Mechanics of Advanced Composite Structures
Volume:5 Issue: 2, Summer and Autumn 2018

This study investigated the effects of high temperature exposure on the compressive, tensile, and flexural strengths of concrete containing glass fiber. A total of 108 cubic specimens (150 mm × 150 mm × 150 mm), cylindrical specimens (300 mm × 150 mm), and prismatic specimens (500 mm × 150 mm × 150 mm) were prepared for compressive, tensile, and flexural strength testing, respectively. The specimens were incorporated with 1%, 2%, and 3% glass fiber and cured for 28 days to derive the desired strengths. The specimens were then annealed and subjected to experiments in which they were exposed to high temperature (600°C) for 30 minutes, one hour, and two hours. The specimens were cooled via slow cooling (exposure to air) and fast cooling (water spraying immediately after exposure to heat). Results showed that the presence of glass fiber exerted different effects on specimen strength and that heat caused the formation of numerous cracks in the specimens.

This study used particle swarm optimization (PSO) to determine the optimal values of effective design variables acting on the stress distribution around a quasi-triangular hole in an infinite orthotropic plate. These parameters were load angle, hole orientation, bluntness, fiber angle, and material properties, which were ascertained on the basis of an analytical method used by Lekhnitskii [3]. The cost function was regarded as the maximum stress created around the hole and was calculated using the aforementioned analytical approach. The finite element method was then employed to verify the results of the analytical calculation. The overlap in the analytical and FEM calculations confirmed the validity of the solution proposed in this research. The findings further indicated that the design variables significantly affect the stress distribution around quasi-triangular holes and structural load-bearing capacity. The performance of the PSO algorithm was also investigated.

This research developed new nanostructured Al–Fe3O4 composites via accumulative roll bonding (ARB). X-ray diffraction (XRD) analysis and field emission scanning electron microscopy were conducted to examine microstructural characteristics and particle distribution in the nanocomposites. Hardness and tensile strength tests were employed to examine their mechanical properties. After eight cycles of XRD analysis, the size of the Al crystals in the nanocomposites reached 198 nm. After eight cycles of tests on mechanical properties, the Al crystals exhibited a tensile strength and a hardness of 204 MPa and 63 HV, respectively. These values are higher than those achieved by pure Al. The depth of nanocomposite rupture observed in fractographic analysis revealed that a ductile fracture occurred in the materials because of the formation and growth of cavities.

This study investigates the time-dependent long-term creep strain in a composite cylinder made of glass/vinylester with a unidirectional ply. The cylinder is subjected to an internal pressure and the boundary condition is free–free and acts as thermal insulation. The classical lamination theory (CLT) is used to derive the governing equations as a second-order equation to determine the radial, circum-ferential, axial, and effective stresses in the cylinder wall. The distribution of the radial and circumferential creep strains is based on the Schapery’s single integral model for nonlinear viscoelastic materials. This study focuses on the effect of the orientation of the fibers on the creep strain distribution in the wall of a cylinder. The results show that the creep strain is lower when than at . As the angle of the fibers increases, the distribution of the creep strain becomes more uniform.

The effects of surface-functionalized Na+-montmorillonite nanoclay particles on the flexural behavior of E-glass fiber-reinforced aluminum (GLARE) laminates were investigated. The nanoclay particles were subjected to surface functionalization using 3-(trimethoxysilyl)propylamine to increase their compatibility with the epoxy matrix and improve their dispersion within the matrix. Experimental results indicated that the GLARE laminates achieved the highest flexural strength (61%) and energy absorption (51%) at an addition of 3 wt% functionalized nanoclay. The highest flexural modulus (67% increase) was observed at an addition of 5 wt% functionalized nanoclay. The flexural properties of the functionalized nanoclay-filled GLARE laminates were significantly better than those of untreated nanoclay-filled GLARE laminates. Microscopic observations suggested that the introduction of functionalized nanoclay particles markedly enhanced the interfacial adhesion between the matrix and the E-glass fibers.

Porous concrete is a mixture of cement and water that may contain fine grains, which play a role in water transfer and permeability. Porous concrete can act as a drain to pass rainwater and recharge groundwater. In this study, 25%, 50%, 75%, and 100% zeolite were used to replace the coarse aggregates in porous concrete. The effects of the zeolite on the compressive strength, permeability coefficient, porosity, and density of the concrete were investigated. The results showed that the zeolite reduced the compressive strength of the concrete samples because of its porous nature. The permeability coefficient and porosity increased with the addition of zeolite. The highest (10.29 MPa) and lowest compressive strength (6.79 MPa) were observed in the 25% and 100% zeolite samples, respectively. The highest porosity (30.97%) and permeability coefficient (1.76 mm/s) were measured in the 100% zeolite sample. For the 25%, 50%, 75%, and 100% zeolite samples, the permeability coefficient increased by 6.99%, 17.39%, 21.3%, and 24.4%, respectively; the density decreased by 7.77%, 10, 15%, and 19.44%, respectively, with respect to the control sample.

Epoxy and dicyclopentadien (DCPD) are two common healing agents, which are introduced into epoxy matrix through encapsulation in order to prepare self-healing composites. In a comparative study, the compatibility of healing agents and epoxy matrix is investigated through experimental tests and DFT calculations. The interaction energy is considered to be the determinative parameter in DFT calculation. The values of total interaction energy are -0.14eV for DCPD and +0.169eV for epoxy absorbing on epoxy matrix. According to the obtained results from DFT, an attraction between DCPD and epoxy matrix is observed. DOS and charge analysis of these systems are fulfilled and demonstrated the charge transfer of 0.07 e from epoxy to DCPD. The obtained data reveal the most charge transfer is occurred in DCPD-epoxy, which affects the mechanical properties of healed composites. To examine the mechanical properties, tensile strength parameters are measured experimentally and demonstrated the improved ultimate strength of 783.49 MPa in DCPD/epoxy system rather than the ultimate strength of 571.87 MPa in epoxy/epoxy system. Also elongation at break in DCPD-epoxy system is improved to 3.44% compared to 1.84% in epoxy/ epoxy blend. These findings highlight the role of interaction energy in mechanical properties of polymeric interface, and prompt further experiments and simulations to confirm this effect.

In the present paper, an analytical approach is used to study the thermal deflections of a simply supported composite plate with a beam-like stiffener. The results for a plate–beam system exposed to a sinusoidal thermal load is used to study the effects of the low Earth orbit (LEO) thermal conditions on the composite plates, which have been used in the structure of satellites and spacecraft. To solve the governing equations of the system, the Laplace transform method for the time domain is used with the Navier series expansions. As the employed method is completely analytical, the results are exact.

The present article investigates the thermoelastic interaction in a three-dimensional homogeneous and isotropic sandwich structure using the dual-phase-lag (DPL) model of generalized thermoelasticity. The incorporated resulting non-dimensional coupled equations are applied to a specific problem in which a sandwich layer of unidentical homogeneous and isotropic substances is subjected to time-dependent thermal loadings; the two outer sides are traction-free. The analytical expressions for the displacement components, stress, temperature, and strain are obtained in the physical domain using the normal mode analysis. The mathematical difficulties in dealing with the hyperbolic heat conduction equation are overcome and the thermophysical quantities of the sandwich structure are depicted graphically. The effect that the two phase lags have on the studied field are highlighted. The results demonstrate the phenomenon of a finite speed of wave propagation in a sandwich structure for each field.