| 1. |
- Andersson, Håkan, 1970-
(författare)
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A Co-Simulation Tool Applied to Hydraulic Percussion Units
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this dissertation, a co-simulation tool is presented that is meant to comprise a more comprehensive environment for modelling and simulation of hydraulic percussion units, which are used in hydraulic hammers and rock drills. These units generates the large impact forces, which are needed to demolish concrete structures in the construction industry or to fragment rock when drilling blast holes in mine drifting. This type of machinery is driven by fluid power and is by that dependent of coupled fluid-structure mechanisms for their operation. This tool consists of a 1D fluid system model, a 3D structural mechanic model and an interface to establish the fluid-structure couplings, which has in this work been applied to a hydraulic hammer. This approach will enable virtual prototyping during product development with an ambition to reduce the need for testing of physical prototypes, but also to facilitate more detailed studies of internal mechanisms. The tool has been implemented for two well-known simulation tools, and a co-simulation interface to enable communication between them has been devel-oped. The fluid system is simulated using the Hopsan simulation tool and the structural parts are simulated using the FE-simulation software LS-DYNA. The implementation of the co-simulation interface is based on the Functional Mock-up Interface standard in Hopsan and on the User Defined Feature module in LS-DYNA. The basic functions of the tool were first verified for a simple but relevant model comprising co-simulation of one component, and secondly co-simulation of two components were verified. These models were based on rigid body and linear elastic representation of the structural components. Further, it was experimentally validated using an existing hydraulic hammer product, where the responses from the experiments were compared to the corresponding simulated responses. To investigate the effects from a parameter change, the hammer was operated and simulated at four different running conditions. Dynamic simulation of the sealing gap, which is a fundamental mechanism used for controlling the percussive motion, was implemented to further enhance the simulated responses of the percussion unit. This implementation is based on a parametrisation of the deformed FE-model, where the gap height and the eccentric position are estimated from the deformed geometry in the sealing gap region, and then the parameters are sent to the fluid simulation for a more accurate calculation of the leakage flow. Wear in percussion units is an undesirable type of damage, which may cause significant reduction in performance or complete break-down, and today there are no methodology available to evaluate such damages on virtual prototypes. A method to study wear was developed using the co-simulation tool to simulate the fundamental behaviour of the percussion unit, and the wear routines in LS-DYNA were utilised for the calculation of wear.
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| 2. |
- Azeez, Ahmed, 1991-
(författare)
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High-Temperature Durability Prediction of Ferritic-Martensitic Steel
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Materials used for high-temperature steam turbine sections are generally subjected to harsh environments with temperatures up to 625 °C. The superior creep resistance of 9–12 % Cr ferritic-martensitic steels makes them desirable for those critical steam turbine components. Additionally, the demand for fast and frequent steam turbine start-ups, i.e. flexible operations, causes accelerated fatigue damage in critical locations, such as grooves and notches, at the high-temperature inner steam turbine casing. A durability assessment is necessary to understand the material behaviour under such high temperatures and repeated loading, and it is essential for life prediction. An accurate and less conservative fatigue life prediction approach is achieved by going past the crack initiation stage and allowing controlled growth of cracks within safe limits. Besides, beneficial load-temperature history effects, i.e. warm pre-stressing, must be utilised to enhance the fracture resistance to cracks. This dissertation presents the high-temperature durability assessment of FB2 steel, a 9-12 % Cr ferritic-martensitic steam turbine steel.Initially, isothermal low-cycle fatigue testing was performed on FB2 steel samples. A fatigue life model based on finite element strain range partitioning was utilised to predict fatigue life within the crack initiation phase. Two fatigue damage regimes were identified, i.e. plastic- and creep-dominated damage, and the transition between them depended on temperature and applied total strain. Cyclic deformation and stress relaxation behaviour were investigated to produce an elastic-plastic and creep material model that predicts the initial and mid-life cyclic behaviour of the FB2 steel.Furthermore, the thermomechanical fatigue crack growth behaviour of FB2 steel was studied. Crack closure behaviour was observed and accounted for numerically and experimentally, where crack growth rate curves collapsed into a single curve. Interestingly, the collapsed crack growth curves coincided with isothermal crack growth tests performed at the minimum temperature of the thermomechanical crack growth tests. In addition, hold times and changes in the minimum temperature of the thermomechanical fatigue cycle did not influence crack closure behaviour.Finally, warm pre-stressing effects were explored for FB2 steel. A numerical prediction model was produced to predict the increase in the apparent fracture toughness. Warm pre-stressing effects can benefit the turbine life by enhancing fracture resistance and allowing longer fatigue cracks to grow within safe limits.
