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1

An elastoplastic constitutive model for assessing ground settlements induced by deep excavations

El-Arja Hiba, Burlon Sébastien, Bourgeois Emmanuel

Studia Geotechnica et Mechanica

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2023

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Vol. 45, nr 3

231--245

EN

Ground movements induced by deep excavations may cause damages on neighboring existing buildings. Finite element simulations generally give acceptable estimates of the horizontal displacements of the retaining wall, but results are less satisfactory for the vertical displacements of the ground surface behind the structure. A possible explanation is that most constitutive models describe volumetric strains in a simplified way. This paper proposes an elastoplastic constitutive model aimed at improving the prediction of vertical displacements behind retaining walls. The model comprises a single plastic mechanism with isotropic strain hardening, but has a specific flow rule that allows to generate contractive plastic strains. Identification of the parameters based on triaxial tests is explained and illustrated by an example of calibration. A numerical analysis of a well-documented sheet pile wall in sand in Hochstetten (Germany) is presented. The results given by the model are compared with the measurements and with those obtained using the Hardening Soil Model. The potential advantages of the proposed model are then discussed.

2

Numerical modelling of uniaxial compressive strength laboratory tests

Nguyen Phu Minh Vuong, Walentek Andrzej, Waclawik Petr, Souček Kamil, Antoniuk Michał

Journal of Sustainable Mining

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2023

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Vol. 22. iss. 4

280--294

EN

In the last decades, numerical modelling has been widely used to simulate rock mass behaviour in geo-engineering issues. The only disadvantage of numerical modelling is the reliability of required input data (e.g. mechanical parameters), which is not always fully provided due to the complexity of rock mass, project budget, available test methods or human errors. On the other hand, it was proven in many cases that numerical modelling is a helpful tool for solving such complex problems, especially when coupled with the results of laboratory and in-situ tests. This paper presents an attempt to determine the proper numerical constitutive model of rock and its mechanical parameters for further simulating rock mass response based on the outcomes of laboratory testing. For this purpose, the available constitutive models, including mechanical parameters, were taken into account. The simulation performance with the selected constitutive models is demonstrated by matching the numerical modelling results with the uniaxial compressive strength laboratory tests of rock samples from the Bogdanka coal mine. All numerical simulations were carried out using the finite difference method software FLAC3D.

3

Research on the linear viscoelastic rheological properties of rejuvenated asphalt mastic based on the discrete element method

Lin Mei, Lei Yu, Li Ping, Shuai Jun, Wang Zhaoli

Archives of Civil Engineering

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2023

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Vol. 69, nr 2

399--416

EN

The rheological property of asphalt is an important factor affecting the pavement performance of asphalt binder, and the fundamental reason for the change of asphalt rheological property is the strong evolution of asphalt material meso structure. However, the internal mechanism of rejuvenated asphalt mastic system is complex and its rules are difficult to grasp. Aiming to study the relationship between meso mechanical parameters and rheological parameters of rejuvenated asphalt mastic, the meso structure model of rejuvenated asphalt mastic was established and improved based on the discrete element method. Moreover, the meso parameters of the model were obtained by the objective function method, and then the influences of various factors were studied to construct the mathematical constitutive model of rheological parameter modulus and meso mechanical parameters. Combing with the reliability of the improved Burgers model was verified based on the rheological test results of rejuvenated asphalt mastic. In addition, the virtual test of dynamic shear rheological dynamic frequency scanning was carried out on the asphalt mastic sample by particle flow software. By adjusting the mesomechanical parameters, the simulation results (complex shear modulus and phase angle) were consistent with the test results. This study clarified the relationship between mesomechanics and macro performance, and this model could be used to obtain the complex shear modulus of rejuvenated asphalt mastic under different types, filler-asphalt ratio and external force environments by adjusting particle flow, wall boundary and other conditions, which can greatly save the workload for the later research and provide a theoretical basis for production experiments.

