Anssi Laukkanen

Anssi Laukkanen
VTT Technical Research Centre of Finland | vtt · Integrated Computational Materials Engineering

D.Sc.(Tech)

About

137
Publications
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2,076
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Introduction
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January 2005 - present

Publications

Publications (137)
Article
Selective laser melting (SLM) can produce outstanding mechanical properties in 316L stainless steel. Nonetheless, the technique can lead to considerable variation in quality. This reflects an incomplete understanding and control of the process-structure-properties linkage. This paper demonstrates how length-scale informed micromechanical behavior c...
Article
High cycle fatigue (HCF) is a frequently limiting failure mechanism of machine elements and modern high strength steels. Present day design rules rely on semi-empirical methods, guidelines and utilization of macroscopic analysis means in origin, such as fracture mechanics. The resulting challenge is that short crack regime, critical for HCF in term...
Article
A binary alloy multi-order parameter phase field model is used to study rapid solidification in Al-Cu under conditions corresponding to recent dynamic transmission electron microscopy (DTEM) experiments. The phase field model’s sharp interface limit is set through a recent matched asymptotic analysis to follow the solute trapping and interface unde...
Article
Erosion-corrosion, the combined loss of material due to combined effects of particle erosion and electrochemical corrosion, has due to its complexity largely evaded modeling efforts. Assessment of the synergy between erosion and corrosion leading in extreme conditions to far greater material losses than for the mechanisms individually has proven el...
Article
Rapid solidification gives rise to solute trapping, which decreases solute partitioning and alters equilibrium solidification velocity-undercooling relationships. These effects influence microsegregation, solidification morphology, and the emergent microstructure length scales. Here, we review solute trapping and solute drag in rapid solidification...
Article
Full-text available
Rapid solidification kinetics of dilute Al–Cu alloys is simulated using a quantum mechanics based bond-order potential (BOP), in free solidification conditions, to determine kinetic and thermodynamic properties of solidification, as well as point defects and chemical ordering of the solidified structures. We measure the anisotropic kinetic coeffici...
Article
Full-text available
The extremely altered topmost surface layer, known as the white layer, formed in a medium-carbon low-alloy steel as result of impacts by angular 10–12 mm granite particles during the slurry erosion process is comprehensively investigated. For this purpose, the characteristics, morphology, and formation mechanism of this white layer are described ba...
Article
Full-text available
When considering the effect of inclusions on fatigue life, the size effect of inclusions is well recognized. However, many of these studies overlooked or decoupled the size effect from the shape features. Therefore, in this study, the influence of the shape characteristics of inclusions with 3 equivalent sizes of 26.6 μm, 13.3 μm, and 4.2 μm on the...
Article
Full-text available
A reduced micromorphic model is formulated in the scope of crystal plasticity and crystalline cleavage damage. The finite strain formulation utilizes a single additional microvariable that is used to regularize localized inelastic deformation mechanisms. Damage is formulated as a strain-like variable to fit the generalized micromorphic microslip an...
Article
Full-text available
Rapid solidification leads to unique microstructural features, where a less studied topic is the formation of various crystalline defects, including high dislocation densities, as well as gradients and splitting of the crystalline orientation. As these defects critically affect the material’s mechanical properties and performance features, it is im...
Article
Full-text available
In the present work, we combine Mindlin’s strain gradient elasticity theory and Gudmundson–Gurtin–Anand strain gradient plasticity theory to form a unified framework. The gradient plasticity model is enriched by including the gradient of elastic strains into the expression of the internal virtual work and free energy. This augments the modelling ca...
Article
Full-text available
Rapid solidification experiments on thin film aluminum samples reveal the presence of lattice orientation gradients within crystallizing grains. To study this phenomenon, a single-component phase-field crystal (PFC) model that captures the properties of solid, liquid, and vapor phases is proposed to model pure aluminium quantitatively. A coarse-gra...
Article
Full-text available
A coupled phase field and crystal plasticity model is established to analyze formation of dislocation structures and residual stresses during rapid solidification of additively manufactured 316L stainless steel. The work focuses on investigating the role of microsegregation related to the intra-grain cellular microstructure of 316L. Effect of solid...
Article
Full-text available
Strain induced phase transformation in metastable 301LN stainless steel generates a heterogeneous multiphase microstructure with a capability to achieve excellent strain hardening. The microstructural deformation mechanisms, prior deformation history and their dependency on strain rate and temperature determine much of the desired dynamically evolv...
