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In this article, experimental tests under static tensile loadings and tension-tension cyclic loadings were conducted for T300/924 unidirectional laminated composites at different porosity levels. On the basis of the experimental tests, a physical-based residual stiffness model for porous CFRP composites was put forward. The present model describes the deterioration of composites under cyclic loading in perspective of the initiation and propagation of cracks in the matrix, and is capable of capturing the effect of voids on fatigue behaviors of the composites. Lastly, the stiffness degradations of laminates with different void contents under various stress levels were predicted, and the predicted stiffness reduction as well as fatigue life of the material agreed well with the experimental data.

With a better balance among good mechanical performance, high freedom of design, and low material and manufacturing cost, chopped carbon fiber chip reinforced sheet molding compound (SMC) composites show great potential in different engineering applications. In this paper, bending fatigue behaviors of SMC composites considering the heterogeneous fiber orientation distributions have been thoroughly investigated utilizing both experimental and computational methods. First, four-point bending fatigue tests are performed with designed SMC composites, and the local modulus is adopted as a metric to represent the local fiber orientation of two opposing sides. Interestingly, SMC composites with and without large discrepancy in local modulus of opposing sides show different fatigue behaviors. Interrupted tests are conducted to explore the bending fatigue failure mechanism, and the damage processes of valid specimens are also closely examined. We find that the fatigue failure of SMC composites under four-point bending is governed by crack propagation instead of crack initiation . Because of this, the heterogeneous local fiber orientations of both sides of the specimen influence fatigue life . The microstructure of the lower side shows a direct influence while that of the upper side also exhibiting influence which becomes more prominent for high cycle fatigue cases. Furthermore, a hybrid micro–macro computational model is proposed to efficiently study the cyclic bending behavior of SMC composites. The region of interest is reconstructed with a modified random sequential absorption algorithm to conserve all the microstructural details including the heterogeneous fiber orientation, while the rest of the regions are modeled as homogenized macro-scale continua. Combined with a framework to capture the progressive fatigue damage under cyclic bending, the bending fatigue behaviors of SMC composites are accurately captured by the hybrid computational model comparing with our experimental analysis.

Fused filament fabrication (FFF) with continuous carbon fiber filaments has proven to be a promising manufacturing technique in engineering applications. To provide guidance in the design of 3D printed carbon fiber reinforced polymer (CFPR) components, the longitudinal compression failure of continuous CFPR composites using the FFF technique is investigated systematically. First, longitudinal compression tests are performed for 3D printed continuous CFRP composites with and without designed waved filaments. The degradation of the failure strength is remarkable when the waved filaments are introduced. Nevertheless, further degradation is limited when more waved filaments are adopted. Next, the fracture morphologies are analyzed, and in-plane and out-of-plane kink-bands are observed in the microscopic images. For the specimens with waved filaments, fracture occurs at the cross-section with the contact region of the waved and regular filaments, as well as the cross-section with the maximum misalignment angle. Correspondingly, a computational framework for 3D printed continuous CFPR composites is established to explore the longitudinal compression failure mechanisms. The meso-scale computational models are reconstructed according to the geometric features of the deposited continuous CFRP filaments and the actual void volume fraction. The elastic properties of the filament are calculated by a micro-scale representative volume element (RVE) model, which is based on the fiber random distribution algorithm. The plastic deformation and failure is described by a filament constitutive model which is established by the Liu-Huang-Stout yield criterion and a simplified Tsai-Wu failure criterion. The experimental validation demonstrates the feasibility of the computational models to predict the stress-strain curves of 3D printed materials, and also capture the realistic longitudinal compression failure behavior.

In this study, integrated experimental tests and computational modeling are proposed to investigate the failure mechanisms of open-hole cross-ply carbon fiber reinforced polymer (CFRP) laminated composites. In particular, we propose two effective methods, which include width-tapered double cantilever beam (WTDCB) and fixed-ratio mixed-mode end load split (FRMMELS) tests, to obtain the experimental data more reliably. We then calibrate the traction-separation laws of cohesive zone model (CZM) used among laminas of the composites by leveraging these two methods. The experimental results of fracture energy, i.e. GIc and GTc, obtained from WTDCB and FRMMELS tests are generally insensitive to the crack length thus requiring no effort to accurately measure the crack tip. Moreover, FRMMELS sample contains a fixed mixed-mode ratio of GIIc/GTc depending on the width taper ratio. Examining comparisons between experimental results of FRMMELS tests and failure surface of B–K failure criterion predicted from a curve fitting, good agreement between the predictions and experimental data has been found, indicating that FRMMELS tests are an effective method to determine mixed-mode fracture criterion. In addition, a coupled experimental-computational modeling of WTDCB, edge notched flexure, and FRMMELS tests are adopted to calibrate and validate the interfacial strengths. Finally, failure mechanisms of open-hole cross-ply CFRP laminates under flexural loading have been studied systematically using experimental and multi-scale computational analyses based on the developed CZM model. The initiation and propagation of delamination, the failure of laminated layers as well as load-displacement curves predicted from computational analyses are in good agreement with what we have observed experimentally.

