In this study four compacted graphite irons (CGIs) and one grey cast iron (FGI) were produced and tested in the laboratory. The molybdenum content of the four CGI grades was varied between 0 and 1·01 wt-%. The purpose of the investigations was to examine the effect of the different molybdenum contents of the CGI on the thermomechanical fatigue (TMF) behaviour. The TMF tests were performed by cycling a constrained specimen between 110 and 600°C. For every material three tests were performed on specimens machined from a Ø20 mm cylinder. Other tests were performed on specimens machined from Ø55 mm and Ø85 mm cylinders respectively. The tests showed that additions of molybdenum improved the fatigue resistance of CGI. It was observed that additions of molybdenum refined the pearlite and that the specimens with a finer metallic matrix had a higher TMF resistance.

In a previous study, the thermomechanical fatigue resistance of four compacted graphite irons (CGIs) and one grey cast iron was investigated. The molybdenum content of the four CGIs varied between 0 and 1.01 wt-%. It was observed that during thermal cycling, the maximum value of the compressive stress continuously decreased while the value of the maximum tensile stress continuously increased. The continuous decrease in compressive stresses showed that stress relaxation occurs at elevated temperatures during thermal cycling. The goal of the present investigation was to investigate the phenomenon of stress relaxation at elevated temperatures. The tests were performed at 350 and 600uC respectively. The results of the stress relaxation tests performed at 600uC showed the same trend observed at thermomechanical fatigue testing. The tests showed that additions of molybdenum improved the fatigue resistance of CGI by lowering the stress relaxation rate.

The paper describes work done using synchrotron light to investigate the microstructure and how it behaves in 3D when a load is applied. Two different cast iron materials with different matrix structures and graphite morphologies were investigated; SiMo51, which is basically a spheroidal iron (SGI) alloyed with Si and Mo, and a lamellar graphite iron (LGI). The tensile test specimens were loaded in steps, at which x-ray tomography as well as 3DXRD measurements were made to characterize the microstructure. The result shows how the crack propagates and which path it takes through the materials. DVC was applied to analyze the strain fields. This work also shows how useful synchrotron experiments can be in the study of the mechanical behavior of cast iron.

Additive manufacturing, or 3D-printing as it is often called, build parts in a layer-by-layer fashion. A common concern, regardless of the specific additive manufacturing technique used, is the risk of inadequate fusion between the adjacent layers which in turn may cause inferior mechanical properties. In this work, the local strain properties of titanium parts produced by Electron Beam Melting (EBM®) were studied in order to gain information about the quality of fusion of the stock powder material used in the process. By using Digital Image Correlation (DIC) the strain fields in the individual layers were analyzed, as well as the global strain behavior of the bulk material. The results show that fully solid titanium parts manufactured by EBM are homogenous and do not experience local deformation behavior, neither on local nor on a global level.

Fracture modeling and experimental validation of Compacted Graphite Iron (CGI) specimens loaded under quasi-static conditions at room temperature are considered. Continuum damage mechanics coupled to plasticity is adopted to describe the evolution of damage. The damage production is based on a recently developed rate dependent damage evolution law, where the damage–plasticity coupling is modeled based on a damage driving energy that involves both stored energy and plasticity contributions. To describe ductile fracture accounting for stress triaxiality on the damage initiation, the inelastic contribution to the damage driving energy is controlled by the Johnson-Cook failure criterion. Three different damage models are defined based on elastic/inelastic damage driving energies. The damage models are validated against experiments on a set of notched specimens made of CGI with different notch geometries, where the global force-displacement curves and corresponding strain fields are obtained using digital image correlation technology. It is shown from the testing and the simulations that plastic strains generally need to be accounted for in order to properly describe the different failure processes of the CGI specimens. In addition, the ductile damage model is shown to more accurately predict the experimental force-displacement response as compared to the more simplistic stress drop, element deletion technique. 

The Metalock method is a mechanical joining technique most commonly employed in cracked castings of iron, aluminum and steel. The marine diesel engine designer MAN Diesel & Turbo uses the Metalock method for crack patching in large cast iron components. The service life of these components can thereby be extended, reducing both replacement costs and environmental impact. The purpose of this study is to investigate the mechanical behavior of the Metalock method. This was studied by full scale testing, using a non-contact deformation measurement technique known as digital image correlation (DIC), of cast iron specimens joined together by the Metalock method. Furthermore, finite element (FE) simulations were performed, and verified by experimental results, in order to study the mechanical behavior in detail and to carry out a parametric study on some of the components included in the joint. Experimental tests show that using the DIC technique gives a good possibility to verify the strain-field achieved by FE simulations and improving the understanding of the Metalock joining technique.

When subjecting cast irons to mechanical loading the deformation and damage mechanisms occur on a microstructural level and are dependent on the inherent microstructure. A deeper understanding of the relation between the different microstructural constituents and the macroscopic mechanical behaviour would be beneficial in material development efforts and for the ability to design and cast components with tailored properties. Traditionally, microscopy examinations on sectioned cast iron samples have been used when analysing the microstructure in cast irons. Since all microstructural heterogeneity is in three-dimensions (3D), methods that provide a three-dimensional characterisation are essential for a deeper understanding of, both the microstructural features as well as the deformation and damage of cast irons. Therefore, different cast iron grades have been studied using synchrotron X-ray tomography and 3D x-ray diffraction (3DXRD) at ESRF in Grenoble, France. The samples were stepwise loaded and unloaded in-situ at in the tomography/3DXRD set-up to study the deformation with regard to microstructural constituents and the microstructural evolution in 3D. Based on the 3D tomography image sequences, digital volume correlation (DVC) was used for full strain field analysis and for the analysis of damage and deformation mechanisms. In addition, 3DXRD data were analysed to provide details on the lattice parameters and lattice strain of individual ferrite grains. This work shows the possibilities of such synchrotron experiments for advanced study of the mechanical behaviour of cast iron.

