One of the challenges that impede the use of the relatively new friction stir welding (FSW) process in joining steels and high temperature alloys, as well as dissimilar materials, is the development of the right pin tool material that can stand the severe welding conditions of these alloys. Recent developments in FSW tool materials include tungsten rhenium (W-Re) alloys. The ductile to brittle transition temperature of pure tungsten is reduced by the addition of rhenium (Re).. The addition of Re also improve fracture toughness of the alloy. The major focus of this paper is studying the process of making a friction stir welding bead on mild steel using a proprietary W-25%Re alloy pin tool and investigating the effects of process parameters (i.e. tool rotational and welding speeds) on microstructure, microhardness as well as tool reaction loads. Grain refining of the steel microstructure was observed in all beads. Certain process conditions produced a bead with needle like microstructure with the highest values of hardness. Reaction forces were found to increase with the increase in the tool welding speed and to decrease with the increase of the tool rotational speed. Although the spectroscopic analysis of the beads confirmed the diffusion wear of the tool, the overall tool has shown excellent resistance to mechanical wear.

This paper presents a possibility to use Resonant Ultrasound Spectroscopy as nondestructive evaluation method for ceramic elements of prosthesis such as ceramic femoral heads. With this method can be emphasized the incorrect sintering of these elements as well as eventually cracks. If the number of resonance peaks is big enough, the elements of elasticity matrix can be determined, demonstrated by effective measurements on zirconia with different stabilizers cylindrical samples taken into study.

Currently parallel robots are finding more and more acceptance in high-speed pick-and-place operations. As for all high-speed mechanisms, vibratory phenomena appear and deteriorate accuracy and dynamic performance at the terminal positions of the pick-and-place path. This paper aims to evaluate the effectiveness of several pick-and-place trajectories in terms of vibration reduction. To address this problem, an elastodynamic model of a five bar mechanism is developed and its behaviour is simulated as it traverses each trajectory. Spectral analysis of the vibrations allows the quality of the vibration reduction to be quantified. The results show that the first and second natural frequencies of the system are excited. It is also shown that long cycle times with smooth motion profiles improve residual error norms, but are outperformed by their discontinuous counterparts when short cycle times are imposed.

This paper presents the method estimating the contribution of vibration sources in gasoline engine with a multiple input system. Multi Dimensional Spectral Analysis (MDSA) has used to identify the cause of a linear dependence indicated by an ordinary coherence function. In order to apply the MDSA to the vibration source identification in gasoline engine, the virtual model of two inputs and single output system is simulated. For the validation of this model, the vibration of alternator was measured by using tri-axial accelerometers attached on the selected vibration source. After calculating the coherence analysis between each source based on the virtual model, the vibration contribution of alternator is calculated.

The present study focuses on the formation of cavitation in cold and hot water and in cryogenic fluid, characterized by strong variations in fluid properties caused by a change in temperature. Cavitation phenomenon is investigated in water and nitrogen flows in a convergent-divergent nozzle through pressure measurements and the optical visualization method. High-speed photographic recordings have been made, the cavitation phenomena evolution and the related frequency content are investigated by means of pixel intensity time series data. The results obtained concur with those obtained with the spectral analysis of the pressure signals. In the case of cryogenic fluid frequency peaks are shifted towards lower frequencies, with respect to cold water and the magnitude of the signal rises, in particular at low frequencies, for nitrogen and hot water. This can be due to thermal effects that contribute also to the low frequencies in the case of cryogenic fluid. To verify the validity of this assumption, a simple model based on the resolution of Rayleigh equation is used.

Dynamical systems with contacts are often exposed to wear even under small loads. The wear develops at the micro, macro or global level and changes the contact shape. This changed contact shape alters the dynamics of the system and can further increase the wear. This research presents a numerical investigation of the interaction between the wear at the contacts and the dynamics. The research involves a dynamical model normally used in the research of car-brake dynamics and simulates the run-in wear of the brake pad and the development of waviness on disc. Special attention is given to the real roughness of the contacting surfaces and to on exact numerical simulation; because concurrent contacts between rough asperities occur, a specifically developed multibody dynamics approach is presented. This research shows that after the run-in period a concave pad produces a waviness pattern on the disc. Using a spectral analysis of the disc’s surface it is possible to show the effect of the wear particle-size and the pad-width on the surface waviness.

This paper presents the resonant ultrasound spectroscopy method that allows, in principle, the determination of the density changing, elastic and geometrical properties of the object to be examined. The method is applied at the noninvasive evaluation of the femoral head prosthetic and of the artificial cervical discs made from yttria stabilized tetragonal zirconia. In the case of density changing, the spectral lines are displacing to smaller frequencies and in the case of the cracks, supplementary peaks appear.

In Low Density Polyethylene (LDPE) plant, the ethylene gas is compressed up to a pressure of 3000 bar. This is achieved by compressing the ethylene gas using two stages as primary [18 °C (64.4 °F), 1700 bar] and secondary [90 °C (194 °F), 3000 bar] stage compressors. The studs under investigation were used to clamp the flange of the suction and discharge valves to the cylinder head (Studs from the Flanges of 1st Stage - Secondary Hyper Compressor). Six cylinders are present in each stage and 6 studs are used to fix each flange on the suction or discharge valve to the cylinder head. The material used to fabricate these studs was B7 and the threads were produced by rolling. In the 1st stage cylinders frequent failures of studs started within two months of operation. Since the start up about 11 studs from different location have been failed. A metallographic examination using optical and scanning electron microscopy as well as energy dispersive spectrometry (EDS) revealed that the failure was due to fatigue.

We report a study on a thermal chemical vapor deposition (CVD) system optimized for the growth of well packed and vertically aligned carbon nanotubes (CNTs) on uncoated silicon substrates. The process of synthesis involves the co-evaporation of a carbon precursor and a metal catalyst in a nitrogen atmosphere inside a high temperature furnace. Beside the formation of CNTs, depending in particular on the deposition temperature, other carbon structures can be deposited, such as nanographite. We show the growth results analyzed by different characterization techniques (electron microscopy, porosity and thermal stability investigations, micro-Raman spectroscopy). In addition, we report an investigation on the development of secondary transversal vortex flows caused by the effects of distribution of temperatures inside the growth system, in order to correlate them with the growth results.