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The assets that are normally accessible in the climate are the keys to the improvement of material science. The utilization of assets as materials is expanding every day for the endurance of humanity which likewise impacts the eco-framework as a boundary. From the development use of the materials, composites assume a fundamental part that is liable for the new speculations, advancements, and applications in various areas of science. As to convey forward the advancement in material science, the quest for elective utilization of engineered or counterfeit polymer composites which are non - degradable is begun because their temperament impacts the supportability, and balance in the climate whichstraightforwardly impacts the everyday routine pattern of experiencing creatures in nature. Subsequently, the way leads to regular composite materials which are bio-degradable and eco-accommodating to the climate. The recuperating capacity peculiarities themselves exist in nature, whichis adjusted to the material science field to build the existence use of the material. Self-composites appeared and were created by numerous analysts and its system and various kinds of approaches are given out exhaustively. In any case, the greater part of one self-healing idea was finished and given out on engineered composite materials. This displayed as an exploration hole and drove us to research the impact of the self-recuperating ideaon regular fiber-supported green composites. This paper gives out a concise viewpoint hypothesis on self-healing composites. [ABSTRACT FROM AUTHOR]

In this paper, an approach to solving the problem of the determination of effective stress-strain, thermophysical and electrophysical properties of filled composite materials on the basis of the variational principles is developed. In the numerical implementation, it might be reduced to the use of the finite element method (FEM). An approach, possessing a certain generality, to finding effective physical-mechanical, thermophysical and electrophysical properties of filled polymer composites is proposed and described. Firstly, a general concept based on obtaining detailed parameters of the composite state under external impact taking into account the actual structure of the material is developed. Then, the averaging procedure aimed at obtaining effective properties of the composites is employed. Secondly, the realization of boundary problems is reduced, for all cases (physical-mechanical, thermophysical and electrophysical), to the formulation of the corresponding variable principles and their realization by the methods of computational mechanics, in particular, by the finite element method. [ABSTRACT FROM AUTHOR]

In this paper, we propose an algorithm for predicting the residual life of structures made of polymer composite materials (PCM) using a structured phenomenological model. In the developed algorithm for estimating the residual life of PCM structures under cyclic loading, it is proposed to use the explicit description of the process of destruction of adhesive layers. The implementation of the algorithm is accomplished in the APDL language in ANSYS Mechanical. The algorithm and the program are tested on a flange type design. Based on the results of numerical experiments, the area of damage is identified. The service life is determined, as well as the allowable value of the PCM flange stiffness drop under cyclic loading. [ABSTRACT FROM AUTHOR]

The paper presents research results on the properties of polymer composite materials based on ultrahigh molecular weight polyethylene and polytetrafluoroethylene modified with carbon fibers. It has been established that an increase in CF concentration is accompanied by a decrease in the stress-strain properties of a PCM based on PTFE, as well as by a change in the behavior of tensile strain curves of the PCM. It has been found that the decrease in stress-strain properties and the change in the failure mode of PTFE-based composites containing CF of the LO-1-12N/40 grade occur at a concentration of 5 wt%, and with the introduction of fibers of the Belum brand, 10 wt% concentration is required. This is probably due to the different values of the critical volume content (φm) of CF in PTFE. It has been detected that the strength is increased by 80% at 5% compression of PCM, and it is doubled at 10% compression in comparison with unfilled PTFE. The rate of mass wear of the PCM based on PTFE containing discrete carbon fibers decreases with an increase in filler concentration. The prospects of using carbon fibers as a reinforcing element of UHMWPE with the aim of obtaining new composites with high tribotechnical characteristics intended for operation under conditions of limited lubrication or dry friction are shown. It has been established that, to improve the stress-strain properties and wear resistance of the PCM based on UHMWPE, it is efficient to use carbon fiber of the Belum brand as a filler, since the interphase interaction of UHMWPE with the fiber is strong due to a hydrophobic fluoroorganic coating on the surface of these carbon fibers. [ABSTRACT FROM AUTHOR]

