Jakob Olofsson

A methodology for microstructure-based structural optimization of cast and injection moulded parts using knowledge-based design automation

A new methodology for geometry optimization with consideration of heterogeneous material behaviour is presented.Mechanical behaviour is based on local microstructure formation predicted by simulations and microstructure models.Design automation and a multi-objective optimization algorithm is used for controlling the knowledge-based implementation.The approach is implemented for cast materials and injection moulded glass-fibre reinforced polymeric materials. The local material behaviour of cast metal and injection moulded parts is highly related to the geometrical design of the part as well as to a large number of process parameters. In order to use structural optimization methods to find the geometry that gives the best possible performance, both the geometry and the effect of the production process on the local material behaviour thus has to be considered.In this work, a multidisciplinary methodology to consider local microstructure-based material behaviour in optimizations of the design of engineering structures is presented. By adopting a knowledge-based industrial product realisation perspective combined with a previously presented simulation strategy for microstructure-based material behaviour in Finite Element Analyses (FEA), the methodology integrates Computer Aided Design (CAD), casting and injection moulding simulations, FEA, design automation and a multi-objective optimization scheme into a novel structural optimization method for cast metal and injection moulded polymeric parts. The different concepts and modules in the methodology are described, their implementation into a prototype software is outlined, and the application and relevance of the methodology is discussed.

Modelling and simulation of local mechanical properties of high silicon solution-strengthened ferritic compacted graphite iron

Abstract This study focuses on the modelling and simulation of local mechanical properties of compacted graphite iron cast at different section thicknesses and three different levels of silicon, ranging from about 3.6% up to 4.6%. The relationship between tensile properties and microstructure is investigated using microstructural analysis and statistical evaluation. Models are generated using response surface methodology, which reveal that silicon level and nodularity mainly affect tensile strength and 0.2% offset yield strength, while Young′s modulus is primarily affected by nodularity. Increase in Si content improves both the yield and tensile strength, while reduces elongation to failure. Furthermore, mechanical properties enhance substantially in thinner section due to the high nodularity. The obtained models have been implemented into a casting process simulation, which enables prediction of local mechanical properties of castings with complex geometries. Very good agreement is observed between the measured and predicted microstructures and mechanical properties, particularly for thinner sections.

Casting and stress-strain simulations of a cast ductile iron component using microstructure based mechanical behavior

The industrial demand for increased component performance with concurrent reductions in component weight, development times and verifications using physical prototypes drives the need to use the fu ...

Simulation of mechanical behaviour of cast aluminium components

Abstract A literature review on methods to consider the mechanical behaviour of cast aluminium alloys in finite element method (FEM) simulations of cast aluminium components has been performed. The mechanical behaviour is related to several microstructural parameters achieved during the casting process. Three different methods to consider these microstructural parameters are introduced. One method predicts the mechanical behaviour of the component using casting process simulation software. The other two methods implement numerical models for the mechanical behaviour of cast aluminium into the FEM simulation. Applications of the methods are shown, including combinations with statistical methods and geometry optimisation methods. The methods are compared, and their different strengths and drawbacks are discussed.

Analysis of Localized Plastic Strain in Heterogeneous Cast Iron Microstructures Using 3D Finite Element Simulations

The design and production of light structures in cast iron with high static and fatigue performance is of major interest in e.g. the automotive area. Since the casting process inevitably leads to heterogeneous solidification conditions and variations in microstructural features and material properties, the effects on multiple scale levels needs to be considered in the determination of the local fatigue performance. In the current work, microstructural features of different cast irons are captured by use of micro X-ray tomography, and 3D finite element models generated. The details of the 3D microstructure differ from the commonly used 2D representations in that the actual geometry is captured and that there is not a need to compensate for 3D-effects. The first objective with the present study is to try and highlight certain aspects at the micro scale that might be the underlying cause of fatigue crack initiation, and ultimately crack propagation, under fatigue loading for cast iron alloys. The second objective is to incorporate the gained knowledge about the microstructural behavior into multi-scale simulations at a structural length scale, including the local damage level obtained in the heterogeneous structure subjected to fatigue load.

