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A micro-meso-macro finite element approach has been developed for simulating the macro-scale damage coupled deformation in a particulate polymer composite (PPC) based structure under tension. A damage model for the PPC structure was developed to define the debonding damage behavior of the structure. The computational results determined in our previous studies by using finite element meso-cell modeling technique were used as the input parameters of the damage model and definition of the constitutive behavior of PPC. A user-defined subroutine VUMAT describing the damage-coupled constitutive behaviour of PPC for defining the material properties of the finite elements for the structure was then built and incorporated into the ABAQUS finite element code. A case example has been given to demonstrate the proposed approach. The macroscale damage process in the simulated component was found to be reasonable.

The damage effects of water sorption on the mechanical properties of the hydroxyapatite particle reinforced Bis-GMA/TEGDMA copolymer (HA/Bis-GMA/TEGDMA) have been predicted using 3D finite cell models. The plasticizer effect on the polymer matrix was considered as a variation of its Young's modulus. Three different cell models were used to determine the influence of varying particle contents, interphase strength and moisture concentration on the debonding damage. The stress distribution pattern has been examined and the stress transfer mode clarified. The Young's modulus and fracture strength of the Bis-GMA/TEGDMA composite were also predicted using the model with and without consideration of the damage. The former results with consideration of the debonding damage are in good agreement with existing literature experimental data. The shielding effect of our proposed model and an alternative approach were discussed. The FCC cell model has also been extended to predict the critical load for the damaged and the undamaged composite subject to the 3-point flexural test.

The elasto-plastic constitutive equation accounting for isotropic hardening coupled with material damage has been implemented in the finite element code ABAQUS. A damage variable, which was defined in meso-scale, was used to reveal the effects of micro-defects within the material. With an explicit integration scheme, deep drawing of a mild steel square cup was simulated using the ABAQUS with a specially designed VUMAT subroutine. The three-dimensional brick element was adopted to build-up the finite element model, and the contact and friction between the blank and tool were taken into consideration. The forming process of deep drawing is a non-proportional loading one, so that the accumulated damage state variable depends on the strain path, or in other words, the loading history. The damage evolution and the wrinkle formation under the influences of Coulomb friction and the blank holding force were analyzed and discussed. Experiments have been conducted to investigate the effect of blank holding force on wrinkling, and determine the position of crack initiation. Experimental results are in good agreement with the predicted ones.

This paper presents an investigation on forming limits of tailor-welded blanks (TWBs) made of 5754-O aluminum sheets using both experimental and numerical approaches. TWBs may be composed of two or more welded flat metal sheets of different thicknesses, shapes, or mechanical properties. Due to the existence of weldment and the individual configurations of base blanks, TWBs should be considered as heterogeneous in its structure. The mechanical properties of those base metals and weld metal required for the simulation were measured individually. With the aid of the acquired data, finite element simulations for analyzing the forming process of TWBs were carried out using a general purpose finite element package, LS-DYNA. A localized necking criterion based on the vertex theory was employed to predict forming limit strains and failure locations of the aluminum TWBs. The theoretical predictions were satisfactorily validated with those obtained from the experiments.

This paper presents the application of anisotropic damage theory to the study of forming limit diagram of Al2024T3 aluminum alloy sheet. In the prediction of limiting strains of the aluminum sheet structure, a finite element cell model has been constructed. The cell model consists of two phases, the aluminum alloy matrix and the intermetallic cluster. The material behavior of the aluminum alloy matrix is described with a fully coupled elasto-plastic damage constitutive equation. The intermetallic cluster is assumed to be elastic and brittle. By varying the stretching ratio, the limiting strains of the sheet under biaxial stretching have been predicted by using the necking criterion proposed. The prediction is in good agreement with the experimental findings. Moreover, the finite element cell model can provide information for understanding the microscopic damage mechanism of the aluminum alloy. Over-estimation of the limit strains may result if the effect of material damage is ignored in the sheet metal forming study.

A three-dimensional finite element analysis was conducted to evaluate the feasibility of predicting the flexural properties of hydroxyapatite-reinforced poly-L-lactide acid (HA/PLLA) biocomposite using three different schemes. The scheme 1, originated from a beam analysis, was used to determine the flexural modulus analytically while the scheme 2 and 3 were designed to have different loading and boundary conditions using a finite element cell modeling approach. An empirical approach using Chow’s formula and experimental data were used for comparison with the predicted results. In order to reduce the computational time and save the storage space involved in determining the effect of varying particle volume fractions on the flexural properties of HA/PLLA, a superelement technique was applied. The results using the scheme 3 and the Chow’s formula were found to be in reasonable agreement with experimental results over the range of particle volume fraction. In addition to the Chow’s formula, local stress distribution and the failure processes in HA/PLLA were simulated using the finite element technique.

