Angle-interlock Woven Composites Research Articles

Multiscale modeling for the impact behavior of 3D angle-interlock woven composites

In this paper, a multiscale modeling framework predicting the impact response of three-dimensional angle-interlock woven composites (3DAWCs) is presented. Multiscale modeling is performed sequentially at the mirco, meso, and macroscales. A microscopic representative volume element (RVE) model is established to characterize the yarn's nonlinear mechanical properties and damage behavior at different strain rates. At the mesoscale, a novel subcell-based discretization scheme is proposed to discretize 3DAWCs, and developing six representative subcells (RSCs) that bridge the microscale and macroscale effective properties. Based on it, a ballistic impact model involving six kinds of homogeneous material bricks is established. Furthermore, elastic-viscoplastic damage constitutive models are developed for the epoxy matrix and the yarn, respectively, to enhance the predicted accuracy of the multiscale model. Ballistic impact tests of 3DAWCs are conducted, and X-ray micro-computed tomography is employed to evaluate the internal damage of the 3DAWC target after impact. Validation work is conducted by comparing the experimental and numerical results of the ballistic impact of the 3DAWC target, which indicates the effectiveness and efficiency of the developed multiscale framework in the impact damage prediction of 3DAWCs.

Effects of thermo-oxidative aging on progressive bending damages and electromechanical behaviors of carbon fiber/epoxy 3D woven composites

The effect of thermo-oxidative aging on mechanical properties is important to designing carbon fiber-reinforced composites serviced in long-term atmospheric environments. Here, we report the progressive bending damage behaviors of carbon fiber/epoxy 3D angle-interlock woven composites (3DAWCs) after thermo-oxidative aging. Three-point bending tests were conducted to characterize bending damage behaviors after different aging days. The electrical resistance change of 3DAWCs was also simultaneously measured with the two-probe method during three-point bending tests. Combining side image and digital image correlation (DIC) technology, we found that the bending strength and modulus deteriorated rapidly during thermo-oxidative aging. The strain distribution and progressive bending damage modes also changed significantly, i.e., a symmetrical strain distribution for the unaged specimens, while the existing interface cracks of the aged specimen changed this symmetry. The electrical resistance method (ERM) effectively identified the early-stage damages, and the first derivative of the rate of resistance change (FDC) revealed differences in the progressive damage modes of aged and unaged specimens.

Anisotropy characteristics of electrical conductivity and compressive strength of 3D carbon fiber/epoxy angle-interlock woven composites

Electrical and compressive performances are important in 3D carbon fiber/epoxy angle-interlock woven (AIW) composites for mechanical-electrical coupling behaviors. Here we investigate the electrical conductivity and compressive strength of.3D AIW composites both in in-plane and out-of plane. Four-probe method is conducted to measure the volume resistance along different directions. Damage evolution and failure modes are recorded with a high-speed camera during compressive test. Electrical conductivity and compressive strength exhibit obvious anisotropic characteristics due to fiber orientation and yarn waviness. The curved warp yarns result in the compromise of the X-direction conductivity by extending the current transmission length and increase of the Z-direction conductivity by forming more contact points to expand the current flow paths. Because of different yarn arrangements, the compressive failure mechanisms of 3D AIW composites in the X, Y and Z directions are buckling failure, double shear bands and indirect tensile failure, individually. Yarn undulation in the X-direction causes premature buckling and exhibits elastic-plastic nonlinear response, resulting in the lowest compressive strength and modulus. The 3D AIW composites have the lowest electrical conductivity and highest compressive strength in the Z-direction, which is suitable for high strength stress-sensing elements.

Thermo-oxidative aging induced multi-scale shrinkage and damage in 3D angle-interlock woven composites

The deterioration of resin and interface in composites deteriorate during high-temperature service, would impact both the thermal stability and overall performance significantly. This paper focused on the experimental characterization of multi-scale damage and resin shrinkage within composites induced by thermo-oxidative aging using Micro-CT, SEM and Confocal Interferometric Microscopy (CIM), and exploring the coupling mechanism between them. The results show that damage distribution and propagation are affected by the hierarchical structure of 3-D angle-interlock fabric. Macro-CIM shows that maximum resin shrinkage depth depends on the resin width and aging time. Resin shrinkage profile evolution demonstrated the accelerating effect of resin crack on shrinkage. Micro-CIM shows that macro yarn cracks form through the accumulation of micro resin cracks in resin-rich areas and fiber/resin interface debonding. The formation of fiber/resin interface crack is tied to the resin shrinkage state, only occurring when the surrounding resin shrinkage slope exceeds a specific threshold value.

