Significant progress has been made in recent years in understanding and modelling the rheology of semi-solid metals. These models show the effects of the microstructure in terms of size and morphology of globules on the material response. More recently it has been shown that semi-solid metals can behave as compacted granular materials such as sand. A particular signature of such deformation is that the deformation becomes concentrated into shear bands which are 10-20 grains wide. Such bands have also been observed in a range of cast products. Recently, it has been clearly shown that shear bands in high pressure die cast (HPDC) products are also the results of Reynolds dilatancy. Shear bands are also known to be a common feature in semi-solid metal products. The segregation banding in semi-solid metal (SSM) material and its dependence of plunger velocity were investigated. Shaped castings were made with the RHEOMETAL™ process with a range of different plunger velocities. The microstructural characteristics were investigated, with a particular emphasis on shear bands. It is shown that ingate velocities influence the location and characteristics of the shear bands.
A mapping of fatigue crack growth rates in thick plates of a high strength aluminium alloy has been done. The plate thicknesses investigated was 100, 150 and 200 mm. In this work, material from near edge at near surface and mid-thickness has been investigated.
Measurements of crack length has been performed using DC potential drop. Cyclic condensation is used in order to reveal crack growth behaviour for stage I and the earlier part of stage II crack growth.
Influence of crack closure, crack branching and slow growing side cracks on fatigue crack growth rate of S-L and L-T oriented specimens are discussed. Variation of difference in growth rate in the upper part of the stage II growth between near surface and mid thickness positioned L-T specimens are found to vary with plate thickness.
It has become more and more common for companies to move part of their production to low cost countries and/or closer to important markets. However, quite often the product development is not moved. The result is an increased distance between product development and production. The interface between the two departments is important to lead time, cost and quality and therefore the cooperation must work smoothly. To achieve this, most literature recommends early and tight cooperation. However this can be complicated by expensive and time consuming travels and/or usage of less rich communication such as emails and phone calls.
It is difficult to make the transition in general from product development to production and the possible problems increase with the distance. The PD-P interface consists of several components and how a problem in one component is affected by problems in other components is not explicitly discussed in literature. The purpose in this paper is to explore if there are such connections i.e. connections between an observable problem and other components in the PD-P interface in a geographically dispersed setting. The paper does so by merging the distributed work literature and the PD-P interface literature.
The analysis is based on four PD-P interface components; technological, organizational, scope and task. The analysis indicates that observable problems as e.g. low frequency of communication can be the symptom of one or a combination of problems. Connections between the components in the PD-P interface are exemplified in a geographically dispersed setting. Furthermore the underlying causes to the problems connected to the geographically dispersed setting in the PD-P interface are elucidated. In the case of low frequency of communication, it could be the technical system hindering communication and the different time zones disrupt it even more. Hence one symptom could be caused by different underlying problems. Each problem needs to be broken down to find the cause and the solution could be found in any of the four interface components.
The results indicate that the actual distance is not the biggest problem but uncertainties (e.g. new collaborations) and differences (culture and work methods) which increase lead time. We have also seen that single underling problems can cause problem in several of the PD-P interface components. This indicates that if these underlying problems can be solved the project results can be vastly improved. For example, trust issues occur in the scope component (affects the willingness to share information) and in the organizational interface component (both competence trust and goodwill trust affects involvement and commitment to the project). Consequently, if problems like this can be solved many other problems will become minor problems and project objectives will be more likely to be obtained. However trust is difficult to achieve with a geographical distance between product development and production. The analysis also indicates that due to the distance more attention is paid to the PD-P interface, e.g. more experienced team members are appointed. This can be contributing to a smoother PD-P interface than expected.
Initially, when implementing a design automation system the focus is on successfully developing a system that generates design variants based on different customer specifications, i.e. the execution of system embedded knowledge and system output. However, in the long run two important aspects are the modelling and management of the knowledge that govern the designs. The increasing emphasis to deploy a holistic view on the products properties and functions implies an increasing number of life-cycle requirements. These requirements should all be used to enhance the knowledge-base allowing for correct decisions to be made. In a system for automated variant design these life-cycle requirements have to be expressed as algorithms and/or computational statements to be intertwined with the design calculations. The number of requirements can be significantly large and they are scattered over different systems. The aim of the presented work is to provide an approach for modelling of manufacturing requirements, supporting both knowledge execution and information management, in systems for automated variant design.
Computer simulation of casting becomes a valuable tool for developing advanced materials and casting components. Recent investigations and validation work on simulated cast components reveal the necessity of reliable analyses methods to determine solidification behaviour and to extract parameters for kinetic models to use at simulation of complex cast iron materials.
The paper will present an inverse modelling method for determination of eutectic growth. The method include an experimental part proper to investigate simultaneously the solidification at three different cooling rates while the cast material has the same metallurgical origin, and a computational part for calculation of grow kinetics. Validation of the inverse method is made together with simulation. The inverse modelling of eutectic growth in grey iron indicates that chemical composition, type and amount of inoculants and cooling condition are strongly influencing the eutectic growth condition and gives different eutectic growth coefficients. By invoking a generalized KJMA* equation, the shape of the growing eutectic interface can be predicted. Deviation from perfectly spherical growth in real solidification cases is the source of variation of eutectic growth coefficients. The results of the inverse model are valuable to simulate differences in solidification behaviour in differently treated grey iron melts.
* KJMA is the abbreviation of the name of the famous scientists Kolmogorow, Johnson, Mehl and Avrami who developed and applied the equation.
Cast iron is one of the oldest technical alloys used for creating objects. Foundrymen from the very beginning of casting was fighting to avoid casting defects. In the beginning a successfully performed casting was associated with witchcraft. Cast component producers suffer yearly substantial expenses due to rejecting or repairing castings. The present work will summarize research efforts to understand formation mechanisms of defects, performed in collaboration with Swedish foundries during the last years. The presented work will focus on defects, specific casting of gray iron components. Studied defects are gas porosity, shrinkage porosity and metal expansion penetration. Novell experimental set up has been developed or existing methods has been improved to study defect formation mechanisms. Today we can realize that casting without defects are possible only by approaching the defect formation mechanism with multidisciplinary science.
The fracture mechanism of gray cast iron was investigated on tension loaded samples produced under different conditions. The parameters studied included the graphite morphology, the carbon content, the inoculation and the cooling condition. The observations made reveal the role of the microstructure on crack propagation. The cracks were found to always propagate parallel with the graphite flakes. The interaction between the metallic matrix precipitated as primary austenite and graphite has been interpreted by a simplified model of the austenite reinforced eutectic cell. The geometrical transcription gave a standard crack component configuration with known mathematical solution. The microstructure observed in the experiments has been analysed by means of a novel interpretation. The fictitious stress intensity at yield and the fictitious maximum stress intensity at failure are strongly related to the relative shape of the eutectic cell and the fraction primary austenite. A different slope is observed for the material cooled at high rate when the precipitation of primary carbide reduces the stress intensity. The observed relations indicate that the tensile strength of the grey cast iron is the result of the collaboration between the toughness of the metallic matrix precipitated as primary austenite and the brittleness of the graphite phase. The shape and distribution of the primary austenite and graphite can be influenced by chemical composition, by inoculation or by the cooling condition, but they will maintain equilibrium with respect to the stress intensity.