Plain Woven Laminates Research Articles

Acoustic emission-based failure load prediction for plain woven laminates under quasi-static indentation

Composites are widely used in engineering applications, and their penetration resistance is critical for performance and safety. However, testing the failure load of composites directly leads to component failure, making it challenging to evaluate the expected residual capacity. To address this issue, this study proposes an artificial neural network (ANN) method that accurately predicts the penetration failure load of composites using acoustic emission (AE) data. A cyclic loading test schedule is designed to capture the AE data during each cycle, and a relationship between AE data and load ratio (LR) is established. To predict the failure load, an extrapolation method (EM) based on uncertainty is proposed in this paper. This approach enables the prediction of failure load intervals when LR equals 1, with relative errors of less than 7.66%. In cases where multiple loads are not feasible, the single-point prediction method (SPM) can be used instead of the extrapolation method. However, it is crucial to avoid training AE data during the initial loading stage for accurate predictions. This study recommends a loading ratio of more than 0.1 for optimal results with this approach.

Automated Characterization of the Ply Stacking Sequence of a Woven Carbon Fiber Composite Using Pulse-Echo Ultrasound

Carbon fiber composites are a popular design material due to their high specific strength. The directional strength of woven composites can be customized by changing the orientation and sequencing of individual lamina within the ply stack. This allows for the potential of specialized parts designed for specific applications, leading to both performance gains and weight savings. One challenge is the ability to characterize non-destructively the orientations of the individual lamina after the manufacturing process. Current industrial methods used to verify the ply stack are destructive to the part, increasing costs and material waste. This creates the need for a non-destructive technique capable of determining the ply stack, both for quality control and for in-service parts, including when there may be access to just a single side of the composite. This research introduces a procedure to scan a fabricated laminated composite using pulse-echo ultrasound coupled with an automated algorithm to determine the layer-by-layer orientation of the ply stack with a specific focus on woven composites. In this work, 12 unique plain-weave laminates ranging from 3 lamina to 18 lamina thick are studied. The orientations of each stacking sequence are different, with some following standard composite design methodologies and others randomly stacked. The mathematical technique presented in this work correctly characterizes non-destructively the orientation of each individual lamina to within 1° with 73% confidence and to within 3° with 98.3% confidence of the as-manufactured orientation.

Study on impact resistance and parameter optimization of patch‐repaired plain woven composite based on multi‐scale analysis

AbstractPatch‐repaired plain woven composite structures were exposed to internal damage caused by impact during service, which reduced mechanical properties. A multi‐scale modeling strategy was proposed to study the impact resistance characteristics of patch‐repaired plain woven carbon‐fiber‐reinforced‐polymer (CFRP) laminates. The micro representative volume element (RVE) was extracted from the yarn; a local homogenization method was used to obtain the equivalent cross‐ply laminate (ECPL) cells corresponding to the mesoscale RVE. The finite element model (FEM) of patch‐repaired plain woven laminate was established by extending the ECPL cells. The FEM was checked by the low‐velocity impact (LVI) tests, and the impact parameter errors were within 10%. Furthermore, impact resistance of repaired specimens under different impact conditions (e.g., the impact energy was 3 ~ 20 J) was studied. Finally, patch parameters (patch thickness, patch size, off‐axis angle) of the repaired specimen were optimized by multi‐objective optimization based on the surrogate model and response surface method (RSM). After multi‐objective function optimization, the optimal patch parameter configuration (the thickness of the patch was 0.87 mm, the diameter was 66 mm, and the off‐axis angle was 44.2°) reduced the absorbed energy value of the repaired specimen from 4.9089 to 4.1640 J, and the delamination area of the repaired specimen from 605 to 280 mm2. All the results provide a reference for patch repair of plain woven composites.

Nonlinear progressive damage model for woven patch-repaired laminate composites

Laminated fiber-reinforced composite materials are vulnerable to damages arising due to impact events like accidental tool drops, bird strikes, etc., which significantly reduce the structural integrity of these materials. Therefore, one of the popular adhesively bonded repair techniques, i.e. patch repair is employed in this work. The present work focuses on developing a three-dimensional energy-based gradual degradation model for patch-repaired laminates, including the effects of shear non-linearity under tensile load. The model utilizes modified Hashin failure criteria for plain woven laminate and maximum shear stress criteria for the adhesive. Using the nonlinear model, the failure strengths for different pristine, drilled and repaired specimens with double-sided patches of [0]2 and [45]2 are studied. Tensile experiments in accordance with ASTM-D3039/D3039M are performed using Digital Image Correlation (DIC) and Acoustic Emission (AE) to validate numerical results. The simulated results based on the proposed model and experimental observations are used to compare the damage mechanisms of pristine, drilled, and patch-repaired laminates. It is observed that matrix cracking is majorly responsible for damage initiation. Subsequently, fiber–matrix debonding and fiber breakage account for the ultimate failure of pristine, drilled and repaired specimens. The developed model is used for studying the effect of different patch sizes of repaired specimens under tensile load.

