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A large number of experiments show that composite materials usually show different modulus properties in tension and compression (bi-modulus). However, for actual composite engineering structures, especially complex models, the numerical simulation calculation is usually based on a single modulus. In order to consider the different modulus characteristics of composite materials in tension and compression, researchers put forward simplified constitutive models of dual-modulus materials. However, these constitutive models have not been verified by a large number of experiments, especially by complex models. In this paper, the GWFMM model is simplified and used to analyze complex structures with different modulus in tension and compression. The experimental results of stiffened plate show that the improved GWFMM model can be used to analyze different modulus of tension and compression of complex stiffened structures. In addition, the influence of elastic modulus ratio in tension and compression under different experimental load conditions is further explored, and the influence law of bending and torsion on structures with bi-modulus is discussed. The relevant conclusions provide reference for the design and optimization of full-scale composite structures in marine engineering. [ABSTRACT FROM AUTHOR]

The homogenization of piezocomposites is a research challenge as the development of analytical models remains a challenge. In this perspective, this work contributes to the development of an analytical model to predict the thermoelectromechanical behavior of the 2-2 piezocomposite where both phases are electrically active. To establish this model the series/parallel method was used and thus the effective homogenised properties of the composite are established. The influence of the volume fraction on the characteristic parameters was studied and found that a numerical simulation of the effective parameters resulting from a {PZT-5A/PVDF-TrFE} composition shows that, volume fraction influences significantly on the properties of the piezocomposite and consequently on its behavior in service. Due to the unavailability of experimental data in the literature, the validation of the model is done with reference to the model applied to the 1-3 piezocomposite. Therefore, to a certain extent, it is found that the results are in agreement. Based on the results of this model and in comparison with those formulated from 1-3 piezocomposite as presented in the paper, the studied 2-2 piezocomposite could be used where 1-3 piezocomposite is sometimes integrated, as the highest performance piezocomposite. However, this remains to be validated experimentally for targeted applications to be useful for the scientific and even industrial communities. [ABSTRACT FROM AUTHOR]

Numerical and experimental research programs have been carried out to investigate the effect of scaling on the tensile strength of notched composites. This paper presents a computational study of scaled open-hole tensile tests using the Discrete Ply Model (DPM) method. This finite element model is discrete, and only a small number of parameters are required from experimental characterization tests. Experimental and numerical strength values are compared here, and reveal that DPM simulations tend to slightly overestimate strength values, with an average discrepancy of 9.7%. However, DPM Results show that such modeling simulates both the reduction in strength when specimen size is increased for sublaminate level scaled specimens, where failure is fiber dominated, and the increase in strength when specimen size is increased for ply level scaled specimens, where failure is delamination dominated. In all cases, increasing the total thickness of the specimen leads to a decrease in strength and this effect is dominant over the effect of increasing hole diameter. As well as the variation in strength, three distinct failure mechanisms are observed: fiber failure with extensive matrix damage (pull-out failure), fiber failure with little or no matrix damage (brittle failure) and delamination failure. Comparisons with experiments demonstrate that tensile strengths, damage propagation scenarios and failure patterns are predicted with acceptable accuracy. [ABSTRACT FROM AUTHOR]

The aim of present paper is to show a procedure to calibrate mechanical properties to be used in a finite element model for a carbon fibre-reinforced plastic laminate that use solid elements. A reduced experimental programme including tensile test, tensile test on specimen with a central hole, three-point bending test and three-point bending test on short beam test were carried out. Every test was numerically reproduced by means of an explicit solver. Properties are determined from the tensile test and unmodified for the other load scenarios which are used as validation benchmarks. Finally, it is demonstrated that the properties determined with the simple tensile tests can guarantee accurate results when adopted to simulate much more complicated stress patterns. [ABSTRACT FROM AUTHOR]

Since the benefits of composite materials have been demonstrated, particularly those relevant to the fields of transports and energy, increasingly high industrial expectations are emerging. As the control of the processes is complex, the thickness of the composite materials does not usually exceed a few millimetres. The aim of the work presented in this paper is to highlight new phenomena related to the oven/autoclave consolidation of thicker thermoplastic composites. In the case of such thick composites, the influence of certain phenomena that are usually neglected becomes important and a physical interpretation becomes necessary (the thermal contact resistance between mold and part and the influence of mold geometry). Here, an experimental approach is compared with numerical simulations of heat transfer and crystallization in order to validate the proposed thermokinetics model. Finally, some numerical observations are discussed and analyzed. [ABSTRACT FROM AUTHOR]

