scholarly journals First Steps of Crack Initiation and Propagation in Fatigue of FCC Crystals Studied by Dislocation Dynamics

2012 ◽  
Author(s):  
C. Déprés ◽  
G. V. Prasad Reddy ◽  
L. Tabourot ◽  
R. Sandhya ◽  
S. Sankaran
Keyword(s):  
Stress Field ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Dislocation Dynamics ◽  
Crack Initiation And Propagation ◽  
Dislocation Dynamic ◽  
Discrete Dislocation ◽  
Initiation And Propagation

3D discrete dislocation dynamic (DDD) simulations are performed to simulate stage-I fatigue crack initiation and propagation along the surface, in the primary grain and its neighbouring grain, in 316L stainless steel. The scenario of crack propagation in primary grain and the evolution of dislocation structure ahead of crack tip are discussed, and in addition crack tip sliding displacement is estimated. Probable mechanisms of crack propagation from primary grain to neighbouring grain are evaluated. In this process, surface relief in the neighbouring-grain under the influence of crack stress field in the primary grain is studied for varying neighbouring-grain orientations. An enhanced evolution of surface extrusions in the neighbouring grain, are observed in the presence of heterogeneous stress field (i.e., in the presence of crack in the primary grain), compared to that in the case of homogeneous stress field. In addition, influence of crack stress field on prior cyclic-deformed substructure is presented.

On the Topology Update of the Numerical Manifold Method for Multiple Crack Propagation

2021 ◽  
pp. 2150030
Author(s):  
Jun He ◽  
Shuling Huang ◽  
Xiuli Ding ◽  
Yuting Zhang ◽  
Dengxue Liu
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Numerical Method ◽  
Crack Tip ◽  
Search Method ◽  
Numerical Manifold Method ◽  
Crack Initiation And Propagation ◽  
Multiple Crack ◽  
Initiation And Propagation ◽  
Numerical Manifold

Crack initiation and propagation are the two key issues of concern in the geotechnical engineering. In this study, the numerical manifold method (NMM) is applied to simulate crack propagation and the topology update of the NMM for multiple crack propagation is studied. The crack-tip asymptotic interpolation function is incorporated into the NMM to increase the accuracy of the crack-tip stress field. In addition, the Mohr-Coulomb criterion with tensile cut off is adopted to be the crack propagation criterion to judge the direction of crack initiation and propagation. Then a crack tip searching method is developed to automatically update the position of the crack tips. The inapplicability of the original loop search method in the NMM is also illustrated and a novel loop search method based on manifold elements is developed for physical loop updating. Moreover, methods for the manifold element updating and physical cover updating are provided. Based on the above study, the developed numerical method is capable to simulate multiple crack propagation. At last, typical rock rupture problems are numerically simulated to manifest the effectiveness of the developed numerical method.

scholarly journals Fretting fatigue crack initiation and propagation in Ti6Al4V sheets under tribocorrosive conditions of artificial seawater and physiological solutions

2020 ◽  
Vol 234 (12) ◽  
pp. 1526-1534 ◽  
Author(s):  
Zeeshan Anjum ◽  
Masood Shah ◽  
Hassan Elahi ◽  
Mushtaq Khan ◽  
Mohammad Mujahid ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Testing Machine ◽  
Fatigue Crack Initiation ◽  
Physiological Solution ◽  
Fretting Corrosion ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Dry Conditions ◽  
Phosphate Buffered Saline

The interaction of mechanical components experiencing relative movements and cyclic loads in a corrosive environment is known as fretting corrosion or tribocorrosion. In the current work, the mechanism of crack initiation and propagation in dovetail slots of Ti6Al4V samples (in contact with carbide rods) under fretting corrosion conditions was investigated. A newly developed test rig installed on a universal testing machine was used to conduct tests at 20 Hz frequency under 5 and 7.5 kN fretting loads. Tests were conducted at room temperature in 3.5% NaCl and phosphate-buffered saline solutions. Crack propagation in all samples was examined by a metallurgical microscope, and the detailed analysis of fractured samples was carried out by a scanning electron microscope. In comparison to dry conditions, early crack initiation and faster crack propagation were observed in salt and physiological solution environments. Colored spots and large amounts of chlorine, sodium, and oxygen were found around cracks, and plastically deformed regions in the 3.5% NaCl environment provided the evidence of a corrosive attack. Large amounts of oxygen, phosphorous, chlorine, potassium, and sodium were detected in the phosphate-buffered saline environment.

