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>

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.

링 전단시험기를 이용한 암석절리의 잔류강도 특성에 관한 연구

권준욱,김선명,윤지선 한국지반공학회 2000 한국지반공학회논문집 Vol.16 No.6

Residual stress is defined as a minimum stress with a large displacement of specimens and the residual stress after peak shear stress appears with displacement volume but there is no provision to select the residual stress. In the previous study, residual stress was recorded when the change of shear load is small in the condition of the strain more than 15%. But, in this study, hyperbolic function((No Abstract.see full/text), b=experimental constant) of soil test is adapted to joint of rock and the propriety is investigated. In a landslide and landsliding of artificial slope, wedge failure of tunnel with a large displacement, tests are simulated from peak stress to residual stress for safety analysis. But now. direct shear stress and triaxial compressive tests are usually performed to find out characteristics of shear stress about joint. Although these tests get a small displacement, that data of peak stress and residual stress are used for safety analysis. In this study, we tried to determine failure criteria for joints of rock using ring shear test machine. The residual stress following shear behavior was determined by the result of ring shear test and direct shear test. In conclusion, after comparing the results of the two test, we found that cohesion(c) and internal friction angle(ø) of ring shear test are 30% and 22% respectively of those of the direct shear test.

Perfobond Rib 전단연결재를 사용한 실험체의 전단강도 분석

최진웅,박병건,김형준,정호성,박선규 한국구조물진단유지관리공학회 2011 한국구조물진단유지관리공학회 논문집 Vol.15 No.1

본 연구의 목적은 직접전단응력 및 휨 전단응력의 비교분석을 통하여 Perfobond Rib 전단연결재를 사용한 구조물의 하중방향에 따른 전단응력 분석이다. 직접전단응력 분석을 위해서 5개의 변수로 Perfobond Rib 전단연결재 실험체 5개를 제작하고Push-out Test를 실시하였다. 실험 후 Perfobond Rib 전단연결재의 전단저항 메커니즘을 규명하고, 직접전단응력에 영향을미치는 주요 인자를 바탕으로 직접전단력을 산출할 수 있는 제안식을 제시하였다. 또한 휨 전단응력의 분석을 위해 강-콘크리트 합성 바닥판 실험체를 제작하고 정적 휨실험을 실시하였다. 정적 휨실험을 바탕으로 휨 거동특성을 분석하고 휨 전단응력을계산하였다. 직접전단응력과 EN 1994-1-1을 통해 계산된 휨 전단응력을 비교하여 하중방향에 따른 전단저항응력에 대해서분석을 하였다. The objective of this study which it sees direct shear stress and comparative analysis of flexural shear stress leads and it is a shear stress analysis which it follows in load direction of the structure which uses Perfobond Rib shear connectors. To analyze direct shear stress, five Perfobond Rib shear connect experiments were fabricated with five variables and conducted Push-out Tests. After experiments, mechanism of Perfobond Rib shear connector was examined and direct shear formula was proposed based on primary factors which influence direct shear stress. Also, for the analysis of flexural shear steel-concrete composite slab specimens were fabricated and static flexural test. Based on the static flexural test it analyzed the flexural behavior and the flexural shear stress it calculated. Direct shear stress and EN 1994-1-1 to lead and be calculated, it compared the flexural shear stress and it analyzed in about the shear resistance stress which it follows in load direction.

응력유도 및 고유 이방성에 따른 전단파 속도 특성

이창호,이종섭,윤형구,쭝훙꿍,조태현 한국지반공학회 2006 한국지반공학회논문집 Vol.22 No.11

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by parameters and exponents that are experimentally determined. The exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant effective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.

Shear Buckling Analysis of Steel Flat and Corrugated Web I-girders

Farhad Riahi,Alaeddin Behravesh,Mikaeil Yousefzadeh Fard,Arastoo Armaghani 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.12

One of the parameters of the economic design of steel I-girders is the use of thin webs. However, in large spans, the use of deep Igirders with thin web leads to the buckling of the web. In order to achieve out-of-plane stiffness and shear buckling resistance without the use of stiffeners or increasing the thickness of the webs, one possible way is to use corrugated plates in the I-girder web. To understand, shear stress distribution of the web a series of three-point load test was performed on four types of the web; (flat, trapezoidal-, sinusoidal-, and the zigzag-corrugated). A non-linear FE analysis method was used to obtain the shear stress distribution in a flat and corrugated web, since it was not possible to obtain the shear stress distribution from the experimental investigation. Based on this research, it was found that the main failure modes of the current models are yielding or shear buckling of the web when it is under the shear. In addition, it shows that the failure of all beams occurred due to shear buckling of the web without any interaction of the flange. In the other hand, the shear stress along the side of the flange is nearly zero; it is clear that the web takes almost all the shear force. The nonlinear analysis results show that shear stress is maximum and uniformly distributed on the web before the buckling. After buckling, the volume of shear stress is reduced and distributed unevenly.According to the results, there are three types of shear buckling: local, global, and interactive in models.

