• 제목/요약/키워드: strain hardening

검색결과 846건 처리시간 0.034초

Sabkha층 탄산질 모래의 침하특성 및 상부기초의 거동 (Settlement Characteristics of a Large-Scale Foundation over a Sabkha Layer Consisting of Carbonate Sand)

  • 김석주;한희수
    • 지질공학
    • /
    • 제23권3호
    • /
    • pp.247-256
    • /
    • 2013
  • 중동지역의 Sabkha층 탄산질 모래는 낮은 전단강도를 나타내며, 입자파쇄시 내부공극의 외부노출로 인한 즉시침하와 파쇄입자의 재배열로 인한 시간 의존적 이차침하가 발생된다. 현장 대형기초에 의한 Sabkha층의 침하특성을 분석하기 위하여 Hydrotest를 수행하였고, 실내시험 결과와 비교하였다. 삼축압축시험 결과 일차입자파쇄의 정도에 따라 Sabkha층 GL-1.5 m에서 Strain-hardening, GL-7.0 m에서 Strain-perfect, GL-7.5 m에서 Strain-softening 형태의 응력-변형 거동이 나타났다. 일반적으로 전반전단파괴는 입자가 조밀하고 지반의 강도가 큰 경우 발생하나 Sabkha층 탄산질 모래에서는 Strain-softening 거동 발생시 Strain-hardening과 Strain-perfect 거동에 비하여 오히려 입자파쇄 강도가 작아지는 현상이 발생하였다. 이러한 응력-변형 특성은 상대밀도 증가시 전단강도가 증가하는 석영질 모래의 특성과는 상이한 것이다. 현장 Hydrotest시 입자파쇄의 영향으로 간극수압 소산 후에도 지속적인 이차압축침하가 발생되었으며, 입자파쇄응력이 상대적으로 작고 Strain-softening 거동, 혹은 Strain-perfect 거동을 나타낸 하부 Sabkha층의 입자파쇄가 기초침하에 지배적인 영향을 미친 것으로 판단된다.

압연강판의 이방성에 관한 연구 (Study of anisoptopy of sheet metals)

  • 인정제
    • 한국소성가공학회:학술대회논문집
    • /
    • 한국소성가공학회 1999년도 춘계학술대회논문집
    • /
    • pp.153.1-156
    • /
    • 1999
  • Based upon the experimental data from multi-stage tensile loading at angles to the rolling direction of steel sheets, anisotropic hardening rules are proposed. Experiments show that orthotropic anisotropy is maintained and the orientations of orthotropy axes are changed during tensile loading. A phenomenological model is proposed which includes the rotations of orthotropy axes, work hardening and kinematic hardening. Using the model, uniaxial tensile stress, R-value and tensile necking strain are predicted and compared with the experimental data.

  • PDF

금속계 플럭스들이 용접이음부의 피로강도 특성에 관한 연구 (A Study on Fatigue Strength Characteristics of Weld Joint using Metal Type Flux Cored Wire)

  • 강성원;신동진;김환식
    • Journal of Welding and Joining
    • /
    • 제12권4호
    • /
    • pp.151-161
    • /
    • 1994
  • FCAW has wide application in ship fabrication, maintenance and field erection. It has many advantages over SMAW.SAW and GMAW process. In many applications, the FCAW provides highquality weld metal. This method can reduce weld defects especially porosity and spatter. But the fatigue characteristics of those deposited metal have been rarely investigated. The purpose of this study is to investigate the cyclic stress-strain behavior and fatigue tests by the constant strain control were carried out on the rounded smooth specimen with deposited metal using the metal type flux cored wire. As the results of this study for the deposited metal welded by the metal type flux cored wire, the hardening or softening characteristics under cyclic load were investigated and cyclic stress-strain curve, strain-fatigue life curve, stress-strain function and fatigue life relation which are useful to estimate the fatigue life under the stress concentration condition were obtained.

