Woven Laminates Research Articles

Progressive failure analysis of woven and non‐woven CFRP composite/steel bolted joints

AbstractDue to recent advancements in textile fabrication, woven fabric reinforcements are used in composite structures as an alternative to traditional unidirectional fiber reinforcing layups. In this paper, experimental work was performed to study the behavior of multiple bolt‐lapped joints under uniaxial tension. Different bolt numbers, composite layups, and fabric configurations were studied. Single‐ and double‐lap configurations were used to investigate the effect of secondary stresses. It was found that the P‐δ curves of lapped joints exhibit four primary stages: a linear elastic stage, followed by a nonlinear hardening stage, then linear hardening leading up to the peak, and finally a softening stage. For double‐lapped non‐woven joints, the curves encompass only the first three stages; however, for woven composites, the last stage is very small. In addition, among the laminates, the non‐woven laminate sustains the highest normalized failure load, except in the staggered case, where the quasi‐isotropic woven laminate exhibits higher strength. Conversely, the bidirectional woven laminate demonstrates the lowest loads and the highest deformation.Highlights A study compared bolted joint performance of woven and uni‐based composites. Lapped joints with different bolt arrangements were experimentally studied. P‐δ curves showed elastic, nonlinear, linear hardening, and softening stages. Woven laminates showed higher displacements compared to non‐woven laminates. Secondary bending induced additional stress with less impact on woven samples. Bearing failure predominated, with variations in extent of bearing damage.

A Modeling Framework for the Thermoforming of Carbon Fiber Reinforced Thermoplastic Composites.

A comprehensive modeling framework for the thermoforming of polymer matrix woven laminate composite was developed. Two numerical indicators, the slip path length and traction magnitude, have been identified to be positively correlated to matrix smearing and wrinkling defects. The material model has been calibrated with picture-frame experimental results, and the prediction accuracy for intra-ply shear and thickness distribution was examined with measurements of the physically formed parts. Specifically, thickness prediction for most locations on the formed parts was accurate within an 11.6% error margin. However, at two points with significant intra-ply shear, the prediction errors increased to around 20%. Finally, a parametric study was conducted to determine the relationship between various process parameters and the quality of the formed part. For the trapezoidal part, orienting the laminate at 45 degrees to the mold axis reduces the likelihood of matrix smear and wrinkling defects. Although this laminate orientation yielded a greater spatial variation in part thickness, the thickness deviation is lower than that for the 0-degree orientation case. Two forming analyses were conducted with ramp rates of 25 mm/s and 80 mm/s to match the equipment's operational limits. It was observed that higher forming rates led to a greater likelihood of defects, as evidenced by a 15% and 10% increase in the formed part areas with longer slip paths and higher traction magnitudes, respectively. It was discovered that shallower molds benefit from faster ramp rates, while deeper molds require slower rates to manage extensive shearing, stretching and bending. Faster forming rates lead to smaller thickness increases at high intra-ply shear regions, indicating a shift from intra-ply shear to out-of-plane bending due to the visco-plastic effect of the molten laminate and can negatively impact part quality. Lastly, it was shown that a well-conceived strategy using darts could improve the part quality by reducing the magnitude of the defect indicators.

Ballistic impact modeling of woven composites using the microplane triad model with meso-scale damage mechanisms

