Volume 58, Issue 5

This paper gives an overview of four measurement techniques that allow to extensively characterize the status of a worn turbine blade. In addition to the measurement of geometry and surface properties, the condition of the two protective coatings needs to be monitored. Fringe projection was used to detect and quantify geometric variances. The technique was improved using newly developed algorithms like inverse fringe projection. A Michelson interferometer was employed to further analyze areas with geometric defects and characterize the surface morphology of the blade. Pulsed high frequency induction thermography enabled the scanning of the blade for small cracks at or close to the surface. High frequency eddy current testing was used to determine the protective layers status and their thickness.

The desirable properties of titanium and titanium alloys, including excellent corrosion resistance, high strength to weight ratio and high operating temperature, have led to their successful application in various fields such as the medical and aerospace industries. Among the reliable treatment techniques, laser welding can provide significant advantages for the titanium alloys because of its precision, rapid processing capability and ability to control the welding parameters and their effects. The morphology and the quality of pulsed seam welds are directly or synergistically influenced by the Nd:YAG laser parameters of pulse shape, energy, duration, travel speed, peak power and frequency of repetition. In this study, a 1.5 mm thick Ti-6Al-4V alloy sheet surface was treated by SigmaLaser ® 300 Nd:YAG pulsed laser. The influence of the pulse frequency on seam morphology and surface effects was then investigated. The seam and surface quality were characterized in terms of weld morphology and microhardness. The results showed that, for Nd:YAG laser seams used for surface treatment, pulse repetition was more effective on the cooling rate than had been expected.

A detector combining indentation method and acoustic emission (AE) technique was developed for evaluating the bonding strengths of sprayed coatings. In order to study the effect of indentation conditions on cracking failure behavior of sprayed coating, FeCrBSi coating was prepared by plasma spraying technique. The AE signals during indentation test were abstracted and investigated. The morphologies of indented samples were observed by scanning electronic microscopy (SEM). The results indicate that indentation equipment can induce the cracking failure of coating and AE technique can define the critical statues. The test by interior load was feasible and accurate for evaluating the bonding strength. The key influential factor of indenter lied in the contact area between indenter and coating. The loading rate had little effect on AE signal. The loading conditions were optimized to use diamond indenter with interior load and a loading rate of 100 pulses per second.

In this study, the resistance spot weldability of DP450 steel and aluminum alloys (AA1050, AA6061 and AA7075) was investigated and the interfacial characteristics of fracture zones was examined via microanalysis, scanning electron microscopy and energy dispersive spectroscopy (EDX). In addition, tensile shear load tests and hardness tests were performed to determine the mechanical properties and fracture behavior of welded joints. These results suggest that the tensile shear strength of the DP450/AA1050 and DP450/AA7075 joints was not affected by the reaction layer formed at the welding interface. This indicates that the spot weldability of DP450/AA6061 is better than DP450/AA1050 and DP450/AA7075 Al alloys.

The effect of Ni on the mechanical properties and microstructure of twinning induced plasticity (TWIP) steels were investigated in this study. TWIP 1 (0.6 C, 24 Mn) and TWIP 2 (0.6 C, 24 Mn, 1 Ni) steels were fabricated and annealed at 700, 800 and 900 °C for 150 minutes and then air-cooled. The results revealed that the Ni containing steel (TWIP 2) exhibits a higher yield strength and tensile strength than the steel TWIP 1. Carbide precipitations have been detected in the microstructure of TWIP 1 and TWIP 2 specimens annealed at 700 °C. However, the microstructure of the steel TWIP 1 annealed at 800 and 900 °C was fully austenitic and some grains included twins. It turned out that with the addition of Ni, the formation of twinning decreased in consequence of the annealing at 800 and 900 °C.

