Ahmet Akdemir

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.

Characterization of styrene butadiene rubber and microwave devulcanized ground tire rubber composites

Abstract Ground tire rubber (GTR) was devulcanized by microwaves at the same heating rate (constant power) and different times of exposure. The devulcanized rubber (DV-R) and untreated GTR were characterized physically and thermally. Composite materials were prepared from different proportions of the GTR, which was used as a filler, and the DV-R, which was used as part of the styrene butadiene rubber (SBR) matrix, and by varying the exposure time of the microwave power. These composites were compared with a control sample that was prepared from virgin SBR. The sol content (soluble part) and Fourier transform infrared spectroscopy (FTIR) analyses of the devulcanized samples were examined to define the efficiency of devulcanization. The cure characteristics and tensile properties of the SBR composites were researched. In this study, it was found that using DV-R as part of the rubber matrix produced much better properties than using GTR as a filler, thereby showing the significant benefits of microwave devulcanization. At the DV-R content of 50 phr, the elongation at break of the DV-R 5 min/SBR composites increased to 445.06% from 217.25% for the GTR/SBR composites, i.e., the elongation at break was enhanced by 105% by the devulcanization of GTR. Scanning electron microscopy (SEM) photographs displayed a better interface coherence between the DV-R 5 min and SBR matrix than the GTR/SBR composites.

Fatigue Crack Growth Behavior of Filament Wound Composite Pipes in Corrosive Environment

The stress corrosion crack growth behavior of ±45°, ±55°, and ±75° filament wound composite pipes with surface crack subjected to 0.6 M HCl acid under alternating internal pressure was investigated. E-glass/epoxy pipes consist of six layers with stacking sequences of (+45/-45) 3, (+55/-55)3, and (+75/-75)3. Dilute (0.6M) HCl acid was applied to the surface crack region by a corrosion cell mounted on the outer surface of the pipe. The specimens were tested at room temperature and exposed to open-ended fatigue tests in which the pipes can deform freely in the axial direction. The tests were performed in accordance with the ASTM D-2992 standard. The surface notches with different a/t and a/c forms were cut on the outer surface of the pipe parallel to the pipe axis. The internal pressure was generated by conventional hydraulic oil for fatigue loading. The low cycle tests were applied with 0.42 Hz frequency and R = 0.05 stress ratio. After the corrosion fatigue test, the fracture surfaces were examined and observed damage mechanisms discussed.

Investigation of microstructure and mechanical properties of steel fibre–cast iron composites

Abstract The aim of the present experimental study was to investigate improvement of the toughness and strength of grey cast iron by reinforcing with steel fibres. The carbon content of the steel fibres was chosen to be sufficiently low that graphite flakes behaving as cracks were removed by carbon diffusion from the cast iron to the steel fibres during the solidification and cooling stages. To produce a graphite free matrix, steel fibres with optimum carbon content were used and the reinforced composite structure was cast under controlled casting conditions and fibre orientation. Three point bend test specimens were manufactured from steel fibre reinforced and unreinforced flake graphite cast iron and then normalising heat treatments were applied to the specimens at temperatures of 800 and 850°C. The fracture toughness and strength properties of the steel fibre reinforced material were found to be much better than those of unreinforced cast iron. The microstructures of the composite at the fibre–matrix transition zone were examined.

Plastic zones in a transversely isotropic solid cylinder containing a ring-shaped crack

In this study, a problem of a ring shaped-crack contained in a infinitely long solid cylinder of elastic perfectly-plastic material is considered.The problem is formulated for a tranversely isotropic matrial by using integral transform technique under uniform load. Due to the geometry of the configuration, Hankel and Fourier integral transform techniques are chosen and the problem is reduced to a singular integral equation. This integral equation is solved numerically by using Gaussian Quadrature Formulae and the values are evaluated for various for discrete points. The plastic zone widths are obtained by using the plastic strip model. They are plotted for various ring-shaped crack sizes and transversely isotropic matrials. It is found that the width of the plastic zone at the inner tip of the crack is greater than the outer one.

