3D Angle-interlock Woven Composites Research Articles

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.

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.

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.

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.

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.

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.

Non-orthogonal FE model with stress smoothing for progressive damage analysis of shear pre-deformed 3D angle-interlock woven composites under compression

3D angle interlock woven fabric usually needs to produce pre-deformation to meet the requirements of the complex shape of the target configuration. This cause the internal fabric angle to change, which makes it difficult to predict the mechanical properties and damage evolution. A novel non-orthogonal mesoscale finite element (FE) model considering local stress smoothing is proposed to predict the effective mechanical properties and reveal the damage evolution process of shear pre-deformed 3D angle-interlock woven composites under compressive load. The spurious stresses in the vicinity of the different material interface caused by the stepped block-like voxel boundaries are efficiently eliminated to improve the failure prediction accuracy. The predicted warp directional compressive stress-strain curves are good agreement with that of experiments, and the failure morphologies are verified by Scanning Electron Microscopy (SEM). The validated simulation model is further to investigate the effects of shear angle on the effective compressive stiffness and strength of 3D angle-interlock woven composites in different direction. And the effects of shear pre-deformation and stress smoothing on the damage and failure mechanisms are discussed. This study is great helpful of providing reliable guidance for analyzing and designing the pre-deformed 3D woven composite complex structures, such as aero-engine fan blades.

Impact compression behaviors of 3D angle-interlock woven composites under thermo-oxidative ageing

Impact compression behaviors after thermo-oxidative ageing are key to design safety and durability of 3D angle-interlock woven composites (3DAWC). This paper experimentally and numerically presents the impact compression properties and damage morphology of composites before and after ageing, which reveals the effects of thermo-oxidative ageing on impact compression behaviors of 3DAWC. The testing results revealed that the composites impact compression mechanical properties, i.e., maximum stress and modulus, decrease with the increasing ageing time. The impact compression properties degradation of 3DAWC is attributed to the epoxy resin degradation and interface debonding. Moreover, the interfacial debonding hinders the propagation of stress waves. The finite element analysis (FEA) results illustrate the ageing interfacial damage changes the crack propagation path during impact compression. The matrix degradation and interfacial weakening after ageing aggravate the interfacial damage and reduce the stress distribution of aged composites. The failure morphology of aged composites is more serious.

A combined machine learning and numerical approach for evaluating the uncertainty of 3D angle-interlock woven composites

The characterization and evaluation of uncertainties caused by the automated manufacturing procedure are essential for the early structural design and application of 3D woven composites. To account for the inherent uncertainties, numerical simulations must be integrated with statistical uncertainty quantification and propagation methods. However, in some cases, it is very challenging and computationally time consuming. In this paper, a multiscale uncertainty quantification method combining finite element analysis, wide & deep neural network and sensitivity analysis is proposed to probabilistically evaluate the tensile response of 3D angle-interlock woven composites. The required dataset for training and validating the model is created by a two-step numerical simulation. With the present model, a framework of the importance of each uncertainty in determining the macroscopic properties’ variance can be established with fewer computational resources. The results indicate that the effect of uncertainties on the material tensile response is significant and the sensitivity information can serve as a guide for reducing uncertainties at the macroscale.

Flexural progressive failure mechanism of hybrid 3D woven composites: Combination of X-ray tomography, acoustic emission and digital image correlation

This paper presents the hybrid effect on the bending progressive damage of three-dimensional (3D) angle-interlock woven composites. Three types of 3D angle-interlock specimens, carbon, hybrid (Carbon/UHMWPE) and UHMWPE, of the warp and weft orientations are experimentally tested via three-point bending method. X-ray micro-computed tomography (Micro-CT), acoustic emission (AE) and digital image correlation (DIC) techniques are combined to evaluate the damage initiation/evolution of hybrid 3D woven composites. Results indicate that hybrid structures have significant effects on the mechanical behaviors, damage models and failure mechanisms. Furthermore, the dominant failure mechanisms of hybrid 90° specimens are delamination, fiber fracture matrix cracking and debonding, whereas those of hybrid 0° specimens are matrix cracking and fiber matrix debonding.

Damage analysis of shear pre-deformed 3D angle-interlock woven composites using experiment and non-orthogonal finite element model

The shear pre-deformed 3D angle-interlock woven composites under tension load is studied using experimental and numerical methods. A novel non-orthogonal mesoscopic finite element (FE) model taking into consideration non-orthogonal periodic boundary conditions and elasto-plastic damage model is developed to predict the effective mechanical properties and reveal the damage and failure mechanisms. The predicted stress-strain curve is agreement with that of experiment, and the failure mechanisms are verified by Scanning Electron Microscopy (SEM). The effects of shear pre-deformed angle on the stiffness and strength of 3D angle-interlock woven composites are discussed based on simulation results. This study can be helpful of providing reliable guidance for analyzing and designing the woven composite complex structures with pre-deformation.