This paper explores the use of thin film piezoresistive pressure mapping sensors as a means to improve resin transfer moulding processes. The pressure mapping sensor was located between the preform and mould, giving information regarding the permeability map prior to infusion. The permeability map is used as an input to a direct numerical simulation of the infusion step of a highly variable reclaimed carbon fibre preform. The pressure sensor was also used to track the flow front position in-situ, due to a change in load sharing between the preform and liquid during the infusion experiment. Flow front tracking with the pressure mapping sensor was validated against conventional camera images taken through a transparent mould. The direct numerical simulation was able to account for local permeability variation in the preform, providing improved flow-front prediction than homogeneous permeability only, and could be part of a wider strategy to improve resin transfer moulding process robustness. [ABSTRACT FROM AUTHOR]

In this paper, a random configuration model for fiber arrangement is proposed and implemented in a computer code. This development enables the investigation of the effect of the random arrangements of the fibers inside the tow on the permeability and the flow properties. Four parameters are considered including three microstructural parameters: side length of the domain L, variation of radii Δr, minimum interfiber distance δmin, and one macro parameter: porosity ɛ. Finite element method is performed for the transverse flow of porous media with random arrangements of fibers. Morris method for global sensitivity analysis is used to study the influence of four parameters. The results have shown that the porosity ɛ has the most obvious influence on the fiber reinforcement permeability. [ABSTRACT FROM AUTHOR]

The 3D printing of continuous-fiber composites is currently relevant to engineers and researchers. This study aims to characterize and predict the mechanical properties of Onyx/glass fiber specimens printed using 3D printing. The work assesses the impact of glass fiber printing parameters on the mechanical behavior of printed parts and proposes analytical and numerical methods to predict mechanical properties. A physicochemical analysis was conducted on 3D printed continuous glass fibers. The study also investigated the impact of fiber printing parameters on composite parts. The results indicate that the 3D-printed glass fibers consist of nylon, continuous glass fibers, and voids (porosity), which range from 58% to 63%, 31% to 38%, and 5% to 8%, respectively. Mechanical characterizations indicate that printing fiber layers in blocks results in superior mechanical properties compared to printing alternating layers of glass fibers and Onyx. Additionally, the concentric mode of fiber printing can be challenging if the 'start rotation' parameter is not adjusted correctly. Premature specimen breakage occurred when fiber printing began within their useful length, resulting in a deformation at break that was approximately 34% less, depending on the starting position. The proposed analytical and numerical prediction methods had prediction errors of approximately 7% to 12% and 5% to 7%, respectively. Engineers can use these prediction approaches during the dimensioning phase of 3D printed composite parts. [ABSTRACT FROM AUTHOR]

Developing a reliable and robust finite element model of a carbon fiber-reinforced plastic (CFRP) composite structure is investigated by using the LS-DYNA solver and Python. This study tries to provide a systematic numerical approach to cover the principal impediment to adaptation of composite energy absorbers, that is the lack of a reliable predictive method. The proposed procedure aims to further the understanding of advanced composite structures' behavior during the crash phenomenon by developing an accurate finite element model. To do so, the mechanical properties of the material were extracted from American Society for Testing and Materials (ASTM) standard test methods, followed by experimental investigation of circular CFRP tubes undergoing quasi-static loading. A numerical simulation framework was then utilized to scrutinize the effectiveness of simulation parameters on the crushing mechanism. Finally, a systematic approach based on machine learning techniques was performed to adjust non-physical modeling parameters for further calibration and validation. In this regard, a versatile Python code was developed to automate pre-processing, processing, and post-processing steps. The code also provides a groundwork to perform machine learning techniques. Interestingly, the numerical and experimental results were highly correlated with a correlation coefficient of almost 90%. Additionally, several non-physical numerical parameters were found to be inactive, while some else were identified as effective parameters, and their corresponding effectiveness was quantitatively extracted and discussed for the first time in the literature. [ABSTRACT FROM AUTHOR]

