Volume 57, Issue 7-8

This work investigates the isothermal oxidation behavior of as cast 26Cr-16Ni, as cold-rolled AISI 309 and as cast AISI 309 at 1,173 K in air flow rate of 40 cm 3 × min −1 using thermogravimetric analysis (TGA). In 33 hours, the oxidation resistance declines from high to low are as cast 26Cr-16Ni, as cold-rolled AISI 309 and as cast AISI 309, respectively. The oxidation kinetic results show that the exponential rate constant of the as cast 26Cr-16Ni, as cold-rolled AISI 309 and as cast AISI 309 are 8.79 × 10 −6 , 4.02 × 10 −5 and 4.35 × 10 −5 g × cm −2 × s -n , respectively. The exponential growth rates of as cast 26Cr-16Ni, as cold-rolled AISI 309 and as cast AISI 309 are 0.42, 0.29 and 0.32, respectively. It indicates that the oxidation kinetic of as cast 26Cr-16Ni approaches a parabolic rate law, but those of as cold-rolled and as cast AISI 309 approach the cubic rate law. The sequence of oxide scale formations on the tested samples is also discussed.

This paper focuses on a study of temperature effects on tensile properties of a polyamide 12 based polymer. Specimens for testing were generated using the additive manufacturing process of laser sintering. Tensile tests were conducted according to DIN EN ISO 527 at temperatures between 20 °C and 140 °C. A Zwick 250N5A was used for the tests. Fine strain up to 0.25 % was measured using a MTS biaxial extensometer. Crosshead displacement was recorded as well and used for generation of stress-strain curves. Within the paper, Young's modulus, Poisson ratio, tensile strength, tensile strain at tensile strength, stress and elongation at break and yielding are reported. The study showed that all analyzed mechanical properties depend significantly on temperature. Above 100 °C strain raised up to 100 %, however, it was limited by the traveling limit of the machine. The collected data were embedded in a table-driven elastic plastic material model for finite element simulation of tensile tests. Good agreements of simulations and experiments were obtained at all temperatures.

The application prospect of aluminum alloys in aerospace, high speed train manufacturing, shipbuilding and automotive industries is increasing and friction stir spot welding (FSSW) is adjudged to be a non-fusion and suitable joining technology for it. Conversely, friction stir spot welding has challenging attributes such as objectionable FSSW tool pin performance and short life span in mass production stage, creation of crack initiation sites like hook defect, material flow voids and probe hole, as well as restrictions on thickness of materials that can be welded. These challenges have caused a lot of tool profile innovative modifications and technological advancement in friction stir spot welding of aluminum alloys. Nevertheless, some of these vital issues are still unresolved and this notion makes FSSW an evolving solid state joining technology. A succinct view of literature on FSSW of aluminum alloys reveals that most researchers have limited their research to the characterization of microstructure and mechanical properties of aluminum welds; thus leaving a blatant research gap in post-weld tool examinations. Tool wear mechanism and void formation mechanism in FSSW processes as well as characterization of friction stir spot welded aluminum alloys are research areas that need critical examinations. Nevertheless, this publication combines the innovative and recently developed friction stir spot welding technologies of aluminum alloys and assesses their generalized process parameters; it also covers microstructural and mechanical properties of aluminum alloys available in literature. This report classifies FSSW of aluminum alloys based on three criteria namely, probe amendment, shoulder adjustment and complexity of tool movement.

Welding is the most important method in modern industry. However, welding distortion and residual stress after welding are inevitable. In this paper, experiments were performed to obtain the angular distortion, temperature field and longitudinal residual stress in two T plate structures after welding and post-weld heat treatment, respectively. Then, a three-dimensional thermal elastic-plastic finite element analysis using internal heat generation was carried out to simulate the deformation and stress. The FE analysis results were in good agreement with the measurements. The results showed that both, the thickness of the plates and the heat treatment, could influence the angular distortion and residual stress distribution. Finally, the welding process at a bogie was also simulated by using the same heat source model as for the T-joint. The deformation and stresses were shown and explained.

