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Due to their high load-bearing capacity and excellent energy dissipation properties, metal honeycomb lightweight sandwich panels are commonly utilized as highly efficient weight-saving components in the automotive, aerospace, and military industries. Especially the auxetic honeycomb sandwich panels have higher yield strength, more robust shear modulus, fracture toughness, less fatigue expansion, and higher vibration and energy absorption. In this paper, the ballistic resistance and energy absorption mechanisms of a novel re-entrant auxetic honeycomb (RSH) sandwich panel are investigated. The ballistic limits and energy absorption of the re-entrant star-shaped honeycomb (RSH), star-shaped honeycomb (SSH), and re-entrant star-shaped honeycomb (RH) sandwich panels are compared and analyzed, as well as the deformation mechanism during projectile penetration. The results show that the RSH sandwich panel has the best in-plane ballistic performance among the three types of honeycomb sandwich panels. For the same relative density, the ballistic limit of the RSH sandwich panel is 17.4% and 7.1% higher than that of the SSH and RH sandwich panels respectively. In addition, the effects of different design parameters on the ballistic resistance of RSH sandwich panels are investigated by changing the panel thickness, the relative density of the core layer, the cell angle and the cell size. It can be concluded that increasing the thickness of the face sheet is more effective in improving the ballistic limit (perforation energy) of the RSH with a thinner core layer. However, increasing the relative density of the core layer is more effective in enhancing the ballistic limit (perforation energy) for thicker core layers. Cell size has a significant effect on the ballistic resistance of RSH sandwich panels compared to cell angle, especially at impact velocities close to the ballistic limit. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the in-plane shear properties of filament-wound composite cylinders and assess the associated damage mechanisms using acoustic emission techniques. Two distinct composite materials, namely carbon/epoxy and glass epoxy, were manufactured for this purpose. The cylinders were subjected to torsion load conditions in accordance with ASTM D5448. Throughout the testing process, various parameters such as torque, angle of torsion, and strain were meticulously recorded. Additionally, the acoustic emission sensors were utilized to capture signals indicating the occurrence of damages. The findings of the study indicate that the in-plane shear strength and shear modulus of the carbon/epoxy specimens surpass those of the glass/epoxy counterparts. The results from acoustic emission testing indicated that in the CFRP specimens, there were no instances of fiber/matrix debonding. Instead, the main mode of damage observed was fiber breakage, accounting for approximately 71% of the total damage detected. On the other hand, in the GFRP specimens, the primary damage mechanism was found to be fiber/matrix debonding, making up approximately 50% of the overall damage recorded. [ABSTRACT FROM AUTHOR]

This paper focuses on the prediction of piezoelectric coefficients, Young's moduli and shear moduli of unidirectional piezoelectric fiber/carbon nanotube (CNT)/graphene nanoplatelet (GNP)-reinforced polymer composites using a novel micromechanics modeling technique. The multiphase composite configuration is that piezoelectric fibers are embedded within a polymer matrix filled by CNT/GNP hybrids. Agglomeration of hybrid nanofillers as a significant factor is identified and incorporated in the micromechanical calculation. Parametric studies are carried out to understand the effect of volume fraction, size and dispersion type of carbonous nanofillers as well as the piezoelectric fiber volume fraction on the effective material constants of multiphase composites. It is found that in comparison with the piezoelectric fibrous composite, the piezoelectric fiber multiphase composite containing CNT/GNP hybrids shows better elastic and piezoelectric properties. Also, further improvement in effective properties can be obtained by increasing the length and percentage of CNTs and GNPs. But, degradation in the elastic and piezoelectric constants is observed by the agglomeration of CNT/GNP hybrids. The current results are found to be in close proximity with the experimental data and other numerical results available in the literature. [ABSTRACT FROM AUTHOR]

This paper focuses on the performance improvement and evaluation of a novel flexible sandwich beam incorporated magnetorheological fluid porous fabric (MRF-PF). As a novel MR material, MRF-PF has been introduced, prepared, and measured to analyze the pre-yield property between complex shear modulus and magnetic fields. MRF-PF is used into the flexible sandwich beam as core layer. Pre-yield property with tunable stiffness is used to adjust the dynamic response. Then, a theoretical model is derived which can precisely describe the performance. Based on experimental results, sandwich beam incorporated MRF-PF has a good performance of controllability. When the magnetic field is applied into the free end, the natural frequency decreases with increasing the currents and filling ratio. In contrast, the frequency and amplitude increase when the clamped end is exposed to the magnetic fields. Comparing with other investigations, this proposed sandwich beam incorporated MRF-PF has a larger frequency range. The first and second natural frequency show the increases of 54.8% and 77.2%, respectively. The reduction of amplitude is closely related to the thickness of face plate. Therefore, the performance of the compound sandwich beam can be significantly improved by MRF-PF. [ABSTRACT FROM AUTHOR]

Dynamic performance of sandwich beam with shear thickening fluid (STF) core subjected to a periodic excitation is investigated. The addition of STF enables the sandwich beam to have a tuning stiffness and damping capacity under dynamic deformation. Here, the constitutive model of STF is described by a complex shear modulus related to the shear rate. The transverse moving beam is modeled based on Newtonian law and derived nonlinear equations are solved by finite difference method. It is found that the resonant frequency of the beam increases with the amplitude of the external excitation by a power law. In addition, the initial damping ratio decreases first and then increases with the increase of the amplitude of the initial excitation for the STF with shear thinning zone. The minimum value of the initial damping ratio should be avoided, which is caused by initial shear thinning. This work can be used to guide the designing of structures with enhanced damping and the preparation of STF materials for application to such structures. [ABSTRACT FROM AUTHOR]

Based on the propagation theory of elastic waves in unsaturated porous medium and single-phase elastic medium, the calculation model of a double-layer wave impeding block (WIB) as vibration isolation barrier in unsaturated soil foundation is established. The analytical solution of the transmission/reflection amplitude ratio of P1 wave passing through a double-layer WIB in unsaturated soil foundation are derived by Helmholtz vector decomposition theorem. The influences of physical and mechanical parameters such as saturation, wave impedance ratio, density, and shear modulus on the vibration isolation effect of the double-layer WIB when P1 wave passing through the double-layer WIB in the unsaturated soil foundation are analyzed by parametric studies. The results show that the saturation has a small effect on the transmission/reflection coefficients of P1 and S waves and a significant effect on the transmission/reflection coefficients of P2 and P3 waves. The wave impedance ratio and the shear modulus and density of the double-layer WIB have a significant effect on the transmission/reflection coefficients. The optimal shear modulus and wave impedance ratio of the double-layer WIB can be selected to obtain the best vibration isolation effect, which provides theoretical guidance for the application of the double-layer WIB in the field of unsaturated ground vibration control. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) materials with excellent magneto-mechanical properties have great application values in the field of vibration reduction and buffering. By combining the advantages of light weight and excellent energy absorption of porous polymer materials, the development of porous MR materials can improve the buffer performance of MR technology. In this paper, we proposed a one-step method for fabricating the 3D microporous MR foam based on polyurethane matrix. Micromorphology of MR foam character by scanning electron microscope shows the existence of a 3D network structure with embedded carbonyl iron particles (CIPs). The unique 3D microporous structure ensures the excellent magneto-mechanical properties of MR foam. The test results analyzed by a rheometer reveal that its compressive modulus and shear storage modulus enhanced significantly with the magnetic field. The influence factors such as CIP content, shear frequency, and shear strain have been systematically studied under the oscillating shear mode. It indicated that the MR foam exhibits obvious viscoelasticity, the dynamic modulus depends on the shear frequency and shear strain, and it has excellent magneto-mechanical properties. This work can provide a new technical solution for fabrication of MR porous materials for MR buffer technology. [ABSTRACT FROM AUTHOR]

