Hydraulic and Mechanical Coupling Analysis of Rough Fracture Network under Normal Stress and Shear Stress

Tianjiao Yang,Shuhong Wang,Pengyu Wang,Ze Zhang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.2

The hydraulic and mechanical coupling characteristics of fracture networks under normal stress and shear stress were studied in this paper. The hydraulic and mechanical coupling model of the fracture network comprehensively considers the normal stress, shear stress, seepage pressure and roughness characteristics. Based on the boundary conditions and reasonable assumptions, COMSOL Multiphysics software was used to develop the hydraulic and mechanical coupling finite element model of the fracture network with different intersection points under normal stress and shear stress, focusing on the study of the effect of normal stress and shear stress on the fracture permeability. The degree of permeability change caused by the normal stress and shear stress is different. The shear stress has a significant influence on the fracture permeability, and when the normal stress is low, the relationship between the fracture permeability and shear stress can be described by a linear relationship. Then, the influence of the number of intersection points in the fracture network on the average fracture width, average water pressure, average seepage velocity and seepage passage of the fractured rock mass was analyzed. The number of intersections in the fracture network has little influence on the average fracture gap width and average water pressure but has a great influence on the flow velocity. The analysis in this paper is very helpful to understand the seepage characteristics in rough fractures under normal stress and shear stress.

Correlation of the maximum shear stress with micro-mechanisms of ductile fracture for metals with high strength-to-weight ratio

Lou, Yanshan,Yoon, Jeong Whan,Huh, Hoon,Chao, Qi,Song, Jung-Han Elsevier 2018 International journal of mechanical sciences Vol.146 No.-

<P><B>Abstract</B></P> <P>Mechanisms of ductile fracture are investigated experimentally in a wide range of loading conditions from compressive upsetting to the balanced biaxial tension for two metals with high strength-to-density ratio of DP980 (t1.2) steel sheets and a bulk aluminum alloy of AA7075. Specimens are carefully designed to achieve various loading conditions from shear at low stress triaxiality to the balanced biaxial tension at high stress triaxiality for DP980, while both tensile and compressive tests are conducted for AA7075. Fractured specimen surfaces are analyzed macroscopically focusing on their relations with the maximum shear stress. It is observed that all the specimens tend to fail along the direction of the maximum shear stress in various loading states of plane strain compression, uniaxial compression, shear, uniaxial tension, plane strain tension and the balanced biaxial tension. Scanning electron microscope analyses of fracture surfaces are also conducted to explore the underlying mechanism of void coalescence since coalescence of voids is viewed as the last step of ductile fracture after nucleation and growth of voids. It is noted that fractured voids elongate along the direction of the maximum shear stress for all specimens with the stress triaxiality ranging from about −0.57 in compression to 0.67 in the balanced biaxial tension. The experiments of DP980 and AA7075 reveal that ductile fracture takes place along the direction of the maximum shear stress in the wide loading conditions of compressive upsetting, shear, uniaxial tension, plane strain tension and the balanced biaxial tension with stress triaxiality below 0.67. Thus, ductile fracture is expected to be governed by the maximum shear stress in these wide loading conditions of compression, shear and tension. It is suggested that effect of the maximum shear stress must be correctly coupled in modeling of ductile fracture in these loading conditions with uncoupled and coupled ductile fracture criteria.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mechanisms of ductile fracture is investigated experimentally in the wide range of loading conditions from compressive upsetting to the tension of notched specimens for two lightweight metals of DP980 (t1.2) steel sheets and a bulk aluminum alloy of AA7075. </LI> <LI> All the specimens tend to fail along the direction of the maximum shear stress in various loading states of plane strain compression, uniaxial compression, shear, uniaxial tension and plane strain tension. </LI> <LI> Fractured voids elongate along the direction of the maximum shear stress for all specimens with the stress triaxiality ranging from negative in compression to 0.57 in the plane strain tension. </LI> <LI> The experiments of DP980 and AA7075 reveal that ductile fracture takes place along the direction of the maximum shear stress in the wide loading conditions of compressive upsetting, shear, uniaxial tension, and plane strain tension with stress triaxiality below 0.6. </LI> <LI> Effect of the maximum shear stress must be correctly coupled in modeling of ductile fracture in these loading conditions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Shear fracture takes place in wide loading conditions of tension, shear and compression. </P> <P>[DISPLAY OMISSION]</P>