The knowledge of biomedical implants ranging from drug delivery devices to tissue engineering and based on bioresorbable polymer composites is increasing, but the study of the crystallization kinetics of these kinds of composites is seldom a concern. The focus of our experimental research was the nonisothermal-crystallization behavior of poly(3-hydroxybutyrate) (PHB)/hydroxyapatite (HA) composites, which was monitored by means of differential scanning calorimetry at different cooling rates. Various macrokinetic models were applied to describe the process of nonisothermal crystallization. The results showed that the modified Avrami model and Mo's approach could describe the nonisothermal crystallization of the composites very well, but the Ozawa analysis alone was thought to be rather inapplicable. The values of the half-time and kinetic crystallizability showed that the crystallization rate increased with increasing cooling rates for both PHB and the composites. The HA particles served as additional nucleation sites, and low levels of HA resulted in dramatic increases in the crystallization rate with respect to pure PHB; however, high HA contents (> 20 wt %) clearly retarded the growth process. The activation energy for nonisothermal crystallization was evaluated with the Kissinger method and was found to vary with the incorporation of HA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5388–5395, 2006

A three-dimensional finite element analysis was conducted to simulate the effects of the varying material parameters on the contraction behaviors of a muscle-tendon complex using an active finite element method. The material behavior of the skeletal muscle was assumed to be orthotropic and the muscle model consists of two parts: the active and the passive parts. An active finite element method was then used for accommodating both the active and passive behaviors of the muscle into the muscle model. In this active-passive muscle model, the active component is governed by an activation level, a time period, a muscle sensitivity parameter and a strain rate. The material property of the passive component was assumed to be viscoelastic and the tendon is assumed to be linear elastic. The effects of activation amplitude and viscoelastic material parameters on the active, passive and total force-length relationship of the cat muscle under isometric contraction were predicted. The predicted results were found to be close to the experimental data reported in the available literature. Hence, the active-passive muscle model was extended to simulate the stress distribution of the cat muscle subject to shortening contraction and different activation amplitude. By varying the magnitude of the material parameters, different muscle behaviors could be generated. The proposed active finite element method lays a good foundation for simulation of human musculoskeletal motion.

International Symposium on Macro-, Meso-, Micro- and Nano-Mechanics of Materials, MM2003, Hong Kong, 8-10 December 2003

Wear of ultra-high molecular weight polyethylene (UHMWPE) and its composites is one of the main obstacles that limit the longevity of total joint replacements. Compression molded UHMWPE/quartz composites with organosiloxane as a cross-linking agent for UHMWPE matrix, were tested in nanoindentation and nanowear. The nanomechanical properties of the composite were examined in the light of nanoindentation experiments performed with a diamond tip of nominal radius of curvature of about 150 nm under conditions of various contact loads. Results from nanowear tests show that, in addition to the nanohardness and elastic modulus, the crosslinking procedure has the most pronounced effect on the tribological properties and at 0.5 phr organosiloxane, composites reache their maximum nanowear resistance. These findings are in agreement with the results of conventional mechanical and wear tests performed on these materials.

A three-dimensional finite element cell modeling technique has been applied to predict the particle–matrix debonding process of particulate polymer composite (PPC) subject to simple shear loading. The particle–matrix debonding in PPC has been simulated by using two different debonding criteria: stress-based and strain-based. The stress-based debonding criterion uses the hydrostatic tensile stress as a critical stress while the strain-based one uses the equivalent plastic strain at failure as a critical factor for element failure. In this analysis, glass beads-reinforced polyphenylene oxide (GB/PPO) has been used for verification of the predicted results. As compared with the results from scanning electron microscopy (SEM) based in situ simple shear test of GB/PPO composite, the model with the stress-based criterion is much more appropriate for simulation of the shear damage process. The importance of selecting an appropriate debonding criterion for achieving correct simulation results could be revealed. The essential information like the threshold strain for initiation of shear damage could then be acquired from the model with the verified stress-based debonding criterion.

In this paper, the deformation behavior of the SiC reinforced aluminum matrix composite in laser forming was investigated. A 2KW Nd:YAG laser was used to deform the composite at different laser powers, scanning speeds, numbers of irradiation passes and beam diameters. It was found that the bending angle increases with an increase in laser power, and a decrease in scanning speed and beam diameter. A relatively linear relationship between bending angle and number of irradiation passes was observed, and the effect of microstructural changes on the deformation behavior was discussed. An analytical model based on the Vollertsen's two-layer model was developed to predict the bending angle of the composite. The trends of the predictions are in good agreement with the experimental results. The effect of reinforcements on deformation behavior of the composite was further theoretically investigated. By modeling the changes of physical, thermal and mechanical properties including yield stress, elastic modulus, surface absorption coefficient and thermal conductivity of the material incorporated with SiC particles, the effect of reinforcement on laser bending angle was analyzed, and it was found that it would result in a larger bending angle. The significance of the findings will be discussed in the paper.