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| 3. |
- Azeez, Ahmed, 1991-
(författare)
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High-Temperature Fatigue in a Steam Turbine Steel : Modelling of Cyclic Deformation and Crack Closure
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Existing conventional thermal power plants are retrofitted for flexible operations to assist the transition toward more renewable energies. The deployment of many renewable energy power plants is necessary to achieve a clean environment with less pollution. However, the intermittent nature of renewable energies, due to weather changes, and the lack of efficient large energy storage systems put renewables at a disadvantage. Flexible operations of power plants imply fast and frequent start-ups. Thus, retrofitted power production plants can be utilised as an energy backup to satisfy the immediate demand during peak energy times or when renewable energies are suddenly limited. Large thermal power plants generally employ steam turbines with high inlet temperature and pressure steam conditions. Materials used for components at the high-temperature turbine sections are expected to withstand harsh environments. The use of 9-12 % Cr martensitic steels is desirable due to, among other things, their superior resistance to creep for temperatures up to 625 °C. Retrofitting for flexible operations put steam turbine components under high-temperature fatigue loading conditions different from how they were designed before. The flexible operations could lead to fatigue cracking at critical locations, such as grooves and notches at the inner steam turbine casing. Thus, fatigue behaviour understanding of steam turbine materials under such loading conditions is essential for components life prediction. Accurate and less conservative fatigue life prediction approach is necessary to extend the turbine components life, which reduces waste and provides economic benefits. This can be done by extending operations past crack initiation phase and allowing controlled propagation of cracks in the components. Within the 9-12 % Cr steel class, the martensitic steam turbine steel called FB2 is studied under high-temperature fatigue. This includes investigating high-temperature fatigue life behaviour, cyclic deformation behaviour, stress relaxation behaviour, and crack propagation behaviour along with crack closure behaviour. This was achieved by experimentally testing samples made from FB2 steel under isothermal low cycle fatigue, isothermal fatigue crack propagation, and thermomechanical fatigue crack propagation.
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| 4. |
- Lindström, Thomas, 1991-
(författare)
-
Fatigue life prediction of additively manufactured ductile nickel-based superalloys : Constitutive and crack initiation modelling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation was produced at the Division of Solid Mechanics at Linköping University, and is the final result of a project that included mechanical testing and modelling of an additively manufactured ductile nickel-based superalloy.The main objective of the work presented in this thesis was to investigate and model the cyclic behaviour and the fatigue life behaviour of an additively manufactured ductile nickel-based superalloy, with emphasis on modelling the stabilised material behaviour, by which fatigue life predictions can be based upon. The mechanical and fatigue behaviour of additively manufactured alloys have shown to often depend on how the components are manufactured in the 3D-printing machine, meaning that the material is anisotropic. This anisotropic effect is important to account for when predicting the life of components. Therefore, in this work models to predict the mechanical response and the fatigue life of such components have been established. Monotonic tensile tests, creep tests and cyclic fatigue tests at constant temperatures, as well as anisothermal cyclic tests, have been performed to investigate the mechanical and the fatigue behaviour of the material, where specimens built in different orientations have been used to also study the anisotropic behaviour of the material. With the tests as a basis, a constitutive model has progressively been developed and implemented in a finite element context that accounts for the anisotropic behaviour under both elastic and inelastic deformations. In addition, a fatigue crack initiation life model has been developed for the tested low-cycle fatigue and thermomechanical fatigue conditions, which account for both material anisotropy and temperature effects.
