Elastic Anisotropy Effect of Crystals on Polycrystal Fatigue Crack Initiation

1995 ◽  
Vol 117 (4) ◽  
pp. 470-477 ◽  
Author(s):  
N. J. Teng ◽  
T. H. Lin
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Elastic Anisotropy ◽  
Crack Nucleation ◽  
Fatigue Crack Initiation ◽  
Surface Plastic ◽  
Fatigue Crack Nucleation ◽  
Crystal Anisotropy ◽  
Equivalent Inclusion Method ◽  
Plastic Shear Strain

Fatigue bands have been observed in both monocrystalline and polycrystalline metals. Extrusions and intrusions at the free surface of fatigued specimens are favorable sites for fatigue crack nucleation. Previous studies (Lin and Ito, 1969; Lin, 1992) mainly concerned the fatigue crack initiation in aluminum and its alloys. The elastic anisotropy of individual crystals of these metals is insignificant and was accordingly neglected. However, the anisotropy of the elastic constants of some other metallic crystals, such as titanium and some intermetallic compounds, is not negligible. In this paper, the effect of crystal anisotropy is considered by using Eshelby’s equivalent inclusion method. The polycrystal analyzed is Ni3Al intermetallic compound. The plastic shear strain distributions and the cumulative surface plastic strain in the fatigue band versus the number of loading cycles were calculated, and the effect of crystal anisotropy on the growth of the extrusions was examined.

scholarly journals The Effect of the Microstructure and Defects on Crack Initiation in 316L Stainless Steel under Multiaxial High Cycle Fatigue

2014 ◽  
Vol 891-892 ◽  
pp. 815-820 ◽  
Author(s):  
Raphaël Guerchais ◽  
Franck Morel ◽  
Nicolas Saintier
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Driving Forces ◽  
Numerical Models ◽  
Fatigue Crack Initiation ◽  
Defect Size ◽  
Cycle Fatigue ◽  
Fatigue Crack Nucleation

The aim of this study is to analyse the influence of both the microstructure and defects on the high cycle fatigue behaviour of the 316L austenitic stainless steel, using finite element simulations of polycrystalline aggregates. High cycle fatigue tests have been conducted on this steel under uniaxial (push-pull) and multiaxial (combined in-phase tension and torsion) loading conditions, with both smooth specimens and specimens containing artificial semi-spherical surface defects. 2D numerical models, using a cubic elastic constitutive model, are created to determine the degree of heterogeneity of the local stress parameters as a function of the defect size. This has been done for one microstructure using several orientation sets generated from the initial texture of the material. The grains are explicitly modelled and the anisotropic behaviour of each FCC crystal is described by the generalized Hookes law with a cubic elasticity tensor. From the simulations carried out with different defect sizes and orientation sets that are representative of the real texture of the tested material, statistical information regarding mesoscopic mechanical fields provides useful insight into the microstructural dependence of the driving forces for fatigue crack nucleation at the mesoscopic scale (or the scale of individual grains). The results in terms of the stress fields and fatigue crack initiation conditions are determined at both the mesoscopic and macroscopic scales. The results from these FE models are used along with an original probabilistic mesomechanics approach to quantify the defect size effect. The resulting predictions, which are sensitive to the microstructure, include the probability distribution of the high cycle fatigue strength.

The role of elastic anisotropy, length scale and crystallographic slip in fatigue crack nucleation

2013 ◽  
Vol 61 (5) ◽  
pp. 1224-1240 ◽  
Author(s):  
C.A. Sweeney ◽  
W. Vorster ◽  
S.B. Leen ◽  
E. Sakurada ◽  
P.E. McHugh ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Elastic Anisotropy ◽  
Crack Nucleation ◽  
Length Scale ◽  
Fatigue Crack Nucleation ◽  
Crystallographic Slip

scholarly journals Fatigue behaviour of AA6061-T6 alloys in the corrosive environment

2018 ◽  
Vol 165 ◽  
pp. 03015
Author(s):  
Ngoc Vu Nguyen ◽  
Peifeng Li
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Structural Integrity ◽  
Electron Backscatter Diffraction ◽  
Crack Nucleation ◽  
Fatigue Crack Initiation ◽  
High Stress ◽  
Corrosive Environment ◽  
Nacl Solution ◽  
Fatigue Crack Nucleation

