Classical Versus Improved Thin Shell Theories: A Theoretical Argument or a Design Concern?

1997 ◽  
Vol 119 (1) ◽  
pp. 96-104
Author(s):  
N. Simos ◽  
C. Chassapis
Keyword(s):  
Stress Concentration ◽  
Stress Field ◽  
Mathematical Formulation ◽  
Local Stress ◽  
Boundary Integral ◽  
Primary Concern ◽  
Theoretical Argument ◽  
Geometric Conditions ◽  
Specific Loading ◽  
The Impact

Differences in the response of thin nonshallow spherical shells resulting from the choice of the adopted shell theory (classical or improved) are addressed analytically and through a series of representative shell problems. The analytical approach utilized to study the variation between the two theoretical models is based on the response resulting from Singular loads. The differences are quantified in a set of problems that reflect on the assumptions used in formulating the analytical description of the two theories in question. The broad scope of this paper is to examine the impact of shear deformability, introduced by the improved theory on the stress field when amplified under specific loading and geometric conditions, when those are of primary concern to the engineers. Such cases associated with stress concentration around cutouts, interaction of shells with nozzles, stress field in the vicinity of concentrated surface loads, etc. The mathematical formulation is based on the derivation of appropriate Green functions and the computational scheme is formed upon a special type of boundary integral equation. Comparison solutions for stress concentration around circular cutouts of twisted and sheared shells, stress amplification in the junction of shell with nozzles, and local stress field induced by concentrated loads are presented for the two theories.

scholarly journals Experiment on Corrosion Fatigue Life of Steel Strands under the Coupling Effects of Chloride Environment and Alternating Loads

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Guowen Yao ◽  
Xuanrui Yu ◽  
Lifeng Gu ◽  
Yixing Jiang
Keyword(s):  
Mechanical Properties ◽  
Weight Loss ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Salt Spray ◽  
Three Dimensional ◽  
Local Stress ◽  
Coupling Effects ◽  
Chloride Environment ◽  
The Impact

Corrosion pits will lead to local stress concentration on the surface of steel strands and even shorter fatigue life and worse mechanical properties of steel strands. In order to explore the corrosion mechanics of steel strands to predict the fatigue life, accelerated salt spray corrosion test is carried out to simulate the corrosion laws of steel strands and record the changes of the corrosion degrees during the experiment, considering the coupling effects of alternating loads and chloride environment. Besides, the impact of stress amplitudes on the corrosion degrees of steel strands is quantitatively studied by the corrosion weight loss, and corroded steel strands in experiment are graded according to the corrosion weight loss to test the mechanical properties, respectively; the results show that the corrosion weight loss and tensile strength of steel strands obey the exponential distribution, and the relationship with elongation is linear. In addition, the relationships between the stress concentration coefficient and the pit length, width, and depth are obtained; with the three-dimensional linear regression theory, the accuracy of the regression model is verified by t-value test, laying a foundation for predicting the corrosion life of the cables.

scholarly journals Reduction of the Local Stress Field around Holes through Porous Shaped Structures

2018 ◽  
Vol 20 (3) ◽  
pp. 36-41
Author(s):  
Stefano Monti
Keyword(s):  
Mechanical Properties ◽  
Stress Concentration ◽  
Stress Field ◽  
Present Article ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Laser Cutting ◽  
Local Stress ◽  
Hole Boundary ◽  
Local Stress Field

Geometrical discontinuities in mechanical components are detrimental for the mechanical properties of the product itself. Actually, in proximity of such features, the stress increases due to the stress concentration factor, that in the case of a circular hole is equal to 3. Several solutions have been proposed to reduce the stress concentration value. In the present article, the application of a particular porous pattern that can be obtained by laser cutting with the appropriate finishing requirements is introduced in order to modify the local stress field and reduce the stress concentration value near the hole boundary.

Geomechanic models using finite element methods show how Cooper Basin structure and sand body geometry impacts stress variation and hydraulic fracturing results

2015 ◽  
Vol 55 (2) ◽  
pp. 439
Author(s):  
Nicole Ditty ◽  
Dennis Cooke
Keyword(s):  
Finite Element ◽  
Stress Field ◽  
Hydraulic Fracture ◽  
Local Stress ◽  
Three Dimensions ◽  
Stress Regime ◽  
Structural Position ◽  
The Impact ◽  
Cooper Basin ◽  
Hydraulic Fracture Stimulation

