Open-hole Composite Laminates Research Articles

Progressive damage modeling in open hole composite laminates with ultrasound-informed drilling-induced delamination

Insertion of fasteners, often used in aerospace and automotive industries, requires drilling that induces non-uniform delamination between lamina of a carbon fiber reinforced plastic (CFRP). Understanding the effect of drilling-induced delamination on the mechanical performance and associated damage mechanisms (progressive damage and failure) is critical to ensure joining integrity. The present work develops an ultrasound testing (UT) method to quantify the drilling-induced delamination at each individual ply interface for CFRP laminates. We then develop a mesoscale finite element (FE) model of an open hole tension specimen by incorporating the UT-obtained drilling-induced delamination at each interface. This delamination is modeled using cohesive zone elements with a bilinear traction-separation law with progressive damage in each ply modeled using the 3D Hashin along with a progressive damage model. Our FE model, with UT-informed delamination, accurately predicts experimental observations of the stress concentration around the hole, damage progression, and open hole tension strength.

Tensile failure of open-hole composite laminates with yarn gaps: Experimental and numerical study

The tensile mechanical behavior and failure mechanism of multidirectional carbon-fiber-fabric-reinforced open-hole composite laminates were investigated in this study. Using digital image correlation (DIC) technology, test specimens were subjected to quasi-static tensile tests to determine their macroscale mechanical properties. An analytical framework was developed to predict the tensile properties, damage evolution, and failure mechanisms of the open-hole composite laminates. Two types of finite element (FE) models: mesoscale model and macroscale-equivalent model, were established. The mesoscale model considers the coupling effect of the yarn gaps and central circular hole. An Abaqus subroutine was written to introduce the Hashin failure criterion, considering the stiffness degradation. The fracture morphology was examined by scanning electron microscopy (SEM) to determine the failure mechanism of the specimens. The results show that the average ultimate load of the specimens is 27.2 kN. The errors predicted by the macroscale-equivalent and mesoscale models are 5.5 % and 1.5 %, respectively. The mesoscale FE model accurately simulated the damage evolution process of each layer under the coupling effect of the yarn gaps and central circular hole. The simulation results and SEM images showed the different failure modes of the fiber layers at different angles.

Progressive damage analysis and experiments of open-hole composite laminates subjected to compression loads

Due to the stress concentration caused by the hole, failure of composite structures is prone to start in the vicinity of the hole edge. Thereby, it is very necessary to investigate the failure of open-hole composite laminates. In the present work, a user subroutine element in the commercial software ABAQUS is proposed for the progressive damage analysis of open-hole composite laminates subjected to compression loads. The proposed element is constructed by making use of the third-order shear deformation theory in conjunction with a two-dimensional progressive damage model. The fiber kink model and Puck criterion are introduced for failure analysis of fiber and matrix, respectively. The element weakening method is also utilized to predict the damage evolution of open-hole composite laminates subjected to compression loads. To verify the reliability of the proposed model, the compression tests of open-hole composite laminates have been carried out. The percentage error of failure load predicted by the proposed element relative to the experimental result is 6.1%. Furthermore, the proposed element presents the damage evolution of fiber and matrix for the lamina with different stacking angles. It is observed that the fiber and matrix damage occurs firstly at the hole edge for the 45 and 0 degree plies, and the damage propagates along the 45 degree direction. This method can contribute to exploring the failure mechanism of open-hole composite laminates, which can also serve as a reference for the design of composite structures.

A novel local to global (L2G) method for progressive fracture analysis of composite laminates

In this paper, we extend a recently developed local to global (L2G) method to capture complex progressive damage processes in composite laminates, which include intra-ply matrix/fiber failure and inter-ply delamination. The L2G builds and solves local problems for individual and interactive cracks, whose local solutions are returned as part of the trial solution for global iteration. It has been demonstrated that the proposed method has advantages of good-accuracy, high-efficiency, and robustness. It can deal with complex problem of cracks branching/merging and multiple interactive cracks. This paper uses the L2G to handle different intra-ply failure modes by adopting Hashin’s criterion, and cohesive zone model (CZM) element is used to capture delamination in inter-plies. Numerical examples of several different stacking open-hole composite laminates show that the proposed L2G is capable of modeling failure processes from minor matrix cracks initiation to final fiber rupture.