A microscopic investigation has been made on the shearing of one leaded and two lead-free solders by using an in situ SEM method. A shear lap joint specimen is designed and fabricated to accommodate a thin layer of solder alloy between copper strips. A non-contact method that measures strains in a very narrow area in the solder was applied. A laser grid was also used on the copper strip for measuring the back-face strain. Simultaneously micrographs at various stages were also taken. Where in situ measurements and micrographs are recorded they can reveal the continual development of damage and fracture mechanisms consistent with observations generated by low-cycle fatigue loading. This means that the shear test can be used as an alternative test to fatigue loading tests. By comparison, two lead-free solder specimens showed much smaller elongation to failure than the leaded solder, although all specimens showed similar sequence of events leading to final failure, including the boundary layer fracture phenomenon. The back-face strain indicator for the formation of a macro crack is due to the shifting of high stress concentration area from the joint-edge region to outside the joint region as revealed by a damage-coupled finite element procedure. The procedure also provides an estimate on the critical back-face strain.

This study descripts processing of biphasic calcium-phosphate (BCP) and poly-L-lactide (PLLA) biocomposite implant material. The composite was obtained by mixing completely dissolved PLLA with granules of high crystalline BCP and was compacted by hot pressing using cylindrical dies at 450 K temperature and 98.1 MPa pressure, for 30 and 60 minutes. Wide-angle Xray structural (WAXS) analyses of BCP, PLLA and BCP/PLLA composite blocks were made followed by calorimetric (DSC) tests in the 320-520 K temperature range. Compression tests revealed that Young’s modulus and compressive strength of the composite increased with extended hot pressing time and were found to be within the bounds of the cortical bone values.

A three-dimensional finite-element meso-cell model has been designed and constructed to predict initiation of the particle/polymer matrix debonding damage and non-linear stress–strain relation of particulate polymer composites (PPC). The meso-cell model consists of a micro-particle, an interface, and a matrix. The initiation of the debonding damage process has been predicted on the basis of a tensile criterion. An experimental investigation has been made on glass beads reinforced polyphenylene oxides for verification of the meso-cell model and the meso-mechanical finite-element technique. In situ scanning electron microscopy has been adopted to study the particle–matrix debonding process in real time under tensile deformation. The predicted results have been found to be in good agreement with the experimental results. The results of the in situ microscopic test also verify the correctness of the meso-cell model.

A double-variable damage model was introduced into the constitutive equations to demonstrate the effect of the material damage for the isotropic elastic, hardening, and damage states, and for the isothermal process. The shear damage variable D s and the bulk damage variable D b may be, respectively, used to describe the effect of shear damage and bulk damage for material properties without the superfluous constraint, D b=D s, that is found in the single-variable damage model. The double-variable damage model was implemented to form the finite element code for analyzing the effect of shear damage and bulk damage. In this article, two numerical simulation examples were completed to model the whole process of initiation and propagation of shear bands in an aluminum alloy. The numerical computational results are coincident with the experimental results.

A cylindrical three-phase unit-cell model was established for predicting mechanical properties of hydroxyapatite (HA)-reinforced polyetheretherketone (PEEK) biocomposite. The model consists of an elastic–brittle HA spherical particle, an elasto-plastic matrix, and a very thin interphase region between the particle and the matrix. Perfect bonding was initially assumed among three phases before occurrence of particle–matrix debonding. For simulation of the particle–matrix debonding process of HA/PEEK, a damage evolution equation was incorporated into the material properties of the interphase region. A ductile damage evolution in the matrix was also taken into account, and was treated as a criterion for the failure of the biocomposite. A user subroutine for the damage-coupled material properties for the matrix and the interphase region was built and incorporated into a finite element code named ABAQUS. The influence of interfacial adhesion on the non-linear stress–strain relation of HA/PEEK has also been simulated by varying the tensile strength of the interphase region. The strength of the interphase region in the composite could be estimated by a comparison between the predicted and experimental results. By using the unit-cell modeling technique incorporated with the stress-based debonding and the composite failure criterion and selection of appropriate interphase strength, the numerical simulation was found to be close to the experimental results from available literatures. In vivo performance of HA/PEEK as implant materials was also discussed.

This paper presents an experimental remeshing process for the large strain analysis of fine-blanking. The research is to be carried out mainly because the severe and localized deformation of fine-blanking greatly obstructs the measurement of strains. In order to solve this problem, a new experimental remeshing process was developed to measure the strain in the major deformation areas of fine-blanking. Without this newly developed process, a more intensive and practical strain analysis of fine-blanking could not have been achieved. Therefore, a study of this remeshing process, with a step increment of 20 per cent, until the total punch penetration is 80 per cent of the material's thickness, is to be performed to verify its effectiveness. Low-carbon steel sheets of JISG3101 were used to split blanks. As a consequence, findings showed that an increase in the total punch penetration will clearly induce an exponential increase in the effective strain, and the severity of deformation will be augmented with the increase in the total punch penetration.