Static longitudinal/transverse tensile tests for unidirectional carbon fiber/polymer (T300/924) laminates and laminates with lay-ups [Formula: see text] at various void levels were conducted, and degradations in stiffness/strength were observed with the presence of voids. The void levels were controlled by compression pressure during the compression molding process. The characterization of voids was achieved by digital microscopy image analysis; the density distributions of equivalent diameters and aspect ratios were analyzed with respect to compression pressure. For the purpose of quantifying the effect of voids on the static mechanical properties of composites, a stiffness prediction method based on the Mori-Tanaka method and void geometric statistical data have been used with the implementation of a finite element model of the representative volume element for unidirectional composites; the prediction results show good correlation with experimental data. Finally, a modified continuum damage model for laminated composites with the presence of voids was proposed, the model is capable of capturing the effect of voids; and gradual damage analysis for carbon fiber/polymer composite laminates at different void levels was conducted to evaluate the effect of voids on their tensile properties.

Fatigue life prediction of advanced high strength steels (AHSS) spot welded joints is of great importance for autobody design with AHSS being increasingly used. In the present work, the fatigue failure behaviors of the DP780GI spot welded joints under the tensile shear (TS) and coach peel (CP) loading conditions are experimentally investigated and numerically modelled. Two failure modes, eyebrow failure and weld button pull out occur in the tests of TS joints, while only interfacial fracture exists in CP joints. A fatigue life prediction method based the crack growth approach is proposed. The TS/CP specimens are simplified to the neural line models, by which the reaction forces and moments directly acting on the spot welds are calculated. Then the stress intensity factor is obtained by using the finite element method and analytical equations fitted to the FE results. Finally, the fatigue life of a spot weld is evaluated by applying the Paris law to the crack front and including the plastic zone in crack path update. The calculated fatigue lives show good agreement with experiment results for DP780GI, within five times error band.

The fatigue behavior of self-piercing riveted (SPR) joints of aluminum alloy 6111-T4 has been experimentally and numerically investigated in current study. The dominant fatigue failure mode under tensile-shear (TS) loading is the corner crack at riveted hole with approximate quarter-elliptical crack front, and interrupted tests revealed that the crack growth life was much shorter than crack initiation life. A fatigue parameter, Smith-Watson-Topper (SWT) was proposed for crack initiation prediction in the 3D finite element analysis, while a structural load based crack growth approach was introduced for crack growth life estimation. Good agreement was found between predictions and experimental results.

In this work, we investigate the effect of sheet stacking orientation on fatigue behavior in friction stir linear welding of AZ31 Mg alloy. It is well known that during friction stir welding, the advancing and retreating flow of the material generated by the tool creates asymmetrical weld features resulting is anisotropic mechanical behavior. As such, friction stir welding of overlap joints was carried out on 2 mm thick sheets, where the orientation of the pull direction of the coupon was varied with respect to the tool rotation direction. Subsequently experimental fatigue tests were performed to evaluate this effect of the sheet stacking orientation on cyclic behavior. The fatigue results showed that the overlap joints loaded on the retreating side exhibited superior performance compared to the advancing side. Post-mortem analysis coupled with finite element results suggest that the geometrical shape of the faying surface produced by the advancing and retreating material flow largely determines the number of cycles to failure in these friction stir linear welded overlap joints.

Woven composites are considered as a promising material choice for lightweight applications. An improved non-orthogonal material model that can decouple the strong tension and weak shear behavior of the woven composite under large shear deformation is proposed for simulating the preforming of woven composites. The tension, shear and compression moduli in the model are calibrated using the tension, bias-extension and bending experiments, respectively. The interaction between the composite layers is characterized by a sliding test. The newly developed material model is implemented in the commercial finite element software LS-DYNA® and validated by a double dome study.

