The Residual Stress Decomposition Method (RSDM): A Novel Direct Method to Predict Cyclic Elastoplastic States

2014 ◽  
pp. 139-155 ◽  
Author(s):  
Konstantinos V. Spiliopoulos ◽  
Konstantinos D. Panagiotou
Keyword(s):  
Residual Stress ◽  
Decomposition Method ◽  
Direct Method ◽  
Stress Decomposition

Assessment of the Cyclic Behavior of Structural Components Using Novel Approaches

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
K. D. Panagiotou ◽  
K. V. Spiliopoulos
Keyword(s):  
Residual Stress ◽  
Decomposition Method ◽  
Plastic Material ◽  
Low Cycle Fatigue ◽  
Direct Methods ◽  
Cyclic Behavior ◽  
Loading History ◽  
Perfectly Plastic ◽  
Stress Decomposition ◽  
Safety Margins

To extend the life of a structure, or a component, which is subjected to cyclic thermomechanical loading history, one has to provide safety margins against excessive inelastic deformations that may lead either to low-cycle fatigue or to ratcheting. Direct methods constitute a convenient tool toward this direction. Two direct methods that have been named residual stress decomposition method (RSDM) and residual stress decomposition method for shakedown (RSDM-S) have recently appeared in the literature. The first method may predict any cyclic elastoplastic state for a given cyclic loading history. The second method RSDM-S that is based upon RSDM is suggested for the shakedown analysis of structures. Both methods may be directly implemented in any finite-element (FE) code. An elastic perfectly plastic material with a von Mises yield surface has been assumed. In this work, through their application to structures that are used as benchmarks in the literature, both methods, applied together, prove their efficiency and capacity to determine shakedown boundaries and reveal unsafe conditions.

Residual Stress of Gear Meshing under Shakedown Condition with Direct Analysis

2012 ◽  
Vol 152-154 ◽  
pp. 877-882
Author(s):  
Yuan Yuan ◽  
Peng Fei Li ◽  
Kai Liu
Keyword(s):  
Mathematical Model ◽  
Residual Stress ◽  
Residual Stresses ◽  
Direct Method ◽  
Direct Analysis ◽  
Numerical Approach ◽  
Operating Life ◽  
Operator Split ◽  
Gear Contact ◽  
Residual Stresses And Strains

A shakedown mathematical model of gear contact has been developed. A direct method is applied to solve the mathematical model. Local coordinates are constructed on different meshing points because curvature of gear profile is not constant. Distributions of residual stresses and strains are given base on variable curvature surface. The numerical approach consists of an operator split technique, which transforms the elastic-plastic problem into a purely elastic problem and a residual problem with prescribed eigenstrains. The eigenstrains are determined using an incremental projection method. Contact stresses and contact residual stresses of meshing gear teeth with standard and modified profile are computed. The results show compressive residual stress can improve capacity of gear and operating life. This aspect may contribute to future developments in the understanding of gear durability.

scholarly journals Cyclic Plasticity Analysis of Welded Joint With Welding Residual Stress Using the Direct Method

2019 ◽  
Author(s):  
Manu Puliyaneth ◽  
Haofeng Chen ◽  
Weiling Luan
Keyword(s):  
Residual Stress ◽  
Power Plants ◽  
Direct Method ◽  
Element Model ◽  
Welding Residual Stress ◽  
Cyclic Plasticity ◽  
Energy Demands ◽  
Inelastic Analysis ◽  
Parametric Studies ◽  
Full Interaction

Abstract To meet the growing energy demands, the power sector continuously strives at enhancing the efficiency of its power plants by increasing the operating temperature. Under cyclic loading conditions, this leads to creep-cyclic plasticity driven damage mechanisms such as cyclically enhanced creep, creep enhanced plasticity and creep ratcheting. A detailed understanding of creep and related damages is therefore essential for predicting any potential failure mechanisms and ensuring confidence in the safe-working of the components. This becomes particularly difficult and challenging in the presence of welds due to two main reason; a) presence of different material zones, namely parent metal, weld metal and heat affected zone; b) introduction of residual stress during welding. An extended Direct Steady Cycle Analysis within the Linear Matching Method (LMM) framework has been previously developed to consider the full interaction between creep and cyclic plasticity. This paper presents the basic theory and an overview behind the LMM framework along with a new application of a welded flange, considering for the first time the effect of residual stress due to welding. A 3D finite element model is adopted for the flange, and it is subjected to a constant pressure and cyclic thermal load of varying dwell. The effects of welding residual stress on the creep-cyclic plastic response of the welded flange are investigated. Additional parametric studies considering different levels of the applied load and dwell period are performed. The results reflect the ease of using LMM over conventional inelastic analysis.

Characterization of frozen hydrated biological specimens by low-loss EELS

1992 ◽  
Vol 50 (2) ◽  
pp. 1572-1573
Author(s):  
Songquan Sun ◽  
Richard D. Leapman
Keyword(s):  
Water Content ◽  
Direct Method ◽  
Internal Standard ◽  
Dry Weight ◽  
Dark Field ◽  
Protein Solutions ◽  
Subcellular Compartment ◽  
Differential Shrinkage ◽  
Electron Energy Loss

Analyses of ultrathin cryosections are generally performed after freeze-drying because the presence of water renders the specimens highly susceptible to radiation damage. The water content of a subcellular compartment is an important quantity that must be known, for example, to convert the dry weight concentrations of ions to the physiologically more relevant molar concentrations. Water content can be determined indirectly from dark-field mass measurements provided that there is no differential shrinkage between compartments and that there exists a suitable internal standard. The potential advantage of a more direct method for measuring water has led us to explore the use of electron energy loss spectroscopy (EELS) for characterizing biological specimens in their frozen hydrated state.We have obtained preliminary EELS measurements from pure amorphous ice and from cryosectioned frozen protein solutions. The specimens were cryotransfered into a VG-HB501 field-emission STEM equipped with a 666 Gatan parallel-detection spectrometer and analyzed at approximately −160 C.

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