Large deformation is a major deformation operation in many metal-forming processes, such as forging, rolling, extrusion, stamping and fine-blanking. It is difficult to study the deformation changes in these processes in a practical way, through the measurement of strains, due to the severe and localized nature of plastic deformation such as in the fine-blanking operation, where only about 30% of the punch penetration through the thickness of the material can be measured through experiment. Therefore, the large strain analysis of most metal-forming processes cannot be carried out successfully by experiments. Thus, this paper aims to present the development of an effective process of strain measurement for severe and localized plastic deformation. To validate the process, an experimental remeshing technique was adopted and applied on a tension test to measure strains in practice. As a result, it was found that, on average, only a 10% difference in effective strains was observed between the experimental findings with and without remeshing. Meanwhile, the developed process was further applied to the fine-blanking operation. Results show that the strain measurement for fine-blanking was accurate. As a conclusion, the process of experimental remeshing presented in this paper can be effectively used to measure strains in severe and localized plastic deformations.

In this study, a large deformation finite element approach for numerical analysis of the strain localization is developed based on the concept of mixed interpolation of displacement/pressure. This finite element approach is suitable for the material constitutive relation in rate form. In order to avoid oscillatory behavior and path dependence observed in some traditional stress rates, the Truesdell stress rate is employed in the integration of the constitutive equation. The corresponding consistent tangent stiffness is derived to maintain the asymptotically quadratic convergence of the Newton–Raphson iterative scheme used in the solution of the implicit equilibrium equations. To illustrate the performance of the proposed element, the numerical simulation of three example cases has been carried out and the result shows that the element is of good capability to capture strain localization especial when remeshing operation is required.

A multilevel superelement technique is applied to model the effects of circular voids on the effective elastic properties of a porous material. A twodimensional representative volume element with a circular void in its center is initially modeled by a superelement. A thin plate of porous material with a macrocircular hole in the center is constructed with this superelement. The finite element computation is then conducted to estimate the effective Young’s modulus, Poisson’s ratio, and the shear modulus of the material using the ABAQUS code for different void sizes. The values of the isotropic damage variables, DE and DG, under various degree of damage are hence determined. These values are compared with those calculated by using a conventional micromechanics damage model. A new isotropic damage model is proposed based on the results of this analysis. To demonstrate the applicability of this damage model, an example case of a notched cylindrical bar under tensile loading is investigated.

In fine-blanking processes, localized deformation is prone to cause tearing failure at the surface of shearing edges, which can influence the quality and functionality of the blanked part. In this paper, a numerical simulation of a fine-blanking process has been conducted by using a coupled thermo-mechanical finite element method. The thermal effect on the material properties has been taken into account in the simulation. On the basis of the results of the simulation, the distributions of equivalent plastic strain and stresses in a fine-blanking process have been analyzed. Moreover, examinations of metallurgical microstructure by means of optical and scanning electron microscopy have been performed. It has been observed that the grains near the shearing edge were highly distorted within a narrow shearing zone. The formation of microvoids under large shear deformation supports the argument that material damage initiates and develops around this local area during the fine-blanking process. It is suggested that tearing failure could initiate from the damaged area of the workpiece adjacent to the tool tips where cracking occurs due to excessive local tensile stress produced by fine blanking attributes and interfacial friction.

This paper presents the numerical simulation of fine-blanking using the large deformation elasto-plastic finite element method (FEM). In this simulation, the finite element mesh is re-zoned when severe element distortion occurs, in order to facilitate further computation and avoid divergence. The finite element software, ABAQUS/Standard PC version 5.8, is used. The updated Lagrangian formulation is adopted and the standard stiffness matrix and the initial stiffness matrix are presented. A precise description of the fine-blanking boundary conditions is essential to achieve a correct simulation result. Therefore, the fine-blanking process is considered as a contact problem and the corner radii of punch and die are taken into account. This study is one of the first attempts to simulate the complete fine-blanking process.

Glass beads were modified with vinyl triethoxyl silane (VTES) followed by in situ copolymerization with styrene (St) and by direct modification with St via in situ polymerization. It was seen that the presence of glass beads did not inhibit the polymerization of St, and FT-IR spectra confirmed that the polystyrene (PS) molecules were grafted on the surfaces of glass beads. When the modified glass beads were filled in a poly(phenylene oxide) (PPO) matrix, the PS segments on the surfaces of glass beads clearly improved compatibility and enhanced interfacial adhesion between the PPO matrix and glass beads, which was responsible for the slightly increased glass transition temperature of the PPO component. Surface modifications, especially by in situ copolymerization of VTES and St, increased significantly notch impact strengths and marginal stiffness and tensile strengths of PPO/glass bead composites.

