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1

Polycrystalline plasticity analysis of cyclic loading and stress relaxation in 316H austenitic stainless steel

Acar Sadik Sefa, Yalçinkaya Tuncay

Computer Methods in Materials Science

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2025

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Vol. 25, No. 3

5--18

EN

The mechanical behavior of 316H austenitic stainless steel is investigated in this study under cyclic strain-controlled loading with and without hold periods at elevated temperatures. Understanding the low-cycle fatigue (LCF) and fatigue-creep interaction (FCI) characteristics is essential for ensuring the structural performance and safety of reactor components, particularly under conditions typical of modular and generation IV reactors. The new generation of nuclear power plants require more resistant and durable materials as the operating environments impose significantly higher demands, including increased neutron irradiation levels and elevated operating temperatures, leading to accelerated material degradation. Acombined isotropic-kinematic hardening model within a crystal plasticity framework is employed to capture the cyclic and time-dependent mechanical response of the material. Model parameters are calibrated by fitting cyclic loading simulation results to experimental data at 550°C using polycrystalline representative volume elements (RVE). Strain-controlled uniaxial loading simulations are performed to analyze peak stress evolution throughout cyclic loading and stress relaxation behavior during strain-hold periods. The RVE simulation results are in strong agreement with experiments under LCF loading. For the loading with strain-holds, stress relaxation during hold periods exhibits two distinct stages: an initial rapid decay followed by a steady decline, both of which are captured in simulations. Beyond the macroscopic response, analyses reveal the heterogeneous evolution of field variables at the microstructural level, as strain hardening during loading and stress relaxation during hold periods varied across grains due to their crystal orientations and interactions with neighboring grains. These findings enhance the understanding of high-temperature mechanical behavior at both macroscopic and microstructural scales, contributing to the efforts for the design, operation, and life extension of nuclear reactor components.

2

Viscoelastic model for bending process of continuous fiber-reinforced thermoplastic sheets

Abadi M. T.

Archives of Mechanics

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2025

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Vol. 77, nr 1

29--51

EN

This paper presents an analysis of the bending process in thermoplastic sheets reinforced with unidirectional continuous fibers. To capture the material’s viscoelastic response during the bending process, a novel viscoelastic model is described based on the concept of transient reversible networks. The model incorporates kinematic constraints of material incompressibility and fiber inextensibility during deformation of the composite sheets. An analytical solution is derived, enabling the determination of the deformed geometry and bending forces as time-dependent functions of the bending angle, the deformation rate, and material parameters. The model’s performance is evaluated through comparisons with existing experimental data and a prior viscous model for bending process at various deformation rates. This comparison aids in identifying the material parameters and characteristic time associated with the transient reversible networks.

3

Stress relaxation in sugar beet root under various mechanical load conditions

Kołodziej Paweł, Stropek Zbigniew, Gołacki Krzysztof

Advances in Science and Technology. Research Journal

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2025

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Vol. 19, no. 2

296--303

EN

Identification and determination of the mechanical properties of biological materials, especially fruits, vegetables and industrial plants, can be made using commonly applied stress relaxation tests. They are of particular significance because their results make it possible to propose a mechanical model of studied material. The aim of the study was to determine the effects of initial deformation and deformation velocity on the parameters of generalised Maxwell model during stress relaxation in the sugar beet root. The tests were carried out by means of the texture analyser (model TA.HD plus, Stable Micro Systems, Goldaming, UK) at the three deformations: 2.0, 3.5 and 5.0 mm and the four deformation velocities: 1, 2, 10, and 20 mm·s–1. The cut sugar beet samples used in the experiment were cylindrical in shape, with a 9.5 mm diameter and a 20 mm height. They were initially compressed along the vertical axis in a state of uniaxial stress and constant deformation was maintained while recording the force response for 35 seconds. The two-branched generalised Maxwell model with an additional elastic element was used to describe the experimental force response curves. The sample dimensions as well as the initial deformation velocity were taken into consideration in the model formula. Two relaxation times of the model decreased with the increasing deformation velocity and increased with the increasing deformation value. The dependences of the obtained relaxation times on the phenomena inside the tissue such as the flow of fluids and gases under the load were interpreted. Changes of model parameters as a function of deformation velocity could testify the appearance of internal micro damages in the material during deformation. The tendency of increase in the peak force response along with the increase of deformation velocity shows typical viscoelastic behaviour of sugar beet root flesh.

