scholarly journals Research on TBM Cutterhead Crack Damage and Fatigue Reliability

2021 ◽  
Vol 11 (5) ◽  
pp. 2111
Author(s):  
Ding Wang ◽  
Chuanyong Qu
Keyword(s):  
Crack Propagation ◽  
Evaluation Method ◽  
Crack Depth ◽  
Tunnel Boring Machine ◽  
Initial Crack ◽  
Strength Analysis ◽  
Propagation Mechanism ◽  
Fatigue Reliability ◽  
Critical Crack ◽  
Geological Conditions

The cutterhead of a tunnel-boring machine (TBM) is the main weighted part in the process of tunneling and bears loadings in different directions. A fatigue failure of a cutterhead would severely affect the construction progress and safety. Therefore, it is of great importance to study the fatigue reliability of its cracks. In this study, the area of the cutterhead with a higher stress was found using static strength analysis and we analyzed the dynamic stress characteristics. In addition, the stress intensity factor of a cutterhead crack was calculated using the submodeling technique, and the crack propagation mechanism and damage characteristics of a cutterhead crack were also analyzed. Then, combined with crack fatigue theory, we proposed a fatigue reliability evaluation method based on the Joint Committee on Structure Safety method (known as the JC method), and the effects of different factors on the reliability were discussed for different geological conditions. The results show that the crack propagation was of the open and tear types in the deepest part of the crack tip, but there are three kinds of propagation modes at both ends. As the initial crack depth increased, the fatigue reliability of the cutterhead decreased significantly. The reliability was positively correlated with the crack shape ratio. However, there were no significant relationships between the reliability and the depth of the critical crack.

scholarly journals Subcritical crack growth parameters in glass as a function of environmental conditions

2020 ◽  
Author(s):  
Christopher Brokmann ◽  
Stefan Kolling ◽  
Jens Schneider
Keyword(s):  
Crack Growth ◽  
Environmental Conditions ◽  
Subcritical Crack Growth ◽  
Growth Parameters ◽  
Crack Depth ◽  
Indentation Test ◽  
Soda Lime ◽  
Initial Crack ◽  
Chemical Compositions ◽  
Critical Crack

Abstract In the present work, subcritical crack growth in soda–lime silicate glass is investigated under different environmental conditions. Crack growth parameters as a function of temperature and humidity were determined by dynamic fatigue tests, which has been verified by using the in-situ method of filming crack growth during experiments. The specimens were pre-damaged for constant initial crack lengths in all specimens using the Vickers indentation test. The determined parameters were compared with those from literature in order to discuss existing deviations of sub-critical crack growth parameters in literature. These deviations may be caused by environmental conditions and different chemical compositions of the glass. Arrest lines were used to determine the ratio of crack width to crack depth in Vickers indented specimens. For the initial crack depth, images of fracture surfaces were taken using an scanning electron microscope. Furthermore, the influence of humidity and temperature on the failure stress of unindented specimens with a constant initial crack length was simulated.

A Sensitivity Study on Numerical Analysis of Dynamic Girth Crack Propagation

1981 ◽  
Vol 103 (2) ◽  
pp. 169-174 ◽  
Author(s):  
A. S. Kobayashi ◽  
A. F. Emery ◽  
W. J. Love ◽  
A. Jain
Keyword(s):  
Crack Propagation ◽  
Large Scale ◽  
Sensitivity Study ◽  
Initial Crack ◽  
Dynamic Crack Propagation ◽  
Opening Angle ◽  
Dynamic Crack ◽  
Critical Crack ◽  
Scale Yielding ◽  
Crack Tip Opening

Dynamic motion of pre-existing girth crack in an axially stressed, 18-in-dia 316 stainless steel pipe in the presence of large-scale yielding was analyzed by a finite difference shell code. A critical crack tip opening angle (CTOA) was used as a dynamic fracture criterion and the sensitivities of dynamic crack propagation to differences in CTOA, finite differences mesh sizes, initial crack sizes and initial crack bluntnesses, were analyzed numerically. Hold-off times for the onset of dynamic crack propagation nearly doubled and tripled, while terminal crack velocities decreased about 22 percent and 47percent when the CTOA was increased from 0.10 to 0.19 and to 0.30, respectively. Doubling of the axial length of the initial crack length and an overdriving condition simulated by a larger CTOA did not change the terminal crack velocity.