Necking is a strain localization phenomenon that can cause catastrophic fracture in metal forming. Therefore, the prediction of necking is important. In the present work, an elasto-plastic constitutive equation accounting for isotropic hardening coupled with damage is implemented in the finite element code ABAQUS. A damage variable, that provides a mesoscopic description of material degradation, is used to quantify the degree of damage due to excessive strain. Using the implicit integration scheme, a cylindrical rod loaded under uniaxial tension is successfully simulated by the finite element code with a specially designed user-defined material subroutine (UMAT). In addition, the distribution of damage caused by the deformation is computed.

Two kinds of shear tests, the Iosipescu shear test and the torsion test were used for studying the shear damage of aluminium alloy 2024T3. In the Iosipescu test, a specially designed shear fixture was used. The Iosipescu specimen was deformed under simple shear. After shear fracture, the Iosipescu specimen was polished and etched for microscopic examination. In the torsion test, the curve surface Moire method was applied to determine the shear damage variable of the aluminium alloy. The results of the microscopic examination show that rotation and distortion of grains, breakage of particles and microcracks occurred in the shear band. It can be concluded that the damage produced by shearing can degenerate the mechanical properties of the aluminium alloy. In addition, the level of the shear damage can be quantified by the shear damage variable D G that can be measured by the proposed load-and-unload torsion test.

Magnetic materials are very popular for high frequency power conversion and their operation frequencies are usually in the region of kHz. This paper examines the processing of the ferrites, and the modelling of the magnetic core loss for high frequency operation. The proposed method is a dynamic model which considers the eddy current, hysteresis and anomalous losses. The loss analysis is based on Preisach modelling. The applications of the model, such as dynamic BH simulation, initial magnetisation curve simulation and major loop simulation, are discussed. It is found that the core loss has frequency and flux density dependent elements. Separation techniques were used to examine each of the loss components and their analytical solutions. The predicted results agree very well with the experimental results. It is confirmed that the proposed techniques can be used for high frequency magnetic design. An optimisation method by considering the winding loss and equivalent circuit is used to investigate the situation of the minimisation of the total loss of the magnetic coils.

An investigation has been made on the formation and propagation of shear band in fine-blanking process. Examinations by optical microscopy and SEM reveal that the highly elongated narrow subgrains extended in the shear direction within the band, while in the other regions, fine equiaxed cell were observed. Both the presence of white-etching trace and the distribution of surface microhardness in the shear band reveal that fine-blanking process involves large deformation and high temperature. Although strain localization is severe in the shear band, especially in the area adjacent to the edges of the punch and die, no cracking has been observed. It is indicated that high hydrostatic pressure, built up by specially designed fine-blanking fixture, plays a significant role to suppress the generation of fracture zones in the sheared surface. On the basis of present findings, the mechanisms of the formation and propagation of shear band in fine-blanking are discussed.

In this study, randomly oriented in situ composites based on liquid-crystalline polymers (LCPs) were prepared by thermal compression moulding. The LCP employed was a semi-flexible liquid-crystalline copolyesteramide with 30 mol% of p-aminobenzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). The matrices were poly(butylene terephthalate) (PBT) and polyamide 66 (PA66). The rheological properties, compatibility and morphological structures of these in situ composites were investigated. The results showed that PA66-LCP and PBT–LCP component pairs of the composites are miscible in the molten state, but partially compatible in the solid state. The ratios of viscosity, λ1 = ηLCP/ηPA66 and λ2 = ηLCP/ηPBT, are all greater than 1.0. However, the melt viscosity of the LCP/PBT and LCP/PA66 blend is much lower than that of PBT and PA66, and it decreases markedly with increasing LCP content. When the LCP/PA66 or LCP/PBT blends are compression moulded, the LCP/PA66 or LCP/PBT melts and flows easily due to their low viscosity, and the LCP phases in the melts deform easily along the flow directions, which are random. It leads to uniformly dispersed LCP micro-fibres randomly orientation in the thermoplastic matrix due to the compatibility between the blending components. © 2003 Society of Chemical Industry

The hydroxyapatite/graphene (HAP/Gr) composite was electrodeposited on Ti using the electrophoretic deposition process to obtain uniform bioactive coating with improved mechanical strength and favorable corrosion stability in simulated body fluid (SBF). Incorporation of Gr was verified by Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron analysis. The HAP/Gr composite coating exhibited reduced surface cracks, nearly double the hardness, and elastic modulus increased by almost 50% compared to pure HAP coating, as estimated by a nanoindentation test. The bioactive HAP/Gr composite coating provided a newly formed apatite layer in SBF with enhanced corrosion stability, as evidenced by electrochemical impedance spectroscopy. The thermal stability of the HAP/Gr coating was improved in comparison to the pure HAP coating, and the Ca/P ratio was closer to the stoichiometric value. No antibacterial activity against Staphylococcus aureus or Escherichia coli could be verified. The HAP/Gr composite coating was classified as non-cytotoxic when tested against healthy peripheral blood mononuclear cells (PBMC). (C) 2014 Elsevier B.V. All rights reserved.

