Welding simulation of complex structures – possibilities and limits

The possibilities of predicting welding distortions are extensive. The boundary conditions used in industrial production play an important role in choosing the right strategy. Not only the right abstraction of the welding process is essential for correct and useful results, the clamping conditions and pre-tack welding are also very important. This article reviews experiments and FEM calculations of welded complex structures of industrial relevance. The examined structure comes from a railway vehicle and contains u-profiles with a sheet thickness of 4 mm. The review starts with the explanation of the researched structure and shows different welding situations, like unclamped and clamped manufacturing. Then the FE model with several weld seams is explained and the used boundary conditions are shown. Finally, the measured and calculated distortions are compared and discussed.     

Mill,material, and process parameters – A mechanistic model for the set-up of wet-stirred media milling processes

Stirred media milling is frequently used to generate nanoparticles for industrial applications such as paints, inks, and food or for the life sciences. Each product suspension has different requirements and therefore different material and formulation parameters. The first attempts to set up a new process are experimental in nature, especially the determination of a suitable composition. To adapt a process to the production scale, more experimental work is often needed to determine suitable operation parameters with regard to energy consumption, throughput, and investment cost. The energy consumption is influenced by operation parameters such as the size of the grinding media or the stirrer tip speed, whereas the investment costs are influenced by the mill geometry and size and the type of grinding media used. Therefore, it is challenging to transfer or scale up processes because lab-scale mills are smaller and may have different geometries than production-scale mills. Moreover, it is well known that the lab-scale operation parameters cannot be easily adapted to the production scale. In this study, the stress model developed by Kwade was improved by introducing parameters corresponding to the mill and the material in addition to the process parameters. Using this model, the optimum operating conditions for stirred media milling processes can be determined with a reduced amount of experimental work, even for geometrically unequal mills.     

Pressure infiltration processes to synthesize metal matrix composites – A review of metal matrix composites,the technology and process simulation

Metal matrix composites (MMCs) acquire their improved physical and mechanical properties through the careful reinforcement of their matrices by a variety of light but strong and stable reinforcement materials. The pressure infiltration process (PIP) is one of the most important techniques used for making MMCs with a high reinforcement content in which a molten metal or alloy is injected and solidified in a mold packed with continuous or discontinuous reinforcement materials. Several factors affect the quality of MMCs made by this process. These include, but are not limited to, the reinforcement type, preform geometry, applied pressure and pressure control, as well as the transport phenomena of the molten metal. This paper presents a review of the various aspects of MMCs, the process in terms of the technological details, the latest developments in the reinforcement materials used and the simulation models developed for pressure infiltration manufacturing of MMCs.     

Electronic structure of boron-doped diamond with B–H complex and B pair

Abstract

The electronic structure of boron–hydrogen complex and boron pair in diamond are studied by first-principles density-functional calculations with supercell models. The electronic structure calculated for the B–H complexes with C_2v or C_3v symmetry and the nearest-neighbor B pair is used to interpret recent experimental results such as B 1s x-ray photoemission spectroscopy, ¹¹B nuclear quadruple resonance and B K-edge x-ray absorption spectroscopy, which cannot be explained solely by the isolated substitutional boron.     

Synthesis and alteration of α-LiFeO2 by mechanochemical processes

The effects of grinding on a stoichiometric mixture of LiOH · H₂O and -FeOOH were studied. It was found that, in the course of grinding, losses of structural water occurred and a phase structurally related to disordered -LiFeO₂ was formed. X-ray diffraction data suggest the occurrence of an ordered phase as intermediate and both -Fe₂O₃ and -Fe₂O₃ were undetected during the comminution process. A prolonged mechanical treatment of this mixture originated an elimination of Li⁺ from the -LiFeO₂ structure and the appearance of the spinel phase, -LiFe₅O₈. Additionally, the mechanical activation of a sample of -LiFeO₂ prepared at high temperatures also leads to a similar rearrangement of cations. The structural transformation is explained with the help of a model in which the vacancies of Li⁺ created during grinding promote the migration of the Fe³⁺ ions from octahedral to tetrahedral sites.     