Preprint
Full-text available
Rapid solidification leads to unique microstructural features, where a less studied topic is the formation of various crystalline defects, including high dislocation densities, as well as gradients and splitting of the crystalline orientation. As these defects critically affect the material's mechanical properties and performance features, it is im...
Article
Surface topography can affect the tribological performance in many applications. The influence of surface roughness and topographic orientation on friction and wear in dry and oil lubricated steel vs steel and diamond-like carbon (DLC) coated steel vs DLC coated steel sliding contacts was investigated. The surfaces had a centerline average roughnes...
Article
Full-text available
It is planned that doped copper overpacks will be utilized in the spent nuclear fuel repositories in Finland and in Sweden. The assessment of long-term integrity of the material is a matter of importance. Grain structure variations, segregation and any possible manufacturing defects in microstructure are relevant in terms of susceptibility to creep...
Article
Efficient separation of valuable metals from various slags is of great interest for the industry to effectively utilize valuable raw materials. Present work focuses on modeling the deformation and damage behavior of manganese containing slag materials at the microstructural level, which dictates the macroscopic material behavior and allows one to i...
Article
Ferritic-austenitic duplex stainless steels are known to offer favorable combinations of good mechanical properties and corrosion resistance to be used for structural purposes. Lean duplex grades have already been introduced for consideration to replace standard 18−8 austenitic stainless steels in various industrial applications. Ferrite and austen...
Article
A vector order parameter phase field model derived from a grand potential functional is presented as an alternative approach for modeling polycrystalline solidification of alloys. In this approach, the grand potential density is designed to contain a discrete set of finite wells, a feature that naturally allows for the growth and controlled interac...
Preprint
Full-text available
Rapid solidification experiments on thin film aluminum samples reveal the presence of lattice orientation gradients within crystallizing grains. To study this phenomenon, a single-component phase-field crystal (PFC) model that captures the properties of solid, liquid, and vapor phases is proposed to model pure aluminium quantitatively. A coarse-gra...
Article
Full-text available
Diamond-like carbon (DLC) coatings have proven to be an excellent thin film solution for reducing friction of tribological systems as well as providing resistance to wear. These characteristics yield greater efficiency and longer lifetimes of tribological contacts with respect to surface solutions targeting for example automotive applications. Howe...
Preprint
Full-text available
A vector order parameter phase field model derived from a grand potential functional is presented as a new approach for modeling polycrystalline solidification of alloys. In this approach, the grand potential density is designed to contain a discrete set of finite wells, a feature that naturally allows for the growth and controlled interaction of m...
Preprint
Fatigue remains a challenge especially for high end metal AM parts and materials. From a design perspective, the fatigue limit of an AM solution can be improved upon by optimizing the manufacturing process for a certain material and part. In addition, improved accuracy of design methodologies aids in capturing the features critical for fatigue and...
Article
Single track scanning is a widely used method to evaluate the effects of rapid solidification of metals and to analyze their printability. Microstructure level stresses play a dominant role in causing material failure during deposition or poor performance on the finished product. This work formulates a thermomechanical crystal plasticity model capa...
Article
A finite-element model for a paste lubricated steel wire vs cast iron contact was developed. The modelled contact included two surfaces with engineering topography and a paste lubricant. The paste lubricant consisted of a synthetic transmission oil, binder and solid manganese oxide particles. The purpose of adding solid particles in the lubricant w...
Article
Full-text available
This study focuses on microstructural and micromechanical modeling of abrasive sliding contacts of wear-resistant Hadfield steel. 3D finite element representation of the microstructure was employed with a crystal plasticity model including dislocation slip, deformation twinning, and their interactions. The results showed that deformation twinning i...
Article
Full-text available
Selective laser melting (SLM) is a promising manufacturing technique where the part design, from performance and properties process control and alloying, can be accelerated with integrated computational materials engineering (ICME). This paper demonstrates a process-structure-properties-performance modeling framework for SLM. For powder-bed scale m...
Conference Paper
For oxide coatings, prepared by applying plasma electrolytic oxidation (PEO) to aluminium alloy Al6082, this conference contribution presents the finite element (FE) microstructural modeling of the PEO coatings. By utilizing the coating phase maps, obtained by electron back-scattered diffraction (EBSD) technique, the corresponding images have been...
