A Plasticity Model for Cyclic Strain Accumulation

1971 ◽  
Vol 38 (4) ◽  
pp. 869-874 ◽  
Author(s):  
T. M. Mulcahy
Keyword(s):  
Cyclic Strain ◽  
Cyclic Creep ◽  
Plasticity Model ◽  
Strain Accumulation ◽  
Structural Elements ◽  
Load Cycling ◽  
Accumulation Phenomenon ◽  
Stress States

A general plasticity model is developed which is able to predict a cyclic strain accumulation phenomenon, sometimes called cyclic creep. To assess the consequences of the phenomenon for nonhomogeneous stress states, simple forms of the model are used in the analysis of two idealized structural elements. Very large stresses are found to develop for continued load cycling.

Overview of Proposed High Temperature Design Code Cases

2016 ◽  
Author(s):  
Peter Carter ◽  
T.-L. (Sam) Sham ◽  
Robert I. Jetter
Keyword(s):  
High Temperature ◽  
Yield Stress ◽  
Creep Damage ◽  
Cyclic Strain ◽  
Inelastic Strain ◽  
Cyclic Creep ◽  
Strain Accumulation ◽  
Temperature Dependent ◽  
Common Basis ◽  
Creep Fatigue

Proposals for high temperature design methods have been developed for primary loads, creep-fatigue and strain limits. The methodologies rely on a common basis and assumption, that elastic, perfectly plastic analysis based on appropriate properties reflects the ability of loads and stress to redistribute for steady and cyclic loading for high temperature as well as for conventional design. The cyclic load design analyses rely on a further key property, that a cyclic elastic-plastic solution provides an upper bound to displacements, strains and local damage rates. The primary load analysis ensures that the design load is in equilibrium with the code allowable stress, taking into account: i) The stress state dependent (multi-axial) rupture criterion, ii) The limit to stress re-distribution defined by the material creep law. The creep-fatigue analysis is focused on the cyclic creep damage calculation, and uses conventional fatigue and creep-fatigue damage calculations. It uses a temperature-dependent pseudo “yield” stress defined by the material yield and rupture data to identify cycles which will not cause creep damage > 1 for the selected life. Similarly the strain limits analysis bounds cyclic strain accumulation. It also uses a temperature-dependent pseudo “yield” stress defined by the material yield and creep strain accumulation data to identify cycles which will not cause average (membrane) inelastic strain > 1% for the design life. The paper gives an overview of the background and justification of these statements, and examples.

Photoelast Method and Possible Applications of Mathematical Statistics in Prediction of Stress State of Structural Elements

2014 ◽  
Vol 611 ◽  
pp. 405-411 ◽  
Author(s):  
Oskar Ostertag ◽  
Eva Ostertagová ◽  
Peter Frankovský
Keyword(s):  
Stress State ◽  
Stress Concentration ◽  
Stress Field ◽  
Statistical Methods ◽  
Mathematical Statistics ◽  
Structural Elements ◽  
State Development ◽  
Stress States ◽  
Structural Parts

The presented article is dedicated to stress state development while assessing the concentration of stresses in samples with continuously changing notches. These samples represent connecting elements of structural parts. The stress states of selected samples were determined experimentally by means of reflection photoelasticity. This method is suitable mainly for determination of stress state in the whole area in question, predominantly though for the analysis of stress concentration and its gradient in the notched area. Within the method of reflection photoelasticity, a layer was used to analyse the stress field. When loaded, this layer exhibits the ability of temporal birefringence. One of the statistical methods was selected in order to predict the stress state of other samples with bigger notches.

A Parametric Approach to Cyclic Creep

1976 ◽  
Vol 43 (1) ◽  
pp. 28-32
Author(s):  
V. M. Radhakrishnan
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Maximum Stress ◽  
Pure Aluminum ◽  
Cyclic Creep ◽  
Steady State Creep ◽  
Strain Accumulation ◽  
Parametric Approach ◽  
Steady State Creep Rate ◽  
Reference Stress

Investigations have been carried out to study the effect of oscillating stress on the strain accumulation in pure aluminum at elevated temperature. The creep rate under the oscillating stress has been found to increase with increasing value of the alternating component of the stress and is somewhat higher than the steady-state creep rate corresponding to the maximum stress, in the range of temperature used. The rupture time is inversely proportional to the cyclic creep rate. A model for obtaining the reference stress has been proposed and based on the data obtained, a parametric approach is presented.

Dwell Sensitive Fatigue Response of Titanium Alloys for Power Plant Applications

2002 ◽  
Vol 125 (1) ◽  
pp. 241-245 ◽  
Author(s):  
M. R. Bache ◽  
W. J. Evans
Keyword(s):  
Titanium Alloys ◽  
Fatigue Testing ◽  
Cyclic Strain ◽  
Peak Stress ◽  
Strain Accumulation ◽  
Cleavage Facet ◽  
Fundamental Cause ◽  
Temperature Strain ◽  
Facet Formation

The phenomenon of “dwell sensitivity” in the α+β and near α titanium alloys and the intrinsic relationship with quasi-cleavage facet formation is discussed. In the present paper, particular emphasis is placed upon the role of “cold creep” and ambient temperature strain accumulation under cyclic loading. A process of stress redistribution between microstructurally distinct regions that demonstrate different strengths is proposed as the fundamental cause of facet development and subsequent dwell failures. A model to describe the redistribution process is validated through a matrix of fatigue testing designed to assess the effects of microstructural form, stress axiality, and periods of dwell loading at peak stress on cyclic strain accumulation.

Effect of High-Strain Fatigue Cycles on the Brittle-Ductile Transition of Two Mild Steels

1965 ◽  
Vol 7 (1) ◽  
pp. 93-100 ◽  
Author(s):  
D. J. Harris ◽  
P. P. Benham
Keyword(s):  
Axial Strain ◽  
Fatigue Cracks ◽  
Tensile Load ◽  
Strain Range ◽  
Cyclic Strain ◽  
Notched Specimens ◽  
Brittle Ductile Transition ◽  
Load Cycling ◽  
Number Of Cycles ◽  
Strain Cycling

Low endurance fatigue curves were obtained for grades A and D mild steel under the following axial conditions: reversed load cycling—plain specimens; repeated tensile load cycling—plain specimens (grade A only); reversed strain cycling—plain material; reversed strain cycling—notched material. Some results were also obtained for reversed strain cycling in bending of notched specimens. The fatigue results were generally as expected, the grade D steel showing a slightly superior fatigue strength. The major part of the programme was then concerned with the effect of plastic strain cycling on the brittle fracture transition behaviour. Prior axial strain cycling initiated fairly blunt fatigue cracks after only a few cycles in all notched specimens and the Tipper test transition was lowered by about 10°C for the grade A steel, but there was little effect on the grade D material. The Charpy transition temperature was raised by various amounts (20°C maximum), depending on the cyclic strain range, number of cycles and type of steel.

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