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| 5. |
- Nilsson, Daniel, 1982-
(författare)
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A ΔJ approach for nonlinear fatigue crack propagation : Experimental and numerical investigation of a ductile superalloy
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation is a product of an academic-industrial collaboration between the Division of Solid Mechanics at Linköping University and Siemens Energy AB. The focus is on enhancing the design optimisation procedures for high-temperature components in industrial gas turbines (IGT). The research is centred around the behaviour of the nickelbased high-temperature superalloy Haynes 230 under service-like conditions with predominant thermal loads. The aim is to improve fatigue crack propagation life predictions for nonlinear conditions.The research findings validate the thermal ageing fatigue effects on Haynes 230 as seen in existing literature, especially on constitutive properties and crack initiation. Additionally, it was observed that thermal ageing has a minor effect on the crack growth rate up to 600 °C, which can be managed by updating the crack driving force with thermally aged properties.The project mainly focused on nonlinear crack propagation at isothermal and thermomechanical fatigue conditions. A new method for crack length description, using a modified compliance method, is introduced. This method simplifies and enhances the accuracy of crack length measurements and has become an established method for evaluating the single edge notch specimen used in the project under thermo-mechanical fatigue conditions.The nonlinear fatigue parameter ΔJ was incorporated into both Finite element method (FEM) computations and test evaluations, revealing linear trends with crack growth rates in loglog. The research highlights the crucial role of crack opening in establishing a correlation between ΔJ and crack growth rate. It was also concluded that the linear fatigue fracture parameter ΔK tends to underestimate the crack growth behaviour, resulting in non-conservative outcomes if the elasto-plastic stresses from the tests are considered.Lastly, a constitutive description of Haynes 230, based on the Ohno-Wang theory, under negligible viscoplastic effects, and an extension of the cycle jumping procedure that takes into account the significant hardening between the initial and midlife stages of the material, is presented. By this the notched geometry in 3D could be simulated with satisfying accuracy.
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| 6. |
- Pant, Prabhat, 1990-
(författare)
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Residual Stress in Additive Manufacturing : Control using orientation and scan strategies
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Components with complex features that are designed with their function as a core aspect often are not viable to be manufactured with traditional methods. This has been a bottleneck in the past, leading to heavier parts with various sub-assemblies and a significant waste of material. With the emergence of additive manufacturing (AM) technology manufacturing of complex components has now turned into reality. Within AM, the laser-based powder-based fusion (LPBF) method is one of the most widely adopted methods to manufacture near net shape complex metal components. However, to be implemented on a larger scale various hurdles must be mitigated first.One of the main persistent issues in LPBF is of residual stresses (RS), which are formed due to repeated sequences of heating and cooling, creating a high thermal gradient between the layers. These RS can play a significant role in the component’s functionality during service, but also can affect the manufacturing process. Therefore, a detailed investigation into the formation and control of RS is of foremost importance. This thesis aims at shedding light on various aspects of the RS formation especially, the effect of build orientations and different scan strategies. For this purpose, Inconel 718 (IN718) was selected as a material for investigation due to its wide use in gas turbine components and good weldability making it a good material for additive manufacturing processes.L-shaped components and test cubes were prepared for residual stress mapping and microstructure study. The RS were measured using neutron and X-ray diffraction methods where applicable. From the investigations, it was revealed that the L-shape components built in different orientations showed significant variation in RS magnitude, but a general trend of RS distribution with tensile stresses at the surface and compressive at the bulk for all the components. A simplified finite element model for RS prediction was established and validated based on the experimental results. Similarly, the use of different scan strategies can lead to a different magnitude of RS for the L-shape components. The remelting strategy with remelting done after every 3rd printed layer seems to decrease the RS magnitude in comparison to the counterparts printed without remelting. This has also been verified with a simplified finite element simulation. The microstructure study showed that crystallographic texture can also vary with the different scan strategies and no significant preferred orientations of the grains were found with the remelting done at every 3rd printed layer. However, with the total fill strategy, strong crystallographic texture was observed in the scan direction. Further investigations into the remelting scan strategies with different variables of remelting such as power, speed, and number of layers between the remelting scan revealed an effect of the laser power in the increment of texture intensity along the building direction. A combination of chess pattern and remelting every 3rd layer decreased the RS magnitude in comparison with other samples, where parameters for remelting strategies were changed. In addition, the crystallographic texture varied with different process parameters used for the remelting. For further reduction of RS without employing post-processing, investigations into novel scan strategies need to be undertaken and at the same time texture formation also needs to be investigated.
