Prediction Of Delamination Growth Research Articles

The peculiar SMart-Time XB approach for delamination growth prediction and its evolution towards fatigue investigations

This paper deals with the Smart Time XB (SMXB) procedure, a parametric 3D methodology to simulate the delamination evolution in composite structures. The SMXB method has been developed almost ten years ago and, over time, has been improved with new features to become a forefront method compared with the state of the art. The SMXB is based on the Virtual Crack Closure Technique, which is nowadays implemented in the principal and most used Finite Elements (FE) commercial software. The main peculiarity of the SMXB is its capability to overcome the limits in terms of load step size and elements size dependences typical of the VCCT approach in mimic the delamination propagation. The SMXB procedure has been validated over years considering different structures and load conditions. The last development, which make the SMXB even more complete and attractive, is the ability to simulate the fatigue-driven delamination. Indeed, the Paris Law has been introduced in the core structure of the SMXB to make it able to mimic the delamination evolution under cyclic loading conditions. This manuscript has the intent to describe the theory behind this peculiar procedure and its evolution toward fatigue simulation. An experimental literature Double Cantilever Beam benchmark has been used to prove the robustness and effectiveness of this computational methodology, highlighting its main peculiarities. Single leg bending example, representative of a mixed mode interaction, has also been presented.

Deep learning-based prediction of delamination growth in composite structures: bayesian optimization and hyperparameter refinement

Abstract In this study, a novel method for detecting the growth of delamination in sandwich structures has been proposed. To this end, we suggested hybridizing the Deep Learning techniques (DL) and Finite Element Method (FEM) for predicting the growth of delamination in this structures. A dataset of simulated delamination growth under different delamination sizes has been produced using the FEM method. Then, a DL model has been trained using this dataset to precisely predict the growth of delamination. This study focused on predicting delamination growth using a tuned and optimized deep learning based regressor. Therefore, to find the ideal set of hyperparameters, the Bayesian optimization algorithm has been used for selecting the best structure and enhancing the regressor performance. Afterward, the model was evaluated and multiple processes were conducted to improve its behavior and solve its stability and overfitting issues. Particularly, an inconsistency between validation loss and training loss has been initially detected in the behaviour of the model, which may indicate overfitting. To tackle this issue, dropout regularization has been added, which improved the consistency between the loss functions but results in less smooth convergence from the expectations. So, in a third study, dropout and L1 regularization has been combined to improve the stability of the model. This combination achieved a consistent and smooth convergence between the validation and training loss functions. The findings highlight the importance of hyperparameter optimization and regularization techniques in improving regression model performance. The study shows the efficiency of Bayesian optimization in hyperparameter tuning and the iterative optimization of a regression model. Furthermore, the outcomes show that the suggested method can identify and predict delamination growth with high accuracy.

A crack growth rate model with load history effects for mode I fatigue-driven delamination under multi-level block loading

Load interaction effects in fatigue-driven delamination in fiber-reinforced polymer composites are neglected in state-of-the-art models although this assumption highly underestimates the delamination growth under variable amplitude (VA) loading. A new phenomenon called “transient delamination growth” has recently been observed in VA fatigue experiments by the authors. In the current work a new crack growth rate model with transient delamination growth capabilities is presented. The new model evaluates the crack growth rate by addition of a steady-state non-interaction term and a transient interaction term. The former term neglects load interaction effects and is characterized from constant amplitude loading tests, while the latter term includes load interaction effects and is characterized from two-level block loading tests. Fatigue tests are conducted on glass/epoxy DCB specimens by means of a new test fixture. The new crack growth rate model is able to accurately represent the crack growth rate at high-to-low load amplitude changes during multi-level block loading tests and reduces the error in delamination growth prediction by nearly 50% compared to non-interaction models.

A spatiotemporal prediction model for rapid prediction of delamination growth in open-hole composite laminates

Delamination of laminates around the hole edge is one of the most common but most threatening forms of damage in composites. The numerical solutions based on the finite element method (FEM) are difficult to meet the requirements of online evaluation and decision-making of the structure operation in terms of prediction efficiency. In this study, an end-to-end spatiotemporal prediction model with Encoder-Translator-Decoder architecture is developed to rapidly predict the delamination growth of laminates under compressive loading. The prediction results of single-hole delamination growth at different locations show that the model has good accuracy and generalization. The trained model can complete an inference prediction at the millisecond level, which is hard to achieve with FEM. Furtherly, a transfer framework is designed to promote the forecasting of multi-hole delamination growth. The framework is designed with a coupling coding block for learning the complex relationship of delamination damage superposition, which can effectively accelerate the training and achieve better prediction accuracy and inference speed. The developed deep learning model has good potential to be extended and applied to predict the spatiotemporal evolution of other physical fields.

