Fractals and Catastrophe Analysis of Fatigue Crack Propagation for Sample by Plastic Deformation

2011 ◽  
Vol 399-401 ◽  
pp. 2169-2172
Author(s):  
Yu Xin Yao
Keyword(s):  
Plastic Deformation ◽  
Fractal Dimension ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Stress Cycle ◽  
Fractal Characteristics ◽  
Stress Cycles ◽  
The Law

Fractals and catastrophe analysis are applied to analyze photos of the law of crack of three sets of fatigue samples under different stress cycles. The results indicate that the law of crack has fractal characteristics. For undestroyed samples, the law of crack appears and develops, and the fractal dimension tends to be constant eventually. For destroyed samples, fractal dimension development is divided into four stages, that is, increasing gradually, increasing stably, decreasing stably and decreasing rapidly to the approximate value of one. When rupture occurs, the catastrophe point is the corresponding number of stress cycle.

Pre-Strain Effects on Mixed-Mode Fatigue Crack Propagation Behaviour of the P355NL1 Pressure Vessels Steel

2018 ◽  
Author(s):  
João Ferreira ◽  
José A. F. O. Correia ◽  
Grzegorz Lesiuk ◽  
Sergio Blasón González ◽  
Maria Cristina R. Gonzalez ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Mixed Mode ◽  
Pressure Vessels ◽  
Mode I ◽  
Pure Mode

Pressure vessels and piping are commonly subjected to plastic deformation during manufacturing or installation. This pre-deformation history, usually called pre-strain, may have a significant influence on the resistance against fatigue crack growth of the material. Several studies have been performed to investigate the pre-strain effects on the pure mode I fatigue crack propagation, but less on mixed-mode (I+II) fatigue crack propagation conditions. The present study aims at investigating the effect of tensile plastic pre-strain on fatigue crack growth behavior (da/dN vs. ΔK) of the P355NL1 pressure vessel steel. For that purpose, fatigue crack propagation tests were conducted on specimens with two distinct degrees of pre-strain: 0% and 6%, under mixed mode (I+II) conditions using CTS specimens. Moreover, for comparison purposes, CT specimens were tested under pure mode I conditions for pre-strains of 0% and 3%. Contrary to the majority of previous studies, that applied plastic deformation directly on the machined specimen, in this work the pre-straining operation was carried out prior to the machining of the specimens with the objective to minimize residual stress effects and distortions. Results revealed that, for the P355NL1 steel, the tensile pre-strain increased fatigue crack initiation angle and reduced fatigue crack growth rates in the Paris region for mixed mode conditions. The pre-straining procedure had a clear impact on the Paris law constants, increasing the coefficient and decreasing the exponent. In the low ΔK region, results indicate that pre-strain causes a decrease in ΔKth.

Fatigue crack propagation modes: plastic deformation mode and damage accumulation mode

2020 ◽  
Vol 222 (1-2) ◽  
pp. 111-122
Author(s):  
Shigeru Hamada ◽  
Kejin Zhang ◽  
Motomichi Koyama ◽  
Masaharu Ueda ◽  
Hiroshi Noguchi
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Damage Accumulation ◽  
Deformation Mode ◽  
Accumulation Mode

Study on Fatigue Crack Propagation at Negative Stress Ratio in 2A12 Aluminum Alloy

2011 ◽  
Vol 335-336 ◽  
pp. 809-812
Author(s):  
Shi Gang Bai ◽  
Jia Zhen Zhang ◽  
Yu Sha
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Stress Ratio ◽  
Compressive Loading ◽  
Stress Cycle ◽  
Made In

This paper intends to get compressive loading effect on fatigue crack growth of 2A12 aluminum alloy. The fatigue crack propagation tests at negative stress ratio R=-0.5, -1and -2 were made in different applied compressive loading. The result showed that the effect of the compressive loading part of the applied stress cycle on fatigue crack growth rate in 2A12 aluminum alloy at negative stress ratio can not be omitted.

scholarly journals The Variation Law of Mechanical Parameters of Type I Fatigue Crack Tip Under High Frequency Resonant Loading

2015 ◽  
Vol 9 (1) ◽  
pp. 379-387
Author(s):  
Gao Hong-Li ◽  
Zheng Huan-Bin ◽  
Qiu Xin-Guo ◽  
Liu Huan ◽  
Liu Hui
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
High Frequency ◽  
Crack Tip ◽  
Type I ◽  
Mechanical Parameters ◽  
Stress Cycle ◽  
Fatigue Crack Propagation Test

This work explores the variation law of mechanical parameters at fatigue crack tip of compact tension specimen with type I pre-notch based on dynamic finite element method (FEM) in the high frequency resonant fatigue crack propagation test. The displacement fields, the strain fields and the stress intensity factors (SIF) at CT specimen fatigue crack tip in one stress cycle and at different crack lengths under constant amplitude high frequency sinusoidal alternating loading condition are calculated and the related variation laws of mechanical parameters are analyzed. In order to calculate the dynamic SIF at fatigue crack tip, the static SIF has been calculated first. The compared results of the static finite element analysis with the theoretical calculation show that finite element modeling and calculating method and respective results are accurate. Secondly, the variation law of SIF at crack tip during the process of fatigue crack propagation test is studied by dynamic FEM. Finally, the high frequency resonant fatigue crack propagation test has been performed and the dynamic strain gauge is used to measure the strain at crack tip during one stress cycle. The research results show that during crack stable propagation stage, the displacement, strain and SIF at type I fatigue crack tip are in the same form having high frequency resonant load, and the displacement, strain and SIF amplitude increase with the crack growth. The error of static SIF between the calculated result by FEM and the theoretical result is 2.51%. The maximum error of the strain at crack tip between the FEM calculating result and the experimental result is 2.93%.

Fatigue-Crack-Propagation Rates Under Random Excitation

1967 ◽  
Vol 89 (1) ◽  
pp. 55-68 ◽  
Author(s):  
R. Plunkett ◽  
N. Viswanathan
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Random Excitation ◽  
Cantilever Beams ◽  
Constant Amplitude ◽  
Stress Cycles ◽  
Level Constant

Fatigue-crack-propagation rates have been measured for 2024-T3 aluminum cantilever beams in reversed bending under constant amplitude, two-level constant amplitude, and random excitations. For the two-level tests there is a large interaction between the crack-propagation rates caused by stress cycles of different amplitudes. The high-low sequence gives a delay and the low-high sequence a higher rate than a simple no interaction assumption would predict. This is confirmed in the random-excitation tests where the crack-propagation rate for low damping is much higher than that for high damping for exactly the same distribution and level of stress peaks.

Fatigue crack propagation in UFG Ti grade 4 processed by severe plastic deformation

2017 ◽  
Vol 98 ◽  
pp. 187-194 ◽  
Author(s):  
S. Fintová ◽  
M. Arzaghi ◽  
I. Kuběna ◽  
L. Kunz ◽  
Ch. Sarrazin-Baudoux
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Severe Plastic Deformation ◽  
Crack Propagation ◽  
Fatigue Crack Propagation
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