Three-dimensional spacer fabrics due to their specific structural features have achieved significant importance to be used as highly effective technical textiles especially in composite manufacturing. Increasing applications of three-dimensional fabrics in technical fields as well as the high ability of knitting process in production of highly structured-knitted preforms made the researchers to be focused on finding novel structures with high potential application as the composite reinforcements in order to achieve some desired properties. Along with others researches, in this paper an especially structured three-dimensional spacer weft-knitted fabrics was produced on an electronic flat knitting machine, using 1680 denier high-tenacity polyester yarn. The fabrics samples were employed in thermoset composite manufacturing process using the epoxy resin. In order to investigate the mechanical behavior of the composite samples in term of their flexural performance, a three-point bending test was performed. For precise investigation, numerical simulation based on finite element method was also applied. Good correlation between the experimental and theoretical results showed such reasonable validity of the proposed model for simulating the mechanical behavior of the spacer-knitted reinforced composite under external bending loads. [ABSTRACT FROM AUTHOR]

Resin infusion (RI) process has been widely used for manufacturing composite parts. The variation of preform thickness brings great difficulty to the three-dimensional simulation of the filling stage. To accurately simulate the preform thickness change and resin flow during resin infusion, precise preform compaction models and dynamically changing geometry models need to be adopted. At present, resin flow is usually considered as two-dimensional and simple compaction models are employed to simplify the simulation, which degrades the prediction accuracy seriously. In this paper, general equations to describe the resin flow in the changing thickness cavity are developed, and the viscoelastic model is adopted which can fully express the dynamic characteristics of the preform compaction. To avoid solving the coupled resin flow/preform deformation equations directly, the volume of fluid method and the dynamic mesh model are employed to implement the tracking of the flow front and updating of cavity geometry model. The resin storage and release induced by porosity variations are adjusted by a master-slave element method to ensure mass conservation. Two simulation examples are carried out to demonstrate the capability of the above approach. The applicability of the approach on arbitrary complex domains and sequential injection strategy is also verified. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation on low velocity impact response of S2 glass/epoxy and aramid/epoxy composite plates. Two different impact energy levels, 20 J and 30 J, were considered for impact tests. The commercial software called LS-DYNA was used in order to perform numerical simulations. The experimental and numerical results were found to be in good agreement. [ABSTRACT FROM AUTHOR]

A methodology for generation of realistic three-dimensional software models of carbon fiber-reinforced polymer (CFRP) structures, dedicated for use in simulation studies of advanced X-ray imaging techniques for non-destructive testing (NDT), has been developed, implemented, and evaluated. Two CFRP models are presented in this paper, one built as a set of stacked layers that contain continuous carbon bundles and a second as a braided textile from woven carbon bundles. The following CFRP defects were modeled: porosity, missing carbon bundles, and non-carbon inclusions. X-ray projection images were generated using an in-house developed X-ray imaging simulator. The obtained preliminary visual and quantitative validation results showed an overall good correlation of characteristics between synthetic and experimental data radiographs and justify the use of this model for research in CFRP X-ray imaging. The application of the CFRP model is demonstrated in a feasibility study that aims to computationally evaluate the appropriateness of two advanced X-ray imaging techniques: cone-beam CT (CBCT) and tomosynthesis (limited arc tomography), as inspection techniques for NDT of CFRP parts. The simulation showed that in all cases the CBCT approach outperformed both conventional radiography and tomosynthesis in terms of defect characterization and visualization. [ABSTRACT FROM AUTHOR]

The thermal properties of carbon/carbon composite are strongly affected by manufacturing porosity. This paper focuses on the characterisation of the manufacturing macro-porosity of a 2D carbon/carbon composite using X-ray computed tomography. The different types of manufacturing porosity were classified and quantified according to their size and location. Three types of macro-porosity were identified using computed tomography, namely trans-tow cracks, interfacial cracks and dry zones. A composite unit cell representing the three types of porosity was developed to model and investigate the effective transverse thermal transport properties (thermal conductivity and diffusivity) of the carbon/carbon composite. Finite element simulations and theoretical calculations were performed and compared with laser flash tests for validation. The influence of the stacking sequence of the laminates on porosity distribution and transverse thermal conductivity of the carbon/carbon composite was also investigated. [ABSTRACT FROM AUTHOR]