4

Evaluation of tensile stress relaxation of selective laser sintering of pa2200 material using the maxwell-wiechert model

Szot Wiktor, Rudnik Mateusz, Szczygieł Paweł, Kowalska Natalia

Acta Mechanica et Automatica

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2025

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Vol. 19, no. 2

292--299

EN

The use of 3D printing for the manufacture of functional components has led to a demand for research into the mechanical properties, including rheological properties, of additive manufactured models. In this article, the results of a study to evaluate the relaxation of tensile stress of samples made by selective laser sintering (SLS) of PA2200 material are presented. The evaluation of tensile stress relaxation was performed using the five-parameter Maxwell-Wiechert model. With the model used, elastic moduli and dynamic viscosity coefficients were calculated. The samples were made in three print orientations (0°,45°,90°) and two types of energy density (𝐸𝑑=0.056 𝐽/𝑚𝑚2, 𝐸𝑑=0.076 𝐽/𝑚𝑚2). The results indicate that increasing the applied energy density leads to higher values of elastic moduli and dynamic viscosity coefficients. A strong fit of the model to the experimental curves was obtained, as confirmed by the obtained coefficients 𝐶ℎ𝑖2 and 𝑅2. This research comprehensively addresses the evaluation of the applicability of selective laser sintering technology, which is increasingly used in various areas of industry, as well as the influence of the process on the relaxation of tensile stress.

5

Comprehensive temperature performance evaluation of asphalt mastics containing hydrated lime filler based on dynamic shear rheometer testing

Ryś Dawid, Jaskuła Piotr, Szydłowski Cezary

Roads and Bridges - Drogi i Mosty

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2024

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Vol. 23, no. 4

355--373

EN

The paper focuses on exploring the potential for effective testing of asphalt mastics in the full range of temperatures using the Dynamic Shear Rheometer (DSR) apparatus. Six various types of asphalt mastics were selected to enable the evaluation of the effects of hydrated lime and bitumen modification, both before and after aging. Different DSR tests covered the whole range of service temperatures from –20°C to 64°C. Multiple Stress Creep Recovery test indicated that in the case of mastics with mixed filler (containing hydrated lime) the non-recoverable compliance at the stress level of 3.2 kPa was lower by half indicating much higher resistance to permanent deformations. Linear Amplitude Sweep Test showed that fatigue life calculated at 2.5% strain is almost 3 times greater when adhesive agent or hydrated lime is applied. Low-temperature rheological properties of mastics were investigated based on relaxation tests and it was concluded that mastics with hydrated lime have slightly lower stress relaxation capacity than the remaining mastics with lime filler.

