scholarly journals Investigation on the Crack Initiation of V-Shaped Notch Tip in Precision Cropping

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Lijun Zhang ◽  
Shengdun Zhao ◽  
Zhenwei Wang
Keyword(s):  
Crack Initiation ◽  
Equivalent Stress ◽  
Initiation Time ◽  
Initiation Point ◽  
Change Rate ◽  
Crack Initiation Angle ◽  
Notch Tip ◽  
Crack Initiation Life ◽  
Microscopic Measurement ◽  
Displacement Extrapolation Method

The crack initiation of V-shaped notch tip has a very important influence on the cross-section quality and the cropping time for every segment of metal bar in course of low stress precision cropping. By the finite element method, the influence of machining precision of V-shaped notch bottom corner on the crack initiation location is analyzed and it is pointed out that the crack initiation point locates in the place at the maximal equivalent stress change rate on V-shaped notch surface. The judgment criterion of the crack initiation direction is presented and the corresponding crack initiation angle can be calculated by means of the displacement extrapolation method. The factual crack initiation angle of the metal bar has been measured by using the microscopic measurement system. The formula of the crack initiation life of V-shaped notch tip is built, which mainly includes the stress concentration factor of V-shaped notch, the tensile properties of metal material, and the cyclic loading conditions. The experimental results show that the obtained theoretical analyses about the crack initiation location, the crack initiation direction, and the crack initiation time in this paper are correct. It is also shown that the crack initiation time accounts for about 80% of the cropping time for every segment of the metal bar.

Effect of Prestrain on the Fatigue Crack Initiation life of X60 Pipeline Steel

2011 ◽  
Vol 311-313 ◽  
pp. 841-844 ◽  
Author(s):  
Mei Bao Chen ◽  
Yu Rong Jiang
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Equivalent Stress ◽  
Fatigue Crack Initiation ◽  
Resistance Coefficient ◽  
Ductile Deformation ◽  
Test Results ◽  
Stress Threshold ◽  
Crack Initiation Life

It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation was used to imitate the defects of the part of material and the U-notch specimens were used to investigate the fatigue crack initiation life of X60 pipeline steel after pre-tension straining with ductile deformation of 0,5%,10% and 15%. Test results show that the prestrain had apparent straining hardening effects, but decreased the plasticity of pipeline steel. The prestrain prolonged the fatigue crack initiation life, and increased resistance coefficient and equivalent stress threshold of the fatigue crack initiation.

Assessment Technology of Fatigue Crack Initiation Life of Weld Structures

2017 ◽  
Vol 86 (1) ◽  
pp. 56-58
Author(s):  
Seiichiro TSUTSUMI ◽  
Fincato RICCARDO ◽  
Mitsuru OHATA ◽  
Tomokazu SANO
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Assessment Technology ◽  
Crack Initiation Life

Technique d'observation de surface in situ (TOSIS) :

1996 ◽  
Vol 84 ◽  
pp. 17-22
Author(s):  
A. Ranaivoarisoa ◽  
J. M. Olive ◽  
D. Desjardins
Keyword(s):  
Aqueous Solution ◽  
Crack Initiation ◽  
Grain Boundaries ◽  
Growth Rates ◽  
Triple Junction ◽  
Crack Nucleation ◽  
Initiation Time ◽  
Mesoscopic Scale ◽  
Crack Growth Rates

An optical method named In Situ Surface Observation Technique (ISSOT) is presented in this paper. This method is used to detect crack nucleation from a flaw (here a pit) at mesoscopic scale during a triangular push-pull cycling test under the control of charge amplitude in aqueous solution ofMgCl2 at 117°C. It can be found that the crack initiation time determined by using this technique represents 2 % of that estimated from a mechanical criterion. Moreover, the follow of the crack tip evolution by the ISSOT allows to measure average local crack growth rates. It has been shown that the variations of the latter were related to the effects of barriers such as grain boundaries, twin boundaries and grain boundaries triple junction.

Fatigue Behavior of Circumferentially Notched Round Bars of Austenitic Stainless Steel Under Torsional and Axial Loads

2010 ◽  
Author(s):  
Masao Itatani ◽  
Keisuke Tanaka ◽  
Isao Ohkawa ◽  
Takehisa Yamada ◽  
Toshiyuki Saito
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Static Tension ◽  
Cyclic Torsion ◽  
Cyclic Tension ◽  
Crack Initiation Life

Fatigue tests of smooth and notched round bars of austenitic stainless steels SUS316NG and SUS316L were conducted under cyclic tension and cyclic torsion with and without static tension. Fatigue strength under fully reversed (R=−1) cyclic tension once increased with increasing stress concentration factor up to Kt=1.5, but it decreased from Kt=1.5 to 2.5. Fatigue life increased with increasing stress concentration under pure cyclic torsion, while it decreased with increasing stress concentration under cyclic torsion with static tension. From the measurement of fatigue crack initiation and propagation lives using electric potential drop method, it was found that the crack initiation life decreased with increasing stress concentration and the crack propagation life increased with increasing stress concentration under pure cyclic torsion. Under cyclic torsion with static tension, the crack initiation life also decreased with increasing stress concentration but the crack propagation life decreased or not changed with increasing stress concentration then the total fatigue life of sharper notched specimen decreased. It was also found that the fatigue life of smooth specimen under cyclic torsion with static tension was longer than that under pure cyclic torsion. This behavior could be explained based on the cyclic strain hardening under non-proportional loading and the difference in crack path with and without static tension.

The Area Fracture Criterion of Iso-εθ Line for Mixed Mode Crack

2012 ◽  
Vol 193-194 ◽  
pp. 708-711
Author(s):  
Si Li Chen ◽  
Tao Yu ◽  
Jian Jun Shi ◽  
Jie Huang ◽  
Kai He Dong
Keyword(s):  
Crack Initiation ◽  
Mixed Mode ◽  
Fracture Criterion ◽  
Shape Change ◽  
Crack Tip ◽  
Fracture Line ◽  
Mixed Mode Crack ◽  
Engineering Significance ◽  
Crack Initiation Angle ◽  
Predicted Values

In practice, the crack in some engineering materials is often compound crack. Therefore, it is important engineering significance to study on fracture problem. Based on the shape change energy near crack tip portion, the area fracture criterion of Iso-εθ line for compound crack was proposed. A crack initiation angle formula and the fracture criterion were established. The results showed that the theoretical predicted values and the measured values are consistent. The compound crack fracture line area of fracture criterion was established.Tthe formulas are easy to be derived and convenient to apply.

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