In contrast with neat polymers, filled polymeric composites of ultrahigh molecular weight polyethylene (UHMWPE) are certainly more efficient in manufacturing industrial products (for instance, when reinforcing fibers are loaded). An experimental-theoretical technique for designing a polymer composite with specified properties is discussed in the paper. An approach to determine control parameters (phase composition, physical and mechanical properties, etc.) in order to design a composite with prescribed effective properties or providing them within a predetermined range is proposed. With the use of the approach based on the experimental data analysis in concern of effective characteristics versus the values of the control parameters, corresponding response surfaces of the physical-mechanical characteristics are constructed in the space of states. This allows one to determine the correct and reachable values of the control parameters. The calculated response surfaces make it possible to reveal the range of values of control parameters for specified characteristics of multicomponent reinforced extrudable UHMWPE polymer composites. [ABSTRACT FROM AUTHOR]

This paper analyses the progressive failure of a variable-stiffness composite structure (VSCS). The composite structure is simulated by means of a design method developed earlier. The design method allows curvilinear fibers to be adapted to various geometric discontinuities (holes, notches, etc.) or non-uniform loading. The fiber orientation and fiber volume fraction are heterogeneous in the VSCS. To model progressive failure, a material property degradation method (MPDM) is used. The properties of the composite structure are locally changed due to the nonuniformity in the fiber volume fraction, and the change of the properties is taken into account in the MPDM. A rectangular plate with a hole under tensile loading is modeled, and it is shown that use of the VSCS is more effective than the use of a composite structure with rectilinear reinforcement (orthotropic material) under identical conditions. [ABSTRACT FROM AUTHOR]

The paper presents first results of obtaining metal-matrix composites based on severe plastic deformation by shear under pressure of layered Al and Cu components. Three-layer composites with different alternation of layers, i.e. Al-Cu-Al and Cu-Al-Cu, were processed by constrained high pressure torsion to produce monolithic disk-shaped samples without pores. Analysis of the macroscopic homogeneity showed that different alternation of layers led to varying degrees of mixing of the starting components. [ABSTRACT FROM AUTHOR]

The paper considers the elastic properties of epoxy composites reinforced by 6 types of silica nanoparticles with different average diameter at the same weight concentration of 1.1%. The addition of silicon nanopowders increases the modulus of elasticity. For powders of the same origin, with an increase of the modulus of elasticity, a decrease in the characteristic diameter of the filler particles at a constant concentration is observed. It is shown that the characteristic average particle size is not the only factor determining the growth of the elastic modulus, since the growth of the modulus is significantly different for powders of different producers. [ABSTRACT FROM AUTHOR]

This paper studies a new way of cladding particles by preliminary mechanical mixing of particles of a refractory material (TiN) with particles of a binding metal (Ti) followed by forming granules containing 20 mass fractions of initial particles of titanium nitride and their further processing in an argon-helium plasma jet in a controlled atmosphere. As a result of experimental studies, a composition powder consisting of spherical particles sized from 0.1 to 40 μm is obtained. The refractory nanoparticles of titanium nitride in it are evenly distributed over the volume of the binding metal (titanium) and completely plated by it. The surface morphology and the internal structure of the particles are studied, the results of X-ray phase analysis are presented, and a map of element distribution over both the surface and volume of the composition particle is obtained. This method of producing nanomodifying compositions helps to improve homogeneity of the distribution of refractory elements in the melt volume, as well as their wettability, which increases the effectiveness of modifying the material properties. [ABSTRACT FROM AUTHOR]

The paper studies the structure, chemical and phase compositions and hardness of Fe-Ni-Ti-C-B composites produced by self-propagating high-temperature synthesis (SHS). It is demonstrated that, when Fe, Ni, Ti, C and B4C are used as initial materials in the form of a powder mixture poured into a steel pipe, a one-piece multilayer plate is formed under SHS, inside which there is a composite with a matrix of a solid solution of Fe in a γ-Ni lattice and reinforcing TiC, TiB2, and Fe2B particles with a hardness of 62 HRC. The inner surface of the steel shell is firmly joined to the composite due to the synthesis products diffusing into the steel. [ABSTRACT FROM AUTHOR]

