Volume 57, Issue 4

Aluminum alloys are used for enhancement of dynamic range, resource optimization and emission reduction in many fields of traffic engineering, whereby aluminum components are manufactured by means of welded, adhesive and screw joints. Friction drilling, as forming process with subsequent manufacturing of threads, offers the opportunity to produce an internal thread in lightweight profiles with a usable thread depth larger than the profile thickness, making use of local material expansion. Moreover, the direct manufacturing offers a huge potential for time and cost saving in comparison to conventional thread machining. Microstructural characterization of mechanical properties of EN AW-6060 internal threads, both in profile and bulk material specimens, was carried out using tensile tests and fatigue tests in the tensile loading range. A comparison was made between the manufacturing techniques tapping, thread forming and thread milling. The maximum tolerable loads of the profile specimens are about 50 % lower in the quasi-static range and about 25 % lower in the cyclic range in comparison to bulk material specimens. Formed threads show the best and cut threads the worst mechanical properties which were correlated with the production-related profile qualities and changes in microstructure. Multiple step tests prove that the fatigue limit of aluminum internal threads, validated in single step tests until 10 7 cycles, can be reliably estimated by means of plastic strain.

In this study, the aging behaviors of high strength low alloyed (HSLA) HC380LA quality steel were investigated. Steel samples were heated in a heat treatment furnace up to 950 °C and kept there for 1 hour, and then quenched in water. Some of the water quenched samples were aged at temperatures between 50–350 °C for 20 min (quench-aged, QA), while the other samples were exposed to the same aging procedure after a 3 % prestraining (strain-aged, SA). Experimental results showed that aging occurred in all QA and SA samples. The highest values for both QA and SA samples were obtained at aging treatment performed at 150 °C for 20 min. When the aging temperature increased to 200, 250, 300 or 350 °C, aging strength decreased. Results of the study suggest that different aging temperatures have an effect on the microstructure and on the mechanical properties of high strength low alloyed steels.

The purpose of this study is to join Armor 500 steel and medium carbon steel (AISI 1040) by using diffusion welding and to experimentally examine the effect of welding temperature on microstructure and mechanical properties. Diffusion welded joints were performed at 700, 800, 900 and 1000 °C, under a pressure of 3 MPa and for a welding period of 30 minutes. In order to determine the structural changes occurring in the joint zone; SEM and EDS analyses were conducted. Also, microhardness and overlapping shifting tests were carried out in order to determine the mechanical behaviors. Based on the experiment results, it was observed that welding temperature had an important effect on the strengths of diffusion welded joints. Consequently, it was determined that a sample joined at 900 °C had a strength of 960 MPa.

An analysis of the parameters of multi-stage controlled strip cooling during the process of rolling of 5.5 mm-diameter C70D high-carbon steel wire rod has been made in this publication. Investigations included also the analysis of the flow rate of the cooling medium and its pressure in the devices for accelerated and controlled cooling of the strip directly in the rolling line, as well as in the STELMOR line. The investigations carried out within the study have determined the cooling capacity of the accelerated strip cooling devices for specific (preset) cooling conditions. The scope of the investigations also encompassed the analysis of the effect of the employed cooling conditions on the temperature distribution and on the properties and microstructure of the steel studied. Moreover, physical modeling of the currently applicable technology of rolling the investigated steel grade was also performed.

The cryogenic treatment process is carried out at sub-zero temperatures down to −184 °C to modify the microstructure and properties of the material. This process is an extension of heat treatment which further improves the properties of the material. This publication focuses on the effect of cryogenic treatment on high speed steel (HSS) T-42 tool material. In this research, cryogenic treatment at −184 °C is conducted and the properties of the material compared with them of untreated material. As the temperature is decreased, microstructure of material is refined and a higher number of carbide precipitates appeared on the surface after the treatment. The microstructural changes result in improvement of properties of HSS, (T-42) tool material. Pin-on-disc wear test is conducted on untreated (UT) HSS and cryogenic treated (CT) HSS specimens. It is observed that the average wear rate of UT-HSS and CT-HSS samples is 6.8 × 10 −8 mm 3 /Nm and 4.1 × 10 −8 mm 3 /Nm, respectively. The average wear rate has been improved by 39.71 % for CT-HSS compared to UT-HSS tool material.

