Stiffness Of Composites Research Articles

Random Stiffness Tensor of Particulate Composites with Hyper-Elastic Matrix and Imperfect Interface.

The main aim of this study is determination of the basic probabilistic characteristics of the effective stiffness for inelastic particulate composites with spherical reinforcement and an uncertain Gaussian volume fraction of the interphase defects. This is determined using a homogenization method with a cubic single-particle representative volume element (RVE) of such a composite and the finite element method solution. A reinforcing particle is spherical, located centrally in the RVE, surrounded by the thin interphase of constant thickness, and remains in an elastic reversible regime opposite to the matrix, which is hyper-elastic. The interphase defects are represented as semi-spherical voids, which are placed on the outer surface of this particle. The interphase is modeled as hyper-elastic and isotropic, whose effective stiffness is calculated by the spatial averaging of hyper-elastic parameters of the matrix and of the defects. A constitutive relation of the matrix is recovered experimentally by its uniaxial stretch. The 3D homogenization problem solution is based upon a numerical determination of strain energy density in the given RVE under specific uniaxial and biaxial stretches as well as under shear deformations. The analytical relation of the effective composite stiffness to the input uncertain parameter is recovered via the response function method, using a polynomial basis and an optimized order. Probabilistic calculations are completed using three concurrent approaches, namely the iterative stochastic finite element method (SFEM), Monte Carlo simulation and by the semi-analytical method. Previous papers consider the composite fully elastic, which limits the applicability of the resulting effective stiffness tensor computed therein. The current study voids this assumption and defines the composite as fully hyper-elastic, thus extending applicability of this tensor to strains up to 0.25. The most important research finding is that (1) the effective stiffness tensor is sensitive to random interface defects in its hyper-elastic range, (2) its resulting randomness is not close to Gaussian, (3) the semi-analytical method is not perfectly suited to stochastic calculations in this region of strains, as opposed to the linear elastic region, and (4) that the increase in random dispersion of defects volume fraction has a much higher effect on the stochastic characteristics of this stiffness tensor than fluctuation of the strain.

Hybridization of MMT/Lignocellulosic Fiber Reinforced Polymer Nanocomposites for Structural Applications: A Review

In the recent past, significant research effort has been dedicated to examining the usage of nanomaterials hybridized with lignocellulosic fibers as reinforcement in the fabrication of polymer nanocomposites. The introduction of nanoparticles like montmorillonite (MMT) nanoclay was found to increase the strength, modulus of elasticity and stiffness of composites and provide thermal stability. The resulting composite materials has figured prominently in research and development efforts devoted to nanocomposites and are often used as strengthening agents, especially for structural applications. The distinct properties of MMT, namely its hydrophilicity, as well as high strength, high aspect ratio and high modulus, aids in the dispersion of this inorganic crystalline layer in water-soluble polymers. The ability of MMT nanoclay to intercalate into the interlayer space of monomers and polymers is used, followed by the exfoliation of filler particles into monolayers of nanoscale particles. The present review article intends to provide a general overview of the features of the structure, chemical composition, and properties of MMT nanoclay and lignocellulosic fibers. Some of the techniques used for obtaining polymer nanocomposites based on lignocellulosic fibers and MMT nanoclay are described: (i) conventional, (ii) intercalation, (iii) melt intercalation, and (iv) in situ polymerization methods. This review also comprehensively discusses the mechanical, thermal, and flame retardancy properties of MMT-based polymer nanocomposites. The valuable properties of MMT nanoclay and lignocellulose fibers allow us to expand the possibilities of using polymer nanocomposites in various advanced industrial applications.

Modeling and Compensation of Motion Errors for 6-DOF Robotic Manipulators

Six degree-of-freedom (6-DOF) robotic manipulators have been increasingly adopted in various applications in industries due to various advantages, such as large operation space, more degrees of freedom, low cost, easy placement, and convenient programming. However, the robotic manipulator has the problem of insufficient stiffness due to the series structures, which will cause motion errors of the manipulator end. In this paper, taking a 6-DOF robotic manipulator as an example, forward and inverse kinematics models are established, and a new modeling method for the joint angle and space stiffness of the end of the manipulator is proposed, which can establish the composite stiffness model of joint link stiffness and joint stiffness. An error compensation model is subsequently established. The experimental results indicate that the proposed error compensation method can effectively reduce the end motion error of the robotic manipulator, and hence, the working performance and accuracy of the manipulator can be improved. The proposed research is helpful for extending the application of robotic manipulators in precision machining and measurement.