Analysis of design methods for composite beams with curvilinear fiber trajectories is considered in this paper. The novelty of this approach is determined by the fact that traditional composite materials are typically formed using prepregs with rectilinear fibers only. The applications of the results are associated with designing shaped members with a composite structure by using of biomechanical principles [1,2]. One of the problems is evaluation of the effect of fiber misorientation on the stiffness and load carry capacity of a shaped composite element with curvilinear fiber trajectories. An equistrong beam with a constant cross-section area is considered as an example, and it can be produced by forming of a unidirectional fiber bunch impregnated by a polymer matrix. Methods for evaluating the effective elastic modulus for structures with curvilinear fiber trajectories are validated. The misorientation angle range (up to 5 degrees), when a material with required accuracy can be considered as homogeneous, is determined, fiber misorientation being neglected. It is shown that, for beams with a fairly small height-to-width ratio, it is possible to consider only 2D misorientation. [ABSTRACT FROM AUTHOR]

In this paper a Voronoi Cell Finite Element (VCFEM) scheme is presented to model ductile damage in metal matrix composites (MMCs). Particle fracture and matrix cracking are used to model failure of the composite. Numerical examples for simple microstructures are used to validate the model. An example of an actual morphological description of a MMC is used illustrate the potential of the method. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The northern regions characterized by harsh climatic conditions should be developed using modern technology employing polymeric materials suitable for use at temperatures down to -60 °C. The creation of polymer composite materials based on polytetrafluoroethylene (PTFE) with highly perfected service characteristics is one of the priority tasks of modern materials science. The paper discusses the physical-mechanical, tribological, and thermodynamic properties of composites based on PTFE and various types of fillers. The results of the study show that complex filling in a certain combination provides a high degree of interaction between the polymer and the filler, thereby significantly improving the properties of PTFE-based composites. [ABSTRACT FROM AUTHOR]

Residual stress in layered composites significantly affects their mechanical properties. One of the most important tasks in the sphere of experimental mechanics is the development of effective methods for the accurate determination of residual stress values. This paper describes a modified destructive testing method implemented through layer-by-layer stitching. It differs from previous analogous methods by the use of electronic speckle pattern interferometry to measure the deformation response of a given sample. The interpretation of the initial experimental data in “stress terms” was carried out based on modeling through the use of the finite element method (FEM). [ABSTRACT FROM AUTHOR]

