Band 58, Heft 6

The general effects of 1, 2, 3 and 4 vol.-% nitrogen and 1, 5 and 10 vol.-% hydrogen in argon shielding gas on weld bead profile (depth/width ratio: D/W) and the δ-ferrite content of AISI 316L pulsed GTAW welds were investigated. The limits for imperfections for the quality levels of welds were based on ISO 5817 B. The plates with a thickness of 6 mm were welded at the flat position and the bead on plate. Increasing hydrogen content in argon shielding gas increases the D/W ratio. Excessive hydrogen addition to argon shielding gas will result in incompletely filled groove and excessive penetration of weld. Increasing welding speed decreases the weld-metal volume and the D/W ratios. Nitrogen addition to argon shielding gas has no effect on the D/W ratio. The addition of a mixture of nitrogen and hydrogen to argon shielding gas on the D/W ratio does not show any interaction between them. An effect on the D/W ratio can be exclusively observed as a function of hydrogen content. Increasing hydrogen content in argon shielding gas increases the δ-ferrite content of weld metal. Increasing either nitrogen content in shielding gas or welding speed decreases the δ-ferrite content of weld metal. The nitrogen addition increases the weld metal nitrogen content, however, the hydrogen addition leads to a decrease of weld metal nitrogen content.

Thin sheet metals from deep drawing steel DC04 are very often used in the production of car body and case parts. Quality improvement of sheet metal components by new constructive solutions (structuring) as well as adapted joining technology is going on. Structured sheet metals differ from each other by their high bending stiffness. At the same time, they show certain anisotropy due to the structure. Therefore a typical testing method of structured semi-finished parts (single sheet metals, sandwiches) is the bending test. The literature review revealed that in many studies no special demands on tests of structured materials were made. This concerns particularly the structure arrangement, structure direction and structure location of the specimen relative to the mandrel position during bending tests, i. e., the direction of the fixed load relative to the structure. The aim of this study was to determine the influence of the test specification on flexural behavior. In the present paper, honeycomb-structured sheet metals were examined using 3-point bending tests. Bending stiffness and lightweight potential were calculated with respect to the location of load application and compared for different structure arrangements, directions and locations. The influence of the anisotropy on flexural behavior of the honeycomb-patterned sheet metals was moderate.

Stimulated material-environment interactions inside and around flowlines of deep or ultra deep wells during oil and gas exploration, and fabrication economy of pipelines have been the major challenges facing the oil and gas industries. Presumably, an extensive focus on high integrity, performance and material economy of flowlines have realistically made supermartensitic stainless steels (SMSS) efficient and effective material choices for fabricating onshore and offshore pipelines. Supermartensitic stainless steels exhibit high strength, good low temperature toughness, sufficient corrosion resistance in sweet and mildly sour environments, and good quality weldability with both conventional welding processes and modern welding methods such as laser beam welding, electron beam welding and hybrid welding approaches. In terms of economy, supermartensitic stainless steels are cheaper and they are major replacements for more expensive duplex stainless steels required for tubing applications in the oil and gas industry. However, weld areas of SMSS pipes are exposed to sulphide stress cracking (SSC), so intergranular stress corrosion cracking (IGSCC) or stress corrosion cracking can occur. In order to circumvent this risk of cracking, a post-weld heat treatment (PWHT) for 5 minutes at about 650 °C is recommended. This paper provides detailed literature perusal on supermartensitic stainless steels, their weldability and corrosion behaviors. It also highlights a major research area that has not been thoroughly expounded in literature; fatigue loading behaviors of welded SMSS under different corrosive environments have not been thoroughly detailed in literature.

The main aim of machining is to provide the dimensional preciseness together with surface and geometric quality of the workpiece to be manufactured within the desired limits. Today, it is quite hard to drill widely utilized Ti-6Al-4 V alloys owing to their superior features. Therefore, in this study, the effects of temperature, chip formation, thrust forces, surface roughness, burr heights, hole diameter deviations and tool wears on the drilling of Ti-6Al-4 V were investigated under dry cutting conditions with different cutting speeds and feed rates by using tungsten carbide (WC) and high speed steel (HSS) drills. Moreover, the mathematical modeling of thrust force, surface roughness, burr height and tool wear were formed using Matlab. It was found that the feed rate, cutting speed and type of drill have a major effect on the thrust forces, surface roughness, burr heights, hole diameter deviations and tool wears. Optimum results in the Ti-6Al-4 V alloy drilling process were obtained using the WC drill.

