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1

On spatial vs referential isotropic fourier’s law in finite deformation thermomechanics

Wcisło Balbina, Pamin Jerzy, Rose Lars, Menzel Andreas

Engineering Transactions

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2023

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Vol. 71, iss. 1

111--140

EN

This paper deals with the issue of isotropic heat conduction in thermomechanical largestrain problems. The aim of the paper is a comparison of different variants of Fourier’s law used in the literature for a large strain problem. In particular, Fourier’s law is specified either in the reference or in the deformed configuration by using different options of heat flux density vectors which are presented and discussed. The paper includes working examples to illustrate the presented theory. Moreover, different formulations of Fourier’s law are tested by using the finite element method to investigate the influence of the applied variant on simulation results. The analysis reveals that in a strongly deformed area the temperature distribution varies.

2

Polyurethane shape memory polymer: structure characterization and estimation of energy storage and dissipation during the tension process

Staszczak Maria, Gradys Arkadiusz, Golasiński Karol, Pieczyska Elżbieta A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2023

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Vol. 71, nr 6

art. no. e147343

EN

Shape memory polymers (SMP) are new multifunctional materials raising increasing interest in various functional applications. Among them, polyurethane shape memory polymers (PU-SMP) are particularly attractive due to their combination of shape memory, high strength and biocompatible properties. Developing new applications for PU-SMP requires comprehensive research on their characteristics. This work involved investigating the structure and mechanical behavior as well as characterizing the energy storage and dissipation of a thermoplastic PU-SMP with a glass transition temperature (Tg) of 25_C during tensile loading-unloading. The process of energy storage and dissipation in the PU-SMP was investigated based on the stress-strain curves recorded by a quasi-static testing machine and the temperature changes, accompanying the deformation process, obtained by using a fast and sensitive infrared camera. The results showed that the thermomechanical behavior of the examined PU-SMP depends significantly on the strain rate. At a higher strain rate, there are higher stress and related temperature changes, which lead to greater energy dissipation. However, the energy storage values estimated during the deformation process turned out to be not significant, indicating that the work supplied to the PU-SMP structure during loading is mainly converted into heat. It should also be noted that the structural investigation revealed no crystalline phase in the investigated PU-SMP.

3

Thermomechanical modeling on the crack initiation of NiTi shape memory alloy

Jiang Dongjie, Xiao Yao

Computer Methods in Materials Science

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2022

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Vol. 22, No. 1

31--42

EN

The fracture of shape memory alloys is distinct from that of conventional metals, owing to the coexistence and interaction of multiple special features such as martensitic transformation, dislocation-induced plasticity, thermomechanical coupling and others. In this paper, the impact of thermomechanical behavior upon the crack initiation of a NiTi shape memory alloy under Mode I loading is investigated numerically and verified experimentally. A constitutive model incorporating phase transformation, plasticity and thermomechanical coupling is established. Via backward Euler integration and finite-element implementation, the longitudinal strain, martensite volume fraction and temperature field in the vicinity of the crack tip are furnished. The effects of grain size and loading rate on J-integral are revealed. The grain size dependence of crack initiation is non-monotonic. For the samples with grain sizes of 1500 nm, 18 nm and 10 nm, the shielding effect takes place in front of the crack. Additionally, the anti-shielding effect is detected for samples with grain sizes of 80 nm and 42 nm. The parametric study shows that loading rate imposes limited influence on J-integral, which is attributed to a small scale transformation. The decrement of yield stress and the increment of transformation hardening modulus can alleviate the anti-shielding effect and arouse the shielding effect upon crack initiation. The presented results shed light on the design and fabrication of high toughness phase transformable materials.