The machining of FRP composites has posed a serious challenge to industry and academia alike as far as the sub-surface damage is concerned caused by fiber-matrix debonding. Proper prediction of sub-surface damage is thus essential for different fiber orientations and fiber-matrix bonding. A Cohesive Zone Modeling (CZM) of the fiber-matrix debonding leading to interfacial separation is presented in this paper. The cohesive bonding strength existing between the fiber and matrix increases with increased separation, reaches a maximum value before causing permanent debonding when the cohesive strength between the interfaces vanishes. An effort is made to implement the Cohesive Zone Model (CZM) and to ascertain the extent of debonding below the trim plane at fiber failure. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The effect of abrasive particle size on the wear behavior of the SiC particle-reinforced aluminium composites produced by liquid metallurgy was investigated under different sizes of SiC grits at a fixed speed. The results show that the wear loss of composite was considerably lower than that of aluminium alloy. The wear loss increased linearly with sliding distance for both materials, but indicating a considerable difference. It increased with increasing SiC abrasive particles. Moreover, SEM examination indicates that abrasive wear observed for the matrix alloy. The depth of wear grooves decreased with decreasing the abrasive particle size and load. For the composites, wear surfaces were found to be a quite smooth indicating that no abrasive grooves appeared. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, statistical continuum mechanics modeling is applied to predict the elastic mechanical properties of an anisotropic Al-SiC composite. Two-point statistics are measured on vertical metallographic planes in three-dimensional microstructures. As a result of anisotropy the correlation functions are orientation dependent. Longitudinal and transverse elastic moduli are calculated for two samples with different PSR and clustering, and the results are compared with upper and lower bound and experimental data. It’s observed that the theoretical results are in good agreement with experimental data and two-point statistics significantly contribute to the estimation of the elastic modulus. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Spatial and temporal limitations of atomistic simulations necessitate the development of multiscale methodologies that link atomic and continuum scales. In this paper, a hierarchical multiscale model is presented to study the thermomechanical behavior of carbon nanotube (CNT) based composites. The method explicitly accounts for the behavior of nanoscale interfaces existing between the matrix and CNT. Molecular dynamics simulations based on Tersoff-Brenner potential are employed to study the interfaces in CNT based composites, while finite element method simulates macro behavior with the link provided by cohesive zone model parameters. The multiscale model is used to study the effect of interface strength on stiffness of the composite. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In sheet forming, the creation of wrinkles in the flange area of the blank commonly occurs. When diaphragm forming aligned-fiber-reinforced thermoplastic composites, observations reveal that the wrinkles tend to occur at angles oriented at forty-five degrees to the axis of the fibers. Intuition suggests that this is related to shear, but this may be misleading. The results of a stress-analysis and buckling analysis of this flange wrinkling problem are discussed. The forming of the thermoplastic sheets occurs at elevated temperatures and the sheet is essentially inextensible in the fiber direction. This leads to high anisotropy ratios of in-plane stiffness properties. The out-of-plane bending of the sheet will be strongly influenced by the presence of polymeric diaphragms. To investigate the buckling problem for this forming situation, a finite-difference formulation was developed. The solution revealed that only when one considers the combined effect of the thermoplastic composite and the polymeric diaphragms does the analysis predict the observed forty-five degree buckles. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The scope of the article is to present a highlight on the most recent and contemporary publications in the field of hybrid materials, which are composed of polysaccharides for the biomedical applications, which are mainly targeted to the field like theranostics, biosensors, actuators, and tissue engineering. Noteworthy discussion presented in this article will focus on the peculiar composite materials based on biological substrates like cellulose and chitin/CS, apart from these biological compounds a focus is also made on the multi-structural substrates to discuss the wide domain of its pros and cons relating to its application. Further, a shadowing glimpse on the use of liquid crystals-based materials as a bio-material substrates is presented in the subsequent section of this, most notably liquid crystalline nanocellulose has been drawn to discuss its effects within the field of scaffolding for tissue engineering. The functionality of Polysaccharides have also been used extensively in the last few decades as the purpose for effective colloidal stabilizers, agents which can increase biocompatibility, supplanting the chemical functionality to nanostructures, namely inorganic nanomaterials such as carbon nanotubes, quantum dots (QDs), gold nanoparticles (AuNPs), and iron oxide (Fe3O4) nanoparticles (NPs). These stoichiometry combinations had led to the development of precise most advanced hybrid materials which is composed mainly of extensively of two components, an organic(Carbonic Substrate) and an inorganic (Non-Carbonic Substrate) that has imparted substantial impact in several research fields, including in the material sciences and foremost in the fields of biomedical applications. [ABSTRACT FROM AUTHOR]

The calculation of elastic stresses generated by an acoustic wave in a plane layer is performed with the aid of the transfer matrix method. The elastic stress transfer matrix is found by the method of polynomials of principal minors. The components of the stress tensor of the crystal layer under conditions of six-beam diffraction of elastic waves are calculated. Conditions for the resonance of acoustic stresses are considered. [ABSTRACT FROM AUTHOR]

Fiber-optic strain sensors (FOSS) perfectly suit for organizing a measuring system of polymer composite materials (PCM) due to small dimensions, measurement accuracy, and the possibility of both placing optical fibers on the surface of the object under study and embedding them into the structure of a composite material. One of the main problems arising in the evaluation of the mechanical state of a structure using optical fibers is the correspondence of the measured strain in the optical fiber to the actual strain in the composite material. In this study, the efficiency of strain transfer from the initial material to the optical fiber placed on the surface or embedded in the PCM structure at various ratios of the mechanical properties of composite materials to the optical fiber properties are investigated. The discrepancy zone of strains in the optical fiber and in the initial material is estimated. For optical fibers placed on the surface of the material, the issue of gluing of the optical fiber along its length is considered. [ABSTRACT FROM AUTHOR]