Effect of direct current direction on electro-thermal damage of carbon fiber/epoxy plain woven laminates

Electro-thermal damage mechanisms on direct current are important for the reliability design of carbon fiber reinforced composites in an electric environment. Here we studied the effect of direct current direction on the electro-thermal damage of carbon fiber/epoxy plain woven laminates. The current was applied on the composite along longitudinal/through-thickness directions. We used an infrared camera to record temperature distribution from Joule heat on the composite surface. The surface temperature distribution under the through-thickness current was more nonuniform than that under the longitudinal current. We conducted three-point bending and micro-CT tests to reveal the effect of direct current treatment on mechanical behavior. We found that the through-thickness current reduced the composite flexural performance, while the longitudinal current did not. The through-thickness current induced the electro-thermal damage in the composites but without crack defect. Interfacial degradation is a new electro-thermal damage mode.

Ballistic penetration damages of hybrid plain-woven laminates with carbon, Kevlar and UHMWPE fibers in different stacking sequences

Hybrid composite materials combine different fibers in preform and take advantages of different mechanical behaviors for improving ballistic impact damage tolerances. Here we report ballistic impact damages of plain-woven laminates with different hybrids and stacking sequences. Three kinds of hybrid laminates, i.e., carbon/Kevlar, carbon/ultra-high molecular weight polyethylene (UHMWPE), and UHMWPE/Kevlar, had been prepared and tested in ballistic penetration with fragment simulating projectiles (FSP). The residual velocities of the projectiles and impact damage morphologies of the laminates have been obtained to show impact energy absorptions for the different hybrid schemes. A microstructural model of the hybrid laminates had also been established to show impact damage mechanisms with finite element analysis (FEA). We found that the UHMWPE/Kevlar hybrid laminates with Kevlar layers as the front face have the highest energy absorption capacity, followed by the carbon/Kevlar hybrid laminates with carbon layers as the front face. The main damage modes are fiber breakages, matrix crack and interlayer delamination. The ballistic damage evolutions from the FEA results show that the major damage is shear failure for front layers, while tension failure for the back layers. We expect that the ballistic impact performance could be improved from the different hybrid schemes.

A non-linear material model for progressive damage analysis of woven composites using a conformal meshing framework

A progressive damage model is presented to investigate the damage and failure behaviors of woven composites. The conformal finite element mesh for the woven composites, used for this analysis, is generated using fabric micro-geometry from DFCA (Digital Element Approach (DEA) Fabric and Composite Analyzer, Kansas State University). The mesh generation strategy is discussed briefly – it does not make any idealized assumptions about yarn geometry and thus can be used for any woven composite micro-geometry. The woven composite domain consists of homogeneous and transversely isotropic yarns, and the surrounding homogeneous isotropic matrix. A recursive stiffness reduction method that allows for combined failure modes is employed to model progressive damage behavior. Two different fabric micro-geometries are studied: a 2D plain-weave laminate and a 3D orthogonal-weave unit cell. To support the validity of the proposed model, numerical results for the mechanical behavior of the two cases are discussed and compared with numerical predictions in literature and available experimental data.

Prediction of Bending, Buckling and Free-Vibration Behaviors of 3D Textile Composite Plates by Using VAM-Based Equivalent Model.

To solve the microstructure-related complexity of a three-dimensional textile composite, a novel equivalent model was established based on the variational asymptotic method. The constitutive modeling of 3D unit cell within the plate was performed to obtain the equivalent stiffness, which can be inputted into the 2D equivalent model (2D-EPM) to perform the bending, free-vibration and buckling analysis. The correctness and effectiveness of the 2D-EPM was validated by comparing with the results from 3D FE model (3D-FEM) under various conditions. The influence of yarn width and spacing on the equivalent stiffness was also discussed. Finally, the effective performances of 3D textile composite plate and 2D plain-woven laminate with the same thickness and yarn content were compared. The results revealed that the bending, buckling and free-vibration behaviors predicted by 2D-EPM were in good agreement with 3D-FEM, and the local field distributions within the unit cell of 3D textile composite plate were well captured. Compared with the 2D plain-woven laminate, the displacement of 3D textile composite plate was relatively larger under the uniform load, which may due to the fact that the through-the-thickness constrains of the former are only dependent on the binder yarns, while the warp yarns and weft yarns of the latter are intertwined closely.

