Surface Stress Effects On Fracture

1995 ◽  
Vol 409 ◽  
Author(s):  
R.C. Cammarata ◽  
K. Sieradzki
Keyword(s):  
Brittle Fracture ◽  
Surface Stress ◽  
Fracture Criterion ◽  
Crack Tip ◽  
Dislocation Emission ◽  
Simple Analysis ◽  
Stress Effects ◽  
Surface Stresses ◽  
Self Similar ◽  
Brittle Fracture Criterion

AbstractThe effects of surface stress on fracture are reviewed. Calculations by Thomson et al. seem to suggest that surface stresses do not affect cleavage fracture when the crack propagates in a self similar manner even though the surface stress can lead to large stresses near the crack tip. However, surface stresses may have an important effect on dislocation emission near the crack tip. A simple analysis is offered to show how these effects may be incorporated into a modified Rice ductile-brittle fracture criterion by adding a term to the unstable stacking energy that takes into account the energy to form an incipient ledge.

Surface Stress Effects On The Critical Thickness Of Thin Film Superlattices

1997 ◽  
Vol 505 ◽  
Author(s):  
R. C. Cammarata ◽  
K. Sieradzki
Keyword(s):  
Thin Film ◽  
Solid Surface ◽  
Surface Stress ◽  
Critical Thickness ◽  
Unit Area ◽  
Solid Surfaces ◽  
Stress Effects ◽  
Surface Stresses ◽  
Solid Phases ◽  
Reversible Work

ABSTRACTSurface stress represents the reversible work per unit area to elastically stretch a solid surface, and can be associated with interfaces between two solid phases as well as free solid surfaces. The effects of surface stresses on the critical thickness for epitaxy in thin film superlattices is given.

Structural Integrity Assessment of RPV With Brittle Fracture Criterion: Issues and Advanced Approaches

2009 ◽  
Author(s):  
George Karzov ◽  
Boris Margolin ◽  
Victoria Shvetsova ◽  
Victor Kostylev
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Crack Front ◽  
Fracture Criterion ◽  
Structural Integrity ◽  
Present Report ◽  
Statistical Nature ◽  
Integrity Assessment ◽  
The Difference ◽  
Brittle Fracture Criterion

A key input to calculation of the structural integrity of the RPV by the brittle fracture criterion is known to be the fracture toughness of a material. When calculating resistance of RPV to brittle fracture it was taken earlier that fracture toughness, KJC, depends only on temperature, and does not depend on thickness of specimens if this thickness is sufficiently large so that the plane strain condition is satisfied. To date it has become clear by many researches that KJC depends on a crack front length. This follows from the statistical nature of brittle fracture in steels. It means that for adequate assessment of RPV structural integrity, the dependence of KJC on the postulated flaw size has to be taken into account. Moreover, it has been shown that the KJC values for specimens with shallow cracks are larger than for specimens with deep cracks, and the KJC values obtained from small-size fracture toughness specimens (for example, pre-cracked Charpy specimens) are larger than the values for CT specimens with thickness of 25 mm, and KJC values may be affected load biaxiality. These findings are explained by the loss of constraint. Thus, for adequate assessment of RPV structural integrity by the brittle fracture criterion, the scale factor has to be taken into account, with two causes being responsible: the physical cause connected with the statistical nature of brittle fracture and the mechanical one related to the difference in constraint for specimens of various geometries. This analysis is important for assessment of RPV structural integrity because i) for most cases the postulated flaws in RPV, due to their size and location, may be considered as shallow cracks; ii) the KJC values for irradiated RPV steels are usually obtained from small-size surveillance specimens that are as a rule, pre-cracked Charpy specimens; iii) for a postulated flaw in RPV, a load acts both perpendicular and along a crack front. i.e. loading is biaxial. For adequate assessment of RPV structural integrity by the brittle fracture criterion it is also necessary to take into account that distribution of the stress intensity factor along a crack front in RPV is heterogeneous, and loading is non-monotonic and non-isothermal. In the present report, advanced approaches are considered for assessment of RPV structural integrity that allow solving the above problems. The considered approaches have been included in Russian Standards for assessment of RPV structural integrity.

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