Article
Full-text available
A multiscale modelling approach was developed in order to estimate the effect of defects on the strength of unidirectional carbon fiber composites. The work encompasses a micromechanics approach, where the known reinforcement and matrix properties are experimentally verified and a 3D finite element model is meshed directly from micrographs. Boundar...
Preprint
Full-text available
A multiscale modelling approach was developed in order to estimate the effect of defects on the strength of unidirectional carbon fiber composites. The work encompasses a micromechanics approach, where the known reinforcement and matrix properties are experimentally verified and a 3D finite element model is meshed directly from micrographs. Boundar...
Article
Full-text available
Roughness and curvature of diamond-like carbon (DLC) surface coatings change with both scale and direction of a measurement. However, the changes are not detected by currently used standard parameters which are designed to work with isotropic surfaces at a single scale, thus providing only a limited information about multiscale and directional roug...
Article
In the current study, the elastoplastic reformulation of the theory of critical distances (TCD) is used for low-cycle fatigue analysis of round specimens with circumferential notches made of a direct-quenched high-strength steel. An attempt is made to investigate the effect of microstructural heterogeneity (which is absent in empirical notch analys...
Article
Full-text available
We carried out large-scale atomistic molecular dynamics simulations to study the growth of twin lamellar crystals of polyethylene initiated by small crystal seeds. By examining the size distribution of the stems—straight crystalline polymer segments—we show that the crystal edge has a parabolic profile. At the growth front, there is a layer of stem...
Conference Paper
Full-text available
Multiscale microstructural and micromechanical modeling has arisen as a candidate to improve upon the classical methodologies for evaluation of fatigue crack initiation and propagation, both concerning improving our understanding of the fundamental material deformation and damage processes as well as in establishing more accurate design rules for e...
Article
The deformation and strain hardening due to dislocation slip and twinning in Hadfield steels is investigated with a crystal plasticity model. A phenomenological interaction and hardening formulation is incorporated to the numerical model based on the microscopic characterization and deformation behavior. Single and polycrystal simulations on a Hadf...
Article
The strain rate history dependency of Hadfield steel is investigated by numerical modeling. A crystal plasticity model is employed to study the effect of strain rate jump/drop on the material's strain hardening and twinning propensity. Single crystal orientations are first examined to assess the importance of the strain rate and its history effects...
Article
This extended abstract summaries the VTT ProperTuneTM materials modelling approach.
Article
Microstructural and micromechanical modeling is arising as a key material modeling technique providing numerical modeling capabilities with an improved description of critical material features and mechanisms. Material characteristics such as microstructural morphologies, individual phases and defects can be included explicitly in numerical models...
Article
A crystal plasticity approach with a phenomenological shear banding mechanism incorporated in a conventional dislocation crystal plasticity model is presented. In the developed framework, the hardening and softening relations are considered both within and between the deformation mechanisms. The study aims to increase the understanding of the impor...
Article
The hardening and deformation characteristics of Hadfield microstructure are studied to investigate the effect of microstucture to the material behavior. A crystal plasticity model including dislocation slip and deformation twinning is employed. The role of deformation twinning to the overall strain hardening of the material is evaluated for two di...
Article
Diamond-like carbon (DLC) coated surfaces exhibit anisotropic and multi-scale characteristics, i.e., their roughness change with both scale and direction. However, most currently used standard surface characterisation parameters and methods work well only with isotropic surfaces at a single scale. This problem can be overcome by variance orientatio...
Article
The effects of surface roughness and topographical orientation on surface stresses influencing wear have been investigated for diamond like carbon (DLC) coated steel surfaces with three levels of surface roughness in the range of 0.004–0.11 μm Ra values, and with topographical groove orientations of 0°, 45° and 90°. A novel multiscale numerical fin...
Article
Full-text available
This paper demonstrates the successful printing and optimization of processing parameters of high-strength H13 tool steel by Selective Laser Melting (SLM). D-Optimal Design of Experiments (DOE) approach is used for parameter optimization of laser power, scanning speed and hatch width. With 50 test samples (1×1×1cm) we establish parameter windows fo...
Conference Paper
Concrete in cold environments is subject to a unique combination of transport and deterioration mechanisms that have a synergetic effect on the deterioration of concrete. Freeze-thaw is well known to efficiently saturate concrete as a result of successive cycles, in addition to inducing internal micro cracking and surface scaling in the presence of...