A Paris-law-informed neural fatigue cohesive model and its application to open-hole composite laminates

Recent developments in machine learning technologies offer new insights for solving traditional engineering problems as well as a new data-driven framework for novel in-situ material characterization scheme. However, the need for large training samples severely limits the applicability of models of this nature. In this work, a novel training strategy utilizing Paris law is proposed for a neural fatigue cohesive (NFCOH) model. By adding regulation terms deduced from Paris law to the loss function of the neural network, the number of training samples required for NFCOH is significantly reduced. In addition, compensation methods for interfacial strength parameters are also proposed and investigated to further increase the flexibility of NFCOH. Finally, the NFCOH model is utilized to predict the fatigue life of complex open-holed composite laminates to demonstrate the effectiveness of the model where good correlations between the numerical predictions and experimental measurements are achieved.

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 numerical study of coupling effects of hygrothermal environment and geometrical parameter on tensile characteristic length of open-hole composite laminates

The open-hole mechanical properties are used to evaluate the superiority of a new composite material in highly-loaded aircraft structures. The critical open-hole tensile strength and characteristic length are significantly affected by both the hygrothermal environment and width-to-hole-diameter ratio (w/D). However, the coupling effects of these two factors remain unknown until now. This paper aims to reveal the coupling effects of hygrothermal environment and w/D on the tensile strength and characteristic length of an open-hole composite laminate by using a proposed two-level finite-element-based method. Seven hygrothermal conditions, which are characterized by a non-dimensional temperature T∗, and four w/Ds are considered. The obtained results show that, both the tensile strength and characteristic length change monotonously with the variation of T∗, suggesting a considerable influence of the hygrothermal condition. Among the seven hygrothermal conditions, −55°C/dry (CTD), 23°C/dry (RTD) and 70°C/wet (ETW) are the crucial conditions. Under the CTD, RTD and ETW conditions, both the tensile strength and characteristic length are significantly increased by the rising w/D. The increase rates of tensile strength and characteristic length are insusceptible to the hygrothermal condition, and they are respectively 81% and 83% when w/D rises from 2.10 to 8.40. For a certain value of w/D, the tensile strength and characteristic length under the CTD condition are larger than those under the RTD condition, and a reverse trend is observed under the ETW condition. The resulting deviation in tensile strength is slightly related to w/D, whereas the resulting deviation in tensile characteristic length strongly depends on w/D.

Analysis of The Progressive Damage of A Notched AS4/PEEK Composite Laminate Subjected To Tensile Loading

The purpose of this work aims to assess the failure of an open-hole composite laminate subjected to tensile loading, using different progressive damage approaches. Within Abaqus, a user-defined material subroutine (UMAT) was developed and implemented by applying a combination of Puck’s failure criterion and the gradual degradation model. In addition, the integrated model in Abaqus based on the Hashin failure criteria coupled with the continuous damage model has been also considered. Moreover, the effect of different specimen sizes on the behaviour of the AS4/PEEK composite laminate has been performed. The predicted results were compared to those available in the literature. The results of this comparative study showed good agreement between the experimental outcomes and the numerical predictions.

The effects of open hole and fiber orientation on Kevlar/Epoxy and Boron/Epoxy composite laminates under tensile loading

Software simulation is the most effective way of visualizing the deformation and stress of materials or structures and hence predicting the maximum force that can be applied before failure or rupture. This paper aims to study the effect of round cut outs on Kevlar/Epoxy and Boron/Epoxy with three fiber orientations using ANSYS. The work is conducted in three stages, mesh convergence analysis, numerical validation of the software used and failure analysis. Failure analysis is conducted by using the finite element method (FEM) with Maximum stress theory as the failure criteria. The results show a significant difference of strength between solid and open hole composite laminates, in which there is a 90% or more reduction in strength for both epoxy laminates. Among Kevlar/epoxy and boron/epoxy, boron/epoxy showed higher tensile failure either in solid or in the lamina with open hole. The direction of fiber orientation also does affect the failure behaviour of the composite laminates. Hence, it is proven that the current study is important in understanding the failure behaviour of the composite plate in which can be useful in contributing the knowledge of these laminates for further study.

The importance of accounting for large deformation in continuum damage models in predicting matrix failure of composites

The work presented in this paper investigates the ability of continuum damage models to accurately predict matrix failure and ply splitting. Two continuum damage model approaches are implemented that use different stress–strain measures. The first approach is based on small-strain increments and the Cauchy stress, while the second approach account for large deformation kinematics through the use of the Green–Lagrange strain and the 2nd Piola–Kirchhoff stress. The investigation consists of numerical benchmarks at three different levels: (1) single element; (2) unidirectional single ply open-hole specimen and (3) open-hole composite laminate coupon. Finally, the numerically predicted failure modes are compared to experimental failure modes at the coupon level. It is shown that it is important to account for large deformation kinematics in the constitutive model, especially when predicting matrix splitting failure modes. It is also shown that continuum damage models that do not account for large deformation kinematics can easily be adapted to ensure that the damage modes and failure strength are predicted accurately.