A criterion for predicting delamination growth in composite laminates

To develop a simplified and physically sound delamination-failure criterion, this paper reports a joint experimental and numerical study in which out-of-plane quasi-static indentations with different indentation forces were applied to the centre of fully clamped rectangular carbon fibre-reinforced polymer (CFRP) laminates. The results show that two basic micro-delamination growth modes, which are separately dominated by opening and sliding microcracks, can be distinguished according to the fracture morphologies of the delaminations along the 0° fibre direction. Both are driven by the out-of-plane shear stress σ13, and the corresponding delamination failure threshold is the out-of-plane shear strength S13. Based on these results, a concise Hashin-type delamination-propagation criterion containing only a single stress component and single strength parameter is proposed, which, by incorporating it into the finite element model, the delamination growth along the fibre directions of multidirectional CFRP laminates can be precisely predicted; the prediction error is less than 10 %.

Delamination buckling of a laminated composite shell panel using cohesive zone modelling

Abstract Laminated composite shell panels take part in several engineering structures. Due to their complex nature, failure modes in composites are highly dependent on the geometry, direction of loading and orientation of the fibers. However, the design of composite parts is still a delicate task because of these fiber failure modes, which includes matrix failure modes or other so-called interlaminar interface failure such as delamination, that corresponds to the separation of adjacent layers of the laminate as a consequence of the weakening of interface layer between them. In this work, impact-induced delamination represented as a circular single delamination is investigated, as it can reduce greatly the structural integrity without getting detected. Furthermore, attention is focused on its effect upon the post-buckling response and the compressive strength of a composite panel. The delamination buckling was modelled using the cohesive element technique under Abaqus software, in order to predict delamination growth and damage propagation while observing their effects on the critical buckling load.

Composites fatigue delamination prediction using double load envelopes and twin cohesive models

This paper presents an explicit finite element methodology for predicting fatigue delamination in composite laminates using twin cohesive models and a combined static & fatigue cohesive formulation; one model is loaded under the peak-load envelope, whilst the other model is loaded under the trough-load envelope. The twin models contain pairs of twin cohesive interface elements that predict delamination growth by exchanging data at every time increment. The cohesive formulation evaluates fracture mechanics parameters, e.g. the local minimum to maximum fracture energy ratio via local information associated with the twin cohesive elements, without the need to know the global loading information, e.g. the global R ratio. The method allows predicting the mechanical condition of a laminate at both the peak and trough loads. This method is validated by multiple test cases with varying mode mixities and R ratios, showing a high computation efficiency.

Mixed-Mode Delamination Growth Prediction in Stiffened CFRP Panels by Means of a Novel Fast Procedure

Carbon 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.

Efficient modelling of delamination growth using adaptive isogeometric continuum shell elements

The computational efficiency of CAE tools for analysing failure progression in large layered composites is key. In particular, efficient approximation and solution methods for delamination modelling are crucial to meet today’s requirements on virtual development lead times. For that purpose, we present here an adaptive continuum shell element based on the isogeometric analysis framework, suitable for the modelling of arbitrary delamination growth. To achieve an efficient procedure, we utilise that, in isogeometric analysis, the continuity of the approximation field easily can be adapted via so-called knot insertion. As a result, the current continuum shell provides a basis for an accurate but also computationally efficient prediction of delamination growth in laminated composites. Results show that the adaptive modelling framework works well and that, in comparison to a fully resolved model, the adaptive approach gives significant time savings even for simple analyses where major parts of the domain exhibit delamination growth.

The Proposal of The Method to Predict Delamination Growth Rate between Resin and Metal

The method to predict delamination growth rate between resin and metal was proposed. This method was used static mechanical properties and energy release rate of the interface crack between Resin and metal.

Prediction of delamination growth in carbon/epoxy composites using a novel acoustic emission-based approach

Delamination is the most common failure mode in laminated composites and it leads to loss of structural strength and stiffness. In this paper, acoustic emission monitoring was applied on the carbon/epoxy laminated composites when subjected to mode I, mode II, and mixed-mode I and II loading conditions. The main objective is to investigate delamination behavior and to predict propagation curve of the delamination in different GII/GT modal ratio values by the acoustic emission. First, a combination of acoustic emission and mechanical data (sentry function) is used to characterize the propagation stage of the delamination. Next, the crack tip location during propagation of the delamination in the specimens is identified using two methods. In the first method, by determining the velocity of the acoustic emission waves in the specimens, the position of the crack tip can be estimated throughout the tests. In the second method, the cumulative energy of the acoustic emission signals is utilized for localization of the crack tip. Agreement between the predicted crack length and the actual crack length verifies the presented procedures. It can be concluded from the results that the acoustic emission method is a powerful approach to investigate the delamination behavior and to estimate the crack tip position in the composites.