Analysis on Crack Propagation Mechanism of Single Crystal Copper by FEAt Method

2012 ◽  
Vol 581-582 ◽  
pp. 827-830 ◽  
Author(s):  
Ge Li ◽  
Qing Long Zhang ◽  
Ming Chen ◽  
Lin Yong Zhou
Keyword(s):  
Crack Propagation ◽  
Single Crystal ◽  
Critical Stress ◽  
Cleavage Plane ◽  
Initial Crack ◽  
Propagation Mechanism ◽  
Type I ◽  
Single Crystal Copper ◽  
Crack Propagation Mechanism ◽  
Dislocation Walls

By FEAt method, the tensile processes of single crystal copper with the type I crack at temperature of 293K were simulated, and the effect of different initial crack lengths to crack propagation mechanism was analyzed. The results indicate that the different initial crack lengths have significant effect on crack propagation mechanism. With the increase of crack length, the critical stress of crack propagation was significantly reduced, the dislocation walls were easy to appear, and mesh staggered of the crack branch along the cleavage plane was more pronounced.

scholarly journals Crack Propagation Analysis of Damaged Solid Propellant under Impact Overload

2021 ◽  
Vol 2125 (1) ◽  
pp. 012061
Author(s):  
Xiao-ming Hou ◽  
Le Fan ◽  
Cun-gui Yu ◽  
Jian-lin Zhong
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Solid Propellant ◽  
Evaluation Method ◽  
Structural Integrity ◽  
Rocket Engine ◽  
Element Model ◽  
Initial Crack ◽  
Propagation Analysis ◽  
Double Base

Abstract The ammunition safety problem is particularly prominent when the storage and transportation launch box is airdropped and landed. A safety evaluation method of rocket air drop based on propellant damage evaluation is proposed. Based on the theory of fracture mechanics and the evaluation method of structural integrity of rocket engine, established a local finite element model of rocket engine with initial damage, the crack propagation analysis is carried out by using the propagation finite element method (XFEM). The results show that when the landing impact overload is 30g (25ms) that the airdrop equipment should be able to withstand, the modified double base propellant has produced the phenomenon of crack instability propagation. When the initial crack direction and load direction are 120 °, the propagation is the most serious and there are safety problems; when the solid propellant is airdropped, it is necessary to increase the buffer to reduce the overload.

scholarly journals Fatigue Life Assessment and Reliability Analysis of Cope-Hole Details in Steel Bridges

2020 ◽  
Vol 15 (1) ◽  
pp. 26-46 ◽  
Author(s):  
Ping Liao ◽  
Yongbao Wang ◽  
Xiucheng Zhang ◽  
Renda Zhao ◽  
Yi Jia ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Propagation ◽  
Reliability Index ◽  
Crack Size ◽  
Initial Crack ◽  
Steel Bridges ◽  
Fatigue Reliability ◽  
Intensity Factors ◽  
Cope Hole

Cope-hole details are widely applied to steel bridges. However, the safety of steel bridges is influenced by the fatigue performance of welded details. So, cope-hole details with flange and web subjected to axial loads were selected as the research object. Based on the basic theory of linear elastic fracture mechanics and the Finite Element Method, the stress intensity factors of cope-holes details were calculated. The influences of geometry size and crack size of the detail on the stress intensity factors were then investigated. The Paris model of fatigue crack propagation predicted the crack propagation life of cope-hole details. Besides, the fatigue limit-state equation was also established to analyse the effect of random variables (such as initial crack size, critical crack size, crack propagation parameter) on the fatigue reliability index. Finally, the recommended value of the detection period was present. The results show that the stress intensity factor gradually increases with the increase of the cope-hole radius, the weld size, the flange plate thickness, the crack length and the web thickness. However, it gradually decreases with the increase of the ratio of the long and short axle to the crack. The predicted number of fatigue cyclic loading required by the fatigue crack depth propagating from 0.5 mm to 16 mm under nominal stress amplitude of 63 MPa is 122.22 million times. The fatigue reliability index decreases with the fatigue growth parameter, the crack shape ratio and the mean of initial crack size increasing, which is relatively sensitive. However, the variation coefficient of the initial crack size has little effect on it. The detection period of cope-hole details is the service time corresponding to the fatigue accumulated cyclic loading of 198.3 million times.

Reliability-Based Fatigue Evaluation Considering Various Initial Conditions of Defects

2019 ◽  
Author(s):  
Lee-Sak An ◽  
Yeun Chul Park ◽  
Ho-Kyung Kim
Keyword(s):  
Initial Conditions ◽  
Crack Depth ◽  
Initial Crack ◽  
Evaluation Procedure ◽  
Fatigue Reliability ◽  
Limit States ◽  
Steel Members ◽  
Distribution Parameters ◽  
Fatigue Evaluation ◽  
Fixed Distribution