Open hole size effects on tensile properties of 3D braided composites

Owing to the excellent integrated structure, notch-insensitivity, delamination-free characteristics, 3D braided composites have a broad range of engineering applications. In this paper, the notch size effects on two types of 3D braided composites were experimentally examined. Style I incorporated 40% of longitudinal lay-in yarns. Style II was the pure braids. The Point Stress Criterion (PSC) was applied to predict the open-hole strength of 3D braided composites. It is found the 3D braided composites can keep higher proportion residual strength after involving the different circular hole sizes compared to plain woven laminates. The open-hole pure braided specimen shows better performance than that the braids with longitudinal yarns, the lay-in longitudinal yarns improve neither specimens’ un-notched strength, nor the modulus. The predicted open-hole strength were compared with experimental results. The traditional analytical method can predict the open-hole strength of 3D braided composite to some extent. Under uniaxial tensile stress, the failure behaviour of two types of 3D braided specimens are different. For un-notched specimen, clear cracks usually show up on the Style II specimen, while it is not true for Style I coupon. For notched specimen, the crack of both notched specimens will propagate along the notch and finally render the specimen to fail

Effect of carbon/Kevlar asymmetric hybridization ratio on the low-velocity impact response of plain woven laminates

The ply structure has a significant effect on the impact resistance and failure behavior of composite laminates. In this paper, carbon/Kevlar hybrid fabric reinforcements were prepared with different Kevlar ratio (0%, 25%, 50%, 75%, 100%) by replacing carbon fabric plies on the non-impact side by Kevlar plies. The low-velocity impact tests for all configurations were carried out under 15 J and 25 J energy respectively. The results show that the maximum deflection, impact duration, impact absorption energy and absorption energy efficiency of hybrid laminates increased with the Kevlar hybrid ratio, whereas the peak force presented a decreasing trend, which indicates that the adding of Kevlar layer makes the laminates more ductile than non-hybrid carbon structure. The damage mechanism of the carbon fiber ply was brittle fiber fracture, resin cracking and resin shedding, while the fibers pull-out and tows splitting was found in Kevlar ply. The critical structural damages start from the non-impact side and evolve to the impact side. And the rules of internal crack volume distribution with Kevlar plies are consistent with the trend of external damage area on the non-impact side. It is suggested that in order to take into account the peak strength and excellent structural resilience, Kevlar asymmetric-hybrid ratio of 25% is the most appropriate. The reason is that an appropriate small ratio of Kevlar cushion ply can not only effectively avoid the tensile fracture at non-impact side happened in the non-hybrid carbon structure, but also withstand enough impact load by maintaining a high carbon fiber content.

Electric potential distributions in carbon fiber/epoxy plain-woven laminates with different current directions

Revealing electric potential distributions in carbon fiber reinforced polymer composites (CFRPs) is important in structural health monitoring (SHM). Here we report effects of current injection modes, probing depth and preform structure on the electric potential distributions in carbon fiber/epoxy plain-woven (PW) laminates. We have conducted a series of electric distribution measurements and established a linear anisotropic conductivity model to show the electric potential distribution. It was found that fiber tow waviness and bridging region in the PW laminates lead to the decrease of electric conductivities along in-plane direction, and the increase along thickness direction. Two pairs of electrodes with vertical current flow paths lead to a positive superposition effect, while a negative superposition effect from opposite current flow paths. The electric current along thickness direction decreases because of high inter-laminar contact resistance.

Size effects in plain-weave Astroquartz® deployable thin shells

The general scaling trend for brittle materials, in which the strength increases when the sample size decreases, is reversed in plain-weave laminates of Astroquartz® and cyanate ester resin. Specifically, both the shear stiffness and the compressive strength decrease for test samples with widths smaller than 15 times the wavelength of the fabric, and observations at the microscale explain this behavior. The derived scaling is applied to the analysis of a deployable thin shell forming a 90∘ corner hinge with five cutouts on each side. The cutouts leave narrow strips of material with width as small as one fabric wavelength, forming structural ligaments whose strength and stiffness are subject to strong size-scaling effects. A numerical simulation of the folding process followed by a failure analysis is presented, using two alternative material models and failure criteria. The size independent model predicts that the structure will remain damage-free after it is folded and deployed, whereas the size-scaled model predicts that failure will occur. The correctness of the size-scaled model prediction is verified by measuring localized damage in a physical prototype, using x-ray CT scans.