4

Study on the temperature and strain fields in gas foil bearings – measurement method and numerical simulations

Zdziebko Paweł, Martowicz Adam

Eksploatacja i Niezawodność

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2021

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Vol. 23, no. 3

540--547

EN

Gas foil bearings belong to the group of slide bearings and are used in devices in which operation at high rotational speeds of the shafts are of key importance, e.g., in gas turbines. The air film developed on the surface of the bearing’s top foil allows this structural component to be separated from the shaft. This ensures a non-contact operation of the bearing. In the case of the mentioned type of bearings, their resultant operational properties are influenced by both thermal and mechanical phenomena. The current work presents a model of a gas foil bearing developed making use of the Finite Element Method. The model takes into account thermomechanical couplings which are necessary for the correct simulation of the operation of physical components of the modeled system. The paper reports the results of numerical analyzes conducted for the elaborated model as well as the relevant conclusions concerning thermomechanical couplings present in gas foil bearings. The method for the experimental identification of the temperature and strain fields in the bearing’s top foil proposed to validate the numerical model is also presented.

5

Temperature-dependent fatigue characteristics of P91 steel

Egner Władysław, Sulich Piotr, Mroziński Stanisław, Egner Halina

Acta Mechanica et Automatica

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2020

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Vol. 14, no. 2

69--78

EN

In this paper, the experimental investigations, constitutive description and numerical modelling of low-cycle fatigue behaviour of P91 steel in non-isothermal conditions are presented. First, experimental tests are performed to recognise different aspects of material behaviour. Then, an appropriate constitutive model is developed within the framework of thermodynamics of irreversible processes with internal state variables. The model describes two phases of cyclic softening, related to plastic mechanisms. An important goal of the presented research is to include thermomechanical coupling in the constitutive modelling. Next, the model parameters are identified based on the available experimental data. Some parametric studies are presented. Finally, numerical simulations are performed, which indicate the significant influence of thermomechanical coupling on the response of the constitutive model in thermomechanical fatigue conditions.

6

Wstępna analiza numeryczna procesu chłodzenia połączenia spawanego wykonanego wiązką laserową ze stali 1.4539

Nasiłowska Barbara, Derewońko Agnieszka, Bogdanowicz Zdzisław

Przegląd Mechaniczny

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2019

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nr 3

44--46

PL

Niezależnie od zastosowanej metody, w procesie spawania obszar spoiny oraz jej otoczenie poddawane są procesom cieplnym. Wstępne symulacje tego procesu przedstawione w pracy obejmowały rozważenie różnego rodzaju zagadnień, co wymagało przyjęcia określonych założeń upraszczających oraz zastosowania odpowiednich algorytmów numerycznych dotyczących tworzenia modeli z efektem sprzężenia termomechanicznego etapu chłodzenia połączenia spawanego. Na podstawie wyników badań termofizycznych, własności mechanicznych oraz analizy literatury określono także rozkład naprężeń własnych Metodą Elementów Skończonych.

EN

Notwithstanding the applied method is in the welding process, the weld area and its vicinity are subjected to thermal processes. Preliminary simulations of this process, presented in the paper, included considering different problems, which required adaptation of specific simplifying assumptions and application of relevant numerical algorithms related to development of models with thermomechanical coupling effect of the welded joint cooling stage. Based on the results of the thermophysical mechanical properties and literature analysis, a distribution of residual stress with Finite Element Method was determined.

7

The influence of thermomechanical coupling on the behaviour of athick-walled metallic tube subjected to internal pressure

Śloderbach Z.

International Journal of Applied Mechanics and Engineering

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2018

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Vol. 23, no. 3

751--766

EN

In this study, the influence of thermomechanical coupling effect - the effect of thermal expansion due to dissipation of the energy of plastic deformation, with and without taking into account the stored energy of plastic deformation (SEPD) for the distribution of stresses, strains, temperature, the applied pressure and the residual stresses is examined. The residual stresses remain in a thick-walled tube (a cylindrical thick-walled tank) after removing the internal pressure in the process of purely elastic unloading. The analysis is made on the example of an analitycal solution for a thick-walled tube subjected to a quasistatically increasing internal pressure for the case of adiabatic processes (without heat flow). Since the loading with internal pressure is quasi-static (monotonic), then neglecting the process of heat flow can lead to some different results in calculated stresses, deformations, temperature, internal pressure and residual stresses. The calculations for isothermal type of processes of deformations (without heat or ideal cooling) are also performed for the estimation of these differences. The results calculated for the process with heat flow should be intermediate between the values obtained for isothermal and adiabatic processes.