Modelling and simulations of ductile iron solidification-induced variations in mechanical behaviour on component and microstructural level

The mechanical behaviour and performance of a ductile iron component is highly dependent on the local variations in solidification conditions during the casting process. Here we show a framework which combine a previously developed closed chain of simulations for cast components with a micro-scale Finite Element Method (FEM) simulation of the behaviour and performance of the microstructure. A casting process simulation, including modelling of solidification and mechanical material characterization, provides the basis for a macro-scale FEM analysis of the component. A critical region is identified to which the micro-scale FEM simulation of a representative microstructure, generated using X-ray tomography, is applied. The mechanical behaviour of the different microstructural phases are determined using a surrogate model based optimisation routine and experimental data. It is discussed that the approach enables a link between solidification- and microstructure-models and simulations of as well component as microstructural behaviour, and can contribute with new understanding regarding the behaviour and performance of different microstructural phases and morphologies in industrial ductile iron components in service.

Influence of Local Microstructure on Stresses, Durability and Fracture Mechanics of Cast Iron Components

Cast iron components show a large variety of different microstructures in dependence on chemical composition, inoculation and cooling conditions. In conventional static and dynamic calculations as well as in fracture mechanics assessment of cast iron components, the influence of local microstructure on the overall behavior of the component is not considered. Usually one material dataset is applied for the whole material. The paper describes recent developments in the field of the prediction of local microstructure and its correlation to local stress-strain, fatigue durability as well as fracture toughness. The benefit of combining casting process simulation with lifetime predictions and fracture mechanics assessment is shown for selected examples. By integrating casting process simulation, microstructure modelling, local material characterization and load analysis, a simulation based approach for predicting the behavior and performance of cast iron components already during the design stage is enabled. Thus, the local assessment helps designers to assess risks and strive for light weight designs before the casting is made.

Local microstructure-based material performance and damage in design and finite element simulations of cast components

Abstract A novel approach to incorporate local microstructure-based material performance into finite element method (FEM) simulations of cast components is presented. By adopting perspectives from natural designs as dinosaur skulls and trees, the discipline-wide approach enables accurate prediction of damage in structures based on a heterogeneous distribution of sub-scale features. It is shown that heterogeneous damage tolerance dictates the performance and failure of cast aluminum, and simulations are compared with experimental results of heterogeneous tensile samples using digital image correlation (DIC). The numerical application of the approach in the industrial product realization process of an industrial casting is demonstrated, and the applicability of the approach to understand the behavior and failure of natural as well as synthetic structures is discussed.

The multi-scale closed chain of simulations – incorporating local variations in microstructure into finite element simulations

Numerical simulations of component behavior and performance is critical to develop optimized and robust load-bearing components. The reliability of these simulations depend on the description of the components material behavior, which for e.g. cast and polymeric materials exhibit component specific local variations depending on geometry and manufacturing parameters. Here an extension of a previously presented strategy, the closed chain of simulations for cast components, to predict and incorporate local material data into Finite Element Method (FEM) simulations on multiple scales is shown. Manufacturing process simulation, solidification modelling, material characterization and representative volume elements (RVE) provides the basis for a microstructure-based FEM analysis of component behavior and a simulation of the mechanical behavior of the local microstructure in a critical region. It is discussed that the strategy is applicable not only to cast materials but also to injection molded polymeric materials, and enables a common integrated computational microstructure-based approach to optimized components.

Understanding Cast Iron Materials and Components: A Never Ending Story

How can an in principal binary alloy of iron and carbon show so many fascinating phenomena and still today give surprises to users, foundrymen and researchers? This paper points out some critical steps in the understanding of the whole chain, from the melt to a cast iron product in service. The understanding of the material is gradually improved, assisted by the advances of other fields, e.g. analyzing methods and computational techniques. The heart in cast iron is the graphite, which is a highly difficult phase to understand but gives the material its unique properties. The linkage between understanding and modelling is necessary to calculate/simulate the processes occurring, where the precipitation, nucleation and growth of the different phases are the keys. Proper nucleation and growth models have been introduced to predict e.g. primary precipitation of austenite and graphite, eutectic growth of different morphologies of graphite or cementite and austenite, solid state transformation of austenite into ferrite and pearlite in both grey and ductile irons, and now gives realistic microstructures and solidification curves for most practical cases. The microstructure formation models gives input to shrinkage and volume calculations to predict porosities, and to predictions of mechanical properties. By linking microstructure formation models, characterization models for mechanical properties and Finite Element Analysis (FEA) it is today possible to use local properties in simulations of the behavior of cast iron components. Many phenomena in cast iron, however, still remain unexplained. As one student labelled one of his experimental files on ductile iron, cast iron materials and simulations are indeed a never ending story, with a bright future in industrial applications.