Behavior Of Composite Laminates Research Articles

Fracture modeling of curved composite shell structures using augmented finite element method

This paper presents an augmented finite element method for the fracture modeling of curved composite shell structures considering geometric nonlinear effects. We first derive the composite shell AFEM (CS-AFEM) formulation using a dynamic implicit algorithm, which enhances the numerical convergence when dealing with unstable crack propagations. Besides, the cohesive zone model featuring with shell kinematics is incorporated into the CS-AFEM to describe the quasi-brittle fracture behaviors of composite laminates. Furthermore, a coordinate transformation scheme is proposed to describe both the local material orientation and the crack evolving path in the curved shell structures. Finally, several benchmark examples are numerically investigated, and the capability of the proposed method in modeling the arbitrary evolving cracks in curved composite shell structures has been thoroughly demonstrated.

Effects of Matrix Cracking-Induced Delamination on Thermal Buckling of Composite Laminate

Abstract Delamination and matrix cracking are common damage modes in composite laminates, significantly impacting their structural integrity and performance. Under elevated temperatures, the collision of anisotropic thermal expansion and nonlinear stiffness responses affect the onset of thermal buckling in flying vehicles. This study implements a multi-scale analysis framework, incorporating finite element modeling and analytical methods to obtain the reduction in mechanical properties of the composite laminate and its stiffness degradation based on an effective stiffness model due to pre-existing matrix cracking in plies. Based on non-linear equations, obtained from the principle of virtual work, in combination with first-order shear deformable theory and von Kármán strain-displacement relations, the thermal buckling temperature, post-buckling behavior of composite laminates are investigated. This work paves the way for developing a model to predict the influence of the laminate stiffness, delamination size, transverse crack location, stacking sequence, and plies thickness on the laminate.

The effect of interfacial imperfection on the nonlinear dynamic behavior of composite laminates under low-velocity impact

The effect of interfacial imperfection on the nonlinear dynamic behavior of composite laminates under low-velocity impact

An experimental study of weave pattern effect on the mechanical and dynamic behavior of composite laminates

An experimental study of weave pattern effect on the mechanical and dynamic behavior of composite laminates

Effect of slit size on low‐velocity impact behavior of composite laminates with regularly arrayed chopped strands: Experimental and numerical analysis

AbstractShort fiber reinforced polymers (SFRP) based on unidirectionally arrayed chopped strands (UACS) offer exceptional formability and great mechanical properties. To ensure its stability and safety in applications, it is crucial to enhance the impact performance of UACS laminates. This study investigated the low‐velocity impact (LVI) responses and damage evolution of UACS laminates with different slit sizes and continuous carbon fiber reinforced polymer (CFRP) laminates under various impact energies (4, 7, and 11 J). The curves of force and energy were recorded during LVI tests, and the post‐impact damage area was detected by the ultrasonic C‐scan technique. Moreover, a user‐defined subroutine VUMAT, containing a progressive damage model and a Johnson‐Cook constitutive model, was written to mimic the damage evolution. Based on experiments and numerical prediction, it was found that when the size was reduced from 25 to 5 mm, the vertical slits had the effect of suppressing delamination and could restrain the propagation of delamination, which explains the distinct difference in delamination area.Highlights The effect of slit size on the impact behavior of UACS laminate was revealed. The damage mechanism was simulated with a progressive damage model. The novel UACS laminate exhibits excellent energy absorption capacity. The resistance of the slits greatly suppresses the delamination behavior.

EXPERIMENTAL ANALYSIS OF THE EFFECT OF THE WOVEN ARAMID FABRIC ON THE STRAIN TO FAILURE BEHAVIOR OF PLAIN WEAVED CARBON/ARAMID HYBRID LAMINATES