Carbon fiber reinforced plastics (CFRPs) are attracting growing attention in industry because of their enhanced properties. Preforming of thermoset carbon fiber prepregs is one of the most common production techniques of CFRPs. To simulate preforming, several computational methods have been developed. Most of these methods, however, obtain the material properties directly from experiments such as uniaxial tension and bias-extension where the coupling effect between tension and shear is not considered. Neglecting this coupling effect deteriorates the prediction accuracy of simulations. To address this issue, we develop a Bayesian model calibration and material characterization approach in a multiscale finite element preforming simulation framework that utilizes mesoscopic representative volume element (RVE) to account for the tension-shear coupling. A new geometric modeling technique is first proposed to generate the RVE corresponding to the close-packed uncured prepreg. This RVE model is then calibrated with a modular Bayesian approach to estimate the yarn properties, test its potential biases against the experiments, and fit a stress emulator. The predictive capability of this multiscale approach is further demonstrated by employing the stress emulator in the macroscale preforming simulation which shows that this approach can provide accurate predictions.

In this work, multi-scale finite element analyses based on three-dimensional (3D) hybrid macro/micro-scale computational models subjected to various loading conditions are carried out to examine the in-situ effect imposed by the neighboring plies on the failure initiation and propagation of cross-ply laminates. A detailed comparative study on crack suppression mechanisms due to the effect of embedded laminar thickness and adjacent ply orientation is presented. Furthermore, we compare the results of in-situ transverse failure strain and strength between the computational models and analytical predictions. Good agreements are generally observed, indicating the constructed computational models are highly accurate to quantify the in-situ effect. Subsequently, empirical formulas for calculating the in-situ strengths as a function of embedded ply thickness and different ply angle between embedded and adjacent plies are developed, during which several material parameters are obtained using a reverse fitting method. Finally, a new set of failure criteria for σ(22)-τ(12), σ(22)-τ(23), and σ(11)-τ(12) accounting for the in-situ strengths are proposed to predict laminated composites failure under multi-axial stress states. This study demonstrates an effective and efficient computational technique towards the accurate prediction of the failure behaviors and strengths of cross-ply laminates by including the in-situ effects.

In current work, the crashworthiness of woven carbon fiber reinforced plastic (CFRP) hat section component is investigated under two types of loading experimentally and numerically, i.e., axial crushing and dynamic three-point bending. The crushing characteristics of woven CFRP hat section sample are evaluated at various impact velocities and layup orientations which exhibit different effects under two types of loading. With impact velocity/energy increasing, the bending behaviors illustrate different evolutions with distinct stages which are affected by the damage development. Layup orientation shows a little effect on the bending behaviors, while it exerts remarkable effects on the axial crushing which leads to different crushing modes and thus different energy absorption capabilities. The finite element model with multiple layers of thick shell element and cohesive element is shown to capture the crushing behaviors reasonably well in both axial crushing and dynamic bending. The corresponding damage evolutions are also analyzed with simulations to explain the crushing behaviors.

We present a data-driven nonlinear uncertainty quantification and propagation framework to study the microstructure-induced stochastic performance of unidirectional (UD) carbon fiber reinforced polymer (CFRP) composites. The proposed approach integrates (1) microscopic image characterization, (2) stochastic microstructure reconstruction, and (3) efficient multiscale finite element simulations enabled by self-consistent clustering (SCA) analysis. To model the complex microstructural variability, the proposed UQ methods take the non-Gaussian uncertainty sources into account through a distribution-free sampling approach leveraging nonparametric and asymptotic statistical tools. A hierarchical conditional sampling strategy enables the simultaneous sampling of multiple sources of uncertainties. Our approach provides insights into the impact of microstructural variabilities, which are shown to have an increasing impact on the nonlinear responses of UD CFRP parts under progressive compression loading and ultimately on the failure rate over time. We discover that before CFRP parts start to fail, a characteristic time period emerges with distinctive uncertainty distributions specific to the microstructure variability and the probability of failure. Identifying the failure time period is crucial to the reliability prediction, which is an essential component of CFRP design.