<p>This study presents the reliability-based fatigue evaluation procedure for deteriorated steel members of a bridge with estimation in initial conditions of defects. For this purpose, deterioration scenarios and limit states are defined when fatigue crack or pitting corrosion are found. Since the initial conditions of the defects, such as the initial crack depth or the time for corrosion nucleation have large uncertainties, the initial conditions are estimated using the inspection results. A numerical example is presented to confirm the applicability of proposed method for typical steel structural members. The initial crack depth and the time for corrosion nucleation estimated by the proposed methods are similar to those proposed in previous studies, depending on the size of the defect. It is also possible to estimate more reasonable initial conditions of defects compared to the fixed distribution parameters or deterministic values which have been presented in previous studies. Therefore, it is expected that the proposed evaluation procedure could facilitate precise fatigue reliability analysis.</p>

Numerical Prediction of the Bending Fatigue Crack Propagation Behaviour in Asymmetric Spur Gears

2020 ◽  
Vol 12 (5) ◽  
Author(s):  
A.Karthik Pandian ◽  
Sachin Singh Gautam ◽  
S. Senthilvelan
Keyword(s):  
Crack Propagation ◽  
Damage Tolerance ◽  
Crack Path ◽  
Spur Gear ◽  
Initial Crack ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Paris Law ◽  
Load Carrying ◽  
Tooth Form

The damage tolerance of a component is crucial for achieving a reliable and smooth operation. The crack propagation in a spur gear critically affects the performance of the transmission system. Asymmetric gears are used for enhancing the load-carrying capacity by increasing the pressure angle of a flank beyond the conventional limits. In this study, the effect of initial crack inclination angle and length in the tooth fillet region on the Stress Intensity Factor (SIF) and the crack path of an asymmetric gear (34°/20°) were studied using numerical simulations. Quasi-static analyses were performed in FRANC2D. The crack propagation life was calculated using Paris law. Results revealed that tooth asymmetry has no effect on the crack path. However, asymmetric tooth form caused a reduction in the SIF value and increased the critical crack length, leading to an increased crack propagation life and damage tolerance.

Mechanism of irregular crack-propagation in thermal controlled fracture of ceramics induced by microwave

2020 ◽  
Vol 21 (6) ◽  
pp. 610
Author(s):  
Xiaoliang Cheng ◽  
Chunyang Zhao ◽  
Hailong Wang ◽  
Yang Wang ◽  
Zhenlong Wang
Keyword(s):  
Crack Propagation ◽  
Industrial Application ◽  
Ceramic Materials ◽  
Advanced Technology ◽  
Analytical Models ◽  
Propagation Mechanism ◽  
Unstable Crack ◽  
Fracture Simulation ◽  
Initial Stage ◽  
Controlled Fracture

Microwave cutting glass and ceramics based on thermal controlled fracture method has gained much attention recently for its advantages in lower energy-consumption and higher efficiency than conventional processing method. However, the irregular crack-propagation is problematic in this procedure, which hinders the industrial application of this advanced technology. In this study, the irregular crack-propagation is summarized as the unstable propagation in the initial stage, the deviated propagation in the middle stage, and the non-penetrating propagation in the end segment based on experimental work. Method for predicting the unstable propagation in the initial stage has been developed by combining analytical models with thermal-fracture simulation. Experimental results show good agreement with the prediction results, and the relative deviation between them can be <5% in cutting of some ceramics. The mechanism of deviated propagation and the non-penetrating propagation have been revealed by simulation and theoretical analysis. Since this study provides effective methods to predict unstable crack-propagation in the initial stage and understand the irregular propagation mechanism in the whole crack-propagation stage in microwave cutting ceramics, it is of great significance to the industrial application of thermal controlled fracture method for cutting ceramic materials using microwave.

scholarly journals The hydrochemical characteristics and quality assessment of groundwater in Shuangliao City, China

2019 ◽  
Vol 98 ◽  
pp. 01034 ◽  
Author(s):  
Mingjun Liu ◽  
Changlai Xiao ◽  
Xiujuan Liang
Keyword(s):  
Groundwater Quality ◽  
Human Activities ◽  
Evaluation Method ◽  
Comprehensive Evaluation ◽  
Fuzzy Comprehensive Evaluation ◽  
Hydrochemical Characteristics ◽  
Analytic Hierarchy ◽  
Liaohe River ◽  
Geological Conditions ◽  
Type Water

In this study, a hydrochemical investigation was conducted in Shuangliao city to identify the hydrochemical characteristics and the quality of groundwater using descriptive statistics and correlation matrices. And on that basis, combined with Analytic hierarchy process (AHP), an improved two-level fuzzy comprehensive evaluation method is used to evaluate the groundwater quality. The results indicate that the major cations and anions in groundwater are Ca2+ and HCO3-, respectively. The chemical types are mainly HCO3—Ca type water, some areas are complicated due to the influence of human activities. The evaluation results show that the water quality in the area is mostly III type water, and the groundwater quality in some areas is IV or V water due to the influence of primary geological conditions or human activities. The groundwater quality in the East Liaohe River Valley and Shuangliao urban area is relatively poor, and in the northwest part which is the saline alkali soil area is also relatively poor.

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