Using the principles of classical micromechanics, analytical equations are developed in this paper to estimate the effective orthotropic properties of a unit cell of strand-based composites according to their constituent phase properties and their microstructural features such as resin thickness, void content and strand geometrical characteristics. Although a special type of strand-based wood composite product, Parallel Strand Lumber, is considered here as an illustrative example, the methodology can be used for other wood composites consisting of high volume fraction of wood strands. The predictive accuracy of the derived analytical equations is investigated through comparisons with numerical results. Finally, applications of these equations in a linear viscoelastic analysis are discussed. The analytical micromechanics models developed here provide an efficient means of computing effective properties of a unit cell of strand-based composites. These models can then be used within a multi-scale modelling framework that has been developed previously to simulate the macroscopic behaviour of structures made of such materials. [ABSTRACT FROM PUBLISHER]

Since train’s frontal nose is the first part of the train which is damaged at the frontal impact, specific attention should be paid to the design of this part. In this study, an effort has been conducted to the design of a nose with light weight which can absorb maximum amount of energy that is possible during a frontal collision. To this aim and with attention to aerodynamic considerations, application of aluminium honeycomb sandwich panel has been studied. This paper includes two main parts. The first part is dedicated to the simulation of aluminium honeycomb sandwich panel, while the frontal collision of nose with different internal layer thicknesses of honeycomb and various nose lengths have been simulated in the second part. Finite element method using LS-DYNA commercial package has been used for the numerical simulation. The results have been validated with available experimental results and an acceptable agreement has been observed. [ABSTRACT FROM AUTHOR]

A modified anisotropic PUFF equation of state for composite materials under elastic and plastic condition is proposed in this paper, which can not only calculate the non-linear behavior of volume change but also reveal anisotropic strength effect of material under compression and dilation. Taking the 2D impact problem and thermal shock wave problem under X-ray radiation of orthotropic composite material for example, a numerical simulation is completed using the finite element program, and the pressures calculated by traditional and modified PUFF equation of state are compared. The results show that the two pressures have obvious difference at low compression and tension state, but with the increase of pressure the difference reduces and the pressures tend to be consistent gradually. These conclusions are coincident with the theory that the anisotropic material tends to be isotropic at high pressure and exhibits anisotropic property at low pressure. [ABSTRACT FROM AUTHOR]

Computer simulation has become an efficient and cost-effective tool for the liquid composite molding (LCM) processes, including the RTM, VARTM, and resin infusion, compared to trial-and-error. The purpose of simulation is to accurately reflect the real situation. Since the simulation is predominantly based on the control volume finite element method (CVFEM), the boundary conditions such as gate and vent definition need to be properly defined. In this paper, the errors of the CVFEM based mold filling simulation were analyzed. The error sources were identified as the mesh near gates and vents, and gate definition. By conducting 3-D and 2-D simulation case studies, the influence of the gate definition on the simulation result was studied. Because many composite parts are shells and can be regarded as surfaces. 2-D simulation is favorable because of the better efficiency and simpler pre-processing. For this purpose, a method for mold filling simulation incorporating the gate size effect the effective gate method (EGM) - was developed. This method was validated through case studies. It shows that the EGM provides an effective and efficient approach to the CVFEM mold filling simulation incorporating the effect of injection gate size. [ABSTRACT FROM AUTHOR]

Orientation tensors are widely used to describe fiber orientations in mold filling simulations of short-fiber-reinforced composite systems. In these flow calculations, a closure is employed that approximates the fourth-order orientation tensor as a function of the second-order orientation tensor. Sixth-order closures have also been proposed. This paper assesses the effect of using closure approximations in fiber orientation predictions by reconstructing the fiber orientation distribution function from successively higher order orientation tensors in a Fourier series representation. This approach recognizes that the orientation tensors are related to the series expansion coefficients of the distribution function. An error metric is introduced and applied that makes it possible to compare closures of varying order. Errors associated with several fourth-order closures and a sixth-order closure are investigated and compared with the truncation error that results from a reconstruction of the exact second-, fourth-, and sixth-order orientation tensors. Examples are provided over a range of interaction coefficients and flow fields typical of injection molded fiber-reinforced composites to illustrate the proposed closure assessment method. [ABSTRACT FROM AUTHOR]

The dynamic response of composite sandwich structures with honeycomb-foam hybrid cores subjected to underwater shock waves was investigated by numerical simulations. The deformation process, core compression, momentum transmitting characteristics, and energy absorbing properties of sandwich structures subjected to underwater shock waves with different initial pressures were analyzed. The dynamic responses of the composite sandwich with different core configurations were also compared. The results show that the composite sandwich structures can provide superior protection from underwater shock waves than mass equal laminate plates and the sandwich structures with hybrid cores have better performance than that with empty honeycomb cores when subjected to underwater shock waves. The research can provide reference for the lightweight design and optimization of protective structures against underwater blast loading. [ABSTRACT FROM AUTHOR]

