The Influence of Notches on Mechanical Behavior at Elevated Temperatures: Some Metallographic Observations

A metallographic study of ruptured and unruptured notch bars is reported in this paper. The alloys are Cr-Mo-V steels tested in the range 1000–1050 deg F. Crack initiation and propagation in these alloys are studied as a function of the steel’s ductility with test bar section size and notch geometry as variables. It is shown that these factors interact in a complex way to control crack initiation and propagation. The mode and rate of crack initiation and propagation in ductile alloys depend mainly on shear processes although principal stress components are important under certain conditions. Alternatively, the maximum principal stress dominates the behavior in low ductility steels. In the former case, notched bar life is limited by crack propagation while in the latter case it is controlled by crack initiation. The influence of geometrical variables and metallurgical factors are discussed.

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Crack initiation and propagation in uranium at elevated temperatures

10.2172/4789745 ◽

1962 ◽

Author(s):

N. E. Daniel ◽

F. R. Shober ◽

E. L. Foster, Jr. ◽

R. F. Dickerson

Keyword(s):

Crack Initiation ◽

Elevated Temperatures ◽

Crack Initiation And Propagation ◽

Initiation And Propagation

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Notch Effect in Low-Cycle Fatigue at Elevated Temperatures—Life Prediction From Crack Initiation and Propagation Considerations

Journal of Engineering Materials and Technology ◽

10.1115/1.3225883 ◽

1986 ◽

Vol 108 (4) ◽

pp. 279-284 ◽

Cited By ~ 7

Author(s):

Masao Sakane ◽

Masateru Ohnami

Keyword(s):

Crack Initiation ◽

Elevated Temperatures ◽

Low Cycle Fatigue ◽

Strain Range ◽

Notch Effect ◽

Cycle Fatigue ◽

Crack Initiation And Propagation ◽

Total Strain Range ◽

Notched Specimens ◽

Initiation And Propagation

This paper describes the notch effect in low-cycle fatigue of an austenitic stainless steel SUS 304 at 873 K in air. Total strain range-controlled tests were carried out using a round unnotched and three round notched specimens. A prediction method for low-cycle fatigue lives of notched specimens was developed by predicting the crack initiation and propagation periods separately. To predict the former Neuber’s rule was applied and a nominal stress/strain criterion was developed to predict the latter. Failure lives, obtained by adding the two prediction lives, closely agree with observed failure lives.

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Mechanisms of Crack Initiation and Propagation in Dense Linear Multihole Directional Hydraulic Fracturing

Shock and Vibration ◽

10.1155/2019/7953813 ◽

2019 ◽

Vol 2019 ◽

pp. 1-15

Author(s):

Jiangwei Liu ◽

Changyou Liu ◽

Qiangling Yao

Keyword(s):

Rock Mass ◽

Crack Initiation ◽

Hydraulic Fracturing ◽

Principal Stress ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Crack Initiation And Propagation ◽

Initiation And Propagation ◽

Coal Rock

Artificially fracturing coal-rock mass serves to form break lines therein, which is related to the distribution of cracked boreholes. For this reason, we use physical experiments and numerical simulations to study the crack initiation and propagation characteristics of dense linear multihole drilling of fractured coal-rock mass. The results indicate that only in the area between the first and last boreholes can hydraulic fracturing be controlled by dense linear multihole expansion along the direction of the borehole line; in addition, no directional fracturing occurs outside the drilling section. Upon increasing parameters such as the included angle θ between the drilling arrangement line and the maximum principal stress σ1 direction, the drilling spacing D, the difference Δσ in principal stress, etc., the effect of directional fracture is gradually weakened, and the hydraulic fractures reveal three typical cracking modes: cracking along the borehole line, bidirectional cracking (along the borehole line and perpendicular to the minimum principal stress σ3), and cracking perpendicular to σ3. Five propagation modes also appear in sequence: propagating along borehole line, step-like propagation, S-shaped propagation, bidirectional propagation (along the borehole line and perpendicular to σ3), and propagation perpendicular to σ3. Based on these results, we report the typical characteristics of three-dimensional crack propagation and discuss the influence of the gradient of pore water pressure. The results show clearly that crack initiation and propagation are affected by both the geostress field and the pore water pressure. The pore water pressure will exhibit a circular-local contact-to-integral process during crack initiation and expansion. When multiple cracks approach, the superposition of pore water pressure at the tip of the two cracks increases the damage to the coal rock, which causes crack reorientation and intersection.

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