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Elium® is a novel liquid Methylmethacrylate thermoplastic (TP) matrix that can be cured at room temperature. Elium® resin provides the properties of TP polymer composites and is a competitive alternative to epoxy-based composites. In this work, a quadriaxial non-crimp (NC) glass fabric/Elium® based polymer composites were manufactured using vacuum assisted resin transfer moulding (VaRTM). The static mechanical properties of these composites were evaluated under the tensile and flexural loads. Further, interfacial properties like interlaminar shear strength (ILSS) and fracture toughness (Mode-I and Mode-II) were characterised. To study the influence of ageing on the mechanical properties of glass fabric/Elium® (GF/E) based composites, the test samples were aged in distilled water at a temperature of 60°C for 60 days. The obtained mechanical properties were compared between dry samples (control) and post-water immersed (aged) samples. It was found that water ageing degraded the properties of tensile, flexural strength, ILSS and Mode-II toughness by 30%, 59%, 46%, 37%, respectively. On the contrary, Mode-I fracture toughness of aged samples was 90% higher, indicating significant fibre bridging due to ageing. The microscopy and scanning electron microscopy (SEM) revealed significant failure as the degradation of fibre/matrix interface due to hygrothermal ageing. The overall performance of GF/E composites with infusible TP resin is sensitive to hygrothermal ageing. [ABSTRACT FROM AUTHOR]

In this study, nonlinear aeroelastic instability of a composite sandwich panel subjected to a supersonic airflow and thermal loading is investigated. The sandwich panel is composed of three-phase composites with polymer/Graphene platelet/fiber skins at the top and bottom surfaces and an auxetic honeycombs core layer with a negative Poisson's ratio. The motion equations of the panel within the framework of higher-order shear deformation theory (HSDT) and von Kármán nonlinearity are driven. In addition to Krumhaar's modified supersonic piston, unsteady aerodynamic pressure in the supersonic flow regime is considered. The governing equations of the sandwich panel are derived by implementing Hamilton's principle and solved by the generalized differential quadrature method (GDQM). Validation of the present formulation is assessed by comparing the numerical results with those available in the open literature. Then, the effects of several parameters such as geometric parameters, volume fraction, Mach number, different boundary conditions, yaw angle, and different inclined angles on the nonlinear aeroelastic stability of sandwich panels are examined. Finally, it was found that the ratio of core thickness, inclined angle, and Mach number have significant effects on aerodynamic pressure. [ABSTRACT FROM AUTHOR]

The effect of hygrothermal aging on the tribological and mechanical behaviors of UHMWPE biocomposites reinforced with different weight fractions of mollusc shell (MS) particles was investigated. The developed MS-UHMWPE biocomposites samples were subjected to accelerated hygrothermal aging in Ringer's solution at 80°C. The results showed that hygrothermal aging increases the tribological behavior of these biocomposites. The effect of hygrothermal aging on the wear resistance depends on the reinforcement rate of the MS particles. The mechanical properties of the MS-UHMWPE biocomposite were affected by hygrothermal aging as well as by the weight content of the added MS particles. The modulus of elasticity increased with increasing MS particle content for all tested materials. A scenario of the wear mechanism of aged biocomposites will be proposed. [ABSTRACT FROM AUTHOR]

The moisture content has an important influence on the strength and stability of coal pillar dams in underground reservoirs. In this paper, the uniaxial compression test was performed on coal samples with three different moisture contents, to study the mechanical properties of them under water intrusion condition. The results show that, water has a significant damaging and softening effect on the mechanical properties of the samples. As the moisture content grows of coal samples, the peak strength and elastic modulus fall exponentially while the peak strain increases exponentially. In addition, the energy characteristics of coal samples with different moisture contents under uniaxial compression were analyzed. The releasable elastic strain energy, dissipated energy and total input energy all experience a decline with water content, and the proportion of the releasable strain energy in the total energy drops. The capacities of energy storage and strain energy release of coal samples both fall under influence of moisture, and more energy was transformed. Given this result, the damage variable on the basis of energy dissipation was introduced to explore the influence of moisture contents on the damage variable of coal samples and the damage evolution equations of coal samples with three different moisture contents were calculated from the results of uniaxial loading tests. Finally, the compaction coefficient considering the influence of immersion time was proposed to describe the compaction degree and being used to amend the damage constitutive model obtained, and the fitted results of the models were compared to experimental data. Results show that the values of damage variables increase exponentially with strains, and the modified damage constitutive equation can give a more accurate description of the compressive deformation of coal samples that contain varying contents of moisture. [ABSTRACT FROM AUTHOR]

The vibration analysis of an axially functionally graded material non-prismatic Timoshenko beam under axial thermal variation in humid environment is carried out using the harmonic differential quadrature method. In this modeling, the length and width of the beam remains constant whereas thickness of the beam is linearly varied along the axis of the beam. The material properties are temperature dependent and are assumed to be varied continuously along the axial direction according to power law distribution. Three types of temperature variations are considered in this study, that is, uniform temperature rise, linear temperature rise, and non-linear temperature rise. The temperature of the beam remains constant under uniform temperature rise condition and it is varied linearly and nonlinearly along the length of beam for rest of the conditions. The beam is subjected to uniform moisture concentration to impose humidity. Hamiltonian's approach is used to derive the governing equations of motion. The resultant governing equations are then solved using the harmonic differential quadrature method to obtain the natural frequencies of the axially functionally graded material non-prismatic beam. The results obtained using the harmonic differential quadrature method are compared with results obtained for special cases. The effects of thermal variation, humidity, non-homogeneity parameter, and end conditions on natural frequencies of the non-prismatic beam are reported. [ABSTRACT FROM AUTHOR]