PL

W artykule przeanalizowano możliwości skutecznego badania właściwości mastyksów asfaltowych w pełnym zakresie wartości temperatury z zastosowaniem reometru dynamicznego ścinania (DSR). Badania przeprowadzono na sześciu różnych mastyksach asfaltowych, aby umożliwić ocenę wpływu wapna hydratyzowanego oraz modyfikacji asfaltu na właściwości mastyksu, zarówno przed starzeniem, jak i po nim. Różne badania przeprowadzone w reometrze dynamicznego ścinania dały obraz właściwości mastyksów w całym zakresie eksploatacyjnych wartości temperatury: od –20°C do 64°C. Test pełzania i nawrotu MSCR wykazał na poziomie obciążenia 3,2 kPa dwukrotnie niższą wartość nieodwracalnej podatności na pełzanie w przypadku mastyksów z wypełniaczem mieszanym (zawierającym mączkę wapienną i wapno hydratyzowane), co wskazuje na ich znacznie wyższą odporność na deformacje trwałe. Test liniowego zwiększania amplitudy LAS wykazał, że trwałość zmęczeniowa obliczona dla odkształcenia 2,5% jest niemal trzykrotnie wyższa dla mastyksów zawierających środek adhezyjny lub wapno hydratyzowane. Właściwości reologiczne mastyksów w niskich wartościach temperatury analizowano na podstawie badań relaksacji. Stwierdzono, że mastyksy z wapnem hydratyzowanym mają nieco niższą zdolność relaksacji naprężeń niż pozostałe mastyksy, zawierające wyłącznie mączkę wapienną.

6

Effect of selective laser sintering on stress relaxation in PA12

Szot Wiktor, Bochnia Jerzy, Zmarzły Paweł

Polimery

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2024

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Vol. 69, nr 3

179--185

EN

Effect of selective laser sintering printing orientation (0°, 45°, 90°) on stress relaxation in PA12 was investigated. The results were highly consistent with the Maxwell-Wiechert model, as evidenced by the average values of the fit coefficients Chi2 = 0.00004 and R2 = 0.996. By changing the printing orientation, anisotropy of rheological properties was achieved.

PL

Zbadano wpływ orientacji wydruku selektywnego spiekania laserowego (0°, 45°, 90°) na relaksację naprężeń w PA12. Uzyskano dużą zgodność wyników z modelem Maxwella-Wiecherta, o czym świadczą średnie wartości współczynników dopasowania Chi2 = 0,00004 oraz R2 = 0,996. Zmieniając orientację wydruku uzyskano anizotropię właściwości reologicznych.

7

Viscoelastic characterization of additively manufactured acrylonitrile butadiene styrene

Witek Szczepan

Computer Methods in Materials Science

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2023

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Vol. 23, No. 2

39--44

EN

The main objective of this work was to characterize the viscoelastic properties of additively manufactured Acrylonitrile Butadiene Styrene based on tensile stress relaxation tests. The stress relaxation measurements were conducted with a temperature range of 25–100°C. The two-layer viscoplastic constitutive model was adopted to describe the elastic and viscous behavior of the investigated material. The model parameters were calibrated using an inverse analysis and stress relaxation data. The model’s predictive capabilities were assessed by comparing the model predictions with experimental data not included in the calibration process.

8

Simulation of Stress Relaxation Behaviour of Composite Propellants with Varying Solid Loading Using the Generalized Maxwell Model

Bihari Bipin Kumar, Kumaraswamy Adepu, Jain Mukesh, Kurva Ramesh, Vipin Lisha

Central European Journal of Energetic Materials

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2023

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Vol. 20, no. 2

221--235

EN

Hydroxyl-terminated polybutadiene (HTPB) based composite propellants possess viscoelastic behaviour and hence time and temperature dependent mechanical properties. The mathematical analysis of viscoelastic behaviour of composite propellants becomes complex due to the non-linearity involved under various loading conditions. In the present study, a linear viscoelasticity assumption was considered to simulate stresses related to storage conditions. In this paper, a study of stress relaxation behaviour of composite propellants was carried out using the Generalized Maxwell model to obtain the material viscoelastic characteristics. The relaxation behaviour of composite propellants having solid loading varying from 85% to 89% were studied at different temperatures, from -27 to +32 °C, using a Dynamic Mechanical Analyser (DMA). The generated relaxation curves were curve fitted using MATLAB (R2022a) with the Generalized Maxwell model. The simulation demonstrated that a maximum of four elemental parameters of the Generalized Maxwell model are sufficient and can represent a best fit of the relaxation behaviour of the studied composite propellants. The equilibrium modulus was also evaluated at different temperatures, along with other material constants that are essential parameters for performing the structure integrity analysis of a solid propellant rocket motor. It was observed that the equilibrium modulus decreases with an increase in temperature, but increases with an increase in solid loading in the propellant composition formulations.