In this study, AA 7075 aluminum alloy has been burnished using different burnishing parameters such as burnishing force, number of passes, feed rate and burnishing speed with a ball burnishing apparatus. Burnishing parameters, which affect the surface hardness, were examined using response surface methodology with rotatable central composite design and analysis of variance. Using the experimental results, a regression model has been developed to predict surface hardness. The statistical analysis showed that, burnishing force and number of passes have the most significant effect on surface hardness. These results, which were obtained from the regression model, are highly consistent with the experiments. The absolute average error between the experimental and predicted values for surface hardness was calculated as 2.79 %. The results of our study show that response surface methodology is a suitable technique that can be efficiently used to predict surface hardness in ball burnishing process.

The goal of this investigation is to understand a distinctive feature observed in differential scanning calorimetry (DSC) measurements of steam sterilized medical polymer products, the formation of a peak upon the first DSC heating, known as the “memory effect”. The observed phenomenon could be used to provide evidence for steam sterilization. For the investigations, polypropylene (PP) and polyethylene (PE) samples were steam sterilized or thermally treated in an oven applying different conditions. Afterwards, the samples were measured by DSC. The influences of thermal treatment and mechanical stress were analyzed. In addition, various polyolefin reference materials (PE and PP) were investigated to address the influence of composition. Furthermore, the durability of the signal with respect to time and temperature effects were examined. The investigation shows that it is possible to produce a stable memory effect.

The use of non-invasive and non-destructive measurement techniques is of fundamental importance for the investigation of samples of great historical, cultural and artistic value. Among different techniques, neutron tomography (NT) allows a close analysis of samples of archaeological interest. Here, we present an overview of some works performed at the neutron tomography instrument CONRAD at Helmholtz Centre Berlin (HZB) including applications to organic metallic and mineral finds.

Kurzfassung In den letzten Jahren werden vermehrt trocken ankoppelbare Ultraschall-Punktkontaktprüfköpfe erfolgreich für Prüfaufgaben im Bauwesen angewendet. Oft werden mehrere Punktkontaktprüfköpfe in einem Gehäuse zu einer Strahlergruppe kombiniert, um die Schallbündelung zu verbessern oder um einzelne Prüfköpfe nacheinander als Sender und Empfänger zu betreiben und die Messsignale nach der Messung einer SAFT-Auswertung zuzuführen. Alternativ können die einzelnen Prüfköpfe einer solchen Gruppe laufzeitgesteuert angeregt und dadurch schon während der Messung das Prüfkopfschallfeld beeinflusst werden. Für diese Technik sind die Bezeichnungen laufzeitgesteuerte Ultraschall-Gruppenstrahler oder „Phased Array“ gebräuchlich. Mit den präsentierten Untersuchungen sollen die Anwendungsmöglichkeiten der Gruppenstrahlertechnik im Niederfrequenzbereich durch den Einsatz von Punktkontaktprüfköpfen verbessert werden. Dazu werden verschiedene Wellenarten eingesetzt und der Einfluss der Anordnung der Strahlerelemente im Array untersucht.

The current manufacturing trend mainly involves automation precisely to offer better productivity and improved quality. In this context, on-line monitoring of tools becomes essential. Acoustic emission is the most recognized technique used for condition monitoring of machine tools. Grinding is a material removal and surface generation process employed to shape and finish components made of metals and other materials. The research work deals with machining of CUMITUFF WR-90 alumina ceramics by employing two different grinding wheels made of aluminum oxide and silicon carbide under varying depth of cut. Surface roughness of the machined component and wear of both grinding wheels were analyzed using acoustic emission technique. For a constant depth, the quality of machining has been improved for the material grinded using silicon carbide wheel, which is inferred from low surface roughness value compared to material grinded using aluminum oxide wheel.

