Predictions of fracture load, crack initiation angle, and trajectory for V-notched Brazilian disk specimens under mixed mode I/II loading with negative mode I contributions

2017 ◽  
Vol 27 (8) ◽  
pp. 1173-1191 ◽  
Author(s):  
Bahador Bahrami ◽  
Majid R Ayatollahi ◽  
AR Torabi
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Initiation ◽  
Extended Finite Element Method ◽  
Fracture Load ◽  
Shear Loading ◽  
Mode I ◽  
Extended Finite Element ◽  
Brazilian Disk ◽  
Crack Initiation Angle

In this paper, first the fracture load, the crack initiation angle and the crack trajectory are experimentally measured for the round-tip V-notched Brazilian disk specimen made of polymethyl-methacrylate under compressive-shear loading. Then, the fracture load and the crack initiation angle are predicted by using the extended finite element method on the basis of the linear cohesive crack criterion. The fracture trajectory of the round-tip V-notched Brazilian disk specimens is also estimated by means of the extended finite element method and the incremental methods. Both the experimental observations and the theoretical fracture models indicate that although the notch bisector line is under compressive-shear loading, one half of the notch border still sustains tensile stresses and fracture takes place from this half. A very good agreement is shown to exist between the theoretical predictions and the experimental results for various notch opening angles and different notch radii.

An Investigation of I-II Mixed Mode Structures With Stop Hole Technique Based on Extended Finite Element Method

2017 ◽  
Author(s):  
Xin-Ting Miao ◽  
Chang-Yu Zhou ◽  
Xiao-Hua He
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Initiation ◽  
Mixed Mode ◽  
Extended Finite Element Method ◽  
Mode I ◽  
Mode Ii ◽  
Extended Finite Element ◽  
The Difference ◽  
Element Method

Extended finite element method (XFEM) is adopted in this paper to study crack growth path and loading capability for modified compact tension shear (CTS) specimen with stop hole ahead of crack tip. Elliptical stop holes with different values of b/h are considered, where b and h are radii of the ellipse parallel and vertical to the crack. When b/h is 1 (circle stop hole), the locations of crack initiation turn clockwise gradually as the loading angle β (angle between the loading direction and the crack plane) decreases. When b/h is not equal to 1 (elliptical stop hole), the locations of crack initiation are all near the long axis end point of the ellipse no matter what the mode mixity is. Curves of load-COD and ultimate loads are presented for different mixed mode loadings, it can be obtained that for mode I dominant crack loading capability increases, though for mode II dominant crack loading capability decreases due to the stop hole technique. For mode I dominant crack the loading capability increases as the value of b/h decreases, and for mode II dominant crack the trend of loading capability with b/h changes gradually oppositely. The difference of crack initiation locations for different stop holes is due to the stress concentration considering both curvatures and the loading modes. And the difference of loading capability for specimens with stop holes under different mixed mode loadings is due to the shear action due to the discrepancy between the positive and negative stresses. Therefore, stop hole technique can be used to change the crack initiation location in order to avoid the important component and improve the loading capability by choosing an appropriate hole shape.

Study of Crack Initiation and Propagation in TBCs by Experiments and Extended Finite Element Method

2013 ◽  
Vol 331 ◽  
pp. 129-132 ◽  
Author(s):  
Jing Xin Su ◽  
Zhao Hui Ji ◽  
Zhi Yong Han ◽  
Hua Zhang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Initiation ◽  
Thermal Cycling ◽  
Extended Finite Element Method ◽  
Interface Roughness ◽  
Crack Initiation And Propagation ◽  
Extended Finite Element ◽  
Initiation And Propagation ◽  
Element Method

CoNiCrAlY bond coat (BC) and top ceramic coating (TCC) was fabricated on the GH99 super alloy by high velocity oxyfuel spray (HVOF) and air plasma spray (APS), respectively. Thermal cycling treatment was applied to the thermal barrier coatings (TBCs). The cross-sectional images of crack initiation and propagation of TBCs after treatment were investigated by scanning electron micrograph (SEM), meanwhile crack initiation and propagation in TBCs were analyzed based upon ABAQUS software using extended finite element method (XFEM). The results show that, crack initiation and propagation can be easily traced via microscopy at the interface areas in TBCs; after thermal cycling treatments, the crack associated with the TCC/TGO interface morphology initiates at interface peak area and propagates along TCC/TGO interface with thermal cycles; the interface roughness affects the crack magnitude in length and width obviously, the rougher the morphology, the bigger the crack is; the XFEM is a novel and effective method to well predict the crack initiation and calculate the crack propagation, and simulation and experimental results fit well.

Calculation on Crack Parameter by Extended Finite Element Method

2014 ◽  
Vol 716-717 ◽  
pp. 751-754
Author(s):  
Bo Zhou ◽  
Dong Xue Wang ◽  
Shi Feng Xue
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Extended Finite Element Method ◽  
High Efficiency ◽  
Simulation Method ◽  
Mode I ◽  
The Finite Element Method ◽  
Extended Finite Element ◽  
Discontinuous Problems ◽  
Element Method

As a new numerical simulation method, the extended finite element method can deal with the discontinuous problems more effectively than the finite element method. In this paper, the basic theory about the extended finite element method is introduced briefly. The stress intensity factor of the crack of mode I is numerically calculated based on the extended finite element method. The numerical calculations show that the extended finite element method is an approach with high-efficiency for the problems with crack.

Crack Initiation and Growth Simulation for CRDM Nozzles by eXtended Finite Element Method

2015 ◽  
Author(s):  
Sung-Jun Lee ◽  
Yoon-Suk Chang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Initiation ◽  
Power Plants ◽  
Extended Finite Element Method ◽  
Zone Model ◽  
Extended Finite Element ◽  
Integrity Assessment ◽  
Head Penetration ◽  
Element Method

The head penetration nozzles of control rod driving mechanisms (CRDMs) are susceptible components on primary water stress corrosion cracking (PWSCC) due to the dissimilar metal welds. The accurate integrity assessment of the CRDM head penetration nozzles is important for the safe operation of nuclear power plants. To resolve the integrity issue, conventional finite element methods, a cohesive zone model, and a virtual crack closure technique have been employed; however, there are still many uncertainties in accuracy and efficiency. In the present study, a specific Strain Rate Damage Model (SRDM) with stress and thermal dependent parameters was adopted to calculate crack initiation time. Also, a level set method, which defines the crack location based on the crack surface and vertical surface of crack tip, was considered to simulate arbitrary crack growth. By taking into account these two features, the eXtended Finite Element Method (XFEM) was implemented to simulate the PWSCC initiation and growth with a user subroutine code. Finally, the validity of the proposed method was evaluated by comparing the reference cracks that occurred in the CRDM head penetration nozzles.

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