Numerical simulation of welding-induced distortion in thin-walled structures

Abstract

A sequentially coupled thermal stress analysis approach is presented for modelling temperature and distortion profiles resulting from welding thin-walled structures. The material is modelled as thermo-elastic–plastic with isotropic strain hardening. The heat source is modelled as a three-dimensional (3-D) double ellipsoid, and 3-D finite element (FE) models are employed for predicting ensuing distortions. Comparisons between the simulation results and experiments performed for eight weld configurations are presented. The weld configurations include bead-on-plate, butt weld and tee joint welds with varying plate thicknesses. Temperature measurements using thermocouples and an infrared (IR) imaging radiometer are directly compared to the thermal simulations. Likewise, distortions measured directly on the experimental set-ups are compared to the FE distortion predictions. Very good correlation is obtained for temperature as well as distortion predictions between experimental and proposed numerical approaches. Lastly, details of a weld simulation for the rear section of a motorcycle frame are presented.     

Effect of some alloying elements on boiling point of magnesium

Abstract

The evaporation capacity of alloys differs with temperature, and this is the basis of a new experimental method to measure the boiling points of various kinds of alloys. In the present work, the effects of Al, Zn, Mn and La additions on the boiling point of magnesium have been studied. It is shown that various elemental additions and their varying contents in magnesium alloys have different influences on the boiling point of the alloys. Among these additions, Zn affected the boiling point of magnesium alloys most obviously, followed by Mn, Al and La. The boiling point of Mg–6 wt-%Zn alloy was the highest in the present study, up to 1715 K.     

Tensile properties of thermally exposed aluminium borate whisker reinforced 6061 aluminium alloy composite

Abstract

The effect of thermal exposure on the tensile properties of aluminium borate whisker reinforced 6061 aluminium alloy composite was studied. The interfacial reaction was investigated by TEM and the mechanical properties were studied using tensile tests. The results indicated that the interfacial reaction had an influence on the mechanical properties of the composite, so that the maxima of Young’s modulus and ultimate tensile strength of the composite after exposure at 500°C for 10 h were obtained for the optimum degree of interfacial reaction. The yield strength, however, was not only affected by the interfacial state but also by many other factors.     

Computational simulation of microstructure evolution during solidification of ductile cast iron

Abstract

This paper presents a thermomicrostructural model for the simulation of the solidification process of an eutectic ductile cast iron. The thermal balance is written at a macroscopic level and takes into account both the structural component being cast and its mould. Models of nucleation and growth represent the evolution of the microstructure, and the microsegregation of silicon is also considered. The resulting formulation is solved using a finite element discretisation of the macrodomain, in which the evolution of the microstructure is taken into account at the Gauss integration points. The numerical results are presented in terms of cooling curves and are compared with available experimental values. Furthermore, the sensitivity of the response with respect to changes in the cooling rate and nucleation parameters are investigated. The agreement between experimental and computational values is acceptable in both quantitative and qualitative aspects. Ways to improve the computational model are suggested.     

Technical note Pitting corrosion of steel pipeline in oil–water–gas multiphase flow system

Abstract

Severe pitting corrosion occurred in a horizontal steel pipeline used to transport multiphase fluid, including water, oil, and natural gas, after 2 months of service. The pitting corrosion rate was up to 42 mm/year. Chemical analysis, X-ray diffractometry, and EDAX showed that the corrosion products mainly consisted of Fe₉ S₈, FeCO₃ , and NaCl. Calcium containing inclusions were also found in the matrix of the steel, which may accelerate corrosion. The early failure was attributed to the high proportion of water, the slow flow velocity, and the use of unqualified material.     

Effects of Ca combined with Sr additions on microstructure and mechanical properties of AZ91D magnesium alloy

Abstract

Weight reduction to improve automobile fuel economy has triggered renewed interest in magnesium. The effects of Ca/Sr separate and composite additions to AZ91D magnesium alloy on its microstructure and mechanical properties have been investigated. The results indicate Ca can refine both the grain and eutectic phase of AZ91D magnesium alloy. Sr hampers microstructure refinement when composite Ca/Sr additions are made. In addition, separate Ca additions to AZ91D magnesium alloy increase yield strength but decrease elongation of this alloy. By adjusting the Ca/Sr composite proportions, additions to AZ91D magnesium alloy are able to improve both microstructure and mechanical properties of the alloy.     