In this investigation, the tribological and mechanical performance of 10 wt.-% filled nano and micro epoxy composites were studied and compared. Nano fillers are Al 2 O 3 , TiO 2 and clay and micro fillers are Al 2 O 3 , TiO 2 and fly ash. Mechanical and wear tests were carried out. Wear tests were performed on pin-on-disc arrangement. Test conditions were 5, 10, 15 N applied load values, sliding speed of 0.8 m × s −1 , 2000 m sliding distance under dry atmospheric conditions. The results show that the mechanical and tribological performance of micro filler filled epoxy composites are better than those of the nano filler filled composites.

6082 Al alloy was investigated in its initial state (IS) and in its multiple forged (MF) state. The MF specimens were obtained using multi-step closed die forging. A cold compression test at room temperature was accomplished in order to measure the deformation anisotropy of MF specimens; it was also used to obtain the standard stress-strain curve. The homogeneity and structure were both evaluated by Vickers hardness measurements. While image analysis was based on optical microscopy investigations. Moreover, the open and closed die forging were simulated using Simufact software. The results showed the effects of the multiple forging process on the material. The outcome of the hardness measurement demonstrated the homogeneity of the structure. Whereas the micrographs described the microstructure development (during the multiple forging process) and the change of the grains shape over the cross section of the MF specimen.

This article describes the fabrication of C 60 -doped carbazole-based bi-functional photorefractive polyacrylates, the C 60 -doped concentrations are 0.0, 0.2, 0.5, 0.7 and 1.0 wt.-%, respectively. For these photorefractive polyacrylates, differential scanning calorimetric runs have been taken under nonisothermal conditions at different heating rates. The result indicates that the glass transition temperature T g first increases and then decreases with increasing of C 60 content. T g of the same sample increases with increasing heating rate. The activation energy of glass transition (E g ) has been evaluated based on the Moynihan and Kissinger model. The results showed that both E g values obtained from Kissinger's and Moynihan's relations are in good agreement.

In this study, the fatigue tests were conducted on the AA6082 alloy sheets both in tempered (softened) and in T6 temper conditions, and the results obtained were examined. In this context, the aim of this study was to determine the effect of the tempering condition on the fatigue characteristics of the alloy. Microstructural evolutions in the tempered samples were examined using SEM (scanning electron microscopy) and interpreted. The investigations have revealed that the tempering condition significantly affects the fatigue life of the alloy.

Metastable austenite stainless steel AISI 316L is sensitive to cold deformation, where transformation from austenite to martensite occurred. The bending deformation as the formation process leads to tensile and compression troughout the thickness of the billet. Tensile testing of the specimen causes differences in the true stress-strain along the contraction neck prior to fracture as well. The aim of the paper is to find correlation between microhardness as brief inspection parameters and extension of martensitic transformation. The total equivalent plastic strain extend diagram obtained by numerical simulation of bending was compared with tensile true stress-strain diagram. Results show very good correlation between hardness, true strain and martesite content. Therefore, one can conclude that by hardness measurement, it is possible to measure the level of equivalent plastic strain until ultimate tensile stress as a linear correlation between hardness, true strain and martesite content.

Monodispersed colloidal silver nanoparticles (Ag-NPs) were synthesized by a simple and rapid microwave method. A precursor, AgNO 3 , was reduced by ethylene glycol (EG) and N,N-dimethylformamide (DMF) in the presence of polyvinylpyrrolidone (PVP) as a stabilizer or capping agent. It was found that the concentration of AgNO 3 significantly affected Ag-NPs particle sizes. The particle sizes decreased when the concentration decreased from 0.1 to 0.05 and 0.01 M, which corresponded to narrow size distribution of the particle diameters of approximately 60 to 80, 30 to 40 and 10 to 20 nm. The spherical-shaped monodispersed Ag-NPs were obtained by using a volume ratio of EG to DMF of 2.75 : 2.25, microwave power of 400 W and heating time of 2 min. The volume ratio of EG to DMF and the microwave power influenced the uniformity of the Ag-NPs shape and size, while the heating time had no effect. For antibacterial application, 60–80 and 10–20 nm Ag-NPs showed good disinfection ability against Escherichia coli (ATCC 25922) at the minimum inhibitory concentrations (MIC) of 32 and 16 µg × ml −1 , respectively. In addition, the electrical resistance of the nanocomposites of DMF-loaded Ag-NPs (20–50 nm) without PVP on single-walled carbon nanotubes and polyethylene terephthalate (PET) was measured. As a result, it is obvious that the Ag-NPs help to increase the electrical conductivity of the nanocomposites as the electrical resistance of the Ag-NPs nanocomposites was 4.68 kΩ × cm −2 compared to that of the nanocomposites without Ag-NPs of 8.76 kΩ × cm −2 .