Effect of Superficial Scratch Damage on Tension Properties of Carbon/Epoxy Plain Weave Laminates

The effect of scratch damage on the tension properties of carbon fiber plain weave laminates has been studied in detail using digital image correlation (DIC) and acoustic emission (AE). A range of scratch lengths was machined onto different laminates. The bearing capacity of the laminates was then compared with that of unaltered samples. The strain field distributions near the scratches were measured and analyzed as a function of scratch length with DIC. Initiation and propagation of damage were monitored during the tensile tests using AE. Failure sites and morphologies were observed and analyzed. The results show that superficial scratches have little effect on the strength of plain weave laminates when the scratch length is less than 80% of the specimen width. Scratches affect the distribution of strain near the scratch but not far away from the scratch or at the back face of the sample. Not all samples broke from the scratch site but instead broke from the free edge of the sample or close to the gripping region.

Interfacial performance and impact resistance of argon plasma treated UHMWPE/STF inter-ply hybrid composites

This study explored the influence of low temperature glow discharged argon (Ar) plasma on interfacial performance and impact resistance of ultra-high molecular weight polyethylene (UHMWPE) inter-ply hybrid composites. The composites were composed of UHMWPE and meta-aramid plain woven laminates with shear thickening fluid (STF). Water contact angle and drop-weight resistance of the composites with various Ar plasma treatment parameters were tested to investigate the interfacial performance and impact properties of the composites. The tested treatment parameters of this study included treating time, treating power, and gas flow rate. It was found that the best interfacial adhesion of UHMWPE and the impact resistance of the composites was realized at the plasma treatment power of 100 W, treatment time of 150 s, and gas flow rate of 4 sccm. In the follow-up research, this study conducted ballistic test to further explore the bulletproof effect and application prospect of this material.

Effects of environmental conditions on the axial tension–compression fatigue behavior of carbon/epoxy plain-weave laminates containing flaws

The objective of this work is to investigate the effects of environmental conditions on the axial fatigue behavior of a carbon/epoxy plain-weave laminate with an embedded flaw subjected to a partially reversed cyclic load (stress ratio R = −0.1) in tension–compression. This specific material is more commonly used in aerospace engineering for the manufacturing of aircraft structural parts, which are directly exposed to various environmental conditions during service. Specific environmental and loading conditions that are appropriate to simulate real-life conditions are considered to observe and collect information about the material's behavior. For the investigation, dry and wet coupons were submitted to room temperature, 82 and 121 ℃ under loading frequencies of 7 and 15 Hz. A maximum allowable strain increase criterion is used to monitor the flaw growth threshold or delamination onset, during fatigue testing. The ultrasonic imaging (C-scan) technique is used to verify and confirm the delamination onset. Results show that the delamination onset strain increase criterion, along with fatigue life, generally decreased as the operating temperature and humidity were increased and that frequency had little effect on the delamination onset fatigue life. The S– N curves obtained from the tension–compression fatigue data were then compared to those of a previous work carried out in tension–tension fatigue loading. Results show a clear degradation in the delamination onset fatigue life of the coupons tested under tension–tension cyclic loading when the minimum tensile component of the cyclic load was replaced with a compressive load of the same magnitude.

Strength prediction of woven composite rings using progressive damage modeling

The ultimate failure of the woven composite pipes has been investigated using progressive damage modeling. The composite pipe specimens were made of (E) glass plain weave fabrics according to the ASTM D2290 standard. The hoop strength of these specimens has been obtained from the tensile tests. The damage initiation and propagation of composite pipe have been predicted by a numerical multi-scale method. For this purpose, the damage of the yarns and resin of the plain weave laminate was investigated by modeling a representative volume element. Then, the macroscopic stresses and strains of the representative volume element were calculated to obtain the equivalent stiffness matrix using suitable boundary conditions. Then, the mechanical properties of the laminate and material properties degradation coefficients were derived by this equivalent stiffness matrix. Hashin and Von Mises failure criteria were utilized in USDLFD subroutine to predict the damage initiation of the yarn and resin in the representative volume element, respectively. The sudden degradation method has been used to investigate the damage propagation in these constituents. Then, the woven composite ring was modeled in ABAQUS software and its ultimate strength was predicted by UMAT subroutine using obtained degradation coefficients of the representative volume element from the previous step. Finally, the numerical results were compared with the experimental data which show good agreement between the results.

