No abstract

A mathematical analysis is conducted on the experimental results of a study conducted on epoxy-based glass fiber reinforced plastics (GFRP) composites. Three different types of reinforcements were used in the form of woven fibers. Fabrics made of glass fibers, carbon fibers, and (glass-carbon) hybrid fibers were used at different volume fractions. E g Longitudinal moduls of elasticity of glass fibers. E c Longitudinal moduls of elasticity of carbon fibers. V m Volume fraction of matrix. V f Volume fraction of fibers. V c Volume fraction of carbon fibers.  1 Fracture stress of composites.  f Fracture stress of fibers.  m Fracture stress of matrix.  hL Fracture stress of hybrid interply composites.  g Fracture stress of glass fibers.  c Fracture stress of carbon fibers .

No abstract

In situ chemical reaction method was used to synthesize Cu-ZrO 2 nanocomposite powders. The process was carried out by addition of NH 4 (OH) to certain amount of dispersed Cu(NO 3 ) 2 ·3H 2 O and ZrOCl 2 ·8H 2 O solution. Afterwards, a thermal treatment at 650 °C for 1 h was conducted to get the powders of CuO and ZrO 2 and remove the remaining liquid. The CuO was then reduced in preferential hydrogen atmosphere into copper. The powders were cold pressed at a pressure of 600 MPa and sintered in a hydrogen atmosphere at 950 °C for 2 h. The structure and characteristics were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results showed that the nanosized ZrO 2 particles (with a diameter of about 30-50 nm) was successfully formed and dispersed within the copper matrix. The density, electrical conductivity, mechanical strength measurements (compression strength and Vickers microhardness) and wear properties of Cu-ZrO 2 nanocomposite were investigated. Increment in the weight % of ZrO 2 nano-particles up to 10 wt.% in the samples, caused the reduction in the densification (7.2%) and electrical conductivity (53.8%) of the nanocomposites. The highest microhardness (146.5 HV) and compressive strength (474.5 MPa) of the nanocomposites is related to the Cu-10 wt.% ZrO 2 . Owing to the good interfacial bonding between uniformly dispersed ZrO 2 nanoparticles and the copper matrix. The abrasive wear rate of the Cu-ZrO 2 nanocomposite increased with the increasing load or sliding velocity and is always lower than that of copper at any load or any velocity.

The mechanical behavior of epoxy reinforced by three different types of woven fibers was studied under compressive and bending loads. The reinforcements used were: woven glass fibers (volume fractions: 9.2%, 18.4%, 27.6%, and 36.8%), woven carbon fibers, and woven hybrid (carbon/glass) fibers at 36.8 vol.%, each. The composites were manufactured using the hand lay-up technique. Pure (unreinforced) epoxy specimens were tested as a reference material. The fracture behavior of the investigated specimens was studied both macroscopically, and using scanning electron microscopy (SEM). It was found that under compressive loads, elastic deformation is nonlinear for pure epoxy as well as epoxy reinforced by low volume fractions of glass woven fibers. At high volume fractions of glass fibers, carbon fibers, or hybrid ones, this non linearity diminished significantly. The modulus of elasticity of epoxy-reinforced by glass fibers (GF) continued to increase as a function of fiber volume fraction. At 9.2 vol.% the modulus of elasticity showed an increase of 65% compared to pure epoxy, while at 36.8 vol.% GF the improvement reached 117%. At the same volume fraction of 36.8% hybrid, and carbon reinforcements the improvements were 160%, and 178%, respectively. Similar trend of improvements were observed for the other mechanical properties under compressive loads. Under bending loads, both the flexure modulus, and flexure strength showed significant improvement as a function of glass fiber volume fraction. At the same reinforcement volume fraction, carbon fiber composites gave the highest mechanical properties, followed by hybrid composites, while glass fiber composites showed lowest improvement (about 348% improvement in flexure strength compared to pure epoxy). Fiber pull-out and debonding are the main fracture mechanisms for glass fiber reinforced epoxy, while interlaminar shearing is the main mechanism for carbon fiber composites. Hybrid (C/G) composites showed a mixed mode mechanism. The fracture process in bending proceeded in stages from the tension side inwards towards the compression side. Each stage is associated with a load drop and audible sound waves.