The Correlation of Fatigue Crack Growth Rates in Rubber Subjected to Multiaxial Loading Using Continuum Mechanical Parameters

2007 ◽  
Vol 80 (1) ◽  
pp. 169-182 ◽  
Author(s):  
W. V. Mars ◽  
A. Fatemi
Keyword(s):  
Energy Density ◽  
Crack Growth ◽  
Growth Rates ◽  
Test Piece ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Driving Forces ◽  
Mechanical Parameters ◽  
Small Cracks ◽  
Crack Growth Rates

Abstract Although both the crack nucleation and growth stages of the fatigue failure process in rubber are manifestations of the same characteristic material behavior, the nucleation stage deserves special attention. In this case, continuum mechanical parameters may be used to characterize the driving forces of small cracks, without reference to the geometry of the test piece. The ability to estimate crack driving forces from continuum mechanical parameters during the growth process of small cracks has been investigated by correlating three different parameters (maximum principal strain, strain energy density, and cracking energy density) to rates of crack growth observed photographically during fatigue tests on initially uncracked specimens. Significant scatter in crack growth rates was observed resulting from high crack density and crack interactions. These results are also compared to crack growth measurements made on a pure shear (planar tension) test piece. The difference between continuum parameters that refer to a specific material plane, and those that do not is emphasized. Generally, the maximum principal strain and cracking energy density parameters provided similar levels of correlation. The strain energy density parameter consistently gave the poorest correlation. An advantage of the cracking energy density is that it considers the experiences of specific planes embedded in the material (i.e. it is a plane-specific parameter).

Fatigue crack propagation prediction of a pressure vessel mild steel based on a strain energy density model

2017 ◽  
Author(s):  
P. J. Huffman ◽  
J. Ferreira ◽  
J.A.F.O. Correia ◽  
A.M.P. De Jesus ◽  
G. Lesiuk ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Energy Density ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Pressure Vessel ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Propagation Model ◽  
Crack Growth Rates

Fatigue crack growth (FCG) rates have traditionally been formulated from fracture mechanics, whereas fatigue crack initiation has been empirically described using stress-life or strain-life methods. More recently, there has been efforts towards the use of the local stress-strain and similitude concepts to formulate fatigue crack growth rates. A new model has been developed which derives stress-life, strain-life and fatigue crack growth rates from strain energy density concepts. This new model has the advantage to predict an intrinsic stress ratio effect of the form ?ar=(?amp)?·(?max )(1-?), which is dependent on the cyclic stress-strain behaviour of the material. This new fatigue crack propagation model was proposed by Huffman based on Walkerlike strain-life relation. This model is applied to FCG data available for the P355NL1 pressure vessel steel. A comparison of the experimental results and the Huffman crack propagation model is made.

scholarly journals Microstructurally small fatigue crack growth rates in aluminium alloys for developing improved predictive models

2018 ◽  
Vol 165 ◽  
pp. 13004
Author(s):  
Madeleine Burchill ◽  
Simon Barter ◽  
Lok Hin Chan ◽  
Michael Jones
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Growth Rates ◽  
Small Crack ◽  
Fatigue Crack Nucleation ◽  
Standard Material ◽  
Growth Phenomenon ◽  
Small Cracks ◽  
Small Crack Growth ◽  
Crack Growth Rates

The fatigue or durability life of a few critical structural metallic components often sets the safe and/or economic useful life of a military airframe. In the case of aluminium airframe components, growth rates, at or soon after fatigue crack nucleation are being driven by near threshold local cyclic stress intensities and thus are very low. Standard crack growth rate data is usually generated from large cracks, and therefore do not represent the growth of small cracks (typically <1mm). Discussed here is an innovative test and analysis technique to measure the growth rates of small cracks growing as the result of stress intensities just above the cyclic growth threshold. Using post-test quantitative fractographic examination of fatigue crack surfaces from a series of 7XXX test coupons, crack growth rates and observations of related growth phenomenon in the threshold region have been made. To better predict small crack growth rates under a range of aircraft loading spectra a method by which standard material data models could be adapted is proposed. Early results suggest that for small cracks this method could be useful in informing engineers on the relative severity of various spectra and leading to more accurate predictions of small crack growth rates which can dominate the fatigue life of airframe components.

scholarly journals Improved computation method in residual life estimation of structural components

2013 ◽  
Vol 40 (2) ◽  
pp. 247-261
Author(s):  
Stevan Maksimovic ◽  
Katarina Maksimovic
Keyword(s):  
Fatigue Crack ◽  
Energy Density ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Computation Method ◽  
Structural Components

This work considers the numerical computation methods and procedures for the fatigue crack growth predicting of cracked notched structural components. Computation method is based on fatigue life prediction using the strain energy density approach. Based on the strain energy density (SED) theory, a fatigue crack growth model is developed to predict the lifetime of fatigue crack growth for single or mixed mode cracks. The model is based on an equation expressed in terms of low cycle fatigue parameters. Attention is focused on crack growth analysis of structural components under variable amplitude loads. Crack growth is largely influenced by the effect of the plastic zone at the front of the crack. To obtain efficient computation model plasticity-induced crack closure phenomenon is considered during fatigue crack growth. The use of the strain energy density method is efficient for fatigue crack growth prediction under cyclic loading in damaged structural components. Strain energy density method is easy for engineering applications since it does not require any additional determination of fatigue parameters (those would need to be separately determined for fatigue crack propagation phase), and low cyclic fatigue parameters are used instead. Accurate determination of fatigue crack closure has been a complex task for years. The influence of this phenomenon can be considered by means of experimental and numerical methods. Both of these models are considered. Finite element analysis (FEA) has been shown to be a powerful and useful tool1,6 to analyze crack growth and crack closure effects. Computation results are compared with available experimental results.

Prediction of Environmentally Assisted Cracking on Gas and Liquid Pipelines

2006 ◽  
Author(s):  
J. Been ◽  
R. Eadie ◽  
R. Sutherby
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Pressure Fluctuations ◽  
Low Frequencies ◽  
Small Pressure ◽  
Environmentally Assisted Cracking ◽  
Pressure Time ◽  
Growing Crack ◽  
Small Cracks ◽  
Crack Growth Rates

A model has been developed to predict crack growth on pipelines from environmentally assisted cracking in near-neutral pH environments (often-termed low-pH stress corrosion cracking (SCC)). The model is based on the results of cyclic loading experiments and is used in conjunction with pressure time variations in the pipeline determined from the operating SCADA records to predict the growth of an assumed existing crack in the pipe. The crack grows through different crack growth regimes, which are determined by the size of the pressure variations and the instantaneous crack dimensions. For a growing crack that experiences relatively high pressure fluctuations, as often encountered on liquid lines, reasonable crack growth predictions were made based on corrosion fatigue. An approach based on crack tip strain rate appears more suitable for the prediction of crack growth of small cracks and for cracks on gas lines with small pressure fluctuations. The model is designed so that the effect of stress intensifiers (like the long seam weld crown) that are often associated with these failures can be included. The model can be used in its present format for prioritizing inspections on both gas and liquid pipelines. Whereas predicted crack growth rates compare favorably with rates measured in the field, further work is required to incorporate additional mechanical and environmental effects, in particular to improve the prediction of small crack growth rates. Low crack velocities may be possible in the presence of small pressure fluctuations and low frequencies, but they may be less probable.

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