Notch Fatigue Crack Initiation and Propagation Life under Constant Amplitude Loading through Residual Stress Field

2013 ◽  
Vol 682 ◽  
pp. 17-24 ◽  
Author(s):  
Mustapha Benachour ◽  
Mohamed Benguediab ◽  
Nadjia Benachour
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Stress Field ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Constant Amplitude ◽  
Crack Initiation And Propagation ◽  
Residual Stress Field ◽  
Alloy Plate ◽  
Initiation And Propagation

The purpose of this paper is to estimate the number of cycles for fatigue crack initiation in notched plate under constant amplitude loading through tensile residual stress field of Aluminum alloy plate. Residual stress field was generated by plastic deformation using finite element method. Simulation of fatigue behavior was made on AFGROW code. It was shown that the fatigue crack initiation and propagation were affected by level of residual stress filed. In this investigation, the presence of tensile residual stresses reduces considerably the total fatigue life. Loading parameter namely stress ratio was studied. The decreasing in this parameter reduces the fatigue crack growth rate (FCGRs).

Local Crack-Tip Strain Concept for Fatigue Crack Initiation and Propagation

1987 ◽  
Vol 109 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Heihachi Shimada ◽  
Yasubumi Furuya
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Local Strain ◽  
Strain History ◽  
Crack Initiation And Propagation ◽  
Fine Grid ◽  
Initiation And Propagation

The existence of the unified local strain field where we can substantially combine the two fatigue stages, crack initiation and propagation, was experimentally confirmed. Using the fine-grid-method, the changes of local notch-root or crack-tip strain and these histories were investigated until the small elemental block of material was broken by crack initiation and propagation. It became clear that the crack-tip strain behavior and its fracture process showed the similarity with local strain damage accumulation on crack initiation process. Especially, when the local strain history in the “elemental size, ρ*” adjacent to the crack-tip was taken into account, very good agreement of two stages could be obtained, ρ* depended on the kind of material. Based on this result, we have proposed a new idea termed “local crack-tip strain concept” that has the possibility for more simple, one parameter approach for future fatigue life analysis. It qualitatively differs from the currently used macroscopic, two parameters approach by combining the gross-strain (Δεtotal) fatigue life curve and fracture mechanics parameter (ΔK).

Fatigue Crack Initiation and Propagation Behaviors in Rotating Bending of SNCM439 Steel in Very High Cycle Regime

2015 ◽  
Vol 664 ◽  
pp. 255-266 ◽  
Author(s):  
Akiyoshi Nakagawa ◽  
Benning Lian ◽  
Takashi Kondo ◽  
Douglas P. Romilly ◽  
Noriyasu Oguma ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Crack Initiation And Propagation ◽  
Surface Fracture ◽  
Initiation And Propagation ◽  
Rotating Bending ◽  
Long Life ◽  
Very High

In order to ensure the long term durability of mechanical structures, the fatigue property of structural components should be clarified in the long life region such as the gigacycle regime. The rotating bending fatigue tests in very high cycle regime were carried out for a nickel chromium molybdenum steel for structural use of machines (JIS Material Code: SNCM439) in this study. Based on the initiation site of the fatigue crack, fracture modes were classified into the following typical three modes: (1) usual surface fracture, (2) surface defect-initiated fracture and (3) interior inclusion-initiated fracture, respectively. InS-Ndiagram, experimental data in the usual surface fracture mode appeared at higher stress levels with fewer loading cycles, whereas the data in the other two fracture modes appeared at lower stress levels with more loading cycles. Thus, the duplexS-Nproperty was confirmed for this steel in the very long life regime. In order to clarify the fatigue mechanism of the interior inclusion-initiated fracture, the quantitative evaluations were made by applying the stress intensity factor range. The fatigue crack initiation and propagation processes in the interior inclusion-initiated fracture were divided into four stages: formation of the fine granular area (FGA) due to initiation and coalescence of micro-debondings, formation of the fish-eye due to penny-shape crack propagation, crack propagation as surface crack and final catastrophic fracture.

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