The mechanical behaviors and damage evolutions of carbon/epoxy woven fabric composites with three different geometries, i.e., one plain weave and two twill weave patterns with different areal densities, are studied under tensile loading. The effects of weave patterns on mechanical properties are investigated by monotonic and cyclic tension tests. Remarkable variations in stress–strain curve, Poisson’s ratio, residual strain and strain map exist in the three composites. Crimp ratio is found to be a critical factor to govern the mechanical properties. With smaller crimp ratio, a quasi-linear stress–strain curve with higher elastic modulus and strength is observed. The stress–strain curves of composites with higher crimp ratio contain transition stages with significant tangent modulus degradation. Elastic modulus, strength and damage initiation are all correlated with the crimp ratio linearly regardless of the fabric pattern. Dramatic nonlinear evolution in Poisson’s ratio occurs in the composite with higher crimp ratio. Cyclic tension results indicate that the residual strain is a more appropriate damage indicator than the unloading elastic modulus. Microstructure examination shows that damage developments are essentially related to the fabric geometry, and result in various mechanical behaviors. This study provides important insights into the geometry-deformation mechanism-mechanical property relationship of the woven composites.

A bottom-up multi-scale modeling approach is used to develop an Integrated Computational Materials Engineering (ICME) framework for carbon fiber reinforced polymer (CFRP) composites, which has the potential to reduce development to deployment lead time for structural applications in lightweight vehicles. In this work, we develop and integrate computational models comprising of four size scales to fully describe and characterize three types of CFRP composites. In detail, the properties of the interphase region are determined by an analytical gradient model and molecular dynamics analysis at the nano-scale, which is then incorporated into micro-scale unidirectional (UD) representative volume element (RVE) models to characterize the failure strengths and envelopes of UD CFRP composites. Then, the results are leveraged to propose an elasto-plastic-damage constitutive law for UD composites to study the fiber tows of woven composites as well as the chips of sheet molding compound (SMC) composites. Subsequently, the failure mechanisms and failure strengths of woven and SMC composites are predicted by the meso-scale RVE models. Finally, building upon the models and results from lower scales, we show that a homogenized macro-scale model can capture the mechanical performance of a hat-section-shaped part under four-point bending. Along with the model integration, we will also demonstrate that the computational results are in good agreement with experiments conducted at different scales. The present study illustrates the potential and significance of integrated multi-scale computational modeling tools that can virtually evaluate the performance of CFRP composites and provide design guidance for CFRP composites used in structural applications.

Fatigue behaviors of hybrid joint, the combination of cold-formed mechanical fastening with adhesive bonding, are yet to be understood comprehensively even though they have been widely used in industries. The lack of understanding is mainly attributed to the complicated load transfer path and possible interactions between the two types of joining techniques, namely mechanical interlocking and adhesive bonding. In the present work, fatigue tests are performed on self-piercing riveted (SPR) joint, adhesive-bonded joint, and the SPR-bonded joint under lap shear and 45° loading conditions. Failure mechanisms are evaluated based on terminated fatigue test and numerical analysis. Periodical and asymmetric failure mode can be identified in SPR-bonded joint. Although both crack pinning and asymmetric failure mode induced by SPR suppress the crack growth in adhesive bonding, the effect of crack pinning is significant only when crack approaches SPR. The asymmetric failure also leads to load transfer path evolution, intensifying damage on SPR joining. A mechanism-based fatigue life evaluation method is proposed by characterizing the interactions with crack growth method and structural stress method. The calculated results are compared with the experimental ones, and good correlations are observed for both lap shear and 45° loading conditions.

The fatigue behavior of self-piercing riveted joints of aluminum alloy AA6111-T4 and steel HSLA340 sheets has been experimentally and numerically investigated in present paper. Fatigue results reveal that the mating sheet stiffness and load ratio have significant impact on the fatigue strength, and the dominant failure mode under tensile–shear loading is eyebrow crack with an approximately semi-elliptical crack front. New stress intensity factor equations are derived for a semi-elliptical surface crack in a finite plate near a rigid cylindrical inclusion with axial shear force and bending moment, including the ratio of crack depth to crack length ranged from 0.2 to 1 and the ratio of crack depth to sheet thickness ranged from 0.2 to 0.8. A new structural load fatigue crack growth model is proposed, and predictions of fatigue lives and final crack aspect ratios show good agreement with experimental results.

