Initial Tensile Modulus Research Articles

Magneto-Mechanical Coupling Study of Magnetorheological Elastomer Thin Films for Sensitivity Enhancement.

Magnetorheological elastomer thin films (MREFs) exhibit remarkable deformability and an adjustable modulus under magnetic fields, rendering them promising in fields such as robotics, flexible sensors, and biomedical engineering. Here, we fabricated MREF by introducing magnetostrictive particles (MSPs) and evaluated the magneto-mechanical coupling effect on the enhancement of sensitivity. The saturation magnetization (Ms) in a parallel anisotropic TbDyFe-PDMS MREF was 5.8 emu/g, and the initial tensile modulus was 55% greater than that of an Iso MREF. We propose a nonlinear magnetorheological formula on the magnetostriction effect, incorporating magnetic dipole interactions and the nonlinear prestress of magnetic particles. This formula highlights the complex nonlinear relationship between the external magnetic field (H) and the key parameters that affect the enhanced MR effect of MSPs-MREF, such as saturation magnetization, remanence (Mr), magnetostriction constant (λs) and stress deviator in ferromagnetic particles (Sed) in the magnetic chain structure. Furthermore, we validate the influence of the key parameters of the rectified magnetorheological formula on a nonlinear magneto-mechanical behavior of MSPs-MREF in PDMS-based MSPs-MREF models by using finite-element simulations. Finally, we developed a biosensor based on MSPs-MREF to detect human serum albumin at low concentrations in human urine samples. There is a 4-fold increase in sensitivity, a lower detection of limit (0.442 μg/mL), and a faster response time (15 min) than traditional biosensors, which in the future might provide an effective way of detecting biomolecules of low concentrations.

Effect of strain rate on the tensile properties of mini-SiC/SiC composites

SiC/SiC composites are the ideal candidates for hot-end components in aerospace and other high-tech fields. In recent years, as one type of material with simple structures, mini-composites have been widely used to study or initially verify the properties of ceramic matrix composites (CMC). Nevertheless, attentions were rarely paid on the influence of strain rate on the mechanical properties of mini-composites . In this study, based on mini-SiC/SiC composites, we investigated the effect of the strain rate on their tensile strength, initial tensile modulus, Weibull modulus, and fracture work. Furthermore, the underlying mechanisms were discussed and the exact constitutive model of the as-prepared mini-SiC/SiC composites was constructed according to the Michaelis-Menten and generalized linear models. This work can fill the gaps in the CMC research in some degree and provide a preliminary theoretical basis for the formulation of tensile properties test standards of mini-composites.

The micro-structure and biomechanics of eyelid tarsus

Eyelid tarsus is a fibrocartilagenous extracellular matrix around meibomian glands providing structural support to eyelids and play important roles in the integrity of the ocular surface. There are no previous studies investigating the relationship between micro-structure and function of eyelid tarsus. To investigate the structure of extracellular matrix and the biomechanical properties of tarsus, rabbit tarsus were stained with hematoxylin and eosin (H&E), MASSON and Verhoeff's Van Gieson (EVG), distribution of collagen and elastin fibers in tarsus extracellular matrix were analyzed with scanning electron microscopy. Tarsus strips were collected and went through uniaxial tensile test with an Instron Universal Testing Machine. Data from 15 tarsus samples were included in the study. The initial tensile modulus was 2.554 ± 1.453 Mpa, and the final tensile modulus was 23.554 ± 3.657 Mpa, with an extensibility of 35.47 ± 7.46%. Collagen fibers formed peripheral layers of lamellae around meibomian glands, while the elastin fibres were organized in a parallel arrangement in horizontal and sagittal section, and in a crossed arrangement around meibomian glands. After tensile test, elastin fibres were stretched and arranged perpendicular to the direction of the collagen fibril lamellae. The findings of this study suggest that the extracellular matrix structure formed by collagen-elastin network contributes to a nonlinear mechanical characteristic of eyelid tarsus.