Fabrication and mechanical properties of woven Al2O3 fibre – ZrO2 matrix minicomposite reinforced Al2O3 matrix composites by slurry infiltration – sintering process

Abstract

A plain woven Al₂O₃ fibre - ZrO₂ minicomposite reinforced Al₂O₃ matrix composite ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃) has been fabricated by a simple, pressureless, multiple slurry infiltration - sintering process. The fabrication process consisted of two major steps: fabrication of the woven Al₂O₃ fibre - ZrO₂ minicomposite ((Al₂O₃)_f/ZrO₂)_mc) and fabrication of the composite ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃. The woven fibre form of ((Al₂O₃)_f/ZrO₂) _mc was made by dipping a plain woven Al₂O₃ fabric into colloidal ZrO₂ solution. Then Al₂O₃ powder dispersed slurry was infiltrated into the open spaces of the woven fabric ((Al₂O₃) /ZrO₂)_mc. The infiltrated minicomposites were stacked, pressed, and sintered in ambient air to form a plate of ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃. The optimum sintering temperature of ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃ was investigated via tensile strength and matrix density. Tensile behaviour and fracture resistance of the composite fabricated under the optimum processing condition were evaluated. The tensile stress - strain behaviour of the optimised composite showed non-catastrophic fracture behaviour with bundle bridging and extensive fibre bundle pullouts. The maximum tensile stress revealed that almost full strength expected from the bare bundle strength was exploited by the proposed process.     

Preparation and thermal degradation behaviour of a layer-type complex consisting of TaS2 and α-naphthylamine

A layer-type complex TaS₂ (α-naphthylamine)_0.46 having a basal spacing of 2.2 nm was prepared by soaking a mixture of the components in an ampoule at 433 K for 25 to 35 days. This complex was resealed in an ampoule after purification, followed by γ-radiation and heating to 473 K. The resulting sample was again heated at various temperatures below 1273 K. On heating to 643 K, the insertedα-naphthylamine polymerized, although with some removal from the complex, with a decrease in basal spacing to 1.35 nm. Another complex appeared faintly simultaneously. This second complex with a basal spacing of 0.96 to 0.92nm formed more abundantly on heating to 773 K and then decreased in amount at higher temperature. The complex decomposed at1273 K to result in TaS₂. Such thermal degradation behaviour is discussed from the standpoint of preparation of the layer-type complex consisting of TaS₂ and carbon.     

Physical property control for innovative powder processes – Rheological control of concentrated slurry and wet granules

The manufacture of materials using slurry-based processes, such as the electrodes of Lithium ion secondary batteries and fuel cells, can be made more productive by increasing the concentration of the slurry or adopting wet granules with extremely high concentrations.Shear thickening, which is a particular issue for such highly concentrated slurries, is derived from collisions between particles, it is important to control the size, size distribution, and concentration of particles, as well as the solvent viscosity. Furthermore, the controlling of electrostatic interaction between particles and mixing of different size particles have direct impacts on shear thickening, the concentration of salt in the slurry and size and mixing ratio of particles are also important characteristics. It may be possible to control rheological behavior using these characteristics.The amount of solvent is reduced beyond the level in a concentrated slurry, the slurry changes from a so-called liquid state to a solid state of wet granules. Fully utilizing the properties of these wet granules would maximize various advantages in the production process. Flowability is the most important characteristic for use of highly concentrated wet granules. This research found that flowability is extremely low when the strain is low, but that higher wet granule concentrations flow more easily under high strain.Our latest research about rheological behavior of concentrated slurry and wet granules open up to the possibilities for ultimate form of the electrode manufacturing process might involve film-creation or forming using particles without any liquid content at all. Resolving issues such as the uniformity of the blended powder and flowability control may enable conventional slurry processes to be replaced by powder processes.     

Uncertain process–based reliability and maintenance modeling for systems under mutually dependent degradation and shock processes

For the systems that experience competing failure processes, an uncertain process–based degradation model is developed to describe the systems. The competing degradation process is composed of internal continuous degradation and external shocks, and the mutual dependence between them is considered. When the magnitude of the internal degradation exceeds the threshold, the soft failure occurs. While for the shock processes involving the randomness and the subjective information, we adopt the uncertain random renewal reward process to characterize it. Hard failure occurs when the damage of the shock process exceeds the strength threshold of the system. By using the belief reliability metric, the reliability of the degraded system is defined as the chance measure that neither soft failure nor hard failure occurs. And the effect of the degradation-shock dependence on the system reliability is performed by the parametric studies. Then the proposed degradation model is introduced into the preventive maintenance strategy to minimize the average maintenance cost. Using the microelectromechanical systems as an example, the effectiveness of the constructed degradation model and maintenance strategy is illustrated, and the proposed model can characterize the system degradation process in a superior way to the stochastic process model. These methods can be applied to other similar degraded systems and provide support for maintenance decisions.     