In 1934, Timoshenko derived and published the torsional rigidity of a rectangular bar of isotropic material by using the membrane analogy. The rigidity depends on the bar's shear modulus, width and thickness. In 1950, Lekhnitskii followed Timoshenko's process to derive the torsional rigidity for an orthotropic bar of unidirectional composite laminate, where the rigidity depends on the laminate's width, the thickness and the shear moduli. In 1990, Tsai, Daniel and Yaniv solved the same case, deriving a quasi-exact solution of torsional rigidity. In the same year, Tsai and Daniel verified their result through multiple experiments. All these rigidities become different when the definitions of thickness and width are swapped. However, they remain identical numerically, lacking mathematic proof for nearly a century. In 2022, Tsai et al. resolved Timoshenko's case by considering all the conditions and energy minimization criterion. By a completely different approach, the torsional rigidity was derived in a completely different form from that of Timoshenko but numerically identical. Moreover, the solution satisfies the rule of swapping, which makes perfect sense physically. This work applies Tsai's process to Lekhnitskii's case. A general solution is derived that satisfies the rule of swapping involving the swapping of shear moduli. [ABSTRACT FROM AUTHOR]

A viscoelastic model is proposed in this approach to determine the sound transmission loss coefficient of a sandwich shell system with double curvature. The structure is composed of a double-walled composite shell subjected to a viscoelastic core. Investigating the efficient impresses of rotary inertia and shear deformation, vibration equations of both outer and inner shells are extracted within the framework of shear deformation shallow shell theory. Besides, the Zener mathematical model is used for viscoelastic material, which is based on a spring connected in series with a parallel mixture of spring and dashpot. This model presents the dynamic response in the whole frequency domain at which shear modulus and bulk complex modulus are frequency dependent. Since the performed studies on the sound transmission loss of this kind of structures are insignificant, the outcomes of plate models with a viscoelastic core are used to provide a reliable sound transmission loss comparison. The results show that the applied strategy can improve the acoustic characteristics of the system at high frequencies compared to that of a single-layer one with the same mass. This issue is more highlighted while the thickness of the viscoelastic layer enhances, which confirms the positive performance of the viscoelastic materials in this range of frequency, particularly in the resonant frequency. In addition to the curvature effect on acoustic features, the vibration response of the system is configured based on various frequencies and materials. [ABSTRACT FROM AUTHOR]

Rubber nanocomposites are being studied because of their unique characteristics. Fillers are used in rubbers and elastomers to increase certain qualities for their ultimate uses. Fillers are used to strengthen rubber such as graphene/graphene oxide for the majority of activities. The hardness, modulus, anti-ageing and gas barrier properties of nanofilled-reinforced rubber are greater than pristine rubber. Studies from the literature depicted 150% increment in elastic modulus, 27.6% increment in modulus of rigidity and 35% increment in hardness of nitrile butadiene rubber when reinforced with graphene oxide (GO). Bulk, shear and Young's modulus of vulcanised rubber rises by 19.13%, 21.11% and 26.89% when infused with carbon nanotube. Because of its unique electrical, thermal and mechanical characteristics, rubber nanocomposites loaded with GO are also in high demand in industrial applications. Rubber nanocomposites, different nanofillers like graphene and graphene oxide and their benefits have been discussed. The review also outlines the rubber/GO nanocomposites' production procedures, novel characteristics and possible uses. [ABSTRACT FROM AUTHOR]

Seashell waste, mainly composed of calcium carbonate and made of a complex microstructure, has been increasingly used as a bio–filler for composite materials, in a crushed or powdered state. Seashell particles present various sizes and shapes which in turn could affect the mechanical properties of the composites. The main aim of this work is to investigate the effect of particles size and shape and inter–phase properties on the overall elastic properties of bio–composite reinforced by seashell particles. For that purpose, a morphological study based on particles size measurement and shape analysis, was first carried out in order to identify the morphological distribution of seashell particles. Seashell particles were classified into six diameters and six types of shape. Afterwards, a numerical homogenization based on finite element and representative elementary volume is used to compute the effective elastic properties of bio–composites, which include bulk modulus, shear modulus, and Young's modulus. We assumed a perfect bond at the polyester/seashell particle inter–phase. Then we incorporate an inter–phase surrounding the seashell particles by considering variable properties (thickness, number of layers). In the present work, the calculations are carried out for two types of microstructures according to particles shapes. Several microstructure configurations were considered by varying particles sizes and volume fractions 6.6, 13.7, 21.4, 25.5, and 29.8%. The results showed that adding seashell particles significantly improves the effective elastic properties of polyester composite and that the morphology of seashell particles and the inter–phase structure has a negligible effect on the effective elastic properties of bio–composite. As for inter–phase thickness, it could have a considerable effect on the effective elastic properties of bio–composites. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced polypropylene (GF-PP) composites have proven a great potential in the designation and manufacturing of control arms, leaf springs, barriers, beams and bridge decks. Two-pass injection molding of GF-PP was investigated in this study. Polypropylene (PP) was injected with different weight fractions (w%) of chopped glass fibers (GFs) with different fiber feedstock lengths (FFSLs). The composites were then crushed and re-injected once again. Some specimens were burned out to check the actual weight fractions and fiber lengths after the injection processes. The fiber lengths dramatically decreased due to damages during two-pass injection processes and crushing. The manufactured specimens were tested in tension, and the results indicated that the tensile strength increased slightly at w = 10% of GF. Further increase of GF weight fraction leads to a drop in the tensile strength below neat PP. The results of SEM micrographs showed an increase in air voids concentrations at high GF percentages which clarifies the reason behind the drop in the tensile strength. Also, in-plane shear tests were carried out using the Iosipescu fixture where a slight increase in the in-plane shear strength was noticed by increasing fiber weight fractions. In-plane shear moduli of all specimens were measured experimentally by strain gauges and calculated theoretically. The shear modulus was enhanced by glass fiber addition and a further increase was noticed by increasing the fiber weight fractions. [ABSTRACT FROM AUTHOR]

