Prediction of failure probabilities for cleavage fracture from the scatter of crack geometry and of fracture toughness using the weakest link model

1983 ◽  
Vol 18 (2) ◽  
pp. 359-375 ◽  
Author(s):  
A. Brückner ◽  
D. Munz
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Crack Geometry ◽  
Weakest Link ◽  
Link Model ◽  
Failure Probabilities

Reliability of Welded Structures Containing Cracks in Heat-Affected Zones

2000 ◽  
Vol 122 (4) ◽  
pp. 225-232 ◽  
Author(s):  
David B. Lanning ◽  
M.-H. Herman Shen
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Crack Front ◽  
Surface Crack ◽  
Material Properties ◽  
Coarse Grained ◽  
Welded Structures ◽  
Weakest Link ◽  
Link Model

This study investigates the reliability of a plate containing a semi-elliptical surface crack intersecting regions of dissimilar material properties. A weakest-link model is developed to express fracture toughness distributions in terms of effective crack lengths that account for the varying stress intensity factor along the crack front. The model is intended to aid in the development of fracture toughness distributions for cracks encountering local brittle zones (LBZ) in the heat-affected zones (HAZ) of welded joints, where lower-bound fracture toughness values have been measured in the laboratory when a significant portion of the crack front is intersecting the coarse-grained LBZs. An example reliability analysis is presented for a surface crack in a material containing alternating bands of two Weibull-distributed toughnesses. [S0892-7219(00)01203-6]

scholarly journals Assessment of Local Approach Methods for Predicting End-of-Life Toughness of RPV Steels

2011 ◽  
Author(s):  
Andrey P. Jivkov ◽  
David P. G. Lidbury ◽  
Peter James
Keyword(s):  
Fracture Toughness ◽  
End Of Life ◽  
Cleavage Fracture ◽  
Failure Probability ◽  
Sufficient Accuracy ◽  
Model Parameters ◽  
Local Approach ◽  
Component Failure ◽  
Weakest Link ◽  
Future Work

Local approach methods are becoming increasingly popular as practical tools for cleavage fracture toughness prediction. Their application involves two distinct elements: calculation of ‘individual’ probabilities of failure, dictated by the local mechanical fields; and summation of these failure probabilities to predict the probability of component failure. In this work, we demonstrate that development of the local approach methods to date has been essentially focused on improving the criterion for predicting local failure as a function of the local mechanical fields. Yet, the existing methods fail to predict with sufficient accuracy the effects of irradiation and defect geometry on fracture toughness when the calculations are based on a common set of model parameters. A possible reason for this, common to all methods, is found in the calculation of the cumulative failure probability, which is based on the weakest-link argument. We discuss the implications of the weakest-link assumption, identify those situations where it needs to be reconsidered, and propose future work that will increase our understanding for improving the calculation of global failure probability.

A Mathematical Model for Competing Failure Modes in Strain Cycle Fatigue

2006 ◽  
Vol 129 (2) ◽  
pp. 293-303 ◽  
Author(s):  
Gerald T. Cashman
Keyword(s):  
Failure Modes ◽  
High Stress ◽  
Local Strain ◽  
Initiation Site ◽  
Weakest Link ◽  
Strain Relationship ◽  
Powder Metallurgy Alloy ◽  
Link Model ◽  
Cyclic Plastic Strain ◽  
Selection Of

Elevated temperature data for powder metallurgy alloy René 95 generated in vacuum are presented to demonstrate that the life differences observed between surface and internally initiated failures are due to an environmental effect. The transition in behavior from a mode at low stress dominated by internal initiations to a surface dominated mode at high stress is quantitatively described in terms of both a weakest-link model and a local strain relationship. A fatigue failure mechanism is provided that explains that the natural selection of initiation site is based upon the concept that the site displaying the highest local cyclic plastic strain is the location where fatigue initiates.

A Weibull Stress Approach Incorporating the Coupling Effect of Constraint and Plastic Strain in Cleavage Fracture Toughness Predictions

2014 ◽  
Author(s):  
Claudio Ruggieri ◽  
Robert H. Dodds
Keyword(s):  
Fracture Toughness ◽  
Plastic Strain ◽  
Cleavage Fracture ◽  
Coupling Effect ◽  
Crack Size ◽  
Parameter Analysis ◽  
Pressure Vessel Steel ◽  
Fracture Parameter ◽  
Vessel Steel ◽  
Weibull Stress

This work describes a micromechanics methodology based upon a local failure criterion incorporating the strong effects of plastic strain on cleavage fracture coupled with statistics of microcracks. A central objective is to gain some understanding on the role of plastic strain on cleavage fracture by means of a probabilistic fracture parameter and how it contributes to the cleavage failure probability. A parameter analysis is conducted to assess the general effects of plastic strain on fracture toughness correlations for conventional SE(B) specimens with varying crack size over specimen width ratios. Another objetive is to evaluate the effectiveness of the modified Weibull stress (σ̃w) model to correct effects of constraint loss in PCVN specimens which serve to determine the indexing temperature, T0, based on the Master Curve methodology. Fracture toughness testing conducted on an A285 Grade C pressure vessel steel provides the cleavage fracture resistance (Jc) data needed to estimate T0. Very detailed non-linear finite element analyses for 3-D models of plane-sided SE(B) and PCVN specimens provide the evolution of near-tip stress field with increased macroscopic load (in terms of the J-integral) to define the relationship between σ̃w and J. For the tested material, the Weibull stress methodology yields estimates for the reference temperature, T0, from small fracture specimens which are in good agreement with the corresponding estimates derived from testing of much larger crack configurations.

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