An Inverse Method to Reconstruct Crack-tip Cohesive Zone Laws for Fatigue by Numerical Field Projection

2022 ◽  
pp. 111435
Author(s):  
H. Tran ◽  
Y.F. Gao ◽  
H.B. Chew
Keyword(s):  
Cohesive Zone ◽  
Inverse Method ◽  
Crack Tip

scholarly journals Critical value of the generalized stress intensity factor for a crack perpendicular to an interface

2015 ◽  
Vol 471 (2183) ◽  
pp. 20150571 ◽  
Author(s):  
George G. Adams
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Crack Tip ◽  
Critical Value ◽  
Zone Model ◽  
Cohesive Stress ◽  
Generalized Stress Intensity Factor

When a crack tip impinges upon a bi-material interface, the order of the stress singularity will be equal to, less than or greater than one-half. The generalized stress intensity factors have already been determined for some such configurations, including when a finite-length crack is perpendicular to the interface. However, for these non-square-root singular stresses, the determination of the conditions for crack growth are not well established. In this investigation, the critical value of the generalized stress intensity factor for tensile loading is related to the work of adhesion by using a cohesive zone model in an asymptotic analysis of the separation near the crack tip. It is found that the critical value of the generalized stress intensity factor depends upon the maximum stress of the cohesive zone model, as well as on the Dundurs parameters ( α and β ). As expected this dependence on the cohesive stress vanishes as the material contrast is reduced, in which case the order of the singularity approaches one-half.

A Crack Close to and Perpendicular to an Interface: Resolution of Anomalous Behavior With a Cohesive Zone

2019 ◽  
Vol 86 (3) ◽  
Author(s):  
George G. Adams
Keyword(s):  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Applied Pressure ◽  
Stress Singularity ◽  
Crack Tip ◽  
Anomalous Behavior ◽  
Work Of Adhesion ◽  
Bimaterial Interface ◽  
Zone Model ◽  
Finite Distance

In this investigation, we consider a crack close to and perpendicular to a bimaterial interface. If the crack tip is at the interface then, depending on material properties, the order of the stress singularity will be equal to, less than, or greater than one-half. However, if the crack tip is located any finite distance away from the interface the stress field is square-root singular. Thus, as the crack tip approaches the interface, the stress intensity factor approaches zero (for cases corresponding to a singularity of order less than one-half) or infinity (for a singularity of order greater than one-half). The implication of this behavior is that for a finite applied pressure the crack will either never reach the interface or will reach the interface with vanishing small applied pressure. In this investigation, a cohesive zone model is used in order to model the crack behavior. It is found that the aforementioned anomalous behavior for the crack without a cohesive zone disappears and that the critical value of the applied pressure for the crack to reach the interface is finite and depends on the maximum stress of the cohesive zone model, as well as on the work of adhesion and the Dundurs' parameters.

Effect of Grain Size on the Fracture Toughness of Bimodal Nanocrystalline Materials

2014 ◽  
Vol 936 ◽  
pp. 400-408 ◽  
Author(s):  
Ying Guang Liu ◽  
Xiao Dong Mi ◽  
Song Feng Tian
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Grain Size ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Cohesive Zone ◽  
Critical Stress ◽  
Crack Tip ◽  
Critical Stress Intensity Factor ◽  
Coarse Grain

To research the effect of grain size on the fracture toughness of bimodal nanocrystalline (BNC) materials which are composed of nanocrystalline (NC) matrix and coarse grains, we have developed a theoretical model to study the critical stress intensity factor (which characterizes toughness) of BNC materials by considering a typical case where crack lies at the interface of two neighboring NC grains and the crack tip intersect at the grain boundary of the coarse grain, the cohesive zone size is assumed to be equal to the grain sizedof the NC matrix. Blunting and propagating processes of the crack is controlled by a combined effect of dislocation and cohesive zone. Edge dislocations emit from the cohesive crack tip and make a shielding effect on the crack. It was found that the critical stress intensity factor increases with the increasing of grain sizedof the NC matrix as well as the coarse grain sizeD. Moreover, the fracture toughness is relatively more sensitive to the coarse grain size rather than that of NC matrix.

On the Size of the Cohesive Zone at the Crack Tip

1985 ◽  
Vol 52 (2) ◽  
pp. 490-492 ◽  
Author(s):  
N. C. Huang
Keyword(s):  
Cohesive Zone ◽  
Crack Tip

Cohesive Zone Modeling of Hydrogen Assisted Cracking in a 15-5 PH Steel and Comparison With Experiments

2015 ◽  
Author(s):  
Giovambattista Bilotta ◽  
Mandana Arzaghi ◽  
Gilbert Hénaff ◽  
Guillaume Benoit ◽  
Clara Moriconi ◽  
...  
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Cohesive Zone ◽  
Hydrogen Pressure ◽  
Crack Tip ◽  
Gaseous Hydrogen ◽  
Zone Model ◽  
Loading Frequency ◽  
High Hydrogen ◽  
Crack Growth Rates

Gaseous hydrogen substantially reduces fracture properties such as threshold stress intensity factor and crack growth resistance in the precipitation-hardened martensitic stainless steel investigated in this study. Fatigue crack propagation tests were performed on CT specimens under different atmospheres (hydrogen pressures from 0.09 to 40 MPa) on the Hycomat test bench, at the Pprime Institute in Poitiers, France. A strongly enhanced crack growth regime was identified at high hydrogen pressure and low-frequency loading. Crack growth rates obtained at a constant load under same pressure levels suggest that a combination of tensile stresses above a threshold (KIscc) and fatigue cycles contribute to the hydrogen embrittlement at the crack tip. These experimental results were compared to the finite element simulation results obtained by a recently developed cohesive zone model at the crack tip. A specifically developed traction-separation law which is suitable to describe the gradual degradation of cohesive stresses under monotonic and cyclic loadings, and which is furthermore sensitive to the hydrogen concentration was used. The effects of the different testing conditions, in terms of loading frequency and hydrogen pressure, on the modeling results are discussed. It was shown that the model qualitatively predicts the detrimental influence of gaseous hydrogen on the crack growth rates.

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