Energy Evolution of Rock under Different Stress Paths and Establishment of a Statistical Damage Model

Wenbo Liu,Shuguang Zhang,Boyi Sun 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.10

In consideration of the influence of energy dissipation on the rock compression process, the traditional elastic stress-strain relationship was improved by adding the energy release rate. The microintensity of the rock was assumed to satisfy the Weibull distribution. The improved stress-strain relationship was transformed into a triaxial stress-strain model in consideration of the loading damage combined with mesodamage mechanics. The characteristic points of the stress-strain curve and the experimental data were utilized to calculate the distribution parameters of the rock under different conditions. The model curve was compared with the experimental data. Results showed that the stress-strain curve of the rock has peak points in the conventional triaxial compression test, but the radial peak of the rock was not evident in the unloading test. The energy of the rock under the loading path was smaller than that under the unloading path. The model curve exhibited a high degree of fitting with the experimental data, and its correlation coefficient was relatively large (> 0.90), which indicated that the model can clearly represent the actual damage and evolution law of the surrounding rock. Furthermore, the established model can also reflect the rock’s stress-strain relationship, which can serve as a practical guide for relevant applications. Finally, the distribution parameters also reflected the evolution law of rock energy and provided a method for the assessment of rock energy and damage trend.

Effect of Residual Stress on Femoral Arterial Stress-Strain Behavior

Chandran, K.B.,Mun, J.H.,Chen, J.S.,Nagaraj, A.,McPherson, D.D. The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.7

It is well established that arteries are subjected to residual stress. Due to the effect of residual stress, the arteries open to a horse-shoe shape when a longitudinal cut is made on an excised arterial segment. Previously, the residual stress has been quantified by the opening angle of the horse-shoe shape. We have employed a finite element analysis of the open arterial segment to restore the same to the original cylindrical shape and computed the circumferential strain as well as the stress distribution in the wall. In this study, the stress distribution in the femoral arteries of miniswine was computed with and without the residual stress for a range of transmural pressures. Our analysis showed that the residual stress has the effect of redistribution of the circumferential stresses between the intima and the adventitia under physiological loading. The redistribution of the stress with the inclusion of residual stress may be important in the studies on effect of wall stresses on the endothelial and vascular smooth muscle cells.

지대치 연결고정에 따른 편측성 후방연장 국소의치에서의 응력분포

안희영,진태호,Ahn Hee-Young,Jin Tai-Ho 대한치과보철학회 2004 대한치과보철학회지 Vol.42 No.2

Statement of problem: In distal extension removable partial denture, the preservation of health of abutment teeth are very important, but they are always subjected to unfavorable stress. Purpose: The purpose of this study was performed to investigate the effects of abutment splinting and design of direct retainer on the stress distribution of abutments in unilateral distal extension removable partial dentures. Material and method: Abutments were splinted by different method. In group 1, autment teeth were not splinted, in group 2, canine and 1st premolar were splinted, and in group 3, canine, 1st and 2nd premolars were all splinted. Three different types of direct retainer such as Akers clasp, RPI clasp, and wrought wire clasp were designed. Strain was measured with Switch & Balance Unit(SB-10, Measurement Group Instruments Division, Raleigh USA) and Strain Indicator(P-3500, Measurement Group Instruments Division, Raleigh, USA) 15kg of vertical and oblique loads was applied at central fossa of missing 2nd molar area. Results : The strain on lingual side of 2nd premolar was the greatest, and abutment splinting induced decrease of strain on buccolingual side of 2nd premolar. The strain of loaded area was decreased by abutment splinting and there was no statistical difference of strain between Group2 and Group 3, and strain on 2nd premolar in wrought wire clasp was the least. Conclusion: Within the limitations of this study, splinting of two distal abutment teeth is enough for stress distribution widely, and wrought wire clasp was more benefitable than others.

Effect of Local Strain Distribution of Cold-Rolled Alloy 690 on Primary Water Stress Corrosion Crack Growth Behavior

Kim, S.-W.,Ahn, T.-Y.,Lim, Y.-S.,Hwang, S.-S. PAS 2017 ARCHIVES OF METALLURGY Vol.62 No.2

<P>This work aims to study the stress corrosion crack growth behavior of cold-rolled Alloy 690 in the primary water of a pressurized water reactor. Compared with Alloy 600, which shows typical intergranular cracking along high angle grain boundaries, the cold-rolled Alloy 690, with its heterogeneous microstructure, revealed an abnormal crack growth behavior in mixed mode, that is, in transgranular cracking near a banded region, and in intergranular cracking in a matrix region. From local strain distribution analysis based on local mis-orientation, measured along the crack path using the electron back scattered diffraction method, it was suggested that the abnormal behavior was attributable to a heterogeneity of local strain distribution. In the cold-rolled Alloy 690, the stress corrosion crack grew through a highly strained area formed by a prior cold-rolling process in a direction perpendicular to the maximum principal stress applied during a subsequent stress corrosion cracking test.</P>

Atomistic Computation of Local Stress and Strain Distribution around an InAs Quantum Dot between a GaAs Capping Layer and a Substrate

( Eun Cheol Do ),( Byeong Joo Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 ELECTRONIC MATERIALS LETTERS Vol.4 No.3

The utilization of self-assembling phenomena is important in nano material processes. For the fabrication of well-aligned multilayered nanodots or nanowires, it is necessary to know the atomistic strain/stress distribution in the capping Layer. In the present study, an atomistic computational approach based on an modified embedded-atom method (MEAM) interatomic potential is used to investigate the atomistic strain/stress distribution in a GaAs capping layer over an InAs quantum dot (QD) on a GaAs substrate. The atomic scale Local strain/stress around the QD can be well predicted by atomistic simulation and the approach can be used to determine the optimum interlayer distances for well-aligned multilayered QDs.

