Journal of Reinforced Plastics and Composites

This study describes a multi-faceted materials selection problem that ultimately produces a new class of polymer—fiber composites with failure strains of near 400% and ultimate tensile strengths (UTS’s) up to 20 MPa. Independent control of the rubbery modulus (proportional to the compressive force the composite can apply) is demonstrated by altering the crosslinker density of the polymer matrix and the fiber weave. The stress the composite can withstand can be modified with changing fiber material and weave geometry. The resulting SMP—fiber composites can be designed with glass transition temperatures (T_g’s) ranging from 0°C to 75°C, and specific multi-layer combinations of these systems provide a promising candidate for orthopedic casts: specifically, a woven anteres nylon lycra mesh rigidized with a polymer synthesized from methyl acrylate, butyl acrylate, isobornyl acrylate, and trimethylol propane triacrylate. The results of this study are intended to enable future orthopedic applications where the ability to accurately and independently position T_g and the ability to tune recoverable force in toughened, fiber-reinforced SMPs are required.

Biodegradable composites were prepared by melt-blending technique using 30 wt% kenaf bast fiber (KBF) to reinforce 70 wt% plasticized poly(lactic acid) (PLA). The KBF was treated with various percentages of sodium hydroxide (NaOH), whereas 5% triacetin was used as plasticizer. The effects of the KBF surface treatments on the tensile, flexural, impact strength, and DMA of the biocomposites were investigated. Tensile, flexural, and impact testing results reveal that 4% of NaOH-treated KBF produced composites with optimum tensile strength (62 MPa), flexural strength (67 MPa), and the impact strength (42 kJ/m²). The removal of the lignin from the fiber during the surface treatment caused the increment in the modulus result. This finding is also supported by the dynamic mechanical analysis. The storage modulus of plasticized PLA/treated KBF is higher than the storage modulus of plasticized PLA/untreated KBF which is attributed to the enhancement of the fiber—matrix adhesion. The loss modulus results showed that the T_g of the plasticized composites was shifting to higher temperature, from 55°C for plasticized PLA/untreated KBF to 65°C for plasticized PLA/treated KBF. The increase in T_g shows that the plasticized PLA has low chain mobility when reinforced with treated KBF, indicating better interaction.

Thermoset/thermoplastic blends, namely diglycidyl ether of bisphenol A/polycarbonate (epoxy/PC) system, with different weight percentages of PC, were cured using aliphatic curing agent triethylene tetramine (TETA) and mechanical properties of the cured resin were studied. Further, series of silane coupling agent treated fly ash in 6 wt% PC/epoxy resin blend matrix cured with TETA were prepared by hand lay-up method. Variation in deformation behavior in the form of mechanical properties namely, tensile, flexural, compression, and impact behaviors with filler content was evaluated. Fractographic study of blends and composites using SEM was investigated.

A novel mechanical extraction process was developed to obtain long bamboo fibers to be used as reinforcement in structural composites. A single-fiber tensile test at four different span lengths for fibers of the bamboo species Guadua angustifolia was performed. Strength values of 800 MPa and Young’s modulus of 43 GPa were obtained. Unidirectional bamboo fiber/epoxy composites (BFC) were produced with untreated and alkali-treated fibers to evaluate the effectiveness of the new reinforcing material. Flexural tests were performed with two fiber orientations (longitudinal and transverse). The longitudinal flexural strength is higher when untreated fibers are used while the treatment benefits the longitudinal flexural stiffness of the composite. Transverse strength increases at lower alkali concentrations, but the transverse three-point bending strength of untreated bamboo in epoxy is already quite high at around 33 MPa. The results illustrate that these bamboo fibers present a natural and renewable option to reinforce composites in several applications where glass fiber and traditional natural fibers are used nowadays.

Approximative formulas for post-buckling analysis of non-linearly elastic columns made of Ludwick material are developed for free-clamp, hinge—hinge, and clamp—clamp supports. The columns have a superellipsoidal cross-section. Comparison between analytically obtained and numerical solutions showed good agreement. Additionally, post-buckling configurations for all three types of columns and materials are given in diagrams, from where the influence of material constants on the shape of the deflection curve can be examined.

In this study, the finite element method is used to analyze the effect of the thermal residual stresses resulting from adhesive curing on the performances of the bonded composite repair in aircraft structures. The stress intensity factor at the crack tip is chosen as the fracture criterion in order to estimate the repair performances. The effects of the curing temperature, the geometrical properties of the patch, and the adhesive properties on the variation of the stress intensity factor are analyzed. The obtained results show a significant negative effect of the thermal residual stresses on the repair efficiency and this effect can be reduced if the different repair parameters are optimized.

The article studied the friction and wear properties of UHMWPE when the surface was probed with micro-defect. The results indicated that the friction coefficient decreased when the micro-defect holes were gradually distributed on the friction surface uniformly. That was mainly because the uniform micro-defect holes formed regular texture, increasing the balance of friction and wear. The wear loss of UHMWPE decreased gradually with the increase of the amount of micro-defect holes, and there was a good linear relationship between them. When the friction surface was filled with uniformly distributed micro-defect holes, not only the wear loss decreased, but also wear debris with ideal size distribution was obtained. So, the theoretical and experimental basis was provided for the idea of the surface texturization of artificial arthrosis.

This study gives the comparative analysis of polypropylene (PP)/oil palm flour (OPF) and PP/oil palm clinker (OPC) composites using maleated polypropylene (MAPP) as a coupling agent. Ground flour and crashed OPC were compounded separately into polypropylene with and without MAPP using a twin-screw compounder. The incorporated OPF and OPC in the composites were up to 40 wt%. The compounded samples were prepared into test specimens by injection molder. The composites were characterized by tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, and melt flow index. The surface morphology of composites was evaluated by scanning electron microscope. Incorporation of coupling agent showed better result than that of without coupling agent. Various properties of composites incorporated with OPC represented considerably close to the composites with OPF.

The results of an experimental study on the cyclic axial loading and unloading behaviors of thin-walled GFRP cylindrical shells are presented. Each specimen was tested first under pure axial compression until the first visible damage occurred, At that point, loading stopped and the unloading step started until the load returned to zero. Based on the results, it seems that for cyclic loading, using stiffened shells is better than using unstiffened shells. On the other hand, the damage growth in the stiffened shells is slower than in the unstiffened shells. For aerospace and aircraft structures, which have been using cyclic axial loading, it seems that composite structures with composite helical stiffeners are better than unstiffened composite structures.

This article reviews the literature reports based on polystyrene nanocomposites using nanoclay as filler. The use of various clay surfactants and different processing conditions, i.e., in situ polymerization, melt intercalation and solution casting used for the preparation of nanocomposites and its effect on the properties and morphology is also reviewed.