scholarly journals Dynamic Strain Evolution around a Crack Tip under Steady- and Overloaded-Fatigue Conditions

Metals ◽  
2015 ◽  
Vol 5 (4) ◽  
pp. 2109-2118 ◽  
Author(s):  
Soo Lee ◽  
E-Wen Huang ◽  
Wanchuck Woo ◽  
Cheol Yoon ◽  
Hobyung Chae ◽  
...  
Keyword(s):  
Crack Tip ◽  
Dynamic Strain ◽  
Strain Evolution

Effects of Dynamic Strain-Aging and Cyclic Loading on Fracture Behavior of Ferritic Steels

2002 ◽  
Author(s):  
K. Linga Murty ◽  
Chang-Sung Seok
Keyword(s):  
Fracture Toughness ◽  
Cyclic Loading ◽  
Strain Aging ◽  
Crack Tip ◽  
Load Ratio ◽  
Seismic Loading ◽  
Dynamic Strain ◽  
Ferritic Steels ◽  
Bend Tests ◽  
Point Bend

Ferritic steels commonly used for pressure vessels and reactor supports in light water reactors (LWRs) exhibit dynamic strain aging (DSA) resulting in decreased ductility and toughness. In addition, recent work indicated decreased toughness during reverse-cyclic loading that has implications on reliability of these structures under seismic loading conditions. We summarize some of our recent work on these aspects along with synergistic effects, of interstitial impurity atoms (IIAs) and radiation induced point defects, that result in interesting beneficial effects of radiation exposure at appropriate temperature and strain-rate conditions. Radiation-defect interactions were investigated on pure iron, Si-killed mild steel, A533B, A516, A588 and other reactor support and vessel steels. In all cases, DSA is seen to result in decreased ductility accompanied by increased work-hardening parameter. In addition to mechanical property tests, fracture toughness is investigated on both A533B and A516 steels. While dips in fracture toughness are observed in A533B steel in the DSA region, A516 steel exhibited at best a plateau. The reasons could lie in the applied strain-rates; while J1c tests were performed on A533B steel using 3-point bend tests on Charpy type specimens, CT specimens were used for A516 steel. However, tensile and 3-point bend tests on similar grade A516 steel of different vintage did exhibit distinct drop in the energy to fracture. Load-displacement curves during J1c tests on CT specimens did show load drops in the DSA regime. The effect of load ratio (R) on J versus load-line displacement curves for A516 steel is investigated from +1 to −1 at a fixed normalized incremental plastic displacement of 0.1 (R = 1 corresponds to monotonic loading). We note that J-values are significantly reduced with decreasing load ratio. The work-hardening characteristics on the fracture surfaces were studied following monotonic and cyclic loading fracture tests along with the stress-field analyses. From the hardness and the ball-indentation tests, it was shown that decreased load ratio (R) leads to more strain hardening at the crack tip resulting in decreased fracture toughness. From the stress field analysis near the crack tip of a compact tension fracture toughness test specimen, a cycle of tensile and compressive loads is seen to result in tensile residual stresses (which did not exist at the crack tip before). These results are important to evaluations of flawed-structures under seismic loading conditions, i.e. Leak-Before-Break (LBB) and in-service flaw evaluation criteria where seismic loading is addressed. In addition, studies on fast vs total (thermal+fast) neutron spectra revealed unexpected results due to the influence of radiation exposure on source hardening component of the yield stress; grain-size of pure iron plays a significant role in these effects.

scholarly journals Dynamic strain evolution in an optically excited Pt thin film

AIP Advances ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 115111
Author(s):  
M. F. DeCamp ◽  
A. D. DiChiara ◽  
K. M. Unruh
Keyword(s):  
Thin Film ◽  
Dynamic Strain ◽  
Strain Evolution

The Measurement of the Fatigue Crack-Tip Displacement and Strain Fields under High Frequency Resonant Loading Applying DIC Method

2015 ◽  
Vol 710 ◽  
pp. 83-90
Author(s):  
Hong Li Gao ◽  
Wei Jiang ◽  
Huan Liu ◽  
Huan Bin Zheng ◽  
Hui Liu
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
High Frequency ◽  
High Speed ◽  
Loading Condition ◽  
Crack Tip ◽  
Dynamic Strain ◽  
High Speed Photography ◽  
Stress Cycle ◽  
Strain Fields

In order to measure the displacement and strain field in the fatigue crack tip area of CT specimens under high frequency resonant loading condition in the fatigue crack propagation test, a method based on the digital image correlation (DIC) and digital high-speed photography technology are proposed in this paper. First, a series of digital speckle images of CT specimen under sinusoidal alternating load were collected by digital high-speed photography equipment, the displacement and strain fields within the region of crack tip in each image were calculated by DIC. The sinusoidal changing strain curve has been obtained by the least square sine wave fitting method, and the characteristic parameters of sinusoidal strain are calculated, such as the amplitude, frequency, phase, mean load . The images of characteristic position in one stress cycle were obtained by comparing the fitted sine curve of strain with the corresponding speckle images. Finally, the dynamic strain gauge was used to measure the strain at crack tip point during one stress cycle, and the accuracy and feasibility of DIC method were verified by the experimental results. The study result presented in this paper will supply a foundation for exploring the crack propagation law and measuring the fatigue crack growth parameters under high frequency resonant loading condition further.