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| 7. |
- Busse, Christian, 1989-
(författare)
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Modelling of Crack Growth in Single-Crystal Nickel-Base Superalloys
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation was produced at the Division of Solid Mechanics at Linköping University and is part of a research project, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys. The main objective of this work was to deepen the understanding of the fracture behaviour of single-crystal nickel-base superalloys and to develop a model to predict the fatigue crack growth behaviour. Frequently, crack growth in these materials has been observed to follow one of two distinct cracking modes; Mode I like cracking perpendicular to the loading direction or crystallographic crack growth on the octahedral {111}-planes, where the latter is associated with an increased fatigue crack growth rate. Thus, it is of major importance to account for this behaviour in component life prediction. Consequently, a model for the prediction of the transition of cracking modes and the correct active crystallographic plane, i.e. the crack path, and the crystallographic crack growth rate has been developed. This model is based on the evaluation of appropriate crack driving forces using three-dimensional finite-element simulations. A special focus was given towards the influence of the crystallographic orientation on the fracture behaviour. Further, a model to incorporate residual stresses in the crack growth modelling is presented. All modelling work is calibrated and validated by experiments on different specimen geometries with different crystallographic orientations. This dissertation consists of two parts, where Part I gives an introduction and background to the field of research, while Part II consists of six appended papers.
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| 8. |
- Loureiro-Homs, Jordi, 1985-
(författare)
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Modelling of TMF Crack Growth in Polycrystalline Gas Turbine Alloys : Accounting for Crack Closure Effects
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of the work presented in this Licentiate of Engineering thesis is to investigate and model the fatigue crack propagation behaviour of the nickel-based superalloy Inconel 792, with special attention to the industrial lifing of high-temperature components. In-phase (IP) crack propagation tests have been performed at different temperatures and loading regimes, including extended hold times. The observations from these tests have been the basis for establishing several hypotheses to describe the crack growth behaviour, which progressively have been verified experimentally and numerically. Most prominently, it has been observed that crack closure has a substantial impact on crack growth and can explain, to a large degree, the crack growth behaviour for this material under the conditions studied. This phenomenon has been observed experimentally and modelled numerically to extend further the precision of the methodology.
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| 9. |
- Andersson, Håkan, 1970-
(författare)
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A Co-Simulation Approach for Hydraulic Percussion Units
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate of Engineering thesis concerns modelling and simulation of hydraulic percussion units. These units are often found in equipment for breaking or drilling in rock and concrete, and are also often driven by oil hydraulics, in which complex fluid-structure couplings are essential for their operation.Current methodologies used today when developing hydraulic percussion units are based on decoupled analyses, which are not correctly capturing the important coupled mechanisms. Hence, an efficient method for coupled simulations is of high importance, since these mechanisms are critical for the function of these units. Therefore, a co-simulation approach between a 1D system simulation model representing the fluid system and a structural 3D FE-model is proposed.This approach is presented in detail, implemented for two well-known simulation tools and evaluated for a simple but relevant model. The Hopsan simulation tool was used for the fluid system and the FE-simulation software LS-DYNA was used for the structural mechanics simulation. The co-simulation interface was implemented using the Functional Mock-up Interface-standard.The approach was further developed to also incorporate multiple components for coupled simulations. This was considered necessary when models for the real application are to be developed. The use of two components for co-simulation was successfully evaluated for two models, one using the simple rigid body representation, and a second where linear elastic representations of the structural material were implemented.An experimental validation of the co-simulation approach applied to an existing hydraulic hammer was performed. Experiments on the hydraulic hammer were performed using an in-house test rig, and responses were registered at four different running conditions. The co-simulation model was developed using the same approach as before. The corresponding running conditions were simulated and the responses were successfully validated against the experiments. A parameter study was also performed involving two design parameters with the objective to evaluate the effects of a parameter change.This thesis consists of two parts, where Part I gives an introduction to the application, the simulation method and the implementation, while Part II consists of three papers from this project.
