Estimation of plastic constraint and local strain at the notch root for notched plates and bars.

1990 ◽  
Vol 56 (528) ◽  
pp. 1861-1867
Author(s):  
Hiroshi UMEDA ◽  
Toshiki ENDO ◽  
Katsuhiko MOTOIE
Keyword(s):  
Notch Root ◽  
Local Strain ◽  
Plastic Constraint

Life Prediction for Notched Components in Nonproportional Low Cycle Fatigue: Experiment and FEM Analysis

2004 ◽  
Author(s):  
Masao Sakane ◽  
Tsuneo Itoh ◽  
Tomoshige Susaki ◽  
Yoshiyasu Kawazoe
Keyword(s):  
Crack Initiation ◽  
Linear Models ◽  
Low Cycle Fatigue ◽  
Notch Root ◽  
Fem Analysis ◽  
Local Strain ◽  
304 Stainless Steel ◽  
Cycle Fatigue ◽  
Notched Specimens ◽  
Strain Paths

This paper studies the low cycle fatigue of circumferential notched specimens of type 304 stainless steel in nonproportional loading. Strain controlled tension-torsion low cycle fatigue tests were carried out using the notched specimens under 15 strain paths. Crack initiation lives detected by a d.c. potential method were discussed in relation to the strain concentration factors and strain histories. Finite element analyses were carried out for evaluating the local strain at the notch root using elastic-perfectly plastic and bi-linear models. The maximum principal strain and nonproportional strain ranges conservatively estimated the crack initiation lives of the notched specimens.

scholarly journals Determination of Local Stresses and Strains within the Notch Strain Approach: Efficient Implementation of Notch Root Approximations

2021 ◽  
Vol 11 (21) ◽  
pp. 10339
Author(s):  
Ralf Burghardt ◽  
Lukas Masendorf ◽  
Michael Wächter ◽  
Alfons Esderts
Keyword(s):  
Service Life ◽  
Newton’S Method ◽  
Newton's Method ◽  
Notch Root ◽  
Local Strain ◽  
Computational Accuracy ◽  
Life Estimation ◽  
Computational Performance ◽  
Service Life Estimation

An estimation of the elastic-plastic stress state using elasticity-theoretical input data is an essential part of the service life estimation with the local strain approach in general and a German guideline based on it, in particular. This guideline uses two different notch root approximations (an extended version of Neuber’s rule and an approach according to Seeger and Beste) for this estimation. Both require the implementation of Newton’s method to be iteratively solved. However, many options are left open to the user concerning implementation in program code. This paper discusses ways in which notch root approximation methods can be implemented efficiently for use in software systems and elaborates an application recommendation. The following aspects and their influence on the computational accuracy and performance of Newton’s method are considered in detail: influence of the formulation of the root finding problem, determination of the derivative required for Newton’s method and influence of the termination criterion. The investigation shows that the advice given in the abovementioned guideline indeed leads to a conservative implementation. By carefully considering the investigated aspects, however, the computational performance can be increased by approximately a factor of 2–3 without influencing the accuracy of the service life estimation.

Local Crack-Tip Strain Concept for Fatigue Crack Initiation and Propagation

1987 ◽  
Vol 109 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Heihachi Shimada ◽  
Yasubumi Furuya
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Local Strain ◽  
Strain History ◽  
Crack Initiation And Propagation ◽  
Fine Grid ◽  
Initiation And Propagation

The existence of the unified local strain field where we can substantially combine the two fatigue stages, crack initiation and propagation, was experimentally confirmed. Using the fine-grid-method, the changes of local notch-root or crack-tip strain and these histories were investigated until the small elemental block of material was broken by crack initiation and propagation. It became clear that the crack-tip strain behavior and its fracture process showed the similarity with local strain damage accumulation on crack initiation process. Especially, when the local strain history in the “elemental size, ρ*” adjacent to the crack-tip was taken into account, very good agreement of two stages could be obtained, ρ* depended on the kind of material. Based on this result, we have proposed a new idea termed “local crack-tip strain concept” that has the possibility for more simple, one parameter approach for future fatigue life analysis. It qualitatively differs from the currently used macroscopic, two parameters approach by combining the gross-strain (Δεtotal) fatigue life curve and fracture mechanics parameter (ΔK).

An Evaluation of the Neuber and Glinka Relations for Monotonic Loading

1992 ◽  
Vol 59 (2S) ◽  
pp. S50-S56 ◽  
Author(s):  
W. N. Sharpe ◽  
C. H. Yang ◽  
R. L. Tregoning
Keyword(s):  
Plane Strain ◽  
Plane Stress ◽  
Low Cycle Fatigue ◽  
Notch Root ◽  
Strain Range ◽  
Local Strain ◽  
Strain Response ◽  
Cycle Fatigue ◽  
Stress Concentrations ◽  
Strain Model

