Volume 58, Issue 4

A good correlation (ρ = −0.912) is found between three dimensional surface features and mechanical properties of laser-sintered parts. This study identifies correlating surface parameters and features out of the wide range of existing evaluation methods resulting from the new possibilities of a three dimensional surface measurement in contrast to a conventional tactile profilometry. Therefore, surface analyses were performed using a confocal microscope and tensile tests according to ISO 527-1 were conducted. Especially the motifs dale and volume of islands analyses show a good correlation concerning the tensile strength, the Young´s modulus and the elongation at break. The differences with regard to each feature and their influence on the mechanical properties are discussed.

One of the main factors influencing the transition of retained austenite into martensite in TRIP structure steels during drawing process is the strain intensity. In drawing processes, it occurs high strain inhomogeneity caused by the conical shape of the die approach section, as well as by the friction occurring between the tool and the material. The occurring redundant strain causes high inhomogeneity in the distribution of mechanical properties on the cross-section of wire being drawn. One of the directions aiming at enhancing the homogeneity of the drawn wire properties is to change the shape of the die working section. The paper presents the results of the investigation of the effect of the quantity of retained austenite in TRIP-type steel wires with a carbon content of 0.29 wt.-% C drawn using conical (conventional), concave and convex dies on the mechanical properties of drawn wires.

In this study, the wear behavior of chilled cast iron and nodular cast iron materials used in camshaft manufacturing has been compared. Nodular cast iron specimens were additionally heat treated at 200 and 300 °C for stress relieving after hardening. Thus, the effect of the stress release treatment on wear behavior was comparatively evaluated with respect to the untreated specimens. The ball-on-disk test described in ASTM G99-05 standard was performed under dry sliding conditions as wear test. The specimens were exposed to dry sliding test under a load of 30 N with a rotational speed of 300 rpm against hardened 100Cr6 counterparts and for the distances of 100, 500 and 1000 m. The results showed two different wear behaviors for the 100 m and 500/1000 m distances, respectively. Under given dry sliding conditions, induction hardened nodular cast iron and slightly stress released specimens exhibited relatively higher wear resistance in the tests over a distance of 500 and 1000 m, while the others showing an increase in wear loss amounts at the same sliding distances.

Single pass, autogenous flat butt welds were made on 6 mm thick duplex stainless steel (2205) plates using gas tungsten arc welding (GTAW) process. Four of the welding process parameters, i. e., arc current, welding speed, shielding gas flow rate and arc gap, were varied each at four levels and welding trials were conducted as per an L 16 orthogonal array derived using the Taguchi methodology. Bead geometry parameters, depth of penetration and aspect ratio (width-to-depth ratio) were measured on polished and etched samples using microstructural image analysis. Tabulated results were subjected to analysis of variance and effects of each parameter on bead geometry were calculated. It has been found that welding current and welding speed are the dominant parameters determining the bead geometry. Gas flow rate also plays a key role in influencing the aspect ratio of the welds. Equations have been presented to predict depth of penetration and aspect ratio of the weld.

To investigate the corrosion behavior and mechanisms of X70 steel in sands, polarization curves (PCs) and electrochemical impedance spectroscopy (EIS) were carried out using an electrochemical test set-up. X70 steel represents a common and standard API designation for pipelines with 70 ksi or 485 MPa strength. For acceleration of the process at different charging times, a direct current (DC) with 6 V voltage was applied. The results show that DC accelerates the corrosion process of X70 steel in sands and that the corrosion rate increases with charging time of the DC. Corrosion potential changes the process of positive-negative-positive charging with increasing process time, indicating that pore water, oxygen substances and corrosion ions of sands all affect the corrosion reaction. Based on the experimental results from the equivalent circuit of EIS, the corrosion process can be divided into the following three phases: developing and formatting of corrosion product film, pitting corrosion, and progressing pitting period. The low-frequency inductive slope on the EIS graph appears during the period of corrosion pitting as resulting from the corrosion product film. The film slows down the corrosion process and reduces the corrosion rate temporarily. With the increasing charging time, the corrosion product film may be damaged and the corrosion rate will thus increase significantly. The testing results of energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM) indicate iron hydroxides as the original corrosion products. With increasing charging time, the original corrosion products may be oxidized to form stable and protective film products such as Fe 2 O 3 and Fe 3 O 4 . Lastly, during the pitting progressing period, oxidized film products will be damaged and the corrosion rate increases with increasing charging time.

In this study, an accelerated test track construction necessary during research and development phase of light commercial vehicles (LCV) is described. By the questionary method, the Turkish customer automotive usages are defined. This paper focuses on defining load spectrum affected by driving shaft torque during acceleration, breaking and different manoeuvres and equivalent fatigue damage of the driving shaft resulting from accelerated tests on a route. Fatigue analysis and estimated lifetime of the part were calculated using finite element analyses (FEA) and verified by the Palmgren-Miner rule. When as customer profile the Turkish automotive user is taken into consideration and accelerated test tracks are designed for reliability and fatigue tests of the related company, linear FEA of the driving shaft represents a convenient procedure.

The effects of hydrothermal aging and low velocity impact loading on E-glass fiber/epoxy composite pipes subjected to a continuous internal pressure were experimentally investigated in this paper. The pipes were manufactured by the commonly adopted filament winding method, which is consisting of six antisymmetric layers with (±55°) 3 winding angles. Then, they were immersed in tap water at intervals of 500, 1000 and 1500 h. Low velocity impact tests were performed at three different energy levels (5, 7.5 and 10 J), followed by internal pressure testing. The results showed that both impact energy levels and water immersion time have significantly affected the burst strength of the pipe. It also indicated that the peak force and displacement increased with the increase of impact energy. During the burst pressure tests, weepage and eruption failures were observed.