Prediction of delamination growth in laminated composites using acoustic emission and Cohesive Zone Modeling techniques

Mode I delamination is the most common failure mode in laminated composite materials. Determination of the crack growth has a vital role in the damage tolerance analyses of the structures which suffer from this type of damage. The main objective of this paper is to determine position of the crack tip during propagation of mode I delamination in the glass/epoxy composite specimens. To this aim, experimental investigation by mechanical and acoustic emission (AE) data and Cohesive Zone Modeling (CZM) technique are carried out. The crack tip position is identified using three methods. First, position of the crack tip is identified using visual observation of the crack tip during the test. The second method utilizes cumulative energy of the AE signals to predict the crack growth. Finite element analysis based on a CZM theory is used as the third method to investigate delamination growth. Because of poor performance of CZM technique, modified CZM based on the R-curve results of the interlaminar fracture toughness is proposed to predict the delamination propagation. The results indicate that AE method and modified CZM technique have a good performance to detect initiation stage and also to determine the crack length in the laminated composite structures.

Numerical investigation of onset and evolution of LVI damages in Carbon–Epoxy plates

In order to study the onset and the evolution of low velocity impact damages in Carbon–Epoxy plates, a numerical investigation has been led. A detailed finite element model has been created by using the finite element code Abaqus® which, thanks to the different implemented algorithms, allowed considering both intra-laminar and inter-laminar failure criteria.In particular, the numerical modelling technique of such failure criteria allowed predicting delamination growth, by using special purpose-elements (cohesive elements) and fiber and matrix failure, by using Hashin criteria.Moreover, with the aim to reduce the required CPU time, a global/local finite element modelling approach has been proposed.For validation purpose, numerical results have been compared with data from two sessions of experimental impact tests. The considered impact energy values are 6J, 10J and 13J respectively.

EFFECT OF NATURAL LOAD ON DELAMINATION BEHAVIOUR OF A NEW HYBRID WOVEN COMPOSITE

The objective of this work is to develop a delamination model that can predict delamination growth in a new woven composite for orthopedic use. This new composite is obtained from a laminated composite woven by incorporating a natural organic load (granulates of date cores) which becomes hybrid composite. The new composite is made of an organic matrix containing methyl methacrylate, a woven reinforcement including a reinforcing glass fiber and a fabric perlon having an absorbing role. The walk cycle has been used to determine the operating conditions of tibiae prosthesis. Hence, the deflection tests were validated by orthopedist experts. 3ENF tests were carried out on the new woven composite to detect delamination phenomenon. We assume that the interface has a bi-linear softening behaviour and regarded as being a whole of several interfacial bonds. Each bond is supposed to be made up of three stiffnesses acting in the three delamination mode directions. A scalar damage variable is introduced and the degradation of the interface stiffness is established. A damage surface which combines stress-based and damage-mechanics-based failure criteria is set up to derive the damage evolution law. The damage model is implemented into a commercial finite element ANSYS to simulate delamination in mode II. Numerical results on (90, 452, 0) are in good agreement with experimental observations.DOI: http://dx.doi.org/10.5755/j01.mech.18.5.2692

Prediction of Delamination Growth in Laminated Structures Loaded by Quasi-static and Cyclic Loads

An approach for the prediction of growth of delaminations in laminated composites made of plies of fiber-reinforced polymers is proposed. It allows to handle arbitrary combinations of force, displacement, temperature, and moisture loads. Quasi-static load cases can be treated as well as load cases where some load components are constant and some load components are cyclic. The proposed approach is based on the Griffith criterion, which is evaluated by means of some finite element procedure. It provides a complete picture of a delamination problem in a given structure and offers systematic understanding of the influence of size and position of a delamination on the growth, on the growth stability, and on the structural response. Two examples, a curved laminate and a T-joint, are investigated in detail to underline the capabilities of the proposed approach.

A non-classical, energy release rate based approach for predicting delamination growth in graphite reinforced laminated polymeric composites

A non-classical, energy release rate based approach is applied to predict delamination growth in four different graphite reinforced laminated polymeric matrix composites, and the results are compared to those obtained using classical, linear elastic fracture mechanics. Both methods predict delamination advance by comparing the energy release rate in a structure to its critical value, or toughness, where the toughness is obtained from a series of tests on unidirectional laminates with midplane delaminations. However, the non-classical method uses a “crack tip element/non-singular field” approach to decompose the energy release rate, which results in non-classical mode I and mode II components. Matrix materials considered include an epoxy, a blended thermoplastic toughened epoxy, a thermoplastic particulate interlayer toughened epoxy, and a thermoplastic. For all materials, the non-classical approach is shown to provide relatively accurate predictions, whereas relatively poor results are obtained when using the classical approach. In view of the range of materials studied, it is concluded that the non-classical approach will likely apply to other current and future generation graphite reinforced polymeric matrix composites, and that this approach will continue to give more accurate results than one that is classically based.