A cyclic plastic-damage multiphase model for evaluation of multiple cracking in strain hardening cementitious composites

Multiple cracking, if formed in an inherently brittle cementitious composite, remarkably boosts its ductility and leads to the desired strain hardening material during tension. The key to predicting multi-crack growth and, ultimately, tuning the composite's tensile properties primarily lies in resolving the competitive propagation of closely spaced microcracks, strung by fibers. A mechanism-based multiphase approach is developed, enabling clarification of the realistic multiple microcracks bridging mechanism arising from the stacked fiber bundles within strain hardening cementitious composites. The proposed multiphase configuration framework establishes reliable models for bridging fiber bundles, interface constitution and matrix cracks, which are critical in all types of fractures, and confronts new challenges arising from competitive opening of stringing cracks. The study has the following novelties: (1) Regarding matrix cracking, a new damage plastic interface model is proposed to characterize the stiffness degradation and gradual recovery of contact stiffness for cementitious composites during cyclic loading. (2) Targeting the crack resistance effect, a unified nonlinear bond-friction model is formulated which is able to capture the elastic bond breaking, friction hardening, fiber rupture, fiber pullout and the cyclic loading behavior of the fiber/matrix interface, simultaneously. (3) Considering the snubbing effect that is intrinsic to cracks, a two-stage evolution algorithm for the fiber bridging force is implemented which distinguishes the bridging efficiency in an intact and cracked medium. We accurately predict the tensile cracking and capture the strain hardening of composites with individual constituent properties, providing further microscopic effects beyond the experimental scope, such as the fiber and matrix stress distributions, through which the development of residual compressive traction in matrix cracks is identified for the first time. This work could serve as a new guide for designing strain hardening cementitious composites with optimal performances.

Phase morphology, mechanical, and thermal properties of fiber-reinforced thermoplastic elastomer: Effects of blend composition and compatibilization.

In this work, recycled high density polyethylene (rHDPE) was compounded with regenerated tire rubber (RR) (35–80 wt.%) and reinforced with recycled tire textile fiber (RTF) (20 wt.%) as a first step. The materials were compounded by melt extrusion, injection molded, and characterized in terms of morphological, mechanical, physical, and thermal properties. Although, replacement of the rubber phase with RTF compensated for tensile/flexural moduli losses of rHDPE/RR/RTF blends because of the more rigid nature of fibers increasing the composites stiffness, the impact strength substantially decreased. So, a new approach is proposed for impact modification by adding a blend of maleic anhydride grafted polyethylene (MAPE)/RR (70/30) into a fiber-reinforced rubberized composite. As in this case, a more homogeneous distribution of the fillers was observed due to better compatibility between MAPE, rHDPE, and RR. The tensile properties were improved as the elongation at break increased up to 173% because of better interfacial adhesion. Impact modification of the resulting thermoplastic elastomer (TPE) composites based on rHDPE/(RR/MAPE)/RTF was successfully performed (improved toughness by 60%) via encapsulation of the rubber phase by MAPE forming a thick/soft interphase decreasing interfacial stress concentration slowing down fracture. Finally, the thermal stability of rubberized fiber-reinforced TPE also revealed the positive effect of MAPE addition on molecular entanglements and strong bonding yielding lower weight loss, while the microstructure and crystallinity degree did not significantly change up to 60 wt.% RR/MAPE (70/30).