Article
Full-text available
TiN and diamond-like carbon (DLC) coatings were deposited on Ti substrates with and without processing by high-pressure torsion (HPT). The HPT processing refined the grain size of titanium from the coarse-grained (CG) size of ~8.6 µm to the ultra-fine grained (UFG) size of ~130 nm and increased the hardness from ~1.83 to ~3.05 GPa. Scratch test res...
Technical Report
Full-text available
The research programme on the creep issues of the nuclear waste disposal canister copper material has continued with long-running uniaxial and multiaxial experiments as well as development of a creep and relaxation model which are used in the FE analysis. The damage in the oxide particle zone in a CT specimen after 50000 hours of testing at 175°C h...
Article
Full-text available
Interface structures are a key feature in developing modern composite material solutions with ever improved performance. We present a nano-microstructural modelling approach for the tungsten carbide (WC)–Co system which can include the interface structures of WC–Co and various other phases present in the microstructure, utilising a methodology whic...
Article
Full-text available
This paper studies failure of birch pulp–polylactic acid composites. Stiffness and strength are calculated using the theory of short fibre composites and the results are compared to experimental data. The results differed from the experimental values by 0–6%. With less aligned fibres the short fibre theory is not feasible. The performance of the 40...
Article
Full-text available
Many different approaches have been proposed for modeling of fatigue crack nucleation and microstructurally short fatigue crack propagation in polycrystalline metals. The mechanisms governing dislocations and slip at micro- and nanoscale have to be taken into account to be able to modify the microstructure of metals and develop materials with impro...
Article
The present work describes the wear behaviour of nodular cast iron in rolling–sliding contact with steel wire ropes and steel wires in laboratory and in-service conditions. In each of the studied examples, the wear had proceeded through a surface fatigue process, in which inter-nodular crack propagation and simultaneous deformation in a thin sub-su...
Conference Paper
Material processing (P) method defines through the forming microstructure (S), what kind of properties (P) the material has in certain environment and how the material performs (P). Integrated computational material engineering (ICME) transfers the traditional material development based on experimental trial and error approach into digital approach...
Article
The effect of surface roughness and topographical orientation on friction and wear has been investigated for diamond like carbon (DLC) coated and uncoated steel surfaces with three levels of surface roughness in the range of 0.004 – 0.11 μm Ra value and with topographical orientations at 0°, 45° and 90° angles from grinding marks. In this first par...
Article
Full-text available
High velocity solid particle erosion may cause severe damage and high wear rates in materials used for wear protection. An experimental work on the behavior of wear resistant steels, including three high- strength martensitic alloys and a carbide-reinforced metal matrix composite, was performed in high rate single impact conditions. Characterizatio...
Article
The deformation and wear behavior of four high strength wear resistant steels were studied in various impact conditions to evaluate their performance in applications involving heavy impacts and impact-abrasion. In the normal direction impacts, the studies were conducted with single and repeated (multiple) drop tests. To better simulate the actual a...
Article
Full-text available
The alloying of Hadfield steels aims at enhanced mechanical properties and improvements in the wear resistance. In this work, the impact and abrasive properties of a chromium-alloyed high-manganese Hadfield steel were experimentally studied using a wide variety of testing techniques and characterization methods. In addition, an in-service sample wa...
Conference Paper
Sustainable design aspects are discussed through hard metal case study. Raw material scarcity, demand for substitution for critical raw materials, need to substitute toxic materials and need for sustainability are driving to material life cycle design and control evidently. Currently, hard metals (also cemented carbides) are the most important powd...
Article
High strength steels (HSS) used in highly abrasive environments, such as in mining and crushing, must endure high stress abrasion. To properly understand the wear behavior of materials under such circumstances, the connection between surface loading, work hardening, and material removal has first to be determined. In this study, wear resistant stee...
Article
The wear resistance of components can be changed remarkably by surface coatings. New processing methods offer many possibilities to tailor the wear resistance of surfaces to match design criteria. Computational modelling and simulation is a systematic approach to optimise the wear performance. Modelling of physical surface phenomena can be carried...
Conference Paper
Multiscale modeling method for thermal spray microstructures is developed using the VTT ProperTune methodology and applied for mechanical and wear behavior modeling of a Cr2O3 coating. The work is carried out following a process-structure-properties-performance (PSPP) type of an analysis emphasizing the couplings between microstructural morphologie...