Existence of undulating fill and warp yarns in woven composite laminae introduces complex unit cell geometries and multi-scale interactions among the constituents. Due to these, the failure process involves various meso-scale constituent-level failure modes under complex loading scenarios such as ballistic impact. This can be challenging to model via conventional macro-scale damage tensor-based models. This challenge is tackled here via the adaptation of the previously developed multi-scale microplane triad model to ballistic impact of woven composites. The model can resolve meso-scale constituent level details (including yarn undulations) and predict not only the elastic constants of a woven lamina but also its fracturing behavior. In the present adaptation, only two damage laws are formulated, one for the fibers and one for the matrix. This enables the model to embody the correct values of the intralaminar mode I and II fracture energies of the woven lamina. The model is calibrated using constituent and lamina level test data, and then used to predict the ballistic impact behavior of a single plain-woven lamina under a wide range of projectile impact velocities. The model is demonstrated to predict very well the projectile residual (rebound and exit) velocities, the energy dissipation, the major failure modes of the lamina and the corresponding extent of damage, as well as the ballistic limit and deformation cone wave propagation speeds. The model’s simple, conceptually clear architecture, and computational efficiency represent a major advantage compared to existing damage tensor-based models. The model is also extended to multi-layer thick section woven laminate impact, where the analyses consider both intralaminar and interlaminar failures. The predictions are found to be comparable to those from MAT162, a commercially available material model in LS-Dyna, with much better computational efficiency. Via detailed sensitivity studies, it is demonstrated that the mode I and II intralaminar fracture energies of the lamina are a crucial model input, necessary for accurate predictions of ballistic impact. Not knowing these can introduce significant uncertainty and therefore, their characterization is an absolute must. Finally, the optimal meshing considerations as well as the advantages and limitations of the microplane triad model are discussed.

Manufacturing multifunctional vascularized composites by through-thickness frontal polymerization and depolymerization: A numerical study on the impact of sacrificial fiber configurations

Concurrent through-thickness frontal polymerization and vascularization (FP-VaSC) is emerging as a promising alternative to conventional multi-step fabrication approaches for vascularized thermoset polymers and composites. This method relies on a localized and self-propagating exothermic polymerization reaction front of the polymer matrix, to simultaneously cure the matrix, and depolymerize pre-embedded sacrificial templates. It delivers fully cured thermoset polymers and composites rapidly and energy-efficiently with the desired vascular system in a single step. While previous studies demonstrated the capability of this method for making woven laminates with a single vascular channel created by embedding a single straight sacrificial fiber, it is desirable to explore the potential of this method for making composites with multiple channels for more practical applications. We employ a previously validated thermo-chemical model from our prior study, to systematically investigate the reaction process with the presence of multiple sacrificial fibers. Two sacrificial fiber configurations are considered, namely, inline and staggered fiber configurations. Within each configuration, we consider a range of horizontal and vertical fiber spacing, which also lead to different sacrificial fiber volume fractions. This study reveals the interactions between the sacrificial fiber and the reactions, identifies the working window of this method for different sacrificial fiber configurations, and provides guidance for manufacturing laminates with multiple vascular channels. We also propose an analytical model that can quickly approximate the maximum sacrificial fiber volume fraction that can lead to successful FP-VaSC for a given carbon fiber volume fraction and compare the results with those from the thermo-chemical modeling.

Impact of textile types and their hybrids on the mechanical properties and thermal insulation of mohair-reinforced polyester Composite laminates

Mohair fibres from animals are a great choice for people who care about the environment. They have low toxicity, are abundant in raw materials and don't pose any health risks. However, when compared to synthetic fibres, their mechanical performance is not as good. Mohair fibres are best suited for low to medium load applications, such as car parts, agricultural equipment, sports equipment and household items. Despite their excellent properties, there is still a lot we don't know about mohair textile-reinforced polyester composites. The novelty of this study is testing different mohair fibre textiles to see which one provides the best characteristics. The three most commonly used locally-made mohair fabrics (woven, knitted and pressed mat) were selected as reinforcement in polyester resin. Nine different laminates of similar and hybrid layers were made by hand lay-up in a closed mold at a constant fibre weight fraction (number of layers), mold pressure, curing time and temperature. The results showed that the composite laminate of mat fabric reinforced polyester provides the maximum tensile strength, elongation, flexural strength and thermal insulation of 22 MPa, 2.2 %, 54.6 MPa, 0.27 J and 0.012 m2°C/W, respectively. Meanwhile, the woven laminate exhibited the highest impact strength of 0.27 J and the hybrid laminates of the mat and woven fabrics offer satisfactory strength of 0.25 J.

