scholarly journals Study of the Growth Process of Original Crack in the Surrounding Rock of Tunnel under the Adjacent Explosive Load

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Kang Liu ◽  
Dongming Guo ◽  
Xinchao Kang ◽  
Jun Zhang
Keyword(s):  
Growth Rate ◽  
Crack Growth ◽  
Stress Wave ◽  
Growth Process ◽  
Damage Mechanics ◽  
High Stress ◽  
Surrounding Rock ◽  
Damage Localization ◽  
Explosive Load ◽  
Original Crack

The surrounding rock damage of a tunnel under adjacent explosive load is often manifested as the growth of the original crack. In order to thoroughly understand the crack growth mechanism, in this study, the growth process of the original crack was investigated in detail by the dynamic caustics experiment. The experimental study shows that the growth of original crack is the result of the combined action of explosion stress wave and explosive gas. The quasi-static stress generated by the explosive gas was superimposed on the weakened stress field, resulting in the formation of the peak of the main stress difference in the surrounding rock, moving towards the adjacent tunnel in the form of an arc wave. With the arc wave moving towards the original crack, the growth rate of the original crack increases rapidly. During the period of 200 μs to 250 μs, the crack growth rate oscillates at the peak, and its size is approximately equal to the moving speed of the arc wave. Based on the experimental results and microscopic damage mechanics, the high stress concentration at the original crack tip under the stress wave first causes damage localization and the weakest chain is formed by the penetration of the damage localization zones by microcracks by special distribution law. Subsequently, the original crack starts to initiate and grow along the direction of the weakest chain.

Evaluation of Crack Growth Rate of Neutron Irradiated Austenitic Stainless Steels at High Stress Intensity Factor Levels

2020 ◽  
Author(s):  
Hitoshi Seto ◽  
Masato Koshiishi ◽  
Shigeaki Tanaka ◽  
Ryoji Obata
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Stainless Steel ◽  
Crack Growth ◽  
Stainless Steels ◽  
High Stress ◽  
Austenitic Stainless Steels ◽  
High K ◽  
Normal Water ◽  
Crack Growth Rates

Abstract Crack growth rates (CGRs) at high K levels (more than 30 MPa·m0.5) were obtained in simulated boiling water reactor normal water chemistry under constant K conditions for Type 316NG stainless steel irradiated up to 2.0 dpa. Valid CGRs were obtained even at high K conditions such as K ≈ 40 MPa·m0.5 although branching was observed on the fracture surface of the specimen after CGR testing. CGRs were compared with predictions by a theoretical model and a disposition curve and it was found that these predictions are applicable even to high K levels around K ≈ 40 MPa·m0.5.

EFFECTS OF OVERLOAD AND SUPPLYING OIL ON CRACK GROWTH BEHAVIOR IN MG ALLOYS

2021 ◽  
Author(s):  
XUECHAO ZHANG ◽  
CHOBIN MAKABE ◽  
TATSUJIRO MIYAZAKI
Keyword(s):  
Growth Rate ◽  
Crack Growth ◽  
Growth Process ◽  
Stress Amplitude ◽  
Crack Tip ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fracture Surface Roughness ◽  
Magnesium Alloy Az31 ◽  
Single Overload

A single overload was applied during the crack growth process under constant stress amplitude, and retardation of crack growth was observed in the case of magnesium alloys as well as carbon steel, aluminum alloys, etc. The retardation of crack growth was related to crack closure, the fracture surface roughness, and crack tip deformation. In addition, the effects of supplying oil into the crack on crack growth behavior of an overloaded specimen were investigated in this study. The crack growth rate in the case of supplying oil became lower than in the case without supplying oil. In the case of the magnesium alloy AZ31, powder of oxide magnesium appeared from the crack after overloading. It is one of the typical behaviors of AZ31. In the case of AZ31 and AZX912, the crack growth behavior after overloading was slightly different due to the deformation of the crack tip.

