Volume 54, Issue 5

For the analysis of residual stress depth distributions the semi-destructive incremental hole drilling method is the process of choice for quick and cost-efficient measurements. Nevertheless, the experimental execution has to be carried out carefully. Minor deviations of the ideal case, for example incorrect depth setting or eccentricity of the drilled hole to the center of the applied strain gage rosette can result in large errors or invalid results. In this paper two different strategies are presented, in order to take eccentricity into consideration. The first strategy requires a specific strain gage rosette consisting of eight single strain gages arranged at 45° angle to each other. The second strategy works with standard strain gage rosettes, but with calibration functions modified for the eccentric case. Both strategies are able to reveal and to correct the consequences of eccentricity on the results of stress analyses. In order to improve the quantitative accuracy of residual stress measurements the latter strategy should be preferred.

This investigation describes rolling contact fatigue phenomena in the wheel/rail-contact area of railway vehicles. In the scope of this paper new calculation, experimental results of stresses and strains within the wheel as well as a new method the determination of fatigue strength are presented. The stress fields in railway wheels introduced by different loads are calculated using the finite element method. The results are validated on a full-scale test rig. The results of the measurements are used to draw conclusions for the fatigue strength of wheels. Furthermore, the fast and cost saving “PHYBAL LIT ” method for the determination of fatigue properties is described.

In today's manufacturing, the emulsions for cooling and lubricating are an extremely important and necessary factor for the performance of machining processes. Depending on their composition, properties and production, emulsions in metal cutting operations have various technology functions such as lubricating the surfaces of the tools, facilitating the process of deformation of the cut layer, improving the quality of machined surface as well as cooling the tool and workpiece by removing the part of the heat created by deformation and friction. Corrosion protection of workpieces and tools during and after treatment is also one of the important functions of technological emulsions for cooling and lubricating. In this paper the effects of different concentrations of three emulsions on the corrosion rate of steel workpieces is reported. The results indicate that a higher concentration of emulsion does not provide better protection against corrosion.

Pure PP film without compatibilizer and nanoclay, nanoclay reinforced PP film without compatibilizer and nanoclay reinforced PP films with compatibilizer were produced to study the effect of nanoclay amount and compatibilizer presence on thermal, morphological and mechanical properties of films. Reinforced films were produced with 1% and 3% nanoclay contents with 3 different compatibilizer amounts to examine if nanoclay addition changes properties of the films in the same manner with different compatibilizer amounts. Melting points of the films slightly increase as the nanoclay content increases. Decomposition temperatures increase, as the nanoclay content increases. As the nanoclay content increases, tensile, burst and tear strengths for the reinforced films decrease. It can be observed that the increase in nanoclay content lowers strain and extension values for reinforced films due to nanoclay dispersion.

Retrogression and re-aging (RRA) process are applied in an attempt to enhance mechanical properties and corrosion resistance of 7075 aluminium alloys. In this study, retrogression and re-aging process have been applied to a 7075 aluminium alloy at 170°C for 5, 40, 80 min and wear resistance of RRA applied samples have been investigated by ball-on-disc wear test apparatus. Sliding distance has been chosen as 300 meters. Re-aging procedure has been carried out at 125°C for 10, 20 and 30 hours. Minimum wear loss has been obtained by retrogression for 40 min and aging for 30 hours.

The purpose of this paper is to examine the effect of curing conditions on interface strength in single-fibre composites. Test specimens produced by using polyester resin and single glass fibre were cured under four different temperatures, which were room temperature, 40°C, 55°C and 70°C for three different curing periods, which were 1 hour, 4 hours and 8 hours. Afterwards they were subjected to tensile test. As a result of the examination under optic microscope, it has been observed that the major damage formations are in the form of matrix cracks and fibre fragments. Young modulus and therefore mechanical properties of single-fibre composite specimens improved after a treatment above 40°C.

Nowadays, non-destructive testing (NDT) is frequently replacing destructive techniques in determining the properties of materials. In this study, defects in Kenaf/epoxy composite materials were detected using an inyyfrared (IR) thermal imaging technique, which is one of the most practical non-destructive techniques currently applied. Kenaf bast fibres were used to fabricate composite materials with epoxy resin as a binding material. The composites were manufactured using a manual lay-up process. The thermography analysis of the IR camera were verified by optical microscope and scanning electron microscope (SEM) investigations. The defect detection accuracy of this technology is 95%.

The results of an experimental investigation of structural, mechanical and electrical characteristics of the alloys in Au-Ga system are presented in this paper. Selected alloys Au x Ga y (x = 0.1 — 0.3) were examined using light microscopy and SEM-EDX analysis as well as hardness, microhardness and electroconductivity measurements.

Some of refractory gold ores represent one of the difficult processable ores due to fine dissemination and interlocking of the gold grains with the associated sulphide minerals. This makes it impossible to recover precious metals from sulphide matrices by direct cyanide leaching even at high consumption of cyanide solution. Research to solve this problem is numerous. Application of bacteria shows that, some types of bacteria have great affect on sulphides bio-oxidation and consequently facilitate the leaching process. In this paper, leaching of Saudi gold ore, from Alhura area, containing sulphides before cyanidation is studied to recover gold from such ores applying bacteria. The process is investigated using stirred reactor bio-leaching rather than heap bio-leaching. Using statistical analysis the main affecting variables under studied conditions werde identified. The design results indicated that the dose of bacteria, retention time and nutrition K 2 SO 4 are the most significant parameters. The higher the bacterial dose and the bacterial nutrition, the better is the concentrate grade. Results show that the method is technically effective in gold recovery. A gold concentrate containing >100 g/t gold was obtained at optimum conditions, from an ore containing < 2 g/t gold i.e., 10 ml bacterial dose, 6 days retention time, and 6.5 kg/t K 2 SO 4 as bacteria nutrition.

According to a new theory poycrystal elements are a comlex self-organized system which gives the possibility to modulate the processes of strengthening by changing temperature within a wide range. An unconventional method for non-destructive determination of the minimal operating temperature (ductile to brittle transition temperature of structural steel T DBTT ), based on the results of measuring the speeds of longitudinal and transversal ultrasonic waves and the achieved values of Poisson's ratio, has been developed.