A porous material –Bi-directional Trapezoid Honeycomb (BDTH) which is different from the traditional honeycomb structure, has same energy absorption properties in the Y and Z directions was studied. The structural parameters (cell size, cell thickness) have a great influence on the compression performance. 3 kinds of cell size (a) and 4 kinds of cell thickness (t 0) totally 7 kinds of BDTH were manufactured. The quasi-static compression test was carried out with experiment and numerical simulation, and the results were obtained. The effects of material deformation modes and energy absorption are analyzed. Next, based on Gibson-Ashby theory, the relationship between density, initial peak stress, plateau stress, densification strain and the ratio of t0/a were deduced. [ABSTRACT FROM AUTHOR]

In this article, we propose a random fiber configuration method to set up quasi-realistic geometric models of the fibrous tow in reinforcement. Finite element method is applied to simulate the injection of resin at dual scales (both intra and inter tows, 2D and 3D models). Permeabilities of dual scales in three directions (in horizonal, vertical and longitudinal directions) are also explored. The influence of variant structure parameters on the permeability is discussed in the meantime. Flow front tracking considering surface tension effect based on the dual-scale model is carried out to predict resin flow through the fibrous reinforcement. [ABSTRACT FROM AUTHOR]

For resin transfer molding in a woven fabric, this study developed a novel framework for optimization by combining a multi-objective genetic algorithm and mold-filling simulation including a void-formation model, which gives us not only the spatial distribution of the mesoscopic and microscopic voids but also the correlations between molding characteristics such as fill time, total amount of void, weld line, and wasted resin. Our experiment observation of one-point radial injection successfully captured the anisotropic distribution of mesoscopic voids, which qualitatively validates the simulated result. As a result of multi-objective optimization for an arrangement of two injection positions, we found the trade-off relations of weld line with the other characteristics, which also have positive correlation with each other. Furthermore, visualization techniques such as self-organizing maps and parallel coordinate maps extracted the design rule of the arrangement. For example, a diagonal gate arrangement with an appropriate distance is required for reducing the both total amount of voids, fill time, and wasted resin; however, the total area of the weld line becomes relatively large. Our framework and the knowledge obtained from this study will enable us to determine the appropriate mold design for resin transfer molding. [ABSTRACT FROM AUTHOR]

Vacuum assisted resin transfer molding is a promising process in advanced composite manufacturing with a wide range of applications in industry. That potential is often misused, though, because of the lack of an efficient and reliable simulation tool to support product development. Most of the simulation methods in use today are based on Darcy’s law, which explains the permeation of a fluid in a porous medium. However, it is known that this law has limitations when applied to the context of dual-scale fibrous reinforcements: macro porosity given by fiber architecture generates resistance to flow, while the inner porosity inherent to fiber tows causes it to absorb resin, affecting the flow. The latter effect cannot be explained by traditional theory. In order to explore these limitations, this work proposes a simplified model to vacuum assisted resin transfer molding process from the point of view of system dynamics, and to prove the viability of such theory. The ultimate goal is to propose a more complete model in light of system dynamics that saves time and cost while offering the same reliability as current simulation models. In order to provide an explanation to both dual-scale phenomena, a parallel association between a resistance and a fluid capacitance is proposed. Model validation is then performed through the analysis of experimental data followed by the comparison between the Darcy infusion profile and the one predicted by the resistor-capacitor-parallel (RC-parallel) circuit model. Thus, this work is able to perform a proof of concept that leads to a novel and yet unexplored field of study. [ABSTRACT FROM AUTHOR]

Disagreement has persisted in the modeling of Fickian moisture diffusion in sandwich structures as to the correct continuity conditions at the core/facesheet interface. The purpose of the present work is to compare moisture diffusion predictions based on two of the most widely used sets of these continuity conditions. The model problem of one-dimensional time-dependent moisture diffusion in a symmetric sandwich slab is selected for analysis. Finite difference numerical solutions reveal very little difference between the predictions of models assuming continuity of relative humidity and continuity of relative concentration over a wide variety of parametric conditions. [ABSTRACT FROM AUTHOR]

