scholarly journals Mechanism of Subordinate Peak Skewing of FBG Sensor during Cracks Propagation Monitoring on Aluminum Alloy Structure

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Bo Jin ◽  
Weifang Zhang ◽  
Feifei Ren ◽  
Meng Zhang ◽  
Wei Dai ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Plastic Zone ◽  
Strain Gradient ◽  
Strain Distribution ◽  
Crack Tip ◽  
Fbg Sensor ◽  
Inhomogeneous Strain ◽  
Study Results ◽  
Fbg Sensors ◽  
Cracks Propagation

This study investigates the variety of the spectra features of fiber Bragg grating (FBG) around the crack tip during fatigue crack propagation. The study results reveal that the turning of the subordinate peak is significantly associated with crack lengths and corresponds to strain gradient along the FBG. Meanwhile, the strain distribution sensed by the FBG changes with the sensing section of the grating. FBG sensors could observe the monotonic plastic zone ahead of the fatigue crack tip. The cubic strain is distributed along the grating, with monotonic plastic zone propagation at the initial and terminal part of the grating, at approximately a 30% ratio of the entire grating. However, the monotonic plastic zone is sensed by the FBG, at ±15% bias of the grating center, with the quadratic strain gradient pattern along the grating. In particular, when the initial and terminal parts of the grating experience highly inhomogeneous strain distribution, the spectrum distortion occurs.

Plastic Strain Distribution at the Tips of Propagating Fatigue Cracks

1976 ◽  
Vol 98 (1) ◽  
pp. 24-29 ◽  
Author(s):  
D. L. Davidson ◽  
J. Lankford
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Plastic Strain ◽  
Plastic Zone ◽  
Strain Distribution ◽  
Dimensionless Parameter ◽  
Fatigue Cracks ◽  
Crack Tip ◽  
Cyclic Plastic Zone ◽  
Plastic Zones

The techniques of selected area electron channeling and positive replica examination have been used to study the plastic zones attending fatigue crack propagation in 304 SS, 6061-T6 aluminum alloy, and Fe-3Si steel. These observations allowed the strain distribution at the crack tip to be determined. The results indicate that the concepts of a monotonic and a cyclic plastic zone are essentially correct, with the strains at demarcation between these two zones being 3 to 6 percent. Strain distribution varies as r−1/2 in the cyclic zone and as ln r in the monotonic plastic zone. The strain distributions for all materials studied may be made approximately coincident by using a dimensionless parameter related to distance from the crack tip.

scholarly journals Quantitative measurement of plastic strain field at a fatigue crack tip

2012 ◽  
Vol 468 (2144) ◽  
pp. 2399-2415 ◽  
Author(s):  
Y. Yang ◽  
M. Crimp ◽  
R. A. Tomlinson ◽  
E. A. Patterson
Keyword(s):  
Fatigue Crack ◽  
Plastic Strain ◽  
Plastic Zone ◽  
Strain Distribution ◽  
Pure Titanium ◽  
Crack Tip ◽  
Plastic Zone Size ◽  
Uniaxial Tensile ◽  
Commercially Pure Titanium ◽  
Zone Size

A novel approach is introduced to map the mesoscale plastic strain distribution resulting from heterogeneous plastic deformation in complex loading and component geometries, by applying the discrete Fourier transform (DFT) to backscattered electron (BSE) images of polycrystalline patches. These DFTs are then calibrated against the full width at half the maximum of the central peak of the DFTs collected from the same material tested under in situ scanning electron microscopy uniaxial tensile conditions, which indicates a close relationship with the global tensile strain. In this work, the technique is demonstrated by measuring the residual strain distribution and plastic zone size around a fatigue crack tip in a commercially pure titanium compact tension specimen, by collecting BSE images in a 15×15 array of 115 μm square images around the fatigue crack tip. The measurement results show good agreement with the plastic zone size and shape measured using thermoelastic stress analysis.

Analytical Prediction Model for Fatigue Crack Propagation Rate under Tension-Compression Loading

2013 ◽  
Vol 842 ◽  
pp. 455-461
Author(s):  
Yu Sha ◽  
Shi Gang Bai ◽  
Ya Hui Wang
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Plastic Zone ◽  
Crack Propagation ◽  
Compressive Stress ◽  
Fatigue Crack Propagation ◽  
Crack Tip ◽  
Plastic Zone Size ◽  
Zone Size ◽  
Compression Loading

Elastic–plastic finite element analyses have been performed to study the compressive stress effect on fatigue crack growth under applied tension–compression loading. The near crack tip stress, crack tip opening displacement and crack tip plastic zone size were obtained for a kinematic hardening material. The results have shown that the near crack tip local stress, displacement and reverse plastic zone size are controlled by the maximum stress intensity factors Kmax and the applied compressive stress σmaxcom under tension–compression. Based on the finite element analysis results, a fatigue crack propagation model using Kmax and σmaxcom as a parameters under tension–compression loading has been developed.The models under tension–compression loading agreed well with experimental observations.

Higher-harmonic imaging of the plastic zone in front of a fatigue crack tip

2014 ◽  
Vol 53 (7S) ◽  
pp. 07KC04 ◽  
Author(s):  
Koichiro Kawashima ◽  
Takumi Aida ◽  
Hazime Yasui
Keyword(s):  
Fatigue Crack ◽  
Plastic Zone ◽  
Crack Tip ◽  
Harmonic Imaging ◽  
Higher Harmonic

Fatigue crack tip plastic zone sizes in aluminum alloys

1978 ◽  
Vol 14 (2) ◽  
pp. R87-R90
Author(s):  
J. Lankford ◽  
D. L. Davidson
Keyword(s):  
Fatigue Crack ◽  
Aluminum Alloys ◽  
Plastic Zone ◽  
Crack Tip

Experimental Determination of Fatigue Crack Growth Behavior and Surface Strain Distribution of ‘Faint-Waist Pure Shear’ Specimens with Different Crack Tip Radii

2006 ◽  
Vol 79 (4) ◽  
pp. 712-733 ◽  
Author(s):  
Christian Feichter ◽  
Zoltan Major ◽  
Reinhold W. Lang
Keyword(s):  
Crack Growth ◽  
Strain Gradient ◽  
Strain Distribution ◽  
Strain Analysis ◽  
Crack Tip ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Analysis Method ◽  
Growth Initiation ◽  
Tip Radius

Abstract The influence of the initial crack-tip radius on the fatigue behavior and the strain distribution in the vicinity of the blunted crack tip was determined experimentally using a servo-hydraulic testing machine and an optical full-field strain analysis method. Two different elastomer grades (SBR, EPDM) were selected for the experimental work. The strain analysis method used, based on the image correlation technique, was found to be an effective tool to determine strains, strain distributions and gradients near the crack tip for elastomeric materials. Different material behavior was observed in the two rubber types investigated. While the crack tip was regularly blunted (half circle shape) for EPDM and the strain gradient was low (less steep), the crack tip was sharp (less blunted) with a higher strain gradient for SBR. Furthermore the crack tip radius was found to be an important influencing factor on the initiation of crack growth, but not on the crack growth behavior after initiation. Based on the experimental results a phenomenological, first-order, crack-growth initiation law was proposed, dependent on the crack tip radius, the tearing energy at crack growth initiation for a sharp crack and a parameter representing the influence of the crack tip radius.

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