Remarkable advances in the research and development of micro/mini Unmanned Aerial Vehicles (UAVs) seek thin, lightweight and strong materials for their structural applications. As these structures involve various loading conditions in both the in-plane and through-the-thickness directions during their life cycle, the assurance of the structural stability in each direction is deemed mandatory. The woven Aramid fibers as high strain materials (HSM) are known to improve the through-the-thickness impact strength. However, the addition of the HSM can affect the overall tensile behavior of composite laminates. This study investigates the effect of the woven Aramid fiber on the in-plane tensile behavior of Carbon/ epoxy laminates. Laminates are fabricated using an easy and cost-effective Vacuum Assisted Resin Infusion Molding (VARIM) setup. A uniaxial tensile test was conducted to analyze the tensile behavior of Carbon/Aramid hybrid composites. The effect of adding the woven Aramid layer and the Carbon fabric sequence on the tensile modulus, strain to failure and modulus of toughness are investigated in this study. The results revealed that the presence of Aramid has a positive hybrid effect on the failure strain, exhibiting pseudo-ductile behavior with a compromise in the tensile modulus of the virgin Carbon/epoxy laminate.

Applicability evaluation of damage evolution models in simulating repeated low-velocity impact behavior of composite laminates

This study aims to provide a valuable reference for selecting appropriate damage evolution models (DEMs) when simulating the behavior of repeated low-velocity impacts (LVIs). Four DEMs are systematically evaluated in simulating mechanical response, dissipated energy, damage evolution, and accumulation under three repeated impacts. 3D Puck failure criteria and various DEMs combined with element characteristic lengths associated with physical fracture modes are used to predict repeated LVI damage behavior. Delamination behavior is simulated by zero-thickness cohesive elements. Two damage indexes are proposed to quantify and compare the damage distribution and accumulation. The post-peak softening and LVI behavior predicted by four DEMs are compared and verified through representative volume elements simulation and LVI experiments. The findings reveal that DEMs have varying degrees of influence on the mechanical response, damage evolution, damage distribution, and accumulation under repeated impacts. The exponential models proposed by P. Maimı et al. and Matzenmiller et al. are more suitable to simulate mechanical response or damage accumulation behavior under repeated impacts than the linear damage evolution model due to their non-linear post-peak softening characteristics. In contrast, Linde model shows brittle behavior due to the rapid damage accumulation during repeated impacts, rendering it unsuitable for repeated impact simulation.

Experimental and numerical investigation on the compression after high-velocity impact behavior of composite laminates

Considering the differences in damage mechanism between high-velocity impact (HVI) and low-velocity impact (LVI), this study conducted HVI tests and compression-after-impact (CAI) tests to reveal the post-impact compression behavior of laminates manufactured by unidirectional prepreg tape and exposed a completely different mechanical response in residual strength compared to that of LVI. By controlling the impact velocity within the range of 200 m/s ̃ 380 m/s, three kinds of impact results were obtained, including un-penetrated and penetrated conditions. Different CAI damage morphologies can be observed in these laminates. In order to fully understand the CAI damage mechanism induced by different HVI events, a surface-based cohesive behavior and a CDM intralaminar damage model were implemented. In addition, a more complete picture of the compression behavior after HVI was observed through the simulation results, which is of great help in estimating the residual strength of post-impact laminates. However, the HVI damage was introduced through the spherical steel projectiles, and the sample size was determined based on ASTM D7137, which might be different factors from the application conditions.

Ordinary state-based peridynamic model for out-of-plane deformation and damage analysis of composite laminates

An ordinary state-based peridynamic (PD) model for predicting out-of-plane mechanical behaviour of composite laminates has been proposed, in which three types of PD bonds are used to describe the reinforcement properties. The non-local strain energy density and peridynamic formulations are obtained based on the principle of virtual work by using Total Lagrange formulation, and the force density is reformulated by interpolation technique. Since the Mindlin plate is regarded as the research object of this PD model, the transverse shear deformation of laminates is considered. Also, the dilatation term is included in the force density vector, and flaws in Poisson's ratio of materials can be overcome. In the proposed PD, the critical strain energy density rather than the critical curvature is adopted as the failure criterion. The capability of the developed PD model was demonstrated by the bending examples of composite laminates with different fiber orientations, and damage analysis was further conducted to demonstrate the strong capability of proposed PD model in replicating the damage process of laminates. In addition, a single-layer material point model (SLMPM) can be implemented in the proposed PD algorithm, and the computational efficiency of numerical models will be greatly improved.