4

Size‑dependent constitutive model incorporating grain refinement and martensitic transformation

Liu Shengqiang, Li Wei, Shen Jinxia, Yang Xiaoming, Wang Baoyu, Liu Jinping

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e38, 2023

EN

The deformation behaviour of materials at the micro-scale level is different from that at the macro-scale level due to the effect of grain size (GS). The mechanism of the influence on martensitic transformation by GS is still unclear, and there are relatively few studies on the relationship between grain refinement and martensitic transformation, most of which focus on the relationship between the initial GS of the material and martensitic transformation. Therefore, in this study, the interaction between grain refinement and martensitic transformation was investigated using a dislocation density-based multiscale constitutive model that incorporated dislocation sliding, strain-induced martensitic transformation (SIMT) related to grain size, and grain refinement. The proposed model evaluated the GS-dependent deformation behaviour of 316L stainless steel (SS). Subsequently, a genetic algorithm was used to determine the parameters of the established model, and the calculated results were compared with that of the experimental data to verify the accuracy of the model. The developed multiscale constitutive model was implemented in Abaqus user subroutine to further investigate the deformation mechanism and validate its accuracy. The results demonstrated that the GS had a significant effect on the SIMT, with the volume fraction of martensite increasing with a rise in the initial austenite GS. In addition, grain refinement affected SIMT and the growth rate of martensite content decreased with the grain refinement caused by deformation. The formation of martensite led to grain refinement, with the refined grains producing negative feedback on the SIMT, thus inhibiting the occurrence of martensitic transformation. This study revealed the microscopic deformation mechanism of 316L SS and provided a constitutive model for micro-forming.

5

New constitutive model based on disturbed state concept for shear deformation of rock joints

Xie Shijie, Lin Hang, Chen Yifan

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e26, 2023

EN

The mechanical behavior and constitutive relation of rock joints have caught more and more attention in the field of geotechnical engineering. The disturbed state concept (DSC) theory offers a powerful tool for building a constitutive model to interpret the mechanical response of geomaterials. In this paper, a new constitutive model for joint shear deformation was developed based on the DSC theory. The characteristics of quasi-elastic phase, pre-peak hardening phase, peak shear strength, post-peak softening phase and residual strength during the whole process of joint shear deformation are considered in this model. In the framework of this shear constitutive model, the rock material was assumed to consist of two kinds of micro-units with different mechanical responses, namely the relatively intact unit and the fully adjusted unit. Subsequently, the DSC theory was used to connect the mechanical behavior of micro-units with the macroscopic joint shear deformation characteristics, and a disturbance factor was introduced to reveal the disturbed state evolution process inside the rock. In addition, the proposed DSC model was simple in form, less in parameters and reasonable in physical meaning. The model was cross-validated by experimental data of different kinds of natural joints and artificial joint replicas. Finally, the model is compared with existing models, and the model effectiveness is quantitatively evaluated through statistical indicators. The values of R2 are greater than 0.9, and the AAREP and RMSE of the proposed DSC model are closer to 0 than those of other models. The research results can provide a valuable reference for further understanding of shear deformation mechanism.

6

Mechanical behavior and constitutive model of lining concrete in triaxial compression infiltration process under pore water pressure

Xue Weipei, Jing Wei, Wang Zhongjian, Zhang Hanwen, Lin Jian

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e20, 2023

EN

Underground concrete structures are affected by groundwater, the effects of which are different from those of stress environments experienced by ground engineering concrete structures. This study experimentally and theoretically investigates the mechanical behavior, permeability evolution, and deformation failure mechanism of lining concrete under pore water pressure. Results show that an increase in pore water pressure promoted the coupling of seepage and stress fields in concrete. This caused the microcracks to propagate further, which led to a decrease in concrete strength and elastic modulus. Through triaxial compression infiltration, the concrete successively underwent initial compaction, linear elastic deformation, and nonlinear deformation after yielding. Accordingly, its permeability exhibited three trends: gradual decrease, stable development, and a sharp increase. The change in permeability was closely related to the number of pores and the development of microcracks in concrete. The concept of primary pore strain was proposed according to the characteristics of deformation and failure. Moreover, a triaxial compression infiltration constitutive model was derived for concrete based on the principle of effective stress. This model considers the influence of pore water pressure and the initial compaction characteristics. This study can be used to guide the design of lining concrete structures in underground engineering.

7

Development of an advanced constitutive model for spoil-structure interaction problems

Doan Nhat-Phi, Liakou Anna, Garala Thejesh Kumar, Cui Ge, Kantesaria Naman, Halder Koushik, Heron Charles M., Marshall Alec M.