Estimating Bed Shear Stress Distribution over Bottom of a Channel on the Moving Vessel

Kim Dong Hyeon,황진환 한국해양과학기술원 2023 Ocean science journal Vol.58 No.1

Shear stress is critical in the determination and estimation of bedload transport and morphological changes. Generally, the bed shear stress is estimated in felds using three-dimensional fow velocities acquired by an acoustic Doppler velocimeter and current profler mounted on the channel bottom or anchored vessel. The temporal measurement and estimation of the bed shear stress by the conventional methods in a fxed point must be signifcantly close to the actual bed shear stress; however, the conventional methods may not provide sufcient information of spatial distribution of the bed shear stress over the entire domain, i.e., the measurements in several fxed points cannot guarantee that the measured values represent the entire domain of interest. Therefore, the present work proposed a framework for acquiring the spatial distributions of shear stress over a domain. Accordingly, a reach with a length and width of 5.6 km and 250 m, respectively, at the end of the Hyeongsan River in South Korea was surveyed through the moving-vessel measurement with ADCP measuring the velocities of that channel reach to estimate shear stress. To collect over a possible maximum spatial domain in a short duration, the moving-vessel technique was applied over the survey region without stopping a vessel. The measurement was conducted in a series of single zigzag transects instead of repeatedly transects over a same cross section. The spiked noises of velocity were observed in high frequencies at a single transect and so the noises were smoothed by moving average over a reasonable circular space. After the spatial interpolation, the accuracy of the spatial distributions of the bed shear stress was compared to the anchoredvessel measurement, and the reliable bed shear stress map was provided as a result.

Rheological characterization of poly(ethylene oxide) aqueous solution under dynamic helical squeeze flow

Kim, Jae Hee,Ahn, Kyung Hyun 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.4

Oscillatory shear flow has been widely used to investigate the flow properties of a wide range of complex fluids. The flow is useful because experimental platform is already fixed and its analysis has sound theoretical background. However it is too simple compared to the complex flows encountered in industry. Accordingly, the rheological response of complex fluids needs to be investigated in more complicated flow field. There were several reports on the superimposed flows in which oscillatory flow was applied either parallel or perpendicular to the steady shear flow. In this paper, we propose dynamic helical squeeze flow (DHSQ) which superimposes oscillatory shear and oscillatory squeeze between parallel plates. The nonlinear response in DHSQ was studied by comparing DHSQ with oscillatory shear (OS) and with oscillatory squeeze (OSQ) in terms of stress shape and Lissajous plot. In DHSQ, both stress curve and Lissajous plot of shear and normal stresses showed nonsymmetric characteristics unlike shear stress in large amplitude oscillatory shear (LAOS). The normal stress in DHSQ was more distorted than that of OSQ. The shear stress in DHSQ showed the onset of nonlinearity at lower strain amplitude than that of oscillatory shear flow (OS). It is due to the coupling of shear and squeeze flows, and the effect was more pronounced in the shear stress than in the normal stress.

전단 스트레스에 의한 심방근세포 커넥신 해미채널의 활성화

김준철(Joon-Chul Kim),우선희(Sun-Hee Woo) 대한약학회 2019 약학회지 Vol.63 No.4

Abstract Shear stress induces global Ca waves in atrial myocytes and this Ca wave has been shown to be sensitive to connexin (Cx) channel interventions. In this study, we investigated whether shear stress activates Cx by measuring dye flux through the Cx channels in rat atrial myocytes. Because the pores of the hemichannels are large enough to permit flux of large molecules up to 1000 MW, we used a Cx channel-permeable dye, Calcein, and a Cx-impermeable dye, Oregon to evaluate Cx-specific activity under shear stress. Application of shear stress (~16 dyn/cm 2 ) using micro-jet apparatus to single atrial cells induced a significant increase in cellular Calcein efflux. The Calcein efflux was largely potentiated by the use of Ca -free external solutions which enhance Cx hemichannel activity. However, it was suppressed by 95% following the pre-treatment of La (2 mM), a gap junction blocker. Pre-exposure to the pannexin inhibitor probenecid (800 mM) did not alter the calcein efflux under shear stress. In contrast, the Oregon signal was not significantly affected by shear stress exposure, suggesting that calcein efflux by shear exposure was not due to nonspecific increase in membrane permeability. In a monolayer of HL-1 atrial cell culture treated by the external solutions containing Cx-permeable Lucifer Yellow dye, cellular dye influx was increased by shear stress. These results suggest that shear stress activates Cx hemichannels in atrial myocytes.

Principal Stress Rotation under Bidirectional Simple Shear Loadings

Yao Li,Yunming Yang,Hai-Sui Yu,Gethin Roberts 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.5

Previous researches have indicated the non-coaxiality of sand in unidirectional simple shear tests, in which the direction of theprincipal axes of stresses does not coincide with the corresponding principal axes of strain rate tensors. Due to the limitation ofapparatus that most of testing facilities can only add shear stress in one direction, the influence of stress history on the noncoaxialityof sand is not fully considered in previous tests. In this study, the effect of stress history on the non-coaxiality of sand is systematicallystudied by using the first commercially available Variable Direction Dynamic Cyclic Simple Shear system (VDDCSS). Samples ofLeighton Buzzard sand (Fraction B) are first consolidated under a vertical confining stress and consolidation shear stress, and thensheared by a drained monotonic shear stress. Angle (θ) between the consolidation shear stress and the drained monotonic shear stressis varied from 0o to 180o, with an interval of 30o. The change of principal axes of stresses is predicted by well-established equations,and the principal axe of strain rate is calculated using recorded data. Results show that the level of non-coaxiality is increased by theincreasing θ, especially at the initial stage of drained shearing.