As a type of intelligent electroactive polymer, dielectric elastomer (DE) exhibits viscoelastic properties. It's worth pointing out that the relaxation time has great significance for studying the mechanical behavior of viscoelastic polymer. In this paper, a generalized Maxwell model is used to describe the viscoelastic property of dielectric elastomer balloon. Meanwhile, a theoretical model with multiple relaxation times is used and the natural frequency of small amplitude oscillation is derived. Subsequently, the model is validated by comparing with experimental results. The model with double relaxation times can describe the deformation of the dielectric elastomer balloon effectively. Then the effect of relaxation time and shear modulus on the dynamic response of DE balloon is studied. Furthermore, the dielectric elastomer balloons in practical application exhibit the strong nonlinearity and the viscoelastic dissipation. Therefore, it is important to precisely control the dynamic response. The proportional-integral-differential (PID) controller in the form of nonlinear combination is adopted to control the above nonlinear dynamic systems actively. The results indicate that it is feasible to achieve desired control effect. [ABSTRACT FROM AUTHOR]

The paper deals with the effect of date stone flour (DSF) as a filler on the elastic properties of biocomposites based on two different matrices, namely, polymethyl methacrylate (PMMA) and green epoxy resin (GER). Potassium permanganate treatment was applied to improve the surface properties of the DSF filler. Fourier transform infrared spectrotroscopy was used to analyze the chemical changes of the functional groups in the untreated DSF and the permanganate treated DSF filler. Different filler content of 10, 20, and 30 wt%, respectively, were used to obtain PMMA/DSF and GER/DSF biocomposites. The elastic properties, namely, longitudinal modulus, shear modulus, bulk modulus, Young's modulus of elasticity, Poisson ratio, ultrasonic micro-hardness, and acoustic impedance of the biocomposites were determined using the ultrasonic through-transmission method. In addition, the morphology was studied using optical microscopy and scanning electron microscopy. Fourier transform infrared spectrotroscopy analysis results revealed the success of the permanganate treatment. The elastic properties of PMMA/DSF biocomposites were decreased, while an improvement of these properties is observed for GER/DSF biocomposites. Morphological results showed the presence of pores and cracks in the PMMA/DSF biocomposites, which is attributed to poor interfacial adhesion between the DSF filler and the PMMA matrix. However, fewer defects were observed in the GER/DSF biocomposites, which is due to better interfacial adhesion between the DSF filler and the GER matrix. [ABSTRACT FROM AUTHOR]

Research indicates that single-walled carbon nanotubes have a unique coupled torsional–radial vibration as one of their fundamental modes. Determination of their vibration frequency is required for efficient use of single-walled carbon nanotube in nano-electromechanical systems. However, there is no mathematical expression for these frequencies and their dependence on single-walled carbon nanotube geometry is unknown. This article examines the effect of diameter, length, and chirality on the fundamental coupled torsional–radial vibration frequency of single-walled carbon nanotube using molecular–structural–mechanics–approach, finite element analysis, and regression analyses. Consequently, a first-ever mathematical form of this frequency is derived. The form quickly and accurately predicts these frequencies at 1.5% in-sample, and 7.2% out-sample mean absolute percentage error. single-walled carbon nanotubes' fundamental coupled torsional–radial vibration frequency is found independent of diameter and inversely proportional to length where the proportionality constant depends on chirality. The coupling of modes and the similarity of the frequency form with cylindrical shell suggest that single-walled carbon nanotube behave like thin shells in these vibrations. A form for effective circumferential shear modulus of single-walled carbon nanotube is also derived. This modulus is found to depend only on the chirality where achiral single-walled carbon nanotubes have higher values than chiral single-walled carbon nanotubes. Proposed mathematical forms can be used for characterization of single-walled carbon nanotubes, determination of single-walled carbon nanotubes' effective shear modulus, and tuning operational frequency of single-walled carbon nanotube-based nano-electromechanical systems. [ABSTRACT FROM AUTHOR]

In technical textile engineering, macro-level phenomenological modelling effectively describes the material's highly nonlinear behaviour. However, existing material laws concentrate on the normal stiffness in the orthotropic yarns and simplify the shear effect because of the two orders of magnitude difference between shear and normal stiffness. This article introduces an improved phenomenological model that includes nonlinear shear behaviour, and it determines the material parameters with a previously applied data fitting method for exponential functions. The nonlinear shear behaviour is valid for the elastic state, that is, at the service level of the loads. Time-dependent, cyclic loading or plastic behaviour is not considered. [ABSTRACT FROM AUTHOR]

This paper study the dielectric and mechanical properties of poly (methyl methacrylate)-nickel silica core-shell nanocomposite. Ni@SiO2/PMMA nanocomposite films were prepared by incorporating Ni@SiO2 nanoparticles in PMMA matrix using the solution casting method. The morphology of the prepared nanoparticles was examined through a High-resolution transition electron microscope (HRTEM), which revealed the formation of SiO2 shell at Ni magnetic nanoparticles. The dielectric properties of the nanocomposite films were studied as a function of temperature and frequency in the ranges of 30–180°C and 100 Hz – 5 MHz respectively. The incorporation of the nano Ni@SiO2 to PMMA has a positive effect on the dielectric constant ε′ of the nanocomposites, as well as, ε′ improved with increasing temperature. The real electric modulus (M′) of composites confirms the occurrence of dispersion in all composites at all temperatures. While dielectric loss tangent ε ″ and the loss part of electric modulus spectra (M) exhibit relaxation peaks which characterize possible relaxation of interfacial polarization in the interface between Ni@SiO2 core-shell and PMMA matrix, these peaks have shifted towards higher frequency with temperature. The relaxation and activation energies, Ec and Ea values decreased from 0.49 to 0.40 eV and from 0.87 to 0.70 eV respectively as Ni@SiO2 content increased. The ac conductivity of the nanocomposite films has deeply increased with increasing temperature and Ni@SiO2 content. The longitudinal modulus (L), shear modulus (G), Young's modulus (E), and bulk modulus (B) of films were studied and they increased as the filler increased from 0 to 15 wt.%. [ABSTRACT FROM AUTHOR]

