An experimental study was conducted to investigate anisotropy effects on tensile properties of two short glass fiber reinforced thermoplastics. Tensile tests were performed in various mold flow directions and with two thicknesses. A shell–core morphology resulting from orientation distribution of fibers influenced the degree of anisotropy. Tensile strength and elastic modulus nonlinearly decreased with specimen angle and Tsai–Hill criterion was found to correlate variation of these properties with the fiber orientation. Variation of tensile toughness with fiber orientation and strain rate was evaluated and mechanisms of failure were identified based on fracture surface microscopic analysis and crack propagation paths. Fiber length, diameter, and orientation distribution mathematical models were also used along with analytical approaches to predict tensile strength and elastic modulus form tensile properties of constituent materials. Laminate analogy and modified Tsai–Hill criteria provided satisfactory predictions of elastic modulus and tensile strength, respectively.

Effects of fiber orientation and anisotropy on tensile strength and elastic modulus of short fiber reinforced polymer composites

Polypropylene (PP) nanocomposites reinforced with 0.1, 0.3, 0.5 and 1.0 wt% multi-walled carbon nanotubes (MWNTs) were prepared via melt-compounding in a twin-screw extruder followed by injection molding. The effects of MWNT additions on the structure, mechanical and yielding behavior of PP were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests. XRD traces showed that PP crystallized exclusively in α-form within the nanocomposite, indicating that the presence of MWNT did not influence the crystal structure of PP/MWNT nanocomposites via injection processing. DSC results confirmed that the corporation of MWNT enhanced the nucleation process on PP crystallization. It was also found that the glass transition temperature ( T g ) and the activation energy (Δ E ) increased with the increase of the amount of MWNT, demonstrating that the mobility of the polymer chain is reduced in the presence of MWNT. DMA analysis showed that the storage modulus and heat deflection temperature of PP/MWNT nanocomposite are improved considerably by adding only 0.3–0.5 wt% MWNT. The PP/MWNT nanocomposites were found to be strain rate and temperature dependence. Their yield stress was described successfully by Erying's equation. An index “ n ” was proposed to characterize the reinforcing effect of MWNTs in PP at a given temperature. The results showed that the n values for the PP/MWNT nanocomposites tend to increase with increasing test temperatures, indicating that the reinforcing effect of MWNTs in PP matrix is more pronounced at higher temperatures.

Mechanical behaviors of polypropylene/carbon nanotube nanocomposites : The effects of loading rate and temperature

A study of the mechanical behaviour of a glass fibre reinforced polyamide 6,6: Experimental investigation

Fatigue behavior and modeling of short fiber reinforced polymer composites: A literature review

Investigation of mechanical impact behavior of short carbon-fiber-reinforced PEEK composites

Tensile behavior of extruded short E-glass fiber reinforced polyamide-6 composite sheet has been determined at different temperatures (21.5°C, 50°C, 75°C, 100°C) and different strain rates (0.05/min, 0.5/min, 5/min). Experimental results show that this composite is a strain rate and temperature dependent material. Both elastic modulus and tensile strength of the composite increased with strain rate and decreased with temperature. Experimental results also show that strain rate sensitivity and temperature sensitivity of this composite change at a temperature between 25°C and 50°C as a result of the glass transition of the polyamide-6 matrix. Based on the experimental stress-strain curves, a two-parameter strain rate and temperature dependent constitutive model has been established to describe the tensile behavior of short fiber reinforced polyamide-6 composite. The parameters in this model are a stress exponent n and a stress coefficient σ*. It is shown that the stress exponent n, which controls the strain rate strengthening effect and the strain hardening effect of the composite, is not only strain rate independent but also temperature independent. The stress exponent σ*, on the other hand, varies with both strain rate and temperature.

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Zhen Wang

Papers

Effects of temperature and strain rate on the tensile behavior of short fiber reinforced polyamide-6