In this paper, the feedback signal of ultrasonic fatigue system was used to deduce the accumulated fatigue damage in situ using the ultrasonic nonlinearity parameter. It was observed that, compared with the decrease in resonant frequency, the ultrasonic nonlinearity parameter shows a greater sensitivity to fatigue damage evolution (i.e. crack initiation and propagation). Ultrasonic nonlinearity parameters obtained from tests conducted under various environmental humidity levels were monitored and analysed. Through changes in the ultrasonic nonlinearity parameter, it was concluded that both of the fatigue crack initiation life and crack propagation life were reduced by increasing the humidity levels.

Fatigue and corrosion damage are the major concerns of automotive adhesive joints, yet literature reports few works about the in situ fatigue durability of adhesive joints in corrosive environment. This study presents an investigation on the fatigue durability of automotive adhesive single lap joints by an in situ corrosion fatigue test. The joints were manufactured with commercial coated AA5754-O aluminum sheets bonded by a toughened epoxy structural adhesive. An in situ corrosion chamber was designed and employed to simulate a humid and corrosive environment by spraying 5% saline solution or distilled water mist around the joints’ overlap area during fatigue testing. The test results show that in the 5% saline solution mist environment, the joints’ fatigue lives encountered a great loss for about an order in magnitude compared to the joints tested in laboratory environment. The difference of fatigue lives between 5% saline solution mist test and distilled water mist test is insignificant. The fr...

The fatigue behavior of self-piercing rivet (SPR) joints joining differing thicknesses of AA6111-T4 aluminum and HSLA340 steel sheets in lap shear geometry was investigated in this paper. Crack initiation in the aluminum sheet was the dominant failure mode, while unexpected rivet shank failure tended to occur at high loading levels. Fretting wear was also observed at interface between aluminum and steel sheets as well as between the rivet and sheets under sinusoidal cyclic tension–tension loading. An Energy Dispersive X-ray (EDX) analysis of fretting debris revealed the presence of oxides of aluminum and zinc. Fretting was shown to be critical to crack initiation. For initiations in the aluminum sheet, micro cracks were found to nucleate early in the fatigue life, and crack initiation life was found to be much shorter than crack growth life.

It is important to have an accurate description of the mechanical behavior of polymer when predicting the warpage of injection-molded part. The viscoplastic model for polymer was developed based on the classical Chaboche viscoplastic model for polycrystalline metals. The cyclic tensile test was performed at three levels of strain rate and six levels of temperature. The ratio between Young’s modulus in the unloading and loading path was described as function of total strain. The warpage prediction for a plaque has been conducted successfully. The simulated deflection has a good agreement with the measured one by the viscoplastic model for polymer. It also exhibits a significant improvement compared with the simulated one by viscoplastic model for polycrystalline metals.

A comprehensive study of fatigue life and damage mechanisms of friction stir linear welded dissimilar aluminum-to-magnesium alloys in lap-shear configuration is presented. The overlap linear welds were created by welding AA6022 aluminum alloy to AM60B magnesium alloy. The test results showed significant scatter in the fatigue life and the corresponding fracture modes. Two distinct modes of failure were observed for the lap-shear specimens. In one of the failure modes observed, fracture occurred when the dominant fatigue crack propagated into either the magnesium or aluminum sheet in a kink-crack formation. In addition, fretting debris was found at locations of crack initiation for this fracture mode. In the other observed mode of failure, fracture occurred by interfacial weld separation, where fractography analysis suggests that the fatigue cracks initiated at weld defects and then propagated through the brittle intermetallic phase formed during welding.

Chopped carbon fiber sheet molding compound has a great potential in lightweight automotive, marine, and aerospace applications. One of the most challenging tasks is to predict the failure strength of the material due to its anisotropy and heterogeneity, as well as complex stress states in real-world working conditions. In this paper, a novel constitutive model of carbon fiber chip is proposed to capture the pre- and post-failure behaviors under different loading modes. On this basis, we propose a new computational micromechanics model, which is calibrated and validated by uniaxial tensile, compressive, and in-plane shear experiments. Furthermore, a set of microstructures representative volume element (RVE) models under complex loading conditions are reconstructed to understand the relationship between the microstructure characteristics and the failure envelopes. Finally, several modified versions of classical failure criteria are proposed for anisotropic materials with consideration of the fiber orientation tensor. The modified Tsai-Wu failure criterion, which shows the best accuracy among all failure criteria, is highlighted in the comparative study.