  • PDF

리올러지 모델을 이용한 열적 기계적 변형 거동 모사 (A Description of Thermomechanical Behavior Using a Rheological Model)

  • 이금오;홍성구;이순복
    • 대한기계학회논문집A
    • /
    • 제30권7호
    • /
    • pp.757-764
    • /
    • 2006
  • Isothermal cyclic stress-strain deformation and thermomechanical deformation (TMD) of 429EM stainless steel were analyzed using a rheological model employing a bi-linear model. The proposed model was composed of three parameters: elastic modulus, yield stress and tangent modulus. Monotonic stress-strain curves at various temperatures were used to construct the model. The yield stress in the model was nearly same as 0.2% offset yield stress. Hardening relation factor, m, was proposed to relate cyclic hardening to kinematic hardening. Isothermal cyclic stress-strain deformation could be described well by the proposed model. The model was extended to describe TMD. The results revealed that the hi-linear thermomechanical model overestimates the experimental data under both in-phase and out-of-phase conditions in the temperature range of $350-500^{\circ}C$ and it was due to the enhanced dynamic recovery effect.

인장-압축하중 하의 파괴저항곡선의 감소현상 해석 (Analyses of the Decrease Phenomenon of Fracture Resistance Curve Under Tension-Compression Loading)

  • 윤병곤;석창성
    • 대한기계학회논문집A
    • /
    • 제24권2호
    • /
    • pp.378-385
    • /
    • 2000
  • Fracture resistance (J-R) curves, which are used for elastic-plastic fracture mechanics analyses, decreased under tension-compression loading condition. This phenomenon was proved by several former researches, but the causes have not been clear yet. The objective of this paper is to investigate the cause of this phenomenon. On the basis of fracture resistance curve test results, strain hardening hypothesis, stress redistribution hypothesis and crack opening hypothesis were built. In this study, hardness tests, Automated Ball Indentation(ABI) tests, theoretical stress field analyses, and crack opening analyses were performed to prove the hypotheses. From this study, strain-hardening of material, generation of tensile residual stress at crack tip, and crack opening effects are proved as the causes of the decrease hypothesis.

나노 인덴테이션의 하중-변위 곡선을 이용한 표면처리강판 코팅층의 기계적 특성 결정 (Determination of the mechanical properties of the coated layer in the sheet metal using load-displacement curve by nanoindentation technique)

  • 고영호;이정민;김병민
    • 한국소성가공학회:학술대회논문집
    • /
    • 한국소성가공학회 2004년도 춘계학술대회 논문집
    • /
    • pp.148-151
    • /
    • 2004
  • Mechanical properties such as Young's modulus and hardness of thin film in coated steel are difficult to determine by nano-indentation from the conventional analysis using the load-displacement curve. Therefore, an analysis of the nano-indentation loading curve was used to determine the Young's modulus, hardness and strain hardening exponent. A new method is recently being developed for plasticity properties of materials from nano-indentation. Elastic modulus of the thin films shows relatively small influence whereas yield strength and strain hardening are found to have significant effect on measured data. The load-displacement behavior of material tested with a Berkovich indenter and nano-indentation continuous stiffness method is used to measure the modulus and hardness through thin films.

  • PDF

On modeling coupling beams incorporating strain-hardening cement-based composites

  • Hung, Chung-Chan;Su, Yen-Fang
    • Computers and Concrete
    • /
    • 제12권4호
    • /
    • pp.565-583
    • /
    • 2013
  • Existing numerical models for strain-hardening cement-based composites (SHCC) are short of providing sufficiently accurate solutions to the failure patterns of coupling beams of different designs. The objective of this study is to develop an effective model that is capable of simulating the nonlinear behavior of SHCC coupling beams subjected to cyclic loading. The beam model proposed in this study is a macro-scale plane stress model. The effects of cracks on the macro-scale behavior of SHCC coupling beams are smeared in an anisotropic model. In particular, the influence of the defined crack orientations on the simulation accuracy is explored. Extensive experimental data from coupling beams with different failure patterns are employed to evaluate the validity of the proposed SHCC coupling beam models. The results show that the use of the suggested shear stiffness retention factor for damaged SHCC coupling beams is able to effectively enhance the simulation accuracy, especially for shear-critical SHCC coupling beams. In addition, the definition of crack orientation for damaged coupling beams is found to be a critical factor influencing the simulation accuracy.