An experimental–numerical study on 3D angle-interlock woven composite under transverse impact at subzero temperatures

Three-dimensional (3D) angle-interlock woven composite may possess different impact properties at subzero temperatures compared with that at room temperatures due to its rate- and temperature-dependent resin. The purpose of this work is to investigate the impact damage behaviors of a 3D angle-interlock woven composite undergoing transverse impact tests at subzero temperatures. The experimental data and high-speed photography obtained from the tests have been compared with numerical results to explore the damage development and temperature rise. A coupled thermo-mechanical constitutive model has been developed to capture the effects of increase in temperature, strain rate sensitivity and fragmentation of the composite material. The proposed model is based on the decomposition of the compliance matrix into elastic and plastic parts. Thermo-mechanical coupling has been considered where temperature rises as a result of plastic work. The proposed model has been implemented in the explicit coupled thermo-mechanical finite element code. The numerical results were compared with transverse impact experiments at room and subzero temperatures.

Elevated temperature effect on tension fatigue behavior and failure mechanism of carbon/epoxy 3D angle-interlock woven composites

This paper reported elevated temperature effect on tension fatigue behavior and failure mechanism of carbon/epoxy 3D angle-interlock woven composites. The S-N curve shows that the composite has good fatigue properties, and the fatigue properties decrease to a certain extent at elevated temperature. The tensile fatigue limit of composite is 38% and 30% stress level at 25 °C and 100 °C, respectively. Tensile modulus-fatigue life curve shows that the composite has obvious three-stage cumulative damage development, while the high temperature increases the material’s viscoelasticity and toughness. Fracture morphologies indicate that the composite exhibits jagged inclined fracture. The main fatigue failure mechanism is matrix microcracks propagate and expand inside the material along warp and weft direction. The microcracks propagate to the fiber/matrix interface, resulting in stress concentration and debonding of the interface. And the fracture of a large number of warp fibers and fiber bundles eventually causes the composite to fail. At high temperatures, the material softens, the interface bonding strength becomes worse, leading to more serious fiber pullout and breakage, and the brittleness of the material weakens.

Effect of bias yarn on tensile fracture mechanism of multiaxial 3D angle-interlock woven composites

A novel 3D woven structure was designed and developed in this paper, namely multiaxial 3D angle-interlock woven composites (MAWC). In order to determine the specific influence of bias yarns on the tensile properties and failure mechanisms, two MAWCs with different weave patterns and 3D angle-interlock woven composites (3DAWC) were fabricated. Based on the meso-structure characteristics of MAWC, a realistic meso-model was proposed. The tensile behavior of MAWCs and 3DAWC were experimentally characterized, and the full-field strain distributions were recorded by digital image correlation (DIC). Moreover, a progressive damage model along with the X-ray micro-computed tomography (Micro-CT) technique were applied to reveal the damage processes and failure mechanisms of composites. Results showed that the axial tensile strength of MAWCs decreased due to the change of yarn orientation. The stress-strain curves of two MAWCs presented nonlinear behavior, while those of 3DAWC could be seen as linear within the whole strain range. Stress concentration regions of two MAWCs were found to be distributed more dispersedly than those of 3DAWC. The local tow splitting, fiber slippage and interfacial debonding were the primary failure modes of bias yarn in MAWCs under tension.

Experimental and numerical study of in-plane shear properties and failure process of multiaxial 3D angle-interlock woven composites

A novel multiaxial 3D angle-interlock woven composites (MAWC) was developed in this paper. Two MAWCs with different weave patterns and 3D angle-interlock woven composites (3DAWC) were manufactured to identify the particular influence of bias yarns on the in-plane shear performance and failure mechanism of the composites. Based on the variable cross-sections, a realistic meso-model of MAWC was proposed. The in-plane shear tests were carried out and the digital image correlation (DIC) was used to record the full-field strain distribution of the specimens. Furthermore, a progressive damage model and X-ray micro-computed tomography (Micro-CT) were implemented to reveal the damage evolution and mechanisms of composites. Results indicated that all load–displacement curves presented nonlinear behavior, and the in-plane shear modulus and strength were significantly improved due to the bias yarns. The fiber slippage, tow splitting and interfacial debonding were the primary failure modes of bias yarns in MAWC architectures.

Weft direction tension-tension fatigue responses of layer-to-layer 3D angle-interlock woven composites at room and elevated temperatures

Elevated fatigue behaviors of resin matrix composites are considerable key to the application of aeroengine that requires fatigue resistance at elevated temperature. However, undeniably, very few studies are focused on this issue, thereby resulting in limitation applications of resin matrix composites in aeroengine components, i.e. blades and case. In this work, the fatigue responses of layer-to-layer 3D angle-interlock woven composites (2.5DWC) were experimentally and numerically studied at room and elevated temperatures. Experimental results show that the weft direction fatigue lives at 20 °C and 180 °C experienced a relatively short cycle (less than 104 cycles) prior to the failure. But, once the stress level declined to a threshold value (dropped by 1–2%), the fatigue limitation would be activated, regardless of temperature. Moreover, the residual strength at 20 °C or 180 °C was reinforced compared to the static strength. Considering the fatigue data and fracture morphology, probable damage mechanisms corresponding to temperature-dependent weft direction fatigue behaviors of 2.5DWC were proposed. A temperature-dependent fatigue life prediction model of 2.5DWC was proposed, based on which the weft direction fatigue lives, damage propagation processes and residual stiffnesses of 2.5DWC at 20 °C and 180 °C were predicted.