In this study, kinetics of boride layers formed on the surface of ferritic GGG 40.3 ductile iron were investigated by conducting a series of experiments in Ekabor I powder at 850, 900 and 950 °C treatment temperature for 1, 2 and 4 h by using Ekabor I powder. Also, box boronizing was carried out at 950 °C for 4 h with Ekabor II powder to investigate effect of powder size. At the same time, it has been investigated whether or not iron boride layers were obtained using different powder mixtures instead of commercial powder (SiC + KBF 4 + B 4 C). Also, the 85 wt.-% B 4 C + 15 wt.-% Na 2 CO 3 powder mixture has been used. The study was aimed to inhibit the release of fluorine gas and to perform environmentally friendly working. After the experiments, it turned out that the depth of boride layers depending on treatment temperature and time ranged from 38 to 198 μm. The presence of borides were confirmed by X-ray diffraction, optical microscopy and scanning electron microscopy. A saw tooth shape morphology of boride layers has been detected in optical microscopy and scanning electron microscopy.

The aim of this study is to investigate the effect of important process parameters and tool parameters on joint strength in fiction stir welding process of high density polyethylene (HDPE) using the Taguchi experimental design method. The tool rotation, feed rate and tool shoulder diameter were considered as varying parameter and used to fabricate the joints. The quality of the joint was evaluated by examining the characteristics of the joint as a result of ultimate tensile strength. For friction stir welding of the plates, the experiments were arranged by using Taguchi's L 9 orthogonal array in randomized way. From the analysis of variance and the signal-to-noise response graphs, the significant parameters and the optimal combination level of the parameters were obtained. It was found that using a tool rotation of 1600 rpm, a feed rate of 20 mm·mm −1 and a shoulder diameter of 20 mm, an improved joint strength can be obtained. A confirmation run is also performed to prove the effectiveness of the Taguchi method. The results show that joint strength was improved by about 25% compared with the initial welding parameters.

In the present experimental work, the effects of vanadium additions on the microstructures and mechanical properties of powder metallurgy (PM) steel and microalloyed powder metallurgy (PM) steels were investigated. The microstructures of the PM steel and microalloyed PM steels were characterized by optic microscope, SEM and EDS. Experimental results showed that vanadium microalloyed steels can be produced by PM technology. The addition of vanadium limits grain growth during austenitization prior to air cooling and increases the strength in the sintered conditions. By limiting austenite grain growth, the precipitates result in significant improvement in strength.

The main purpose of this paper was the theoretical and laboratory analysis of 20 mm AZ31 magnesium alloy rods rolled in the three-high skew rolling mill process. For this, the numerical analysis was carried out by using Forge2011 ® computer program. Based on the theoretical results, the distributions of stress, strain and temperature were determined. It turned out that rolling on the three-high skew rolling mill allows the rolling process to be run with high elongation factors in a single pass, which makes the skew rolling more economical and reduces the losses for roll mechanical working. After the rolling in three-high skew rolling mill, the rods of 20 mm diameter were straight, without surface defects and a low ovality.

In this study, the drop weight impact response of cured hybrid composite plates has been investigated. Experiments were conducted on two groups of hybrid composite plates. The first group was based on upper and lower surfaces that are made of carbon (c) with the inner plates of glass (g), while for the second group the upper and lower surfaces were examined which are made of glass (g) with the inner plates of carbon (c). The orientation angle of the plates was 0, 15, 30 and 45° and the collision energy was 12 J. Contact forces were obtained and compared for the plates with respect to the different sequence and orientation angles. Peak forces increased for all the sequences and orientation angles. However, the (g-c-c-g) stacking sequence showed a larger sensitivity to an orientation angle change. The deflections decreased for the (c-g-g-c) stacking sequence when the orientation angle increased.