Atomistic Computation of Local Stress and Strain Distribution around an InAs Quantum Dot between a GaAs Capping Layer and a Substrate

도은철,이병주 대한금속·재료학회 2008 ELECTRONIC MATERIALS LETTERS Vol.4 No.3

The utilization of self-assembling phenomena is important in nano material processes. For the fabrication of well-aligned multilayered nanodots or nanowires, it is necessary to know the atomistic strain/stress distribution in the capping layer. In the present study, an atomistic computational approach based on an modified embedded-atom method (MEAM) interatomic potential is used to investigate the atomistic strain/stress distribution in a GaAs capping layer over an InAs quantum dot (QD) on a GaAs substrate. The atomic scale local strain/stress around the QD can be well predicted by atomistic simulation and the approach can be used to determine the optimum interlayer distances for well-aligned multilayered QDs

Double Cantilever Beam 방법을 이용한 다결정 알루미나의 Bridging 응력효과 해석 III. 다결정 알루미나의 Bridging 응력분포

손기선,이성학,백성기 한국세라믹학회 1996 한국세라믹학회지 Vol.33 No.5

The purpose of the present study is to investigate the microstructural effect on the R-curve behavior in three aluminas with different grain size distributions by analyzing the bridging stress distribution. The crack opening displacement (COD) according to the distance behind the stationary crack tip was measured using an in situ SEM fracture method. The measured COD values in the fine-grained alumina agreed well with Wiederhorn's sollution while they deviated from Wiederhorn's solution in the two coarse-grained aluminas because of the increase of the crack closure due to the grain interface bridging in the crack wake. A numerical fitting procedure was conducted by the introduction of the power-law relation and the current theoretical model together with the measured COD's in order to obtain the bridging stress distribution. The results indicated that the bridging stress function and the R-curve computed by the current model were consistent with those computed by the power-law relation providing a reliable evidence for the bridging stress analysis of the current model. The strain-softening exponent in the power-law relation n, was calculated to be in the range from 2 to 3 and was closely related to the grain size distribution. Thus it was concluded from the current theoretical model that the grain size distribution affected greatly the bridging stress distribution thereby resulting in the quantitative analysis of microfracture of polycrystalline aluminas through correlating the local-fracture-cont-rolling microstructure.

Al-10%Si-2%Cu-1%Mg-0.5%Mn 합금 주괴의 고온변형

張畯然,文仁淇 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.8

Hot compression test was performed on Al-10%Si-2%Cu-1%Mg-0.5%Mn ingot in the temperature range 440∼500℃ and in the strain rate range 0.1∼10/sec in order to understand the hot deformation features and to explore the possibility of uniform distribution of eutectic Si particles. A typical stress-strain curve was well established where the stress increases sharply in the beginning of the deformation, and then decreases gradually in the strain rate of 0.5∼10/sec. Apparent activation energy of 65 ㎉/㏖ and stress exponent of 8.4 were evaluated from the peak stress. Deformation at low strain rate and high temperature is favorable in view of low flow stress and relatively uniform distribution of Si particles. Hard Si eutectics between primary Al grains begin to deform after soft Al grains are easily elongated in an early stage of the deformation. This type of deformation mode strongly demands at least 0.7 true strain to break the net-work structure of eutectic Si effectively. It is suggested that suitable heat treatment prior to the hot deformation be employed to ensure uniform distribution of fine Si particles.

초고강도 콘크리트에 적합한 응력-변형율 모델과 응력분포 모델의 제안

장일영,박훈규 한국콘크리트학회 1997 콘크리트학회지 Vol.9 No.5

본 연구에서는 기존의 초고강도 콘크리트에 대한 실험자료를 근거로 합리적인 통계적 기법을 이용하여 초고강도 콘크리트의 설계 실용화를 위한 응력-변형율 관계 모델과 응력분포 모델을 제안하는 것이 목적이다. 이를 위하여 첫째, 콘크리트의 응력-변형율 특성을 결정하는 재료 변수들(탄성계수, 최대 압축강도시 변형율 등)에 대한 검토를 수행하였다. 둘째, 이를 바탕으로 일반성과 정확성을 동시에 갖춘 초고강도 콘크리트(700~1400kg/$\textrm{cm}^2$)에 적합한 응력-변형율 모델을 제안, 비교, 고찰하엿다. 셋째, 제안된 응력-형율 모델로부터 초고강도 콘크리트 구조의 극한강도를 평가하기에 적합한 응력분포모델을 제안, 일반성과 정확성을 비교 검증하였다.

Flowability and mechanical characteristics of self-consolidating steel fiber reinforced ultra-high performance concrete

Jiho Moon,Kwang Soo Youm,Jong-Sub Lee,윤태섭 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.43 No.3

This study investigated the flowability and mechanical properties of cost-effective steel fiber reinforced ultra-high performance concrete (UHPC) by using locally available materials for field-cast application. To examine the effect of mixture constituents, five mixtures with different fractions of silica fume, silica powder, ground granulated blast furnace slag (GGBS), silica sand, and crushed natural sand were proportionally prepared. Comprehensive experiments for different mixture designs were conducted to evaluate the fresh- and hardened-state properties of self-consolidating UHPC. The results showed that the proposed UHPC had similar mechanical properties compared with conventional UHPC while the flow retention over time was enhanced so that the field-cast application seemed appropriately cost-effective. The self-consolidating UHPC with high flowability and low viscosity takes less total mixing time than conventional UHPC up to 6.7 times. The X-ray computed tomographic imaging was performed to investigate the steel fiber distribution inside the UHPC by visualizing the spatial distribution of steel fibers well. Finally, the tensile stress-strain curve for the proposed UHPC was proposed for the implementation to the structural analysis and design.