Mechanical alloying (MA) is a powder metallurgy processing technique involving cold welding, fracturing and rewelding of powder particles in a high-energy ball mill. In the present study, the intermetallic matrix composites (IMCs) of Ni-Al reinforced by M 7 C 3 were produced by powder metallurgical routes via solid state reaction of Ni, Al and M 7 C 3 particulates by mechanical alloying processes. Ni, Al and M 7 C 3 powders having 100 μm were mixed, mechanical alloyed and the compacts were combusted in a furnace. The mechanically alloyed (MAed) powders were investigated by X-ray diffraction (XRD), microhardness measurement, optic microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The presence of the carbides depressed the formation of unwanted NiAl intermetallic phases. The mechanical alloyed M 7 C 3 particles were unstable and decomposed partially within the matrix during alloying and sintering, and the morphology of the composites changed with the dissolution ratio of M 7 C 3 and sintering temperature.

The present paper reports about the application of fuzzy expert system for estimating failure loads of two serial pinned/bolted sandwich composite plates. Considered composite material for present application was produced by a glass fiber reinforced layer and aluminum sheets to create sandwich structures. Briefly outlines, the experimental data of a previous study were related to different geometrical boundary conditions and also numerous preload moments as 0 (pinned), 2, 3, 4 and 5 (bolted) Nm. Anyway, both a fuzzy expert system and a regression analysis were applied depending on mentioned geometrical parameters and pinned/bolted joint arrangements in this work. Obtained results point out that the fuzzy expert system was more suitable than regression analysis method for modeling and estimation of analyzed sandwich composite. Achievements of the fuzzy expert system and the regression analysis methods were considered in terms of error ratios and mean absolute deviations.

This paper represents the fuzzy logic model for modeling and prediction of tensile shear strength and percent elongation of parts produced by the friction stir welding (FSW) process. A Taguchi L 16 orthogonal array is used to plan and select the parameters and their levels. Weld travel speed, pin diameter and tool rotation are used as input variables. Therefore, a three-input and two-output fuzzy model is used to correlate these variables to the responses of tensile shear strength and percent elongation using the fuzzy rules generated based on experimental results. Close agreement is obtained between the fuzzy predicted and experimental results with the correlation coefficients of 0.931 and 0.895 for tensile shear strength and elongation, respectively.

In the last decades, the use of metal matrix composites (MMCs) has increased enormously in many engineering applications such as aerospace, automotive, marine and railway. Such materials are known as difficult to machine materials due to the presence of very hard and abrasive reinforcements. The purpose of this study is to determine the influence of the cutting parameters, cutting environment and heat treatments on the surface roughness after drilling A 356/15 SiC MMCs. Experiments were conducted at different cutting speeds, feed rates, heat treatments (as-received, solution annealed and aged) and cutting environments (MQL, compressed air and dry). Improved surface roughness values were obtained with increased cutting speeds and decreased feed rates. The surface roughness using the MQL technique was lower than the surface roughness obtained for the other cutting environment. The optimal machining parameter combination has been obtained and the cutting conditions in terms of the cutting speed of 15 m × min −1 , the feed rate of 0.1 mm × rev −1 and the cutting environment MQL represent applicable solutions for the annealed materials.

In this study, a detailed analysis of hybrid weld manufacturing technologies that can significantly contribute to the joining of materials has been carried out. Past, present and future projection, advantages, dis advantages, technological barriers and drawbacks of the processes are given. Detailed explanations of the recent developments of hybrid weld manufacturing technologies and main components are given. Potential industrial applications are assessed and evaluated using economic and technological results. The developments in hybrid welding manufacturing technologies generally improved metallurgical and mechanical properties of weld joints. Hybrid processes usually combine the benefits of each individual process. Due to low heat input, hybrid welds create fine grain structures, minimize base material dilution and achieve high toughness and mechanical properties. These processes are especially appropriate for high performance alloys and dissimilar metal joining. The results of this study conclude that reasonable costs and improved properties of the processed materials will lead to massive use of hybrid welding manufacturing technologies.

Laser repair welding of mold and die components has been applied in the background of maintenance, repair and overhaul technologies for refurbishing military, space and civilian equipment. It enables to perform safe and sound weldments with narrow heat affected zones. A novel laser-based repair technique was proposed to perform repair of 1.2312 steel die plate. The results of this study verified the importance of laser repair welding for the mold making industry.

The effects of hybridization between woven mengkuang fiber/woven silk on mode II delamination (GIIC) of laminated composites were investigated by performing the end-notched flexure (ENF) test. Various configurations of woven mengkuang/woven silk layers were considered. The composite samples were prepared using hand lay-up, along with the cold press method. After fabrication, the test specimens were subjected to end-notch flexure testing for mode II delamination based on ASTM D790-03. During the test, the crack propagation was observed; the sudden drop in load meant that the sample experienced crack growth. The configuration of woven silk in between the pre-crack provided an excellent improvement in G IIC . Further addition of woven silk layers for similar configuration also yielded significant improvements in the G IIC result. The rate of critical strain energy release increases with an increase in number of woven silk layers for the configuration of silk in between the pre-crack. The scanning electronic microscopy (SEM) result shows the cross-section of the samples. The study also demonstrated that surface interaction between woven silk/epoxy/woven silk was better than woven mengkuang/epoxy/woven mengkuang lamination.