Influence of nanoscale deformation twins near a slant edge crack tip on crack blunting in nanocrystalline metals

2017 ◽  
Vol 184 ◽  
pp. 286-295 ◽  
Author(s):  
Tengwu He ◽  
Miaolin Feng
Keyword(s):  
Edge Crack ◽  
Crack Tip ◽  
Nanocrystalline Metals ◽  
Deformation Twins ◽  
Crack Blunting

Comparison of Strip Yield and Net Section Plasticity Models for a Bar in Bending With a Single Edge Crack

2017 ◽  
Author(s):  
Wolf Reinhardt ◽  
Don Metzger
Keyword(s):  
Edge Crack ◽  
Large Scale ◽  
Stress Singularity ◽  
Crack Tip ◽  
Small Scale ◽  
Single Edge ◽  
Yield Model ◽  
Strip Yield Model ◽  
Crack Tip Plasticity ◽  
Stress And Deformation

The strip yield model is widely used to describe crack tip plasticity in front of a crack. In the strip yield model the stress in the plastic zone is considered as known, and stress and deformation fields can be obtained from elastic solutions using the condition that the crack tip stress singularity vanishes. The strip yield model is generally regarded to be valid to describe small scale plasticity at a crack tip. The present paper examines the behavior of the strip yield model at the transition to large-scale plasticity and its relationship to net section plasticity descriptions. A bar in bending with a single edge crack is used as an illustrative example to derive solutions and compare with one-sided and two-sided plasticity solutions.

Atomistic simulation for configuration evolution and energetic calculation of crack in body-centered-cubic iron

2006 ◽  
Vol 21 (10) ◽  
pp. 2542-2549 ◽  
Author(s):  
Li-Xia Cao ◽  
Chong-Yu Wang
Keyword(s):  
Low Temperatures ◽  
Crack Tip ◽  
Dislocation Nucleation ◽  
Effect Of Temperature ◽  
Body Centered Cubic ◽  
Partial Dislocations ◽  
Higher Temperature ◽  
Crack Blunting ◽  
Increasing Temperature ◽  
Extended Dislocation

The molecular dynamics method has been used to simulate mode I cracking in body-centered-cubic iron. Close attention has been paid to the process of the atomic configuration evolution of the cracks. The simulation shows that at low temperatures, partial dislocations are emitted before the initiation of crack propagation, subsequently forming the stacking faults or multilayer twins on {112} planes, and then brittle cleavage and extended dislocation nucleation are observed at the crack tip accompanied by twin extension. These results are in agreement with the experimental observation that twinning and fracture processes cooperate at low temperatures. Furthermore, an energetics analysis has been made on the deformation behavior observed at the crack tip. The effect of temperature on the fracture process is discussed. At the higher temperature, plastic deformation becomes easier, and crack blunting occurs. With increasing temperature, the fracture resistance increases, and the effect of the lattice trapping can be weakened by thermal activation.

Fracture Initiation Due to Asymmetric Impact Loading of an Edge Cracked Plate

1990 ◽  
Vol 57 (1) ◽  
pp. 104-111 ◽  
Author(s):  
Y. J. Lee ◽  
L. B. Freund
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Edge Crack ◽  
Crack Tip ◽  
Fracture Initiation ◽  
Stress Wave Propagation ◽  
Normal Velocity ◽  
Asymmetric Impact ◽  
Original Crack

The two-dimensional elastodynamic problem of a semi-infinite plate containing an edge crack is considered. Initially, the plate is stress-free and at rest. To simulate the asymmetric impact of a projectile on the cracked edge of the plate, a normal velocity is suddenly imposed on the boundary of the plate on one side of the edge crack. The boundary of the plate and the crack faces are otherwise traction-free. Due to the nature of the loading, a combination of transient mode I and mode II deformation fields is induced near the crack tip. The corresponding stress intensity factor histories are determined exactly by linear superposition of several more readily obtainable stress wave propagation solutions, including a fundamental solution arising from a particular problem in the dynamic theory of elastic dislocations. The stress intensity factor histories are determined for the time interval from initial loading until the first wave scattered at the crack tip is reflected at the plate edge and returns to the crack tip. In experiments on fracture initiation in a high-strength steel based on essentially this specimen and loading configuration, Kalthoff and Winkler (1987) reported a fracture grew from the original crack either as a tensile crack inclined to the original crack plane or as a straight-ahead shear fracture, depending on the intensity of the applied velocity. The observations are considered in light of the solution reported here.

