• Title, Summary, Keyword: 초기변형률

Search Result 289, Processing Time 0.041 seconds

Prestrain-induced Reduction in Skin Tissue Puncture Force of Microneedle (초기변형률에 의한 미소바늘의 피부조직 관통력 감소)

  • Kim, Jonghun;Park, Sungmin;Nam, Gyungmok;Yoon, Sang-Hee
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.40 no.10
    • /
    • pp.851-856
    • /
    • 2016
  • Despite all the recent advances in biodegradable material-based microneedles, the bending and failure (especially buckling) of a biodegradable microneedle during skin tissue insertion remains a major technical hurdle for its large-scale commercialization. A reduction in skin tissue puncture force during microneedle insertion remains an essential issue in successfully developing a biodegradable microneedle. Here, we consider uniaxial and equibiaxial prestrains applied to a skin tissue as mechanophysical stimuli that can reduce the skin tissue puncture force, and investigate the effect of prestrain on the changes in skin tissue puncture force. For a porcine skin tissue similar to that of humans, the skin tissue puncture force of a flat-end microneedle is measured with a z-axis stage equipped with a load cell, which provides a force-time curve during microneedle insertion. The findings of this study lead to a quantitative characterization of the relationship between prestrain and the skin tissue puncture force.

Two Dimensional Elasto-plastic Stress Analysis by the B.E.M. (경계요소법에 의한 2차원 탄소성응력해석)

  • 조희찬;김희송
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.16 no.4
    • /
    • pp.621-629
    • /
    • 1992
  • This study is concerned with an application of the Boundary Element Method to 2-dimensional elastoplastic stress analysis on the material nonlinearities. The boundary integral formulation adopted an initial stress equation in the inelastic term. In order to determine the initial stress increment, the increment of initial elastic strain energy due to elastic increment in stressstrain curve was used as the convergence criterion during iterative process. For the validity of this procedure, the results of B.E.M. with constant elements and NISA with linear elements where compared on the thin plate with 2 edge v-notches under static tension and the thick cylinder under internal pressure. And this paper compared the results of using unmedical integral with the results of using semi-analytical integral on the plastic domain integral.

Study on the Estimation of Duncan & Chang Model Parameters-initial Tangent Modulus and Ultimate Deviator Stress for Compacted Weathered Soil (다짐 풍화토의 Duncan & Chang 모델 매개변수-초기접선계수와 극한축차응력 산정에 관한 연구)

  • Yoo, Kunsun
    • Journal of the Korean Geoenvironmental Society
    • /
    • v.19 no.12
    • /
    • pp.47-58
    • /
    • 2018
  • Duncan & Chang(1970) proposed the Duncan-Chang model that a linear relation of transformed stress-strain plots was reconstituted from a nonlinear relation of stress-strain curve of triaxial compression test using hyperbolic theory so as to estimate an initial tangent modulus and ultimate deviator stress for the soil specimen. Although the transformed stress-strain plots show a linear relationship theoretically, they actually show a nonlinearity at both low and high values of strain of the test. This phenomenon indicates that the stress-strain curve is not a complete form of a hyperbola. So, if linear regression analyses for the transformed stress-strain plot are performed over a full range of strain of a test, error in the estimation of their linear equations is unavoidable depending on ranges of strain with non-linearity. In order to reduce such an error, a modified regression analysis method is proposed in this study, in which linear regression analyses for transformed stress-strain plots are performed over the entire range of strain except the range the non-linearity is shown around starting and ending of the test, and then the initial tangent modulus and ultimate deviator stresses are calculated. Isotropically consolidated-drained triaxial compression tests were performed on compacted weathered soil with a modified Proctor density to obtain their model parameters. The modified regression analyses for transformed stress-strain plots were performed and analyzed results are compared with results estimated by 2 points method (Duncan et al., 1980). As a result of analyses, initial tangent moduli are about 4.0% higher and ultimate deviator stresses are about 2.9% lower than those values estimated by Duncan's 2 points method.