Synthesis of zwitterionic polymer and its application in textile stiffening finish

AbstractDevelopment of formaldehyde‐free stiffening finish agents is highly desirable in modern environmental‐friendly textile chemical processing technologies. Herein, two zwitterionic monomers are synthesized and used to synthesize a series of acrylate soap‐free emulsions. The prepared acrylate soap‐free emulsion was analyzed by nanoparticle size analyzer to determine grain size and PDI. The properties of polymer film obtained from emulsion were characterized by IR, DSC, and DMA. The results showed that zwitterionic monomer in acrylate emulsion can greatly improve the glass transition temperature (Tg) and initial tensile modulus of polymer film, and that ambient temperature had little effect on initial tensile modulus. It was found that when the amount of zwitterionic monomer is 3% of the total monomer dosage, the synthesized polymer emulsion can achieve the same stiffening effect as that of commercial stiffening agents. Meanwhile, the stiffness of finished fabric is less affected by the change in ambient temperature. The effective Tg increase and high initial tensile modulus of these zwitterionic polymers demonstrate their applicability in stiffening finish for seat belts.

Fatigue and Tensile Properties of Aramid Fibers Measured by Single Fiber Mechanical Tests

Aramid fibers, with superior mechanical properties, have been widely used in a lot of industrial fields. From a safety point of view, long-term durability is required for these aramid fibers. In this study, the fatigue and tensile properties of two types of single aramid fibers, poly(para-phenylene terephthalamide) (PPTA) and poly(para-phenylene-co-3,4′-oxydiphenylene terephthalamide) (PPODTA), were investigated. Single fiber tensile and fatigue tests, cyclic tensile tests, tensile tests for post-fatigue test specimens, and optical microscopic observations were conducted. The stress–strain curves of the cyclic tensile tests indicated that PPTA and PPODTA fibers could be deformed above the elastic limit, and the strain at 2.0 GPa stress and the initial tensile modulus in subsequent tensile tests were changed by the cyclic stress. In fatigue tests, the cumulative probabilities of fatigue failure increased with the number of stress cycles for both the PPTA and PPODTA fibers. The fatigue behavior was influenced by the stress conditions and gauge length of the specimens. The initial tensile modulus in subsequent tensile tests was increased by the fatigue tests for both the PPTA and PPODTA fibers. However, regarding the tensile strength, significant decreases due to the fatigue tests were not observed. Fibrils detached from the fiber surface were observed in the post-fatigue test PPTA and PPODTA fiber specimens by optical microscope observations, with the loss of these fibrils contributing to the changes in modulus.

Anisotropic conductive, tough and stretchable heater based on nacre-like crumpled graphene composite

In this work, the nacre-like styrene-butadiene rubber/crumpled graphene nanosheets heater (NSGH) with integrated superior performance, including excellent anisotropic conductivity (safety), flexible stretchable Joule heating performance and comprehensive mechanical performance, is prepared on a large-scale by the blade-coating technique. The excellent flexible stretchable Joule heating performance, almost constant of the saturation temperature (163 °C) at the excitation of 8 V suffering 70% strain and 4000 times of bending, is originated from the selection of elastic styrene-butadiene rubber matrix and introduction of flexible conductive crumpled graphene nanosheets. The excellent comprehensive mechanical performance (increment of 215.7% on toughness and 531.85% on initial tensile modulus) and the ultrahigh anisotropic conductivity are attributed to the distinctive nacre-like structure. Moreover, the heating model of the NSGH is proposed and validated, that the heating performance can be tailored and forecasted.

Compressive Behavior of Sustainable Steel-FRP Composite Bars with Different Slenderness Ratios

This paper presents experimental studies on the compressive behavior of a sustainable steel-fiber reinforced composite bar (SFCB) under uniaxial compressive loading. The SFCB, combined with steel and fiber reinforced polymer (FRP), is expected to significantly enhance structural safety and sustainability. A new test method with LVDT and extensometer sensors was developed and verified through experiments to test the tensile and compressive behavior of the SFCB. Fifty-four specimens including SFCB and inner steel bar (ISB) with different slenderness ratios were tested. The test results indicated that the initial compressive elastic modulus of the SFCB was essentially the same as its initial tensile elastic modulus. The compressive yield load of the SFCB was essentially irrelevant to the slenderness ratio, and the ultimate compressive stress of the SFCBs varied inversely with the slenderness ratios. The squash load of the SFCB tended to be conservative for predicting the compressive yield load of the SFCB, while the equivalent critical global buckling load of the SFCB was much higher than its corresponding compressive yield load and ultimate load due to the inelastic buckling mechanism of the SFCB within the range of the equivalent slenderness ratios studied in this paper.