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| 10. |
- Busse, Christian, 1989-
(författare)
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Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate of Engineering thesis is a product of the results generated in the research project KME-702, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys.The main objective of this work is to model the fatigue crack propagation behaviour in single-crystal nickel-base superalloys. To achieve this, the influence of the crystal orientations on the cracking behaviour is assessed. The results show that the crystal orientation is strongly affecting the material response and must be accounted for. Furthermore, a linear elastic crack driving force parameter suitable for describing crystallographic cracking has been developed. This parameter is based on resolved anisotropic stress intensity factors and is able to predict the correct crystallographic cracking plane after a transition from a Mode I crack. Finally, a method to account for inelastic deformations in a linear elastic fracture mechanics context was investigated. A residual stress field is extracted from an uncracked finite-element model with a perfectly plastic material model and superimposed on the stress field from the cracked model with a linear elastic material model to account for the inelastic deformations during the determination of the crack driving force. The modelling work is validated by material testing on two different specimen geometries at different temperatures.This Licentiate of Engineering thesis consists of two parts, where Part I gives an introduction and background to the research area, while Part II consists of three papers.
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| 11. |
- Pant, Prabhat, 1990-
(författare)
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Residual Stress Distributions in Additively Manufactured Parts : Effect of Build Orientation
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive manufacturing (AM) of parts using a layer by layer approach has seen a rapid increase in application for production of net shape or near-net shape complex parts, especially in the field of aerospace, automotive, etc. Due to the superiority of manufacturing complex shapes with ease in comparison to the conventional methods, interest in these kinds of processes has increased. Among various methods in AM, laser powder bed fusion (LPBF) is one of the most widely used techniques to produce metallic components.As in all manufacturing processes, residual stress (RS) generation during manufacturing is a relevant issue for the AM process. RS in AM are generated due to a high thermal gradient between subsequent layers. The impact of residual stresses can be significant for the mechanical integrity of the built parts and understanding the generation of RS and the effect of AM process parameters is therefore important for a broader implementation of AM techniques. The work presented in this licentiate thesis aims to investigate the influence of build orientation on the RS distribution in AM parts. For this purpose, L-shaped Inconel 718 parts were printed by LPBF in three different orientations, 0°, 45°, and 90°, respectively. Inconel 718 was selected because it is a superalloy widely used for making gas turbine components. In addition, IN718 has in general good weldability which renders it a good material for additive manufacturing.Residual stress distributions in the parts removed from the build plate were measured using neutron diffraction technique. A simple finite element model was developed to predict the residual stresses and the effect of RS relaxation due to the separation of the parts and build plate. The trend of residual stress distribution predicted was in good agreement with experimental results. In general, compressive RS at the part center and tensile RS near the surface were found. However, while the part printed in 0° orientation had the least amount of RS in all three principal directions of part, the part built in 90° orientation possessed the highest amount of RS in both compression and tension. The study has shown that residual stress distributions in the parts are strongly dependent on the building process. Further, it has shown that the relaxation of RS associated with the removal of the parts from the build plate after printing has a great impact on the final distribution of residual stress in the parts. These results can be used as guidelines for choosing the orientations of the part during printing.