Górnictwo Odkrywkowe

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2022

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R. 63, nr 3

43--50

EN

Revitalisation options for mine spoil heaps is an important issue to consider when planning for post-mining land use. One option is the installation of wind turbines on the spoil heaps, which provide a sustainable energy source. This option poses challenges for foundation design due to the nature of the spoil material, which is usually highly heterogeneous due to the way spoils are deposited, and can contain high proportions of high-plasticity cohesive soils (clay). This paper presents results obtained using an advanced constitutive model that was developed to simulate cohesive mine spoil behaviour and presents model results for the prediction of foundation response under both monotonic and cyclic loading. The model is a modified version of the original isotropic bounding surface plasticity model that additionally involves a damaged-based plastic modulus in order to realistically represent soil strength degradation induced by cyclic action. The model is used for the simulation of shallow foundations for onshore wind turbines on a cohesive clay with a heterogeneous (linearly increasing) undrained shear strength (random spatial variability is not considered). Two different loading scenarios of a shallow strip foundation are considered in the paper: a pure moment-vertical loading (M-V), and a moment-horizontal-vertical loading (M-H-V). The effect of the adopted spoil-foundation interface type is also considered: (1) a fully-bonded interface and (2) a tensionless interface. Results demonstrate that, though the vertical bearing capacity is only slightly affected by the interface properties, the moment capacity is shown to be strongly influenced by the predefined contact conditions. For the footing system under M-H-V loading, a dominant footing uplift mechanism is obtained for light structures and the opposite holds for heavily loaded structures, where significant settlement accumulation occurs during cyclic loading. Based on the analysis, the moment bearing capacity of the footing system decreases as the slenderness ratio and/or the vertical safety factor increase, and the opposite mechanism is obtained as the strength heterogeneity degree increases.

PL

Możliwości rewitalizacji zwałowisk są ważnym zagadnieniem przy planowaniu zagospodarowania terenów pogórniczych. Jedną z opcji jest instalacja na hałdach turbin wiatrowych, które stanowią zrównoważone źródło energii. Opcja ta stanowi wyzwanie dla projektowania fundamentów biorąc pod uwagę charakter materiału zwałowego, który ze względu na sposób deponowania jest zwykle wysoce niejednorodny i może zawierać dużo wysokoplastycznych gruntów spoistych (iłów). W artykule przedstawiono wyniki uzyskane przy użyciu zaawansowanego modelu konstytutywnego, który został opracowany w celu symulacji zachowania spoistego materiału zwałowego oraz zaprezentowano wyniki modelowania dla przewidywania reakcji fundamentu będącego zarówno pod obciążeniem monotonicznym jak i cyklicznym. Model jest zmodyfikowaną wersją oryginalnego izotropowego modelu plastyczności powierzchni granicznej, który dodatkowo zawiera moduł plastyczności oparty na zniszczeniu w celu realistycznego przedstawienia degradacji wytrzymałości gruntu wywołanej działaniem cyklicznym. Model jest wykorzystywany do symulacji płytkich fundamentów turbin wiatrowych na iłach spoistych o niejednorodnej (liniowo wzrastającej) wytrzymałości na ścinanie bez odpływu (nie uwzględniono losowej zmienności przestrzennej). W pracy rozpatrzono dwa różne scenariusze obciążenia płytkiej ławy fundamentowej: czyste obciążenia moment-pionowe (M-V) oraz obciążenia moment-poziome-pionowe (M-H-V). Rozważono również wpływ przyjętego rodzaju styku zwałowisko-fundament: (1) całkowicie związany oraz (2) beznaprężeniowy. Wyniki pokazują, że choć nośność pionowa tylko w niewielkim stopniu zależy od właściwości styku, to okazuje się, że nośność momentu jest silnie uzależniona od zdefiniowanych wcześniej warunków kontaktowych. Dla systemu stopy fundamentowej pod obciążeniem M-H-V, w przypadku lekkich konstrukcji uzyskuje się dominujący mechanizm unoszenia stopy, a w przypadku konstrukcji silnie obciążonych odwrotny, gdzie podczas cyklicznego obciążenia następuje znaczna akumulacja osiadań. Na podstawie przeprowadzonej analizy można stwierdzić, że nośność systemu stopy fundamentowej maleje wraz ze wzrostem współczynnika smukłości i/lub pionowego współczynnika bezpieczeństwa, a odwrotny mechanizm uzyskuje się wraz ze wzrostem stopnia niejednorodności wytrzymałości.