Rheological Behavior of Polymer/Layered Silicate Nanocomposites under Uniaxial Extensional Flow

  • Park Jun-Uk;Kim Jeong-Lim;Kim Do-Hoon;Ahn Kyung-Hyun;Lee Seung-Jong;Cho Kwang-Soo
    • Macromolecular Research
    • /
    • 제14권3호
    • /
    • pp.318-323
    • /
    • 2006
  • We investigated the rheological behaviors and orientation of three different types of layered silicate composite systems under external flow: microcomposite, intercalated and exfoliated nanocomposites. Rheological measurements under shear and uniaxial extensional flows, two-dimensional, small-angle X-ray scattering and transmission electron microscopy were conducted to investigate the properties, as well as nano- and micro-structural changes, of polymer/layered silicate nanocomposites. The preferred orientation of the silicate layers to the flow direction was observed under uniaxial extensional flow for both intercalated and exfoliated systems, while the strain hardening behavior was observed only in the exfoliated systems. The degree of compatibility between the polymer matrix and clay determined the microstructure of polymer/clay composites, strain hardening behavior and spatial orientation of the clays under extensional flow.

Size-dependent plastic buckling behavior of micro-beam structures by using conventional mechanism-based strain gradient plasticity

  • Darvishvand, Amer;Zajkani, Asghar
    • Structural Engineering and Mechanics
    • /
    • 제71권3호
    • /
    • pp.223-232
    • /
    • 2019
  • Since the actuators with small- scale structures may be exposed to external reciprocal actions lead to create undesirable loads causing instability, the buckling behaviors of them are interested to make reliable or accurate actions. Therefore, the purpose of this paper is to analyze plastic buckling behavior of the micro beam structures by adopting a Conventional Mechanism-based Strain Gradient plasticity (CMSG) theory. The effect of length scale on critical force is considered for three types of boundary conditions, i.e. the simply supported, cantilever and clamped - simply supported micro beams. For each case, the stability equations of the buckling are calculated to obtain related critical forces. The constitutive equation involves work hardening phenomenon through defining an index of multiple plastic hardening exponent. In addition, the Euler-Bernoulli hypothesis is used for kinematic of deflection. Corresponding to each length scale and index of the plastic work hardening, the critical forces are determined to compare them together.

CF8M 스테인리스 강 저주기 환경피로 실험의 주기적 변형률 경화 특성 (Characteristics of the Cyclic Hardening in Low Cycle Environmental Fatigue Test of CF8M Stainless Steel)

  • 정일석;하각현;김태룡;전현익;김영신
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2007년도 춘계학술대회A
    • /
    • pp.17-22
    • /
    • 2007
  • Low-cycle environmental fatigue tests of cast austenitic stainless steel CF8M at the condition of fatigue strain rate 0.04%/sec were conducted at the pressure and temperature, 15MPa, $315^{\circ}C$ of a operating pressurized water reactor. The used test rig was limited to install an extensometer at the gauge length of the cylindrical fatigue specimen inside the small autoclave. So the magnet type LVDT's were used to measure the fatigue displacement at the specimen shoulders inside the high temperature and high pressure water autoclave. However, the displacement and strain measured at the specimen shoulders is different from the one at the gauge length for the geometry and the cyclic strain hardening effect. FEM calculated the displacement and the strain of the gauge length from the data measured at the shoulders. Tensile test properties in elastic and plastic behavior of CF8M material were used in the FEM analysis. A series of low cycle fatigue tests simulating the cyclic strain hardening effect verified that the FEM calculation was well agreed with the simulated tests. The process and method developed in this study would be so useful to produce reliable environmental fatigue curves of CF8M stainless steel in pressurized water reactors.

  • PDF