Prediction of the Stress-Strain Curve of Materials under Uniaxial Compression by Using LSTM Recurrent Neural Network (LSTM 순환 신경망을 이용한 재료의 단축하중 하에서의 응력-변형률 곡선 예측 연구)

  • Byun, Hoon;Song, Jae-Joon
    • Tunnel and Underground Space
    • /
    • v.28 no.3
    • /
    • pp.277-291
    • /
    • 2018
  • LSTM (Long Short-Term Memory) algorithm which is a kind of recurrent neural network was used to establish a model to predict the stress-strain curve of an material under uniaxial compression. The model was established from the stress-strain data from uniaxial compression tests of silica-gypsum specimens. After training the model, it can predict the behavior of the material up to the failure state by using an early stage of stress-strain curve whose stress is very low. Because the LSTM neural network predict a value by using the previous state of data and proceed forward step by step, a higher error was found at the prediction of higher stress state due to the accumulation of error. However, this model generally predict the stress-strain curve with high accuracy. The accuracy of both LSTM and tangential prediction models increased with increased length of input data, while a difference in performance between them decreased as the amount of input data increased. LSTM model showed relatively superior performance to the tangential prediction when only few input data was given, which enhanced the necessity for application of the model.

Analysis on Thermomechanical Response to Tensile Deformation of GaN Nanowires (GaN 나노와이어의 인장 변형에 의한 열기계적 거동 해석)

  • Jung, Kwangsub;Zhou, Min;Cho, Maenghyo
    • Journal of the Computational Structural Engineering Institute of Korea
    • /
    • v.25 no.4
    • /
    • pp.301-305
    • /
    • 2012
  • In this work the mechanical behaviors of GaN nanowires are analyzed during tension, compression, and unloading deformations. The thermal conductivity of the nanowires at each deformed state is evaluated using an equilibrium Green-Kubo approach. Under tensile loading, the [0001]-oriented nanowires with hexagonal cross-sections undergo a phase transformation from wurtzite to a tetragonal structure. The phase transformation is not observed under compressive loading. The thermal conductivity decreases on going from compressive strains to tensile strains. The strain dependence of the thermal conductivity results from the relaxation time of phonon. A reverse transformation from the tetragonal structure to the wurtzite structure is observed during unloading. The thermal conductivities in the intermediate states are lower than the conductivity in the wurtzite structure at same strain. Such differences in the thermal conductivity between different atomic structures are mainly due to changes in the group velocity of phonon.

Mathematical Expressions for Stress-Strain Curve of Metallic Material (금속재료 응력-변형률 곡선의 수학적 표현들)

  • Hyun, Hong-Chul;Lee, Jin-Haeng;Lee, Hyung-Yil
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.32 no.1
    • /
    • pp.21-28
    • /
    • 2008
  • Stress-strain curves based on Ramberg-Osgood and Hollomon relations are strongly dependent upon the regressed range of strain. This work investigates mathematical expressions of true stress-strain curves of metallic materials. We first observe the variation of yield strength, strain hardening exponent and stress-strain curve with regressed range of stain. Based on sectional regression and expression using one or two parameters, we propose an optimal strain range for which yield strength and nonlinear material behavior are quite appropriate.

Development of Stress-Strain Relationship Considering Strength and Age of Concrete (콘크리트의 강도와 재령을 고려한 응력-변형률 관계식의 개발)