Based on the theory of electrochemical impedance spectroscopy (EIS) and the properties of compacted cemented soils (CS) at different early curing time, an equivalent circuit model was developed to study the physical meanings of EIS parameters. EIS was also used to investigate the properties and hardened mechanisms of CS at different curing time. The relationships among the unconfined compressive strengths (UCS) of CS and EIS parameters are discussed. In addition, a useful multi-linear regression equation for UCS is proposed. The proposed model and EIS parameters help to understand the processing of cement hardened soils and the properties of CS. The study results offer more reasonable explanations for the EIS spectra.

The compressive strength and thermal conductivity of recycled thermal insulation nano concrete with different contents of recycled aggregates were determined. By comparing the micro morphology, it was concluded that the glazed hollow beads, rather than air pores, reduced the strength loss of concrete. This was due to the tight adherence between the glazed hollow beads and the cement mortar, which is more effective than foaming the pores to strengthen concrete by lowering the thermal conductivity. Finally, the pore fractal dimension was established by mercury injection test data. The correlations between fractal dimensions under various recycled aggregate replacement rates and compressive strength/thermal conductivity were compared, and it was discovered that the macro pore fractal dimensions could be used to characterize the changes of concrete strengths and that the average fractal dimension could be employed to describe the variations of thermal conductivity of concrete.

In this work, the influence of electrolytic plasma nitriding on the structure and tribological properties of R6M5 high-speed steel were investigated. We found out that after electrolytic plasma nitriding of R6M5 steel a surface modified layer is formed with a thickness of 20 to 40 μm and with increased microhardness of 9000–12 200 MPa. It is established, that after nitriding surface friction coefficient of the sample steel decreased from 0.90 to 0.65, and sample wear rate reduced up to 5 times compared to the original, which indicates considerable wear resistance increase and hardness of R6M5 steel surface layer. It was also determined that abrasive wear resistance of R6M5 steel surface layer increased to 25 % as a result of electrolytic plasma nitriding. Thus, studies have demonstrated the feasibility and applicability of electrolytic plasma nitriding in order to improve the service time of cutting tools working under friction and wear conditions.

In Egypt, large amounts of limestone dust are accumulated in running limestone quarries every year. Disposal of these wastes is a rapidly growing problem and causes certain serious environmental problems as well as health hazards. Therefore, research for utilizing these disposals is urgently needed. The main aim of this study is to investigate both physical and mechanical properties of brick specimens containing combinations of limestone dust and small amount of Portland cement as a binder for producing house building brick. Limestone dust and cement were mixed, humidified and molded by two methods, manual method and mechanical molding method. After demolding, the produced specimens were dried in air at room temperature for 28 days. The obtained values of water absorption, bulk density, slake durability index and compressive strength satisfy the Egyptian standard of fired clay building units for non-load bearing walls. The test results indicate that brick specimens contain 14 % cement which satisfy the requirements of building of non-load bearing walls in Egypt. The process undertaken can easily be applied in the working Egyptian brick plants using semi mechanization system. The positive use of these wastes converts them into useful products, saving natural resources and can alleviate the disposal and environmental problems.

Alkaline treatment of the black rice husk ash (BRHA) was done by immersing BRHA in 8 % sodium hydroxide, NaOH, solution for 24 hours and then the treated BRHA (TBRHA) was neutralized, washed and dried in an oven. The TBRHA was subsequently compounded with the polypropylene (PP) by using single screw extruder machine, and followed by compression molding at 185 °C. The physical properties results showed that the density and the water absorption behavior of the TBRHA filled PP biocomposite (TBRHA-PP) are higher and lower, respectively, when compared with the untreated BRHA filled PP biocomposites (UBRHA-PP). The melt flow index value of the TBRHA-PP biocomposite is also higher in comparison with the UBRHA-PP biocomposites. The mechanical properties results exhibited that the tensile stress, tensile strain, flexural modulus and impact strength of the TBRHA-PP biocomposite are higher than of the UBRHA-PP biocomposites. However, the tensile modulus of the TBRHA-PP biocomposite is slightly lower as compared with the UBRHA-PP biocomposites. Therefore, it could be concluded that the alkaline treatment of the BRHA has improved some of the physico-mechanical properties of the BRHA filled PP biocomposites.