Mixed modes crack propagation of orthogonal woven-layer in carbon/aramid/epoxy laminates

This work presents a combined formulation for the fracture model of carbon/aramid fiber reinforced plastic woven laminates (CARPWLs). The structural crack is implemented based on Extended Finite Element Method (XFEM) and Cohesive Zone Model (CZM) with a mixed-mode loading. This work considers four types of fracture mechanics CARPWLs testing samples, each composed of five woven layers with different stacking sequences. The loading device for mixed modes is achieved through a fixture with a secondary level rotating wheel configured with samples via bolting. Additionally, a new velocity control servo script for driving force is proposed to obtain R-curves during the fracture process of Type I, II and III. The energy release rate G for I/II/III mixed modes are also studied by experimental and numerical methods on account of fracture mechanics. The numerical verification performs highly accuracy to experiments, and it provides an efficiency approach for evaluating failure response of laminates.

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.

Post-weld annealing of friction stir welded carbon fiber reinforced low-melt polyaryletherketone

This study explores the influence of post-weld annealing on friction stir welded (FSW) carbon fiber reinforced thermoplastic (CFRTP) in woven laminate form. Field advancement occurs in three key areas including furthering the understanding low-melt polyaryletherketone (LMPAEK) welding/processing, effects of post-weld annealing on CFRTP joints, and determining feasibility for friction stir welding (FSW) of thermoplastics reinforced with continuous carbon fibers. High temperature annealing just below LMPAEK’s melting point improved ultimate tensile strength by up to 30% and weld toughness by up to 91%. Improvements to mechanical performance result from increases in joint crystalline content from 14.09% in non-annealed joints to 27.91% in joints subject to 280 ◦C annealing. Annealing does not reduce porosity in the weld zones, rendering necessary further improvements to the FSW process for CFRTP joints. Further analysis also indicates that despite its slight molecular modifications, LMPAEK has highly similar crystalline structure and response to thermal treatment compared to PEEK.

Friction stir welding of lapped low-melt polyaryletherketone carbon fiber reinforced thermoplastic laminate

Carbon fiber reinforced thermoplastics (CFRTP) have increasing use in aerospace structures due to improved process-ability and weldability. In this study, lap joints between carbon fiber reinforced low-meltpolyaryletherketone (LMPAEK) are formed by friction stir welding (FSW). This study presents novelty by applying FSW to continuous carbon fiber composites in woven laminate form. FSW disrupts the fibers in the weld zone and distributes fragments as small as several microns in length. Thermal analysis shows that the weld zones degrade at 40°C cooler temperatures than the base laminate material due to enhanced polymer mobility surrounding the disrupted carbon fibers. Though optimized joints have regions of over 9% porosity, tensile strengths of up to 73.8 MPa retains up to 50% joint efficiency of a comparable short carbon fiber reinforced composite. CFRTP also requires lower processing forces during FSW than metals, and the power consumption of 67 W during the traverse period for strength optimized welds retains energy efficient characteristics.

Multi-scale finite element analysis on the soft impact behavior of twill weave laminate

This work proposed an impact momentum flexibility (IMF) to precisely and concisely characterize the soft impact behavior of twill weave laminate based on multi-scale finite element analysis. A multi-scale finite element model taking into consideration the microstructure and properties of constituents is established for twill weave laminate. The equivalent properties of fiber tows and twill weave laminate are predicted by micro-scale model and meso-scale model, respectively. Then the soft impact behavior of the laminate is investigated by macro-scale model. The multi-scale model is validated on different scales by comparing the experimental and simulated results of quasi-static compression and soft impact. On this basis, the deformation and failure of the laminate under soft impact are analyzed. The soft impact response is categorized according to the damage morphology and impact velocity. Moreover, the IMF is proposed to depict the ability to resist soft impact deformation of the laminate, and can be further adopted to rank the soft impact property of different materials.

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.