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

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

A phase-field framework for failure modeling of variable stiffness composite laminae

Three-dimensional (3D) printing of continuous fiber-reinforced composites (FRCs) and automated fiber placement (AFP) technology have enabled the fabrication of variable stiffness composites (VSCs), a kind of advanced composite materials reinforced by curvilinear fibers, which have been demonstrated with superior global mechanical properties. However, the fracture behaviors, an indispensable factor in the engineering structure design, of the VSC are still unclear due to a lack of research. To fill in the gap, the paper presents a multi-phase-field approach to perform the failure analyses of VSC laminae at mesoscale through which the VSC lamina is modeled as an anisotropic while nonhomogenous brittle material. The proposed model is validated against experimental results of fracture behaviors of single edge cracked and open-hole FRC laminae. Then a systematic investigation of the failure analyses of the pre-cracked and open-hole VSC laminae under different designs is performed. The results reveal that the propagations of cracks are always along with the fiber orientations in notched VSC laminae. In addition, a progressive failure mode demonstrated by the load–displacement curve can be amazingly observed in some designs. Moreover, the guidance in the design of VSCs with discontinuities is also provided based on the modeling results. Our presented fundamental insights in designing the novel fracture-resistant FRCs may promote the application of VSCs in automotive and aerospace structures.

Effect of the addition of aliphatic diamine-functionalized carbon nanotubes on the interfacial adhesion of glass fiber/epoxy composites

To improve the interfacial adhesion of glass fiber (GF)/epoxy composites, the GF surface was treated by dispersing aliphatic diamine-functionalized multi-walled carbon nanotubes (MWCNTs). Carboxyl MWCNTs were first modified by aliphatic diamine with different alkyl chain lengths and then deposited on the surface of GF. The effect of aliphatic diamine chain lengths on the MWCNTs’ dispersion and interfacial properties of resultant composites was investigated in detail. The results showed that uniform dispersion of MWCNTs and strong fiber/matrix interfacial adhesion could be achieved, based on the grafting of 1,8-octanediamine onto MWCNTs. Compared with the control sample, the interlaminar shear, flexural, and tensile strengths of the treated composites increased by 41%, 29%, and 30%, respectively; the interlaminar fracture toughness and storage modulus in the glass region were significantly enhanced; and the glass transition temperature increased by more than 8°C. This work demonstrates that the carbon nanotubes functionalized by appropriate chain lengths of amine modifier can improve the fiber/matrix interfacial interactions and thus enhance the strength, toughness, and stiffness of fiber-reinforced composites.

Evaluation of mechanical performance and water absorption properties of modified sugarcane bagasse high-density polyethylene plastic bag green composites

Enormous amounts of plastic wastes are generated worldwide and the approaches related to plastic recycling or reusing have become the research focus in the field of composite materials. In this study, green composites were prepared via melt-blending method using high-density polyethylene (HDPE) sourced from plastic bags as a matrix and sugarcane bagasse (SCB) fiber as reinforcing filler. The effects of fiber loading (5, 10 and 15 wt%) and fiber modification on the mechanical and dimensional stability (weight gain by water absorption) properties of the green composites were investigated. Results showed that the inclusion of SCB fiber into recycled HDPE matrix increased the composite stiffness but decreased the mechanical strength and resistance to water absorption. With the fiber modification through alkali treatment, the mechanical strength was remarkably improved, and the modulus and water absorption of the composites were found to be reduced. From the finding, it can be concluded that the prepared green composites free of coupling agent could add value to the plastic and agricultural wastes, and serve a potential candidate to replace some conventional petroleum-based composites.

Systematic analysis of a new novel variable stiffness stable composite structures using theory, FEM and experiment

A new theoretical model of variable stiffness composite structures in this paper is presented, then a finite element model is established by ABAQUS and a test specimen is manufactured to verify the accuracy. Firstly, the out-of-plane displacement of the initial and second stable configuration of theoretical and simulation results for two kinds of structures (Orthogonal/Antisymmetric/Orthogonal and Antisymmetric/Orthogonal/Antisymmetric) are compared. Secondly, the force-displacement of variable stiffness composite is investigated by the numerical and experimental methods. Reasonable agreement can be obtained from the results of theoretical analysis, finite element method and experiment test. Thirdly, the effect of material parameters on out-of-plane displacement and force-displacement are discussed. It is shown that we can use the current model to predict the equilibrium configurations and load condition of a variable stiffness composite structures.