On the basis of the results of the conducted experiments it was shown that the behavior of a cross-ply unidirectional fibrous composite under tension and compression conditions differs significantly. It is argued that this difference is due to the fact that, when the [ +45° / -45° ] 2s specimens are under tension, the fibers of the composite are under shear stresses and tension by normal stresses in the transverse direction. Under compression conditions, the sign of the shear stresses changes, and in the transverse direction the fibers are under compression by normal stresses. When cyclic compression with a maximum stress in a cycle is equal to the tensile stress, higher residual strains are formed in the composite, and the secant modulus of elasticity is lower than under tension. This effect also occurs under tension-compression, when the hysteresis loops are shifted to the region of negative residual strain. [ABSTRACT FROM AUTHOR]

New materials with a multilevel hierarchical structure, with specified strength properties, require a regular study of the stability of their state. For this purpose, a new method for modeling acoustic monitoring of a block-layered elastic medium with several inclusions of different physical-mechanical hierarchical structures has been developed. An iterative process of solving the direct problem for the case of acoustic field penetrating three hierarchical inclusions of the l-th, m-th and s-th ranks based on the use of 2D integro-differential equations is developed. The degree of hierarchy of inclusions is determined by the values of their ranks, which can be different. The results of the study demonstrate that hierarchical inclusions are located in different layers, one on top of the other: the top is abnormally plastic, the second is anomalously elastic and the third is abnormally plastic. The degree of filling of each rank with inclusions for all the three hierarchical inclusions may be different. The simulation results can be used for monitoring studies of the stability of structures of a complex hierarchical arrangement under various mechanical influences. [ABSTRACT FROM AUTHOR]