An experimental study has been performed to investigate the shear damage mechanism of aluminium alloy 2024T3 by an in-situ single shear test using scanning electron microscope (SEM). The observation of microstructural change and measurement of shear strain in mesoscale have been undertaken simultaneously. Hence, the shear damage mechanism and the shear stress–strain curve have been obtained. By measuring the deformed grid of a laser-marked sample, the shear strain distribution has also been found. On the basis of the experimental results, the relation between the shear damage evolution and the corresponding shear stress–strain state have also been obtained. It has been observed that two groups of microshear bands were formed in the shear process. When the shear stress is close to the shear strength of the alloy, slipping within the microshear bands occurs. The causes of macro-shear band formation and the interrelation and interaction among different types of microdefects are also discussed.

The tensile, impact and bending properties of calcium carbonate (CaCO3) filled acrylonitrile-butadiene-styrene copolymer (ABS) composites were measured at room temperature. It was found that the tensile modulus increased nonlinearly with increasing the weight fraction φ + of the fillers, and the tensile strength and tensile fracture stress decreased gently with the increase of. The Charpy notched impact strength decreased quickly when φ≤ 10%, and then decreased gently with increasing φ. While the bending strength increased when φ≤ 10%, and then it decreased gradually with increasing φ. However, the effects of filler size and its surface treatment on these mechanical properties were insignificant. Furthermore, the Vicat softening temperature (TV) of the samples was measured at a constant loading and a temperature ramp rate. The result showed that TV increased with the addition of. It indicates that CaCO3 fillers are beneficial to improve the heat resistant properties of the resin.

This study focuses on development of a method for predicting effective elastic properties of damaged particulate polymer composites. Two damage parameters were introduced and defined by volume fraction of both the void-damage and the debonding-damage. The former parameter was determined by 3-dimensional strain measurement of damaged composite samples, while the latter were estimated from a typical experimental data of the repeatedly load-unload tensile tests. Based on M-T micro-mechanics theory, the equations for estimation of the effective elastic properties of the damaged particulate composites in response to the longitudinal true uni-axial strain were formulated The effects of two damage mechanisms and glass-bead contents on the effective elastic properties of glass bead filled polyphenylene oxide (GB/PPO) composites were investigated by this approach. The predicted results for the effective elastic modulus were close to the experimental data.

In order to achieve a more intensive understanding of the forming mechanism of the fine-blanking process, a numerical simulation has been carried out by using a mixed displacement/pressure (u/p) finite element method. According to the special requirement of the fine-blanking technique, the major process attributes, such as the vee-ring, the ejector and the edge radii of tools, have been taken into account in the finite element model. The punch–die clearance was set to 0.5% of the thickness of the workpiece. To verify the effectiveness of the simulation, the equivalent strain on the sheared surface of a SS400 steel specimen has been determined experimentally. The experimental values of the equivalent strain have been estimated by measuring the relative displacements of the local grids pre-etched on the meridian plane of the specimen. The results of the finite element simulation are in proper agreement with the experimental findings. The distributions of the shear stress and the equivalent plastic strain have been computed for discussion. Moreover, a diagram of the blanking force versus the punch penetration has also been constructed. In order to investigate the fracture mechanism in the fine-blanking process, the concept of damage mechanics has been applied. By using a void growth model, the evolution of damage at different stages of the fine-blanking has been evaluated. It has been realized that the compressive hydrostatic stress built up by the fine-blanking fixture plays an important role to suppress the initiation of macrocracks.

Increasingly more applications require ceramic parts or components with good surface integrity. This paper attempts to study the surface integrity of electro-discharge machined engineering ceramics and their surface modification by ultrasonic polishing. Flexural strength is used for evaluating the effect of the two machining processes on the surfaces of the machined specimens. The distributions of the strength data are further analyzed by the Weibull statistical method to give quantitative measures of the surface integrity of the machined specimens.

A piece of SiC whisker-reinforced aluminium composite sheet has been deformed by using a computer-controlled superplastic bulge tester under a constant strain rate of 0.2 s −1 and an operation temperature at 808 K. The components of fracture strain have been measured from deformed grid circles pre-printed on the surface of the composite sheets. In order to predict the fracture limit of the superplastic composite induced by the initiation and growth of damage for different strain paths, a surface continuity parameter ψ s is defined to describe the damage of the material in a large plastic deformation process. The relationship between the classical damage variable D and the continuity variable ψ is derived. A continuity deterioration equation, which takes into account the stress triaxiality, has been established based on continuum damage mechanics and plasticity theory. Hence, a ductile fracture criterion is developed from the continuity deterioration equation. This fracture criterion may be used to determine the fracture strain in the whole range of possible strain ratios for a sheet metal forming process. The predicted fracture strains of the superplastic composite sheet match well with the experimental measurements.