A comparative study on the low velocity impact behavior of UD, woven, and hybrid UD/woven FRP composite laminates

This study is aimed at comparing the response and damage of unidirectional (UD), woven fabric (WF) and hybrid UD/WF fiber reinforced polymer (FRP) laminates subjected to low velocity impact. The unidirectional tape and/or woven fabric (plain weave) carbon/epoxy prepregs are laminated and hot-pressed to produce UD, WF and sandwich-like hybrid UD/WF specimens. Impact responses of specimens are determined through low velocity impact (LVI) tests with impact energies of 10 J, 17 J and 25 J. After the LVI tests, the damage of specimens is characterized and analyzed using a combination of visual inspection, ultrasonic phased-array inspection, micro-computed tomography (CT) inspection, cross-sectional microscopic observation, and thermal de-ply test. Also, the LVI damage mechanisms of the three types of specimens are quantitatively compared by using the inter fiber crack volume ratio, total delamination area and fiber fracture length. It is concluded that the fiber architecture plays an important role in determining low velocity impact behavior of composite laminates. Especially, for the sandwich-like hybrid UD/WF laminates whose surface is a WF layer and the core is a UD layer, the WF layer on the surface plays an important role in reducing matrix cracking, delamination and fiber fracture, thus improving its LVI resistance.

Influence of various damage mechanisms on the low‐velocity impact response of composite laminates

AbstractThis study exhibits the effect of different damage mechanisms on the mechanical behavior of composite laminates subjected to low‐velocity impact load. To achieve this, seven low‐velocity impact energies were applied to laminates with five different thicknesses and four unique stacking sequences. The extent of damage was quantitatively evaluated through contact measurements and ultrasonic C‐scan techniques. Numerical simulations, showing good agreement with experimental results, characterized the distribution and evolution of damage within the laminates. The findings reveal that when matrix and delamination damage are predominant, the dent depth increases slowly and is visually invisible, while the delamination area expands almost linearly. Conversely, When fiber damage prevails, the laminate absorbs more energy, leading to rapid increases in dent depth, the appearance of visible cracks, and the occurrence of sharp fluctuations with multiple peaks in contact force and displacement curves. Nonetheless, the delamination area and projection tend to be stable and unchanged. Furthermore, alterations in thickness and stacking sequence directly affect the damage characteristics and energy absorption properties. This research offers valuable theoretical insights and serves as a reference for enhancing the comprehension of the failure mechanism of laminates and optimizing their performance.Highlights Demonstrate the utility of dent depth in identifying changes in damage mechanisms. Evaluate the delamination damage of laminates after impacts by ultrasonic C‐scan techniques. Reveal the regulation of impact response parameters for different damage mechanisms. Investigate the effect of variation in thickness on damage characteristics and energy absorption. Evaluate the impact resistance of laminates with different stacking sequences.

Numerical investigation of the low-velocity impact damage resistance and tolerance of composite laminates with preloads

Composite materials employed in engineering services are often subjected to preloads such as pre-tension and pre-compression, necessitating a comprehensive understanding of their effects on the Low Velocity Impact (LVI) damage resistance and tolerance. Driven by this, a Finite Element Analysis (FEA) model, accounting for fibre damage, matrix damage, and delamination, has been developed to capture the LVI behaviors of composite laminates subjected to various preloads. Furthermore, the developed model has also been employed to predict the Compression After Impact (CAI) strength of these composite laminates which have been impacted under pre-loading conditions. By comparing the modelling results with experimental data, the fidelity of the model is demonstrated, especially revealing a deviation of less than 10 % between the measured and predicted CAI strengths. The validated model is then employed to further explore the relationships between LVI behaviors, CAI strength, and different types and magnitudes of preloads under varying impact energies. The findings indicate that a monotonic transition in preloading from compression to tension leads to a reduction in LVI delamination area and energy dissipation, while for CAI strength, it is related with the stacking sequence.