The properties of metals can be substantially changed by various methods, one of them is using heat treatment processes. Moreover, ultrasonic testing is the most preferred and effective, nondestructive testing technique for characterization of mechanical material properties. Austenitic stainless steel AISI 304 serves in many applications due to high strength and corrosion resistance. In certain applications, it is important to evaluate the mechanical properties of AISI 304 stainless steel. In this study, the ultrasonic method (attenuation measurement technique) is used to evaluate the hardness of AISI 304 stainless steel samples which were heat treated at different levels. Due to the heat treatment process, each sample has its specific microstructure and hardness which attenuate ultrasonic waves appropriately. The ultrasonic and hardness test show that it is possible to evaluate the hardness of AISI 304 stainless steel by ultrasonic attenuation coefficient. In addition, the relationship between ultrasonic attenuation coefficients and time of heat treatment is investigated.

There are many technical applications in which wear is a critical issue. Copper can be filled with particulate materials to enhance the tribological behavior, mechanical and physical properties as well. Copper matrix containing 10 vol.-% Al 2 O 3 and B 4 C particles were produced using the powder metallurgy method and their dry wear behavior was investigated at different sliding conditions against a hardened alloy steel counterface using Taguchi technique. Four control factors like lubrication, load, sliding distance and hardness were designed in a L 18 factorial orthogonal array for the experiments to investigate the wear behavior of the metal matrix composites. Moreover, a correlation derived from the results of Taguchi experimental design was proposed, resulting in a predictive equation for estimation of these properties. The experimental results showed that the weight loss was highly influenced by the lubrication factor, followed by the load factor. However, these were then followed by hardness and sliding distance. The estimated weight loss was calculated and a good agreement was observed between the predicted and actual weight loss at a confidence level of 90%. The wear resistance was significantly better for B 4 C particle-reinforced composites than that for the Al 2 O 3 particle-reinforced composites. Moreover, the results were approved by scanning electron microscope micrographs of worn surfaces of the samples.

An efficient method based on Taguchi's design of experiment coupled with the grey relational analysis was studied, concentrating on the optimization of process parameters over surface roughness, cutting force and tool wear rate in milling of mild steel. This study consists of three stages: experimental work, single response optimization using Taguchi's S/N value and multi-response optimization using grey relational analysis. In the first stage, the experimental work was carried out using Taguchi's design of experiments. The effects of process parameters (spindle speed, feed rate and depth of cut) on surface roughness, cutting force and tool wear rate were investigated using analysis of variance. In the second stage, Taguchi's signal-to-noise ratio was used to optimize the responses. Finally, multi-response optimization was carried out using grey relational analysis. Additionally, the analysis of variance (ANOVA) was applied to determine the most significant factor for the optimal response for milling of mild steel. From the ANOVA table, the most significant factor is the spindle speed. This proposed method can be an effective approach to enhance the multi-response optimization for milling process.

In terms of modification of the properties of MoS 2 -Ti composite films, especially tribological properties, significant advances have recently been recorded. However, the commercially production of MoS 2 -Ti composite films is still limited, because the production of desirable MoS 2 -Ti composite coating is only possible by using closed field unbalanced magnetron systems and by the selection of convenient deposition parameters. This requirement has focused the researchers’ attention on optimization of deposition parameters. This study is concentrating on the effect of the bias voltage and the target currents for MoS 2 -Ti composite films deposited by pulsed magnetron sputtering (PMS). It is found that the bias and the target currents clearly affect the mechanical, structural and tribological properties of MoS 2 -Ti films.

Due to intense competition in automotive industry, new car models have to be launched as quickly as possible. A re-evaluation of the design and development phases has reshaped product development in order to get product earlier than competitors. Prototype production is one of the longest stages of product development due to physical verification activities. Shortening of this process will provide more opportunity to get project schedule earlier. Rapid prototype technologies are usually used as a guide for visual and packaging analysis. However, there is a requirement to use these parts for functional testing as well. Developing alternative rapid tooling methods which shorten the physical prototype production phase, while adequately supporting visual, packaging and functional aspects of sheet metal forming, can lead to considerable savings in vehicle prototype development. In this study, sheet metal prototype part using recyclable low melting point alloy was experimentally investigated by analysing dimensional conformance of tools and parts. In addition to wear performance, thickness reduction was investigated for stamped parts.