The Neuber relation is widely used to compute elastoplastic stresses and strains at stress concentrations, but a newer relation has been developed by Glinka. Prediction of local strain response is important because low cycle, fatigue life models are based on the strain range. The effects of notch root constraint on the response have been difficult to predict or measure. This paper evaluates the abilities of six models of notch root behavior by comparing them with experimental results over a range of constraints. The models are: the Neuber model, the Neuber model as modified by Walker, the Glinka models for plane stress and for plane strain, and two modifications of the Glinka models that are presented in this paper. Comparisons are made with strains measured at the roots of notches by resistance gages or by laser-based interferometry; data come from previous works as well as some new results of the authors. The constraints vary from plane stress to plane strain with several intermediate cases. Conclusions must take into account the fact that elastoplastic strain measurements have scatter arising from the gage length relative to the grain size. But, in general, one can say that the Neuber model is best for plane stress and the Glinka plane-strain model is best for very large constraint. Response for intermediate amounts of constraint are predicted better by one of the other models.

Quantitative analysis of in situ straining experiments in the case of strong frictional forces

1978 ◽  
Vol 36 (1) ◽  
pp. 570-571
Author(s):  
F. Louchet ◽  
L.P. Kubin
Keyword(s):  
Strain Rate ◽  
Radiation Effects ◽  
Dislocation Line ◽  
Critical Length ◽  
Local Strain ◽  
Local Flow ◽  
Double Kink ◽  
Dislocation Densities ◽  
Frictional Forces ◽  
Local Strain Rate

Investigation of frictional forces -Experimental techniques and working conditions in the high voltage electron microscope have already been described (1). Care has been taken in order to minimize both surface and radiation effects under deformation conditions.Dislocation densities and velocities are measured on the records of the deformation. It can be noticed that mobile dislocation densities can be far below the total dislocation density in the operative system. The local strain-rate can be deduced from these measurements. The local flow stresses are deduced from the curvature radii of the dislocations when the local strain-rate reaches the values of ∿ 10-4 s-1.For a straight screw segment of length L moving by double-kink nucleation between two pinning points, the velocity is :where ΔG(τ) is the activation energy and lc the critical length for double-kink nucleation. The term L/lc takes into account the number of simultaneous attempts for double-kink nucleation on the dislocation line.

TEM and cathodoluminescence of precipitates in II-VI semiconductors

1988 ◽  
Vol 46 ◽  
pp. 488-489
Author(s):  
Joanna L. Batstone
Keyword(s):  
Crystal Growth ◽  
Band Gap ◽  
Local Strain ◽  
Wide Band ◽  
Optoelectronic Device ◽  
Wide Band Gap ◽  
Bulk Crystal Growth ◽  
Transmission Electron ◽  
Device Applications ◽  
Stoichiometry Control

Interest in II-VI semiconductors centres around optoelectronic device applications. The wide band gap II-VI semiconductors such as ZnS, ZnSe and ZnTe have been used in lasers and electroluminescent displays yielding room temperature blue luminescence. The narrow gap II-VI semiconductors such as CdTe and HgxCd1-x Te are currently used for infrared detectors, where the band gap can be varied continuously by changing the alloy composition x.Two major sources of precipitation can be identified in II-VI materials; (i) dopant introduction leading to local variations in concentration and subsequent precipitation and (ii) Te precipitation in ZnTe, CdTe and HgCdTe due to native point defects which arise from problems associated with stoichiometry control during crystal growth. Precipitation is observed in both bulk crystal growth and epitaxial growth and is frequently associated with segregation and precipitation at dislocations and grain boundaries. Precipitation has been observed using transmission electron microscopy (TEM) which is sensitive to local strain fields around inclusions.

Strain analysis with nanometer resolution using a conventional transmission electron microsopy technique: electron diffraction contrast imaging revisited

1995 ◽  
Vol 53 ◽  
pp. 168-169
Author(s):  
Koenraad G F Janssens ◽  
Omer Van der Biest ◽  
Jan Vanhellemont ◽  
Herman E Maes ◽  
Robert Hull
Keyword(s):  
Electron Diffraction ◽  
Strain Field ◽  
Elastic Strain ◽  
Strain Analysis ◽  
Local Strain ◽  
Contrast Imaging ◽  
Strain Characterization ◽  
Physical Mechanisms ◽  
Diffraction Contrast ◽  
Transmission Electron

There is a growing need for elastic strain characterization techniques with submicrometer resolution in several engineering technologies. In advanced material science and engineering the quantitative knowledge of elastic strain, e.g. at small particles or fibers in reinforced composite materials, can lead to a better understanding of the underlying physical mechanisms and thus to an optimization of material production processes. In advanced semiconductor processing and technology, the current size of micro-electronic devices requires an increasing effort in the analysis and characterization of localized strain. More than 30 years have passed since electron diffraction contrast imaging (EDCI) was used for the first time to analyse the local strain field in and around small coherent precipitates1. In later stages the same technique was used to identify straight dislocations by simulating the EDCI contrast resulting from the strain field of a dislocation and comparing it with experimental observations. Since then the technique was developed further by a small number of researchers, most of whom programmed their own dedicated algorithms to solve the problem of EDCI image simulation for the particular problem they were studying at the time.

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