9

The viscoelasticity, anisotropy and location-dependence of mechanical properties of rabbit iris investigated using uniaxial tensile tests

Li Tan, Qin Xiao, Liu Zhicheng, Zhang Haixia, Li Lin

Acta of Bioengineering and Biomechanics

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2023

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Vol. 25, no. 2

85--92

EN

Abnormal iris mechanical properties have been considered to be an important cause of pupillary-block and angle-closure glaucoma. In this research, viscoelasticity, anisotropy and location-dependence of mechanical properties of rabbit iris were investigated using uniaxial tensile test. Methods: Iris strips were taken along three directions: inner-circumferential direction (ICD), outer-circumferential direction (OCD) and radial direction (RD), respectively. Quasi-static tensile tests and stress–relaxation tests were applied on the iris strips. Then, the stress–stretch data was fitted with third order Ogden model; the stress–relaxation data was fitted with the third order Prony series model. Through comparing the tangent modulus and relaxation limit of the strips from different directions and locations, the viscoelasticity, anisotropy and location-dependence of mechanical properties of rabbit iris were explored. Results: The tangent moduli of iris at the stretch of 1.05 along ICD, OCD, and RD were 3.2 ± 1.4 kPa, 4.2 ± 2.6 kPa, 1.5 ± 0.8 kPa, respectively. Iris strips in ICD and OCD were found to have almost the same stress–relaxation behavior, and both relaxed slower than iris strips in RD. Conclusions: The mechanical properties of the iris were typically nonlinear, viscoelastic, anisotropic and location-dependent. The stress growth rate of the circumferential direction iris strip is significantly lower than that of RD and the stress–relaxation rate is significantly higher than that of the RD. That is, the iris is more prone to deformation in RD and the stress–retention ability after deformation in RD is weak, which is consistent with the fact that the iris bombe more likely happens in RD in vivo. The results of this study may also help us to establish a more accurate finite element model to simulate the flow field of humor aqueous and find the key factor of pupillary-block.

10

Numerical simulation of single- and multi-step shear stress relaxations of isotropic magnetorheological elastomer using fractional derivative viscoelastic models

Nam T. H., Petríková I., Marvalová B.

Archives of Mechanics

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2022

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Vol. 74, nr 4

251--266

EN

The paper presents numerical simulations of single- and multi-step shear stress relaxations of isotropic magnetorheological elastomer (MRE) using fractional derivative Maxwell and Kelvin–Voigt viscoelastic models. The isotropic MRE has been fabricated by filling micro-sized carbonyl iron particles in silicone rubber. Fractional derivative Maxwell and Kelvin–Voigt viscoelastic models were used to fit the experimental data of the isotropic MRE measured by single- and multi-step relaxation tests at different constant strains and external magnetic fields. The fractional Maxwell viscoelastic model showed a relatively large difference between the measured and calculated results. The fractional Kelvin–Voigt model was fitted well with the experimental data of the isotropic MRE at various constant strain levels under different magnetic fields in both single- and multi-step shear stress relaxations. The calculated shear stress with the long-term prediction is in excellent agreement with the measured one. Therefore, the fractional derivative Kelvin–Voigt viscoelastic model is applicable to predict the long-term stress relaxation of the isotropic MRE.