In this study, the machinability of Al6061-T4 aluminum alloy sheets was experimentally investigated by drilling process using uncoated HSS and TiBN coated HSS drill bits. In experiments, the tool feed rate, cutting speed and drill diameter were varied to explore their effects on surface roughness of the machined holes, hole circularity, chip and burr formation, respectively. The hole qualities were determined by using an atomic force microscope (AFM) and a profilometer. The measured values were also analyzed statistically. It was demonstrated that the surface roughness increased with decreasing cutting speed and increased with feed rate of the tool. TiBN coated drill bits provided better hole surfaces compared to uncoated drill bits. The most significant factor on the surface roughness was found to be the cutting speed while the coating material was the second significant factor. In addition, the burst-type burr formations were observed only at a 4 mm drill diameter and high drill speeds with uncoated tools, while the TiBN coated tools gave burr-free surfaces.

A device and the basic technology has been developed for tensile testing pipe sections samples (tensile testing PSS) for quantitative estimating ultimate tensile and yield stresses in ring samples (PSS samples) cut from pipes. This tensile testing device provides the opportunity for compensating frictional forces during the tensile test, and using exchangeable bearings, the device can be adapted to a wide assortment of pipes. Research has been carried out regarding the shape and size of a stress concentrator introduced into the sample. Relationships have been derived between the shape of the tensile loading curves and the characteristic forces for different types of stress concentrators. It is proposed to use PSS with stress concentrators to prevent plastic deformation in one of the supporting sections (this also allows to correlate the applied forces to one section). The concentrator should be introduced into the tube wall of the sample as a drilled hole. This method is comparatively simple with respect to established testing methods.

The role of Ti-Al-O inclusions on nucleation of intragranular acicular ferrite (IAF) was investigated by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). From SEM-EDS mapping images, two kinds of titanium containing oxides are observed. Type I is a Ti-Al-O phase, in which the elements of Al and Ti coexist. Type II is the titanium containing oxide, which precipitates on Al 2 O 3 . By statistical analysis, it can be seen that Type I is dominating in number, and its molar ratio of Ti/Al varied in a wide range, which reflects its composition complexity. After etching, microstructure of IAF is observed. It can be seen that sulfur accumulates on the periphery of nucleation Ti-Al-O inclusion, which is attributed to the precipitation of MnS. Moreover, this accumulation accompanies increasing in content ratio of Al/Ti, which could be explained by titanium vacancies. These vacancies can absorb Mn ions from the steel matrix around inclusions, which leads to a Mn depletion zone (MDZ). Its existence is confirmed by EDS line scanning, and considered to facilitate the formation of IAF since Mn is an austenite stabilizer.

For this study, the strengths against impact effects of multi-layer composite sandwich panels reinforced by additional lamination structures using 3D spacer fabric have been investigated. To determine the impact strengths of the produced sandwich panels, falling weight tests with a constant impact energy of 15 J were performed on all of the samples, and the loads and absorbed energy were monitored as a function of time. In addition, the damage mechanisms occurring in the structure during impact were examined. Overall, according to the analysis of the damaged surface, the different impacts created a regional penetration area. Furthermore, no deviation in the breakdown of the surface texture was observed in the regions outside of the penetration area.

In this study, effect of sintering temperature on transverse rupture strength (TRS) of Cu-TiC composites produced using hot pressing (HP) technique has been studied. Copper matrix composites reinforced with 10 wt.-% TiC particles were produced under a pressure of 50 MPa, at 600, 700 and 800 °C, and for a sintering time of 4 minutes, respectively. The TRS of the composites were determined using three-point bending test. SEM was used to analyze the fractured surfaces of composites. SEM results showed that with increasing sintering temperature, pores and gaps in the fractured surfaces decreased. The ultimate transverse rupture strength of Cu-TiC composites was found to increase with increasing sintering temperature.

In the present study, Grey based fuzzy algorithm was used for the optimization of complex multiple performance characteristics of the ball burnishing process. Experiments have been planned according to Taguchi's L 16 orthogonal design matrix. Burnishing force, number of passes, feed rate and burnishing speed were selected as input parameters, whereas surface roughness and microhardness were selected as output responses. Using Grey relation analysis (GRA), Grey relational coefficient (GRC) and Grey relation grade (GRG) were obtained. Then, Grey-based fuzzy algorithm was applied to obtain Grey fuzzy reasoning grade (GFRG). Analysis of variance (ANOVA) was carried out to find the significance and contribution of parameters on multiple performance characteristics. Finally, a confirmation test was applied at the optimum level of GFRG to validate the results. The results also show the feasibility of the Grey-based fuzzy algorithm for continuous improvement in product quality in complex manufacturing processes.