  • 오태근;이성태;김진근
    • Journal of the Korea Concrete Institute
    • /
    • v.13 no.5
    • /
    • pp.447-456
    • /
    • 2001
  • Many investigators have tried to represent the nonlinear behavior of stress-strain relationship of concrete using mathematical curves. Most of empirical expressions for stress-strain relationship, however, have focused on old age concrete, and were not able to represent well the behavior of concrete at an early age. Where wide understanding on the behavior of concrete from early age to old age is very important in evaluating the durability and service life of concrete structures. In this paper, effect of 5 different strength levels and ages of from 12 hours to 28 days on compressive stress-strain relationship was observed experimentally and analytically. Tests were carried out on $\phi$100${\times}$200mm cylindrical specimens water-cured at 20${\pm}$3$^{\circ}C$. An analytical expression of stress-stain relationship with strength and age was developed using regression analyses on experimental results. For the verification of the proposed model, the model was compared with present and existing experimental data and some existing models. The analysis shows that the proposed model predicts well experimental data and describes well effect of strength and age on stress-strain relationship.

Cyclic Strength and Deformation Characteristics of Marine Cohesive Soil (해성 점성토의 동적 강도 및 변형 특성)

  • Kim, Yong-Seong;Seo, Min-Woo;Oh, Sang-Eun
    • Journal of The Korean Society of Agricultural Engineers
    • /
    • v.54 no.3
    • /
    • pp.159-168
    • /
    • 2012
  • 본 연구에서는 해성 점성토에 대하여 반복 삼축시험을 실시하고 응력-변형률 관계 및 유효응력경로 특성 분석을 통해 동적 변형 및 강도 특성을 조사하였다. 시험에 사용된 시료는 일본 도쿠시마현의 코마츠시마 항 인근에서 채취된 점성토이며, 반복 삼축시험으로 동적 비배수 삼축시험, 동적 비배수 삼축시험 후 동적 삼축변형시험, 다단계 동적 비배수 삼축시험, 동적 삼축 변형시험 등 4종류의 시험을 수행하고, 시험 주파수로서 0.1 및 0.01 Hz을 적용하였다. 본 연구 결과 0.01 Hz로 수행된 동적 삼축시험 결과는 0.1 Hz로 수행된 삼축시험 결과보다 평균유효응력의 감소량이 크며, 반복 하중은 해성 점성토의 구조적 약화를 초래하고 초기 거동시 발생하는 간극수압과 밀접하게 관련이 있는 것으로 나타났다. 또한 미소변형률 영역에서 등가 탄성계수는 시험 횟수가 증가함에 따라 점차 감소하며, 감쇠비는 점차 증가하는 것으로 보아 변형계수는 반복 하중으로 인한 전단변형률의 축척에 따른 변형률 의존 거동에 관련하는 것으로 판단된다.

Study on Strain Response Converted from Deformation in Tensile Test of Carbon Fiber Reinforced Polymers (CFRP) (탄소섬유보강폴리머의 인장시험시 변형으로부터 환산한 변형률 응답에 대한 연구)

  • Kim, Yun-Gon
    • Journal of the Korea institute for structural maintenance and inspection
    • /
    • v.23 no.4
    • /
    • pp.137-144
    • /
    • 2019
  • In coupon test of carbon fiber reinforced polymers (CFRP) as brittle materials, the converted strain derived from total deformation and effective length was introduced and its advantages were described. In general, measured value from strain gauge is used for determining the tensile properties of material, but it is not quite effective in CFRP because brittle material can not redistribute its stress and it only represents local behavior. For this reason, the converted strain response can be utilized effectively as a supplementary indicator, which evaluated the average value of tensile properties in brittle material and confirmed the strain measured by strain gauge. In addition, the converted strain clearly visualized 1) the effect of initial internal strain caused by fabrication errors and setup misalignment when applying gripping force and 2) post-response of partial rupture of CFRP caused by non-uniform strain distribution. non-uniform strain distribution.

Fatigue Life Analysis and Prediction of 316L Stainless Steel Under Low Cycle Fatigue Loading (저사이클 피로하중을 받는 316L 스테인리스강의 피로수명 분석 및 예측)

  • Oh, Hyeong;Myung, NohJun;Choi, Nak-Sam
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.40 no.12
    • /
    • pp.1027-1035
    • /
    • 2016
  • In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.