Volume 59, Issue 7-8

Besides the energy-intensive secondary metallurgical recycling route, aluminum chips can alternatively be extruded to final profiles by extrusion. The mechanical properties of the extruded profiles have a dependency on the quality of the weldments of the chips, which differs locally due to the batch process. To characterize the influence of this dependency on the mechanical properties, round pre-compacted chip blocks consisting of EN AW-6060 were pre-heated for six hours at 550 °C, extruded with flat-face dies at a recipient temperature of 450 °C and divided into three zones: profile, transition and contact zone. A micro-computed tomographic defect analysis was performed on the samples. It has been shown that the profile samples of both geometries have a very low defect quantity and volume, while towards the contact zone the number and volume increases significantly and small delaminations occur on the surface. For the determination of the hardness distribution, a macro hardness mapping was performed. The coarse grain edge in the outer region of the specimens, which has resulted from increased temperature as a result of the recipient friction and shear stress, shows a slightly increased hardness. Round profiles show a concentric hardness decrease and square profiles a linear drop towards the center of the cross section of the specimens.

In welding, the change of the aggregate state solid-liquid-solid is, via a localized heat action at the welding point used for the material binding joining of parts. Due to the thermal expansion and also due to structural changes, heat residual stresses and transformation residual stresses develop which often exert a negative influence on the precision of the part. When the shrinkage-induced residual stresses exceed the temperature-dependent yield stress, weldment distortion is the consequence. For reduction of the distortion and the residual tensile stresses in welded seams on carbon manganese steels, low transformation temperature materials (LTT) were developed. These materials use the volume expansion effect during martensitic transformation. The volume expansion counteracts volume shrinkage during cooling. The metallographic analysis of an electron beam welded seam in unalloyed steel with LTT filler material has been demonstrated in Part 1. This second part shows the effect on near-surface residual stresses examined by hole drilling method in combination with an optical evaluation by electronic speckle pattern interferometry.

This study establishes a database containing the results of fatigue tests from the linear region of the S-N curve using sources from the literature. Each set of test results originates from testing metallic components on a single load level. Eighty-nine test series with sample sizes of 14 ≤ n ≤ 500 are included in the database, resulting in a sum of 6,086 individual test results. The test series are tested in terms of the type of distribution function (log-normal or 2-parameter Weibull) using the Shapiro-Wilk test, the Anderson-Darling test and probability plots. The majority of the tested individual test results follows a log-normal distribution.

The blind-hole method is widely applied in measuring the residual stress of metal component surfaces. In this paper, the Monte Carlo method is used to analyze the uncertainty of strain release coefficients which are influenced by the unreasonable assumptions made in the process of residual stress measurement. Based on a theoretical formula, MATLAB programs were designed to evaluate the error dispersion of the strain release coefficients for the blind-hole method. Compared with the values calibrated by test, it is shown that the uncertainty of the strain release coefficients can be evaluated reasonably by the use of the Monte Carlo method. In addition, the values predicted by the Monte Carlo method are more meaningful and suited to practical application.

To investigate the effect of weld induced residual stresses on the crack performance, standard compact tension specimens were cut into two pieces, then joined to form welded specimens under various welding conditions. The crack opening displacement was measured by digital image correlation technique. It is found that specimens welded in the opposite direction show smaller crack opening displacement than those welded in the same direction. The crack opening displacement decreased as the distance from the crack tip to the center of weld line was increased from 8 mm to 30 mm. The crack opening displacement of the specimens with 30-minute time interval was lower than that of the specimens without interval, regardless of welding directions.

Duplex stainless steels are extremely attractive construction materials for their usage in intense aggressive environments. They offer numerous advantages compared to the austenitic stainless steels having an excellent behavior to pitting and cavernous corrosion, and a high resistance to stress cracking corrosion in chlorides media. However, their corrosion properties are largely dependent on the microstructural factors such as: the quantitative ratio of the two phases ferrite/austenite (F/A), the presence of intermetallic compounds and the distribution of the alloying elements between the ferrite and austenite. As a result of the thermal cycles experienced by the base metal without a post-weld heat treatment, the mechanical properties are significantly different in the heat affected zone and the deposited metal compared with the properties of the base metal. The present paper highlights the effect of the post-weld solution treatment in order to restore the balance between austenite and ferrite in the welded joint areas and also to limit undesirable precipitation of secondary phases with implications for increasing the corrosion resistance.