Effects of debulk temperature on air evacuation during vacuum bag-only prepreg processing

Air removal prior to cure is critical for limiting porosity during vacuum bag-only (VBO) processing of prepregs. In this study, the effects of pre-cure dwell temperature (debulk) on air evacuation were investigated for both plain weave (PW) and unidirectional (UD) prepregs. In situ observations revealed that increasing dwell temperature promoted inter-ply air evacuation (by as much as 2x for UD prepregs). Through-thickness gas permeability increased with increasing temperature and decreased with increasing number of plies. The decrease in in-plane permeability during heated debulk was attributed to increased tow impregnation. The findings provide guidelines for cure cycle optimization. Heated debulk enhanced air evacuation in PW laminates, particularly as laminate width/thickness ratios exceed a threshold value. However, warm debulks were less effective, particularly for thicker laminates (>8 plies).

Translaminar fracture toughness and fatigue crack growth characterization of carbon‐epoxy plain weave laminates

An experimental investigation of mode‐I translaminar fracture toughness and fatigue crack growth behavior of a carbon fiber‐epoxy plain weave laminate manufactured by resin infusion under flexible tooling (RIFT) is presented in this article. Pre‐cracked compact tension (CT) specimens were used to perform both quasi‐static and fatigue tests. Different data reduction techniques for fracture toughness calculation were used and compared with each other. The ASTM E399 test method was modified to account for the material orthotropy and specimen geometry effects using a correction function based on a numerical evaluation of the strain energy release rate. The proposed modification shows good agreement against other experimental methods found in the literature and its application was validated for fatigue tests. Fatigue testing shows that failure in undesired modes is likely to occur prior to translaminar fracture, which was attributed to a higher tensile fatigue threshold than compression or shear fatigue threshold presented by the composite in analysis. Increasing the specimens’ initial notch length was a solution for avoiding these types of failure. The experimental results were compiled in the form of a Paris curve, and their particularities were discussed. A fractographic analysis was carried out to define damage patterns and its evolution process in both types of tests. POLYM. COMPOS., 40:3791–3804, 2019. © 2019 Society of Plastics Engineers

Flexural damage behavior of CF/PA6 plain woven laminates with different layers

This study investigated the flexural properties and failure behavior of CF/PA6 plain woven laminates with different layers (i.e., 2, 4, 10 and 16 plies) fabricated by the hot compression technique. Step-by-step interrupted three-point flexural tests and optical observation were performed to study the failure mechanisms of CF/PA6 plain woven laminates with different layers. Incremental cyclic flexural loading tests were carried out to investigate cyclic cumulative damage. The results indicate that the flexural strength of various CF/PA6 plain woven laminates follows the Weibull distribution and that 16-layer laminates show a higher Weibull modulus than the other types of laminates. The flexural initial fracture point (matrix cracking), flexural knee point (intralaminar cracking) have also been identified based on the observation of about 50 specimens for each type. The knee point plays a critical role in determining the flexural properties of composites whereas initial fracture is not a critical factor for the flexural properties. The typical three stages (i.e., initial stage, smooth stage and damage stage) of a fatigue degradation process of various CF/PA6 plain woven laminates during incremental cyclic loading flexural tests were observed. The flexural knee point stress is near the abrupt stiffness degradation limit stress in the present study.

Predicting mechanical properties of thin woven carbon fiber reinforced laminates

While plain woven composite has been widely used over decades most studies are limited to predicting in-plane properties of multi-layer laminates or overall response of single-layer composites. Deployable space applications require them to be ultra-thin and hence generally made of one to six layers of thin-woven composites where out-of-plane behavior is dominant. Classical lamination theory over predicts the out-of-plane stiffness when they are made of one to two layers and relative positioning of each layer can have a significant effect on predictions for two-layer composites. This paper focuses on predicting micro-mechanical behavior of two-ply plain weave laminates under small strains. A representative volume element and its properties are obtained through micrographs to develop a homogenised Kirchohoff plate model for predicting constitutive relationship in the form of a six by six ABD stiffness matrix. Effect of different idealization of cross-sectional and weave profiles are examined using five different tow models and the predictions are validated against experimental results obtained from uni-axial tension and four-point bending tests performed on 0/90 and ± 45 laminates. Further it is shown that relative positioning of plies influences both axial stiffness and bending stiffness of the laminate.