Coupling of single-layer material point peridynamics and finite element method for analyzing the fracture behavior of composite laminates

In this paper a novel method, Single-Layer Material Point (SLMP) Peridynamics is proposed to simulate in-plane problems of composite laminates using a single layer of material points. Assuming that there is no relative displacement between the layers of laminates, the Single-Layer Material Point Peridynamics doesn’t need to create multi-layer material points. To further improve the calculation efficiency, a coupling model of single-layer material point Peridynamics and finite element method (FEM) is then developed to simulate the damage initiation and evolution of the composite laminates. Linear elastic deformation problems are studied with the SLMP Peridynamic model and the coupling model respectively, and the results are compared with those of FEM. Damage initiation and evolution problems are also analyzed by the coupling model and the results are compared with those of experiments. It is demonstrated that the presented method is of high accuracy.

Nonlinear Ultrasonic Imaging for Porosity Evaluation.

The influence of porosity on the mechanical behaviour of composite laminates represents a complex problem that involves many variables. Therefore, the evaluation of the type and volume content of porosity in a composite specimen is important for quality control and for predicting material behaviour during service. A suitable way to evaluate the porosity content in composites is by using nonlinear ultrasonics because of their sensitivity to small cracks. The main objective of this research work is to present an imaging method for the porosity field in composites. Two nonlinear ultrasound techniques are proposed using backscattered signals acquired by a phased array system. The first method was based on the amplitude of the half-harmonic frequency components generated by microbubble reflections, while the second one involved the frequency derivative of the attenuation coefficient, which is proportional to the porosity content in the specimen. Two composite samples with induced porosity were considered in the experimental tests, and the results showed the high accuracy of both methods with respect to a classic C-scan baseline. The attenuation coefficient results showed high accuracy in defining bubble shapes in comparison with the half-harmonic technique when surface effects were neglected.

Damage and energy absorption behaviour of composite laminates under impact loading using different impactor geometries

The present paper compares the damage and energy absorption behaviour of composites subjected to low-velocity impact using different frontal geometries for the impactor, with the composites possessing a layup of [02/902]2s. In this study, the rigid impactors with either round-nosed or flat-ended frontal geometry are employed to perform drop-weight tests at various impact energies ranging from 10 to 30 J. The measured loading response and energy absorption are analysed and compared. Additionally, the types and extent of impact-induced damage in the composite specimens are assessed via ultrasonic C-scan, optical microscopy (OM) and scanning electron microscopy (SEM) studies. It is shown that the impact energy threshold for damage initiation is greater than 20 J when using the flat-ended impactor but is less than 10 J when using the round-nosed impactor. In both cases, delamination initiates between the plies in the composite laminate. However, for the flat-ended impactor, the damage behaviour of the fibres exhibits kinking fracture, which differs from the pull-out fibre-fracture caused by the round-nosed impactor. These differences in behaviour are attributed to impactor/composite contact geometry effects which leads to different extents of indentation damage, which in turn directly affects the degree of delamination and fibre damage in the composite.

Assessment and simulation of the thermomechanical tensile and creep behavior of C/PEKK composites for aircraft applications above the glass transition temperature

The present work focuses on the assessment and the simulation of the thermomechanical tensile and creep behavior of Poly Ether Ketone Ketone 7002/carbon fibers composites behavior under tensile and creep solicitation between the glass transition temperature and 200 °C, via a multiscale approach starting from the behavior of the PEKK 7002 neat polymer.Tensile and creep polymer and composite experimental curves are employed to develop and validate generalized Semi – Analytical Homogenization / Localization Method for the simulation of the thermomechanical tensile and creep behavior of composite laminates. Through the employment of the model, a similarity of behavior between polymer and composites is demonstrated.The proposed algorithm capabilities of simulating the thermomechanical tensile and creep behavior of composites with different ply orientations and stacking sequences are then presented.