Diamond tools are widely used in cutting process of natural stones. In the manufacturing process of diamond tools, matrix material can be sintered via different sintering methods such as spark plasma sintering (SPS), hot isostatic pressing (HIP) and conventional sintering (CS). CS method provides higher production capacity and lower cost when compared to other sintering methods, but mechanical properties are inferior to other sintering methods. Recent studies have the aim to obtain similar performance level as achieved by means of CS method. In this study, samples were prepared with three different compositions to be used for the CS method and characterized to evaluate their performance as a diamond bead matrix material. Experimental results showed that a study can be conducted to reach similar performances with Co matrix by using Ni matrix, and a high copper rate in matrix is undesirable since diamond tools are exposed to impact forces.

In order to study the uniaxial tensile damage characteristics of steel fiber reinforced concrete at medium loading rate, tests at different steel fiber contents up to 1.5 % are performed and the acoustic emission wavelet energy spectrum is analyzed. Within the 20 to 40 kHz band, the peak frequency decreases with the increase of the steel fiber content at all damage stages. The peak frequency is affected by the size and the number of cracks, while the latter has a stronger effect. With the accumulation of damage, the amplitude and the energy of the waveform increase, the energy proportion in the low frequency bands also shows the same trend, but the peak frequency decreases. Thus, a nondestructive means for identifying the damage stage is provided.

Multi-run high strength low alloy (HSLA) steel plates welded by manual metal arc (MMA) process were investigated. Heterogeneous weld metal microstructure was studied accompanied with its effect on the mechanical properties of the joint. Microstructural studies revealed: (1) in the last run, there were intergranular acicular ferrite and pro-eutectoid ferrite, (2) in previous weld runs, there were refined grains with precipitated particles and (3) in the interlayer region of previous runs, there were some heterogeneous ferrite grains, grain boundary discontinuities and precipitated microalloying elements. In the last run, in fusion zone weld and heat affected zone interface, the solidification is a phenomenon of an epitaxial growth type structure. However, in previous weld runs, there was neither epitaxial growth nor typical refined grain structure. The mechanical properties varied in different parts of the welded plate due to the metallurgical characteristics of weld metal in comparison with the production procedure of HSLA steels and their metallurgical parameters.

This paper deals with the design of a series of tools which could assist the preparation of samples, the positioning and the measurement to resolve the problems that exist in mechanical properties testing. In order to decrease the operational difficulty and improve the quality of preparation, two kinds of fixtures are made to clamp the hardness sample and be used to grind or polish by the grinder. For the measurement of percentage elongation after fracture and percent reduction of area, a special device is assembled to quickly splice the fractured test pieces. By applying a single transverse fastening force, the efficiency of splicing of the test pieces can be increased substantially and it provides enough operation space for the vernier caliper. To raise the placing efficiency and avoid the dragging of Charpy impact test piece, a special gripping plier is designed to ensure the coincidence of the plane of symmetry of the notch and the swing plane of the striker. By using the supports of testing machine and separating the function of alignment and fixation, the new structure resolves the matters of existing method as unsatisfied placing effect or dragging of the test piece. In order to accurately install the fixtures of electro-hydraulic servo fatigue test system, a set of positioning brackets and plate tool are made to adjust the location of the large base and check the deflection between the fixtures.

The aim of this study is to investigate the effect of clay nanosheets on the galvanic protection behavior of zinc in scribed areas of polymer zinc-rich coating. The scribed area is a simulation of damage in the coating in such a way that steel gets in contact with a corrosive solution and sacrificial behavior of zinc becomes important. Ultrasonic was applied to disperse nanosheets of clay in the epoxy resin. The clay content in the coating was varied from 0 to 3 wt.-%. The coatings were scratched for studying the galvanic behavior of zinc under damaged condition. Electrochemical impedance spectroscopy, open circuit potential measurements and surface techniques were chosen to investigate the corrosion protection performance of the coating and sacrificial properties of zinc. Transmission electron microscopy illustrated the separations of clay layers which interacted with epoxy resin. In addition, TEM images showed the dispersion of clay nanosheets between zinc particles in coating matrix. Open circuit potential (OCP) measurements showed that with increasing immersion time, the OCP shifted to the less negative potential values. The cathodic protection period and sacrificial properties improved in the presence of clay in coatings. Electrochemical impedance results indicated that addition of 1 wt.-% clay nanosheets enhances the corrosion protection performance of the epoxy zinc-rich coating without decreasing its sacrificial properties after long exposure times.