Fatigue damage modeling in laminated composite by using Rx-FEM and strength tracking method

The durability and residual load carrying capacity of composite materials is of critical importance for increasing their applicability. Regularized eXtended Finite Element Method framework for discrete modeling of damage evolution and interaction in laminated composites has been extended to increase the limit of crack density for a given mesh size. The formulation allows multiple twining of original nodes while the displacement discontinuity is represented by a pair of element twins maintaining the Gauss integration schema of the original element. Residual Strength Tracking methodology was applied for mesh independent crack insertion as well as in the initiation phase of the fatigue Cohesive Zone Model (CZM). An automatic cycle jump step selection algorithm within implicit framework was implemented to provide solution stability. The predictions were compared with the experimental data for three different open hole composite laminates under tension–tension fatigue and showed excellent agreement.

Strength prediction and progressive damage analysis of carbon fiber reinforced polymer-laminate with circular holes by an efficient Artificial Neural Network

The composite laminates with circular holes find numerous applications in aerospace, automobile manufacturing and other fields due to the design and assembly of structural components. The failure analysis of composite laminates with notches or holes is of great importance in structural applications. In this work, a finite element method (FEM) based artificial neural network (ANN) model is presented to predict the strength and progressive damage behavior of carbon fiber reinforced polymer (CFRP) laminates with holes subjected to the external loads. The activation functions in the model design are reasonably chosen. The ANN prediction results are found to be in good agreement with the simulation results, thereby confirming the accuracy of ANN model. The developed ANN model is suitable for the rapid prediction of progressive damage failure behavior of the open-hole composite laminates. The elastic deformation and the progressive damage behavior of the CFRP laminates with circular holes are predicted by the proposed ANN model, which provides a good machine learning platform with high efficiency and finds potential applications in other fields.

Progressive failure analysis of open-hole composite laminates using FLWT-SCB prediction model

This paper presents the original incorporation of the smeared crack band (SCB) damage model within the full layerwise theory (FLWT) framework, to contribute to the increase of the computational efficiency of the progressive failure analysis of open-hole laminar composites loaded in tension, simultaneously preserving the accuracy of the conventional 3D finite element models. The developed FLWT-SCB prediction model was implemented into an original FLWTFEM framework allowing for the accurate 3D stress fields and excellent visualisation capacity. The response of damaged lamina, in both fiber and matrix directions, was described by distinct bilinear strain-softening curves. The mesh dependency problem was minimized by scaling the fracture energy using a characteristic element length.Both the failure initiation and failure modes were determined using the Hashin failure criterion. To verify the model effectiveness, the obtained results were compared against the experimental and benchmark data from the literature. Mesh dependency was analysed to confirm the benefits of suggested model, as well. The obtained results agreed with the experimental ones and those from the literature.According to the numerical results, FLWT-SCB allows for coarser meshes than those used in the standard finite element models, leading to improved computational efficiency without compromising the accuracy. The model also demonstrated the weak dependency between the size of the structure and the mesh. The advantages of using FLWT-SCB damage model in achieving significant improvements in computational efficiency are highlighted.

Multi-Scale Nonlinear Progressive Damage and Failure Analysis for Open-Hole Composite Laminates

In order to study the nonlinear behaviors and interactions among the constituents for the composite material structure under the tensile load, multiscale damage model using generalized method of cells (GMC) and a lamina-level progressive damage model were established, respectively, for fiber reinforced composite laminates with a central hole, which were based on the thermodynamic Schapery Theory (ST) at either the micro-level or the lamina level. Once the nonlinear progressive degradation of the matrix material reached the lower limit value for the ST method, matrix failures naturally occurred, the failure of the fiber was determined by the maximum stress failure criterion. For the multiscale progressive damage model, the GMC model consisting of a fiber subcell and three matrix subcells was imposed at each integral point of FEM elements, and the three matrix subcells undergo independent damage evolution. The load versus displacement curves and failure modes of the open-hole laminates were predicted by using the two progressive failure models, and the results were compared with that obtained by the Hashin-Rotem progressive failure model and the experimental results. The results show that the ST based method can obtain the nonlinear progressive damage evolution states and failure states of the composite at both the lamina level and the multiscale level. Finally, the damage contours and failure paths obtained are also presented.