Fiber volume fraction is a driving factor in mechanical properties of composites. Micromechanical models are typically used to predict the effective properties of composites with different fiber volume fractions. Since the microstructure of 3D-printed composites is intrinsically different than conventional composites, such predictions need to be evaluated for 3D-printed composites. This investigation evaluates the ability of the Voigt, Reuss, and Halpin–Tsai models to capture the dependence of modulus and strength of 3D-printed composites on varying fiber volume fraction. Tensile coupons were printed with continuous carbon fiber-reinforced Onyx matrix using a Markforged Mark Two printer. Specimens were printed at five different volume fractions with unidirectional fibers oriented at either 0 ° , 45 ° , or 90 ° to obtain longitudinal, shear, and transverse properties, respectively. It is shown that the Voigt model provides an excellent fit for the longitudinal tensile strength and a reasonable fit for the longitudinal modulus with varied fiber content. For the transverse direction, while the Reuss model fails to capture the transverse modulus trend, the Halpin–Tsai model provides a reasonable fit as it incorporates more experimental parameters. Like conventional composites, addition of fibers degrades the transverse strength, and the transverse strength decreases with increasing fiber volume fraction. The shear modulus variation with fiber content could not be fitted reasonably with either Halpin–Tsai model or Reuss model. [ABSTRACT FROM AUTHOR]

The digital image correlation (DIC) technique is employed to measure the strain fields and the five independent elastic material constants of a glass/vinyl ester plain weave laminated composite. Transverse (through-thickness) tensile and Iosipescu shear properties were measured using thick (∼19 mm) laminates, and the strain fields were compared against those predicted by a homogenized linear elastic finite element analysis. DIC reveals that the strain fields of the laminates may present heterogeneous zones, which are attributed to the heterogeneous nature of the woven fabric architecture. Homogenization of the DIC strain fields to produce two-dimensional stress-strain plots yields average strains and elastic properties of the woven composite which can be similar to those measured by conventional (localized) strain gages. Important differences were found for the transverse tensile and Iosipescu shear tests, where differences of 26.4%, 28.6% and 11.9% were obtained for the measured transverse elastic modulus (Ez), in-plane shear modulus (Gxy) and transverse shear modulus (Gxz), respectively. [ABSTRACT FROM AUTHOR]

This work describes the use of transverse reinforcement in eco-friendly sandwich panels made from aluminium skins and a core of upcycled bottle caps. The Design of Experiments technique identifies the effect of the position of the metal rivets on the panel. The results show a moderate increase in strength and a significant enhancement of the sandwich panel stiffness when the rivets are placed on the upper skin, with a remarkable improvement in terms of the core shear modulus. The use of metal rivets has also increased the specific mechanical strength and stiffness of the panels, which highlights the effectiveness of the transverse reinforcement in bottle caps panels. [ABSTRACT FROM AUTHOR]

Recent researches show that the embedment of hollow spheres in the matrix phase of composite materials improves the strength of these structures against crack propagations. Rare studies are reported for calculating equivalent elastic constants of fiber reinforced composites containing hollow spheres. In this paper, the effects of hollow spheres on mechanical characteristics of fiber reinforced composite are studied for the first time. To achieve this aim, a micromechanics based finite element method is employed. Representative volume elements (RVEs) including hollow spheres with different radius, thickness and volume fraction of hollow spheres, are modeled by using 3D finite elements. The equivalent elastic constants are calculated through homogenization technique. The results are compared with available experimental works. Good agreements find between two sets of results. Also, the volume fraction, number and thickness of hollow spheres as effective parameters on mechanical properties of composite were investigated. The results show the equivalent elastic properties increase with increasing the volume fraction and number of hollow spheres and decrease with increasing the number of hollow spheres. Furthermore, the equivalent Young's modulus in transverse directions to the fiber direction and shear modulus of the composite increase with increasing the thickness of hollow spheres. As a final result, the presence of hollow spheres in the matrix phase generally increases the equivalent elastic constants without significant changes in the weight of structures. [ABSTRACT FROM AUTHOR]

Honeycomb sandwich structure finds immense applications in aerospace manufacturing and other similar fields. The Nomex honeycomb sandwich structural material exhibits a complex structure and boundary conditions, making it difficult to obtain exact solutions for the equivalent out-of-plane shear modulus and shear strength of the Nomex honeycomb using current analytical methods. To this end, based on the energy method, the Kelsey model is simplified in this paper. Then, distribution of the shear forces in the longitudinal and transverse directions of the Nomex honeycomb core is analysed using the simplified model. Considering the effect of the wall thickness of the honeycomb core on the ultimate strength, the analytical expressions of the out-of-plane shear modulus and shear strength of the Nomex honeycomb are proposed. The shear properties and failure process of the Nomex honeycomb in two directions are then analysed experimentally. The accuracy of the analytical expressions of the equivalent shear modulus and shear strength is verified experimentally. The equivalent out-of-plane shear modulus and shear strength of the honeycomb was demonstrated to be effectively predicted by the analytical approach. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental and analytical studies on the behaviour of sandwich beams fabricated with layered cores and glass fiber-reinforced polymer (GFRP) composite facings. The GFRP facings were fabricated using a unidirectional fiberglass fabric and epoxy resin, and the cores were fabricated using a thin non-woven continuous-strand polyester fiber mat with a thickness of 4.1 mm. A total of 30 sandwich beams with the width of 50 mm were prepared tested with five varying core configurations including cores made with one, two, or three layers of the fiber mat core and with or without the inclusion of intermediate GFRP layers. The specimens were tested up to failure under four-point bending at two different spans to characterize flexural and shear properties of the specimens. Two types of failure were observed, namely crushing of the compression facesheet and core shear. The load-deflection, load-strain, and moment-curvature behaviour were analyzed and using the results the flexural stiffness, shear stiffness, and core shear modulus were calculated. An analytical model was also developed to predict load-deflection behaviour and failure loading of sandwich specimens with varying core layouts. After verification, the analytical model was used for a parametric study of cases not considered in the experimental study, including additional GFRP and fiber mat core layers. It was shown that additional fiber mat core layers and the inclusion of intermediate GFRP layers can increase the strength and overall stiffness of a sandwich beam, while additional GFRP layers can only increase the overall stiffness of the system. The analytical model can be used to optimize the configuration of layered sandwich composites for cost effective rehabilitation techniques of culverts, pipelines, and other curved-shape structures where a thin, flexible core is needed to accommodate the curvature of the existing structure. [ABSTRACT FROM AUTHOR]

Fish Cells as a new metamaterial with zero Poisson's ratio in two planar directions is introduced with application in morphing aircraft skin. In order to tailor the design of this metamaterial for arbitrary loadings, equivalent elastic properties of the Fish Cells metamaterial are derived and analyzed using analytical and numerical methods. The admissible range of geometric parameters is presented and variation of elastic properties with parameters is studied. The effective elastic modulus of the metamaterial is derived analytically and verified with finite element models. The in-plane and transverse shear modulus of the metamaterial are evaluated using finite element analysis where accurate periodic boundary conditions for in-plane shear loading are investigated. The lower and upper bounds of the transverse shear modulus are derived based on strain and complementary energy relations which are verified with finite element results. As zero Poisson's ratio behavior of the Fish Cells topology is proved, derivative geometries from this topology with zero Poisson's ratio behavior are also presented. [ABSTRACT FROM AUTHOR]