A Novel Interlaced-helical Wrapping Yarn with Negative Poisson’s Ratio

The two-component complex yarn with helical wrapping structure has been reported with auxetic behavior and unique performance, however, the residual torque could lead to the slippage of the wrap component from the core in the natural state and poor stability and applicability. Therefore, this paper aims to introduce a novel interlaced-helical wrapping yarn with negative Poisson’s ratio, stable structure, practicability and continuous preparation. The differences in geometry and auxetic behavior between helical structure and interlaced-helical structure were presented and analyzed. Both the structure stability and auxetic effect of the interlaced-helical complex yarn have advantages over the helical wrap yarn with same materials and initial wrap angle. It can be shown that the interlaced-helical wrap yarns with lower initial wrap angle and bigger tensile modulus of the stiff yarns will produce better auxetic effect. Besides, the deformation mechanism and the manufacturing process were described in detail. Several kinds of yarns have been fabricated to discuss the effect of initial wrap angle and tensile modulus on the Poisson’s ratio of the structure. The maximum value of Poisson’s ratio for the yarns manufactured was -2.8. It is also expected that auxetic yarns with novel braided structure can prompt the applications of auxetic textiles.

Double layer aligned‐graphene nanosheets/styrene‐butadiene rubber composites: Tribological and mechanical properties

ABSTRACTWe enhanced tribological and mechanical properties of styrene‐butadiene rubber (SBR) by designing double layer aligned‐graphene nanosheets (aligned‐GNSs)/SBR composites with one‐step emulsion polymerization preparation method. The composites consisted of two layers, one is the SBR layer and the other is aligned‐GNSs/SBR layer, in which the graphene nanosheets (GNSs) regularly aligned. The resulted composites exhibited mega increase of tribological property as well as mechanical property. With the increase of GNSs contents from 0.5 to 5 wt %, both the friction coefficient and volume wear rate steadily declined, and the mechanics dramatically increased. Such as 59% decrease of friction coefficient and 1778% increase of the initial tensile modulus when the addition of GNSs is 5 wt %. The above results are mainly due to the well aligned‐GNSs in SBR, which can take full advantage of the unique properties of GNSs two‐dimensional materials. The detailed mechanisms of improving tribological and mechanical properties were discussed in the study. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 46939.

In situ synthesis of bilayered gradient poly(vinyl alcohol)/hydroxyapatite composite hydrogel by directional freezing-thawing and electrophoresis method

Bilayered poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogels with anisotropic and gradient mechanical properties were prepared by the combination of directional freezing-thawing (DFT) and electrophoresis method. Firstly, PVA hydrogels with aligned channel structure were prepared by the DFT method. Then, HA nanoparticles were in situ synthesized within the PVA hydrogels via electrophoresis. By controlling the time of the electrophoresis process, a bilayered gradient hydrogel containing HA particles in only half of the gel region was obtained. The PVA/HA composite hydrogel exhibited gradient mechanical strength depending on the distance to the cathode. The gradient initial tensile modulus ranging from 0.18MPa to 0.27MPa and the gradient initial compressive modulus from 0.33MPa to 0.51MPa were achieved. The binding strength of the two regions was relatively high and no apparent internal stress or defect was observed at the boundary. The two regions of the bilayered hydrogel also showed different osteoblast cell adhesion properties.