Polarization Raman spectroscopy characterizations of microscopic stress in 3D angle-interlock woven composites during thermo-oxidative ageing

Investigating stress distribution of three-dimensional carbon fiber epoxy woven composites after thermo-oxidative ageing, especially the microscopic stress, is key to safety design of composite materials. Here, polarization Raman spectroscopy combined with the Raman stress sensitivity of carbon fiber was employed to characterize the microscopic stress in the carbon fiber along the warp and weft direction, as well as the microscopic stress mapping in the warp and weft interwoven interfaces. Under thermo-oxidative ageing, the carbon fiber was forced with compressive stress caused by the thermo-oxidative shrinkage of resin. The fitting lines of compressive thermo-oxidative ageing stress (TAS) distribution in the warp and weft were similar to the yarn alignment paths. Meta-regression analysis indicated that the compressive TAS in carbon fibers is positively correlated with ageing time. Furthermore, the correlation between the compressive TAS and ageing time in warp yarns is greater than that in weft yarns. The stress distributed unevenly with the synergistic effect of the structure and ageing time, and interfacial failure was generated where interfacial stresses exceeded the interfacial strength. The interfacial failure further propagated with ageing time, leading to matrix cracking.

Microstructural modeling on electrical conductivities of 3-D carbon/epoxy woven composites along different directions

Carbon fiber composites have widely been used in aircrafts and high speed vehicles. Electrical conductivity of the carbon fiber composites is critical to electrical safety for the aircrafts and vehicles under high voltage applications. Here we report microstructural modeling on electrical conductivities of three-dimensional (3-D) carbon/epoxy angle-interlock woven composites along on-axis and off-axis directions. A 3-D resistor network model and finite element analysis (FEA) model based on fabric microstructure have been developed to reveal the electric conductivities along different directions. We have found that the conductivity of the woven structure exhibits full anisotropy. The difference of electrical conductivity between in-plane and through-thickness direction decreased due to the existence of through-the-thickness carbon fibers. The electrical conductivity through-thickness direction increases with warp directional length. With increasing off-axis directional length, the conductivity perpendicular to the off-axis direction increases, while the conductivity parallel to the off-axis direction remains basically unchanged. Electric potential distribution and electrical current density are highly related with fabric structure and current directions. Owing to the dependence of mechanical properties are also related with fabric structure and directions, it is expected that both the electrical and mechanical properties of the 3-D woven carbon/epoxy composites could be optimized simultaneously from the composite microstructure designs.

Influence of realistic microscopic fiber misalignments on compressive damage mechanisms of 3D angle-interlock woven composites: In-situ measurements and numerical simulations

Stochastic fiber misalignments have been proven to have a significant impact on the compressive strength of traditional unidirectional laminates. However, these inherent manufacturing defects are rarely considered when dealing with 3D woven composites, due to the difficulty in characterizing the misalignment angles of individual fibers within all yarns. The current work provides the first in-situ measurements of fiber misalignments in 3D angle-interlock woven composites (3DAWCs) at the microscale, where the continuous fibers inside the warp, weft, and binder yarns are systematically examined using a high-resolution optical microscope. Statistical analysis reveals that the microscopic fiber misalignments follow a normal distribution, and the magnitude of the misalignment angle increases slightly with the degree of yarn fluctuation. Through a developed user subroutine, SDVINI, the obtained misalignment distributions are initialized in the corresponding yarns that belong to the constructed high-fidelity model. In comparison to the idealized one, the model introducing realistic fiber misalignments can effectively correct the overestimated predictions, and exhibits better agreement with the performed experiments. Furthermore, the influence of fiber misalignments on compressive damage mechanisms, particularly kinking failure, is also parametrically studied by incorporating different misalignment distributions.

