On the use of the extended finite element and incremental methods in brittle fracture assessment of key-hole notched polystyrene specimens under mixed mode I/II loading with negative mode I contributions

2017 ◽  
Vol 88 (4) ◽  
pp. 587-612 ◽  
Author(s):  
H. R. Majidi ◽  
M. R. Ayatollahi ◽  
A. R. Torabi
Keyword(s):  
Finite Element ◽  
Brittle Fracture ◽  
Mixed Mode ◽  
Mode I ◽  
Extended Finite Element ◽  
Incremental Methods ◽  
Negative Mode ◽  
Fracture Assessment ◽  
Negative Mode I

Energy-based assessment of brittle fracture in VO-notched polymer specimens under combined compression-shear loading conditions

2018 ◽  
Vol 28 (5) ◽  
pp. 664-689 ◽  
Author(s):  
HR Majidi ◽  
MR Ayatollahi ◽  
AR Torabi ◽  
A Zaheri
Keyword(s):  
Energy Density ◽  
Brittle Fracture ◽  
Strain Energy Density ◽  
Mixed Mode ◽  
Strain Energy ◽  
General Purpose ◽  
Mode I ◽  
Brazilian Disk ◽  
Negative Mode ◽  
Negative Mode I

This research presents some experimental, numerical, and theoretical results on brittle fracture of disk-type test specimens weakened by V-notches with end-holes under mixed mode I/II loading with negative mode I contributions. First, 54 fracture tests are conducted on VO-notched Brazilian disk specimens made of the general-purpose polystyrene under mixed mode I/II loading with negative mode I contributions. Then, two energy-based brittle fracture criteria, namely the averaged strain energy density and averaged strain energy density based on the equivalent factor concept are proposed to predict the experimentally obtained fracture loads of the tested general-purpose polystyrene specimens. Additionally, the fracture initiation angles of the tested VO-notched Brazilian disk specimens are predicted by using averaged strain energy density criterion. The finite element analyses, as well as the experimental observations, show that although brittle fracture in the specimens under mixed mode I/II loading takes place from the applied load side of the notch border by local tensile stresses, the notch bisector line and the other sides of the notch border sustain compressive stresses. In fact, this phenomenon states the concept of mixed mode I/II loading with negative mode I contributions. Finally, it is shown that good agreement exists between the experimental results and the theoretical predictions of the two energy-based fracture criteria.

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.

scholarly journals Fatigue Crack Growth Analysis with Extended Finite Element for 3D Linear Elastic Material

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 397
Author(s):  
Yahya Ali Fageehi
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Propagation Path ◽  
Loading Conditions ◽  
Extended Finite Element ◽  
Linear Elastic

This paper presents computational modeling of a crack growth path under mixed-mode loadings in linear elastic materials and investigates the influence of a hole on both fatigue crack propagation and fatigue life when subjected to constant amplitude loading conditions. Though the crack propagation is inevitable, the simulation specified the crack propagation path such that the critical structure domain was not exceeded. ANSYS Mechanical APDL 19.2 was introduced with the aid of a new feature in ANSYS: Smart Crack growth technology. It predicts the propagation direction and subsequent fatigue life for structural components using the extended finite element method (XFEM). The Paris law model was used to evaluate the mixed-mode fatigue life for both a modified four-point bending beam and a cracked plate with three holes under the linear elastic fracture mechanics (LEFM) assumption. Precise estimates of the stress intensity factors (SIFs), the trajectory of crack growth, and the fatigue life by an incremental crack propagation analysis were recorded. The findings of this analysis are confirmed in published works in terms of crack propagation trajectories under mixed-mode loading conditions.

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