numerical and experimental data taken from literature
Interlaminar and intralaminar damage evolution in composite stiffened panels under compressive loads: a global/local approach
No full textThe damage phenomenology of composite laminate is extremely complex and may involve different geometric scales in the initiation and progression of damage, and different typologies of failure. In recent years, delaminations and intralaminar damage onset and propagation have been extensively investigated separately [1-3] both numerically and experimentally and when possible analytical models have been developed. However, results of a few works [4-5] have shown that the correct simulation of the damage phenomenology for composite laminate structure can be achieved only by considering interlaminar and intralaminar damage interaction. In fact, to neglect this interaction would mean not only an incorrect prediction of the structural stiffness in presence of damage but also a significant overestimation of the residual structural strength.
A numerical procedure has been developed and implemented in the parametric language of the ANSYS © finite element code. Within this procedure both delamination growth and progressive damage onset and evolution have been taken into account.
The interlaminar damage evolution is based on the evaluation of the Strain energy Release Rate at the delamination front [7] computed by means of the modified virtual crack closure technique (MVCCT) and on releasable connections which allow the debonding between adjacent sub-laminates to be simulated. Furthermore, an iterative numerical procedure has been introduced to simulate the progressive matrix and fibre breakage by adopting respectively the Hashin’s failure criteria [8] to check the stress state and instantaneous degradation rules for the reduction of the damaged material properties [3].
The effectiveness of this procedure has just been proved on flat composite laminate plates [4]. In the present work the interlaminar-intralaminar interaction phenomenon is analysed for a more complex structure: a stiffened composite panel with a circular embedded delamination.
In order to reduce the computational efforts requested for the numerical analysis a global/local approach has been used to connect differently modeled substructures.
Results obtained by numerical approaches characterised by a different degree of accuracy (only interlaminar damage, damage interaction) are compared with experimental results [9] thus highlighting the intralaminar/interlaminar damage interaction effects on the residual stiffness and strength of the structure under consideration
A fracture mechanics based energy approach for the determination of the damage tolerance of a composite wing box: Sensitivity Analysis to the Delamination Dimension and Position
No full textNowadays composite material structures are widely adopted in the aerospace field however their capabilities
cannot be best exploited due to uncertainties in the definition of their behaviour in presence of damage.
Aimed at overcoming this lack, within the Task 2.3 of the CESAR project a finite element model of a composite
wing box, fully parametric in terms of both geometry and damage location and extension, has been
built and a fracture mechanics based approach has been defined and implemented in ANSYS© in order to
measure the damage tolerance of the structure under consideration.
The sensitivity of the wing box to the damage has been analysed by using the model developed and by considering
several configurations which differ from one another in position and dimension of the debonded area. As major outcome
of the analysis performed, critical areas in terms of damage tolerance have been identified on the basis of the computed
growth of initiation load
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