Applicability of exponential stress-strain models for carbonate rocks

Palchik, Vyacheslav Techno-Press 2018 Geomechanics & engineering Vol.15 No.3

Stress-strain responses of weak-to-strong carbonate rocks used for tunnel construction were studied. The analysis of applicability of exponential stress-strain models based on Haldane's distribution function is presented. It is revealed that these exponential equations presented in transformed forms allow us to predict stress-strain relationships over the whole pre-failure strain range without mechanical testing of rock samples under compression using a press machine and to avoid measurements of axial failure strains for which relatively large values of compressive stress are required. In this study, only one point measurement (small strain at small stress) using indentation test and uniaxial compressive strength determined by a standard Schmidt hammer are considered as input parameters to predict stress-strain response from zero strain/zero stress up to failure. Observations show good predictive capabilities of transformed stress-stress models for weak-to-strong (${\sigma}_c$ <100 MPa) heterogeneous carbonate rocks exhibiting small (< 0.5 %), intermediate (< 1 %) and large (> 1 %) axial strains.

Numerical Evaluation of Compressive Strain Capacity for API X100 Line Pipe

Seung-Jung Lee,Woo-Yeon Cho,Ki-Seok Kim,Goangseup Zi,Young-Cheol Yoon 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.8

In the strain-based design, pipeline steels are required to satisfy not only the stress capacity but also the strain capacity. Thus,considerable efforts have been made to meet the various requirements of the pipe-material properties that might undergo largedeformation during the installation stage in various hostile environments. An adequate compressive strain capacity can helpeffectively avoid local buckling. Hence, highly deformable steel becomes crucial in achieving the required strain capacity. This studyproposes a nonlinear finite element procedure based on the commercial software ABAQUS combined with the User-definedMaterial Module (UMAT), which is created using Fortran language. The Gurson–Tvergaard–Needleman (GTN) model isimplemented in UMAT to fully consider the nonlinear behavior of an API X100 pipe subjected to compressive loading. Thenumerical simulation results of the full-scale bending test were compared with the experimental results to verify the nonlinear finiteelement procedure equipped with the GTN model. The simulation results are in good agreement with the experimental results. Theparametric studies reveal the effects of geometric imperfections and material properties on the compressive strain limit.

이축 압축 변형에 따른 철갈륨디텔루라이드의 자성 특성 변화

한진명(Jinmyeong Han),홍지상(Jisang Hong) 한국자기학회 2024 韓國磁氣學會誌 Vol.34 No.4

본 연구에서는 제일원리 계산과 와니어 함수 계산을 이용하여 단층 철갈륨디텔루라이드 (Fe3GaTe2) 박막의 이축 압축 변형에 따른 자성 특성 변화에 대해 연구하였다. 이축 압축 변형 하에서 강자성 성질이 유지되었으며 자성 상호작용 인자는 변형의 유무에 따라 감소, 자기 이방성 에너지는 변형의 유무에 따라 증가함을 확인할 수 있었다. 퀴리 온도는 순수한 단층 박막과 차이가 거의 없는 300 K을 유지하였다. 거기다 비정상 홀 효과는 변형에 따라 -14 S/cm ~ -342 S/cm 범위의 큰 폭으로 요동치며 화학 퍼텐셜 준위에 따른 변화가 순수한 단층 박막에 비해 억제되었다. 비정상 네른스트 효과는 순수한 단층 박막과 비교하여 크게 줄었다. 이는 이축 압축 변형에 따라 베리 곡률이 변화하면서 생긴 현상이다. In this study, we investigate the biaxial compressive strain-dependent magnetic properties of monolayer Fe₃GaTe₂ using first principle calculation and wannier function calculation. The Fe₃GaTe₂ retains its ferromagnetic ground state under biaxial compressive strain. The exchange coupling parameter diminishes under the existance of biaxial compressive strain, while the magnetic anisotropy energy enhances under the existance of compressive strain. As a result of them, the Curie temperature is unchanged under strain, about 300 K. The anomalous Hall conductivity fluctuates under strain, in range of -14 S/cm ~ -342 S/cm. Its variation with chemical potential level is suppressed compared to that in pristine system. Anomalous Nernst conductivity decreases significantly under strain. These phenomena may originate from the changes in the Berry curvature under biaxial compressive strain.