Prediction of Delamination Growth and Opening Near Intersection of Transverse Matrix Cracks and Delamination

The use of advanced composite materials for cryogenic fuel tanks reduces the mass of the structure but microscopic damage can cause fuel leakage. The amount of leakage depends on the connectivity of the damage and crack opening displacements. In this paper, the damage growth and the opening near the intersection of transverse matrix cracks (TMC) and a delamination are discussed. Three-dimensional finite element analysis (FEA) was used to analyze cross-ply and angle-ply graphite/epoxy laminates. The strain energy release rates (SERR) along the delamination front were calculated based on the virtual crack closure technique. The strain energy release rate has a very large variation along the delamination front and is sensitive to a variety of geometric and load parameters. There is an extreme gradient of the strain energy release rate near the intersection of the delamination front and the TMC. Based on the SERR results, likely delamination shape and size for cross- and angle-ply laminates were determined. Prediction of the likely shape and size will help one to understand the conduit for leakage. The opening near the intersection of the TMC and the delamination was calculated. The effect of ply thickness on the SERR and the opening is also discussed.

Accuracy assessment of a three-dimensional, crack tip element based approach for predicting delamination growth in stiffened-skin geometries

Experimental observations of delamination growth in two stiffened-skin geometries are compared to predictions made using a three-dimensional crack tip element based approach. Each geometry consists of a six-ply graphite/epoxy skin co-cured to a six-ply, hat-shaped stiffener containing a preimplanted teflon delamination between the skin and stiffener at the stiffener termination point. One stiffened-skin geometry was loaded in three-point bending and the other had in-plane tension loads applied to the skin. To predict delamination growth, a three-dimensional crack tip element analysis was first performed on each geometry in order to determine the total energy release rate, G, as well as its mode I, II and III components, G I, G II and G III, respectively. These results were used to define a mode mix at each point along the delamination front, G s/G, where G s=G II + G III. To obtain the delamination toughness, G c, it was assumed that G c exhibits the same dependence on G s/G as on GII/G, where the results for G c versus G II/G were taken from an earlier experimental study. Next, a comparison of the energy release rate to the toughness at each position along the delamination front was performed, and these results were scaled appropriately in order to predict the sequence of loads and corresponding locations at which the delamination will advance. The predictions were then compared to experimental results that included c-scan images of the test specimens taken at each increment of observed growth, and very good quantitative and qualitative correlations were obtained for both geometries. These results indicate the practicality of, and considerable computational savings that may be achieved by, employing crack tip element analyses for delamination growth predictions in realistic structural geometries.

Numerical simulation of fatigue-driven delamination using interface elements

This paper presents a computational technique for the prediction of fatigue-driven delamination growth in composite materials. The interface element, which has been extensively applied to predict delamination growth due to static loading, has been modified to incorporate the effects of cyclic loading. Using a damage mechanics formulation, the constitutive law for the interface element has been extended by incorporating a modified version of a continuum fatigue damage model. The paper presents details of the fatigue degradation strategy and examples of the predicted fatigue delamination growth in mode I, mode II and mixed mode I/II are presented to demonstrate that the numerical model mimics the Paris law behaviour usually observed in experimental testing. Copyright © 2005 John Wiley & Sons, Ltd.

An efficient model of mixed-mode delamination in laminated composites including bridging mechanisms

A refined model is developed to analyse delamination in composite laminates accounting for bridging stresses at crack faces. The analysis adopts a first-order shear deformable layer-wise kinematics for the laminate and an interface model simulating mixed-mode fracture in the presence of a bridged delamination. A penalised interface simulates adhesion between layers and provides energy release rates through its strain energy density while a two-parameter softening interface with a limit displacement models bridging stresses. Delamination evolution analysis is performed by solving the non-linear boundary value problem resulting from a stress analysis coupled with opportune propagation conditions. Numerical examples are presented for composite laminates subjected to both pure mode and mixed-mode loading conditions and the results are compared with those obtained adopting classic delamination models. Analytical formulae for energy release rate evaluation are also proposed to carry out an investigation of the main factors governing accuracy in predicting delamination growth. The proposed approach captures important effects which are not included in classic delamination models. The accuracy of the model is assessed by comparisons with 2D finite element results obtained by using delamination interface elements. The finite element model agrees well with results obtained by using the proposed approach.