This article is focused on the development and characterization of highly controllable magnetorheological materials for stiffness and damping control in semi-active control applications. Two types of magnetorheological materials are developed in-house: magnetorheological elastomer with soft base elastomer, and magnetorheological fluid encapsulated in regular elastomer, namely magnetorheological fluid-elastomer. In both cases of magnetorheological elastomers and magnetorheological fluid-elastomers, the samples are evaluated using in-house-developed shear and compression test rigs, which are equipped with electromagnets and Hall effect sensors for measuring the magnetic field. These features provide the capability to precisely control a wide range of magnetic fields during the experiments. In the case of magnetorheological elastomers, the experimental results of the in-house magnetorheological elastomers are compared with commercially available counterparts made of hard base elastomer. It is shown that the controllability of the material, that is, the relative magnetorheological effect, is significantly improved in the case of magnetorheological elastomer with soft base elastomer. In addition to various magnetic fields, the samples are subjected to a range of loading amplitudes and frequencies. A general trend is observed where the frequency and strain amplitude cause an opposite effect on both the shear and compressive moduli: the increase in frequency gives rise to a higher value of modulus whereas the increase in amplitude reduces the modulus. Furthermore, the effect of bonding on the performance of the magnetorheological elastomers in compression mode is evaluated and the results indicate a significant increase in the modulus and decrease in the loss factor. In all the cases, however, the change of loss factor does not exhibit a predictable trend as a function of magnetic fields. In order to investigate a magnetorheological-based solution for controlling the damping of a semi-active system, magnetorheological fluid-elastomer samples are made in-house. These samples are fabricated using three different iron concentrations, and are tested in compression (squeeze) mode. The results of these experiments confirm that the equivalent damping coefficient of the material rises with the increase in magnetic field, and this effect becomes stronger as the iron concentration of magnetorheological fluids increases. It is also demonstrated that the magnetorheological effect is highly dependent on the loading frequency and amplitude, where the equivalent damping coefficient decreases with the increase in loading frequency and amplitude. In all the aforementioned cases, the stiffness of magnetorheological fluid-elastomers exhibits minor changes, which offers the in-house-developed magnetorheological fluid-elastomers as a damping only control option, a development that is different from the magnetorheological fluid-elastomers reported in the literature. [ABSTRACT FROM AUTHOR]

This work presents an experimental and numerical investigation of the effects of pre-existing core damage on aluminum honeycomb core composite sandwich structures. Quasi static flexural and compression experiments were performed, where the effects of core damage on the shear modulus and Young's modulus were quantified. In addition, finite element analysis was performed on the sandwich structures to elucidate the effects of the core damage on the structural response. Comparisons of experimental and finite element responses are presented for sandwich structures consisting of carbon fiber facesheets and an aluminum honeycomb core. The pre-existing core damage is observed to cause up to an 8% reduction in shear modulus and a 9% reduction in elastic modulus. It is also determined that the presence of pre-existing core damage results in an asymmetrical compressive load distribution in the composite structures. [ABSTRACT FROM AUTHOR]

The mechanical properties of tissues in terms of elasticity and viscosity provide useful information for tumor detection. Recently, shear wave imaging has been developed to quantify tissue elasticity by estimating the parameters of the complex shear modulus (CSM). The current challenges of CSM estimation are estimation accuracy, computational complexity, and dealing with heterogeneous media. In this paper, we propose a two-dimensional CSM imaging method based on the extended Kalman filter (EKF). Firstly, particle velocities at spatial locations are acquired by using a Doppler ultrasound system. Then, the EKF is used to estimate the CSM at each spatial point, and hence for an area of interest using ray scanning. Finally, the CSM images are also enhanced using several image processing algorithms. Simulated experiment and performance studies are carried out to confirm the quality of the proposed method. [ABSTRACT FROM AUTHOR]

The concept of the "effective stiffness" for plies in laminates containing intralaminar cracks is revisited presenting rather accurate fitting expressions for the effective stiffness dependence on crack density in the ply. In this article, the effective stiffness at certain crack density is back-calculated from the stiffness difference between the undamaged and damaged laminate. Earlier finite element method analysis of laminates with cracked 90-plies showed that the effective longitudinal modulus and Poisson's ratio of the ply do not change during cracking, whereas the transverse modulus reduction can be described by a simple crack density dependent function. In this article, focus is on the remaining effective constant: in-plane shear modulus. Finite element method parametric analysis shows that the dependence on crack density is exponential and the fitting function is almost independent of geometrical and elastic parameters of the surrounding plies. The above independence justifies using the effective ply stiffness in expressions of the classical laminate theory to predict the intralaminar cracking caused stiffness reduction in laminates with off-axis plies. Results are in a very good agreement with (a) finite element method calculations; (b) experimental data, and (c) with the GLOB-LOC model, which gives a very accurate solution in cases where the crack face opening and sliding displacements are accurately described. [ABSTRACT FROM AUTHOR]

The present work aims to improve the mechanical properties of Epocast 50-A1/946 epoxy via incorporation of alumina nanoparticles using an ultrasonic agitation method. The optimum weight percentage of alumina nanoparticles was determined based on the improvement in the shear and impact properties of the nanocomposites at room temperature and 50 ℃. Accordingly, neat epoxy panels and nanocomposite panels with 0.5, 1.0, 1.5, and 2.0 wt% alumina nanoparticles were fabricated. The shear and thermo-mechanical impact properties of the panels were measured using an instrumented drop-weight impact machine and an Iosipescu shear test fixture, respectively, according to ASTMs D5379 and D7136. The maximum improvement in shear strength and modulus was 10.9% and 8.1%, respectively, for the nanocomposites containing 1.0 and 1.5 wt% alumina nanoparticles. The predicted shear moduli of the nanocomposites agreed well with the measured values with a maximum error of 6.52%. The optimal performance of impact properties was achieved by incorporating 1.0 wt% of alumina nanoparticles. Namely, the maximum impact-bending stiffness, contact force, and absorbed energy were increased by 12.9%, 13.0%, and 23.4%, respectively. The test temperature of 50 ℃ was found to have a negative effect on the impact-bending stiffness and the maximum contact force. On the other hand, the absorbed energy was increased up to 12.1%. [ABSTRACT FROM AUTHOR]

This study examined the thermal wear comfort of clothing made from flame-retardant (FR) rayon- and cotton-blended fabric using a thermal manikin and wearer trials. In addition, the tactile hand property of the FR rayon-blended fabric was predicted and compared with that of the cotton-blended one using the Fabric Assurance Simple Testing system. The FR rayon-blended fabric exhibited a lower heat insulation rate than that of the cotton-blended one in the thermal manikin experiment and lower microclimate humidity during 40 min walking in the human subject experiment. The FR rayon-blended fabric was more extensible than the cotton-blended one, with a lower bending rigidity and shear modulus. This study showed that FR rayon-blended fabric has better thermal wear comfort and a superior tactile hand feel compared with the cotton-blended one, without any significant difference of pilling compared to the cotton-blended modacrylic one. [ABSTRACT FROM AUTHOR]