Synthesis and characterization of lignin carbon fiber and composites

In this study, continuous lignin fibers from switchgrass have been successfully synthesized via multifilament melt-spinning and converted to carbon fibers using optimized stabilization and carbonization techniques. Unidirectional lignin carbon fiber reinforced composites are produced using a vacuum assisted resin transfer molding process for the first time. Produced lignin carbon fiber is evaluated in mechanical, interfacial, and microstructural areas. Single fiber mechanical properties are characterized using a unique MTS Bionix Nano-UTM. Interfacial properties and resin/fiber behavior are evaluated using single fiber fragmentation. Microstructural properties are determined using wide-angle x-ray diffraction. Mechanical results indicated an initial tensile modulus along fiber axis of 36 GPa and a failure stress of 600 MPa for single carbon fibers. Lignin carbon fibers demonstrate a nonlinear increase in modulus with applied tensile strain similar to recently observed for commercial poly-acrylonitrile (PAN) carbon fibers. Microscopy revealed few defects within and along the lignin carbon fibers, and the processed lignin fibers demonstrated minimal crystalline regions and crystallite alignment when compared to commercial PAN based fibers. Interfacial shear strength with epoxy resin was found to be 17 MPa with a fiber fracture length of 228 μm. Unidirectional composite coupons achieved tensile modulus of 9 GPa and a failure strength of 85 MPa at 1% failure strain. Lignin carbon fiber and composites produced are targeted for non-structural applications as mechanical properties are currently less than PAN carbon fibers and therefore are not suitable to replace PAN carbon fiber at this stage. Relatively low composite strength is the likely result of fiber layup, fiber fusing, and non-continuous fibers across the gage length of the composite. Nano-tensile and interface shear strength results presented here have important implications for lignin carbon fiber composite development to optimize fiber/resin bonding. In addition, composite manufacturing procedures detailed here are a major step forward in the development of sustainable carbon fiber composite production.

Effect of Colorant Additive and Thickness on Tensile Properties of Oxo-Biodegradable PE Plastic Bags in Alkaline Solution

Polyethylene (PE) is widely used as packaging materials in the form of plastic bags. After end-use, some of these plastic bags are not properly disposed and may persist in different kinds of environment. Oxo-biodegradable plastics are PE films incorporated with pro-oxidants to promote degradation. As part of the continuing study, changes on the tensile properties of oxo-biodegradable PE plastic bags immersed in alkaline solution at 60 °C are investigated. The effects of colorant additive (varied at two levels) and thickness (varied at three levels) on tensile properties of PE films are reported. Specifically, the tensile strength [MPa], strain at break [%], and elastic modulus [MPa] are monitored with time. It is observed that films undergo degradation which is exhibited by a decrease in all tensile properties after 1008 hours of immersion in alkaline solution. Analysis of variance (ANOVA) shows that the initial tensile strength and elastic modulus, as well as the strain at break and elastic modulus after 1008 hours of immersion, are all affected by colorant additive.

Theoretical analysis of geometrical and mechanical parameters in plain woven structures

An analytic solution for the estimation of structural parameters and initial tensile modulus of plain woven fabrics under uniaxial tensile loading in their linear elastic domain of deformation is presented. For this purpose, a new approach in straight line geometry with a parallel segment to the fabric plane and an inclined segment at the weave intersection in 3D form is proposed which leads to the theoretical estimation of all the structural parameters of plain woven fabrics with saw-tooth geometry. Defining and applying of JJ2 Ratio in the model enable us to modify the geometrical model and estimate the value of structural parameters considering the history of samples influenced mainly by its manufacturing process. The strain energy method and Castigliano’s theorem are used for the mechanical analysis of the structure. The elasticity, bending, shearing, and compression rigidity of yarns are incorporated into the model. It has been shown that predicting the geometrical and mechanical parameters of woven fabrics before production are possible if and only if the crimp value of the fabrics can be estimated before their production. The proposed theory is validated and compared by applying into some experimental data and a previous model.