Results of High Stress Ratio and Low Stress Intensity on Fatigue Crack Growth Rates for 304 Stainless Steel in 288°C Water

2002 ◽  
Author(s):  
William M. E. Evans ◽  
G. L. Wire
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
High Stress ◽  
304 Stainless Steel ◽  
Crack Growth Rates

Fatigue crack growth rate tests were performed on a 304 stainless steel compact tension (CT) specimen in water with 40–60 cc/kg H2. Data in the literature for CT tests show minor environmental effects in hydrogenated water, but higher effects in oxygenated water. However, the PWR data presented by Bernard, et al (1979) were taken at low stress ratios (R = 0.05) and high stress intensity levels (ΔK = 16–41 MPa√m). The purpose of these tests is to explore the crack growth rate characteristics of 304 SS in hydrogenated water at higher R values (0.7 and 0.83) and lower ΔK values (11.0 and 7.7 MPa√m) Each set of R, ΔK conditions were tested at frequencies of 0.1, 0.01 and 0.001 Hz. The results show a pronounced effect on crack growth rates when compared to available literature data on air rates.

Simulation of Crack Propagation in Three-Point Bending Piezoelectric Beam Based on Three-Dimensional Anisotropic Piezoelectric Damage Mechanics

2011 ◽  
Vol 27 (4) ◽  
pp. 521-531 ◽  
Author(s):  
X. H. Yang ◽  
W. Z. Cao ◽  
X. B. Tian
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Propagation ◽  
Crack Growth ◽  
Electric Fields ◽  
Damage Mechanics ◽  
Three Dimensional ◽  
Crack Tip ◽  
Three Point Bending ◽  
Electrical Loads

ABSTRACTA finite element method combined with three-dimensional anisotropic piezoelectric continuum damage mechanics is presented to simulate quasi-static crack propagation behavior in piezoelectric ceramics in this paper. In this method, the three-dimensional anisotropic piezoelectric damage constitutive model is utilized for characterizing the effects of mechanical and electrical damages on the fields near the crack tip, the combined-damage from the dominant mechanical and electrical damage components is regarded as the fracture criterion, and the gradient of combined-damage is assumed to control crack growth direction. A set of numerical simulations of the midspan crack propagation in a three-point bending PZT-4 beam are performed in various loading conditions. After the numerical results are validated by comparison with the corresponding experimental ones, the effects of mechanical and electrical loads on the cracking be havior are respectively evaluated. It is found from the obtained results that mechanical and electrical loads influence on the damage fields in the vicinity of the crack-tip, as well as the crack growth rate, in a significant way. With the increment in mechanical loading, the crack growth rate obviously increases. This means that positive and negative electric fields enhance and inhibit crack propagation, respectively.

scholarly journals Effect of water flow and depth on fatigue crack growth rate of underwater wet welded low carbon steel SS400

2021 ◽  
Vol 11 (1) ◽  
pp. 329-338 ◽  
Author(s):  
E. Surojo ◽  
J. Anindito ◽  
F. Paundra ◽  
A. R. Prabowo ◽  
E. P. Budiana ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Carbon Steel ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Water Flow ◽  
Water Depth ◽  
Water Flow Rate ◽  
Low Carbon Steel ◽  
Low Carbon

Abstract Underwater wet welding (UWW) is widely used in repair of offshore constructions and underwater pipelines by the shielded metal arc welding (SMAW) method. They are subjected the dynamic load due to sea water flow. In this condition, they can experience the fatigue failure. This study was aimed to determine the effect of water flow speed (0 m/s, 1 m/s, and 2 m/s) and water depth (2.5 m and 5 m) on the crack growth rate of underwater wet welded low carbon steel SS400. Underwater wet welding processes were conducted using E6013 electrode (RB26) with a diameter of 4 mm, type of negative electrode polarity and constant electric current and welding speed of 90 A and 1.5 mm/s respectively. In air welding process was also conducted for comparison. Compared to in air welded joint, underwater wet welded joints have more weld defects including porosity, incomplete penetration and irregular surface. Fatigue crack growth rate of underwater wet welded joints will decrease as water depth increases and water flow rate decreases. It is represented by Paris's constant, where specimens in air welding, 2.5 m and 5 m water depth have average Paris's constant of 8.16, 7.54 and 5.56 respectively. The increasing water depth will cause the formation of Acicular Ferrite structure which has high fatigue crack resistance. The higher the water flow rate, the higher the welding defects, thereby reducing the fatigue crack resistance.

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