A novel damage evaluation of CFRPs under mode-I loading by using multi-instrument structural health monitoring methods

Mode-I fracture toughness test provides valuable information in the thickness direction of fiber reinforced polymer matrix composites. However, damage propagation under mode-I loading is dependent on the configuration of reinforcing material of the laminate. Understanding the damage types and their growth rate in mode-I fracture toughness test is a vital factor to obtain material allowable for safe design. In this study, mode-I tests are conducted on unidirectional, and twill woven carbon fiber reinforced polymer composite laminates. A new approach is proposed to interpret passive infrared thermography results based on correlating acoustic emission and thermography results in time whereby thermal activities can be classified into two main groups corresponding to matrix and fiber dominant failure types. It is demonstrated that matrix and fiber dominant failures lead to thermal activities with line-wise and point-wise form, respectively. Results show that four different damage types can be seen for mode-I fracture of both laminates. The temporal observations during thermoelastic cooling of the materials show that twill woven laminate releases relatively higher energies due to matrix dominant damage developments which means this configuration type is more prone for delamination failures.

Identification of damage properties of glass/epoxy laminates using machine learning models

In the present research, the possibility of estimating damage properties of Glass/Epoxy woven laminates using machine learning (ML) models is investigated. The dynamic response of laminates under low-velocity impact (LVI) was characterized and used as training data sets for ML models. The suitability of four numerical models was investigated for LVI modeling, and based on their accuracy and simulation run-time, an appropriate method was selected. The MAT054 material model was selected for LVI simulations for two energy states (15 J and 20 J). After characterizing the results of these simulations a set of 13 dynamic characteristics were extracted from the dynamic response of each simulation. Moreover, for each energy state, four ML regression models, namely MLP, KNN, DT, and SVR, were performed with the numerical input sets and the random laminate damage properties in each simulation as the output sets. For each ML model the input vector was the same however only one damage property was set as an output vector. The trained ML models were able to estimate 4 out of 6 damage properties of Glass/Epoxy woven laminates namely Longitudinal modulus, Longitudinal tensile strength, Longitudinal compressive strength, In-Plane shear strength. Additionally, the output of the trained ML models was compared with damage properties obtained from experimental results and it was found that the trained models were able to estimate the said damage properties within 4% – 6% of the experimental results.

Role of discontinuous fiber core material on the mechanical behavior of hybrid sandwich polyester composites

This study investigated the potential for improving the mechanical behavior of glass fiber polyester composites by using symmetric hybrid sandwich configurations that combine continuous woven composite and different discontinuous reinforcements used as a core. The discontinuous reinforcements included sheet molding compound (SMC), bulk molding compound (BMC), and the discontinuous prepreg based platelets that were chopped from the woven trim scrap. Hybrid sandwich configurations using different core materials exhibited improvements in flexural mechanical properties, while providing more progressive failure under both flexural and compressive loading. Compressive strength in polyester SMC and woven laminate was significantly lower than flexural strength, while BMC and chopped platelets exhibited similar levels of strength in flexure and compression. Overall, hybridized compression molding produced sandwich structures can be used to control the failure progression and to improve the structural characteristics of composite, especially under flexural loads. The trim scrap core sandwich configuration had mechanical properties comparable with the BMC core hybrid. Therefore, trim scrap upcycling can be an efficient approach to reducing the amount of material waste during the manufacturing.

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.

Effect of interactions of two holes on tensile behavior of patch repaired carbon/epoxy woven laminates

The conventional case of patch repair involves bonding a patch over single damage/hole in the laminate. This work investigates the effect of interaction of two holes on the tensile behavior patch repaired carbon epoxy woven laminates. The specimens of [0°/45°/45°/0°] laminates were repaired with adhesively bonded two-ply [45°]2 external patches. Three different cases of drilled specimens were produced with different hole arrangements viz. specimens with single central hole (SH), with two holes aligned along the longitudinal axis (LH) and with two holes along transverse axis (TH). The two-hole specimens were repaired with two different types, i.e. single large patches (SP) and with the two smaller patches (DP) of combined bonding area equal to the single large patches. Digital image correlation (DIC) was employed to capture strain contours. The results reveal the difference in the load transfer through the patches depending upon the arrangement of holes. The TH repaired specimen exhibit significant load recovery (SP-32.75%, DP-34.62%) while the LH specimens result in very marginal (SP- 6.11%, DP-4.10%) recovery compared to their drilled case. The TH specimen failed by crack growing through both the holes beneath the patch, while the LH specimens failed by the failure through only one hole. The use of single large patch over multiple holes and multiple small patches individually over each hole has no significant influence on load recovery.

