A probabilistic Haigh diagram for notched components considering notch root plasticity due to high mean stresses

2020 ◽  
Vol 140 ◽  
pp. 105813
Author(s):  
Alexander Klawonn ◽  
Tilmann Beck
Keyword(s):  
Notch Root ◽  
Root Plasticity ◽  
Mean Stresses ◽  
Notched Components

The Use of Strain Energy and Fracture Correlation to Determine Life Expectancy for Notched Components

2009 ◽  
Author(s):  
Onome Scott-Emuakpor ◽  
Tommy George ◽  
Charles Cross ◽  
M.-H. Herman Shen
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Cross Section ◽  
Strain Energy ◽  
Notch Root ◽  
Stress Gradient ◽  
Strain Curve ◽  
Experimental Results ◽  
Cyclic Process ◽  
Notched Components

An energy-based method for predicting fatigue life of half-circle notched specimens, based on the nominal applied stress amplitude, has been developed. This developed method is based on the understanding that the total strain energy dissipated during a monotonic fracture and a cyclic process is the same material property, where the density of each can be determined by measuring the area underneath the monotonic true stress-strain curve and measuring the sum of the area within each Hysteresis loop in the cyclic process, respectively. Using this understanding, the criterion for determining fatigue life prediction of half-circle notched components is constructed by incorporating the stress gradient effect through the notch root cross-section. Though fatigue at a notch root is a local phenomenon, evaluation of the stress gradient through the notch root cross-section is essential for incorporating this method into finite element analysis minimum potential energy process. The validation of this method was carried out by comparison with both notched and unnnotched experimental fatigue life of Aluminum 6061-T6 (Al 6061-T6) specimens under tension/compression loading at the theoretical notch fatigue stress concentration factor of 1.75. The comparison initially showed a slight deviation between prediction and experimental results. This led to the analysis of strain energy density per cycle up to failure, and an improved Hysteresis representation for the energy-based prediction analysis. With the newly developed Hysteresis representation, the energy-based prediction comparison shows encouraging agreement with unnotched experimental results and a theoretical notch stress concentration value.

scholarly journals A cloud-based fatigue analysis tool with interactive Neuber’s master curve

2019 ◽  
Vol 300 ◽  
pp. 08006
Author(s):  
Daniel Kujawski
Keyword(s):  
Master Curve ◽  
Educational Software ◽  
Hot Spot ◽  
Notch Root ◽  
Hysteresis Loops ◽  
Fatigue Analysis ◽  
Analysis Tool ◽  
Life Estimation ◽  
Fatigue Life Estimation ◽  
Notched Components

A cloud-based fatigue analysis and life prediction tool is presented. Users around the globe may access it via Internet by means of multiple platforms such as desktop and laptop computers, tablets and/or smart-phones. It is an intuitive educational software, aimed also to assist designers in the pre-prototyping stage in fatigue life estimation for smooth or notched parts subjected to constant amplitude, block loading, and spectrum loading histories. For spectrum amplitude loading a dedicated spectrum software package is provided, which is essential for a potential clean-up and/or desired modifications of a raw spectrum data. Subsequently, a rainflow method is utilized and the corresponding hysteresis loops at the notch-root or critical “hot spot” location are determined and plotted. For notched components, an interactive Neuber’s master curve is utilized and discussed. It is shown, that the Neubers’s master curve is only material dependent and is applicable for both monotonic and cyclic loading situations.

Fatigue Life Prediction of Notched Components Based on Multiaxial Local Stress-Strain Approach

2009 ◽  
Author(s):  
Baoxiang Qiu ◽  
Zengliang Gao ◽  
Xiaogui Wang
Keyword(s):  
Strain State ◽  
Notch Root ◽  
Constitutive Relations ◽  
Local Stress ◽  
Cyclic Plasticity ◽  
Multiaxial Stress ◽  
Stress Strain ◽  
Stress Strain State ◽  
Multiaxial Stress State ◽  
Notched Components

A multiaxial local stress-strain approach based on the Armstrong-Frederick type cyclic plasticity theory was proposed to perform the stress analysis and the fatigue analysis on the notched components. A robust cyclic plasticity model was adopted to describe the non-Masing behavior of 16MnR steel. The incremental form of the multiaxial local stress-strain approach was formulated with the incremental constitutive relations and the incremental Neuber’s rule. The multiaxial stress-strain state at the notch root of notched components subjected to proportional and nonproportional loading was predicted by the multiaxial approximate approach. On the basis of the multiaxial local stress-strain state and the Fatemi-Socie criterion, the fatigue lives of the notched components were predicted. The analytical results show that the proposed multiaxial local stress-strain method can describe the multiaxial stress state at the notch root very well, and the predicted fatigue lives correlate well with the experimental data.