Effect of drilling-induced defects on progressive damage of open-hole composite laminates under compression

In this study, the effect of drilling-induced defects on open-hole compression progressive failure and buckling and post-buckling behavior of composite laminates was investigated numerically. First, drilling-induced defects were identified from X-ray computed tomography data using image processing software, from which delamination and fiber pull-out defects were quantified on the specimen. These defects were then incorporated into finite element mesh, and numerical analyses simulating ASTM open-hole compression tests were performed in Abaqus. Hashin failure criterion and energy-based linear softening law were employed to determine in-plane failure initiation and evolution. Interlaminar failure was accounted for by cohesive zone modelling inserting cohesive elements at delaminated interfaces. The numerical model with defects was validated against experimental results and very good agreement was obtained. Next, simulations were performed on both defect-free and defective open-hole composite laminate models to study the effect of drilling-induced defects on compressive strength and progressive failure behavior. Finally, analyses were performed with buckling deformation allowed and the effect of buckling and post-buckling on compression failure behavior was investigated.

A Numerical Study of Coupling Effects of Hygrothermal Environment and Geometrical Parameter on Tensile Characteristic Length of Open-Hole Composite Laminates

A Numerical Study of Coupling Effects of Hygrothermal Environment and Geometrical Parameter on Tensile Characteristic Length of Open-Hole Composite Laminates

Study on Tensile Properties of Reinforced Composite Laminates with Open Holes

The performance of open-hole composite laminates with different sizes and fillets under tensile load was analyzed by experiments and finite element software of ABAQUS. The effects of different hole sizes and fillet radius on the tensile properties of laminates were discussed. The results showed that the tensile failure load decreased with the increase of the hole size, and the trend was obvious. As the fillet radius of the hole increased, the failure load tended to increase.

Damage mode identification of open hole composite laminates based on acoustic emission and digital image correlation methods

This paper focuses on damage mode identification of composite laminates based on acoustic emission and digital image correlation methods. The effect of different fiber/matrix materials on the damage progression of quasi-isotropic laminates with one open hole was investigated first. The effect of different hole orientations with respect to load direction on the damage mechanism of laminated composites with two interacting holes was studied next. For this purpose, correlation and Principal Component Analyses (PCA) were performed to select the most effective acoustic emission (AE) parameter in clustering. After performing PCA, peak frequency parameter was selected to cluster acoustic emission signals due to its great contribution to the principal component. Damage mechanisms were identified based on cumulative counts and energy parameters of AE events for both aspects mentioned above. The findings of the AE measurement were successfully verified by digital image correlation (DIC) measurements.

A Novel and Highly Effective Natural Vibration Modal Analysis to Predict Nominal Strength of Open Hole Glass Fiber Reinforced Polymer Composites Structure

Glass fiber reinforced polymer (GFRP) composite laminates are considered the key material in many industries such as the infrastructure industries and the aerospace sector, and in building structures due to their superior specific strength and lightweight properties. The prediction of specimens’ nominal strength with open holes is still an attractive and questionable field of study. The specimen size effect is referred to its strength degradation due to the presence of holes when specimen geometry gets scaled. The non-destructive test used to measure the nominal strength of such material is a great tool for fast selection purposes, but not secure enough for several purposes. Furthermore, the destructive tests which are more expensive and time-consuming should be avoided in such structures. The present work aims to predict the nominal strength of open-hole GFRP’s composite using modal analysis of their natural frequency as non-destructive tests. At this end, the natural frequency, which is measured using modal analysis procedures, is combined with both linear elastic fracture mechanics (LEFM) and the theory of elasticity to predict the nominal strength of open-hole composite laminates. This advanced model employs two parameters of surface release energy resulting from a simple tension test and Young’s modulus based on vibration modal analysis. It is well established that these types of materials are also subjected to a size effect in dynamic response. Inversely to the known static loading size effect, the size effect in dynamic response increases with specimen size. The novel model gives excellent and acceptable results when compared with experimental and finite element ones. Size effects curves of a nominal strength of these laminates have a very close relative value with those obtained from finite element and analytical modeling. Moreover, the received design tables and graphs would be highly applicable when selecting suitable materials for similar industrial applications.

Numerical study on failure behavior of open-hole composite laminates based on LaRC criterion and extended finite element method

A new numerical model combining LaRC failure criterion and extended finite element method (XFEM) is created to describe the failure behavior in fiber-reinforced polymer (FRP) composites. In this model, the onset of intralaminar damages are predicted based on the LaRC failure criterion, and the crack propagation and stiffness degradation are described explicitly by the XFEM. The user subroutine UDMGINI of ABAQUS defines the initial damage criterion and a mixed-mode, energy-based fracture criterion is employed to describe the crack onset and propagation in the enriched region of XFEM. The proposed model is used to investigate the failure behavior of two sets of open-hole laminates under tension. It is demonstrated that the proposed numerical method can predict the experimental data well.