Separation of skin and stringer is likely to be a failure mode in co-cured composites stiffened panels where there is considerable out-of-plane deformation. Such deformations are possible when a stiffened skin structure is loaded in compression/shear beyond buckling or in structures which contain a disbond/delamination at the skin–stringer interface. Prediction of damage initiation and progressive growth in numerical simulations require parameters such as interface fracture toughness which have to be obtained through specimen tests. Since interface toughness is generally mode dependent, this study deals with the design and testing of three different configuration of blade stiffened co-cured composite skin–stringer specimens under mode-I and mode-II dominated loading. Finite element numerical models are developed using three-dimensional cohesive elements to predict the disbond growth under mode-I and mode-II dominated loading. The work also addresses the complexities in the convergence of numerical simulations that arise due to cohesive elements. A systematic way to obtain the best values for cohesive element parameters while finding a balance between accuracy of the results, computation time and numerical stability is presented. The present cohesive element modelling and analysis methodology successfully predicted the disbond growth in skin–stringer specimen and can be used to predict disbond/delamination onset or growth in composite stiffened structures subjected to high bending. [ABSTRACT FROM AUTHOR]

Laminated composite structures manufactured via the automated fiber placement process inherently contain process defects know as gaps and overlaps. These defects raise concerns when they are located on or near holes intended for mechanical fastening. This investigation attempts to predict the effect of automated fiber placement-generated defects on the open-hole compression strength by combining both experimental tests and numerical simulation. Tested open-hole compression specimens containing gaps and overlaps oriented at 0° or 90° and centered on or shifted near the hole show that, depending on their location, the gaps and overlaps may have negative, negligible, or positive effects on the open-hole compression strength. The better than expected effects are compatible with microscopic observations that clearly show the rearrangement of the plies during the consolidation process, which prevent the formation of deleterious discontinuities. Incorporating these observations in a numerical model, which simulates gaps and overlaps embedded inside the composite laminates, and applying a progressive failure analysis, confirms that the effects of automated fiber placement defects depend as much on their type as on their location relative to the hole center. Finally, the results obtained from a parametric study provided further explanation on the effects of automated fiber placement defects on the failure strength of perforated composite laminates. [ABSTRACT FROM AUTHOR]

The second world-wide failure exercise is an international activity, organised by Kaddour and Hinton, aiming at a better understanding of the limitations of existing failure criteria to predict failure under triaxial stressing. The present work is a response to an invitation to take part and employ Hashin's failure criteria to the 12 test cases defined by the organizers of the second world-wide failure exercise. Methods, based on nonlinear analysis, used to perform the required simulations are explained and the predictions are presented. Observed problems are discussed. [ABSTRACT FROM AUTHOR]

A mesh-free Galerkin approach for modeling damage in plain woven fabric composite is presented. The model is based on the continuum damage mechanics and is applied to both mosaic and smooth fabric idealizations of the plain woven composite. A mesh-free Galerkin method is formulated for the first time to include the continuum damage mechanics for micromechanics model of woven fabric composites. An incremental technique of applied displacement/strain is developed to obtain the relationship between the representative volume cell stresses and strains. Also presented for the first time is an analytical formulation for damage in the mosaic unit cell representation of the woven fabric composite. Several examples are presented to demonstrate the application of the proposed methods and comparisons are made between the newly developed analytical formulation and the proposed mesh-free method. [ABSTRACT FROM PUBLISHER]

Numerical simulations are used to design test geometries and loading histories that are suitable for probing the large-scale bridging effects of through-thickness reinforcement that is shearing at high strain rates. The bridging effects are represented by a cohesive law and tests are sought that will determine any rate dependence in its parameters. The end-notched flexure test is studied, because it allows easy application of time-dependent loading and has proven to be an information-rich test in the quasi-static case. However, dynamic conditions greatly complicate fracture behavior, with possible regimes of hammering and multiple cracking, which should be avoided when maximum information is sought. Information content is addressed by focusing on regimes within the full computed solution space where crack growth is approximately steady state and the information content of experiments can be most easily assessed. Numerical results show that the hypothetical rate dependence in the cohesive law causes strong and measurable changes in the regime of steady-state behavior, if the tests are properly selected to vary the crack sliding speed. The estimates of information content are conservative, because the information available from all possible tests of specimens designed by analysis of the steady-state regime will necessarily exceed the information deduced by analyzing the steady-state regime alone. [ABSTRACT FROM AUTHOR]