11

Badanie relaksacji i pełzania wybranych papierów pakowych

Szmidt Karolina, Stanisławska Anna

Przegląd Papierniczy

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2021

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R. 77, nr 12

661--667

PL

Celem pracy było opracowanie metody testowej umożliwiającej badanie pełzania i relaksacji naprężeń oraz zastosowanie tej metody do oceny właściwości reologicznych papierów pakowych. Wyznaczono zależność reologiczną obciążenie-odkształcenie, a także obciążenie zrywające i wydłużenie w momencie zerwania. Podczas badań relaksacji naprężeń i pełzania, zadane odkształcenia i obciążenia stanowiły 60% tych wartości dla granicy wytrzymałości danego materiału. Dla wszystkich przebadanych papierów relaksacja naprężeń była wyższa dla kierunku maszynowego (MD), a pełzanie było na ogół większe dla kierunku poprzecznego (CD). Najwyższą relaksacją naprężeń charakteryzował się liner-MD, a najniższą – clupak-CD. Z kolei najwyższe pełzanie zaobserwowano dla papieru clupak-CD, a najniższe dla papieru natron-MD. Najmniejszą anizotropię relaksacji naprężeń i pełzania zaobserwowano dla papieru clupak. Uzyskane wyniki pozwoliły na przeprowadzenie analizy zachowania się wybranych papierów pakowych podczas wystawienia ich na działanie obciążeń nieniszczących.

EN

The objective of the presented work was to develop a test method that enables the study of creep and stress relaxation and the use of this method to assess the rheological properties of packaging papers. The rheological dependence load – elongation, breaking load and elongation at break were determined. During the stress relaxation and creep experiments, the set elongation and load were equal to 60% of these values at break. For all tested papers, the stress relaxation was higher for the machine direction (MD), and the creep was generally greater for the cross direction (CD). The highest stress relaxation was found for the liner-MD, and the lowest – for the clupack-CD. The highest creep was observed for clupak-CD paper, and the lowest for natron-MD paper. The lowest anisotropy of stress relaxation and creep was for the clupack paper. The applied method made it possible to analyze the behavior of selected packaging papers when subjected to non-destructive loads.

12

Stress relaxation in samples made of acrylonitrile butadiene styrene material manufactured by fused deposition modeling

Szot Wiktor

Mechanik

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2021

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R. 94, nr 12

46--50

EN

Increased interest in fused deposition modeling (FDM) resulting, for example, from its use in the production of utility models determines the undertaking of research on mechanical and rheological properties of materials. Mechanical and rheological properties of models made of materials used in FDM technology depend on technological parameters. In this paper, the effect of 0° and 90° print orientation on stress relaxation was analyzed. Additionally, the usefulness of the rheological model to describe the relaxation curve was evaluated. Stress relaxation tests were performed by tensile testing. The five-parameter Maxwell-Wiechert model was used to describe stress relaxation. The tests showed little effect of print orientation on the rheological parameters of the five-parameter model. The Maxwell-Wiechert model showed a very good approximation to the stress relaxation curves.

PL

Wzrost zainteresowania technologią osadzania topionego materiału (FDM), wynikający m.in. z zastosowania jej do produkcji modeli użytkowych, wymusza podjęcie badań nad właściwościami mechanicznymi w tym reologicznymi materiałów. Właściwości mechaniczne (i reologiczne) modeli wytwarzanych z materiałów stosowanych w technologii FDM zależą od parametrów technologicznych. W prezentowanym artykule poddano analizie wpływ orientacji wydruku 0° i 90° na relaksację naprężeń. Dodatkowo oceniono przydatność modelu reologicznego do opisu krzywej relaksacji. Testy relaksacji naprężeń wykonano poprzez próbę rozciągania. Do opisu relaksacji naprężeń zastosowano pięcioparametrowy model Maxwella-Wiecherta. Badania wykazały niewielki wpływ orientacji wydruku na parametry reologiczne modelu pięcioparametrowego. Model Maxwella-Wiecherta wykazał bardzo dobrą aproksymację do krzywych relaksacji naprężeń.