Hydrogen induced damage is a dangerous phenomenon affecting the weld quality with regard to construction service life even without visible indication. The determination of diffusible hydrogen in weld metal has been standardized at an international level in ISO 3690:2012. This international standard specifies the sampling and analytical procedure for the determination of diffusible hydrogen in martensitic, bainitic and ferritic steel weld metal which arises from the welding of such steels using arc welding processes with filler metal. In this study, S960QL steel is extensively used in the heavy transport, lifting and mining industry, where mobile or fixed structures have to carry high loads – often in safety critical situations. In order to sustain extreme characteristics of these high strength low alloy steels, it is a must to reduce the manufacturing defects. In the investigations presented in this paper, the influence of arc length on the weld metal hydrogen concentration was studied according to the ISO DIS 3690 in S960QL type steel with submerged arc welding. Measurement of the diffusible hydrogen was carried out by means of carrier gas hot extraction method. The weld seams with different arc length have similar chemical compositions. Maximum hardness values in the range of 410–425 HV1 were measured in the HAZ on both vertical and horizontal rows in welded structure with two mm wire diameter due to recrystallization condition. For four mm wire diameter, the hardness decreasing which is depending on the grain coarsening in the welded samples with two mm was not occurred in the weld seam-HAZ interface. The larger weld pool and the long arc length increased possibility of hydrogen pick-up and absorbing. Because of this reason, the diffusible hydrogen contents in the welded structure increased in accordance with the arc length.

In order to reduce the weight of automotive parts, lightweight materials like the press hardened AlSi coated high strength steel 22MnB5 is used. This steel enables a reduction of wall thicknesses and simultaneously ensures a high stiffness of the part, e. g., the B pillar. The usage of these steels requires suitable joining technologies. Therefore, a laser GMA hybrid welding process for fillet welds in overlap configuration was designed. This process provides high welding velocities and process tolerances against gaps and misalignments. In this case a single-mode fiber laser was used in order to reduce the thermal impact. Due to the fact that the laser focus spot has only a small diameter of 25 µm, a beam oscillation was used in order to distribute the laser energy over the melt pool width. This paper is focused on the cyclic load tests which were carried out and analyzed by the staircase method. The influences of laser power and oscillation width are dominating, whereas welding velocity and wire velocity have only a minor influence. By analyzing the failure location and crack propagation of specimens after the cyclic load test, the influence of the AlSi coating can be determined. Coating agglomerations at the fusion line of the melt pool are origins of crack initiation. This is attributed to the formation of brittle intermetallic phases.

Some natural stones, such as marble, onyx and limestone are translucent and commonly used in night lamps, lampshades, and backlit decorations in hotel lobbies and other facilities. However, there is no study in literature with respect to the luminous transmittance or transparency of natural stones. In this study, the luminous transmittance of 12 different carbonate based natural stones was assessed. An apparatus consisting of a light source, a light conducting tube and a luxmeter was designed to determine luminous transmittance. Also, the samples have been examined with regard to grain size to define their mineralogical and petrographical characteristics. As a result of the studies, it has been found that marble and onyx marble can transmit light to a greater extent compared to limestone. And it has been seen that the efficient factors in those samples are color, crystal type, grain sizes and cement substance of the rock.

Kurzfassung Für die Installation von Dehnungsmessstreifen muss die Oberfläche vorbereitet werden. Bei groben Oberflächen muss diese glatt geschliffen werden. In dieser Studie wurde der Einfluss des Schleifens der Oberfläche auf den oberflächennahen Eigenspannungszustand untersucht. Dafür wurden die Eigenspannungen nach der Bohrlochmethode an verschieden geschliffenen Oberflächen ermittelt und mit dem ungeschliffenen Zustand verglichen. Als Schleifmittel wurde eine Teller-, Schrupp- bzw. Fächerscheibe verwendet.

In machining operations, achieving better surface roughness is one of the important goals, furthermore, composite materials are increasingly replacing conventional materials. But their machinability differs from metals, because of anisotropic properties of the composites. In this research, the influence of milling parameters (feed, cutting speed, depth of cut) on surface roughness of bidirectional carbon fiber reinforced composite was investigated. Measurements were performed on both parallel and perpendicular directions of feed motion. Taguchi experimental design was used to determine the optimum milling condition and the effective parameter on the surface roughness. The optimum condition was obtained with a cutting speed of 125 m × min −1 , a feed of 0.1 mm × rev −1 and a depth of cut of 1.5 mm. In addition, the most effective parameter on the surface roughness of parallel direction (Ra x ) was found to be feed and that of perpendicular direction (Ra y ) was found to be cutting speed.