The mechanical properties and damage evolutions of carbon/epoxy woven fabric composites with three different fabric architectures, including one plain weave and two twill weave patterns, are experimentally investigated under multiaxial stress states. In particular, the effects of weave patterns are investigated by monotonic and cyclic off-axis tension tests. Both elastic modulus and strength degrade remarkably with increasing off-axis loading angle, while Poisson's ratio is much higher than that measured from on-axis tests and increases with loading strain gradually. Different fabric architectures show limited effects on the modulus and strength under multiaxial stress states, and they are well predicted by transformation equation and Tsai-Wu failure criteria, respectively. However, significantly different failure behaviors are observed in three fabric composites, and microstructure observation shows that fabric architecture affects the stress concentration and the damage development. Smaller crimp ratio and compacted structure postpone the damage development but result in more abrupt failure under multiaxial stress states.

This study focuses on the notch effect on the fatigue failure of chopped carbon fiber chip-reinforced sheet molding compound (SMC) composites by using both experimental and numerical methods. The S-N diagrams of notched specimens are first obtained experimentally, which exhibit large scatter and are shown to depend on the spatial distribution of local fiber orientations. After considering the effect of this spatial distribution by adopting a new fatigue damage parameter to normalize the results, we achieve a much better correlation in the normalized S-N diagram for all the notched specimens with different hole diameters. Next, compared with the fatigue results of smooth specimens without notches, we find that SMC composites under tension-tension fatigue loading exhibit notch-insensitivity, which renders this type of composites a better candidate in joints or similar applications. Meanwhile, the fatigue failure mechanisms of notched SMC composites are explored through a microstructure characterization procedure. On this basis, a computational micromechanics model considering the notch effect and an improved multi-scale progressive damage fatigue law, calibrated by coupon-level fatigue tests of smooth SMC composites under different loading conditions, are employed to predict the fatigue behavior of notched SMC composites. We show that detailed failure processes and fatigue life of notched SMC composites can be efficiently and adequately predicted by this computational framework.

The dynamic crushing characteristics of unidirectional carbon fiber reinforced plastic composites under two loading types, dynamic three-point bending and axial crushing, are investigated by experiment and finite element simulation. Hat section samples with two different layup orientations are tested at various impact velocities to investigate its effects. The experiment results show that delamination plays a critical role in dynamic bending deformation. Different layup orientations lead to similar crushing bending behaviors, but remarkable variations in delamination pattern evolutions. In contrast, layup orientation exerts more significant effects on failure modes and energy absorption in axial crushing. A finite element model with multiple layers of thick shell element and cohesive element is established, and simulations are performed for both dynamic three-point bending and axial crushing. The model can capture the crushing behaviors in the two loading types reasonably well. The damage evolution and energy absorption through various mechanisms at different loading conditions are discussed.

This paper addresses the challenge of reconstructing nonuniformly orientated fiber-reinforced polymer composites (FRPs) with three-dimensional (3D) geometric complexity, especially for fibers with curvatures, and proposes a framework using micro X-ray computed tomography (μXCT) images to quantify the fiber characteristics in 3D space for elastic modulus prediction. The FRP microstructure is first obtained from the μXCT images. Then, the fiber centerlines are efficiently extracted with the proposed fiber reconstruction algorithm, i.e., iterative template matching, and the 3D coordinates of the fiber centerlines are adopted for quantitative characterization of the fiber morphology. Finally, Young's modulus is predicted using the Halpin-Tsai model and laminate analogy approach, and the fiber configuration averaging method with the consideration of the fiber morphology. The new framework is demonstrated on both injection-molded short and long carbon fiber-reinforced polymer composites, whose fiber morphology and predicted mechanical properties are validated through previous pyrolysis and quasi-static tensile tests, respectively.

This paper presents a predictive multiscale modeling scheme for Unidirectional (UD) Carbon Fiber Reinforced Polymers (CFRP). A bottom-up modeling procedure is discussed for predicting the performance of UD structures. UD material responses are computed from high fidelity Representative Volume Elements (RVEs). A data-driven Reduced Order Modeling approach compresses RVEs into Reduced Order Models so material responses can be computed in a concurrent fashion along with the structural level simulation. The approach presented in this paper is validated against experimental data and is believed to provide design guidance for future fiber reinforced polymers development.