In this study, double scalar damage variables have been used to characterize the state of isotropic damage. The damage influence tensorrelating to the double scalar damage variables of damaged material isthus formulated based on the hypothesis of stress equivalence for this model. The specific damage energy release rate is adopted to represent the thermodynamics force conjugating to the double damage variables. Based on the irreversibility laws of thermodynamics, these forceshave been formulated directly from the degradation of effective engineering elastic coefficients in stress space. The contribution of bothdilatation and distortion of material to the specific damage energy density release rate in loading process has been explained. The doublescalar damage variables of isotropic solid material with penny-shape cracks and spherical voids randomly distributed have been determined on the basis of the micro-mechanics theory, respectively. In addition, the damage influence tensor and the specific damage energy release rate were obtained by using the experimental results of pre-strained aluminum alloy 2024T3 specimens under uni-axial tension tests.

Liquid crystalline polymer/polyamide 66 (LCP/PA66) and LCP/poly(butyl terephthalate) (LCP/PBT) blends were compounded using a Brabender Plasticorder equipped with a mixing chamber. The LCP employed was a semi-flexible liquid crystalline copolyesteramide based on 30 mol% of p-amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). The Flory-Huggins interaction parameters (χ12) of the LCP/ PA66 and LCP/PBT blends are estimated by melting point depression from DSC measurement. The results indicate that c12 values all are negative for LCP/PA66 and LCP/PBT blends, and when the LCP content in these blends is more than 10 mass%, the absolute value of χ12 decreases. Thereby, we can conclude that LCP/PA66 and LCP/PBT blends are fully miscible in the molten state, the molecular interaction between the LCP and PA66 is stronger than that between LCP and PBT. As the LCP content in LCP/PA66 and LCP/PBT blends is more than 10 mass%, the molecular interaction between LCP and matrix polymer decreases.

Ultra high molecular weight polyethylene (UHMWPE) crosslinked by organosilane was thermal compression molded. The organosilane used was the tri-ethyloxyl vinyl silane. Its gelation, melting behavior, crystallinity, mechanical and wear-resisting properties were systematically investigated. The results showed that the gel ratio of UHMWPE increases with the incorporation of organosilane. At a low content of organosilane, the melting point and crystallinity of the crosslinked UHMWPE increase, and hence the mechanical and wear-resisting properties are improved. However, at a high content of organosilane, these performances of the crosslinked UHMWPE become worse. At 0.4 phr silane, the wear resistance of crosslinked UHMWPE reaches its optimum value.

In this work, a surfactant-free emulsion polymerization method was utilized to synthesize poly(styrene-ran-methyl acrylate) (PSMA) at a styrene/(methyl acrylate) mole ratio of 75/25 with the aim to compatibilize high impact polystyrene (HIPS)/poly(lactic acid) (PLA) interface. HIPS/PLA blends with different PSMA contents were prepared. Their phase morphologies, mechanical properties, and rheological and crystallization behaviors were investigated using scanning electron microscopy, tensile tests, rotational rheometry, and differential scanning calorimetry. The rheological results showed that the complex viscosity, storage moduli, and loss moduli of PLA/HIPS blends were enhanced with increasing PSMA content. A decrease in the degree of crystallinity of PLA in PLA/HIPS blends with the addition of PSMA was observed in the differential scanning calorimetry results. It was also revealed that the addition of a small amount of PSMA can effectively improve the compatibility and thus the interfacial adhesion of the PLA/HIPS blends, thereby reducing the size of the HIPS dispersion phase. When 1 wt % of PSMA was used, compared with the PLA/HIPS blends without PSMA, the tensile strength and notched Charpy impact strength of PLA/HIPS blends were improved by 95.3% and 104.8%, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45799.

Failure of the bone-implant interface in a joint prosthesis is a main cause of implant loosening. The introduction of a bioactive substance, hydroxyapatite (HA), to a metallic bone-implant may enhance its fixation on human bone by encouraging direct bone bonding. Ti6Al4V/TiC/HA composites with a reproducible porous structure (porosity of 27% and pore size of 6-89 μm) were successfully fabricated by a rapid microwave sintering technique. This method allows the biocomposites to be fabricated in a short period of time under ambient conditions. Ti6Al4V/TiC/HA composites exhibited a compressive strength of 93 MPa, compressive modulus of 2.9 GPa and microhardness of 556 HV which are close to those of the human cortical bone. The in vitro preosteoblast MC3T3-E1 cells cultured on the Ti6Al4V/TiC/HA composite showed that the composite surface could provide a biocompatible environment for cell adhesion, proliferation and differentiation without any cytotoxic effects. This is among the first attempts to study the in vivo performance of load-bearing Ti6Al4V/TiC and Ti6Al4V/TiC/HA composites in a live rabbit. The results indicated that the Ti6Al4V/TiC/HA composite had a better bone-implant interface compared with the Ti6Al4V/TiC implant. Based on the microstructural features, the mechanical properties, and the in vitro and in vivo test results from this study, the Ti6Al4V/TiC/HA composites have the potential to be employed in load-bearing orthopedic applications.