8

Influence of strain rate and temperature on the mechanical behaviour of additively manufactured AlSi10Mg alloy – experiment and the phenomenological constitutive modelling

Stanczak Magda, Rusinek Alexis, Broniszewska Paula, Fras Teresa, Pawłowski Piotr

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2022

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Vol. 70, nr 4

art. no. e141983

EN

The paper is related to the material behaviour of additively manufactured samples obtained by the direct metal laser sintering (DMLS) method from the AlSi10Mg powder. The specimens are subjected to a quasi-static and dynamic compressive loading in a wide range of strain rates and temperatures to investigate the influence of the manufacturing process conditions on the material mechanical properties. For completeness, an analysis of their deformed microstructure is also performed. The obtained results prove the complexity of the material behaviour; therefore, a phenomenological model based on the modified Johnson–Cook approach is proposed. The developed model describes the material behaviour with much better accuracy than the classical constitutive function. The resulted experimental testing and its modelling present the potential of the discussed material and the manufacturing technology.

9

Effects of early‑age temperature and salt ion corrosion on the macroproperty deterioration of concrete and corresponding micromechanism

Xue Weipei, Fan Hongjun, Liu Xiaoyuan, Shen Lei

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 2

art. no. e98, 1--16

EN

This paper experimentally examines variations in the macroscopic properties of concrete under the interaction of early-age temperature and salt ion corrosion and investigates the microscopic mechanism of these variations from the perspective of pore structure and microcracks. The results show a prominent initial defect compaction stage of the compressive stress-strain curves of the specimens under the interaction of two factors, an increase in the number of pores and a high degree of crack development. Accordingly, the peak strength, secant elastic modulus and porosity of the specimens are greatly affected by the interaction between early-age temperature and salt ion corrosion, as reflected by the obvious deterioration trend. Based on a theoretical analysis, the concept of the initial defect strain ratio is proposed, the relationship between the total deformation and two indicators (initial defect deformation and matrix deformation) is clarified, and a constitutive model that reflects the initial defect compaction characteristics is established.

10

Effect of loading characteristics and specimen size in split Hopkinson pressure bar test on high-rate behavior of phyllite

Mishra Sunita, Khetwal Anuradha, Chakraborty Tanusree, Basu Dipanjan

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 4

art. no. e212, 2022

EN

Split Hopkinson pressure bar (SHPB) tests are performed on Himalayan phyllite rock with five different specimen sizes and with different gas gun pressures and striker bar lengths of the SHPB device. The high-strain-rate phyllite parameters investigated are the peak stress, strain at peak stress, dynamic increase factor (DIF), strain energy absorbed, and dynamic modulus. It is observed that the dimensions of the phyllite specimens and the SHPB loading characteristics (i.e., the gas gun pressure and striker bar length) have a strong impact on the phyllite response. Given that SHPB specimen dimensions are small compared to any field rock mechanics problem, the rate-dependent rock mass properties are also determined for each rock using Hoek–Brown criteria. Numerical simluations of the SHPB tests are performed using finite element (FE) analysis in conjunction with the strain rate-dependent Johnson–Holmquist (JH-2) constitutive model to calibrate the JH-2 model parameters for phyllite. The calibrated JH-2 model parameters are dependent on the phyllite specimen size and on the magnitudes of the gas gun pressure and striker bar length. The different calibrated parameters corresponding to different specimen sizes and different SHPB loading characteristics are used to perform FE analysis of a tunnel constructed in phyllite rock and subjected to a blast load. The FE results show that the tunnel responses can significantly differ with strain rate-dependent JH-2 model parameters with difference in the mean stress and vertical displacement at the crown of the tunnel in the phyllite rock as high as 126% and 250%, respectively.

11

Constitutive modeling of rock materials considering the void compaction characteristics

Xie Shijie, Han Zhenyu, Chen Yifan, Wang Yixian, Zhao Yanling, Lin Hang

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 2

art. no. e60, 1--15

EN

The study of constitutive model is of great significance to engineering safety evaluation and geological disaster prevention. In this paper, rock materials were regarded as a composite geological material composed of voids and rock matrix, and then a piecewise constitutive model bounded by the yield point was proposed. It can reflect the complete stress–strain curves of rocks, including the compaction stage, the elastic stage, the plastic yield stage and the post-peak stage. Primarily, an objective method to determine the yield point based on the stress difference was proposed. For the rock deformation before yielding, the relationship between the strain of rock materials and the strains of voids and rock matrix was analyzed to establish the corresponding constitutive model. Subsequently, based on the modified Weibull distribution, a damage statistical constitutive model of rocks was established to describe the nonlinear deformation after the yield point. Meanwhile, the determining method of model parameters was given. Finally, the uniaxial and triaxial compression test data of different types of rocks were used to verify the proposed model. The results indicate that the model curves are in good agreement with the experimental results. Hence, it is feasible and reasonable to divide the macroscopic strain of rocks into the strains of voids and rock matrix. Additionally, there is a power function attenuation relationship between the deformation ratio of voids to rock matrix and the axial stress.

