• 제목/요약/키워드: Plasticity zone

검색결과 162건 처리시간 0.02초

금형강 STD61의 온도에 따른 기계적 성질의 변화 (Temperature-dependence of Mechanical Properties of Die Steel STD61)

  • 여은구;이용신
    • 소성∙가공
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    • 제13권5호
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    • pp.435-440
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    • 2004
  • The temperature in hot forming of metallic materials, such as hot extrusion and hot forging, ranges from $300^{\circ}C$ to $900^{\circ}C$. Correspondingly, the die also exhibits high temperatures close to that of a work piece and its life is limited generally by high temperature fatigue. Thus, the analysis of high temperature fatigue would need the mechanical properties over the wide ranges of temperature. However, very few studies on the high temperature fatigue of brittle materials have been reported. Especially, the study on the fatigue behavior over such transition temperature regime is very rare. In this paper, the stress-strain curves and stress-life curves of a die steel such as STD61 are experimentally obtained. The wide ranges of temperature from $300^{\circ}C$ to $900^{\circ}C$ are considered in experiments and the transition temperature zone is carefully examined.

The uniaxial strain test - a simple method for the characterization of porous materials

  • Fiedler, T.;Ochsner, A.;Gracio, J.
    • Structural Engineering and Mechanics
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    • 제22권1호
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    • pp.17-32
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    • 2006
  • The application of cellular materials in load-carrying and security-relevant structures requires the exact prediction of their mechanical behavior, which necessitates the development of robust simulation models and techniques based on appropriate experimental procedures. The determination of the yield surface requires experiments under multi-axial stress states because the yield behavior is sensitive to the hydrostatic stress and simple uniaxial tests aim only to determine one single point of the yield surface. Therefore, an experimental technique based on a uniaxial strain test for the description of the influence of the hydrostatic stress on the yield condition in the elastic-plastic transition zone at small strains is proposed and numerically investigated. Furthermore, this experimental technique enables the determination of a second elastic constant, e.g., Poisson's ratio.

A mesoscale model for concrete to simulate mechanical failure

  • Unger, Jorg F.;Eckardt, Stefan;Konke, Carsten
    • Computers and Concrete
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    • 제8권4호
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    • pp.401-423
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    • 2011
  • In this paper, a mesoscale model of concrete is presented, which considers particles, matrix material and the interfacial transition zone (ITZ) as separate constituents. Particles are represented as ellipsoides, generated according to a prescribed grading curve and placed randomly into the specimen. In this context, an efficient separation procedure is used. The nonlinear behavior is simulated with a cohesive interface model for the ITZ and a combined damage/plasticity model for the matrix material. The mesoscale model is used to simulate a compression and a tensile test. Furthermore, the influence of the particle distribution on the loaddisplacement curve is investigated.

Determining a novel softening function for modeling the fracture of concrete

  • Hossein, Karimpour;Moosa, Mazloom
    • Advances in materials Research
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    • 제11권4호
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    • pp.351-374
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    • 2022
  • Softening function is the primary input for modeling the fracture of concrete when the cohesive crack approach is used. In this paper, based on the laboratory data on notched beams, an inverse algorithm is proposed that can accurately find the softening curve of the concrete. This algorithm uses non-linear finite element analysis and the damage-plasticity model. It is based on the kinematics of the beam at the late stages of loading. The softening curve, obtained from the corresponding algorithm, has been compared to other softening curves in the literature. It was observed that in determining the behavior of concrete, the usage of the presented curve made accurate results in predicting the peak loads and the load-deflection curves of the beams with different concrete mixtures. In fact, the proposed algorithm leads to softening curves that can be used for modeling the tensile cracking of concrete precisely. Moreover, the advantage of this algorithm is the low number of iterations for converging to an appropriate answer.