The nonlocal strain gradient theory, when combined with the first-order shear deformation theory, provides many capabilities in size-dependent structures. The aim of the present study is evaluation of the free vibration behavior of two vertically aligned fluid-conveying single-walled boron nitride nanotubes in hygrothermal environments considering slip boundary condition based on Knudsen number. These two adjacent nanotubes are coupled in the context of linear deformation through van der Waals interaction according to Lennard–Jones potential function. Actually, the contribution of the present work, compared with those previously reported, is investigating the simultaneous effect of hygrothermal loading and slip boundary condition on the dynamic behavior of two vertically aligned fluid-conveying single-walled boron nitride nanotubes. As an additional step to achieve a more accurate model of low-scale structures, both hardening and softening effects of materials are taken as important variables in the nonlocal strain gradient approach. To derive the motion equations and associated boundary conditions, Hamilton's variational principle is used. The equations are then solved with the aid of differential quadrature method. Numerical studies are also performed to depict the effects of a number of parameters such as boundary conditions, size scale, aspect ratio, inter-tube distance, and temperature alteration on the variations of dimensionless eigenfrequency and critical flow velocity. [ABSTRACT FROM AUTHOR]

This paper aimed to evaluate hygrothermal aging effects on polymethyl methacrylate modified with TiO2, SiO2, and Al2O3 nanoparticles in 0.5, 1, and 2% weight fractions. The distribution of nanoparticles was characterized by the scanning electron microscopy (SEM) method. Moisture absorption behavior and mechanical properties of samples in terms of elastic modulus, tensile strength, impact strength, and hardness were investigated. Furthermore, the coefficient of hygrothermal expansion (CHE) for each sample was calculated thanks to experimental data. Finally, by applying the multi-criteria decision making (MCDM) technique, the optimum composition for superior performance was obtained in 0.5 wt% of nanoparticles, more specifically for SiO2. [ABSTRACT FROM AUTHOR]

This work aims to characterize the influence of hygrothermal conditioning on the mechanical and thermal behavior as well as the fractographic aspects of the interface of poly(ether imide) and glass fiber composite joints welded by electrical resistance using 400 mesh of AISI 304 stainless steel. The composites were mechanically characterized by Lap Shear Strength (LSS) and End Notched Flexure (ENF) testing to investigate maximum shear stress and energy from mode II interlaminar fracture toughness. Fractography was performed by SEM, while the influence on glass transition temperature and working temperature were evaluated by Dynamic-Mechanical Analysis and thermogravimetry. In the conditioned samples, the mechanical properties reduced 23% in the LSS test and 28% in the ENF test, while the fractography studies revealed elements of interlaminar and intralaminar fracture in both conditions. Thermal properties did not change significantly to disqualify this composite when applied to welding. [ABSTRACT FROM AUTHOR]

The present article deals with the vibration and damping characteristics of functionally graded carbon nanotubes reinforced hybrid composite skewed shell structure in different hygrothermal conditions. Carbon nanotube reinforced polymer as a matrix phase and carbon fibre as a reinforcing phase are used, and carbon fibre is graded with uniform distribution along the thickness direction for the shell panel according to the power law distribution. The Mori–Tanaka scheme and strength of materials are used to determine the mechanical properties of such functionally graded carbon nanotubes reinforced hybrid composite materials. Finite element modelling has been done by considering an eight-noded shell element with the transverse shear effect according to Mindlin's hypothesis, and an oblique coordinate system is used for the functionally graded carbon nanotubes reinforced hybrid composite skewed shell structures. Damping is incorporated into such carbon nanotube–based hybrid skewed shell structure based on the Rayleigh damping model. A MATLAB-based in-house computer code has been developed for the proposed formulation and verified with published research work before using for the present dynamic analysis of functionally graded carbon nanotubes reinforced hybrid composite skewed shell structure under hygrothermal conditions. The effect of the carbon nanotube, carbon fibre, material distribution as per power law index and hygrothermal conditions on the damping behaviour of such functionally graded carbon nanotubes reinforced hybrid composite skewed shell structures have been studied. Furthermore, parametric studies are carried out for the first resonant frequency, absolute amplitude, settling time and carbon nanotube impact on the vibrational behaviour of different functionally graded carbon nanotubes reinforced hybrid composite skewed shell structures under different hygrothermal conditions. [ABSTRACT FROM AUTHOR]

A new fourth-order in-plane displacement field based refined higher-order zigzag theory is proposed for analysis of laminated sandwich plate (for both skew and non-skew shaped) subjected to hygro-thermal conditions. In order to predict behavior of thick laminated sandwich plates, third-order transverse displacement field is taken. Zig-zag effects are introduced using linear unit Heaviside step function. The theory satisfies zeros transverse normal and shear stress condition at the bottom and top surface of the plate along with continuity condition at interface. The proposed model is free from any kind of C-1 or penalty function requirements. Nine-noded isoparametric finite element having twelve degrees of freedom per node is used during analysis. Since, the present theory incorporates transverse displacement field along with continuity conditions, is able to predict the behavior of thick sandwich plates more efficiently. In literature no results are present for skew laminated composite and sandwich plates therefore, present results for skew plates are entirely new and will serve as benchmark for future studies. [ABSTRACT FROM AUTHOR]