12

A Pressure-Dependent Plasticity Model for Polymer Bonded Explosives under Confined Conditions

Wei Qiang, Huang Xi-cheng, Chen Peng-wan, Liu Rui

Central European Journal of Energetic Materials

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2021

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Vol. 18, no. 3

339--368

EN

The safety of explosives is closely related to the stress state of the explosives. Under some stress stimulation, explosives may detonate abnormally. It is of great significance to accurately describe the mechanical response of explosives for the safety evaluation of explosives. The mechanical properties of polymer bonded explosives (PBXs) strongly depend on pressure. In this study, the mechanical behaviour of PBXs under confined conditions was investigated. It was found that the stress-plastic strain response of a PBX under high confining pressures is a combination of the non-linear and linear hardening portions. However, the linear hardening portion has often been neglected in characterizing the mechanical behaviour of a PBX under such pressures. The Karagozian and Case (K&C) model was applied to characterize the mechanical behaviour of PBXs. The numerical results demonstrated that when the confining pressure was high, the K&C model could not adequately match the experimental data due to the limitation of the damage model. Therefore, a new damage model was developed by means of considering intragranular damage and transgranular damage. This modification made it possible to introduce a linear hardening process into the original K&C model. The method proposed to describe the stress-strain results under high confining pressures was to consider the stress-plastic strain curve, including the nonlinear and linear hardening portions. The damage evolution of the original K&C model and a linear hardening model were applied for the nonlinear and linear hardening portions respectively. The influence of the linear hardening model on the damage evolution of the original K&C model was included when describing the nonlinear hardening portion. A comparison between simulation and experiment showed that the modified K&C model could well describe the mechanical response of PBXs under different confining pressures.

13

Złożone modele konstytutywne w analizach badawczych i obliczeniach inżynierskich. Podstawy analiz zadań kontaktowych

Fedorowicz Lidia, Fedorowicz Jan

Builder

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2021

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R.25, nr 8

22--26

PL

Aby stać się w pełni świadomym użytkownikiem współczesnych systemów obliczeniowych, nasza wiedza inżynierska powinna sięgać „korzeni”, tu w zakresie mechaniki gruntów oraz modeli konstytutywnych pozwalających coraz pełniej opisywać zachowanie gruntu. W artykule przedstawiono specyfikę dwóch grup modeli gruntowych stosowanych w analizach zagadnień kontaktowych budowla-podłoże gruntowe, pokazując równocześnie ich możliwości i ograniczenia przy ocenie bazowych zagadnień geotechniki. Zwrócono uwagę na warunki prawidłowej budowy modelu obliczeniowego podłoża. Pokazano zalety modelu stanu krytycznego MCC, ze zwróceniem uwagi na związek prawidłowej oceny stanu in situ podłoża z wynikami przeprowadzonej analizy.

EN

Basics of analysis of contact tasks. In order to become a fully conscious user of modern computing systems, our engineering knowledge should reach the "roots", here in the field of soil mechanics and constitutive models, allowing for a more and more complete description of soil behavior. The article presents the specificity of two groups of soil models used in the analysis of the contact tasks: building structure - subsoil; showing at the same time their possibilities and limitations in the assessment of the basic issues of geotechnics. The conditions for the correct construction of the computational model of the subsoil have been taken into account. The advantages of the MCC critical state model are shown, with attention being paid to the relationship between the correct in situ state assessment of the substrate and the results of the analysis.