The accuracy and reliability of any ultrasonic testing depends on the calibration procedure and sensitivity settings. In the present experimental research, it has been investigated how the changes of ultrasound beam shape influence the disc size evaluation. It was investigated how three selected factors and their interactions affect the disc size evaluation when probe frequencies are changing what is in correlation with changing the ultrasound beam shape. The experiment revealed that different factors and their interactions are significant for disc size evaluation.

S235JR low carbon steel material with web and flange thicknesses of 8 mm was welded by conventional GMAW and double channel shielding gas method to form double fillet T-joints. The differences between these two methods were characterized by measurements of mean welding parameters, Vickers hardness profiles, molten and HAZ areas of the joints and thermal camera temperature measurements. According to the results, lower mean arc voltage along with lower heat input was obtained using double channel shielding gas method. Vickers hardness values were higher using conventional GMAW. Moreover, mean filler metal molten area values were higher using double channel shielding gas method, which depicted that this method increased productivity. Smaller HAZ area values acquired with double channel shielding gas method is an indication of more intense heat input.

Brake linings used in automotive disks are usually composed of various components. The expected properties of a brake lining are the standard values of wear resistance, friction coefficient and the economical manufacturing. Brake lining extremely warms up during braking due to friction. The braking performance of braking lining can change or the braking lining undergoes mechanical deformation due to excessive temperature. In this study, the effect of granite powder in the brake friction material on various aspects of friction characteristics were investigated. Three friction material specimens were produced based on an experimental formulation, and they contained 2, 6 and 10 % granite powder, respectively, with fixed composition of the other ingredients. Tribological properties of the friction materials were obtained using a brake dynamometer. Results showed that the friction materials containing 2 and 6 % granite powder had improved friction stability and fade resistance.

Due to their superior mechanical and physical properties, carbon nanotubes seem to hold a great promise as an ideal reinforcing material for composites of high strength and low density. In most of the experimental results up to date, however, only modest improvements in the strength and stiffness have been achieved by incorporating carbon nanotubes in polymers. In the present paper, the stiffening effect of carbon nanotubes is quantitatively investigated by micromechanics methods. The Mori-Tanaka effective field method has been adopted to calculate the effective elastic moduli of composites with aligned or randomly oriented straight nanotubes. The rule-of-mixtures is used to calculate the modulus of elasticity for nanocomposite. The results of micromechanics methods indicated that the CNTs are highly anisotropic, with Young's modulus in the tube direction two orders of magnitude higher than that normal to the tube. The results of micromechanics methods were compared by those obtained from the rule-of-mixtures and good agreement was also achieved when the efficiency parameter Φ = 1 and typical results were achieved with Φ = 0.25. To predict the mechanical properties of the composite materials, it is worth considering the conventional rule-of-mixtures using exact value of the efficiency parameter Φ. To predict the elastic modulus of nanocomposite reinforced by SWCNT using the conventional rule-of-mixtures, the exact value of the efficiency parameter Φ is equal to 0.25 when using nanotubes with chirality (8,3) for determination the elastic modulus of SWCNT. However, for zigzag orientation and chirality (8,0) the efficiency parameter Φ is equal to 1. The conventional rule-of-mixtures is a powerful tool and easy method compared to the micromechanics methods.

Several manufacturing methods have been adopted to modify old grinding machines. The purpose of the present study has two aspects: the design of a novel bear housing and a rigid ball screw system, and their exact manufacture to provide accuracy and reduce voices at the cross axis. The components of the new ball screw system were manufactured and they were integrated in a legendary Jones Shipman grinding machine.

There is a need for special machines and methods for machining of an involute worm gear drive. Due to these necessities, the machines for involute profile machining are limited and the production costs are also excessive. There are general approaches applicable for various types of gearwheel machining. As known, involute worm gears are generally machined in two ways, namely by the rolling method and by form milling. The rolling method is the most widely used one. In this study, the aim is to develop a novel machining method for involute worm gear drive production, which can be more often used in industrial production. Furthermore, this method should reduce machining costs andsimplify the manufacturing process for involute gear drives. Thus, theoretical calculations for the involute form of worm gear drive have been done and an analytical model has been set up using Matlab M file. Machining coordinates of involute worm gear have been created and transformed to G codes. So, the involute curve has been formed. Accuracy of those derived machining codes has been tested by using a CNC Simulator program. Finally, an involute worm gear drive has been machined in a CNC lathe (with two axes) machine using grooving tool and the newly designed special tool holder.