Based on Continuum Damage Mechanics (CDM), a damage model for glass-bead-filled modified polyphenylene oxide (GB/PPO) has been proposed to describe its damage behavior at various levels of tensile strain by considering the reduction of effective loading area. Hence, an equation for prediction of effective elastic modulus of the damaged GB/PPO composites in terms of the three principal true strains was derived. The tensile properties and damage behaviors of the GB/PPO composites with different volume percentages of glass beads were investigated using standard tensile tests and load-unload tests, respectively. The addition of glass beads increases Young's modulus of PPO but has a weakening effect on its tensile strength. A maximum value of tensile work to break and tensile strain at break was found when 5 vol% of glass beads with a mean diameter of 11 μm was blended with PPO. These results were justified through microscopic examination of the fracture surfaces of the tensile specimens by using a scanning electron microscope (SEM). In-situ observations of the strain damage processes were made through the SEM equipped with a tensile stage to determine the strain at fully debonding of glass beads. The volumetric strain of GB/PPO composites increases because of micro-cavitation during strain damage. In general, the prediction for the effective elastic modulus of the damaged GB/PPO composites at different true strains is slightly higher than the experimental results. The damage evolution rates after fully debonding of glass beads from the matrix are close to those predicted by the proposed damage model.

The effects of different interphase properties on Young’s modulus, maximum stress concentration factor and stress distribution in glass bead-filled polycarbonate (GB/PC) and interphase-coated glass bead-filled polycarbonate (GB/INT/PC) have been investigated using the finite element method. A three-dimensional unit cell model has been built for modeling both two-phase and three-phase composites. The results from the predictive model allow the deduction of the optimum interphase properties for reduction of the stress concentration and minimization of the drop in elastic modulus of the resulting composites.

The purpose of this study is to provide a numerical method to model the constitutive behavior of aluminum matrix NiTi fiber-reinforced smart composite along the fiber direction. In the present approach, pseudo-elasticity, shape-memory, and strain-hardening effects have been taken into account. During phase transformation, the strain–temperature relation of NiTi fibers has been assumed to be linear. Hence, the incremental stress–strain relationship of the fibers has been derived for each temperature range where phase transformation takes place. A bi-linear and isotropic hardening elasto-plastic model has been employed to describe the stress–strain relation of the aluminum matrix. With the consideration of the fabrication procedure, the stress–strain behavior of the composite has been computed.

An experimental method used to measure the Young's modulus of the conductive thin film is proposed in this paper. This technology has utilized the electrothermal effect and strain response of conductive thin film coatings on glass substrates. On the basis of the thermo-elastic analysis of composite mechanics, the measurement principle and corresponding formula are given. The Young's modulus of conductive SnO2 thin film has been estimated by means of the formula and the thermal bend beam test presented.

This study focuses on investigating the stable damage and crack growth process of high impact polystyrene (HIPS) by using the damage mechanics approach and the moire method. Under excessive tensile loading, HIPS will be damaged due to multiple crazing that causes volume dilatation. A damage variable is defined by the dilatation of the representative volume element to characterize the craze-damage. The relationship between the dilatation and the total strain has been determined experimentally. A specimen with a sharp initial discontinuity is tested under tensile force to study the damage and crack growth process. It is observed that an elliptical damage zone is formed in front of the crack tip. The crack propagation is stabilized by the damage zone. Moire fringe patterns show that the deformation within the damage zone is non-uniform. A dynamic configuration of deformation, which comprises the elastic zone, the transition zone, the damage processing zone, and the residual damage zone, has been established. The non-linear strain and stress fields inside the transition zone and the damage processing zone are analyzed. The experimental result also shows that a critical plastic strain criterion may be used to predict the stable growth of macrocracks for HIPS.

A strip-craze model is proposed to study crack propagation in polymers. A nonlinear differential equation is derived to govern the dynamic process of crack propagation. The viscous feature of the material in the craze zone is taken into account by means of an experimentally determined relationship between the craze stress and crack speed. By fitting experimental data of PMMA into the model, some parameters including the strip-craze length are deduced. A non-singular stress is introduced to control the crack propagation with a strip craze at its tip. Variations of the crack length and the crack speed with time are computed and their dependence on the non-singular stress is investigated. For PMMA, three stages of crack propagation are identified in terms of initial non-singular stress σns0. When σns0 a −8 mm/s and the crack is basically stationary; when 60 10 −8 a −2 mm/s the crack is in slow propagation; when σns0>95 MPa, then a >10 −2 mm/s and the crack is in rapid propagation. The proposed model is applicable only in slow crack propagation.