Long-Life Notch Strength Reduction Due to Local Biaxial State of Stress

1977 ◽  
Vol 99 (3) ◽  
pp. 215-221 ◽  
Author(s):  
B. N. Leis ◽  
T. H. Topper
Keyword(s):  
Notch Root ◽  
Three Dimensional ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Experimental Investigations ◽  
Strength Reduction Factor ◽  
Long Life ◽  
Predicted Values ◽  
Notch Strength ◽  
Notched Components

An explanation for the observed difference between the values of the long-life, fatigue-notch strength-reduction factor (Kf) and the elastic stress concentration factor based on the influence of biaxial-notch root stresses is presented for a limited class of problems for which the local stresses are elastic. Results of three-dimensional linear elasticity solutions for notch stresses are reviewed and then used in conjunction with a biaxial fatigue criterion suitable for elastic straining to predict values of Kf for a variety of notched components for which values have been experimentally determined. Comparison of actual and predicted values of Kf indicates a close correspondence suggesting that the influence of local biaxial stresses on the life to crack initiation of notched components is responsible for the reduced notch severity observed in many of the experimental investigations of long-life (fatigue) notch sensitivity.

scholarly journals Approximation of elastic-plastic local strains in surface-hardened notched components

2021 ◽  
Vol 349 ◽  
pp. 04008
Author(s):  
Patrick Yadegari ◽  
Teresa Schlitzer ◽  
Michael Vormwald
Keyword(s):  
Notch Root ◽  
Core Material ◽  
Plastic Strains ◽  
Local Strains ◽  
Elastic Plastic ◽  
Approximation Formulas ◽  
Potential Failure ◽  
Structural Failures ◽  
Step Algorithm ◽  
Notched Components

Elastic-plastic strains at points relevant for structural failures are usually approximated using formulas based on the stresses determined by elasticity theory. For this purpose, the Neuber approximation is a common method to estimate the local elastic-plastic strains in the notch root, although this is currently only approved for homogeneous components. For surfacehardened notched components, these approximation formulas need to be modified to cover two potential failure points: The notch root as well as the interface between the stronger surface layer and the weaker core material. In the following, a multi-step algorithm is shown that allows the estimation of elastic-plastic local strains at these two points, based on a single elasticitytheoretical solution. A comparison of the approximated values with those from finite element analyses (FEA) reveals that this results in only minor inaccuracies, while the usability is remarkable.

A New Extreme-Value Probabilistic Framework for Predicting Fatigue Crack Initiation Life of Notched Components

2011 ◽  
Author(s):  
Gbadebo Owolabi ◽  
Horace Whitworth
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Strain Field ◽  
Life Prediction ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Fatigue Life Prediction ◽  
Probabilistic Framework ◽  
Notched Components

Traditional deterministic methods for predicting the fatigue life of notched components require a number of approximations based on heuristics and phenomenological data rather than solid theoretical underpinning and still yield unsatisfactory and inconsistent results when applied to complex components under service loads. Microstructural inhomogeneities in the materials are still an important issue, but are not explicitly accounted for in the traditional deterministic methods. Recent developments in computational crystal plasticity and microstructure-scale modeling have provided deeper understanding of the complex correlations between properties and structures and further indicate the limitations of conventional fatigue life prediction approaches. These modeling approaches have the potential to substantially reduce the need for costly large scale experimental programs to determine scatter in fatigue, for example. At present, however, there is a lack of simulation-based strategy for considering interactive effects of stress/strain field gradients at the notch-root and microstructure-scale behavior in predicting notch-root fatigue crack initiation. In this paper, the distribution of a shear-based fatigue indicator parameter computed within a well-defined fatigue damage process zone at the notch are used along with a novel probabilistic mesomechanics approach to obtain the probability distribution of fatigue crack initiation of notched components, thus extending fatigue life prediction to explicitly incorporate microstructure sensitivity via probabilistic arguments. The new probabilistic framework presented in this paper takes into account the complete plastic shear strain field around the notch root and also links the variation in the materials microstructure and associated slip activations to observable scatter in fatigue strength of the notched component. The use of such probabilistic approach can be beneficial as it avoids conservatism that may result from the use of deterministic approach for fatigue life prediction.

Fatigue Failure Analysis Using the Theory of Critical Distance

2011 ◽  
Vol 462-463 ◽  
pp. 663-667 ◽  
Author(s):  
Ruslizam Daud ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Al Emran Ismail
Keyword(s):  
Stress Concentration ◽  
Fatigue Failure ◽  
Notch Root ◽  
High Stress ◽  
Critical Distance ◽  
Future Research ◽  
Element Analysis ◽  
Linear Elastic ◽  
The Finite Element Analysis ◽  
Elastic Fracture

This paper explores the initial potential of theory of critical distance (TCD) which offers essential fatigue failure prediction in engineering components. The intention is to find the most appropriate TCD approach for a case of multiple stress concentration features in future research. The TCD is based on critical distance from notch root and represents the extension of linear elastic fracture mechanics (LEFM) principles. The approach is allowing possibilities for fatigue limit prediction based on localized stress concentration, which are characterized by high stress gradients. Using the finite element analysis (FEA) results and some data from literature, TCD applications is illustrated by a case study on engineering components in different geometrical notch radius. Further applications of TCD to various kinds of engineering problems are discussed.

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