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| 12. |
- Saarimäki, Jonas, 1985-
(författare)
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Cracks in superalloys
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas turbines are widely used in industry for power generation and as a power source at hard to reach locations where other possibilities for electrical power supplies are insufficient. New ways of producing greener energy is needed to reduce emission levels. This can be achieved by increasing the combustion temperature of gas turbines. High combustion temperatures can be detrimental and degrade critical components. This raises the demands on the high temperature performance of the superalloys used in gas turbine components. These components are frequently subjected to different cyclic loads combined with for example dwell-times and overloads at elevated temperatures, which can influence the crack growth. Dwell-times have been shown to accelerate crack growth and change cracking behaviour in both Inconel 718, Haynes 282 and Hastelloy X. On the other hand, overloads at the beginning of a dwell-time cycle have been shown to retard the dwell-time effect on crack growth in Inconel 718. More experiments and microstructural investigations are needed to better understand these effects.The work presented in this thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", where I have mainly looked at fatigue crack growth mechanisms in superalloys subjected to dwell-fatigue, which can have a devastating effect on crack propagation behaviour. Mechanical testing was performed under operation-like cycles in order to achieve representative microstructures and material data for the subsequent microstructural work. Microstructures were investigated using light optical microscopy and scanning electron microscopy (SEM) techniques such as electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at maximum load (0 % overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. The crack growth rate decreases with increasing overload levels in Inconel 718 when an overload is applied prior to the dwell-time. At high temperature, intergranular crack growth was observed in Inconel 718 as a result of oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along δ-phase boundaries with subsequent oxidation of the δ-phase. This thesis comprises two parts. Part I gives an introduction to the field of superalloys and the acting microstructural mechanisms related to fatigue and crack propagation. Part II consists of five appended papers, which report the work completed as part of the project.
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| 13. |
- Lindström, Thomas, 1991-, et al.
(författare)
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Accounting for anisotropic, anisothermal, and inelastic effects in crack initiation lifing of additively manufactured components
- 2023
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Ingår i: Fatigue & Fracture of Engineering Materials & Structures. - : Wiley. - 8756-758X .- 1460-2695. ; 46:2, s. 396-415
-
Tidskriftsartikel (refereegranskat)abstract
- The crack initiation life of a ductile additively manufactured nickel-based superalloy is studied and modeled for low-cycle fatigue and thermomechanical fatigue conditions up to 600 degrees C. Isothermal experiments were performed on smooth specimens at temperatures up to 600 degrees C with different applied strain ranges. Additionally, thermomechanical fatigue experiments at 100-450 degrees C and 100-600 degrees C were performed on smooth specimens under in-phase and out-of-phase conditions. A life prediction model accounting for the anisotropy was developed, where the temperature cycle is accounted with a Delta T$$ \Delta T $$-functionality, generating good agreements with the experiments. The model was also validated on notched specimens undergoing thermomechanical fatigue conditions at 100-500 degrees C using simplified notch correction methods.
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| 14. |
- Simonsson, Kjell, 1964-
(författare)
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Finite element simulation of transformation plasticity in martensitic transformation
- 1992
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study is concerned with the simulation of transformation plasticity in martensitic transformation. In the first paper the concept of a transformation plasticity strain is introduced from a phenomenological point of view. The basic physical mechanisms behand the phenomenon are discussed, and existing models concerning the evolution of transformation plasticity strain are reviewed. In the second and third paper a micromechanical finite element simulation of a martensitic transformation is presented. The second paper is mainly devoted to a model description, while results are presented and discussed in the third paper. In the fourth paper the thermodynamics of a continuous body containing a moving interface is reviewed, and as an application of the theory, the case of a martensitic transformation is considered.
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| 15. |
- Simonsson, Kjell, 1964-
(författare)
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Micro-mechanical FE-simulations of the plastic behaviour of steels undergoing martensitic transformation
- 1994
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is concerned with the mechanical behaviour of steels undergoing martensitic transformation. More specifically, the aim has been to develop a method to numerically stimulate the mean strain (or stress) response associated with a prescribed temperature and mean stress (or strain) variation.Based on the simplification that the jump of deformation gradient associated with the propagating martensitic interfaces for each martensitic variant can be treated as a welldefined metallurgical parameter, a constitutive description of a grain has been developed, in which evolution equations for the microscopic plastic strain and volumic fractions of the different variants are specified. Thus, also the kinetics of the transformation can be extracted from the simulation results.A trilinear isoparametric finite element based on the adopted constitution has been implemented in the FE code TRINITAS. The updating of the internal variables in the integration points has been accomplished with an elastic predictor - plastic corrector procedure, in which the different couplings between the inelastic processes are considered.By modelling a representative cell of the material as a cubical stacking of dubical grains, where each grain is represented by one finite element, numerical creep test simulations of a Fe-25Ni-0.66C steel have been performed. The results obtained are found to be in qualitative agreement with experimental results for both the plastic behaviour and the transformation kinetics.
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