Experimental and numerical study of hybrid (CFRP-GFRP) composite laminates containing circular cut-outs under shear loading

Previous works have established the response and failure behaviour of hybrid (CFRP-GFRP) laminates when subjected to a wide range of destabilising loads. However, to date no works have focused on plates with cut-outs under shear loading and quantified the influence of selective laminate shapes and hybridisation on their post-buckling response. Herein, the plate collapse behaviour of a novel X-braced hybrid (CFRP-GFRP) twill woven laminate containing a large circular cut-out (diameter to width ratio of 0.35), subjected to in-plane shear loading is investigated. The study includes a hybrid and a baseline pure CFRP design and employs both experimental and numerical analysis. The experimental results illustrate that despite having less CFRP material, a hybrid laminate design with shaped CFRP plies exhibits greater failure load (+9%), and a greater failure load to buckling load ratio (1.26 compared to 1.12). However, this comes at the cost of a marginally lower initial plate buckling load (-3%). Additionally, the combined experimental and numerical analysis reveals the detailed failure mechanism of both the pure CFRP and hybrid laminates, demonstrating similar behaviour but that the hybrid design endures significantly more widespread shear damage of the matrix.

Low-velocity impact behavior of carbon woven laminates after exposure to varying temperatures

The present study reports the low-velocity impact (LVI) performance of carbon woven reinforced polymer (CWRP) composites with varying temperatures. The fabrication of carbon woven lamina and carbon woven reinforced two-layered laminate (named CWRP-1 and CWRP-2) was done using a vacuum-assisted resin transfer molding (VARTM) process. CWRP-1 samples were tested at varying impact velocities of 1, 2, 3, and 4 m/s at −25, 25, and 50 °C for each incident velocity. CWRP-2 samples were tested at room temperature at varying incident velocities to determine the effect of multiple woven layers. The impact resistance of the first-crack load, peak impact load, and absorbed energies were recorded and evaluated under different loading conditions. In addition, the Weibull probability method is adapted to forecast failure behavior as a function of load. Visual inspection, optical microscopy, and scanning electron microscope (SEM) images were used to assess the damage pattern and failure morphologies in forecasting the failure phases during LVI. The low-velocity impact behavior of CWRP-1 at −25 °C with various velocities was shown to be random due to the polymer matrix freezing condition. The softening of the resin matrix at 50 °C is responsible for the difference in damage tolerance. The relevance of multiple layered composites for better impact resistance characteristics was demonstrated during testing of CWRP-2 at room temperature. Overall, the results of this experiment showed that CWRP lamina and laminates are highly sensitive to the impact velocities and external temperatures.

Symmetric and asymmetric intercalation effect on the low-velocity impact behavior of carbon/Kevlar hybrid woven laminates

Hybrid fiber composite laminates with the same materials, manufacturing methods and molding processes may present different mechanical behaviors. In this paper, the effect of intercalation sequence on the mechanical performance of carbon/Kevlar plain laminates were studied. According to different intercalation methods, the hybrid layout was divided into symmetric and asymmetric configurations. It is found that the symmetric intercalation structures (KCCK and CKKC) possess better load-bearing and resilience capacity compared with asymmetric structures (CCKK and CKCK), even better than pure carbon structure (CCCC) under high energy impact. The impact damage volume of symmetric specimens was significantly smaller than that of asymmetric specimens by quantitative micro-CT analysis. The apparent damage index (df and dr) can be used to estimate the internal damage data (dCT, H and V). KCCK, a typical symmetric sandwich-like structure, presented the most slight damage among all symmetric and asymmetric configurations, with shear cracks observed at the brittle carbon fiber core layers, while the delamination cracks between Kevlar-carbon interlayers were away from the central damaged region. In CKCK, interlaminar cracks were formed at each carbon-Kevlar interlayers, which shared and relieved the primary interlaminar crack at the core layers compared with CCKK.