대퇴 골두 연골하 스트레스 골절

송원석(Won Seok Song),김종원(Jong Won Kim),유정준(Jeong Joon Yoo),구경회(Kyung-Hoi Koo),윤강섭(Kang Sup Yoon),김상림(Sang Rim Kim),김영민(Young-Min Kim),김희중(Hee Joong Kim) 대한정형외과학회 2004 대한정형외과학회지 Vol.39 No.7

목적: 대퇴 골두 연골하 스트레스 골절(subchondral stress fracture of the femoral head)은 드문 질환으로서 최근에 주로 부전 골절(insufficiency fracture)의 형태로 발생한 예들에 대해 보고되고 있다. 본 연구에서는 부전 골절 및 피로 골절(fatigue fracture) 형태로 발생한 스트레스 골절 환자의 임상적, 방사선학적 특정을 평가하였다. 대상 및 방법: 1998년 1월부터 2003년 4월 사이에 대퇴 골두 연골하 스트레스 골절로 진단 및 치료 받은 8명 10예를 대상으로, 이들의 임상적 방사선학적 소견에 대해 평균 33개월 추시 결과를 평가하였다. 결과: 피로 골절의 양상으로는 6명의 젊고 건강한 군인에게서 입대 후 5개월 이내에 발생하였고, 부전 골절의 양상으로는 1명의 노인과 1명의 골형성 부전증 환자에게 발생하였다. 1명을 제외한 모든 환자에서 대퇴 골두 무혈성 괴사의 위험 요소 및 뚜렷한 선행 외상의 과거력은 있지 않았다. 최초의 단순 방사선 사진상 6명 7예에서 이상 소견이 관찰되었다. 이 중 4예에서 대퇴 골두의 함몰 소견이 관찰되었다. 골 주사 검사상 대퇴 골두에 증가된 흡수 음영 소견이 관찰되었다. 자기 공명 촬영에서 대퇴 골두 연골하 이상 신호 선(MR crescent sign)과 전반적인 골수의 부종 소견이 관찰되었다. 결론: 대퇴 골두 연골하 스트레스 골절은 부전 골절 및 피로 골절의 양상으로 모두 나타날 수 있으며, 의심되는 환자의 경우 골 주사 검사 등을 통하여 조기 진단함으로써 대퇴 골두의 함몰을 방지할 수 있을 것이다. Purpose: Subchondral stress fracture of the femoral head is a rare condition that usually occurs as an insufficiency fracture in people with poor bone quality. This study evaluated the clinical and radiographic aspects of the subchondral stress fracture of the femoral head that occurred in the form of an insufficiency or a fatigue fracture. Materials and Methods: Between January 1998 and April 2003, 10 cases of the subchondral stress fracture of the femoral head in 8 patients were treated. The characteristics of this condition were determined by assessing the clinical course and findings of the radiographs, bone scintigram and MR images. Results: A fatigue fracture developed in 6 young healthy conscripts within 5 months after recruitment. An insufficiency fracture developed in one senile patient and in one known osteogenesis imperfecta patient. All patients except for one did not have any predisposing factors for osteonecrosis and antecedent trauma. On the initial radiographs, femoral head collapse was observed in 4 hips. Bone scintigraphs showed increased radionuclide uptake in the femoral head. The MR images demonstrated an subchondral abnormal signal intensity line (MR crescent sign) and a bone marrow edema pattern. Conclusion: A subchondral stress fracture of the femoral head can occur as a fatigue fracture as well as an insufficiency fracture. Bone scintigraphy is a valuable tool for screening patients suspected of having a subchondral stress fracture.