Unconventional reservoirs such as tight sands and shales require hydraulic fracture stimulation to improve productivity. The success of reservoir stimulation is controlled by the local stress field but decisions are often made knowing only the average stress field. This study uses geomechanical modelling to help explain lateral stress variability using structural geology, lithology contrast and boundary conditions. Changes in vertical and horizontal stresses are related to depth, lithology and structural position, yet these effects are not always accounted for. This is evident in the Cooper Basin, Australia, where, for example, unexpected changes in minifrac pressure are commonly observed in adjacent wells in a field. This study presents results from conceptual geomechanical models to help explain such variations in stress. Model scenarios are constructed using finite element package to investigate the impact of structural position, rock mechanical properties and stress regime on the patterns of horizontal and vertical stress magnitudes in a layered antiform sequence. Key findings suggest that: stress magnitude is affected by structural positioning; different patterns of stress exist across different lithologies; and, stress regime impacts on patterns of stress, especially in combination with curvature of structures. These challenge traditional methods of one-dimensional mechanical earth models and show that, rather than employing methods developed for simple layer-cake geology in extensional basins, geomechanical models should be constructed in two- or even three-dimensions. Results of this study highlight part of the solution to the unconventional resource potential of the Cooper Basin. Improved prediction of field-scale stress variations should enable further optimisation of hydraulic fracture stimulation treatments.

Impact of Quality of Unfamiliar Shopping App on Initial Trust Formation: A Moderated Mediation of Risk Attitude

2021 ◽  
pp. 097226292098454
Author(s):  
Vipul Patel ◽  
Richa Pandit
Keyword(s):  
Information Search ◽  
Purchase Intention ◽  
Risk Attitude ◽  
Moderated Mediation ◽  
Primary Concern ◽  
Initial Trust ◽  
Trust Formation ◽  
Online Retailers ◽  
The Impact

Today, all phases of consumers' buying process from pre-information search, evaluation of alternatives, order placing and post-purchase service are conducted in shopping apps installed in smartphones. A shopping app is omnipresent and is a powerful retail channel for retailers all over the world. However, the primary concern for many customers is that online shopping is not secure. This insecurity is more if customers have to purchase from an unfamiliar shopping app. Customers generally hesitate to purchase using unfamiliar shopping apps, unless they feel that the app is trustworthy. Based on the survey of 264 respondents, this study attempts to measure the impact of the quality of unfamiliar shopping apps on initial trust formation and subsequently, purchase intention. An attempt was also made to study the moderated mediation impact of risk attitude on the relationship between shopping app quality and initial trust formation. The findings of this paper may be of practical use for the online retailers by providing a better understanding of the adoption of unfamiliar shopping apps among prospective customers. It will also provide strategic inputs to online retailers to craft suitable strategies for the adoption of unfamiliar shopping apps.

scholarly journals Influence of Orthotropy on Biomechanics of Peri-Implant Bone in Complete Mandible Model with Full Dentition

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Xi Ding ◽  
Sheng-Hui Liao ◽  
Xing-Hao Zhu ◽  
Hui-Ming Wang
Keyword(s):  
Orthotropic Material ◽  
Tooth Enamel ◽  
Local Stress ◽  
Isotropic Case ◽  
Stress And Strain ◽  
Isotropic Model ◽  
Bone Interface ◽  
Multiple Data ◽  
Cad Models ◽  
The Impact

Objective.The study was to investigate the impact of orthotropic material on the biomechanics of dental implant, based on a detailed mandible with high geometric and mechanical similarity.Materials and Methods.Multiple data sources were used to elaborate detailed biological structures and implant CAD models. In addition, an extended orthotropic material assignment methodology based on harmonic fields was used to handle the alveolar ridge region to generate compatible orthotropic fields. The influence of orthotropic material was compared with the commonly used isotropic model and simplified orthotropic model.Results.The simulation results showed that the values of stress and strain on the implant-bone interface almost increased in the orthotropic model compared to the isotropic case, especially for the cancellous bone. However, the local stress concentration was more obvious in the isotropic case compared to that in orthotropic case. The simple orthotropic model revealed irregular stress and strain distribution, compared to the isotropic model and the real orthotropic model. The influence of orthotropy was little on the implant, periodontal ligament, tooth enamel, and dentin.Conclusion.The orthotropic material has significant effect on stress and strain of implant-bone interface in the mandible, compared with the isotropic simulation. Real orthotropic mechanical properties of mandible should be emphasized in biomechanical studies of dental implants.

scholarly journals Numerical Simulation of Heat Mass Transfer Effects on MHD Flow of Williamson Nanofluid by a Stretching Surface with Thermal Conductivity and Variable Thickness

Coatings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 684
Author(s):  
Saeed Islam ◽  
Haroon Ur Rasheed ◽  
Kottakkaran Sooppy Nisar ◽  
Nawal A. Alshehri ◽  
Mohammed Zakarya
Keyword(s):  
Thermal Conductivity ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Differential Equations ◽  
Variable Thickness ◽  
Heat Mass Transfer ◽  
Mathematical Formulation ◽  
Stretching Surface ◽  
Nanofluid Flow ◽  
The Impact