13

Stress relaxation phenomena in polymeric orthodontic ligatures

Milewski Grzegorz

Engineering of Biomaterials

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2021

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Vol. 24, no. 162

2--6

EN

Elastomeric products are applied in orthodontics mainly as elastic ligatures or chains and have become an alternative to wire ligation made of titanium alloy or stainless steel. Despite their popularity among the dentists and undoubtful advantages, some essential warnings are being raised regarding the degree of load loss. This relaxation phenomenon seems to be a dominant feature in the time-dependent behaviour of those elements in orthodontic procedures, such as dentition corrections or teeth extrusions. The aim of the paper was to examine and analyse the rheological properties of biocompatible orthodontic elastomeric ligatures. Five different polymeric orthodontic ligatures were examined in the following experiments: a simple relaxation test, relaxation simulating orthodontic extrusion and the two-steps relaxation process, which stands for so-called ‘secondary tightening’, resulting in the increase of the orthodontic force. The results of the relaxation experiments proved that among various descriptions of that phenomenon, the power-law descriptions fit the best time-dependent behaviour during orthodontic procedures. Power-law models give the most intensive initial relaxation, which is characteristic for elastomeric ligatures. The obtained results and analyses allow precise control of the treatment progress in the orthodontic extrusion procedure.

14

The influence of material aging on the structural behavior of a flexible roof with a polymer membrane shell

Chesnokov Andrei V., Mikhailov Vitalii V., Dolmatov Ivan V.

Computer Methods in Materials Science

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2021

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Vol. 21, No. 1

13--24

EN

The roof structure considered in the research consists of continuous cables and a number of spreaders forming a three-dimensional frame. The frame is covered with a polymer membrane made of flexible architectural fabrics. The elements of the roof are compact and suitable for transportation to remote construction sites. The roof also has advantages for developing areas with harsh climatic conditions. The flexible elements of the roof, however, only provide transmission of tensile forces. Under compression, cables slacken and the membrane becomes wrinkled. Pre-tension of the flexible elements, which is introduced to retain the operability of the roof, tends to gradually diminish due to material aging. The aging results in the alteration of strength properties and creep elongation of the structural elements. It induces membrane tearing on local areas. Force alteration in primary structural members is examined in the present study, with statistical methods used for data analysis. They include significance hypothesis testing and correlation coefficients estimation. The data are obtained by the Finite Element simulation of the roof using EASY-2020 software. The results of the work may be used for life expectancy assessment of flexible roof structures, providing important information for the preliminary design stage. The work contributes to the safety enhancement of cable-membrane structures and the expansion of their scope in permanent building constructions.

15

Comparative Study of Long- and Short-Stretch Woven Compression Bandages

Aboalasaad Abdelhamid R. R., Sirková Brigita Kolčavová, Bílá Pavlína, Khalil Amany A. S.

Autex Research Journal

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2021

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Vol. 21, no. 4

435--444

EN

Compression therapy using bandages or socks is the most common treatment for venous leg ulcers and edema. This article aims to compare the compression between long- and short-stretch bandages (LSB and SSB, respectively). Load-elongation curves, cyclic loading, and elastic recovery are investigated for both Cotton/Polyamide/Polyurethane and 100% bleached cotton bandages as LSB and SSB, respectively. Static (resting) and dynamic (working) pressures are measured on seven male legs, 31 ± 3.6 years old, using both two and three layers bandaging. Picopress pressure tests are performed on the ankle and mid-calf positions at gradual decreasing compression from the ankle to the knee. The deviation percentage between the experimental results by Picopress and theoretical calculations using Laplace's law and Al-Khaburi equations is compared. LSB recovered approximately 99% of its original length after stress-relaxation whereas SSB recovered only 93% of its original length after 5 days of cyclic load-relaxation. Moreover, SSB lost approximately 28.6% of its activity after wearing on the human leg for 5 days.

