scholarly journals Approximation of the crack-tip field in fatigue cracks in bridge steel specimens: DIC analysis of different constraint levels

2019 ◽  
Vol 13 (49) ◽  
pp. 97-106
Author(s):  
Stanislav Seitl ◽  
Petr Miarka ◽  
Vladimir Ruzicka ◽  
Lucie Malikova ◽  
Alejandro Cruces ◽  
...  
Keyword(s):  
Fatigue Cracks ◽  
Crack Tip ◽  
Crack Tip Field ◽  
Bridge Steel

A Comparison of Crack-Tip Field Parameters for Large and Small Fatigue Cracks

1986 ◽  
Vol 108 (3) ◽  
pp. 206-213 ◽  
Author(s):  
K. S. Chan ◽  
J. Lankford ◽  
D. L. Davidson
Keyword(s):  
Crack Growth ◽  
Fatigue Cracks ◽  
Crack Tip ◽  
Integral Approach ◽  
Crack Tip Field ◽  
Cyclic Plastic Zone ◽  
Small Cracks ◽  
Experimental Strain ◽  
Path Dependent ◽  
Crack Growth Rates

A comparison of the elastic-plastic crack-tip fields of large and small fatigue cracks has been made using the ΔJ-integral approach. Using experimental strain and displacement range measurements obtained by means of the stereoimaging technique, the ΔJ-integral has been computed for an aluminum alloy containing either large or small fatigue cracks, by performing line-contour integration along a variety of rectangular paths around the crack tip. These calculations reveal that for both large and small cracks the ΔJ-integral is path-dependent, and that the value of ΔJ increases with decreasing distance from the crack tip. Using an average local ΔJ or one estimated from the CTOD, the enhanced crack growth rates associated with small fatigue cracks can be explained on the basis of the large average ΔJ-integral within the cyclic plastic zone. The effect of crack closure on the computed local ΔJ (or ΔK) and crack growth is discussed.

Experimental Determination of Crack Driving Forces for Small Cracks

2016 ◽  
Vol 258 ◽  
pp. 495-500
Author(s):  
Angelika Brueckner-Foit ◽  
Pascal Pitz ◽  
Phillip Grahlmann ◽  
Frank Zeismann
Keyword(s):  
Stress Intensity ◽  
Driving Forces ◽  
Fatigue Cracks ◽  
Crack Tip ◽  
Image Correlation ◽  
Mode Ii ◽  
Crack Tip Field ◽  
Small Cracks ◽  
Experimental Values

The crack tip field of small fatigue cracks was measured using digital image correlation DIC. For this purpose, smooth specimen were fatigued until a certain amount of damage was visible on the surface. This specimens were then placed in a micro-tensile device in the SEM. The grey value patterns obtained at two different load levels were analyzed with DIC. Fitting the Williams series for the crack tip field to the corresponding DIC-displacement field in the crack tip area yielded the mode-I, and the mode-II stress intensity factors together with the T-stresses. It was found that the experimental values of the stress intensity factor were comparatively high with pronounced mode-II contributions.

Mismatch Effect on the Mixed Mode Type Creep Crack within Weldment

2016 ◽  
Vol 853 ◽  
pp. 281-285
Author(s):  
Jun Hui Zhang ◽  
Yan Wei Dai
Keyword(s):  
Mixed Mode ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Crack Tip Field ◽  
Creep Crack ◽  
Loading Mode ◽  
The Difference ◽  
Engineering Practices ◽  
Mismatch Effect ◽  
Transient And Steady State

Creep crack within weldments are very common in engineering practices, and the cracking location in these welding structures always appears at the HAZ location. The mismatch effect on the mixed mode creep crack is still not clear in these available literatures. The aim of this paper is to investigate the mismatch influence on the creep crack of mixed mode thoroughly. A mixed mode creep crack within HAZ is established in this paper. The leading factor that dominates the creep crack tip field under mixed loading mode is studied. The influences of mismatch effect on mode mixity, stress distribution and stress triaxiality are proposed. The difference of mixed mode creep crack and normal mode I or mode II creep crack are compared. The influence of mixity factor on the transient and steady state creep of crack tip are also analyzed.

INVESTIGATIONS ON THE DYNAMIC NEAR-CRACK-TIP FIELD USING THE GRID METHOD

1988 ◽  
Vol 49 (C3) ◽  
pp. C3-307-C3-312
Author(s):  
K. KUSSMAUL ◽  
T. DEMLER ◽  
A. KLENK
Keyword(s):  
Crack Tip ◽  
Grid Method ◽  
Crack Tip Field

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.

Modeling Dislocation-Mediated Hydrogen Transport and Trapping in Fcc Metals

2021 ◽  
pp. 1-54
Author(s):  
Theodore Zirkle ◽  
Luke Costello ◽  
Ting Zhu ◽  
David L. McDowell
Keyword(s):  
Transport Model ◽  
Constitutive Relations ◽  
Crack Tip ◽  
Lattice Diffusion ◽  
Hydrogen Transport ◽  
Crack Tip Field ◽  
Coupled Diffusion ◽  
Crystal Plasticity Model ◽  
Physically Based ◽  
Material Ductility

Abstract The diffusion of hydrogen in metals is of interest due to the deleterious influence of hydrogen on material ductility and fracture resistance. It is becoming increasingly clear that hydrogen transport couples significantly with dislocation activity. In this work, we employ a coupled diffusion-crystal plasticity model to incorporate hydrogen transport associated with dislocation sweeping and pipe diffusion in addition to standard lattice diffusion. Moreover, we consider generation of vacancies via plastic deformation and stabilization of vacancies via trapping of hydrogen. The proposed hydrogen transport model is implemented in a physically-based crystal viscoplasticity framework to model the interaction of dislocation substructure and hydrogen migration. In this study, focus is placed on hydrogen transport and trapping within the intense deformation field of a crack tip plastic zone. We discuss the implications of the model results in terms of constitutive relations that incorporate hydrogen effects on crack tip field behavior and enable exploration of hydrogen embrittlement mechanisms.

scholarly journals Mixed-mode crack tip fields in a polycrystalline aluminum alloy

2019 ◽  
Vol 300 ◽  
pp. 11004 ◽  
Author(s):  
Marcel Wicke ◽  
Angelika Brueckner-Foit
Keyword(s):  
Mixed Mode ◽  
Crack Tip ◽  
Strain Partitioning ◽  
Crack Tip Field ◽  
Polycrystalline Aluminum ◽  
Digital Twin ◽  
Crack Tip Fields ◽  
Mixed Mode Crack ◽  
Threshold Regime ◽  
Near Threshold

Carefully performed experiments with long cracks in the near-threshold regime have shown that the crack tip field of these cracks significantly deviate from the expected mode-I butterfly-shaped ones and resemble strongly to mixed-mode crack tip fields. A simulation study using a crystal plasticity (CP) approach has been utilized in order to understand this phenomenon. To this end, a digital twin of an aluminum sample fatigued in the near-threshold regime was generated with the help of electron backscatter diffraction (EBSD) and X-ray tomography. Once set-up, the digital twin was loaded in uniaxial tension using the fast spectral solver implemented in the Düsseldorf Advanced Material Simulation Kit (DAMASK). The versatility of this experimental-computational approach for studying the strain partitioning at the crack tip is demonstrated in this work.

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