Stress analysis and optimization of Nd:YAG pulsed laser processing of notches for fracture splitting of a C70S6 connecting rod

Shuqing Kou,Yan Gao,Yong Zhao,Baojun Lin 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5

The pulsed laser pre-processing of a notch as the fracture initiation source for the splitting process is the key mechanism of an advanced fracture splitting technology for C70S6 connecting rods. This study investigated the stress field of Nd:YAG pulsed laser grooving, which affects the rapid fracture initiation at the notch root and the controlled crack extension in the critical fracture splitting quality, to improve manufacturing quality. Thermal elastic-plastic incremental theory was applied to build the finite element analysis model of the stress field of pulsed laser grooving for fracture splitting based on the Rotary-Gauss body heat source. The corresponding numerical simulation of the stress field was conducted. The changes and distributions of the stress during pulsed laser grooving were examined, the influence rule of the primary technological parameters on the residual stress was analyzed, and the analysis results were validated by the corresponding cutting experiment. Results showed that the residual stress distribution was concentrated in the Heat-affected zone (HAZ) near the fracture splitting notch, which would cause micro-cracks in the HAZ. The stress state of the notch root in the fracture initiation direction was tensile stress, which was beneficial to the fracture initiation and the crack rapid extension in the subsequent fracture splitting process. However, the uneven distribution of the stress could lead to fracture splitting defects, and thus the residual stress should be lowered to a reasonable range. Decreasing the laser pulse power, increasing the processing speed, and lowering the pulse width can lower the residual stress. Along with the actual production, the reasonable main technological parameters were obtained.

Involvements of Stress Triaxiality in the Brittle Fracture during Earthquakes in Steel Bridge Bents

Hiroshi Tamura,Eiichi Sasaki,Hitoshi Yamada,Hiroshi Katsuchi,Theeraphong Chanpheng 한국강구조학회 2009 International Journal of Steel Structures Vol.9 No.3

Stress triaxiality is proposed as one of the key parameters to discuss the cause of brittle fracture during earthquakes in steel structures. This study analytically investigated the features of stress triaxiality in steel bridge bent subjected to earthquakes. The target structure is a steel bridge bent actually fractured during the South Hyogo prefecture Earthquake. From the investigations, it was confirmed that high stress triaxiality was generated at a point supposed as fracture origin. There is a possibility that the triaxiality was involved in the fracture strongly through the increase of maximum principal stress. Moreover, from the analyses accounting for several kinds of large earthquake waveforms, it was indicated that threre is possibility that the distribution of triaxiality around the fracture origin was not affected by significantly by each cycle and each waveform. Stress triaxiality is proposed as one of the key parameters to discuss the cause of brittle fracture during earthquakes in steel structures. This study analytically investigated the features of stress triaxiality in steel bridge bent subjected to earthquakes. The target structure is a steel bridge bent actually fractured during the South Hyogo prefecture Earthquake. From the investigations, it was confirmed that high stress triaxiality was generated at a point supposed as fracture origin. There is a possibility that the triaxiality was involved in the fracture strongly through the increase of maximum principal stress. Moreover, from the analyses accounting for several kinds of large earthquake waveforms, it was indicated that threre is possibility that the distribution of triaxiality around the fracture origin was not affected by significantly by each cycle and each waveform.

Stress sensitivity in naturally fractured reservoirs: a case study of the Lower Cretaceous Xiagou Formation, Qingxi Oilfield, Jiuxi Basin, northwestern China

Wei Ju,Xiaolong Fu,Weifeng Sun,Haoran Xu,Shengyu Wang 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.3