Wear behaviour of polymeric materials reinforced with man-made fibres: A comprehensive review about fibre volume fraction influence on wear performance

In the mineral processing, mining, oil and gas industries, it is not uncommon to find mechanical components exposed to degradation and wear from slurries. Polymeric matrix composites (PMCs) are considered as potential alternatives to replace metallic materials in such severe environments because of their high strength to weight ratio, ease of production, high wear resistance and good corrosion/chemical resistance. Often, seemingly erratic wear behaviour is observed making preventive maintenance and time-to-failure difficult to manage. A major culprit is the complex physical and chemical interaction with the slurry, such as exposure to high temperatures, high alkalinity, high slurry density, insoluble inorganic contents, high hardness of suspended particles and humidity. It is well understood that the addition of reinforcing fibres greatly improves the stiffness and strength of polymeric matrix composites. However, the effect the reinforcement has on the wear performance is far less established and a framework to analyse the effect of fibre volume fraction is yet to be established. The difficulties in establishing such a framework lay in the multi-factorial contributions and the potential trade-offs with mechanical performance. This makes it much more difficult to isolate clear trends. The objective of the present work is to present a comprehensive review on the influence reinforcing fibres play on wear behaviour of PMCs. The influence of fibre volume fraction on wear performance of polymeric composites reinforced with man-made fibres is presented. The applied load, fibre length, coefficient of friction and chemical treatment of fibres are analysed with respect to wear performance of PMCs. Future trends in the use of fibre-reinforced polymeric composites in wear critical applications are identified. Research gaps in designing composites for wear applications are explained, aiming at motivating future research to address these gaps.

The Effect of Graphene Oxide and SEBS-g-MAH Compatibilizer on Mechanical and Thermal Properties of Acrylonitrile-Butadiene-Styrene/Talc Composite.

In this study, acrylonitrile butadiene styrene (ABS)/talc/graphene oxide/SEBS-g-MAH (ABS/Talc/GO/SEBS-g-MAH) and acrylonitrile butadiene styrene/graphene oxide/SEBS-g-MAH (ABS/GO/SEBS-g-MAH) composites were isolated with varying graphene oxide (0.5 to 2.0 phr) as a filler and SEBS-g-MAH as a compatibilizer (4 to 8 phr), with an ABS:talc ratio of 90:10 by percentage. The influences of graphene oxide and SEBS-g-MAH loading in ABS/talc composites were determined on the mechanical and thermal properties of the composites. It was found that the incorporation of talc reduces the stiffness of composites. The analyses of mechanical and thermal properties of composites revealed that the inclusion of graphene oxide as a filler and SEBS-g-MAH as a compatibilizer in the ABS polymer matrix significantly improved the mechanical and thermal properties. ABS/talc was prepared through melt mixing to study the fusion characteristic. The mechanical properties showed an increase of 30%, 15%, and 90% in tensile strength (TS), flexural strength (FS), and flexural modulus (FM), respectively. The impact strength (IS) resulted in comparable properties to ABS, and it was better than the ABS/talc composite due to the influence of talc in the composite that stiffens and reduces the extensibility of plastic. The incorporation of GO and SEBS-g-MA also shows a relatively higher thermal stability in both composites with and without talc. The finding of the present study reveals that the graphene oxide and SEBS-g-MAH could be utilized as a filler and a compatibilizer in ABS/talc composites to enhance the thermo-mechanical stability because of the superior interfacial adhesion between the matrix and filler.

Mechanical and free vibration properties of Phoenix sp. fiber reinforced epoxy composites: Influence of sodium bicarbonate treatment

AbstractIn this research work, the Phoenix sp. fiber‐based epoxy composites were fabricated using compression molding technique and investigated their mechanical and free vibration characteristics by varying the fiber length and content. The test results indicated that the fiber length and content influence the properties of composites significantly. The composites showed higher mechanical and free vibration properties than the neat epoxy due to increased composite stiffness. In particular, the composites reinforced with 20 wt% of 15 mm length fiber offer better overall properties. In addition, an effort was made to improve the properties of the optimized composites by reinforcing the sodium bicarbonate treated Phoenix sp. fibers. The treatments showed a positive impact on the composite properties, especially the 120 h treated fiber reinforced composites offered highest mechanical and free vibration properties than the other composites investigated. This could be attributed to increased fiber‐matrix interfacial bonding and the existence of small protrusions on the fiber surface that act as a mechanical interlocking mechanism, and the same was confirmed through morphological analysis. The experimental results showed that the sodium bicarbonate treatment is efficient in increasing the properties of Phoenix sp. fiber composites, as well as being less harmful to the environment after disposal.