Carbon fiber reinforced composites have received growing attention because of their superior performance and high potential for lightweight systems. An economic method to manufacture the parts made of these composites is a sequence of forming followed by a compression molding. The first step in this sequence is called preforming that forms the prepreg, which is the fabric impregnated with the uncured resin, to the product geometry, while the molding process cures the resin. Slip between different prepreg layers is observed in the preforming step, and it is believed to have a non-negligible impact on the resulting geometry. This paper reports a method to characterize the interaction between different prepreg layers, which should be valuable for future predictive modeling and design optimization. An experimental device was built to evaluate the interactions with respect to various industrial production conditions. The experimental results were analyzed for an in-depth understanding about how temperature, relative sliding speed, and fiber orientation affect the tangential interaction between two prepreg layers. Moreover, a hydro-lubricant model was introduced to study the relative motion mechanism of this fabric-resin-fabric system, and the results agreed well with the experiment data. The interaction factors obtained from this research will be implemented in a preforming process finite element simulation model.

The effect of low temperature forging on the microstructure, quasi-static response and stress-controlled fatigue behavior of cast AZ31B Mg alloy was investigated. The forging process was conducted at a temperature of 275 °C and a forging rate of 20 mm/s. Fully reversed stress controlled cyclic tests were performed on cast and forged material under total stress amplitudes of 120–160 MPa. Neckless type bimodal grain structure, an indication of incomplete dynamic recrystallization was observed in the forged microstructure in addition to the development of a sharp basal texture. The obtained mechanical test results show that the forged material achieved significantly improved yield and tensile strengths along with longer fatigue life. The improvement in the quasi-static properties was attributed to the strengthening effect of partial grain refinement and activation of non-basal slip modes due to texture modification.

In this paper, the feedback signal of ultrasonic fatigue system was used to in situ deduce the accumulated fatigue damage via ultrasonic nonlinearity parameter. It was observed that compared with the resonant frequency, the ultrasonic nonlinearity parameter shows a greater sensitivity to fatigue damage like crack initiation and crack propagation. Conventional fatigue testing was carried out and the variation of specimen rigidity and plastic strain of the material were obtained which correlated well with the ultrasonic nonlinearity parameter. Also, the ultrasonic fatigue crack initiation was verified by interrupted test.

The fiber orientation distribution is one of the important microstructure variables for thermoplastic composites reinforced with discontinuous fibers. In this paper, the long fibers in the injection molded part are measured in detail by micro X-ray CT. A three dimensional (3D) structure of the sample is built and two dimensional images are generated for image analysis. The orientation tensor of fibers is calculated in the flow plane. It shows a symmetric distribution of fibers through the thickness direction, which consists of outer skin, transition zone and the core. The skin layer is so thin that it has only one layer of highly oriented fibers. The core layer also has highly oriented fibers but the direction of fibers is different from that in the skin layer. Nevertheless, the clustering of the fibers is characterized quantitatively in the core. The transition zone can be divided into two subzones by the principal directions of the tensor.

In this paper, thermomechanical fatigue life (TMF) prediction is performed on an automotive exhaust manifold using in-house postprocessor code (Hotlife) with four different constitutive models: elastoplastic model with kinematic hardening, two-layer viscoplastic model, and two unified elasto-viscoplastic models based on the equations proposed by Sehitoglu and Chaboche, respectively. Commercial FEA software Abaqus has been used for the analysis. The first two models are already available in Abaqus; the Chaboche and Sehitoglu models were implemented using a user material subroutine (UMAT, available in Abaqus). The stress and strain histories calculated by these four models are output to Hotlife for post-processing. The results from the prediction are then compared to the experimental TMF life obtained from a component thermal fatigue bench test. Result show the Hotlife calculations based on the two implemented elasto-viscoplastic models yield better correlation with test results.

Carbon fiber composites have received growing attention because of their high performance. One economic method to manufacturing the composite parts is the sequence of forming followed by the compression molding process. In this sequence, the preforming procedure forms the prepreg, which is the composite with the uncured resin, to the product geometry while the molding process cures the resin. Slip between different prepreg layers is observed in the preforming step and this paper reports a method to characterize the properties of the interaction between different prepreg layers, which is critical to predictive modeling and design optimization. An experimental setup was established to evaluate the interactions at various industrial production conditions. The experimental results were analyzed for an in-depth understanding about how the temperature, the relative sliding speed, and the fiber orientation affect the tangential interaction between two prepreg layers. The interaction factors measured from these experiments will be implemented in the computational preforming program.