Investigation on Validity of J-Integral of Edge Crack under Cold Rolling Condition

2014 ◽  
Vol 556-562 ◽  
pp. 696-699
Author(s):  
Jian Jun Chen ◽  
Xiao Xue Li ◽  
Hong Liang Pan
Keyword(s):  
Cold Rolling ◽  
Edge Crack ◽  
Crack Tip ◽  
Simulation Method ◽  
Rolling Process ◽  
J Integral ◽  
Strip Steel ◽  
Failure Region ◽  
Incremental Theory Of Plasticity

In this paper the characterization of the edge crack in the strip steel are studied by using numerical simulation method. The developments of the stress and strain near the crack tip are obtained and the value of the J-integral of edge crack under the rolling process is then examined. FE simulation result shows that the J-integral is not always path independent in the whole rolling process. When the crack is far away from the roller, the J-integral is path independent. When the crack enters the cold rolling region, the unload phenomena will occur near the crack tip which cause the incremental theory of plasticity failed and the conservation of the J-integral is not valid any more. The J-integral failure region is then determined by a series of FE simulations.

Effect of Crack Blunting on the Ductile-Brittle Response of Crystalline Materials

1998 ◽  
Vol 539 ◽  
Author(s):  
D.M. Lipkin ◽  
G.E. Beltz ◽  
L.L. Fischer
Keyword(s):  
Crack Tip ◽  
Dislocation Nucleation ◽  
Crack Advance ◽  
Dislocation Emission ◽  
Crystalline Materials ◽  
Self Consistent ◽  
Crack Blunting ◽  
Cohesive Stresses ◽  
Crack Tip Geometry ◽  
Crack Tip Blunting

AbstractWe propose a self-consistent criterion for crack propagation versus dislocation emission, taking into account the effects of crack-tip blunting. Continuum concepts are used to evaluate the evolving competition between crack advance and dislocation nucleation as a function of crack- tip curvature. This framework is used to classify crystals as intrinsically ductile or brittle in terms of the unstable stacking energy, the surface energy, and the peak cohesive stresses achieved during opening and shear of the atomic planes. We find that ductile-brittle criteria based on the assumption that the crack is ideally sharp capture only two of the four possible fracture regimes. One implication of the present analysis is that a crack may initially emit dislocations, only to reinitiate cleavage upon reaching a sufficiently blunted crack-tip geometry.

scholarly journals The effect of a crack-tip radius on the validity of the singular solution

2004 ◽  
Vol 218 (7) ◽  
pp. 693-701 ◽  
Author(s):  
D Dini ◽  
D A Hills
Keyword(s):  
Singular Solution ◽  
Edge Crack ◽  
Process Zone ◽  
Crack Tip ◽  
Local Stress ◽  
Scaling Factor ◽  
Root Radius ◽  
Finite Crack ◽  
Tip Radius ◽  
Local Stress Field

The influence of the finite crack-root radius on the local stress field at the root of a crack is found explicitly. This is then applied as an inner asymptotic solution, embedded with the conventional crack-tip singular solution, to quantify the possible influence of local rounding on the ability of the singular solution to capture the characteristics of the crack-tip process zone. The scaling factor employed is the conventional crack-tip stress intensity, and the example of a simple edge crack in a tension field is used to illustrate the method.

