• Title/Summary/Keyword: maximum shear stress

Search Result 555, Processing Time 0.022 seconds

Fracture Behaviors of Alumina Tubes under Combined Tension/Torsion (알루미나 튜브의 인장/비틀림 조합하중하의 파괴거동)

  • Kim, K.T.;Suh, J.;Cho, Y.H.
    • Journal of the Korean Ceramic Society
    • /
    • v.28 no.1
    • /
    • pp.20-28
    • /
    • 1991
  • Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test($\tau$/$\sigma$= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio $\tau$/$\sigma$. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

  • PDF

Effects of fines content on void ratio, compressibility, and static liquefaction of silty sand

  • Lade, Poul V.;Yamamuro, Jerry A.;Liggio, Carl D. Jr.
    • Geomechanics and Engineering
    • /
    • v.1 no.1
    • /
    • pp.1-15
    • /
    • 2009
  • Many aspects of the behavior of sands are affected by the content of non-plastic fine particles and these various aspects should be included in a constitutive model for the soil behavior. The fines content affects maximum and minimum void ratios, compressibility, shear strength, and static liquefaction under undrained conditions. Twenty-eight undrained triaxial compression tests were performed on mixtures of sand and fine particles with fines contents of 0, 10, 20, 30, 50, 75, and 100% to study the effects of fines on void ratio, compressibility, and the occurrence of static liquefaction. The experiments were performed at low consolidation pressures at which liquefaction may occur in near-surface, natural deposits. The presence of fines creates a particle structure in the soil that is highly compressible, enhancing the potential for liquefaction, and the fines also alter the basic stress-strain and volume change behavior, which should be modeled to predict the occurrence of static liquefaction in the field. The void ratio at which liquefaction occurs for each sand/fines mixture was determined, and the variation of compressibility with void ratio was determined for each mixture. This allowed a relation to be determined between fines content, void ratio, compressibility, and the occurrence of static liquefaction. Such relations may vary from sand to sand, but the present results are believed to indicate the trend in such relations.

Numerical study of airfoil thickness effects on the performance of J-shaped straight blade vertical axis wind turbine

  • Zamani, Mahdi;Maghrebi, Mohammad Javad;Moshizi, Sajad A.
    • Wind and Structures
    • /
    • v.22 no.5
    • /
    • pp.595-616
    • /
    • 2016
  • Providing high starting torque and efficiency simultaneously is a significant challenge for vertical axis wind turbines (VAWTs). In this paper, a new approach is studied in order to modify VAWTs performance and cogging torque. In this approach, J-shaped profiles are exploited in the structure of blades by means of eliminating the pressure side of airfoil from the maximum thickness toward the trailing edge. This new profile is a new type of VAWT airfoil using the lift and drag forces, thereby yielding a better performance at low TSRs. To simulate the fluid flow of the VAWT along with J-shaped profiles originated from NACA0018 and NACA0030, a two-dimensional computational analysis is conducted. The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the two-equation Shear Stress Transport (SST) turbulence model. The main objective of the study is to investigate the effects of J-shaped straight blade thickness on the performance characteristics of VAWT. The results obtained indicate that opting for the higher thickness in J-shaped profiles for the blade sections leads the performance and cogging torque of VAWT to enhance dramatically.

Effect of fence porosity on the velocity field of wake flow past porous wind fences (다공성 방풍벽의 다공도가 펜스후류 속도장에 미치는 영향에 관한 연구)

  • Kim, Hyeong-Beom;Lee, Sang-Jun
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.22 no.7
    • /
    • pp.915-926
    • /
    • 1998
  • Velocity fields of near turbulent was behind a porous wind fence were measured using the 2-frame PTV method in a circulating water channel. The fences used in this study had different geometric porosity(.epsilon.) of 0, 20, 40 and 65%. The fence was embedded in a thin laminar boundary layer, i.e., .delta./H ~ = 0.1. Reynolds number based on the fence height H and free stream velocity(U$\_$o/) was about 8,400. As a result, a recirculating flow region was formed behind the fence for the .epsilon.=0% and 20% wind fence. For the wind fences having porosity larger than .epsilon.=40%, it was difficult to see separation bubbles behind the fence. The .epsilon.=20% porous fence reveals the maximum velocity reduction, however, the turbulent intensity and Reynolds shear stress are much greater than those of .epsilon.=40% fence. Among the wind fence tested in this study, the porous wind fence of .epsilon.=40% porosity is the most effective for abating wind erosion.