Artificial neural network (ANN) based multi-parameter inversion method is proposed to characterize transversely isotropic composite lamina using Lamb wave group velocity measurements. The ANN is first trained using numerical simulations and known micromechanics based formulae before being deployed on experimental samples. The group velocities obtained from the experiments were fed to the trained network. The network so trained, predicted the elastic properties, fiber volume fraction, and density. [ABSTRACT FROM AUTHOR]

This article demonstrates the use of response sensitivities in numerical simulation of composite processing via four different application examples: real-time result validation, model calibration, reliability analysis, and optimization. The analyses are carried out with integrated simulation software with new response sensitivity capabilities. Notably, the response sensitivities are computed by the direct differentiation method. This is an efficient and accurate alternative to the finite difference approaches. A brief review of the derivation and implementation of sensitivity equations is provided. The primary objective of this article is to demonstrate and promote a suite of techniques to incorporate uncertainties into the simulation of the composite manufacturing process, facilitated by efficient sensitivity computations. [ABSTRACT FROM AUTHOR]

In this article we derive, implement, and verify equations to compute the sensitivity of responses from numerical simulation of composites manufacturing. The responses considered are part temperature and degree of cure, as well as process-induced deformation of the cured part. The 'direct differentiation method' (DDM) is used, which entails a one-time investment of effort to differentiate the governing response equations analytically. The implementation of the derivative equations facilitates efficient and accurate computation of response sensitivities in all subsequent analyses. This article extends the DDM methodology developed earlier for mechanical problems. Novel 'shape sensitivity' equations and efficient implementation techniques are also included. In order to verify the implementations, the model predictions are compared with those obtained from the less efficient finite difference approach. A comprehensive example is presented where the usefulness and interpretation of response sensitivities are emphasized. It is observed that the responses are particularly sensitive to certain model parameters, for which further data gathering and model improvement efforts should be focused. [ABSTRACT FROM AUTHOR]

The Matzenmiller-Lubliner-Taylor (MLT) model, a continuum damage mechanics (CDM) based model, was used in modeling energy absorption of composite structures in crashworthiness applications. It was found that the assumption of linear elastic unloading and reloading in MLT model resulted in a lower calculated energy absorption in thin wall composite tube axial crush simulations. A modification to compressive unloading was proposed and tested in an MLT-based user material model. The modified model improved the stability of the tube crush simulation and the simulation results. This study demonstrates the importance of properly representing the unloading response of damaged composites in energy absorption prediction. [ABSTRACT FROM AUTHOR]

The linear thermoelastic and thermophysical behavior of a short fiber reinforced composite material with planar random fiber arrangement is investigated by advanced numerical and analytical micromechanical methods. On the one hand, finite element based multi-fiber unit cells are introduced that contain 40-50 short fibers in arrangements approximating 2D random orientation distributions. On the other hand, the same fiber arrangements are investigated by an extended Mori-Tanaka mean field approach that can handle both statistical and discrete descriptions of the fiber orientations. Within the Mori-Tanaka scheme average microfields are extracted for individual fibers, and finite-length cylindrical reinforcements are modeled via averaged dilute concentration tensors that are evaluated numerically by finite element analysis. Homogenization and localization are performed for a metal matrix composite consisting of copper, reinforced by 21 vol% of carbon fibers that closely approximate a planar random arrangement. Simulation results on the macroscopic and microscopic linear elastic, thermoelastic, and thermal conductivity responses obtained by the two approaches are compared and excellent agreement is found. [ABSTRACT FROM AUTHOR]

An investigation of the permeability for viscous flow through random fiber structures used as preforms in composite fabrication processes is presented. A method derived from the electrical conduction principles is employed to predict the viscous permeability of the fiber structures directly from their formation factor, specific surface area, and porosity. The recent Brownian diffusion random-walk simulation results on the molecular survival time are used to derive an upper bound and an approximation to the viscous permeability of these structures. The results are compared to experimental data and theoretical models of the literature. It is found that the conduction-based method provides very good permeability estimates in most cases, resulting in an overall ratio of the theoretical prediction to experimental measurement in the proximity of 1 for the over 500 experimental points utilized. This is one of the most comprehensive experimental validations of the conduction-based method to date and its first validation for anisotropic particle beds. A tortuosity analysis indicates a stronger pore-geometry effect on viscous flow relative to any type of diffusional flow, enhancing the understanding of the differences between pressure-driven and diffusion-driven composite manufacturing techniques. [ABSTRACT FROM AUTHOR]