A Closed-Form Solution for Circular Openings in an Elastic-Brittle-Plastic Extended Spatial Mobilized Plane Medium

  • Wu, Chuangzhou;Guo, Wei;Jang, Bo-An
    • 지질공학
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    • 제32권1호
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    • pp.1-12
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    • 2022
  • Based on the extended spatial mobilization plane (SMP) criterion, we present an elastic-brittle-plastic solution for an axisymmetric cylindrical tunnel. The influences of the intermediate principal compressive stress and material strain-softening behavior are considered. Closed-form formulas for the critical support force, radius of plastic zone, and distributions of stress and displacement in surrounding rock are proposed. The elastic-plastic solution based on SMP is compared with the Kastner solution to verify the credibility of the obtained elastic-plastic solution. The elastic-brittle-plastic solution following the SMP criterion and the current solution based on the Mohr-Coulomb criterion are also compared. The rock strain-softening rate and the intermediate principal stress affect the stability of the surrounding rock. The results provide guidance for optimizing the design of support systems for tunnels.

Helicobacter pylori Strain 51 (Korean Isolate): Ordered Overlapping BAC Library, Combined Physical and Genetic Map, and Comparative Analysis with H. pylori Strain 26695 and Strain J99

  • KANG HYUNG-LYUN;LEE WOO-KON;SONG JAE-YOUNG;CHOI SANG-HAENG;PARK SEONG-GYU;RYU BOK-DEOK;LEE EUN-JOO;KIM JI-SUN;PARK JEONG-UCK;BAIK SEUNG-CHUL;CHOI MYOUNG-BUM;YOUN HEE-SHANG;KO GYUNG-HYUCK
    • Journal of Microbiology and Biotechnology
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    • 제15권4호
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    • pp.844-854
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    • 2005
  • We constructed a defined physical and genetic map of H. pylori strain 51, previously isolated from a Korean patient with a duodenal ulcer, by combining a restriction analysis by pulse-field gel electrophoresis with the construction of a BAC library. A Notl-digest of H. pylori strain 51 genome yielded seven fragments, from which the genomic size was estimated to be 1,698$\pm$24 kb. The BAC library was constructed from 50 to 200 kb fragments of HindIII-digested genomic DNA. From 700 BAC clones, an ordered overlapping maxi-set of 82 BAC clones was assembled that covered the entire genome. The positions of 15 genes were localized in the strain 51 genome with 4-22 kb of resolution and were compared with their orthologues in strain 26695 and strain J99. The arrangement of the 15 genes was identical in strain 51 and strain J99, except for flaA and hpaA. The plasticity zone of strain 51, like that of strain J99, was located in the single region, and was shorter than those of strain 26695 and strain J99. The strain 51 plasticity zone consisted of ORFs common only to strain 51 and J99 or to strain 51 and 26695, as well as strain 51-specific ORFs. Three genetic translocations and/or inversions were found between orthologue ORFs in strain 51 and strain J99. These results show that the chromosomal organization of strain 51 differs from Western strains such as strain 26695 and strain J99.

초고강도 합금강의 이종마찰교반 접합부에서의 미세조직 특성 및 기계적 물성 연구 (Microstructural and Mechanical Analysis of a Friction Stir Welded Joint of Dissimilar Advanced High-Strength Steels)

  • 이지우;조훈휘;;;홍성태
    • 소성∙가공
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    • 제29권1호
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    • pp.11-19
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    • 2020
  • For microstructural analysis of a friction stir welded (FSWed) joint of advanced high-strength steels, dual phase (DP) and complex phase (CP) steels, are studied. FSWed joints are successfully fabricated in the following four cases: (i) DP/DP; (ii) CP/CP; (iii) DP/CP, where the advancing side is DP and the retreating side is CP; (iv) CP/DP, where the advancing side is CP and the retreating side is DP. The stir zone (SZ) of (i) the DP/DP joint mainly consists of lath martensite, while the stir zone of (ii) the CP/CP joint consists not only of lath martensite but also of bainite. In the case of (iii) DP/CP and (iv) CP/DP, they exhibit a similar microstructure including acicular-shaped phases in the joints; however, cross-sections of the joints show differences in material mixing in each case. In (iv) the CP/DP joint, temperature towards the CP steel is sufficient to cause softening, thus leading to better mixing than that in (iii) DP/CP. The phases of the SZ in each of the four cases are formed by phase transformation during the FSWed process; however, the transformed phase volume fraction of CP steel is lower than that of DP steel, indicating that dynamic recrystallization occurs mainly in CP steel. The hardness values of the SZ are significantly higher than those of the base materials, especially, the SZ of (iii) the DP/CP joint has the highest value due to highest fraction of lath martensite.