Elemental chromium (Cr) does not occur in nature, but Cr exists in chromite ores as FeOCr 2 O 3 . There are some processes to obtain Cr from chromite. For all processes milling process is essential. In milling process of chromite, ball mills are generally used, because follow-up processes need fine particle size. Due to the fact that chromites with a high iron content are hard, mill components like liner and grinding media wear faster than many mines which is a significant problem in chromite grinding. This paper presents an experimental investigation of the influence of liner profile design and speed on chromite ball milling process. For evaluation of the experiments, power consumption, particle size and wear rate datas are calculated. In this experimental study, five liner profiles were designed and worked with three speeds (60, 70 and 80 % critical speed). By this combination, this study contains fifteen experiments. The ball milling process efficiency is related with shape of grinding media, kind of grinding media and product filling degree, ball size distrubition, etc., all other factors are kept constant. It was investigated the effects of liner profiles-milling speed variations on milling efficiency. 70 % critical speed was the optimum speed for all liner types. Best particle size result was meausured in the 10 th experiment as 95 μm which has the highest liner. Also, the steepest liner profile has the second-best result at a critical speed of 70 %. Energy saving is important for selecting liner profile. Besides, shallowest design with 80 % critical speed has the worst particle size result. Although highest liner profile Type 5 has the best result for particle size, the difference of wear rates is nearly two times (160 g versus 90 g) compared to Type 3 which has a particle size result of 100 μm. This means nearly half life time difference between two liners. By considering three parameters, power consumption, particle size and wear rate, the best results occurred with the steepest and medium liner profile, and these may even be further improved.

The main aim of this study is to estimate the bearing strength on pin loaded composite plates using test data of different ambient conditions depending on time. Artificial neural network (ANN) tool is used for prediction purpose. Artificial neural network program is developed by MATLAB software. The composite plates were divided into nine groups, each one contains 60 specimens. These groups were kept in different environment conditions. To obtain the optimum geometrical dimensions of specimens, the distance from hole axis to the side of the test sample of the pin diameter ratio (E/D) and the sample width to pin diameter ratio (W/D) were changed systematically in the experimental samples. Data from fatigue test results obtained from the multi-layered, feedforward and backpropagation algorithm were used to train the artificial neural network model. In modeling of artificial neural network, the test conditions, the test periods, the day intervals, the distance from hole axis to the side of test sample of the pin diameter ratio (E/D) and the sample width to pin diameter ratio (W/D) were used as input parameters and the bearing strength data was used as output parameter. The values obtained from the artificial neural network training and testing were evaluated by applying statistical analyses that are widely used in ANN models. It is widely known that difficult experimental studies and complexity of the analytical expression could be solved by ANN models as it was seen in many studies. This study has also shown that artificial neural network is a convenient method for predicting the bearing strength on pin loaded composite plates.

Condition of cutting tool determines the quality of machining operation performed on a material. Wear is the main phenomenon that deteriorates the tool life and indeed affects the quality of machined products. The research work deals with enhancing the wear resistance of tungsten carbide (WC) tool by mono- and multilayered film coating. The following WC-C/TiAlN/TiCN multilayered thin films were deposited on the surface of WC cutting tool insert using cathodic arc evaporation process. For comparison, monolayer TiAlN, TiCN and bilayer TiAlN/WC-C coatings were also prepared. Microhardness, surface roughness, wear behavior, frictional coefficient of uncoated and coated specimens were analyzed using Knoop & Vickers hardness tester, surface roughness tester, pin-on-disk wear tester, respectively. Multilayer coating comprising WC-C/TiAlN/TiCN exhibited lower friction coefficient, lower wear loss and higher hardness (25.83 GPa) compared to other thin film layered specimen and pure substrate (WC) owing to the presence of multilayer and hard layer. TiCN/TiAlN/WC-C multilayer coating exhibits lower coefficient of friction (COF) at a higher load (15 N) running for long distances (1900 m).

Nano-quartz fiber with a length of 150–400 nm was modified with 3-aminopropyltriethoxy silane coupling agent (KH-550) on the surface. Subsequently, the modified nano-quartz fiber and methyl methacrylate (MMA) were used to prepare polymer composites by in-situ polymerization. The FTIR image reveals that KH-550 successfully grafted on the surface of nano-quartz fiber. This paper studied the result with different concentrations of KH-550 for composite mechanical property. The results demonstrate that the strength of the composite reach the highest value when KH-550 and deionized water volume fraction ratio was 1 : 5. With a fiber content of 0.3 wt.-%, the tensile strength and impact strength of composite reached the maximum value as 61.83 MPa and 55.66 kJ × m −2 , and respectively increased by 13 % and 43 % compared to pure polymethyl methacrylate (PMMA).