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Smart laminated composite structures with piezoelectric patches are widely used in vibration control applications in several engineering fields. Precise mathematical models are required for the coupling of base structural and piezoelectric field variables. This paper presents the electro-structural analysis and optimization studies of piezoelectric energy harvester with laminated composite substrate plate subjected to base excitations. The coupled electro-mechanical equations are derived from recently proposed first-order shear deformation theory via the Hamilton's principle by considering hygrothermal effects. The coupled-field solution is obtained from Ritz-approximation and validated with three-dimensional finite element analysis. Effects of multiple piezoelectric patch topologies over the plate surface on the open-circuit voltage and displacement response are illustrated. Furthermore, the influences of piezoelectric-patch sizes, ply-orientation, size, and location of the tip mass are initially studied on the magnitude of output power and efficiency. An optimization study is conducted to identify the geometric and material variables for improvement of the harvester power output and efficiency. [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]

Analytical and numerical results on transverse shear stresses of angle-ply composite plates subjected to hygrothermal loadings are scarce in literature. Thus, a higher order global-local model a priori satisfying the continuity condition of transverse shear stresses is proposed for hygrothermal analysis of angel-ply composite plates. Based on the higher order global-local model, a triangular element is developed by using the refined element approach. Comparing the results from available three-dimensional elasticity solution, the proposed model can produce promising transverse shear stresses directly from constitutive equations without any smoothing technique. By analyzing hygrothermal response of composite plates with general configurations, the effects of material properties, lamination angles, boundary conditions, transverse normal strain, and hygrothermal expansion coefficients on the hygrothermal response have also been studied. Differing from previous work, the corrected hygrothermal expansion coefficients are used for hygrothermal analysis of composite plates. [ABSTRACT FROM AUTHOR]

The effect of moisture and temperature on the strength of composite single-lap bonded joints were extensively investigated. Secondary bonded-joint specimens were immersed in tap water and 3.5% salt water at 71°C for different durations up to a maximum of 300 days. A total of 160 specimens were tested under six different moisture contents and two different temperature environments. Test results showed that while the strengths of the joints with 2.1% or more tap water moisture content decreased compared with those of dry joints, the strengths of pre-saturated joints with up to 1.0% moisture content increased at both room and elevated temperature. However, the strengths of saturated joints at 2.5% moisture content decreased by 34% (room temperature) and 44% (71°C) compared with those of the dry joints. In the joints with 1.0% or lower moisture content, the higher temperature environments resulted in slightly increased strengths, whereas the elevated temperature degraded the strengths in the joints with 2.1% or greater moisture content. The major failure modes of the joints were delamination and intralaminar failure of the composite adherend; the joints with high moisture content tested under elevated temperature showed cohesive failure of adhesive. The strengths and failure modes of the joints that were immersed in salt water did not show a remarkable difference from the joints that absorbed tap water. [ABSTRACT FROM AUTHOR]

Experimental and analytical investigation was conducted to understand the hygrothermal properties of uniweave T300/QY9512 laminates. Tests were performed under hygrothermal and room temperature environment separately. Effect of stitching parameters upon strength performance of laminates was predicted using FEM model. Compressive strength of laminates, under different environmental conditions, was also predicted. Test results have shown that hygrothermal environment condition has a severe effect on the compressive strength of laminates and the reduction in compression strength for stitched laminates reached up to 50%. Stitching might improve the compressive strength of laminates depending upon the environmental conditions and lay-up sequence of stitched laminates. [ABSTRACT FROM AUTHOR]

This work reports hygroscopic, thermal, and mechanical properties of biomass composites comprising sisal fiber reinforcing castor oil PU resin. The effects of reinforcement geometry and alkaline treatment of fibers were evaluated. In general, alkaline treatment improved quasi-static tensile properties of composites with short randomly oriented and long aligned sisal fibers, respectively. On the other hand, an adverse effect of alkaline treatment was observed in the mechanical behavior of the composite with bidirectional fabric architecture. The outstanding influence of moisture on thermo-mechanical properties of biomass composites was confirmed through thermogravimetric and differential scanning calorimetry techniques. Dynamical-mechanical thermal analysis showed increased storage modulus (i.e., stiffness) and decreased damping properties of biomass composites as compared to neat PU matrix. Dynamical-mechanical testing also detected unexpected decrease on glass transition temperature of composites in regard to the neat polymer resin; resin plasticization due to moisturized fibers and/or alkaline treatment residues was identified as probably the culprit. [ABSTRACT FROM AUTHOR]

Effect of temperature, moisture, and temperature and moisture combined (i.e., hygrothermal) on the compressive strength of four types of uniaxially fiber-reinforced polymer matrix composites (PMCs) have been evaluated using the theoretical model [12] of fibers microbuckling as the cause of failure under compression. The purpose is to show the severity of reduction in compressive strength of PMCs caused solely due to plasticization of the matrix, when the geometrical and material imperfection factors, which are almost unavoidable and cause further reduction in strength, are not incorporated and accounted for in the analysis. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effect of hygrothermal aging on both the static and thermo-mechanical behavior of polyetherimide composites. Tensile testing and dynamic mechanical thermal analysis were performed on the hygrothermally aged polyetherimide composites in the climatic cabin. The decrease in the Tg temperature, also following a decrease in the yield energy, indicated the plasticization for hygrothermally aged glass fiber reinforced PEI composite, but both tensile and DMTA analysis pointed out that glass fiber reinforced PEI composite retained its static and dynamic behavior on a large scale. The higher thermal expansion mismatch problem between carbon fiber and PEI matrix caused a remarkable decrease in the static energy values of the composite. [ABSTRACT FROM AUTHOR]

On the basis of the existence of strong bonding between carbon nanotubes (CNTs) and polymer matrix, and considering the axial and radial thermal expansion coefficients of CNTs as nonlinear functions of temperature changes, this article presents an analytical method to investigate hygrothermal effects on the interfacial stress transfer characteristics of single-multiwalled CNTs-reinforced composites system under hygrothermal loading by means of thermoelastic theory and conventional fiber pullout models. According to the known literature, the thermal expansion coefficient of CNTs is considered as transverse isotropy, and is a nonlinear function of temperature changes. The thermal expansion coefficient of polymer matrix is isotropy, and is a linear function of temperature changes. Numerical examples show that the interfacial shear stress transfer behavior can be described and affected by several parameters such as the temperature changes in CNTs-polymer composite, the moisture concentration changes in polymer matrix, the layer numbers, volume fractions, and chiral vectors of CNTs. From the results obtained it is found that mismatch of the thermal and moisture expansion coefficients between the CNTs and polymer matrix may be more important in governing interfacial stress transfer characteristics of CNTs-reinforced composites system. [ABSTRACT FROM AUTHOR]