Volume 57, Issue 6

Borated stainless steels are used in nuclear power plants to control neutron criticality in reactors as control rods, shielding material, spent fuel storage racks and transportation casks. In this study, bead on plate welds were made using gas tungsten arc welding (GTAW) and electron beam welding (EBW) processes. Electron beam welds made using beam oscillation technique exhibited higher tensile strength values compared to that of GTA welds. Electron beam welds were found to show fine dendritic microstructure while GTA welds exhibited larger dendrites. While both processes produced defect free welds, GTA welds are marked by partially melted zone (PMZ) where the hardness is low. EBW obviate the PMZ failure due to low heat input and in case of high heat input GTA welding process failure occurs in the PMZ.

In this paper, alumina ceramics were compacted and shaped by cold isostatic pressing. This method provides high-density green compacts, uniformly distributed over the volume, without large pores. Green bodies were sintered at a temperature of 1650 °C. Effects of spray dried granule size distribution and compaction pressure on the density of the green and sintered alumina were investigated. It was found that the density in the green and sintered state slightly increased with increasing compaction pressure and decreased with the increasing alumina granule size. The axial and radial shrinkage of ceramic samples ranged between 20 and 22 %.

The effect of the amount of Al 2 O 3 content on microstructure, tetragonal phase stability and mechanical properties of 3YSZ-Al 2 O 3 composites are investigated in this study. The ceramic composites are obtained by means of uniaxial compacting at 210 MPa and green compacts are sintered at 1550 °C for 3 h in air. The monoclinic zirconia (m-ZrO 2 ) phase has completely been transformed into tetragonal zirconia (t-ZrO 2 ) phase with corresponding higher Al 2 O 3 content. The t-ZrO 2 grains induce transgranular fracture mode that has contribution in improvement of fracture toughness. The maximum flexural strength of 340 MPa, Vickers hardness value of 14.31 GPa and fracture toughness of 5.1 MPa × m 1/2 in the composition containing 40 wt.-% Al 2 O 3 is attributed to the microstructure with t-ZrO 2 grains as inter- and intragranular particles in the Al 2 O 3 grains, which makes it suitable for dental applications.

A numerical investigation has been carried out to examine the behavior of stiffened steel plates subjected to different shock loads resulting from an underwater explosion (UNDEX). The aim of this work is to enhance the dynamic response to resist UNDEX and obtain the optimal configuration for stiffened plates to resist underwater shock loading. A non-linear dynamic numerical analysis of the underwater explosion phenomena associated with different geometrical stiffened steel plates is performed using the ABAQUS/Explicit finite element code. Special emphasis is focused on the evolution of mid-point displacements and velocity. Further investigations have been performed to study the effects of including material damping and the rate-dependent material properties at different shock loads. The results indicate that stiffeners configurations and shock loads affect greatly the overall performance of steel plates and are sensitive to the materials data. Also, the numerical results can be used to obtain design guidelines of floating structures to enhance resistance of underwater shock damage, since explosive tests are costly and dangerous.

Mechanical properties of powder metal parts are directly related to the shape, distribution and the amount of pores. In this study, mechanical properties of induction sintered Fe based components were investigated dependent on the changing of sintering time and pore structures. For this purpose, compression tests were applied to sintered bushings and microstructural photographs were taken. The compression tests were accompanied by respective finite element analyses. The numerical values were compared to experimental results. It turned out that the micro-stress values were dependent on the amount and distribution of porosity.

In this study, the mechanical and physical properties of hybrid reinforced (Al/B 4 C/Ni(K)Gr) metal matrix composite (MMC) materials were investigated. The MMC materials were produced using the powder metallurgy (PM) production method of hot pressing (HP). The aluminum alloy Alumix 13 was used as matrix material and boron carbide (B 4 C) and nickel-coated graphite (Ni(K)Gr) as reinforcement elements. The microstructural characteristics, hardness, 3-point bending strength and density values of the produced hybrid reinforced MMC materials were determined. The reinforcement element B 4 C was kept at constant concentration of 8 wt.-%. Four different MMC materials were produced with the addition of 0, 3, 5 and 7 wt.-% Ni(K)Gr in the B 4 C. From the SEM images of the MMC materials produced by the HP technique, it was observed that the reinforcement element exhibited a uniform distribution. Moreover, the particles showed an approach to each other depending on the particle size and the amount (wt.-%) of the reinforcement element. With increasing graphite content in the structure density, hardness and 3-point bending test values decreased.

The purpose of this study is to investigate the influence of the welding parameters in the hot plate welding process of polymer composites, polyamide 6 glass fiber reinforcement 15 wt.-%, by using the Taguchi method. Four welding parameters, namely the plate temperature, heating time, welding displacement and welding time, were optimized under the consideration of the joint strength. The Taguchi approach of the parameter design was used as a statistical procedure to set the optimal welding parameters. For hot plate welding of the specimens, the combination of process parameters based on three levels of the L 9 orthogonal array was utilized. The signal to noise and the analysis of variance were employed to find the optimum levels and to indicate the impact of the welding parameters on joint strength by tensile tests of welded joints. It was shown that choosing 270 °C as plate temperature, 1.0 mm of weld displacement and 25 s of heating time, reveals an improved joint strength. For the optimized parameters it was verified that the welding time does not have a significant influence and the most effective factor on joint strength is the plate temperature. The weld displacement and heating time only slightly influenced the joint strength. A confirmation run was also performed to prove the effectiveness of the Taguchi method after determination of the optimum levels of the process parameters. The results showed that the joint strength was improved by about 27 % as compared to the initial welding parameters and the joint efficiency increased from 56 % to 71 %.