scholarly journals Crack tip strain evolution and crack closure during overload of a growing fatigue crack

2017 ◽  
Vol 11 (41) ◽  
pp. 143-148 ◽  
Author(s):  
De-Qiang Wang ◽  
Ming-Liang Zhu ◽  
Fu-Zhen Xuan
Keyword(s):  
Fatigue Crack ◽  
Crack Closure ◽  
Crack Tip ◽  
Strain Evolution

Effect of Inertia on Finite Near-Tip Deformation for Fast Mode-III Crack Growth

1985 ◽  
Vol 52 (2) ◽  
pp. 281-286 ◽  
Author(s):  
J. D. Achenbach ◽  
N. Nishimura
Keyword(s):  
Explicit Expression ◽  
Crack Growth ◽  
Finite Deformation ◽  
Crack Tip ◽  
Dynamic Strain ◽  
Mode Iii ◽  
Moving Crack ◽  
Crack Line ◽  
Transition Boundary ◽  
Small Strains

The combined effects of finite deformation and material inertia have been analyzed for fast crack growth under antiplane loading conditions. A steady-state dynamic solution has been obtained for the finite strain on the crack line, from the moving crack tip to the moving transition boundary with the zone of small strains. The crack propagates in a material with a response curve in uniform shear that is linear at small strains, and which remains constant once a critical strain has been exceeded. The corresponding quasi-static solution is given in the full zone of large deformation. For the dynamic formulation, an explicit expression for the crack-line strain has been obtained by expanding the displacement in a power series in the distance to the crack line, with coefficients that depend on the distance to the moving crack tip. Substitution in the equation of motion yields a nonlinear ordinary differential equation for the relevant coefficient, which can be solved rigorously. The finite deformation crack-line fields have been matched to appropriate small-strain fields at the transition boundary. The principal result is that the dynamic strain remains bounded at the crack tip, apparently due to the effect of material inertia. The crack-line strain has been plotted for several crack-tip speeds. It decreases with higher crack-tip speed. An explicit expression has been given for the extent of the zone of finite deformation, as a function of the crack tip speed and the far-field loading.

Neutron diffraction studies on lattice strain evolution around a crack-tip during tensile loading and unloading cycles

2005 ◽  
Vol 53 (8) ◽  
pp. 971-975 ◽  
Author(s):  
Yinan Sun ◽  
Hahn Choo ◽  
Peter K. Liaw ◽  
Yulin Lu ◽  
Bing Yang ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Lattice Strain ◽  
Crack Tip ◽  
Tensile Loading ◽  
Strain Evolution ◽  
Loading And Unloading

Simulation and Contrast Analysis of tem Images of Cracks

1990 ◽  
Vol 48 (1) ◽  
pp. 578-579
Author(s):  
D. Goyal ◽  
A. H. King
Keyword(s):  
Displacement Vector ◽  
Crack Tip ◽  
Perfect Crystal ◽  
Operating Conditions ◽  
Displacement Fields ◽  
Fringe Contrast ◽  
Orthogonal Geometry ◽  
Moire Fringe ◽  
Moiré Fringe

TEM images of cracks have been found to give rise to a moiré fringe type of contrast. It is apparent that the moire fringe contrast is observed because of the presence of a fault in a perfect crystal, and is characteristic of the fault geometry and the diffracting conditions in the TEM. Various studies have reported that the moire fringe contrast observed due to the presence of a crack in an otherwise perfect crystal is distinctive of the mode of crack. This paper describes a technique to study the geometry and mode of the cracks by comparing the images they produce in the TEM because of the effect that their displacement fields have on the diffraction of electrons by the crystal (containing a crack) with the corresponding theoretical images. In order to formulate a means of matching experimental images with theoretical ones, displacement fields of dislocations present (if any) in the vicinity of the crack are not considered, only the effect of the displacement field of the crack is considered.The theoretical images are obtained using a computer program based on the two beam approximation of the dynamical theory of diffraction contrast for an imperfect crystal. The procedures for the determination of the various parameters involved in these computations have been well documented. There are three basic modes of crack. Preliminary studies were carried out considering the simplest form of crack geometries, i. e., mode I, II, III and the mixed modes, with orthogonal crack geometries. It was found that the contrast obtained from each mode is very distinct. The effect of variation of operating conditions such as diffracting vector (), the deviation parameter (ω), the electron beam direction () and the displacement vector were studied. It has been found that any small change in the above parameters can result in a drastic change in the contrast. The most important parameter for the matching of the theoretical and the experimental images was found to be the determination of the geometry of the crack under consideration. In order to be able to simulate the crack image shown in Figure 1, the crack geometry was modified from a orthogonal geometry to one with a crack tip inclined to the original crack front. The variation in the crack tip direction resulted in the variation of the displacement vector also. Figure 1 is a cross-sectional micrograph of a silicon wafer with a chromium film on top, showing a crack in the silicon.

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