The addition of colloidal shear thickening fluids (STFs) to Kevlar fabrics has been shown to enhance the ballistic penetration resistance of the fabric, under conditions of low velocities and small target sizes. It is believed that this improvement in ballistic properties is related to the resistance of the STF to deformation at high strain rates, since the addition of Newtonian fluids to Kevlar fabric does not improve ballistic performance. However, the precise role of the STF, and its rheological properties, in the ballistic defeat process are not known. In this study, ballistic and rheological experiments are performed to determine the effect of fluid viscosity, particle loadings, and particle size and shape on the behavior of STF-Kevlar composites. These results will be help to determine which rheological parameters are most critical to achieving enhanced composite properties. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Short fiber reinforced polymer composite systems are often represented by the application of orientation tensors. These orientation tensors, along with the required closures, capture the stochastic nature of concentrated fiber suspensions in a compact form suitable for numerical computation and make it possible to evaluate fiber orientation states during complex polymer composite melt flow simulations. Recent research on fitted closures has provided improved approximations of the fourth-order orientation tensor in simple flow fields, but has not addressed the need for using higher-order tensors during fiber orientation simulations. The accuracy of closures is investigated using a Fourier series expansion of the fiber distribution function, and reconstructing the distribution function from the orientation tensors. It is demonstrated that fourth-order orientation tensors are not sufficient to represent the higher-order information contained in distribution functions typical of polymer processing applications. In addition, evolution simulations of the fourth-order orientation tensor that employ the sixth-order hybrid and quadratic closures illustrate that improved reconstructions of the distribution function are possible. For the case of concentrated suspensions, a recently developed sixth-order fitted closure is shown to yield a more accurate representation of the distribution function than any of the existing closures for select flow fields. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The morphology and rheology of carbon nanofiber suspensions is studied. Untreated and acid-treated vapor-grown carbon nanofibers are dispersed in 90wt% glycerol water solutions. Microscopy analysis shows that the suspensions of the untreated fibers are poorly dispersed, containing some dispersed nanofibers, but also un-dispersed nanofiber clumps that interact during flow to form continuous networks. In contrast, the treated fibers are observed to be well-dispersed, and subsequent sonication further disperses the nanofibers, but with the cost of greatly shortening the nanofibers. The rheology of the CNF/glycerol-water suspensions is found to be highly non-Newtonian both in shear and extensional flows, with strong dependence on the dispersion, particle length, and concentration of the CNFs. We have developed kinetic theory-based models for the carbon nanofiber suspensions from SEM measurements of their morphology, and through these models deduce the bulk rheological properties of the composite systems from the microstructural SEM measurements. The rheology and morphology of nanofiber suspensions are related by identifying morphology of the suspensions with the assumptions of the elastic and rigid dumbbell constitutive models. Of those investigated, the elastic dumbbell model with anisotropic hydrodynamic drag is the most successful, quantitatively predicting the strongly non-Newtonian viscoelastic behavior of the composite system that we observe in our experiments. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Two types of nanoparticles are studied: carbon nanofibers and nanoclays. These nanoparticles are incorporated into a polystyrene matrix using different techniques. For the carbon nanofiber/PS composite, solvent casting assisted with sonication and melt compounding methods are used. For nanoclay/PS system, exfoliated and intercalated composites are prepared using in-situ polymerization and melt compounding methods, respectively. Dispersion of these nanoparticles in the PS matrix is studied using TEM, SEM and XRD. Rheological characterization of these composites is studied using the Rheometrics Mechanical Spectrometer (RMS800) for shear rheology and Rheometrics Melt Extensiometer (RME) for extensional rheology. Effects of the nanoparticle concentration and dispersion methods on the rheology are studied. The morphology of the composites is studied after the samples have been deformed in the rheometers at certain stage. The orientation of the nanoparticles is quantified based on TEM micrographs. Models are developed to relate the rheology the rheology of nanoparticle/polymer composites to particle concentration, orientation, and length; these model predictions are compared with our experimentak measurements. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Trellis shear is the main deformation mode in the thermo-stamping process of woven fabric composites. To model the shear properties of woven fabrics analytically, the equilibrium equation of the unit cell of a 4-harness satin weave glass/polypropylene woven fabric is studied. Frictional resistance moment and lateral compaction resistance moment are then predicted by studying the geometry of the unit cell. Then the model is used to predict the load versus shear angle curves in the picture frame test to reduce or eliminate the test itself. A parametric study is carried out to determine the sensitivity of the friction coefficient. To validate the model, picture-frame experimental results are presented. A very close correlation is observed between the model predictions and the experimental results. Results of plain weave fabrics are included to show the analytical model’s ability to predict the effect of weave pattern. Results from an international benchmark testing are also presented to help establish the test standards for experimental characterization of the shear properties of woven fabrics in the thermo-stamping process. