Measurement of Stress Distribution Near Fatigue Crack in Ultra-Fine Grained Steel by Synchrotron Radiation

2005 ◽  
Vol 490-491 ◽  
pp. 118-123 ◽  
Author(s):  
Yoshiaki Akiniwa ◽  
Keisuke Tanaka ◽  
Hidehiko Kimura
Keyword(s):  
Fatigue Crack ◽  
Synchrotron Radiation ◽  
Stress Distribution ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Closure ◽  
Experimental Result ◽  
Ultrafine Grained ◽  
Ultrafine Grained Steel

Single-edge-notched specimens of ultrafine-grained steel were fatigued. The mean grain size of the steel is about 2 micrometers. Propagation behavior of fatigue cracks was observed with the crack closure. The resistance of the crack propagation of ultrafine-grained steel was larger than that of conventional steels. The crack closure acted as an important role for the larger resistance of fatigue crack propagation. After fatigue tests, stress distribution near the fatigue crack was measured by monochromatic X-rays from synchrotron radiation. The irradiated area was 100 µm x 100 µm. Residual and loading stress distributions ahead of the crack tip and on the crack wake was measured at the maximum stress intensity factor and zero applied load. The stress was determined by sin2ψ method. The measured stress was compared with the value calculated by FEM and the fatigue crack propagation model. The stress distribution at the maximum load and residual stresses agreed very well with the calculated results. The crack opening stress calculated by the residual stresses agreed with the experimental result.

Heterogeneous Microstructure Effect on Residual Stress and Fatigue Crack Resistance in Dual-Phase Materials

2009 ◽  
Author(s):  
Masahito Mochizuki ◽  
Yoshiki Mikami
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Stress Distribution ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Compressive Residual Stress ◽  
Fatigue Tests ◽  
Residual Stress Distribution ◽  
Experimental Result ◽  
Microstructure Effect

The effect of transformation-induced microscopic residual stress on fatigue crack propagation behaviour of ferrite-martensite lamellar steel was discussed. Fatigue tests of prestrained and non-prestrained specimens were performed. Inflections and branches at ferrite-martensite boundaries were observed in the non-prestrained specimens. On the other hand, less inflections and branches were found in the prestrained specimens. The experimental results showed that the transformation induced microscopic residual stress has influence on the fatigue crack propagation behaviour. To estimate the microscopic residual stress distribution, a numerical simulation of microscopic residual stress induced by martensitic transformation was performed. The simulation showed that compressive residual stress was generated in martensite layer, and the result agree with the experimental result that inflections and branches were observed at ferrite-martensite boundaries. In addition, the change in the microscopic residual stress distribution by prestraining was also calculated to show the compressive residual stress changed to tensile by prestraining. This also agree with the experimental result of the observation of fatigue crack path.

scholarly journals P-Texture Effect on the Fatigue Crack Propagation Resistance in an Al-Cu-Mg Alloy Bearing a Small Amount of Silver

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2481 ◽  
Author(s):  
Yangcheng Hu ◽  
Zhiyi Liu ◽  
Qi Zhao ◽  
Song Bai ◽  
Fei Liu
Keyword(s):  
Electron Microscopy ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Closure ◽  
High Intensity ◽  
Damage Tolerance ◽  
Mg Alloy ◽  
Random Texture ◽  
Texture Effect

P-texture effect on the fatigue crack propagation (FCP) resistance in an Al-Cu-Mg alloy containing a small amount of Ag, is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattering diffraction (EBSD). Results shows that the high intensity P-texture sheet has lower σ0.2/σb, lower FCP rate and higher damage tolerance than random texture sheet. Fracture analysis indicates that the striations spacing of high intensity P-texture sheet is much smaller than that of random texture sheet and it has a rougher fatigue fracture surface, which causes a significant roughness induced crack closure (RICC) effect. The calculation results manifest that high intensity P-texture sheet possesses a higher crack closure level reaching 0.73 as compared to random texture sheet (only 0.25). The statistical analysis results reveal the P-grains have large twist angle of 105–170° and tilt angle of 5–60° with neighboring grains, which is similar to Goss-grains. This is the fundamental reason that P-texture sheet has the same FCP resistance and induces fatigue crack deflection as Goss-texture sheet. Additionally, the most {111} slipping planes of P-grains are distributed in the range of 30–50° deviating from transverse direction of the sheet. This results in more {111} slipping planes to participate in cyclic plastic deformation, which is beneficial to reduce fatigue damage accumulation and improve the damage tolerance of Al-Cu-Mg-Ag alloy.

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