J. Compos. Sci., Volume 1, Issue 2 (December 2017) – 9 articles

The exact three-dimensional analysis of a large group of geometries is accomplished here using the same formulation written in orthogonal mixed curvilinear coordinates. This solution is valid for plates, cylindrical shells, cylinders and spherical shells. It does not need specialized equations for each proposed geometry. It makes use of a formulation that is valid for spherical shells and automatically degenerates in the simpler geometries. Second order differential equations are reduced of an order redoubling the number of variables, and then they are solved via the exponential matrix method. Coefficients of equations vary through the thickness when shells are considered. M mathematical layers must be introduced into each physical layer to approximate the curvature. The correlation between M and the order of expansion N for the exponential matrix is analyzed in this paper in order to find their opportune combined values to obtain the exact results. As their effects may depend on different parameters, several geometries, lamination sequences, thickness ratios and imposed half-wave numbers are taken into consideration. Full article

Sheet molding compounds (SMC) are discontinuously fiber-reinforced thermosets, attractive to the automotive industry due to their outstanding specific strength and stiffness, combined with a cost efficient manufacturing process. Increasingly important for structural components, a structural SMC-based improved resin formulation featuring no fillers is investigated in this study. The influence of fiber volume content, fiber length, and manufacturing induced fiber orientation on quasi-static and dynamic mechanical properties of vinylester-based SMC is characterized. Stiffness and strength increased with increasing fiber volume content for tensile, compression, and flexural loadings. Fiber length distribution did not significantly influence the mechanical properties of the material. The movement of the conveyor belt leads to an anisotropic fiber orientation and orientation-dependent mechanical properties. Acoustic emission coupled with machine learning algorithms enabled the investigation of the damage mechanisms of this discontinuous glass fiber SMC. The acoustic emission analysis was validated with micro computed tomography of damaged specimens. The dominant failure mechanisms of the SMC exposed to bending loading were matrix cracking and interface failure. Full article

Post-consumer recycled polypropylene (PP) with differing harakeke and hemp fibre contents was used to fabricate a range of 3D printing feedstock filaments. The most successful filaments in terms of tensile properties contained 30 wt % harakeke and had a tensile strength and Young’s modulus of 41 MPa and 3.8 GPa respectively. Comparing these results to those of post-consumer recycled PP filament, showed improvements in tensile strength and Young’s modulus of 77% and 275%. The composite that showed the least shrinkage consisted of 30 wt % harakeke with a shrinkage value of 0.34% corresponding to a net reduction of 84% relative to post-consumer PP. Full article

Processing parameters (e.g., exfoliation extent and volume fraction) of clay particles in polymeric resins play a crucial role in the mechanical properties of polymer nanoclay composites (PNCs). This paper is aimed to investigate the effects of clay aspect ratio and volume fraction on the global mechanical properties (e.g., effective stiffness, yield strength, and ultimate tensile strength) of PNCs. During the process, computational micromechanics models are adopted to simulate the nonlinear elastoplastic behavior of the PNCs of varying clay particle volume fractions and aspect ratios subjected to uniaxial tension. A representative volume element (RVE) of the PNCs is employed for the finite-element-method (FEM) based computational simulations. The polymeric matrix is treated as an idealized elastoplastic solid with isotropic hardening behavior, and the clay particles are treated as stiff elastic platelets distributed evenly in the stack and stagger configurations in the matrix. Seven volume fractions (V_f = 0.5%, 1%, 2%, 5%, 7.5%, 10%, and 15%) and seven aspect ratios (the ratio of platelet length over thickness ρ = 1, 2, 5, 10, 20, 50 and 100) of the reinforcing clay particles are utilized. Numerical experiments show that the effective modulus of the PNCs at small strains increases with the increase of either the clay volume fraction or the platelet aspect ratio largely following those predicted by classic micromechanics models. However, at the low particle aspect ratios (e.g., ρ = 1, 2, 5 and 10), the ultimate tensile strength of the clay composite is nearly independent of the clay volume fraction up to 5% in the present study, i.e., the polymeric matrix governs the PNC strength; at the large particle aspect ratios (e.g., ρ = 20 and 50), the ultimate tensile strength is significantly enhanced with growing clay volume fraction higher than 5% and reaches ~150% of that of the polymeric matrix at ρ = 50 and V_f = 10%. A comparative study is conducted for stack and stagger models for the prediction of the mechanical properties of PNCs. It shows that the stack model predicts slightly larger values of the effective stiffness and tensile strength than the stagger model. The numerical study shows that a large platelet aspect ratio through full exfoliation of the clay particles in matrix is crucial to achieving the preferable mechanical properties of PNCs as evidenced in experiments. The present results can be utilized to quantitatively explain the mechanical properties of clay particle-reinforced composites and PNCs within the framework of classic micromechanics, and provide guidelines for computer-aided nanocomposites design for processing property-tailorable PNCs. Full article