14

Analizy bezpieczeństwa konstrukcji budowlanych ulegających degradacji na podłożach górniczych. Część 2. Obliczenia numeryczne

Fedorowicz Lidia, Fedorowicz Jan

Builder

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2021

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R.25, nr 8

16--21

PL

Wobec założeń upraszczających stosowanych w tradycyjnych metodach oceny bezpieczeństwa konstrukcji na podłożach ulegających deformacjom górniczym wielokrotnie podejmowano próby pełniejszego sformułowania rozważanego zagadnienia brzegowego. Uzyskany rozwój w tej dziedzinie jest wynikiem badań nad reologią zjawiska deformacji poeksploatacyjnych oraz prac dotyczących rozbudowy modeli opisujących zachowanie deformującego się podłoża gruntowego oraz współpracującej z nim budowli. W artykule przedstawiono współczesne tendencje rozwoju numerycznego modelowania zagadnień brzegowych budowla-podłoże górnicze z odniesieniem do doświadczeń własnych autorów oraz przeprowadzonych analiz obliczeniowych wykorzystujących w opisie zaawansowane związki konstytutywne. Pokazano, w jaki sposób jakość i dokładność analiz obliczeniowych związana jest z budową geometryczną modelu MES oraz sprzęgnięta z wymogami parametrycznymi stosowanych modeli konstytutywnych.

EN

In view of the simplifying assumptions used in traditional methods of assessing the safety of structures in mining areas, many attempts have been made to formulate the boundary problem under consideration. The development obtained in this field results from research on the rheology of the post-exploitation deformations and works on the models describing the behavior of the deforming subsoil and structures cooperating with it. The article presents contemporary trends in the development of numerical modeling of boundary issues: building-mining subsoil; with reference to the authors' own experiences and the computational analyzes carried out, using advanced constitutive relationships in the description. It shows how the quality and accuracy of computational analyzes is related to the geometric structure of the FEM model and coupled with the parametric requirements of the constitutive models used.

15

Constitutive modeling of softening mechanism and damage for Ti–6Al–4V alloy and its application in hot tensile simulation process

Yang Xiaoming, Wang Baoyu, Zhou Jing, Xiao Wenchao, Feng Pengni

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

479--491

EN

In this paper, a unified viscoplastic constitutive model for Ti–6Al–4V alloy coupling with damage and softening mechanisms was established to predict the flow behaviors and damage evolution in hot tensile process. To obtain the flow behaviors of Ti–6Al–4V alloy, the hot tensile tests were performed at temperatures between 750 °C and 850 °C and strain rates of 0.01–1 s−1. Then the evolution of microstructure was investigated by scanning electron microscope (SEM) under hot tensile conditions. Otherwise, the macro-fracture morphology of the tensile specimen was observed by SEM. The flow stress and microstructure evolution were predicted based on the set of constitutive model. The constitutive model was embed in ABAQUS by coding a user-defined material subroutine. The results show that the flow stress increases with the temperature decreasing and the strain rate increasing. By comparing the experimental and calculated results, the flow stress and damage evolution can be accurately predicted by the constitutive model. The fracture due to damage can be well predicted by the simulation model, indicating the good predictability of the constitutive model.

16

A crystal plasticity finite element-based approach to model the constitutive behavior of multi-phase steels

Liu Hongguang, Shin Yung C.

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

707--720

EN

Steels are the most commonly used multi-phase materials in the industry, and their mechanical behaviors depend on the microstructure, composition, and phase fractions. Generally, the material behaviors need to be measured by experiments like a tensile test or split Hopkinson bar test, which is very time-consuming and expensive. Once the heat treatment and phase fractions are changed, it needs to be tested again, and, to avoid this, a better method is required to obtain the material behavior quickly and easily. In this study, a novel multi-scale approach is described to predict the material behaviors of multi-phase steels based on the phase fractions. A crystal plasticity finite element method is used to obtain the material behavior of each phase at a micro-scale with elevated strain rates, which is validated with experimental data or theoretical models at static or quasi-static conditions. Then a homogenization procedure with the rule of mixture method, which is based on the phase fractions measured from the microstructure characterization, is used to get the macro-scale constitutive behavior, and it is then implemented into the commercial software Abaqus/Standard to simulate the process of tensile test and compared with the experimental data. Good agreements are obtained between simulation and experimental results.