Effect of collagen degradation on the mechanical behavior and wrinkling of skin.

Chronological skin aging is a complex process that is controlled by numerous intrinsic and extrinsic factors. One major factor is the gradual degradation of the dermal collagen fiber network. As a step toward understanding the mechanistic importance of dermal tissue in the process of aging, this study employs analytical and multiscale computational models to elucidate the effect of collagen fiber bundle disintegration on the mechanical properties and topography of skin. Here, human skin is modeled as a soft composite with an anisotropic dermal layer. The anisotropy of the tissue is governed by collagen fiber bundles with varying densities, average fiber alignments, and normalized alignment distributions. In all finite element models examined, collagen fiber bundle degradation results in progressive decreases in dermal and full-thickness composite stiffness. This reduction is more profound when collagen bundles align with the compression axis. Aged skin models with low collagen fiber bundle densities under compression exhibit notably smaller critical wrinkling strains and larger critical wavelengths than younger skin models, in agreement with in vivo wrinkling behavior with age. The propensity for skin wrinkling can be directly attributable to the degradation of collagen fiber bundles, a relationship that has previously been assumed but unsubstantiated. While linear-elastic analytical models fail to capture the postbuckling behavior in skin, nonlinear finite element models can predict the complex bifurcations of the compressed skin with different densities of collagen bundles.

Molecular dynamics investigation of structural and mechanical properties of silica nanorod reinforced dental resin composites

In this work, molecular dynamics simulations are conducted to investigate the structural and mechanical properties of dental materials, i.e., the silica nanorod reinforced Bis-GMA/TEGDMA resin composite. The effects of loading content and size of the silica nanorods on the composite stiffness were performed by examining resin chain conformation, hydrogen bonds and matrix/filler binding energy. It is revealed that the presence of the silica nanorod causes polymer chain expansion, endowing the resins with higher stiffness. Moreover, the volumetric hydrogen bonds and binding energy increase considerably with the loading content, but decrease gradually with the diameter or show almost independence of the length. Furthermore, the composite moduli were quantified by the micromechanics models and the transverse moduli were well predicted by the Counto model, signifying a perfect bonding between the matrix and nanorod. The chain expansion and energetic matrix/filler interactions are believed to contribute to the significant mechanical reinforcement of the composites with the loading content. However, the length of the nanorod has a little effect on the composite moduli due to the unaltered interfacial interaction. In contrast, a smaller diameter is supposed to give a larger modulus, and this is not observed in this work due to the synergic effects of improved matrix/filler interaction and actual reduced filler volume fraction. The mechanical enhancement by the rod-like structures is more influenced by the loading content, but less so by the size of the nanorod, and it also exhibits superior mechanical performance as compared to nanoparticles. The findings thus extend the current understanding of the nanostructure and mechanical properties of silica nanorod reinforced dental resin composites from an atomic/molecular perspective.

Investigations of the 80/20 (wt/wt) PA6/ABS blends system in presence of SMA co-polymers as Reactive Compatibilizer and Encapsulated Multiwall Carbon Nanotubes (MWNTs)