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Over the years several methods have been proposed for the determination of the effective elastic properties of particle reinforced composites. The material microstructures used in the present analysis is a real microstructure and a numerically generated microstructure. X-ray microtomography is used to determine the material microstructure and with this method the interior microstructure is determined in a non-destructive way. Using the commercially available equipment, SkyScan 1072, the maximum resolution is approximately 5 microns. The data obtained from the tomographic examination is used to generate three-dimensional finite element models of the microstructure. The models contain a large number of elements, up to 1 million, and are solved iteratively using an element-by-element formalism. Models containing 100 particles have been statistically generated and the material properties of each particle is assigned using a Gaussian distribution of the properties. Various distributions have been used to determine how the variation of particle properties influences the effective elastic properties. From this examination it was found that the larger the variation of the particle properties is the softer the composite material gets. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Ongoing work aims to relate microstructural properties of Al2O3-SiCw composites such as whisker orientation and size distributions to the macroscopically measured electrical properties of the composite. The tools of the study include newly developed stereological techniques, impedance spectroscopy and Monte Carlo simulations. The key results will relate the microstructure to electrical properties through theoretically or experimentally determined percolation properties of the composite. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The tensile modulus of individual nanotubes and nanotube-polypropylene composites has been determined using molecular dynamics simulations. Simulations of individual single-walled carbon nanotubes showed that their tensile modulus was dependent on the tube structure and the diameter if the diameter was below 1,6 nm. The tensile modulus was determined for an infinite single-walled carbon nanotube embedded in an amorphous polypropylene matrix and for a finite and capped single-walled carbon nanotube embedded in a polypropylene matrix. For the infinite nanotube-polypropylene system the modulus was found to correspond to the one given by the Voigt approximation. For the finite nanotube-polypropylene system the reinforcing effect of the nanotube was not very pronounced. A pull out simulation showed that the length of the nanotube in the simulation was much smaller than the critical length and hence no load transfer between the nanotube and the matrix existed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Particle and fiber reinforced ductile matrix composites are subject to a number of damage modes on the microscale, one of which is ductile failure of the matrix. In the present study Finite Element based micromechanical models that employ unit cells with appropriate material descriptions for the matrix are discussed in view on investigating this behavior. Among the most important continuum models capable of describing the loss of stiffness and strength of ductile materials due to void nucleation and growth are the Gurson and Rousselier models. Alternatively, element elimination algorithms controlled by ductile damage indicators can be used to model ductile cracks. All of these methods have the drawback of showing a marked mesh dependence of the solutions, which can, however, be resolved by regularization schemes. These involve, for example, the enrichment of the formulation by higher order gradients or the use of nonlocal averaging, both of which introduce an absolute length scale into the material description. Averaging-based nonlocal versions of the Gurson and Rousselier models and of the ductile damage indicator were implemented into the Finite Element code ABAQUS/Standard in order to provide a capability for studying ductile damage effects in particle and fiber reinforced MMCs. Applications of such descriptions to fiber reinforced composites are presented and discussed in terms of the microscopic and overall responses to mechanical loading. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Ductile (or plastic) damage often occurs during some metal forming processes caused by large plastic flow localisation. Accordingly, it is primordial for numerical tools used to simulate these processes to use fully coupled constitutive equations accounting for both isotropic and kinematics hardening and damage. In this work, fully coupled constitutive equations accounting for both combined isotropic and kinematic hardening with thermal effects as well as the ductile damage are used with the general purpose Finite Element code ABAQUS. First, the fully coupled constitutive equations in the framework of Continuum Damage Mechanics are presented. The associated numerical aspects are then presented using an implicit integration scheme for local time integration of the fully coupled constitutive equations and a dynamic explicit scheme to solve the associated initial and boundary value problem. This numerical approach is applied to the virtual forming of an axisymmetric wheel made in commercial steel. Starting from a cylindrical billet, the wheel is forged using rigid tools. The central hole of the billet is obtained with blanking operation. Finally the deburring operation is used to cut off the burr resulting from the forging operation. Both the temperature and the damage fields are carefully analysed for each forming stage. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Pushing a conical die into a pipe, a forming process also known as ‘flaring’, is a way of changing the shape of a thin cylindrical tube into that of a conical shell. Interest in predicting the forming limits for this specific process motivated the present study, in which experiments and Finite Element simulations were employed for the identification of two limiting mechanisms: (a) diffuse necking caused by local loss of material stability at the free, expanding end of the pipe, and (b) loss of global stability due to elasto-plastic ‘Concertina’ buckling of the straight pipe part. The former mechanism leads to the formation of periodic necks and subsequent failure by strain localization and rupture, while the latter mechanism is characterized by a periodic buckling pattern that is similar to the one observed in typical crash elements. Whether collapse or rupture is the limiting factor depends on geometrical parameters and material parameters, such as, for example, the hardening exponent in the Ludwik law. There are some publications of analytical considerations of the flaring process, describing the load displacement behavior of the stamp and the development of plastic deformations in the tube. However, the aspect of material and structural instability requires a deeper insight into the problem, which is provided by the experimental results and the numerical studies presented here. It appears to be important to take the tridimensionality of the stress and strain states into account when reliable predictions of necking and rupture limits are to be made. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]