Low Velocity Impact Behaviour of Composite Laminates Containing TiC and ZrC Nanoparticles in Resin System

Composite structures utilized in defence and aerospace applications might be subjected to impacts due to bird strike, tool dropping and bullet penetration. One of the approaches to this problem is to add nano tubes and nano particles to resin systems in order to improve bonding between fibres and matrix materials. Different nano-particles or nano-tubes of clays, alumina, silica, carbon and graphene have been analysed in composite systems in the literature so far because of the improved mechanical properties. In this study, the low velocity impact behaviour of the aramid fibre reinforced epoxy composite plates, containing two new nano-particles of TiC and ZrC which are not studied formerly, are searched experimentally. After the low velocity impact tests, it is concluded that plates containing titanium carbide nano-particles and zirconium nano-particles yielded 19 % and 4 % respectively less penetration in comparison with particle free plates. In other words, titanium carbide nano-particles contained plates showed more resistance against the impact by 19 % against to particle free plates. These results showed that TiC and ZrC nano particles might be also good contributors for the impact resistance of composite structure.

Numerical simulation of composite grid sandwich structure under low-velocity impact

Abstract The low-velocity impact finite element model of the carbon fiber-reinforced composite grid sandwich structure was established by ABAQUS. Its panels and grid are both carbon fiber-reinforced composite laminates. The constitutive relation of composite laminates is written into the VUMAT user subroutine using the Fortran language. Simulation of intralaminar failure behavior of composite laminates using the three-dimensional Hashin failure criterion. The quadratic stress criterion and the B-K energy criterion were used to simulate the interlaminar failure behavior, and the delamination damage of the composite panel and the interface debonding damage were simulated. The finite element models of four different types of composite grid sandwich structures, including quadrilateral configuration, triangular configuration, mixed configuration, and diamond configuration, were established. The influence of the single grid width and the height of the grid on the impact resistance of each composite grid configuration was studied. Compared with other geometric configurations, triangular grid sandwich structure provides the best energy absorption characteristics, and T-6-10 has the highest fracture absorption energy (15816.46 mJ). The damage propagation law of carbon fiber-reinforced composite grid sandwich structure under impact load is analyzed.

A study of the fracture mechanisms of hybrid carbon fiber reinforced polymer laminates reinforced by thin‐ply

AbstractThe main stress component which creates delamination in bonded single lap joints with composite adherends is the transverse tensile stress. Therefore, the following study investigates the behavior of composite laminates (reference and hybrid laminates reinforced by thin‐ply) under transverse tensile loading. Texipreg HS 160T700 and NTPT‐TP415 were used as the conventional carbon fiber reinforced polymer (CFRP) and thin‐ply respectively. Hybrid composite laminates were studied using different amounts of thin‐ply, applied through the thickness. The manufactured laminates, of unidirectionally stacked construction, were tested under transverse tensile loading. Digital image correlation was performed to investigate the average peel strain distribution for the composite and to better understand the phenomena associated to the use of hybrid laminates. Experimental results show that the reinforced hybrid composite laminates, created using thin‐plies, present higher failure load compared to the reference conventional CFRP or thin‐ply laminates. This was found to be due to the higher ductility enabled by the presence of thin‐plies. Distributing a constant amount of thin‐ply through the thickness was found to increase the laminate transverse strength, as the thin‐ply laminates act as a barrier against crack propagation. A representative volume element was studied for each configuration since this numerical method brings the opportunity to investigate the studied configurations in microscale.

An Experimental and Numerical Study of the Influence of Temperature on Mode II Fracture of a T800/Epoxy Unidirectional Laminate.

Studies on mode II fracture have promoted the establishment of the delamination theory for unidirectional composite laminates at room temperature. However, under thermal conditions, the fracture behavior of composite laminates will exhibit certain differences. The delamination theory should be extended to consider the temperature effect. To achieve this goal, in this study, the mode II static delamination growth behavior of an aerospace-grade T800/epoxy composite is investigated at 23 °C, 80 °C and 130 °C. The mode II fracture resistance curve (R-curve) is experimentally determined. A fractographic study on the fracture surface is performed using a scanning electron microscope (SEM), in order to reveal the failure mechanism. In addition, a numerical framework based on the cohesive zone model with a bilinear constitutive law is established for simulating the mode II delamination growth behavior at the thermal condition. The effects of the interfacial parameters on the simulations are investigated and a suitable value set for the interfacial parameters is determined. Good agreements between the experimental and numerical load-displacement responses illustrate the applicability of the numerical model. The research results provide helpful guidance for the design of composite laminates and an effective numerical method for the simulation of mode II delamination growth behavior.