Introduction: The modification of a polymeric material with tailored properties was carried out either by blending with another polymer or by using suitable filler or by taking the advantages of both. The immiscible polymer blends were generally forming coarse and unstable phase morphology, which hamper mechanical properties of the materials. Therefore, it was essential to control and stabilize a desired type of morphology in order to generate polymeric materials with favourable properties through controlling composition, processing conditions, viscosity of the materials and can be compatibilized by using either reactive compatibilizer or filler or combination of both to reduce the interfacial tension. Methods: Keeping these aspects in mind, a novel strategy was introduced during melt-mixing of 80/20 (wt/wt) polyamide6 (PA6) and acrylonitrile-butadiene-styrene (ABS). Styrene maleic anhydride (SMA) co-polymer having 8, 14 and 50 wt% of maleic anhydride (MA) content was utilized as reactive compatibilizers for 80/20 (wt/wt) PA6/ABS blends system. Multiwall carbon nanotubes (MWNTs) were considered as a filler material to improve the stiffness and strength of the blends composites. To overcome the van der Waals’ forces of the MWNTs and achieve the uniform dispersion of the MWNTs in the blends phosphonium based modifier, namely octadecyl triphenyl phosphonium bromide (OTPB) was studied with Raman spectroscopy and transmission electron microscopic analysis (TEM). To restrict the MWNTs in one of the phase and/or at the interfaces and taking the advantages of the compatibilizer and filler, the MWNTs were encapsulated by the SMA (8, 14, 50) co-polymer. A simple solution method was adopted for the preparation of the SMA (8, 14, 50) encapsulated MWNTs. Results & Discussions: A detail morphological analysis was carried out in context to the migration of the MWNT along with a decrease in dispersed droplet size of ABS phase with varying interfacial energy differences between the matrix and the dispersed phase. The morphological observations were further substantiated by FTIR spectroscopy and DSC non-isothermal crystallization studies. To understand the morphological changes (refinement) in 80/20 (wt/wt) PA6/ABS binary blends in presence of SMA encapsulated MWNTs in context to melt-viscosity factor and thermodynamic aspect during melt-mixing. These observations were supported by the torque rheometry, FTIR analysis and TEM images. Conclusions: Dynamic mechanical thermal analysis (DMTA) concluded that all combinations enhances the storage modulus with decrease in Tg compared to the 80/20 (wt/wt) PA6/ABS blends. However, SMA encapsulated MWNTs enhances highest storage modulus, may be due to the better interfacial adhesion between filler and polymers. Hence, a novel compatibilization strategy was developed and evaluated for 80/20 (wt/wt) PA6/ABS blends using a hybrid compatibilizer involving MWNT. Keywords: PA6/ABS blends, Reactive and hybrid compatibilizers, Multi-wall carbon Nanotubes, Encapsulation Acknowledgment: Professor Arup Ranjan Bhattacharyya, MEMS and SAIF Indian Institute of Technology Bombay (IITB), Mumbai. References B.F. Jogi, M. Sawant, M. Kulkarni and P.K. Brahmankar, Dispersion and Performance Properties of Carbon Nanotubes (CNTs) Based Polymer Composites: A Review. Journal of Encapsulation and Adsorption Science, Scientific Research Publishing, 2012;(2):69–78. doi: 10.4236/jeas.2012.24010. G.S. Lohar, P.B. Tambe, B.F. Jogi, Influence of dual compatibilizer and carbon black on mechanical and thermal properties of PP/ABS blends and their composites. Composite Interfaces, Taylor and Francis, 2020;(12)1101–1136. https://doi.org/10.1080/09276440.2020.1726137. R.M. Dhajekar, B. F. Jogi and S.R. Nirantar, Preparation and Characterization of PAEK based Polymer Nanocomposites in the Presence of MMT Clay as Nanofiller to Study Tensile and Impact Properties. Materials Today: Proceedings, 2018;(5),6848–6854.

Remote-Controlled 3D Porous Magnetic Interface toward High-Throughput Dynamic 3D Cell Culture.