The Effects of Cutting Speed and Depth of Cut on Machinability Characteristics of Austempered Ductile Iron

Ductile iron can acquire enhanced thermal and mechanical properties from austempering heat treatment. The present study aims to identify the function of different cutting parameters affecting machinability and to quantify its effects. Turning was performed to test machinability according to the ISO3685-1993 (E) standard. After austenitizing at 900 C for 90 min, austempered ductile iron (ADI) specimens were quenched in a salt bath at 380 C for 90 min. The cutting force signals along three directions were measured in real time, whereas flank wear and surface roughness were measured offline. For the cutting parameters, the cutting speed and depth of cut were varied, but the feed rate was kept constant. In the flank wear tests, machining length was corresponded to tool life. In addition, in order to find out the effect of cutting parameters on surface roughness (Ra), tangential force (Ft), and flank wear (VB) during turning, response surface methodology (RSM) was utilized by using experimental data. The effect of the depth of cut on the surface roughness was negligible but considerable in the cutting forces. The increased cutting speed produced a positive effect on surface roughness. It is found that the cutting speed was the dominant factor on the surface roughness, tangential force, and flank wear. [DOI: 10.1115/1.4005805]

Effects of Production Parameters and Conditioning upon Ballistic Characteristics of Para Aramid Light Armors

Composite materials are increasingly used in armors design due to their high strength to weight ratios and energy absorption capacities. It is very important to determine the best production parameters for armor production. On the other hand, the armors must show superior durability against harsh working conditions. So it is crucial to know the ballistic characteristics of such composite armors. In this study the effect of production parameters upon the terminal ballistic properties of para-aramid composite armor were examined under different conditionings. The composite armor plates were produced by hot pressing with four different pressing times. Before ballistic test, the armor plates conditioned at +21, +63, and -35°C at 50% of relative humidity and +21°C immersed into water temperature for 24h, in which weapons, ammunition, and equipment designed for use in the battlefield, are expected to fully operate.

Friction and wear properties of friction materials containing nano/micro-sized SiO2 particles

Purpose – Among the components used for a car brake lining, the chemical and structural properties of the abrasives, jointly with the morphology and size of the particles influence the friction parameters and stability of the composite. This paper aims to investigate the effect of nano SiO2 particles in brake pads on friction and wear properties. Design/methodology/approach – In this paper, the effects of SiO2 (Silica) particles of varying size on the friction-wear properties of polymeric friction composites are investigated. Four friction composites were prepared containing (5, 10 Wt.%) micro silica (MS) particles and (5, 10 Wt.%) nano silica (NS) particles. The samples were produced by a conventional procedure for a dry formulation following dry-mixing, pre-forming and hot pressing. Friction and wear characteristics of the specimens against to a disk made of cast iron were studied. Friction coefficient, specific wear rate and hardness of specimens were obtained. Detailed examinations on the worn surface...

Improving electrical and mechanical properties of a conductive nano adhesive

Abstract In this experimental study, lap shear strength and electrical conductivity of nanohybrid adhesives containing multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles were investigated. Ag nanoparticles were produced via arc-discharge method in liquid nitrogen. For characterizing the Ag nanoparticles, X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy (SEM) were performed. Tensile lap shear properties were determined in accordance with ASTM D 1002-10 standard. Mechanical and the electrical properties of nanohybrid adhesives were compared with neat epoxy adhesive. The best electrical conductivity of nanohybrid adhesive was obtained for the 1% wt MWCNT-2% wt Ag-contained sample. However, the samples which contain 0.5% wt. MWCNT–0.5% wt. Ag nanoparticles reached the highest lap shear strength. The results showed that Ag nanoparticles enhance the conductivity in the presence of MWCNT. It is concluded that the MWCNT act as conductivity bridges among epoxy adhesive and facilitate the electron transfer. As seen in the tensile test results, the ductility of the adhesive was improved by adding the nanoparticles in to the epoxy resin.