16

Stress relaxation of porcine tendon under simulated biological environment: experiment and modeling

Łagan Sylwia D., Liber-Kneć Aneta

Acta of Bioengineering and Biomechanics

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2021

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Vol. 23, no. 1

59--68

EN

Purpose: The aim of the study was to investigate the viscoelastic response in the low and high physiological strain with the use of experimental and modeling approach. Methods: Viscoelastic response in the low, transition and high physiologic strain (3, 6 and 9%) with consideration of simulated biological environment (0.9% saline solution, 37 °C) was measured in relaxation tests. Preconditioning of tendons was considered in the testing protocol and the applied range of load was obtained from tensile testing. The quasi-linear viscoelasticity theory was used to fit experimental data to obtain constants (moduli and times of relaxation), which can be used for description of the viscoelastic behavior of tendons. The exponential non-linear elastic representation of the stress response in ramp strain was also estimated. Results: Differences between stress relaxation process can be seen between tendons stretched to the physiological strain range (3%) and exceeding this range (6 and 9%). The strains of 6% and 9% showed a similar stress relaxation trend displaying relatively rapid relaxation for the first 70 seconds, whereas the lowest strain of 3% displayed relatively slow relaxation. Conclusions: Results of the model fitting showed that the quasi-linear viscoelastic model gives the best fit in the range of low physiological strain level.

17

Verification of the Peleg and Normand equation at varied loads and moisture during stress relaxation of wheat

Łysiak Grzegorz, Kulig Ryszard, Wójcik Monika

Agricultural Engineering

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2019

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Vol. 23, No. 3

89--99

EN

Wheat kernel is made up of structures of different apparent viscosities with varied ability to withstand stress and dissipate strain energy. Its complex mechanical behaviour determines technological susceptibility and is important for wheat quality assessment. The aim of the study was the examination of the Peleg and Normand model to characterize the overall stress relaxation behaviour of wheat kernel at varying loading conditions. The relaxation experiments were made with a help of a universal machine Zwick Z020 in compression at four distinct initial load levels, i.e., 20, 30, 40, and 50 N. The measurements were made for intact wheat kernels at seven levels of moisture content. Relaxation characteristics were approximated with the help of Peleg and Normand formula. An interactive influence of the load level and moisture on Peleg and Normand constants have been confirmed. The initial loading level had none or only slight effect on the model coefficients (Y(t), k1 and k2). The parameters of the Peleg and Normand model decreased with the increase of water content in kernels. For moist kernels, a higher amount of absorbed compression energy was relaxed, since less energy was necessary to keep the deformation at a constant level.

PL

Ziarniak pszenicy składa się ze struktur o różnych własnościach lepko-sprężystych, różnej wytrzymałości i zdolności do rozpraszania energii odkształcenia. Jego złożone zachowanie mechaniczne determinuje podatność technologiczną i jest ważne dla oceny jakości ziarna. Celem badań była analiza zmienności parametrów modelu Pelega i Normanda w różnych warunkach obciążenia początkowego. Pomiary przeprowadzono przy wykorzystaniu uniwersalnej maszyny Zwick Z020. Zastosowano test jednoosiowego ściskania pojedynczych ziarniaków dla czterech początkowych poziomów obciążenia, tj. 20, 30, 40 i 50 N. Badania wykonano dla siedmiu poziomów wilgotności. Charakterystyki relaksacyjne aproksymowano za pomocą równania Pelega i Normanda. Potwierdzono interaktywny wpływ poziomu obciążenia i wilgotności na stałe modelu. Początkowy poziom obciążenia nie miał żadnego lub wpływał tylko nieznacznie na współczynniki modelu (Y(t), k1 i k2). Parametry modelu Pelega i Normanda spadały wraz ze wzrostem zawartości wody w ziarniakach. W przypadku wilgotnych ziarniaków relaksacji podlegała istotnie większa wartość zaabsorbowanej energii, potrzeba było też mniej energii aby utrzymać odkształcenie na stałym poziomie.

18

Analiza wpływu przebiegu procesu odkształcenia na nawrót sprężysty asfaltów modyfikowanych polimerami – część I

Jurczak R.