Stress sensitivity is the variation of rock petrophysical parameters resulting from changes in effective stress. In fractured reservoirs, experimental methods exhibit a certain amount of error in the quantitative analysis of reservoir rock stress sensitivity. In addition, fracture-bearing experimental rock samples are difficult to obtain and prepare. Therefore, in the present study, reservoir rock stress sensitivity in naturally fractured reservoirs was investigated based on geomechanical modeling using a case study of the Lower Cretaceous Xiagou Formation in the Qingxi Oilfield. The results indicate that the Xiagou fractured reservoir experiences strong stress sensitivity with a fracture permeability damage rate reaching 94.38%. Natural fractures influence reservoir rock stress sensitivity. The degree of filling and type of filled minerals within natural fractures have great effects on the permeability damage rate. A higher permeability damage rate suggests stronger rock stress sensitivity. Generally, I) for reservoir rocks with unfilled natural fractures, the permeability damage rate is extremely high; II) for reservoir rocks with partially filled natural fractures, the permeability damage rate is high, and if the minerals within the natural fractures are insoluble, the permeability damage rate is slightly higher than if the materials are soluble; III) for reservoir rocks with completely filled natural fractures, the permeability damage rate is extremely low if the minerals within the natural fractures are insoluble; however, if the materials are soluble, the permeability becomes slightly higher with the increase of effective stress. Most importantly, this study provides a practical method for analyzing stress sensitivity in naturally fractured reservoirs.

Correlation of localized residual stresses with ductile fracture toughness using in situ neutron diffraction and finite element modelling

Wang, Huai,Woo, Wanchuck,Lee, Soo Yeol,An, Gyubaek,Kim, Dong-Kyu Elsevier 2019 International journal of mechanical sciences Vol.160 No.-

<P><B>Abstract</B></P> <P>Localized residual stresses were correlated to ductile fracture toughness quantitatively in steel and aluminium alloys using in situ neutron diffraction method coupled with elastic-plastic finite element modelling. Local out-of-plane compression (LOPC) method generated compressive and tensile residual stresses in the vicinity of the fatigue pre-crack front in two compact tension (CT) specimens, respectively, and the evolution of the stress fields was simultaneously measured using in situ neutron diffraction technique under mode-I fracture loading. The results clearly showed that the localized tensile residual stress apparently accelerated stress transfer at the mid-thickness of the CT specimen compared to the specimen having compressive residual stress. The coupled quasi-static ductile fracture simulations and neutron diffraction results revealed a clear correspondence of fracture initiation toughness with localized residual stresses in both steel and aluminium alloys. In the aluminium case, tensile residual stress of 208 MPa was obviously detrimental to the fracture toughness resulting in a 43% reduction while compression of −220 MPa increases by up to 14%. On the other hand, localized residual stress in steel hardly affected fracture initiation toughness due to high plastic dissipation energy. This experiment-simulation coupled study quantitatively elucidates the distinctive role of plastic deformation and stress triaxiality in ductile fracture initiation between steel and aluminium alloy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Spatially-resolved stress/strain mapping is done inside the material under loading. </LI> <LI> Ductile fracture initiation reveals a clear correlation to localized residual stresses. </LI> <LI> Accumulation of plastic deformation dominates fracture of the EH40 steel. </LI> <LI> Increase of stress triaxiality governs fracture of the Al5083 aluminium. </LI> <LI> Tensile residual stresses reduce 43% of fracture toughness of the Al5083 aluminium. </LI> </UL> </P>

In situ stress states at KURT, an underground research laboratory in South Korea for the study of high-level radioactive waste disposal

Jo, Yeonguk,Chang, Chandong,Ji, Sung-Hoon,Park, Kyung-Woo Elsevier 2019 Engineering geology Vol.259 No.-