Mechanical behavior of crumb rubber concrete under axial compression

Ren, Rui,Liang, Jiong-Feng,Liu, Da-wei,Gao, Jin-he,Chen, Lin Techno-Press 2020 Advances in concrete construction Vol.9 No.3

This paper aims at investigating the effect of crumb rubber size and content on compressive behaviors of concrete under axial compression. Concrete specimens are designed and produced by replacing natural aggregate with crumb rubber content of 0%, 5%, 10%, 15% and three different sized crumb rubbers (No. 20, No. 40, No. 80 crumb rubber). And the failure mode, compressive strength, elastic modulus, stress-strain curves, peak strain and ultimate strain are experimentally studied. Based on the test results, formulas have been presented to determine the compressive strength, elastic modulus, the relationship between prism compressive strength and cube compressive strength, stress-strain curves and peak strain of crumb rubber concrete (CRC). It is found that the proposed formulas agree well with the test result on the whole, which may be used to practical applications.

Determination of the radial inertia-induced transition strain-rate in split Hopkinson pressure bar tests

Yubin Lu 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.11

The transition strain-rate represents the start of significant contributions from radial inertia-induced lateral confinement to the axial compressive strength of the tested materials. However, it has been misinterpreted for decades by many studies as the start of significant strain-rate effect on the dynamic uniaxial compressive strength of the tested materials. Based on the dimensional analysis and numerical and experimental data, a semi-empirical formula to determine the transition strain-rates for various engineering materials is proposed. Errors in SHPB tests due to the contribution of the lateral confinement effect are estimated. It is found that, except for metals, transition strain-rates of concrete-like, rock-like and polymeric materials are unfortunately located in the valid range of SHPB tests that has been commonly accepted by research communities. Thus SHPB tests cannot be treated as valid measurements under uniaxial stress state when strain-rates are greater than the transition strain-rate.

Tension-Compression Asymmetry of a Rolled Mg-Y-Nd Alloy

Bo Song,Hucheng Pan,Weijie Ren,Ning Guo,Zehong Wu,Renlong Xin 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.4

In this work, tension and compression deformation behaviors of rolled and aged Mg-Y-Nd alloys were investigated. The microstructure evolution and plastic deformation mechanism during tension and compression wereanalyzed by combined use of electron backscatter diffraction and a visco-plastic self-consistent crystal plasticitymodel. The results show that both rolled and aged Mg-Y-Nd sheets show an extremely low yield asymmetry. Elimination of yield asymmetry can be ascribed to the tilted basal texture and suppression of {10-12} twinning. The rolled sheet has almost no yield asymmetry, however exhibits a remarkable strain-hardening behavior asymmetry. Compressed sample shows lower initial strain hardening rate and keeps higher strain hardening rate at thelater stage compared with tension. The strain-hardening asymmetry can be aggravated by aging at 280 C. It is consideredthe limited amount of twins in compression plays the critical role in the strain hardening asymmetry. Finally, the relevant mechanism was analyzed and discussed.

변형률에 따른 모래-고무 혼합재의 거동 특성: 실험적 관찰

이창호,이종섭,변용훈 한국지반공학회 2011 한국지반공학회논문집 Vol.27 No.3

Mixtures of sand and rubber particles (Dsand/Drubber = 1) are investigated to explore their characteristics under different stain level. Mixtures are prepared with different volumetric sand fractions (sf = Vsand/Vtotal). Experimental data are gathered from a resonant column, an instrumented oedometer, and a direct shear tests. Results show that sand and rubber differently control the behavior of the whole mixture with strain level. Non-linear degradation of small strain stiffness is observed for the mixtures with sf≥0.4, while the mixtures with low sand fraction (sf≤0.2) show significantly high elastic threshold strain. Vertical stress-deformation increases dramatically when the rubber particle works as a member of force chain. The strength of the mixtures increases as the content of rubber particle decreases, and contractive behavior is observed in the mixtures with sf≤0.8. Rubber particle plays different roles with strain level in the mixture: it increases a coordination number and controls a plasticity of the mixture in small strain; it prevents a buckling of force chain in intermediate strain; it leads a contractive behavior in large strain.