In this experimental study, six pearlitic grey cast irons with different Cu and Cr content, different section thicknesses and different eutectoid cooling rates have been examined. The eutectoid cooling rate was approximated by casting simulation analysis. The purpose of the experiments was to study the effect of the matrix structure on the overall mechanical properties. An emphasis is put on the pearlite interlamellar spacing because this controls the resulting mechanical properties to a large extent. By keeping the graphite structure constant, the effect of the matrix structure was able to be studied. This was achieved by shake-out at temperatures above the eutectoid transformation range followed by subsequent cooling in air, mould or in a furnace. The pearlite interlamellar spacing ranged from 90 to 330 nm for the matrices studied. Comparing the strength of the fine structured and coarse structured materials, the tensile and yield strength was reduced by almost 50%. Regarding the elastic deformation, a weak increase in the tangent modulus with increasing alloying content was observed. It was also observed that lower cooling rate decreased the tangent modulus. The tangent modulus ranged between 70 and 110 GPa. Analysing the plastic deformation of the materials, in terms of strain hardening exponent, n, and strength coefficient, K, a strong dependence on the pearlite coarseness was observed. It was concluded that the effect of graphite particle length on tensile strength was negligible and the major improvement on the strength was due to refinement of the pearlite.

The matrix structure formation of cast irons is strongly affected by the casting process where different alloying elements and cooling conditions are methods used to achieve the desired structure and performance of the material. In the presented study, six pearlitic grey cast irons have been analysed regarding how the pearlitic structure formation might be controlled. Different amounts of copper and chromium were added, ranging from 0.07 to 1.11 wt% and 0.08 to 0.60 wt%, respectively. Three different section sizes (Ø20, Ø45 and Ø85 mm) and three different cooling conditions through the eutectoid transformation were used to control the matrix structure formation. The three different cooling conditions were achieved by shake-out at 950°C and cooling in air or furnace, or by keeping the casting in the mould. The present paper focuses on the pearlite appearance, since it strongly affects the mechanical properties. The analysis shows that the refining effect of Cr is much stronger than that of Cu. Comparing the low alloyed base melt with the ones alloyed with Cu and Cr, it is seen that additions of 0.75 wt% Cu refines the pearlite by approximately 10%. Keeping this Cu level constant and adding Cr, it is observed that an addition of ∼0.6 wt% refines the pearlite by another 20%. The most potent refining effect of Cr is achieved by additions up to 0.35 wt%. Keeping the Cr constant at 0.35% and changing the Cu content (0.35 to 1.10 wt%), almost no variation is observed in the overall interlamellar spacing. The eutectoid cooling rate most strongly affects the interlamellar spacing down to cooling rates of about -0.75 °C/s. At higher (i.e. lower value) cooling rates the interlamellar spacing is fairly constant. In addition to studying the interlamellar spacing, the graphite structure has also been analysed and evaluated concerning effects from the different casting variables.

The demands on strength and ductility of cast components are continuously increasing. To understand how the microstructure controls the strength, ductility and deformation behaviour of cast materials, and thereby be able to tailor new and improved materials and, additional characterisation methods are needed. This paper shows how the deformation behaviour and stress - strain data of different industrial cast materials, such as; cast irons, with lamellar, compacted and spheroidal graphite and aluminium, can be described by using certain characterization methods. Based on different mathematical models the characterisation methods have been derived and used for the evaluation of stress - strain curves. From the evaluation, parameters describing the elastic, plastic and creep properties of the materials are extracted. By altering the microstructure of the analysed materials, by e.g. adding different alloying elements or changing the cooling conditions, the influence of microstructural parameters on the derived mechanical parameters can be found. Often in simulations of stresses and strains of a cast product subjected to loading, constant material properties throughout the casting are used. By the determination/prediction of the microstructure at a given point, it is possible to calculate the local material properties from our microstructure - mechanical parameter correlations. Furthermore, to achieve even more realistic load simulation, residual stresses can be added. Some simulation examples are also included in the paper showing a useful application of the presented characterisation methods. The presented characterization methods have improved the understanding of the mechanical behaviour of complex cast materials and components.

This paper presents an experimental methodology for the characterization of thermomechanical displacement and friction properties in a free-floating press-pack structure, and evaluation of the tensile stress on the semiconductor die through simulation of different mechanical and thermal loading conditions. The press-pack structure consists of a single silver-metallized (1 μm) silicon carbide die (400 μm) in contact with rhodium-coated (0.4 μm) molybdenum square plates. The thermomechanical displacements in the press-pack structure have been obtained using the digital image correlation technique, and the mean random error has been $± $0.1 μm, which is approximately 10 ppm of the measured length (10.5 mm). The developed experimental method has led to an analytical estimation of friction coefficients on the interfaces' silicon carbide-molybdenum and molybdenum-copper. The results demonstrate that the thin silver layer behaves as a solid film lubricant. A 2-D finite-element model representing the experimental setup has been implemented. The difference in displacement between measurement and simulation is less than 8%. Furthermore, the coinfluence of the design parameters on the thermomechanical performance of the stacked structure has been analyzed through simulations. Finally, design guidelines to reduce the tensile stress on the silicon carbide die have been proposed regarding free-floating press-pack power electronics packaging.