Simulation of Ratcheting Responses of Elbow Piping Components

2009 ◽  
Author(s):  
Tasnim Hassan ◽  
Syed M. Rahman
Keyword(s):  
Damage Accumulation ◽  
Fatigue Cracks ◽  
Local Stress ◽  
Operating Conditions ◽  
Cyclic Plasticity ◽  
Plastic Collapse ◽  
Simulation Studies ◽  
Loading Conditions ◽  
Design Code ◽  
Thermal Operating Conditions

Ratcheting damage accumulation in piping components may occur under repeated reversals of loading induced by earthquakes, mechanical and thermal operating conditions, and other extreme loading conditions. Ratcheting damage accumulation can cause failure of structures through fatigue cracks or plastic collapse. A major challenge in structural mechanics is the prediction of ratcheting responses of structures under various cyclic loading conditions. Accurate prediction of ratcheting-fatigue and ratcheting-collapse of elbow components is imperative in order to incorporate the ratcheting related failures into the ASME design Code in a rational manner. This would require predictions of both local (stress-strain) and global (load-deflection) responses simultaneously. Towards achieving this goal, a set of experimental responses of elbow piping components is developed. Advanced cyclic plasticity models, such as, modified Chaboche, Ohno-Wang, modified Ohno-Wang and Abdel Karim-Ohno, are implemented into ANSYS for simulating the experimental responses. Results from the experimental and simulation studies are presented in order to demonstrate the state of structural ratcheting response simulation by these models.

Advanced Cyclic Plasticity Models in Simulating Ratcheting Responses of Straight and Elbow Piping Components, and Notched Plates

2005 ◽  
Author(s):  
Syed M. Rahman ◽  
Tasnim Hassan
Keyword(s):  
Damage Accumulation ◽  
Solid Mechanics ◽  
Fatigue Cracks ◽  
Constitutive Models ◽  
Local Stress ◽  
Weather Conditions ◽  
Operating Conditions ◽  
Cyclic Plasticity ◽  
Integration Schemes ◽  
Current State

Ratcheting is defined as the accumulation of strain or deformation in structures under cyclic loading. Damage accumulation due to ratcheting can cause failure of structures through fatigue cracks or plastic collapse. Ratcheting damage accumulation in structures may occur under repeated reversals of loading induced by earthquakes, extreme weather conditions, and mechanical and thermal operating conditions. A major challenge in structural and solid mechanics is the prediction of ratcheting responses of structures under any or combination of these loading conditions. Accurate prediction of ratcheting-fatigue and ratcheting-collapse is imperative in order to incorporate the ratcheting related failures into the ASME design Code in a rational manner. This would require predictions of both local (stress-strain) and global (load-deflection) responses simultaneously. In progressing towards this direction, a set of experimental ratcheting responses for straight and elbow piping components and notched plates is developed. Advanced cyclic plasticity models, such as, modified Chaboche, Ohno-Wang, and AbdelKarim-Ohno models, are implemented in ANSYS for simulation of these experimental responses. Various integration schemes for implementing the constitutive models into the structural analysis code ANSYS are studied. Results from the experimental and analytical studies are presented and discussed in order to demonstrate the current state of simulation modeling of structural ratcheting.

Polymer spur gears behaviors under different loading conditions: A review

2017 ◽  
Vol 232 (2) ◽  
pp. 210-228 ◽  
Author(s):  
Akant Kumar Singh ◽  
Siddhartha ◽  
Prashant Kumar Singh
Keyword(s):  
Modeling And Simulation ◽  
Polymer Composites ◽  
Tribological Properties ◽  
Failure Modes ◽  
Operating Conditions ◽  
Spur Gears ◽  
Simulation Studies ◽  
Loading Conditions ◽  
Comprehensive Review ◽  
Tooth Modification

The significance of polymer gears to transmit power and motion is increasing continuously due to their inherent characteristics. Polymer gears have established themselves as attractive alternatives to traditional metal gears in plethora applications. They are light in weight, have lower inertia, and run noiseless than their metal counterparts. This article presents a comprehensive review of the research on polymer spur gears operating under low (0–8 Nm) and moderate (>8 and ≤17 Nm) loading conditions. Different polymers and polymer composites used till date for the fabrication of such gears are included along with different operating conditions. Various design features of polymer gears and tooth modification techniques for the improvement of the performance and durability of these gears have also been included in this review. The aspects of the modeling and simulation studies of the polymer gears are also emphasized in this paper for completeness of the review. The concept of hybrid gears is discussed along with their tribological properties. Various methods of manufacturing of polymer gears and their failure modes are discussed so as to make the article useful for researchers.