Strain-dependent-deformation property of Gyeongju compacted bentonite buffer material for engineered barrier system

나베아 이반 제프,BALAGOSA JEBIE,윤석,추연욱 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.5

This study aims to investigate the strain-dependent-deformation property of Gyeongju bentonite buffer material. A series of unconfined compressive tests were performed with cylindrical specimens prepared at varying dry densities (ρd = 1.58 g/cm3 to 1.74 g/cm3) using cold isostatic pressing technique. It is found that as ρd increase, the unconfined compressive strength (qu), failure strain, and elastic modulus (E) of Gyeongju compacted bentonite (GCB) increases. Normalized elastic modulus (Esec/Emax) degradation curves of GCB specimens are fitted using Ramberg-Osgood model and the elastic threshold strain (εe,th) is determined through the fitted curves. The strain-dependency of E and Poisson’s ratio (v) of GCB were observed. E and v were measured constant below εe,th of 0.14 %. Then, E decreases while v increases after exceeding the strain threshold. The Esec/Emax degradation curves of GCB in this study suggests wider linear range and higher linearity than those of sedimentary clay in previous study. On top of that, the influence of ρd is observed on Esec/Emax degradation curves of GCB, showing a slight increase in εe,th with increase in ρd. Furthermore, an empirical model of qu with ρd and a correlation model between qu and E are proposed for Gyeongju bentonite buffer materials.

Failure Evolution Characteristics and Resistivity Damage Model of Expansive Clay with Filled Fissures under Uniaxial Compression

Zhiao Gao,Lingwei Kong,Zhenhua Zhou,Shuangjiao Wang 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.8

The fissure in expansive soil is an important factor to control the failure and stability of expansive soil foundation, slope, and underground engineering. This study utilizes the uniaxial compression–resistivity testing system to investigate the damage evolution of expansive clay with filled fissures by evaluating the stress–strain–resistivity curves of filled fissures with inclination angles of 0o, 15o, 30o, 45o, and 60o. Within the study context, the samples were continuously photographed and observed during the test, and the local strain was analyzed using digital image correlation technology. Moreover, a mechanical damage model of fissured expansive soil was proposed based on the resistivity testing data. Generally, the test results haveshown increasing the inclination angles of fissures decreases the strength linearly and changes the stress–strain behavior from hardening to softening. The failure modes of various fissure morphologies are classified into three main types: compressive fracture failure (0o), slip-fracture coupling failure (15o and 30o), and slip failure (45o and 60o). The development characteristics of local strains with different fissure inclination angles are significantly different. Moreover, the soil’s effective conductivity and strain have shown significance when developing damage models. This study provides a reference for understanding fissured soil’s failure process and applying comprehensive resistivity testing technology in fissured soil mechanics.

Effect of Temperature and Strain Rate on the Hot Deformation Behaviour of Ferritic Stainless Steel

Guoqing Zu,Yukuan Lu,Yi Yan,Xiaoming Zhang,Jingwei Zhao,Wei Du,Xu Ran,Zhengyi Jiang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.2

The fow behaviour and microstructure characteristics of a ferritic stainless steel were investigated using plain strain compression test on a Gleeble 3500 thermo-mechanical test simulator with a hydrawedge system in the temperature range of850–1100 °C and strain rate range of 0.1–50 s−1. The phenomenological constitutive model and the relationship betweenthe Zener–Hollomon (Z) parameter and fow stress were established. The results reveal that the fow softening phenomenonoccurs at high strain rate, which is caused by the coupling efect of the adiabatic heating and dynamic recrystallisation (DRX). New grains nucleate preferentially at the original grain boundaries by strain-induced grain boundary migration. With anincrease of temperature or strain rate, a part of new grains form in the interior of deformed grains. The DRX grain size andfraction increase with the increase of temperature, however, exhibit a non-linear relationship with strain rate.