The combined effects of corrosion and fatigue are known to be hazardous threats to structural integrity of aluminium alloys that are being extensively used in marine applications. This work investigated the fatigue crack initiation and growth behaviour of AA6061-T6 alloys in 3.5 wt% NaCl simulated seawater using scanning electron microscope and electron backscatter diffraction characterisation techniques. It was found that the fatigue resistance of AA6061-T6 is drastically downgraded when subjected to the corrosive environment of 3.5 wt% NaCl solution. High stress concentration at both sides of a pit mouth in conjunction with attacked grain boundaries facilitates fatigue crack nucleation, while the presence of hydrogen formed by corrosion reactions causes crack tip embrittlement and thus increases crack growth rate. Fractographic analysis reveals that there is a change in fatigue crack growth mechanism of AA6061-T6 alloys tested in the NaCl solution. At short crack length, the crack develops transgranularly along crystallographic planes due to hydrogen-enhanced decohesion process. Further crack growth is dominated by adsorption induced dislocation emission process, resulting in the mixed mode of intergranular and transgranular crack growth.

Assessment Technology of Fatigue Crack Initiation Life of Weld Structures

2017 ◽  
Vol 86 (1) ◽  
pp. 56-58
Author(s):  
Seiichiro TSUTSUMI ◽  
Fincato RICCARDO ◽  
Mitsuru OHATA ◽  
Tomokazu SANO
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Assessment Technology ◽  
Crack Initiation Life

scholarly journals Crack Propagation in the Tibia Bone within Total Knee Replacement Using the eXtended Finite Element Method

2021 ◽  
Vol 11 (10) ◽  
pp. 4435
Author(s):  
Ho-Quang NGUYEN ◽  
Trieu-Nhat-Thanh NGUYEN ◽  
Thinh-Quy-Duc PHAM ◽  
Van-Dung NGUYEN ◽  
Xuan Van TRAN ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Fracture Prevention ◽  
Patient Specific ◽  
Extended Finite Element ◽  
Tibia Bone ◽  
Age Related ◽  
Final Failure

Understanding of fracture mechanics of the human knee structures within total knee replacement (TKR) allows a better decision support for bone fracture prevention. Numerous studies addressed these complex injuries involving the femur bones but the full macro-crack propagation from crack initiation to final failure and age-related effects on the tibia bone were not extensively studied. The present study aimed to develop a patient-specific model of the human tibia bone and the associated TKR implant, to study fatigue and fracture behaviors under physiological and pathological (i.e., age-related effect) conditions. Computed tomography (CT) data were used to develop a patient-specific computational model of the human tibia bone (cortical and cancellous) and associated implants. First, segmentation and 3D-reconstruction of the geometrical models of the tibia and implant were performed. Then, meshes were generated. The locations of crack initiation were identified using the clinical observation and the fatigue crack initiation model. Then, the propagation of the crack in the bone until final failure was investigated using the eXtended finite element method (X-FEM). Finally, the obtained outcomes were analyzed and evaluated to investigate the age-effects on the crack propagation behaviors of the bone. For fatigue crack initiation analysis, the stress amplitude–life S–N curve witnessed a decrease with increasing age. The maximal stress concentration caused by cyclic loading resulted in the weakening of the tibia bone under TKR. For fatigue crack propagation analysis, regarding simulation with the implant, the stress intensity factorand the energy release rate tended to decrease, as compared to the tibia model without the implant, from 0.152.5 to 0.111.9 (MPa) and from 10240 to 5133 (J), respectively. This led to the drop in crack propagation speed. This study provided, for the first time, a detailed view on the full crack path from crack initiation to final failure of the tibia bone within the TKR implant. The obtained outcomes also suggested that age (i.e., bone strength) also plays an important role in tibia crack and bone fracture. In perspective, patient-specific bone properties and dynamic loadings (e.g., during walking or running) are incorporated to provide objective and quantitative indicators for crack and fracture prevention, during daily activities.

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