An Investigation on the Effect of Creep Shakedown on the Creep Behavior of an Industrial Gas Turbine Blade

2015 ◽  
Author(s):  
Jun Zhao ◽  
Ashok K. Koul ◽  
Avisekh Banerjee
Keyword(s):  
Finite Element ◽  
Gas Turbine ◽  
Damage Accumulation ◽  
Creep Damage ◽  
Local Stress ◽  
Operating Conditions ◽  
Time Dependent ◽  
Strain Accumulation ◽  
Accumulation Process ◽  
Creep Life

The creep life computation of gas turbine hot section components using any damage modeling technique requires typical inputs of stress and temperature under actual engine operating conditions. The magnitude of these inputs is governed by the static or dynamic transient loading conditions that a component may be subjected to during service. The long term creep damage accumulation process in a hot section component leads to strain accumulation in the component with time. The rate of change of this strain accumulation in different regions of a component is controlled by the magnitude of the local stress, stress gradient and temperature. In some regions, the creep damage accumulation process may lead to a substantial change in the local stress distribution, also called the “Creep Shakedown”, and this time-dependent stress redistribution can have a substantial impact on the component creep life. The creep shakedown based creep life analysis of a GE Frame 7EA first stage turbine blade under off-design base-load engine operating conditions is studied. The evolution of the stress and strain in different regions of the blade with service time was analyzed using the finite element method. A user defined Garofalo model with hyperbolic sine creep rule was incorporated in the finite element analysis (FEA). The creep shakedown in the component is demonstrated to cause a local time-dependent stress redistribution effect in the FEA simulation. The significant stress variation and creep strain accumulation was observed in the creep critical regions where local stress raisers were present and/or a high temperature gradient due to internal cooling design existed. These effects are discussed in detail from a materials engineering perspective.

Low Cycle Fatigue Analysis of Marine Structures

2006 ◽  
Author(s):  
Xiaozhi Wang ◽  
Joong-Kyoo Kang ◽  
Yooil Kim ◽  
Paul H. Wirsching
Keyword(s):  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Prediction Method ◽  
Local Stress ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Stress Concentrations ◽  
Damage Prediction ◽  
Marine Structure ◽  
Number Of Cycles

There are situations where a marine structure is subjected to stress cycles of such large magnitude that small, but significant, parts of the structural component in question experiences cyclic plasticity. Welded joints are particularly vulnerable because of high local stress concentrations. Fatigue caused by oscillating strain in the plastic range is called “low cycle fatigue”. Cycles to failure are typically below 104. Traditional welded joint S-N curves do not describe the fatigue strength in the low cycle region (< 104 number of cycles). Typical Class Society Rules do not directly address the low cycle fatigue problem. It is therefore the objective of this paper to present a credible fatigue damage prediction method of welded joints in the low cycle fatigue regime.

Numerical Simulation of Stress Relaxation and Creep Response of X20 Steam Piping under Diverse Operating Conditions

2021 ◽  
Vol 57 ◽  
pp. 19-32
Author(s):  
Smith Salifu ◽  
Dawood A. Desai ◽  
Schalk Kok
Keyword(s):  
Steady State ◽  
Stress Relaxation ◽  
Damage Accumulation ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Operating Conditions ◽  
Creep Model ◽  
Element Analysis ◽  
Peak Period ◽  
Creep Response

The creep response and stress relaxation of X20 CrMoV12-1 steam piping under diverse operating conditions were simulated using finite element analysis (FEA) code, Abaqus alongside fe-safe/Turbolife software. In the study, steady-state creep and creep analysis characterized by 24 hours daily cycle consisting of a total of 6 hours peak, 4 hours transient and 14 hours off-peak period was considered. Modified hyperbolic sine creep model used in the analysis was implemented in Abaqus via a special creep user-subroutine to compute the stress relaxation and creep behaviour, while the useful service life and creep damage was estimated using fe-safe/Turbolife. The optimum creep strain, stress, damage, and worst life were found at the intrados of the piping, with the steady-state analysis having a higher useful creep life and slower creep damage accumulation. Furthermore, slower stress relaxation with faster damage accumulation was observed in the analysis involving cycles. Finally, a good agreement was obtained between the analytical calculated and simulated rates of the piping.

scholarly journals Simulation Studies on the Effect of Material Characteristics and Runners Layout Geometry on the Filling Imbalance in Geometrically Balanced Injection Molds

Polymers ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 639 ◽  
Author(s):  
Krzysztof Wilczyński ◽  
Przemysław Narowski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Relaxation Time ◽  
Thermal Diffusivity ◽  
Shear Rate ◽  
Transfer Coefficient ◽  
Operating Conditions ◽  
Optimization Approach ◽  
Simulation Studies ◽  
Layout Geometry

Simulation studies were performed on filling imbalance in geometrically balanced injection molds. A special simulation procedure was applied to simulate properly the phenomenon, including inertia effects and 3D tetrahedron meshing as well as meshing of the nozzle. The phenomenon was investigated by simulation using several different runner systems at various thermo-rheological material parameters and process operating conditions. It has been observed that the Cross-WLF parameters, index flow, critical shear stress (relaxation time), and zero viscosity, as well as thermal diffusivity and heat transfer coefficient strongly affect the filling imbalance. The effect is substantially dependent on the runners’ layout geometry, as well as on the operating conditions, flow rate, and shear rate. The standard layout geometry and the corrected layout with circled element induce positive imbalance which means that inner cavities fills out faster, and it is opposite for the corrected layouts with one/two overturn elements which cause negative imbalance. Generally, for the standard layout geometry and the corrected layout with circled element, an effect of the zero shear rate viscosity η0 is positive (imbalance increases with an increase of viscosity), and an effect of the power law index n and the relaxation time λ is negative (imbalance decreases with an increase of index n and relaxation time λ). An effect of the thermal diffusivity α and heat transfer coefficient h is negative while an effect of the shear rate is positive. For the corrected layouts with one/two overturn elements, the results of simulations indicate opposite relationships. A novel optimization approach solving the filling imbalance problem and a novel concept of global modeling of injection molding process are also discussed.

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