Nanosmearing due to process shear – Influence on powder and tablet properties

The objective of the study was to investigate the influence of process shear, blend composition and mixing order on thin film nanosmearing of lubricant and glidant on particle surfaces as a function of powder and tablet properties. Multiple pharmaceutical blends containing avicel 200 and micronized acetaminophen were prepared at three different mixing orders at a shear rate of 80 rpm and a shear strain of 640 rev. Chemical analysis such as inductively coupled plasma mass spectroscopy (ICPMS), scanning electron microscopy with X-ray microanalysis/energy dispersive spectroscopy (FESEM/EDS) and focused ion beam (FIB) were done for sheared powder samples. Powder hydrophobicity and tablet dissolution were carried out to test for powder and finished product properties. Experimental techniques were developed to interpret the general aspects of % area nanosmearing distribution obtained from EDS mapping combined with cameo imaging. Their % area distributions on particle surfaces were quantified for the first time. Applied process shear on powder particles had a significant effect on powder and tablet properties. The nanoscale investigation measured in terms of extent of nanosmearing (% area), amount and thickness of nanosmearing clearly showed that nanosmeared structures influenced the powder hydrophobicity and drug release rate.     

Pentaerythritol crystallization – Influence of the process conditions on the granulometric properties of crystals

The quality of crystals depends on many factors that determine their granulometric properties. In order to obtain crystals of desired size distribution, proper selection of the operating conditions is of a great importance. Commonly, the unseeded cooling crystallization is controlled by selecting the appropriate cooling profile. The crystallization process can also be controlled by adding a certain number of seed crystals of a uniform size in the crystallizer at the saturation temperature. This paper investigates the influence of the process conditions (mixing intensity, cooling profile, batch time, saturation temperature and seeding) on the granulometric properties of pentaerythritol obtained by batch cooling crystallization. All investigated process conditions influence the crystal size distribution (seeded and unseeded experiments). On the other hand, the shape of crystals was the same for all experimental conditions. Optimal cooling profile, lower retention time, higher mixing rate, and smaller initial seed surface area improves the final crystal size distribution.     

Application of electrical capacitance tomography in particulate process measurement – A review

Particulate process measurement presents challenges because it often involves multiphase flow. Due to its advantages over other tomography modalities, electrical capacitance tomography (ECT) is widely applied in monitoring and measuring particulate processes. This paper presents a review on the application of ECT in particulate process measurement, including the monitoring of flow regime and solids distribution, solids flow velocity measurement, and fluidized bed dryers. The electrostatic phenomenon and the effect of electrostatics on the performance of ECT systems are also addressed. Finally, the challenges to ECT for particulate process measurement are given.     

Failure analysis of bainitic steel pipe – Failed during cold working process

Cracked thin wall steel pipe was received for failure analysis. The samples of the cracked pipe, un-cracked pipe and starting material were subjected to different experiments. In this regard, optical and electron microscopes, universal testing machine and hardness tester were utilized for characterization. A series of heat treatment made on starting material to obtain the similar mechanical properties and microstructure as that of cracked pipe. The surface of the opened cracks were observed in scanning electron microscope and revealed high concentration of non-metallic inclusions. Finite element model was utilized for the confirmation of different stress conditions during the fabrication process.     

Breakage process of mineral processing comminution machines – An approach to liberation

Mineral liberation and size reduction are the most critical steps before mineral separation. Several investigations showed that mineral liberation degree could be affected by ore texture and/or loading mechanisms. However, varied definitions have been used for the breakage fundamentals as the leading cause of mineral liberation. This review identifies the breakage fundamentals and analyzes them in terms of process and ore breakage behavior. It is highlighted that the breakage fundamentals are essential for optimizing of comminution environments and designing the comminution machines. Three main areas of breakage processes in regard to fundamentals of breakage are classified and addressed as “Loading mechanism”, “Breakage mechanism”, and “Breakage mode”. Despite the fact that many advances have been made in the design of the comminution machines; still, the combined effect of breakage fundamentals and ore properties such as ore texture in a quantitative manner is not fully understood. In this regard, this study identifies and discusses the material and process factors influencing the breakage phenomenon. This potentially paves the way for improving the comminution environment concerning a particular ore type.     