17

Nonlinear shear constitutive model for peak shear-type joints based on improved Harris damage function

Xie Shijie, Lin Hang, Wang Yixian, Cao Rihong, Yong Rui, Du Shigui, Li Jiangteng

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

454--467

EN

The majority of jointed rock mass failures mainly occur along the joints in shear mode, which promotes a wide investigation on the proposal of a reasonable and reliable shear constitutive model of rock joints. In this paper, based on Improved Harris function and laboratory shear tests, a new constitutive model of saw-tooth joints was proposed. Firstly, a series of laboratory direct shear tests were carried out on saw-tooth joint specimens made of rock-like materials (cement mortar) to obtain the shear stress-displacement curves. Subsequently, the test results were divided into sliding failure type and peak shear type according to whether there is a significant stress drop between peak stress and residual stress. It is assumed that rock elements can be divided into undamaged parts and damaged parts during the shearing process. The stress-displacement relation of the undamaged part satisfies Hooke’s law, while the damaged part provides residual stress. Via the comparison with commonly used micro-element failure probability density functions, the Improved Harris distribution function was selected as the standard to characterize the strength of micro rock units. Finally, derived from the theory of damage statistical mechanics, a damage statistical constitutive model was proposed, which can reflect the deformation characteristics of rock joints. Compared with previous models and experimental data, the model proposed in this paper can represent the trend of peak shear curve variation with higher accuracy, the parameters are easy to be solved and have obvious physical significance, which verifies the advantages and applicability of this model.

18

Determination of Uniaxial Tensile Behavior of Hypodermis in Porcine Skin Based on Rule of Mixtures

Choi Junsuk, Kim Sanghoon, Rhim Sungsoo, Rhee Kyong-Yop

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 2

491--494

EN

In this study, we investigate the mechanical behavior of each skin layer, in terms of the nominal stress-strain curve by uniaxial tensile tests using specimens of porcine skin in two forms: dermis containing epidermis, and all three layers. All tests were performed under cyclic loading at the constant strain rate of 10-3 s-1 at ambient temperature. To measure the precise initial crosssectional areas of each layer, the thickness of each skin layer was quantified by counting the number of pixels on the photo-image using image-processing software. In the tensile test, force-strain curves of the total skin and dermis with epidermis were obtained. Subsequently, a rule of mixtures was applied to determine the nonlinear mechanical properties of the hypodermis layer. In conclusion, we could define the uniaxial tensile behavior of the hypodermis, and additionally predict the weight effect of the dermis and hypodermis layers in the tensile test.

19

Calibration of Visco-Hyperelastic Model for Tensile Behavior of Porcine Skin

Shin Heonseop, Han Doyeon, Kim Sanghoon, Rhim Sungsoo

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 3

819--822

EN

Uniaxial tensile tests were performed on porcine skin to investigate the tensile stress-strain constitutive characteristic at qua-sistatic deformations using uniaxial tensile tests. Experimental results were then used to determine the parameters of the various constitutive model types for rubber, including the Mooney-Rivlin, Yeoh, Ogden, and others. The Prony series viscoelastic model was also calibrated based on the stress relaxation test. To investigate the calibrated constitutive equations (visco-hyperelastic), the falling impact test was conducted. From the viewpoint of the maximum impact load, the error was approximately 15.87%. Overall, the Ogden model predicted the experimental measurements most reasonably. The calibrated constitutive model is expected to be of practical use in describing the mechanical properties of porcine skin.

20

Mechanical guidelines on the properties of human healthy arteries in the design and fabrication of vascular grafts: experimental tests and quasi-linear viscoelastic model

Faturechi Rahim, Hashemi Ata, Abolfathi Nabiollah, Solouk Atefeh

Acta of Bioengineering and Biomechanics

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2019

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Vol. 21, no. 3

13--21

EN

Knowledge of mechanical behavior of healthy human arteries as the guidelines to target properties of vascular grafts deserves special attention. There is a lack of mathematical model to characterize mechanical behavior of biomaterial while many mathematical models to reflect mechanics of human arteries have been proposed. The objective of this paper was set to measure mechanical properties of healthy human arteries including Common Carotid Artery (CCA), Abdominal Aorta Artery (AAA), Subclavian Artery (SA), Common Iliac Artery (CIA) and Right and Left Iliac Artery (RIA and LIA) and compare them to those of commercial ePTFE and Dacron®. Methods: Series of stress relaxation and strain to failure tests vere performed on all samples. The experimental data was utilized to develop quasi-linear viscoelastic (QLV) model of both natural and artificial arteries. Results: ePTFE is the stiffest sample, while the CCA is the most compliant one among all. RIA and CIA are more viscous than the other natural arteries, while AA and CCA are less viscous. The proposed model demonstrated an accurate fit to the experimental results, a proof of its ability to model both nonlinear elasticity and viscoelasticity of the human arteries and commercial ones. Conclusions: ePTFE and Dacron® are much stiffer than human arteries that may lead to the disruption of blood hemodynamic and may not be biomechanically feasible as a replacement.