Study on Anisotropic Mechanical Behavior at near Pre-Crack for AZ31B Sheet under Biaxial Stress

2013 ◽  
Vol 750 ◽  
pp. 196-199
Author(s):  
Jian Gang Wang ◽  
Dong Ying Ju ◽  
F.X. Yin ◽  
Lei Mao
Keyword(s):  
Stress State ◽  
Deformation Behavior ◽  
Basal Slip ◽  
Crack Tip ◽  
Tensile Loading ◽  
Biaxial Stress ◽  
Deformation Twins ◽  
Biaxial Tensile ◽  
Biaxial Stress State ◽  
Loading Ratio

In this study, a biaxial tensile test of cruciform specimens containing centre notch was conducted in order to clarify the deformation behavior near the crack tip at the early stages of crack initiation when objected to a biaxial stress state. Results show that the hardness and stress value within the deformed zone increased with increase in the loading ratio. Observation of the microstructure reveals that the deformation is dominated by basal slip under equal biaxial tensile loading. The asymmetrical biaxial tensile loading generates deformation twins near the crack tip. These results indicate that existing deformation twins contribute to higher hardness, and there is obvious anisotropism in the vicinity of crack tip under asymmetrical biaxial tensile loading.

scholarly journals A New Scheme for Crack Growth Modeling by Coupling Modified Quarter Point Crack-Tip Element and the Level Set Method

2013 ◽  
Vol 10 (2) ◽  
pp. 46
Author(s):  
Y Abdelaziz
Keyword(s):  
Crack Growth ◽  
Level Set Method ◽  
Level Set ◽  
Edge Crack ◽  
Numerical Test ◽  
Growth Modeling ◽  
Crack Tip ◽  
Plate Specimen ◽  
Crack Tip Element ◽  
Crack Growth Modeling

 In this paper, an efficient, numerical procedure is presented to track crack growth modeling without remeshing. The method's key feature is the coupling of a modified quarter-point crack tip element (MQPE) with the level set method (LSM) for crack growth problems. The LSM was used to represent the crack location, including the location of crack tips. The MQPE was used to compute the stress and displacement fields necessary for determining the rate of crack growth. Numerical test cases including various geometrical exceptions (the center-crack plate specimen, the single edge-crack plate specimen, and the double-edge crack plate) demonstrate the accuracy, robustness, and efficiency of the MQPE/LSM coupling. The extrapolation technique was used to estimate numerically the calibration factor for various specimens. This work confirms the feasibility of the MQPE/LSM to model accurately the singularity existing in the vicinity of the cracks. It allows an economic and adequate calculation of the stress intensity factors, which can be introduced into the various criteria of fracture or laws of propagation of the crack. The new method reduces the need for remeshing, and results agree well with reference data. 

scholarly journals Effect Of Crack Blunting On Subsequent Crack Propagation

1995 ◽  
Vol 409 ◽  
Author(s):  
J. SchiØtz ◽  
A. E. Carlsson ◽  
L. -M. Canel ◽  
Robb Thomson
Keyword(s):  
Crack Propagation ◽  
Brittle Material ◽  
Crack Tip ◽  
Dislocation Emission ◽  
Dislocation Source ◽  
Blunt Crack ◽  
Ductile Materials ◽  
Noticeable Increase ◽  
Greens Function ◽  
Crack Blunting

AbstractTheories of toughness of materials depend on an understanding of the characteristic instabilities of the crack tip, and their possible interactions. In this paper we examine the effect of dislocation emission on subsequent cleavage of a crack and on further dislocation emission. The work is an extension of the previously published Lattice Greens Function methodology[1, 2, 3]. We have developed a Cavity Greens Function describing a blunt crack and used it to study the effect of crack blunting under a range of different force laws. As the crack is blunted, we find a small but noticeable increase in the crack loading needed to propagate the crack. This effect may be of importance in materials where a dislocation source near the crack tip in a brittle material causes the crack to absorb anti-shielding dislocations, and thus cause a blunting of the crack. It is obviously also relevant to cracks in more ductile materials where the crack itself may emit dislocations.

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