Cu/Al 및 Fe/Al 층상복합재료 압출공정에서 구성재료의 불균일 변형 (Inhomogeneous Deformation Between Construction Materials in the Cu/Al and Fe/Al Co-extrusion Processes)

  • 서정민;노정훈;민경호;황병복;함경춘;장동환
    • 소성∙가공
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    • 제16권7호
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    • pp.530-537
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    • 2007
  • This paper is concerned with the analysis of plastic deformation of bimetal co-extrusion process. Two sets of material combination have been adopted for analysis, i.e. combinations of Cu/Al and Fe/Al. In the first set of material combination, the selected materials are AA 1100 aluminum alloy as hard material and CDA 110 as soft one. This type of material selection is to examine the effect of hard core and soft sleeve and vice versa on the deformation pattern in terms of plastic zone and velocity discontinuity along the contact surface between construction materials. Four different cases of co-extrusion process in terms of material combination and interference bonding were simulated to investigate the effect of material arrangement between core and sleeve, and of bonding on the plastic zones and velocity discontinuity. In the other set of material combination, model materials used as core and sleeve were AA 1100 and AISI 1010, which are relatively soft and hard, respectively. Process parameters except diameter ratio of core to sleeve material such as semi-die angle, reduction in area in global sense and die comer radius have been set constant throughout the simulation to concentrate our effort on the analysis of influence of diameter ratio on deformation behavior such as deformation zone, surface expansion, exit velocity discontinuity between composite materials, and extrusion forces.

비파괴 계장화 압입시험을 이용한 저항 점용접부 물성 평가 (Evaluation of Mechanical Properties by Using Instrumented Indentation Testing for Resistance Spot Welds)

  • 최철영;김준기;홍재근;염종택;박영도
    • 한국분말재료학회지
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    • 제18권1호
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    • pp.64-72
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    • 2011
  • Nondestructive instrumented indentation test is the method to evaluate the mechanical properties by analyzing load - displacement curve when forming indentation on the surface of the specimen within hundreds of micro-indentation depth. Resistance spot welded samples are known to difficult to measure the local mechanical properties due to the combination of microstructural changes with heat input. Particularly, more difficulties arise to evaluate local mechanical properties of resistance spot welds because of having narrow HAZ, as well as dramatic changed in microstructure and hardness properties across the welds. In this study, evaluation of the local mechanical properties of resistance spot welds was carried out using the characterization of Instrumented Indentation testing. Resistance spot welding were performed for 590MPa DP (Dual Phase) steels and 780MPa TRIP (Transformation Induced Plasticity) steels following ISO 18278-2 condition. Mechanical properties of base metal using tensile test and Instrumented Indentation test showed similar results. Also it is possible to measure local mechanical properties of the center of fusion zone, edge of fusion zone, HAZ and base metal regions by using instrumented indentation test. Therefore, measurement of local mechanical properties using instrumented indentation test is efficient, reliable and relatively simple technique to evaluate the tensile strength, yield strength and hardening exponent.

Investigation lateral deformation and failure characteristics of strip coal pillar in deep mining

  • Chen, Shaojie;Qu, Xiao;Yin, Dawei;Liu, Xingquan;Ma, Hongfa;Wang, Huaiyuan
    • Geomechanics and Engineering
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    • 제14권5호
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    • pp.421-428
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    • 2018
  • In deep mining, the lateral deformation of strip coal pillar appears to be a new characteristic. In order to study the lateral deformation of coal-mass, a monitoring method and monitoring instrument were designed to investigate the lateral deformation of strip coal pillar in Tangkou Coalmine with the mining depth of over 1000 m. Because of without influence of repeated mining, the bedding sandstone roof is easy to break and the angle between maximum horizontal stress and the roadway is small, the maximum lateral deformation is only about 287 mm lower than the other pillars in the same coalmine. In deep mining, the energy accumulation and release cause a discontinuous damage in the heterogeneous coal-mass, and the lateral deformation of coal pillar shows discontinuity, step and mutation characters. These coal-masses not only show a higher plasticity but also the high brittleness at the same time, and its burst tendency is more obvious. According to the monitoring results and theoretical calculations, the yield zone of the coal pillar width is determined as 15.6 m. The monitoring results presented through this study are of great significance to the stability analysis and design of coal pillar.