Electromechanical behavior and damage index system of 3D carbon fiber angle-interlock woven composites with FEA and data processing tools

The relationship between structural damage and electrical resistance change of carbon fiber reinforced composites is important to structural health monitoring. Here, we investigated the electromechanical behavior and damage index system for identification of various damage types in 3D angle-interlock woven composites under tensile loading in the warp direction. The mechanism of electrical resistance change was explored by combining current injected from both ends (Electrical current is in the plane of the laminate and goes through the entire cross section of the specimen) and current injected diagonally (Direction of electrical current between the in-plane direction and the through-thickness direction). A finite element model was established to analyze the electric potential distribution and tensile damage evolution process of composites. We found current injected from both ends can only detect with yarn damage and current injected diagonally can detect with matrix cracks, interface cracking and yarn damage. Based on the electrical resistance data of current injected diagonally, we used principal component analysis and K-means clustering methods to establish a damage index system to reflect the damage accumulation degree of different damage modes. The finite element analyses verified the rationality of the damage index system.

Investigation on the off-axis tensile failure behaviors of 3D woven composites through a coupled numerical-experimental approach

Computational models with high precision and efficiency are in urgent need for the damage analyses of 3D angle-interlock woven composites which are widely accepted in composites industry. A novel concurrent multi-scale damage evolution modeling scheme is established based on a meso-scale representative volume cell (RVC) model and the multiphase finite element method to characterize the off-axis tensile response of carbon/epoxy composites. Modified Puck criterion and maximum shear stress criterion are adopted for fiber yarns. Parabolic yield criterion is adopted for the matrix. The fiber breakage, the inter-fiber fracture and matrix cracking are considered at mesoscopic level. To validate the proposed multi-scale damage model, off-axis tensile test is conducted with the help of 3D Digital Image Correlation (DIC) method. A reasonably good agreement is achieved between numerical predictions and experimental observations. Furthermore, the validated damage model is used to predict the tensile response of the composites considering full range on-axis and off-axis angles.

Size-dependent mechanical behaviors of 3D woven composite under high strain-rate compression loads

Dynamic characterization of textile composites is confronted with great challenges due to its large unit-cell size and the inherent limitations in specimen size for the Hopkinson bar-based test system. The small specimen size will inevitably introduce variations in effective mechanical response and failure mechanism, and bring about additional problems in determining the realistic dynamic properties of the material. This work experimentally investigated the dynamic compression behavior of three-dimensional angle interlock woven composite (3DWC) using the split Hopkinson pressure bar (SHPB). Specimens with different sizes were designed to explore the size dependency, strain-rate dependency and orientation dependency for the compressive behavior of the 3DWC. A high-speed camera and an optical microscope were introduced to elaborate on the damage progressing process and fracture morphology under different loading conditions. With an increase in strain rate, the measured strength of warp-direction specimens increased by approximately 7.6%, 4.8%, and 2.6% for three different sizes of specimens, accompanied by more severe intra-tow damage. Different-sized dynamic specimens exhibited comparable failure processes but modest variations in measured properties. When the number of unit cells in a specimen increased from two to three and four, the strength was observed to rise by around 14.9% and 21.9% respectively. In comparison to the warp-direction specimen, the weft-direction specimens exhibited substantially higher strength and failure strain, as well as distinct dominant failure modes of yarns. This work provides valuable insights into the determination of dynamic properties for 3D woven composites, and the designing and interpretation of dynamic test methods.

Mechanical-electrical coupling behaviors of 3-D carbon fiber angle-interlock woven composites under quasi-static and cyclic tension

Mechanical-electrical coupling behaviors of carbon fiber composites is important to structure health monitoring (SHM). Here, we investigated the mechanical–electrical coupling behaviors of 3D carbon fiber angle-interlock woven composites (3DAWC) under tensile loading. Different loading modes including monotonic, cyclic, and fatigue tests were adopted to find the relationship between electrical resistance and tension damages. We also developed a mechanical–electrical constitutive model to reveal the relationship between internal damage modes and the electrical resistance. The tensile deformation and damage of the 3DAWC lead to the increase of the electrical resistance. The increased range is related to the degree of the deformation, damage, and damage accumulation. The transition point of the electrical resistance change represents the initial point of warp yarn longitudinal damages. The irreversible deformation of warp yarns leads to an increase in resistance after unloading. The stress–strain curve and the resistance vs. strain curve can be obtained simultaneously to reveal the internal structural deformation and inner damage mechanisms.