Prediction and analysis of optimal frequency of layered composite structure using higher-order FEM and soft computing techniques

  • Das, Arijit;Hirwani, Chetan K.;Panda, Subrata K.;Topal, Umut;Dede, Tayfun
    • Steel and Composite Structures
    • /
    • v.29 no.6
    • /
    • pp.749-758
    • /
    • 2018
  • This article derived a hybrid coupling technique using the higher-order displacement polynomial and three soft computing techniques (teaching learning-based optimization, particle swarm optimization, and artificial bee colony) to predict the optimal stacking sequence of the layered structure and the corresponding frequency values. The higher-order displacement kinematics is adopted for the mathematical model derivation considering the necessary stress and stain continuity and the elimination of shear correction factor. A nine noded isoparametric Lagrangian element (eighty-one degrees of freedom at each node) is engaged for the discretisation and the desired model equation derived via the classical Hamilton's principle. Subsequently, three soft computing techniques are employed to predict the maximum natural frequency values corresponding to their optimum layer sequences via a suitable home-made computer code. The finite element convergence rate including the optimal solution stability is established through the iterative solutions. Further, the predicted optimal stacking sequence including the accuracy of the frequency values are verified with adequate comparison studies. Lastly, the derived hybrid models are explored further to by solving different numerical examples for the combined structural parameters (length to width ratio, length to thickness ratio and orthotropicity on frequency and layer-sequence) and the implicit behavior discuss in details.

The properties of hydrophobic concrete prepared by biomimetic mineralization method

  • Huang, Chung-Ho;Fang, Hao-Yu;Zhang, Jue-Zhong
    • Computers and Concrete
    • /
    • v.23 no.5
    • /
    • pp.351-359
    • /
    • 2019
  • In this study, the calcium hydroxide, an inherent product of cement hydration, was treated using biomimetic carbonation method of incorporating stearic acid to generate the hydrophobic calcium carbonate on concrete surface. Carbonation reaction was carried out at various $CO_2$ pressure and temperatures and utilizing the Scanning Electron Microscope (SEM), chloride-ion penetration test apparatus, and compression test machine to investigate the hydrophobicity, durability, and mechanical properties of the synthesized products. Experimental results indicate that the calcium stearate may change the surface property of concrete from hydrophilicity to hydrophobicity. Increasing reaction temperature can change the particles from irregular shapes to needle-rod structures with increased shear stress and thus favorable to hydrophobicity and microhardness. The contact angle against water for the concrete surface was found to increase with increasing $CO_2$ pressure and temperature, and reached to an optimum value at around $90^{\circ}C$. The maximum static water contact angle of 128.7 degree was obtained at the $CO_2$ pressure of 2 atm and temperature of $90^{\circ}C$. It was also found that biomimetic carbonation increased the permeability, acid resistance and chloride-ion permeability of the concrete material. These unique results demonstrate that the needle-rod structures of $CaCO_3$ synthetized on concrete surface could enhance hydrophobicity, durability, and mechanical properties of concrete.

Effect of irradiation temperature on the nanoindentation behavior of P92 steel with thermomechanical treatment

  • Huang, Xi;Shen, Yinzhong;Li, Qingshan;Li, Xiaoyan;Zhan, Zixiong;Li, Guang;Li, Zhenhe
    • Nuclear Engineering and Technology
    • /
    • v.54 no.7
    • /
    • pp.2408-2417
    • /
    • 2022
  • The nanoindentation behavior of P92 steel with thermomechanical treatment under 3.5 MeV Fe13+ ion irradiation at room temperature, 400 and 700 ℃ was investigated. Pop-in behavior is observed for all the samples with and without irradiation at room temperature, while the temperature dependence of pop-in behavior is only observed in irradiated samples. The average load and penetration depth at the onset of pop-in increase as the irradiation temperature increases, in line with the results of the maximum shear stress. Irradiation induced hardening is exhibited for all irradiated samples, but there is a significant reduction in the hardness of sample irradiated at 700 ℃ in comparison to the samples irradiated at room temperature and 400 ℃. The ratio of hardness to elastic modulus for all samples decreases with increasing penetration depth except for samples at 700 ℃. With the increasing of irradiation temperature, the ratio of the irreversible work to the total work gradually decreases. In contrast, it increases for samples without irradiation.