Based on the equivalent single-layer linear theory for laminated shells, free and forced vibrations of thin cylindrical sandwich panels with magnetorheological core are studied. Five variants of available magnetorheological elastomers differing in their composition and physical properties are considered for smart viscoelastic core. Coupled differential equations in terms of displacements based on the generalized kinematic hypotheses of Timoshenko accounting for transverse shears with coefficients depending on the complex shear modulus for a smart core are used to govern vibrations of cylindrical panels. Assuming conditions of simple support for straight and curvilinear edges, solutions in the explicit form describing natural modes as well as an equation with respect to the required complex eigenfrequencies are found. To predict the shell response to an external harmonic force, the general solution of non-homogeneous governing equations is derived in the form of series in natural modes. To estimate damping capability of magnetorheological elastomers under consideration, the principle tunable parameters, the lowest natural frequencies and associated logarithmic decrements are calculated for the same panels with different magnetorheological elastomers under the action of a magnetic field of different intensities. Finally, the amplitude–frequency plots for magnetorheological elastomer-based panels of different opening angles with and without magnetic field are presented. [ABSTRACT FROM AUTHOR]

This article presents an exact analysis for the three-dimensional buckling problem of embedded multilayered magnetoelectroelastic and simply supported nanoplates/graphene sheets with nonlocal effect. The interaction between the multilayered nanoplates/graphene sheets and their surrounding medium is simulated by a Pasternak-type foundation. The critical loads for embedded multilayered magnetoelectroelastic nanoplates/graphene sheets under uniaxial and biaxial compression at small scale are then derived by solving the linear eigensystem and making use of the propagator matrix method. A comparison between the present anisotropic three-dimensional model and previous results (an asymptotic nonlocal elasticity theory for single elastic graphene sheet and classical orthotropic plate theories) is made to show the effectiveness and correctness of the present anisotropic three-dimensional model. Numerical examples are then presented for the variation of the dimensionless critical buckling loads for the homogeneous elastic graphene sheet with nonlocal effect, the homogeneous orthotropic thick plate without nonlocal effect, and the sandwich magnetoelectroelastic nanoplates made of piezoelectric and magnetostrictive materials with nonlocal effect. Furthermore, the effects of the thickness of nanoplates, nonlocal parameter, Winkler stiffness, and shear modulus of the elastic medium on the critical load of sandwich magnetoelectroelastic nanoplates/graphene sheets are demonstrated. These results should be very useful as benchmarks for the future development of approximate nanoplate/graphene sheet theories and numerical methods for modeling and simulation of multilayered nanoplates/graphene sheets with nonlocal effect. [ABSTRACT FROM AUTHOR]

The in-plane shear properties of nanostitched three-dimensional (3D) carbon/epoxy composites were investigated. Adding the stitching fiber or multiwalled carbon nanotubes or nanostitched fiber into carbon fabric preform slightly improved the shear strength and modulus of stitched and stitched nanocomposites. The in-plane shear fracture of the base and nanostructures was extensive delamination and tensile fiber failures in the sheared region. But, the stitched and stitched nanocomposites had angular deformation of the stitching yarns in the fiber scissoring areas, shear hackles in the matrix and successive fiber breakages in the interlayers. Probably, this mechanism prohibited extensive interlayer opening in the nanostitched composites. The results exhibited that introducing the stitching fiber (1.44%) and multiwalled carbon nanotubes (0.03125%) in the base structure enhanced its transverse fracture properties as a form of confined delamination area. Therefore, the damaged tolerance properties of the stitched nanocomposites were enhanced. [ABSTRACT FROM AUTHOR]

Characterizing the thermomechanical properties of thermoplastic resins and associated composites is of outmost importance to understand the development of process-induced stresses. To that extent, the characterization of a low viscosity PA66 matrix is proposed thanks to a homemade volumetric dilatometer named PvT-XT and a dynamic mechanical analyser on a wide temperature range. The PvT-XT results, reported for the first time, permit to identify the evolution of the coefficients of thermal expansion, of crystallization shrinkage and of the bulk modulus with temperature. Dynamic mechanical analyser experiments lead to the estimation of the Young's modulus. The shear modulus as well as the Poisson's ratio are then estimated thanks to analytical relations for isotropic and homogeneous materials. These properties are used to feed a new analytical model estimating the coefficients of thermal expansion of quasi-unidirectional composites. All the results are compared with the values from the literature or from complementary experiments, showing a good agreement which permits to validate the developed methodology. [ABSTRACT FROM AUTHOR]

The buckling of a woven fabric influences its performance throughout processing and during actual use. In addition, this phenomenon reflects on the recovery of the textile–polymer composites. The mechanics of the buckling behavior of woven, knitted or non-woven fabrics have a large number of different approaches, and the obvious inconsistency of applying the classical beam theory to the textile problem remains. The buckling of textile materials is a deciding factor of their drape and conformability. Fabric buckling also defines the ability of a fabric to fit to a different shape object without wrinkling. An empirical approach foundation to quantitatively compare the buckling of existing and new flexible textile materials, no matter what their composition, was developed. The buckling coefficient was found to be highly correlated to the fabric modulus of rigidity, fabric Young's modulus and fabric weave design. For the twill structure, the value of twill line angle to the direction of buckling force has a significant effect. In this paper, the buckling of woven fabric with or without holes was analyzed. It has been proven that major modes of deformation in the buckling of fabrics with holes are fabric bending rigidity, fabric design and the ratio of the volume of the hole to sample volume. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the contribution of viscoelastic material (VEM) to the control performance of the viscoelastic tuned mass damper (VTMD). Firstly, the equivalent fractional derivation Kelvin model is used to describe the frequency dependence of viscoelasticity in VTMD, and an index is proposed to characterize the level of frequency dependence. Then the effects of the high loss factor of VEM and frequency dependence of viscoelasticity on the effectiveness and robustness of VTMD control are analyzed by numerical examples. At last, a design strategy for VTMD is proposed to select the type of VEM and optimize its stiffness contribution. The results show that the frequency dependence of shear storage modulus of VEM is beneficial to further reduce the dynamic response of the primary structure equipped with VTMD, and the loss factor of VEM determines the optimum frequency ratio and control effect of VTMD. Compared to the conventional tuned mass damper, VTMD has a better robustness for the positive error of the natural frequency of VTMD but has a worse robustness for the negative error. The frequency dependence of shear storage modulus of VEM is beneficial to the robustness of VTMD for both the positive and negative errors of the natural frequency of the primary structure. The VEM with a strong frequency dependence of shear storage modulus is the ideal VEM for VTMD, and the proposed design strategy can deal with the trade-off between the control effectiveness and control robustness of VTMD. [ABSTRACT FROM AUTHOR]