The current analysis deals with radiative aspects of magnetohydrodynamic boundary layer flow with heat mass transfer features on electrically conductive Williamson nanofluid by a stretching surface. The impact of variable thickness and thermal conductivity characteristics in view of melting heat flow are examined. The mathematical formulation of Williamson nanofluid flow is based on boundary layer theory pioneered by Prandtl. The boundary layer nanofluid flow idea yields a constitutive flow laws of partial differential equations (PDEs) are made dimensionless and then reduce to ordinary nonlinear differential equations (ODEs) versus transformation technique. A built-in numerical algorithm bvp4c in Mathematica software is employed for nonlinear systems computation. Considerable features of dimensionless parameters are reviewed via graphical description. A comparison with another homotopic approach (HAM) as a limiting case and an excellent agreement perceived.

An Optimization Design Platform for Fir-Tree Root and Groove for Steam Turbine

2018 ◽  
Author(s):  
Deqi Yu ◽  
Xiaojun Zhang ◽  
Jiandao Yang ◽  
Kai Cheng ◽  
Weilin Shu ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Steam Turbine ◽  
Gas Turbines ◽  
High Speed ◽  
Optimization Design ◽  
Turbine Blades ◽  
Local Stress ◽  
Optimization Method ◽  
Steam Turbines ◽  
Geometry Configuration

Fir-tree root and groove profiles are widely used in gas turbine and steam turbine. Normally, the fir-tree root and groove are characterized with straight line, arc or even elliptic fillet and splines, then the parameters of these features were defined as design variables to perform root profile optimization. In ultra-long blades of CCPP and nuclear steam turbines and high-speed blades of industrial steam turbine blades, both the root and groove strength are the key challenges during the design process. Especially, in industrial steam turbines, the geometry of blade is very small but the operation velocity is very high and the blade suffers stress concentration severely. In this paper, two methods for geometry configuration and relevant optimization programs are described. The first one is feature-based using straight lines and arcs to configure the fir-tree root and groove geometry and genetic algorithm for optimization. This method is quite fit for wholly new root and groove design. And the second local optimization method is based on B-splines to configure the geometry where the local stress concentration occurs and the relevant optimization algorithm is used for optimization. Also, several cases are studied as comparison by using the optimization design platform. It can be used not only in steam turbines but also in gas turbines.

Numerical Simulation of the Stress Field of Thick 7B04 Aluminum Alloy Board during Continuous Manufacture Procedure

2007 ◽  
Vol 127 ◽  
pp. 259-264
Author(s):  
Hong Yuan Fang ◽  
Cheng Iei Fan
Keyword(s):  
Numerical Simulation ◽  
Aluminum Alloy ◽  
Stress Concentration ◽  
Stress Field ◽  
Solution Treatment ◽  
Simulation Method ◽  
The Core ◽  
Manufacturing Procedure ◽  
Continuous Manufacture ◽  
Simulation Results

Numerical simulation method is employed in the article to analyze the stress field of thick 7B04 aluminum alloy board during manufacturing procedure of solution treatment, calendaring and stretching. The simulation results show that the surface of the board endures compressive stress while the core segment endures tensile stress, and the distribution of the stress is very inhomogeneous. The calendaring procedure helps to decrease the stress and redistribute the stress uniformly, but it also leads to stress concentration at the two ends of the board, which engenders bad influence on the subsequent processing. The board deforms plastically when being stretched, thus the stress decreases greatly and is redistributed uniformly.

Introducing a new dataset on leadership change in rebel groups, 1946–2010

2018 ◽  
Vol 56 (2) ◽  
pp. 306-315 ◽  
Author(s):  
Carmela Lutmar ◽  
Lesley G Terris
Keyword(s):  
Civil War ◽  
Future Research ◽  
Theoretical Argument ◽  
War And Peace ◽  
Leadership Change ◽  
Rebel Groups ◽  
Interstate Disputes ◽  
Leadership Changes ◽  
The Impact ◽  
Qualitative Literature

Leaders and leadership changes are found to influence states’ foreign policy decisions, in particular with respect to war and peace between states. Although this issue is also addressed in the qualitative literature on intrastate wars, the influence of leadership turnovers in civil war has received limited systematic attention. One reason for this is the scarcity of quantitative data on rebel group leaderships. To fill this gap, we present a comprehensive dataset on leadership changes in rebel groups, 1946–2010, organized by rebel-month. The effects of leadership changes among parties engaged in civil war are argued to be more complex than those found in interstate disputes. In this article we present our theoretical argument followed by presentation of the variables in the dataset and descriptive statistics. To demonstrate the potential research value of the dataset we examine the impact of leader shifts on civil war settlement in Africa. We conclude with avenues for future research which might benefit from this dataset.

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