Numerical Study on the Erosion Tendency of Centrifugal Slurry Pump Impeller for Thermal Power Plants (화력발전소용 원심 슬러리 펌프 임펠러의 침식경향 해석적 연구)

  • Cheon, Min-Woo;Lee, Chul-Hee
    • Journal of the Korean Society of Manufacturing Process Engineers
    • /
    • v.21 no.2
    • /
    • pp.101-108
    • /
    • 2022
  • Centrifugal pumps are typically used in many slurry industries to transport solid materials. Solid particles in the slurry frequently shock the walls inside the pump, significantly abrading the flow path. Wear damage causes replacement of the pump components, which wastes manpower and time. Therefore, previous studies have been conducted on factors to improve efficiency and life time. This study identifies trends in pumps supplying lime to desulfurized devices from thermal power plants. The shear stress transport(SST) model is used to determine the erosion trend of the centrifugal pump that transfers lime slurry. The purpose of this study is to identify efficiency and erosion trends by selecting three of the various impeller design elements. The three impeller blade design variables mentioned above represent the inlet draft angle and blade angle of leading edge(L.E) and trailing edge(T.E). The maximum value of the erosion density rate tends to be similar to the Input power.

Dynamic Behavior of the Breasting Dolphin Caused by Wave Power (파력에 의한 돌핀의 거동 특성)

  • Cho, Won Chul;Yoon, Gyeong Seug
    • KSCE Journal of Civil and Environmental Engineering Research
    • /
    • v.29 no.3B
    • /
    • pp.281-287
    • /
    • 2009
  • In this study, the behavior of breasting dolphin caused by the maximum wave height in the coastal area of Incheon has been investigated. The dynamic deflection, shear stress and moment of pile are analyzed using the coefficient of horizontal subgrade reaction resulted from loading tests for different DWT (Dead Weight Tonnage). The dynamic characteristics of pile in accumulated and dredged soils show almost the same pattern. It is shown that the resistance of dolphin to external load increases as the diameter of pile increases. The bettered pile dolphin is more than 10 times stable than the vertical pile type based on the study of dynamic characteristics of dolphin.

Loss Analysis by Impeller Blade Angle in the S-Curve Region of Low Specific Speed Pump Turbine

  • Ujjwal Shrestha;Young-Do Choi
    • New & Renewable Energy
    • /
    • v.20 no.2
    • /
    • pp.35-43
    • /
    • 2024
  • A pump turbine is a technically matured option for energy production and storage systems. At the off-design operating range, the pump turbine succumbed to flow instabilities, which correlated with the pump turbine geometry. A low specific speed pump turbine was designed and modified according to the impeller blade angle. Reynolds-Average Navier-Stokes is carried out with a shear stress transport turbulence model to evaluate the detailed flow characteristics in the pump turbine. The impeller blade inlet angle (𝛽1) and outlet angle (𝛽2) are used to evaluate hydraulic loss in the pump turbine. When 𝛽1 changed from low to high value, the maximum efficiency is increased by 4.75% in turbine mode. The S-Curve inclination is reduced by 8% and 42% for changes in 𝛽1 and 𝛽2 from low to high values, respectively. At α = 21°, the shock loss coefficient (𝜁s) is reduced by 16% and 19% with increases of 𝛽1 and 𝛽2 from low to high values, respectively. When 𝛽1 and 𝛽2 values increased from low to high, the impeller friction coefficient (𝜁f) increased and decreased by 20% and 8%, respectively. Hence, the high 𝛽2 effectively reduced the loss coefficient and S-Curve inclination.