Enhanced mechanical properties of graphene/natural rubber nanocomposites at low content

Graphene/natural rubber (GE/NR) nanocomposites were prepared by a modified latex mixing method combined with in situ chemical reduction. It was found that the GE nanosheets are well dispersed and have strong interfacial interaction with NR. Thus, adding a low content of GE can remarkably increase the tensile strength and the initial tensile modulus of NR. With incorporation of as low as 0.5 phr of GE, a 48% increase in the tensile strength and an 80% increase in the initial tensile modulus are achieved without sacrificing the ultimate strain. But further increasing the GE loading degrades the tensile strength and the ultimate strain. Dynamic mechanical measurement indicates that the storage modulus of the nanocomposites is greatly enhanced with addition of GE, while the loss tangent peak is depressed due to the reduced mobility of the rubber molecules. The reinforcement effect of GE on NR is interpreted as a change in the strain induced crystallization and network structure of the nanocomposites, based on the analysis of Mooney − Rivlin plots and the tube model.© 2013 Society of Chemical Industry

A Novel “Fiber-Spacing” Model of Tensile Modulus Enhancement by Shortening Fibers to Sub-Millimeter in an Injection-Molded Glass Fiber Reinforced Polymer Bulk Molding Compound (GFRP-BMC)

Up to now, increasing modulus of fiber reinforced polymers (FRPs) by shortening fibers has not been reported however, shortening fiber length from commercial 6.4 to 0.44mm by additional mixing of paste prior to injection molding was found to increase initial and maximum tensile modulus 5 to 25% in a 3-phase system of highly CaCO3 filled 20mass% E-glass fiber reinforced thermoset polyester/styrene-butadiene polymer bulk-molding compound (GFRP-BMC). The increased number of spaces between fibers appears to allow for action of coefficient of thermal expansion (CTE) difference between fibers and matrix to increase thermal compressive residual stress sites during shrink and cool-down. A novel “fiber-spacing” model incorporating the “rule of mixtures” is constructed based on physical meaning to predict effect of fiber length (lf), fiber volume fraction (Vf), filled-matrix modulus (Em) fiber modulus (Ef), and nominal fiber diameter (d), valid for fiber orientation parameter (0.43 < ©o < 0.54) on tensile modulus (d·/d¾)o to be useful in BMC composite design. The “fiber-spacing” model exhibited a good fit with the experimental data of 20mass% fiber composite and predictions were made for 10, 30, and 40mass% fiber composite agreeing with data in the literature. [doi:10.2320/matertrans.M2014070]

Effect of temperature on strength and stiffness properties of near-surface mounted FRP reinforcement

This paper presents results from an experimental study on the effect of temperature on tensile strength and elastic modulus of two types of near-surface mounted (NSM) reinforcement, CFRP strip and CFRP rod, in 20–600°C temperature range. Results from these tests indicate that both CFRP strip and rod retain most of their initial tensile strength and elastic modulus properties up to 200°C. However, these properties degrade significantly beyond 300°C due to decomposition of FRP resin. Further study shows NSM strip and rod possess relatively higher strength than those used for internal reinforcement and external laminates. Data from tests is utilized to propose empirical relations for variation of strength and modulus of NSM CFRP reinforcement with temperature.

The effect of carbon nanotube orientation and content on the mechanical properties of polypropylene based composites

Finite element method (FEM) is used to predict the tensile and compressive stress–strain curves of single wall carbon nanotube (SWCNT) reinforced polypropylene (PP) composites. The numerical simulations, using shell and tetrahedron elements, are first carried out to investigate the effect of SWCNT orientation on the mechanical properties of the nano-composites. Second, the Grunfest–Young constitutive equation is selected to determine the effect of strain rate and solve the finite element program to analyze the mechanical behavior of the nano-composites. Third, the effect of SWCNT volume fraction is studied. In all cases, the shear and normal stresses distribution along the nanotube axis are investigated and compared with the macroscopic tensile or compressive stresses on the composites. At the same time, the stresses of the interface between SWCNT and the matrix along the loading direction are analyzed. Finally, the effects of SWCNT orientation, content and strain rate on the strength of the nano-composites are studied. From the results obtained, it was shown that strain rate can substantially affect the tensile and shear stresses of the composites, but do not significantly influence the initial tensile or compressive elastic moduli. This is especially the case for SWCNT orientation angles less than 30° and volume fractions higher than 0.74%.