Mechanical stimuli have been shown to play a large role in cellular behavior, including cellular growth, differentiation, morphology, homeostasis, and disease. Therefore, developing bioreactor systems that can create complex mechanical environments for both tissue engineering and disease modeling drug screening is appealing. However, many of existing systems are restricted because of their bulky size with external force generators, destructive microenvironment control, and low throughput. These shortcomings have preceded to the utilization of magnetic stimuli responsive materials, given their untethered, fast, and tunable actuation potential at both the microscale and macroscale level, for seamless integration into cell culture wells and microfluidic systems. Nevertheless, magnetic soft materials for cell culture have been limited due to the inability to develop well-defined 3D structures for more complex and physiological relevant mechanical actuation. Herein, we introduce a facile fabrication process to develop magnetic-PDMS (polydimethylsiloxane) porous composite designs with both well-defined and controllable microlevel and macrolevel features to dynamically manipulate 3D cell-laden gel at the scale. The intrinsic stiffness of the magnetic-PDMS porous composites is also modulated to control the deformation potential to mimic physiological relevant strain levels, with 2.89-11% observed in magnetic actuation studies. High cell viability was achieved with the culturing of both human adipose stem cells (hADMSCs) and human umbilical cord mesenchymal stem cells (hUCMSCs) in 3D cell-laden gel interfaced with the magnetic-PDMS porous composite. Also, the highly interconnected porous network of the magnetic-PDMS composites facilitated free diffusion throughout the porous structure showcasing the potential of a multisurface contact 3D porous magnetic structure in both reservoir and 96-well plate insert designs for more complex dynamic mechanical actuation. In conclusion, these studies provide a means for establishing a biocompatible, tunable magnetic-PDMS porous composite with fast and programmable dynamic strain potential making it a suitable platform for high-throughput, dynamic 3D cell culture.

Detailed characteristics of shear stiffness for coated biaxial warp-knitted fabrics subjected to coupled shear-tension loads

In order to reveal shear deformation mechanisms of architectural non-crimp fabric (NCF) composites, detailed shear stiffness-nonlinearities for a typical coated warp-knitted NCF composite under shear-tension coupling loading were studied from experimental investigation and FEA models. Shear-tension coupling effects on shear stiffness of the NCF composite were investigated for different stress states. Its shear stiffness shows significant nonlinear characteristics which are highly tensile stress level (TSL) related, and therefore a critical TSL value was obtained for the studied material. Moreover, a new method for determination of shear stiffness was proposed, and its feasibility was verified by FEA simulation using UMAT. In addition, differences in shear stiffness and micro-deformation mechanisms between NCF and plain-woven fabric (PWF) composites were analyzed specifically. Apparently, the yarn-to-yarn compression on the yarns could contribute to the different stiffness variations between these two composites.

Implementation of multiscale modeling and failure mechanism in investigating load bearing capacity of 3D integrated multi-cellular knitted composites

Load bearing capacity analysis of E-glass/epoxy composites reinforced with 3 D integrated multi-cellular weft-knitted spacer fabrics is focused in this paper. Three groups of composite varied in their cross-sectional shapes were prepared via vacuum resin transfer molding. From the experimental three-point bending test, it was found that the structural geometry has significant effect on mechanical performance and energy absorbability of the 3 D composites. Theoretically, based on FEM model, the composites stiffness matrix and Hashin-failure criteria were implemented in a simulated multi-scale model. Good compliance between the experimental and theoretical force-displacement curves suggested good compatibility of the proposed failure-based model.

Multivariable optimization design method of composite stiffener based on critical stiffness

Based on the optimization design of ship structure, in view of the current situation that the structural safety margin is too high and the stiffener of stiffened plate is over matched, the concept of the critical stiffness of the stiffener matching was proposed, and the relationship between the stiffness ratio of plate and stiffener was derived. The optimization model of T-type composite stiffener was established. Based on Isight software platform, sensitivity analysis of design variables was carried out to simplify design variables. The Multi-Island genetic algorithm was used to carry out the multivariable optimization design of stiffener. Then, combined with the engineering practice, the design scheme was determined on the basis of the stiffener optimization results. The feasibility of the multivariable optimization design method was verified by the experimental study on the mechanical properties of composite stiffened plates. Research shows that the stiffness ratio formula of the stiffened plate can be used to guide the design of stiffener stiffness matching. In the optimization design of T-type composite reinforcement, the effect of web height on the optimization target is the most obvious. Under the condition of equal stiffness constraint, the optimal design scheme of T-type stiffener can achieve the optimization goal and ensure the better economy.