Replacement of damaged or missing bone tissue is a serious problem in orthopedic surgery. Although various artificial materials are available, none of them fulfil the requirements completely. In this study, new bone substitute materials, silica aerogel-based β-tricalcium phosphate, and hydroxyapatite composite ceramics, along with a control sample were synthesized and tested. Porosities and pore size distribution curves were determined by nitrogen gas adsorption/desorption porosimetry, and surface morphology changes were studied by scanning electron microscopy. Bioactivities were tested in vitro by soaking the samples in simulated body fluids (SBF). Three new advanced SBFs containing eight essential amino acids and bovine serum albumin were developed, extending the complexity of the original simulated body fluid in order to approximate the human blood plasma’s composition more accurately. Each sample was treated with SBF1–SBF4 for two weeks. According to our results, it seems to be necessary to re-evaluate hydroxyapatite deposition as proof of bioactivity of artificial bone substitutes when synthetic body fluids analogous in their composition to human blood plasma are used in studies. Full article

Finite element analysis is used to simulate the magnetoelectric response of magnetostrictive-piezoelectric NiFe2O4-Bi0.36Pb0.64Sc0.36Ti0.64O3 ceramic two-layer, three-layer, and multilayer structures considering finite geometry and introducing the conductivity of the magnetic component. Results are compared with those obtained with existing approximate analytical solutions, and with the experimental data available for high-quality layered composites. Limitations of the widely used analytical solution for a bilayer are revealed, and the reported good agreement with experimental coefficients is shown to be coincidental. Magnetoelectric coefficients obtained by simulation using realistic material parameters are systematically above the experimental values for three-layer and multilayer composites. Possible mechanisms for the reduction in response are analyzed. Strain relaxation across the piezoelectric layer, strongly associated with its mechanical performance, is shown to be the most feasible cause. Full article

Laser composite surfacing of aluminum alloys with ceramic particles has been extensively investigated for improving tribological properties. However, the process often results in incomplete penetration of ceramic particles in the melt pool and undesirable interfacial reactions. In this paper, laser composite surfacing of 2024 aluminum alloy with SiC particles is investigated using two distinct approaches: laser remelting and laser melting under the influence of ultrasonic vibrations of preplaced powder mixture. Detailed analysis of variation of clad layer thickness, microstructure in the composite clad layer, phase/texture development, surface roughness, and sliding wear performance with laser processing conditions is presented. The analysis showed that remelting and ultrasonic vibration assist results in significant improvement in clad layer thickness and microstructure (reduction in needle-like α-Si phase). While the laser remelting resulted in significant reduction in wear rate, the specimens processed with ultrasonic vibration-assisted laser melting showed variable wear rate, likely due to complex effects of microstructural modification and enhanced surface roughness. Full article

Multiscale epoxy/glass composites were fabricated by using E-glass fibers (GF) coated with different types of graphene nanosheets deposited by electrophoretic deposition. Graphene oxide (GO) was first synthesized using modified Hummer’s method and its subsequent ultrasonication in de-ionized water created a stable suspension of GO. GF were immersed in the water/GO suspension near a copper anode. The electrical potential applied between the electrodes caused GO to migrate towards the anode. Moreover, the GO coated yarns were exposed to hydrazine hydrate at 100 °C to obtain reduced graphene oxide (rGO) coated yarns. Both GO and rGO coated GF yarns were used to create unidirectional epoxy-based multiscale composites by hand lay-up. The presence of a conductive rGO coating on GF improved both the electrical and thermal conductivities of composites. Moreover, enhanced permittivity was obtained by rGO based epoxy/glass composites, thus giving the option of using such structures for electromagnetic interference shielding. Full article

Fiber-reinforced polymer (FRP) materials have been introduced recently in the construction of new structural systems, particularly in footbridge systems. Innovative systems that combine concrete with FRP materials lead to lighter and more slender structures as compared to conventional reinforced concrete structures, which can bring about vibration problems. In this work, a vibration analysis of a composite slab subjected to human activities is performed, both experimentally and numerically. The slab is composed of a concrete top laid on glass fiber-reinforced polymer (GFRP) I-section pultruded profiles. In the experimental analysis, two prototypes of 0.80 m width and 4.00 m span, representing a slab strip, were subjected to walking and jumping by several volunteers. In the numerical analysis, the slab was modeled by finite elements under dynamic loadings that simulate walking and jumping. Both the experimental and numerical results have indicated that the dynamic behavior under human activities of the composite slab must be considered in the design. Full article