Aggregation structure development and mechanical properties of biodegradable poly(butylene succinate‐co‐terephthalate) fibers

AbstractBiodegradable poly(butylene succinate‐co‐terephthalate)(PBST) copolyester, with 70 mol % butylene terephthalate (BT), was melt‐spun into fibers at various take‐up velocities ranging from 2.0 to 4.0 km/min. The structure development and mechanical properties of the as‐spun PBST fibers were intensively investigated via birefringence, wide angle X‐ray diffraction (WAXD) measurement, tensile test, and cyclic stretch test. With increasing the take‐up velocity, the initial tensile modulus and breaking strength of PBST fibers increased, while elongation at break decreased. These were attributed to the increasing degree of orientation and crystallinity, which were resulted from the elevating tension of spinning line at higher take‐up velocity. To elucidate the effects of soft butylene succinate (BS) unit on the tensile and elastic properties of PBST fibers, poly(butylene terephthalate) (PBT) fibers were adopted as a comparison sample. The results showed that the combination of soft BS unit and hard BT unit for PBST fibers made contribution to the lower initial modulus, higher elongation at break and better elastic recovery than those of PBT fibers. Moreover, PBST fibers were found to undergo PBT‐like crystal form transition from α‐form to β‐form crystal structure under tension load through the measurement of WAXD. A relatively wider strain region for the crystal transition of PBST fibers also endowed them with higher elastic recoverability than PBT fibers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Study on the Preparation and Properties of Thermoplastic Tapioca Starch / Magnesium Hydroxide Composites

Thermoplastic tapioca starch(TPS) was prepared with the mixed plasticizer, formamide and urea (mass ratio 2:1). The introduction of magnesium hydroxide(MH) in TPS could rapidly increase processing torque on a high level(40~60Nm) at 130°C. Studies in the dependence of mechanical properties of thermoplastic tapioca starch/magnesium hydroxide composites(MHTPS) on the MH content from 0 to 20phr, the initial tensile strength and elastic modulus were increased up to the maximum 3247 MPa and 48.5 MPa at 20phr MH content respectively, while the elongation at break was reduced from 72% to 2.5%. TG mass loss curves showed that thermal stability of this composites had great improved under 500°C. The limited oxygen index(LOI) of MHTPS reached to 31% while the content of Mg(OH)2 was 20phr, and then the result of vertical flame testing achieved UL94 V-0 level.

Quantum chemistry and molecular dynamics studies of the entropic elasticity of localized molecular kinks in polyisoprene chains

We investigate the thermodynamic consequences of the distribution of rotational conformations of polyisoprene on the elastic response of a network chain. In contrast to the classical theory of rubber elasticity, which associates the elastic force with the distribution of end-to-end distances, we find that the distribution of chain contour lengths provides a simple mechanism for an elastic force. Entropic force constants were determined for small contour length extensions of chains constructed as a series of localized kinks, with each kink containing between one and five cis-1,4-isoprene units. The probability distributions for the kink end-to-end distances were computed by two methods: (1) by constructing a Boltzmann distribution from the lengths corresponding to the minimum energy dihedral rotational conformations, obtained by optimizing isoprene using first principles density functional theory, and (2) by sampling the trajectories of molecular dynamics simulations of an isolated molecule composed of five isoprene units. Analogous to the well-known tube model of elasticity, we make the assumption that, for small strains, the chain is constrained by its surrounding tube, and can only move, by a process of reptation, along the primitive path of the contour. Assuming that the chain entropy is Boltzmann's constant times the logarithm of the contour length distribution, we compute the tensile force constants for chain contour length extension as the change in entropy times the temperature. For a chain length typical of moderately crosslinked rubber networks (78 isoprene units), the force constants range between 0.004 and 0.033 N/m, depending on the kink size. For a cross-linked network, these force constants predict an initial tensile modulus of between 3 and 8 MPa, which is comparable to the experimental value of 1 MPa. This mechanism is also consistent with other thermodynamic phenomenology.