Division of character zones and elements distribution of Fe3Al/Cr–Ni alloy fusion bonded joint

Abstract

A Fe₃Al/Cr–Ni alloy fusion bonded joint was divided into four character zones of a homogeneous mixture zone, a partial mixture zone, a partially fused zone and a heat affected zone. The microstructures, elements distribution and phase constitutions of the various character zones were analysed via metalloscope, SEM, electron probe microanalysis and X-ray diffraction. The results indicated that the microstructures were dissimilar in the different character zones. A 0·04–0·05 mm austenite rich band existed in the partial mixture zone. The diffusion of Fe, Al, Cr, Ni and C mainly occurred in fusion zone where Cr and Ni diffused into Fe₃Al to substitute some Fe on α ₁, α ₂, and β sublattices to form substitutional solid solution. The phase constitutions of Fe₃Al/Cr–Ni joint were Fe₃Al, γ-Fe, FeAl, NiAl, an unidentified Fe–C compound and an Fe–Cr–C compound (Cr₉Fe)₇C₃.     

Analysis of ductile cast iron solidification: numerical simulation and experimental validation

Abstract

This paper presents an experimental and numerical study of the solidification process of ductile cast iron under slightly hypereutectic conditions. The material thermo-microstructural behaviour is measured in tests performed using standardized cups. Cooling curves at the centre of the cup were recorded, and metallographic studies were carried out to investigate the number and size of graphite nodules at the end of the process. Different models were tested: a model based on a uninodular theory and two models which represent the multi-nodular theory. The cooling curves predicted by these models are in good agreement with the experimental measurements. Some scatter is found, however, in the numerical–experimental comparison for the graphite nodule density at different points of the sample.     

Application of experimental design to study and control properties and behaviour of cast Al–10 ? 8Si eutectic alloy

Abstract

An attempt was made to investigate the effect of compositional variationson the mechanical properties of an experimental T6 aged Al–10·8Si eutectic alloy. Experimental data were used to evaluate the regression coefficients of polynomial equations. The equations show that increasing Cu, Mn and Mg contents results in an increase in hardness and tensile strength. Copper makes the highest contribution of all three elements to the strength for the composition range studied. All four elements reduce the elongation and toughness, with Cu having the greatest effect. Detailed analysis indicates that the interaction coefficients of these variables do not appear to contribute significantly to the mechanical properties of the alloys. The accuracy of the equations in predicting the properties has been verified by carrying out random experiments in the range of variation of these four variables.     

Progress of electroless amorphous and nanoalloy deposition: a review – Part 1

Abstract

The progress and longitudinal history of electroless plating from its discovery to its present development, from published research reports and, particularly, patents are discussed and reviewed in this paper. The progress of electroless plating can be divided into five stages: the discovery of electroless plating; the early stage of development; the period of slow growth; the period of rapid development; and the period of deeper, more fundamental development and nanoelectroless plating. The contents of each stage are described and discussed in detail. Investigating and understanding the history of electroless plating can not only make clearer the process of development and characteristics of electroless plating, but also clarify to some degree the scientific and technical direction of the process and its applications. In the current Part 1, the authors review the first three stages noted above and some details from the period of fast development including the wealth of information gathered from numerous studies on the properties of electroless deposits. Part 2, to be published in a forthcoming issue of Transactions, will deal with further studies from the period of rapid development, including large scale applications, ternary and multicomponent alloys and composites, the impressive developments in China, now the world’s biggest market in electroless nickel plating, and development of electroless Fe–B alloy plating, again much of which took place in Chinese laboratories. In addition, in Part 2, the authors will discuss what they consider to be a period of sustained deep and fundamental research into the theory and mechanism of electroless plating, and development of nanoelectroless plating.