Magazyn Autostrady

|

2018

|

Nr 10

56--60

PL

Ze względu na coraz trudniejsze warunki pracy nawierzchni pożądana jest zdolność mieszanek mineralno-asfaltowych do rozpraszania naprężeń (relaksacji), która wiąże się przede wszystkim z obecnością lepiszcza. Zatem użyty w mieszance asfalt powinien wykazywać zdolność do relaksacji w możliwie jak najszerszym zakresie temperatur. Przydatnych informacji o podatności lepiszcza do większej relaksacji naprężeń powstających w mieszance może dostarczyć pomiar nawrotu sprężystego.

EN

Because of more and more difficult working conditions of the surface, the ability of asphalt mixtures to dissipate stresses (relaxation) is desired, which is mainly related to the presence of a binder. Therefore, the asphalt used in the mixture should have the ability to relax in the widest possible temperature range. A test of elastic recovery can provide useful information about the binder’s susceptibility to greater stress relaxation in the mixture.

19

Effect of cyclic hardening on stress relaxation in SUS316HTP under creep-fatigue loading at 700ºC: experiments and simulations nobutada

Ohno N., Sasaki T., Shimada T., Tokuda K., Yoshida K., Okumura D.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 2

497--510

EN

Cyclic hardening and stress relaxation experiments of SUS316HTP were performed under creep-fatigue loading with tensile strain holding at 700ºC. Experiments revealed that under strain holding, the slow stress-relaxation stage satisfying Norton’s law with slight cyclic hardening followed a rapid stress-relaxation stage that was noticeably affected by cyclic hardening. This suggests that in the slow stress-relaxation stage, inelastic deformation mechanisms different from that of viscoplasticity occurred. Experiments were simulated using a cyclic viscoplastic-creep model in which the inelastic strain-rate was decomposed into viscoplastic and creep components that were affected differently by cyclic hardening. The simulation accurately reproduced the experiments.

20

Nieliniowo lepkosprężyste równanie konstytutywne gąbczastej tkanki kostnej i identyfikacja stałych materiałowych

Pawlikowski M., Jankowski K., Kokot G., Skalski K., Makuch A.

Inżynieria Powierzchni

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2018

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nr 1

12--17

PL

W pracy sformułowano nowe równanie konstytutywne dla gąbczastej tkanki kostnej człowieka. Zapostulowano funkcję energii odkształcenia, która opisuje sprężystą odpowiedź tkanki na obciążenie. W modelu konstytutywnym uwzględniono także nieliniową lepkosprężystość. Stałe materiałowe w równaniu konstytutywnym zidentyfikowano na podstawie wyników testów relaksacji naprężeń i monotonicznego ściskania metodą dopasowania krzywych. Wykorzystano tutaj algorytm Levenberga-Marquardta metody najmniejszych kwadratów. Na podstawie testów relaksacji zidentyfikowano wartości czasów relaksacji, natomiast na podstawie testów monotonicznego ściskania określono stałe sprężyste i lepkosprężyste. Testy były wykonane w temperaturze pokojowej na prostopadłościennych próbkach kości gąbczastej uzyskanych z główek kości udowej podczas operacji wszczepienia endoprotezy stawu biodrowego.

EN

In the paper a new constitutive equation for human cancellous bone tissue was formulated. A strain energy function was postulate, which describes the elastic response of the tissue to the load. The nonlinear viscoelasticity was also taken into account in the constitutive model. The material constants in the constitutive equation were identified on the basis of the results of stress relaxation tests and monotonic compression tests using the curve fitting method. The Levenberg-Marquardt algorithm of the least square method was used here. On the basis of the relaxation tests, the values of relaxation times were identified, while the elastic and viscoelastic constants were determined on the basis of monotonic compression tests. The tests were performed at room temperature. On the cuboidal samples of cancellous bone obtained from femoral heads during the surgeries of hip joint prosthesis implantation.