<P><B>Abstract</B></P> <P>The Korea Atomic Energy Research Institute Underground Research Tunnel (KURT) is an underground research laboratory in South Korea, built for investigations into the geological disposal of high-level radioactive waste. We characterize in situ stress states at KURT using data from a series of hydraulic fracturing (HF) tests and borehole image logs to depths of ~700 m in two boreholes. The tensile fractures induced by HF tests, plus several borehole stress indicators (e.g., drilling-induced tensile fractures and borehole breakouts) measured from image logs, consistently indicate an ESE–WNW oriented maximum horizontal principal compressive stress (<I>S</I> <SUB> <I>Hmax</I> </SUB>). This site-scale <I>S</I> <SUB> <I>Hmax</I> </SUB> orientation varies slightly from the regional-scale <I>S</I> <SUB> <I>Hmax</I> </SUB> orientation, likely reflecting a local stress perturbation resulting from a fault network that traverses the site. Estimated magnitudes of the minimum horizontal principal compressive stress (<I>S</I> <SUB> <I>hmin</I> </SUB>), determined either from the shut-in pressures recorded during HF tests or from stress indicators on image logs, are comparable to the vertical stress, indicating that the stress regime at the KURT site straddles the boundary between strike-slip and reverse faulting. The depth-dependent trend in estimated <I>S</I> <SUB> <I>Hmax</I> </SUB> magnitudes deviates at ~500 m depth, which we attribute to variations in the distribution of natural fractures in the granitic rock mass. This depth-dependent variation in <I>S</I> <SUB> <I>Hmax</I> </SUB> magnitudes has implications for the slip stability of pre-existing fractures at the site. That is, at shallow depths, <I>S</I> <SUB> <I>Hmax</I> </SUB> lies within the Coulomb stress limit for optimally oriented fractures and faults with a frictional coefficient of 0.6, whereas at greater depths, <I>S</I> <SUB> <I>Hmax</I> </SUB> exceeds this limit, meaning that pre-existing fractures at shallow depth are more susceptible to slip reactivation. Our stress estimation results suggest that the site-scale stress state is strongly coupled with characteristics of natural fractures, emphasizing the importance of detailed geologic and stress data for subsurface utilization and its stability evaluation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The stress at KURT is estimated from hydrofrac tests and borehole stress indicators. </LI> <LI> Site-scale stress orientations deviate from regional stress due to local faults. </LI> <LI> Horizontal stress magnitudes vary with the distribution of natural fractures. </LI> </UL> </P>

제5중족골 피로골절의 형태 분석: 시상면 및 관상면상의 위치

이경태 ( Kyung Tai Lee ),양기원 ( Ki Won Young ),박영욱 ( Young Uk Park ),제갈혁 ( Hyuk Jegal ),서정현 ( Jeong Hyun Seo ) 대한스포츠의학회 2016 대한스포츠의학회지 Vol.34 No.2

From a biomechanical standpoint, the main pathologic abnormality of fifth metatarsal stress fracture is the location where repetitive tensile stress concentrated. Decreasing tensile force in this region would be a proper treatment. Therefore, the purpose of this study is to evaluate the precise sagittal and coronal location of the fifth metatarsal stress fracture. Between June 2012 and May 2013, 38 athletes with a fifth metatarsal stress fracture were treated. To evaluate the precise sagittal location of the fracture, the entire length of the fifth metatarsal was measured and the distance from tuberosity to the fracture line was measured. To evaluate the precise coronal location of the fractures, coronal computed tomography images were obtained for incomplete fracture cases. The fracture location was classified as four quadrants. Thirty patients were classified into zone III fracture. However, the fracture is located in zone II for remaining eight cases. The median value of ratio between whole length and the distance from tuberosity to the fracture was 0.35 (range, 0.29-0.40) Among 33 incomplete fracture cases, there were 28 patients whose fracture developed in plantolateral quadrant, four patients at the lateral side and a patient for plantar side. The main pathologic abnormality is at the plantar lateral side because of the repetitive stress concentrated there.

레이저용접부의 파괴에 미치는 잔류응력의 영향

조성규,양영수,노영진 한국레이저가공학회 2008 한국레이저가공학회지 Vol.11 No.2

The integrity of laser welded structures is decided in fracture strength and fatigue strength. This study made an effort to understand the fracture behavior considering residual stress. Experiments are conducted and analyses are performed to explore the influence of residual stress on fracture behavior of bead-on laser welded compact specimen. Fracture experiments are performed using ASTM 1820. The performed analyses included thermo-elasto-plastic analyses for residual stress and subsequent J-integral calculation. A modified J integral is calculated in the presence of residual stresses. The J-integral is path-independent for combination of residual stress field and stress due to mechanical loading. The results indicates that the tensile residual stress near crack front bring the low fracture load while the compressive residual stress bring the high fracture load compared to no residual stress specimen. These results quantitatively understand the influence of residual stress on fracture behavior.