In this study, the punch shear properties and damage mechanism of three-dimensional braided carbon/epoxy composites with different thicknesses are investigated both experimentally and numerically. Three kinds of specimen thickness are prepared: 3 mm, 5 mm, and 8 mm. A modified split Hopkinson pressure bar with a specially designed punch shear fixture are used to conduct the punch shear tests. The results indicate that the punch shear modulus increases along with the specimen thickness, whereas the peak punch stress shows insensitivity to the change in thickness. The specific energy absorption decreases with an increase in thickness due to a reduction in composite damage. Moreover, the dominant failure modes under punch shear loadings are discussed through SEM examinations and finite element analysis. The results show a high level of agreement between the experimental and finite element analysis models. Particularly, the finite element analysis model simulates the punch shear damage evolution at various high strain rates. Both the stress distribution and stress propagation process are also investigated in the model. It is found that a low-stress zone appeared in the punch region and the zone area decreases as the thickness increases. [ABSTRACT FROM AUTHOR]

In this study, the magnetic fatigue properties of a magnetorheological elastomer were evaluated with and without a magnetic field. To accomplish the process, a magnetic fatigue tester and magnetorheological elastomer samples were designed and fabricated. The mechanical properties of the magnetorheological elastomer were determined under various fatigue cycle numbers and fatigue frequencies with and without a magnetic field. The shear modulus of the magnetorheological elastomer was also measured before and after the test to evaluate its mechanical properties. The results show that the shear modulus of the magnetorheological elastomer was larger in the presence of a magnetic field and decreased as the number of fatigue cycles increased because the internal structure became loose. Scanning electron microscopy images showed that the internal structure of the magnetorheological elastomer was loose under repeated application of magnetic fields. [ABSTRACT FROM AUTHOR]

Variabilities of mesostructures existing in textile composites can affect their mechanical properties. Most of the deterministic mechanical models are based on the assumptions of ideal Representative Volume Element, which cannot predict the mechanical properties accurately. Two analytical models predicting the elastic constants of C/Epoxy plain-weave composites by considering the realistic mesostructures are presented in this paper. These models utilize the variable metric stochastic theory to introduce the fluctuations of yarn feature parameters (yarn path and elliptical cross-section parameters) into the model of macro elastic properties. C/Epoxy plain-weave composite is taken as an example to quantify the influences of realistic yarn feature parameters on the elastic constants of the composite. The predicted elastic constants by analytical models and finite element method are verified by the results of mechanical experiments. It can be concluded that for C/Epoxy plain-weave composite the stochastic fluctuations of yarn feature parameters reduce in-plane elastic moduli by a maximum of 4%, and increase the in-plane shear modulus and Poisson's ratio by a maximum of 15% and 33%, respectively. [ABSTRACT FROM AUTHOR]

Novel structural supercapacitors have been fabricated which can simultaneously carry mechanical loads as well as store electrochemical energy. Structural supercapacitors are fabricated by impregnating activated carbon fibre mat electrodes and glass fibre mat separator with crosslinked polymer electrolytes using the resin infusion under flexible tooling method. Mesoporous silica particles are also used as reinforcements to further improve the electrochemical and mechanical performance of structural supercapacitors. The fabricated structural supercapacitors have been characterised through chronoamperometry method and impedance spectroscopy to evaluate the electrochemical performance and in-plane shear properties to evaluate the mechanical performance. A multifunctional structural supercapacitor, exhibiting simultaneously a power density of 34 W kg[sup -1], an energy density of 0.12 Wh kg[sup -1] and a shear modulus of 1.75 GPa, has been fabricated. [ABSTRACT FROM AUTHOR]

An exact analytical approach based on Mindlin plate theory is considered for free vibration analysis of fluid-saturated porous annular sector plates. The interconnected network of pores is saturated by inviscid fluid and the fluid is trapped in the network. The plate’s radial edges are considered to be simply supported and four auxiliary functions are used to evaluate the natural frequencies of porous plates under undrained condition. The mechanical properties of the material are considered to vary through the thickness by expressing shear modulus and density in terms of a simple cosine rule in case of plates with pores free of fluid. The present method is validated by comparing it with the results of other accurate solutions found in the literature. The influence of the coefficient of plate porosity, geometrical parameters as well as the effect of fluid on natural frequency response of porous annular sector plates under various boundary conditions are comprehensively investigated. It is found that the presence of fluid in the interconnected network of pores causes the fundamental natural frequency to increase. The method proposed in this paper may provide useful information for the future assessments of the dynamic response of porous structures when fluid–solid interaction effects are fully taken into account. [ABSTRACT FROM AUTHOR]

Chopped carbon fiber tape-reinforced thermoplastic material is specifically developed for the high-volume production of lightweight automobiles. With excellent design processability and flexibility, the carbon fiber tape-reinforced thermoplastic material is manufactured by compressing large amounts of randomly oriented, pre-impregnated unidirectional tapes in a plane. Therefore, the carbon fiber tape-reinforced thermoplastic material presents transversely isotropic properties. Transverse shear effect along the thickness direction of carbon fiber tape-reinforced thermoplastic beam has a distinct influence on its flexural deformation. Accordingly, the Timoshenko beam theory combined with vibration frequencies was proposed to determine the set of transverse flexural and shear moduli. Meanwhile, the transverse flexural and shear moduli of carbon fiber tape-reinforced thermoplastic beam were finally determined by fitting all the first seven measured and calculated eigenfrequencies with the least squares criterion. In addition, the suggested thickness to length ratio for the 3-point bending test and Euler–Bernoulli model was given. [ABSTRACT FROM AUTHOR]

Magnetorheological gels typically are colloids of spherical micrometer magnetic particles dispersed in a high-viscosity polymer matrix. However, some major parameters of this kind of mono-disperse magnetorheological gel, such as the shear storage modulus and yield stress, cannot meet the needs of practical engineering application. In this study, a systematic experiment was investigated on the use of dendritic carbonyl iron particles to enhance the comprehensive performance in conventional (microsphere-based) magnetorheological gels formulated in polyurethane matrix. Two kinds of carbonyl iron particles that have very similar magnetic properties but very different morphologies (one is spherical and the other is dendritic) are employed. The dimorphic magnetorheological gels were prepared by adding dendritic carbonyl iron particles into the conventional spherical carbonyl iron particle–based magnetorheological gel and a series of dimorphic magnetorheological gel samples were prepared. The magnetorheological properties of those samples, both under oscillatory and rotational shear rheometry, were systematically tested. It was found that the dendritic carbonyl iron particle additives can significantly improve the shear storage modulus and response time of the dimorphic magnetorheological gels compared with conventional magnetorheological gels. Meanwhile, when the mass ratio of dendritic particles to carbonyl iron particles is 25% and 50%, the shear stress, static shear yield stress, and dynamic shear yield stress of dimorphic magnetorheological gels can also be greatly enhanced. [ABSTRACT FROM AUTHOR]