Influence of process parameters on superplasticity of friction stir processed nugget in high strength Al – Cu – Li alloy

Abstract

A parametric study was carried out to evaluate the influence of friction stir processing (FSP) parameters (tool rotation speed and feed rate) on the superplasticity of the weld nugget. Dynamically recrystallised AA 2095 thin sheets with a fine grain size of 2 μm were welded using four feed rates and three rotational speeds. High temperature tensile testing was employed to understand the significance of the FSP parameters and to optimise the parameters for maximum elongation. The tool rotation speed was found to be the most decisive parameter for controlling superplastic behaviour. A strain rate sensitivity of 0·68 was measured for the highest rotational speed at the optimum superplastic forming (SPF) temperature of 495°C. A maximum percentage 'elongation to failure' of 550% was achieved for the sheets subjected to FSP at 1000 rev min^?1 and 4·2 mm s^?1, compared with 475% obtained for the base metal at the optimum SPF temperature and strain rate of 495°C and 10^?3s^?1, respectively.     

Annealing kinetics of gold and iron–gold complex

Thermally induced defects in heat treated and then quenched in water n-silicon samples have been studied using deep level transient spectroscopy. Two deep levels at energies E _c-0.55 eV, and E _c-0.23 eV are observed in high concentration. The emission rate signature and annealing characteristics of energy state E _c-0.55 eV identify it as Au(A). During annealing a level emerges at energy position E _c-0.35 eV. This level has been identified as Au–Fe complex. Au(A) and Au–Fe showed an interesting reversible reaction in temperature range 175 °C–325 °C which follows the following theoretical relation that adds a new parameter in identifying Au(A) and Au–Fe complex.

SHS process and structure formation of Al–Ti–B grain refiner made with the use of fluxes

Grain refiners of Al–5% Ti–1% B were prepared by using the self-propagating high-temperature synthesis (SHS) in molten aluminum with various process parameters. The initial temperature of melt and fluxes (Na₃AlF₆ and K_1–3AlF₆) were found to have a large effect on the reaction delay time and character of the SHS reaction. The lowest temperature of melt (750 °C) resulted in the longest delay time and melt splashing from the crucible. The fluxes promoted a higher violence of the SHS reaction, led to contamination-free fractures and caused a significant change in the grain refiner microstructure. Their use resulted in an increase of the size of Al₃Ti, some reduction in their quantity and change in their morphology from blocks to needle-like. The most pronounced changes in the SHS reaction and microstructure were revealed with K_1–3AlF₆ flux.     

Internal stresses and Barkhausen noise of Fe80B20 amorphous alloy treated by annealing and hydrogenation–dehydrogenation processes

Internal stresses as a consequence of structural changes of the Fe₈₀B₂₀ amorphous alloy during annealing and hydrogenation–dehydrogenation processes were observed by structurally sensitive properties as a stress induced anisotropy, a coercive force, a demagnetizing factor and the Barkhausen noise parameters.     

The preparation and properties of CeO2–TiO2 film by sol–gel spin-coating process

Ultraviolet absorbing CeO₂–TiO₂ coatings were prepared by the sol–gel spin-coating process heat treated at 500 °C. The films obtained were brilliant yellow, adherent and had some pattern on the soda-lime glass substrate. The optical transmittance, thickness and hardness of the films as a function of the number of coatings, aging time (0, 24, 48, 96 h) or aging temperature (28, 35, 40, 50 °C) were determined, and surface microstructure of the films was observed by SEM. We found some pattern on the surface of films. This pattern was similar to that of the stage for fixing the substrate. The pattern on the surface of films would be caused by the difference of thermal conductivity to slide glass in the part of metal of the stage and hollow part of the stage.     

Assessment and modelling of isothermal forging of intermetallic compounds Part 2 – Ti3 Al

Abstract

In this, the second of four papers devoted to the isothermal forging of intermetallic compounds, the Ti₃ Al based alloy Superalpha-2 has been deformed in compression at constant strain rate, over temperature and strain rate ranges of 900–1050°C and 0·0003–0·035 s^-1, respectively. Calculation of the material property parameters suggests that this material deforms via dynamic recrystallisation of the B2 phase. Microstructural examination has shown that isothermal forging generates non-equilibrium microstructures. Deformation modelling has been successful in predicting the forging behaviour. Finally, the possibility of explosive grain growth immediately after forging raises questions as to whether the mechanical properties of this material can usefully be controlled by isothermal forging.