Ballistic performance and damage behavior of three-dimensional angle-interlock woven composites under high velocity impact: Experimental and numerical studies

Three-dimensional angle-interlock woven composites (3DAWCs) are usually employed as exposed components in aerospace and other high-tech areas due to their superior impact resistance. In this work, the experimental characterization and numerical modeling are combined together to study the ballistic performance and damage behavior of 3DAWCs under high velocity impact (HVI). The initial-residual velocity relation is examined by ballistic impact test and the penetration process is recorded by high-speed camera. A nonlinear finite element (FE) model based on a multi-scale modeling framework is established to simulate the ballistic impact response and damage behavior of 3DAWCs. The proposed FE model is verified by comparing the predicted initial-residual velocity curve and penetration propagation with the experimental data. Parameter analysis is conducted to address the influences of projectile diameter and impact angle on the impact performance of 3DAWCs and the corresponding damage mechanisms are revealed in detail. The present work provides a transferable approach for studying the HVI problems of other textile composite structures.

Effect of fabric structural stability on the tensile property of bidirectional angle-interlock woven composites

Three-dimensional bidirectional angle-interlock woven (3DBAW) composites exhibit the orthogonal high modulus, which has the potential to be used in load-bearing components. 3DBAW preforms prepared using the certain and uncertain cross-sectional yarns exhibit various structural characteristics, and the mechanical properties of composites show the high variation. To investigate the effect of fabric structural stability on the elastic properties of 3DBAW composites and broaden its application, contrast analysis of quasi-static tensile properties of composite specimens was proposed, and the failure mechanism was analysed. The results showed that the high tensile initial elastic modulus of 3DBAW composites was attributed to the low curvature of load-bearing yarns. For composites with stable fabrics, the tensile process was smooth and steady owing to the uniform fiber spacing, and the tensile elastic modulus and strength show the smaller coefficient of variation. The tensile crack surfaces of composites with stable structural fabrics were regular, and making the full use of the load-bearing yarns. 3DBAW preforms with stable structure can effectively reduce the fluctuation of changes at the initial stage of loading, and the translaminar fracture and adhesive matrix failure are the main failure modes without the obvious interlaminar fracture. The results provided the support for the application of 3DBAW composite in load-bearing components.

Thermo-chemical-mechanical multiphysics coupling simulation of thermo-oxidative ageing behavior in 3D angle-interlock woven composites

Thermo-oxidative ageing has a significant impact on the mechanical properties of 3D angle-interlock woven composites, but there is no simulation research on the thermo-oxidative ageing behavior of composites. This study developed a coupled thermo-chemical-mechanical multiphysics model using a multi-step parallel algorithm to simulate the thermo-oxidative ageing process of 3D angle-interlock woven composites. The model focuses on the thermo-chemical-mechanical weak coupling between the oxidation reaction of the oxygen diffusion and the thermodynamics of the temperature change while considering the residual stress state of the composite after curing. The oxidized layer distribution and interface cracks in finite element analysis have good agreement with nanoindentation and microscope experiments, validating the effectiveness of the model. The numerical results are in good agreement with the experimental dates. The proposed model contributes to evaluating the complex stress and interface damage related to multiphysics coupling in the composite during thermo-oxidative ageing.

Spatial electric potential distributions and damage mapping in 3D carbon fiber/epoxy angle-interlock woven composites with different current directions

Exploring electric potential distributions in carbon fiber reinforced polymer composites (CFRPs) is important in electrical-based structural health monitoring for in situ damage detection. Here we investigate influences of current injection angles, electrode locations, and current injection pairs on the electric potential distributions in 3D carbon fiber/epoxy angle-interlock woven (AIW) composites. We have conducted different types of electric potential measurements and established a linear anisotropic conductivity model to reveal the electric potential distributions. It was found that the curved warp yarns form many contacts and increase the conduction path, leading to lower electric conductivity and flatter potential field than those of the weft yarn with straight alignment. The orientation and value of surface electric potential field change depend on current flow direction caused by current injection mode (CIM) and conduction mechanism due to yarn arrangement. Oblique current directed at an angle of 45° is more sensitive in indicating interior damage than that of current parallel to the yarn direction. It is recommended that the oblique current injection should be used to provide effective damage sensing for CFRPs with complex structures.