The corrosion behavior of commercially available Haynes ® 230 ® nickel-based alloy samples was investigated by exposure to coal-gasifying integrated coal gasification combined cycle pilot plant facilities affiliated with the Institute for Advanced Engineering (2.005 MPa and 160-300 °C). The morphological and microstructural analyses of the exposed samples were conducted using scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis on the external surface of the recovered corrosion test samples to obtain information of the corrosion scale. These analyses based on the pre- and post-exposure corrosion test samples combined with thermodynamic Ellingham-Pourbaix stability diagrams provided preliminary insight into the mechanism of the observed corrosion behavior prevailing in the piping materials that connected the particulate removal unit and water scrubber of the integrated coal gasification combined cycle pilot plant. Uniform material wastage was observed after 46 hours of operation, and a preliminary corrosion mechanism was suggested: the observed material waste and corrosion behavior of the Haynes ® 230 ® nickel-based alloy samples cut off from the coal syngas integrated coal gasification combined cycle plant were explained by the formation of discontinuous (complex) oxide phases and subsequent chlorine-induced active oxidation under the predominantly reducing environment encountered. This contribution continues the already published studies of the Fe-Ni-Cr-Co alloy Haynes ® 556 ® .

In this study, stress analyses have been performed for adhesively bonded and multi pinned metal matrix composite plates. The joint can be defined as hybrid structure providing various aims such as increasing loading capacity, corrosion resistance between plates etc. The finite element method was used for determination of three dimensional stresses acting on the hybrid joint. It is designed of metal matrix composite plates with epoxy adhesive and four pins. Both, the modeling and solution processes have been carried out using the ANSYS software which is well-known as a reliable finite element program. Stresses have been assumed as a consequence of tensile loadings at 80, 120, 160, 200, 240 N and uniform temperatures at 55, 65, 75, 85, 95 °C. According to the obtained analysis results, thermal stresses were especially concentrated around the pin holes. Hence, it has to be anticipated that any failure of the hybrid joint may start from pin hole zone firstly. Furthermore, the magnitudes of stresses were increased by increasing both, the tensile loading and the uniform temperature.

This study investigates the applicability of joining an aluminum matrix composite, reinforced with 5, 10, and 15 wt.-% of SiC p particles, to AISI 304 austenitic stainless steel by using friction welding technique. In this study, optical and electron microscopes, lap shear strength test, and microhardness measurements were used to assess the quality of bonding of Al-Cu-SiC p and AISI 304 austenitic stainless steel joints performed by using friction welding. The strength of the friction welded joints was significantly affected by process parameters (rotation speed, friction time, friction pressure, forging time and forging pressure). Additionally, lap shear and axial shortening test results were analyzed by using analysis of variance (ANOVA) with a confidence level of 95 % to find out presence of a statistically significant difference.

The literature review reveals that the honeycomb-structured thin sheet metals are not adequately investigated with regard to their fatigue strength. A question that remains almost completely ignored in the process is the direct comparability of structured thin sheet metals with flat reference specimens. A thin sheet is not a classic specimen to determine the fatigue strength because of the known problem of the fracture mechanics. Structured thin sheet metals of deep-drawing steel DC04 with a thickness of 0.5 mm were examined. Flat specimens were used as reference material. The frequency analysis was used for comparison. Fundamental differences in the mechanical behavior between flat and structured sheets under cyclic load were observed. Whereas an extremely flat S-N curve in the low-cycle region with a high slope coefficient was observed for the smooth thin sheets, the structured specimens show a curve typical for notched specimens. Moreover, the smooth sheets have a specific cyclic hardening and/or softening behavior. The state of plane stress of a fine sheet in contrast to a multi-axial one for the structured sheet complicates the direct comparison. For this reason, such a comparison with respect to their fatigue strength in the Wohler diagram should only be considered with caution. This contribution is the second of a series of articles on this subject.

Controlling and monitoring of dynamic responses are very important to ensure consistent test results and understand mechanical behaviors, as they are closely related to the solder joint failure mechanism. The failure of a solder joint during drop impact is induced by printed circuit board (PCB) bending. The failure criteria must be clear to determine the absolute impact life for direct comparison of drop test results. In this publication, a multi-channel real time electrical monitoring system is introduced, which can measure the dynamic voltage of daisy-chained solder joints in real-time during drop impact. A new failure criteria of board level drop test is developed, which takes the function of the component into account.

In this study, pure aluminum powders were turned into bulk material using equal channel angular densification (ECAD)/equal channel angular pressing (ECAP) and further deformed up to 16 passes at 100 °C. For comparison, pure aluminum powders were also compacted in a mold without ECAD/ECAP process at the same temperature. The microstructures were characterized using TEM for grain size and shape measurements. In general, the grains were finer in the specimens processed by ECAD/ECAP than in the compacted specimen without ECAD/ECAP process. The high density which is very close to the full density of pure aluminum (2.7 g × cm -3 ) was reached at the second pass of ECAD/ECAP. By the application of ECAD/ECAP process, severe plastic deformation enabled particles to be compacted into fully dense materials at much lower temperatures and shorter times, compared to the conventional sintering process. The ECAD/ECAP process was shown to provide an effective method for producing nano-sized grain and nearly full densification in aluminum powder.

Conceptual profit engines method is a novel design approach to shorten preparation and manufacturing times from the perspective of enterprise objectives. It illustrates conceptual steps of design operation for knowledge-based laser micro-machining information system and provides new insights into decision-making systems with reducing human interaction. This method facilitated laser micro-machining by setting unknown parameters, and it reduced the process time to 47 % with actively reducing operations preventing complex decisions.