Braided composites can be manufactured in a variety of braid patterns: Diamond (1/1), Regular (2/2), and Hercules (3/3) and with longitudinal reinforcement (Triaxial). The complex strain fields, which could help reveal phenomenological behavior of braids, have not been experimentally assessed. As such, the objectives of this article were to investigate the effect of braid pattern (Diamond, Regular), braid angle (35°, 45°, 55°), and load (tensile, torsion) on the strain field and elastic properties (longitudinal and shear moduli) using a three-dimensional digital image correlation method. The methodology presented in this manuscript will be used to validate a new analytical model, which predicts the elastic properties of tubular braided of both varying braid type and braid angle. [ABSTRACT FROM AUTHOR]

In this paper, the effect of damage on the effective dynamic Young's and shear moduli of a viscoelastic adhesive is investigated, in both linear and nonlinear regions of adhesive behavior. The investigation method is based on the measurement of the nonlinear Frequency Response Function (FRF) of adhesive bonded structure and inverse eigen sensitivity identification technique. Several single-lap joint specimens are manufactured in healthy and damaged configurations and their linear and nonlinear FRFs are then measured, using the Optimum Equivalent Linear FRF (OELF) concept. The measured FRFs are then used to extract linear and nonlinear bending and shear modes of the bonded structure. The modes of healthy and damaged structures are further used for identifying of Young's and shear moduli at different frequencies. The results show that, for both linear and nonlinear regions, damages as small as 5% in the adhesive joint can be detected by the proposed technique, through their effects on the identified effective mechanical properties. [ABSTRACT FROM AUTHOR]

A novel technique to predict the manufacturing process-induced distortions and deformations in thick unidirectional carbon fiber reinforced plastics laminates is detailed in this article. An integrated numerical model is developed to account for non-isothermal resin flow, related compaction, transient resin cure, and resin shrinkage effects to predict the final shape of the autoclave cured thick prepreg laminate. The associated physics are mathematically coupled to solve for the process variables interactively. The results illustrate reduction in the thickness of the laminate prior to the start of curing when initial fiber volume fractions are pre-set. This confirms that the initial transverse deformation of B-stage prepreg is due to the applied vacuum and/or pressure. Once curing initiates, deformation of the laminate due to compaction increases, proportionally, with the increase in fiber volume fraction. Furthermore, the thermo-chemical residual strains contribute to additional compaction. The final distorted shape observed in simulation of the originally flat laminate matches with the shape of the fabricated laminate with 6.6 mm thickness. A solution to minimize the distortion is discussed in detail. This procedure is extended to simulate a curved laminate’s processing; where, the shear moduli were observed to influence the final shape of the laminate. The findings are presented and deliberated in this article. [ABSTRACT FROM AUTHOR]

Matrix damage, in the form of cracks parallel to the fiber, is a common failure mode for composite laminates, yet little is known concerning the associated shear modulus degradation. This study proposes a novel experimental technique to study shear modulus degradation under biaxial loading. An Iosipescu coupon was modified that induced transverse tension and compression loads while applying shear loading. The axial loads were induced using unbalanced layups with coupled normal–shear response. An analytical, closed-form solution was generalized to include unbalanced layups under a shear loading boundary condition. It was observed that the shear modulus degradation depends on the normal stress acting on the matrix transverse cracks. While compressive normal stress increased the effective shear modulus, the tension normal stress reduced the shear modulus, compared to pure shear loading. [ABSTRACT FROM AUTHOR]

Shape memory polymers show high promise in the area of morphing structures. Thermally activated shape memory polymers will exhibit shape memory effect under appropriate loading and thermal configurations. In this article, the steps in which a one-dimensional thermo-mechanical viscoelastic model is expanded into three-dimensional form are fully described. For the one-dimensional constitutive model, the standard linear viscoelastic arm is in series with a thermal and storage element. The three-dimensional translation is initiated by transforming Young’s modulus into bulk and shear modulus. Also, the compliance and stiffness matrix for correlating elements are defined and applied into the model. A binding factor is defined by the authors in the one-dimensional model in order to account for the storage strain energy within the polymer. To program the three-dimensional model into finite element analysis software, it was rendered into a time discrete form. The time discrete form was used to develop a UMAT subroutine code within ABAQUS to generate a numerical simulation. Finally, the results of this model are compared to available experiment data and previous model developed by the authors. Numerical simulation results clearly exhibit the thermo-mechanical properties of the polymer which include shape fixity, shape recovery, and recovery stress. [ABSTRACT FROM AUTHOR]

This article proposes an idea for the development of a novel frequency-tunable electromagnetic energy harvester, which mainly consists of a frequency-tuning system component and an electromagnetic energy-harvesting component. A magneto-rheological elastomer, a kind of smart material, was utilized in the design of the frequency-tuning part using its unique rheological characteristic that its shear modulus can be altered by changing the strength of an external magnetic field. When external excitation is provided to the system, the tip magnet oscillates relative to the coil to produce electricity. The stiffness of the system’s equivalent torsional spring composed of magneto-rheological elastomer blocks can be altered by changing the gap distance between two tuning magnets, which results in a shift in the primary natural frequency of the system and significant improvement of energy-harvesting efficiency. This article presents the detailed process for the design, simulation, experiment, and fabrication of the proposed energy harvester. Experiments and numerical simulations were also conducted under band-limited random excitation to support the validity of the present system. [ABSTRACT FROM AUTHOR]

The main focus of this paper is the experimental comparative analysis of the viscoelastic properties of acrylic- and silicon-based viscoelastic materials. These materials are widely used in the aeronautic industry for structural and/or damping applications. It is therefore required to determine their viscoelastic properties such as shear modulus and loss factor following their integration to aircraft composite structures. The influence of material thickness, bonding quality, curing and cocuring with composite material was evaluated using dynamic mechanical analysis machine in plan shear configuration. This comparative analysis in the 0–600 Hz frequency range provides useful information that should be taken into consideration when designing bonded joints for structural and/or damping applications. The small variation of the acrylic-based material loss factor over a wide range of frequencies suggests that this material is a good candidate for damping applications at room temperature in metallic structures where no curing is required. However, cocuring of acrylic-based material with composite laminae increases its shear modulus up to six times with respect to the uncured material whereas its loss factor is reduced by about 20%. On the other hand, the silicon-based material remains stable after thermal treatment (curing and cocuring) suggesting that it is well suited for in situ damping treatment involving laminate composite structure. However, at room temperature its shear modulus after cocuring is lowered by almost 25% due to poor bonding quality, which depends on the nature of the substrate. [ABSTRACT FROM AUTHOR]