Fiber architecture effect on tensile and compressive damage mechanisms of 3D angle-interlock woven composites

Due to the intricate fiber architecture of 3D textile composites, understanding their failure mechanisms presents a challenge. Here we experimentally studied the quasi-static tensile and compressive properties of 3D angle-interlock woven composites (3D AWC) under both warp-loading (AWC-warp) and weft-loading (AWC-weft). Damage morphologies and mechanisms were examined using optical microscopy and X-ray computed tomography. In order to demonstrate the effect of fiber architecture, the results were combined and compared with that of unidirectional (UD) composites with the same total fiber volume fraction (FVF). The fiber architecture effects in 3D AWC can be manifested as the on-axis FVF dependency and fiber undulation influence. When on-axis load-bearing fiber is undulating-free, the difference in mechanical properties is primarily determined by the on-axis FVF. However, the presence of fiber undulation can further weaken the mechanical properties. Moreover, for AWC-warp specimens, fiber undulation has a significant impact on the modes and characteristics of damage, resulting in fiber breakages and kinks that primarily occur in the connection region of warp yarns.

Investigation on mechanical properties and damage evolution of thermo-oxidative aged 3D angle-interlock woven composites under quasi-static tension

This paper reports tensile strain distribution and damage evolution of 3D angle-interlock woven composites (3DAWCs) after thermo-oxidative aging from tests and finite element analysis (FEA). It is found that the retention ratio of modulus in warp-directional loading (WP) is lower than that in weft-directional loading (WF) after 32 aging days. Aged samples exhibited reduced failure stress and strain. The surface strain distributions and damage patterns correlated with the woven structure. In WP, transverse cracks start from the resin-rich zone with the length limited to the distance between the warp yarns, followed by longitudinal cracks appearing at the warp-resin interface after loading to higher stress. In WF, only transverse cracks are initiated in the fiber-resin interface on the warp float and then propagate to the surrounding resin-rich zone. The crack initiation time is advanced and the failure strain decreases with the aging day. The FEA results support digital image correlation measurements and demonstrate that surface strain is influenced by the mesostructure in addition to the component's inherent properties.

Fiber inclination model for the anti-penetration performance of a new type three-dimensional angle-interlock woven composite

Fiber inclination model for the anti-penetration performance of a new type three-dimensional angle-interlock woven composite

Compressive behaviors of thermo-oxidative aged three-dimensional angle-interlock woven composites under different strain rates

The mechanical behaviors of three-dimensional angle-interlock woven composites (3DAWCs) after thermo-oxidative aging under different strain rates are imperative to retain safety in high-temperature conditions. This work presents the thermo-oxidative aging effects on strain rate sensitivity and compression failure mechanism of 3DAWCs based on the digital image correlation technique and finite element analysis. The results revealed that the compressive modulus and maximum stress of the 3DAWCs are strain rate sensitive, while the thermo-oxidative aging would reduce the strain rate sensitivity. The strain rate coefficient of the resin and composite decreased by approximately 9% and 25% after thermo-oxidative aging, respectively. The compressive damage failure modes of the 3DAWCs mainly include resin cracks, interfacial debonding, and yarn fracture. The strain rate has effects on damage initiation and brittle-ductile fracture behavior. The aging effect changes the crack propagation path, but does not affect the inclined 45° shear mode. In addition, the strain rate effects on strain localization were found and will be enhanced after thermo-oxidative aging.

Experimental investigation on high-velocity impact damage and compression after impact behavior of 2D and 3D textile composites

This paper investigates the impact resistance and damage tolerance of 2D triaxially braided composites and 3D angle-interlock woven composites panels using high-velocity impact tests and compression after impact tests. Both materials present equivalent impact resistance with similar ballistic limit and energy absorption ratio. Nevertheless, the damage patterns of the two materials are quite different, among which, 2DTBC is characterized by global response and yarn debonding, while 3DAWC is characterized by localized damage without yarn debonding. However, in compression after impact tests, 3DAWC exhibits higher damage tolerance because the binder yarns resist buckling failure and kink bands formation during compression, resulting in higher residual compressive strength. In addition, how the damage morphology varies spatially due to the different deformation and damage modes caused by high-velocity impact is learned from X-ray CT scanning. Different from the relationship between impact energy and residual compressive strength pointed out by most research, this study also reveals a unique trend of residual compressive strength as a function of impact energy, considering both penetration and rebound conditions.