Necmettin Tarakçioğlu

Strength of filament wound GRP pipes with surface crack

In this work, the effect of surface cracks on strength has been investigated theoretically and experimentally for glass/epoxy filament wound pipes, which are mainly used for bazooka launchers. The pipes with surface crack which have several notch-aspect ratios a/c and notch-to-thickness ratios a/t in the axial direction were exposed to open-ended internal pressure. Critical stress intensity factors were determined experimentally for several winding angles by tensile tests with center notched ring specimens. The strength values of pipes with surface cracks are compared with internal pressure test results and theoretical results.

Stress corrosion crack growth in glass/polyester composites with surface crack

The propagation characteristics of stress corrosion surface cracks and crack growth rates in a range of unidirectional glass/polyester composites exposed to 0.6 N dilute HCl acid were examined using a fracture mechanics test. Glass/polyester composites were produced from continuous rovings using filament winding method. The shallow surface cracks with various a/c and a/t ratios were machined on the specimens and under uniaxial tension were exposed to one side stress corrosion. The stress intensity factors for glass/polyester composites with surface cracks are obtained from Newman‐Raju, Nishioka, and single edge notch expressions. The material constants, such as A and n, are related to crack growth rate and the stress intensity factors were obtained for the test conditions. q 2001 Elsevier Science Ltd. All rights reserved.

Enhancing Fatigue Life of Filament Winding Laminar and Curved Pipes Containing Carbon Nanotubes, and Their Fatigue Failure

In this study, the fatigue life of glass fibre-epoxy matrix material produced by the filament winding composite pipes and matrix material reinforced with multi-walled carbon nanotubes (MWCNTs) nanocomposite filament winding tubes were studied experimentally under the influence of internal pressure. Glass-reinforced plastic (GRP) pipes which were reinforced with carbon nanotubes were tested in the conditions of an open-ended test. The winding angle of test specimens was ±55° and they had six layers. During all the experiments, the fatigue life effect of reinforced carbon nanotubes was investigated. Unreinforced glass, as a reference material, was compared with reinforced plastic with the addition of nano-reinforced material using two different rates of 0.5% and 1%. Fatigue tests of specimens have been carried out in accordance with ASTM D-2992. Later on, the results obtained by determining the material properties with the reinforcement of carbon nanotubes GRP pipes were evaluated. As a result of this study, it has been found that MWCNTs reinforcement increases the fatigue life of the GRP tubes. Inter-laminar fracture strength was developed via the mechanical locking of MWCNTs. The critical MWCNTs usage value was between 0.5% and 1%.

Elastic-Plastic Stress Analysis in a Thermoplastic Composite Cantilever Beam Loaded by Bending Moment

In this study, an elastic-plastic stress analysis is carried out in a thermoplastic composite cantilever beam loaded by a bending moment at the free end. The composite beam is reinforced unidirectionally by steel fibers at 0, 30, 45, 60, and 90° orientation angles. An analytical solution is performed for satisfying both the governing differential equation in the plane stress case and boundary conditions for small plastic deformations. The solution is carried out under the assumption of the Bernoulli-Navier hypotheses. It is found that the intensity of the residual stress component of σ x is maximum at the upper and lower surfaces or at the boundary of the elastic and plastic regions. The composite material is assumed to be as hardening linearly. The Tsai-Hill theory is used as a yield criterion.