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.

scholarly journals A Local Approach to Assess Effects of Specimen Geometry on Cleavage Fracture Toughness in Reactor Pressure Vessel Steels

2018 ◽  
Author(s):  
Diego F. B. Sarzosa ◽  
Rafael Savioli ◽  
Claudio Ruggieri ◽  
Andrey Jivkov ◽  
Jack Beswick
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Pressure Vessel ◽  
Crack Tip ◽  
Crack Size ◽  
Size Ratio ◽  
Additional Contribution ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Shallow Crack

This work presents recent improvements in the micromechanical failure criterion based on the Weibull stress (σw) concept for prediction of cleavage fracture in ferritic steels. The model is applied in SE(B) specimens extracted from an ASTM A533 pressure vessel steel having different levels of stress triaxiality at the crack tip. Nonlinear 3D finite element models with dimensions matching the tested specimens were built to provide the necessary crack tip stresses at the fracture process zone for calculation of the σw-J evolution from wich the variation of characteristic toughness values (J0) between different cracked geometries can be estimated. Application of this methodology for the material used at this study is able to predict J0 for SE(B) specimens with very shallow crack size ratio a/W = 0.05, short crack a/W = 0.2 and deep crack a/W = 0.4. The reported fracture toughness values for specimens having very shallow crack size ratio is an additional contribution of this study.

A Micromechanics Approach for Assessing the Applicability of Precracked Charpy Specimens to Determine the T0 Reference Temperature

2013 ◽  
Author(s):  
Rafael G. Savioli ◽  
Claudio Ruggieri
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Pressure Vessel ◽  
Reference Temperature ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Toughness Testing ◽  
The Relationship ◽  
Resistance Data ◽  
Weibull Stress

This work describes an application of a micromechanics model for cleavage fracture to determine the reference temperature for pressure vessel steels from precracked Charpy (PCVN) specimens. A central objective is evaluate the effectiveness of the Weibull stress (σw) 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 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 σw and J from which the variation of fracture toughness across different crack configurations is predicted. 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.

scholarly journals Incorporation of Obstacle Hardening into Local Approach to Cleavage Fracture to Predict Temperature Effects in the Ductile to Brittle Transition Regime

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1224
Author(s):  
Maria S. Yankova ◽  
Andrey P. Jivkov ◽  
Rajesh Patel
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Cleavage Crack ◽  
Pressure Vessel Steel ◽  
Transition Regime ◽  
Vessel Steel ◽  
Integrity Assessment ◽  
Brittle Transition ◽  
Ductile To Brittle Transition ◽  
Weibull Stress

Ductile-to-brittle-transition refers to observable change in fracture mode with decreasing temperature—from slow ductile crack growth to rapid cleavage. It is exhibited by body-centred cubic metals and presents a challenge for integrity assessment of structural components made of such metals. Local approaches to cleavage fracture, based on Weibull stress as a cleavage crack-driving force, have been shown to predict fracture toughness at very low temperatures. However, they are ineffective in the transition regime without the recalibration of Weibull stress parameters, which requires further testing and thus diminishes their predictive capability. We propose new Weibull stress formulation with thinning function based on obstacle hardening model, which modifies the number of cleavage-initiating features with temperature. Our model is implemented as a post-processor of finite element analysis results. It is applied to analyses of standard compact tension specimens of typical reactor pressure vessel steel, for which deformation and fracture toughness properties in the transition regime are available. It is shown that the new Weibull stress is independent of temperature, and of Weibull shape parameter, within the experimental error. It accurately predicts the fracture toughness at any temperature in the transition regime without relying upon empirical fits for the first time.

Prediction of Cleavage Fracture in the Ductile-to-Brittle Transition Region of Pressure Vessel Steels: A Probabilistic Model

2006 ◽  
Vol 324-325 ◽  
pp. 283-286
Author(s):  
Xiao Sheng Gao ◽  
Gui Hua Zhang ◽  
T.S. Srivatsan
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Pressure Vessel ◽  
Stress Triaxiality ◽  
Weibull Model ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Proposed Model ◽  
Modified Weibull ◽  
Weibull Stress

This paper presents a modified Weibull stress model, which accounts for the effects of plastic strain and stress triaxiality at the crack tip region. The proposed model is applied to predict cleavage fracture in a modified A508 pressure vessel steel. It is demonstrated that the Weibull modulus (m) remains constant in the temperature range considered, while the threshold Weibull stress (σw-min) decreases with an increase in temperature due to reduction of the yield stress and the scale parameter of the Weibull model (σu) increases with temperature reflecting the influences of temperature on both material flow properties and toughness. The proposed model accurately predicts the scatter of the measured fracture toughness data and the strong effects of constraint and temperature on cleavage fracture toughness.

A Monte Carlo Implementation of the James-Ford-Jivkov Microstructurally Informed Local Approach Applied to Predict Fracture Toughness Across Irradiation Conditions

2016 ◽  
Author(s):  
Michael Ford ◽  
Peter James
Keyword(s):  
Fracture Toughness ◽  
Monte Carlo ◽  
Transition Region ◽  
Crack Size ◽  
Model Parameters ◽  
Pressure Vessel Steel ◽  
Local Approach ◽  
Vessel Steel ◽  
Reactor Pressure Vessel Steel ◽  
Monte Carlo Implementation

The need to predict changes in fracture toughness for materials where the tensile properties change through life, such as with irradiation, whilst accounting for geometric constraint effects, such as crack size, are clearly important. Currently one of the most likely approaches by which to develop such ability are through application of local approach models. These approaches appear to be sufficient in predicting lower shelf toughness under high constraint conditions, but may fail when attempting to predict toughness in the transition region, for low constraint geometries or for different irradiation states, when using the same parameters, making reliable predictions impossible. Cleavage toughness predictions in the transition regime are here made with a stochastic, Monte Carlo implementation of the recently proposed James-Ford-Jivkov model. This implementation is based around the creation of individual initiators following the experimentally observed distribution for specific reactor pressure vessel steel, and determining if these initiators form voids or cause cleavage failure using the model’s improved criterion for particle failure. This implementation has been presented previously in PVP2015-45905, where it was successfully applied across different constraint conditions; in the work presented here it is applied across different irradiation conditions for a second type of steel. The model predicts the fracture toughness in a large part of the transition region, demonstrates an ability to predict the irradiation shift and shows a level of scatter similar to that observed experimentally. All results presented, for a given material, are obtained without changes in the model parameters. This suggests that the model can be used predicatively for assessing toughness changes due to constraint-, irradiation- and temperature-driven plasticity changes.

scholarly journals Incorporation of Temperature and Plastic Strain Effects into Local Approach to Fracture

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6224
Author(s):  
Sergiy Kotrechko ◽  
Vladislav Kozák ◽  
Oleksandra Zatsarna ◽  
Galyna Zimina ◽  
Nataliya Stetsenko ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Plastic Strain ◽  
Bulk Density ◽  
Formation Rate ◽  
Theoretical Concept ◽  
Manganese Steel ◽  
Effect Of Temperature ◽  
Pressure Vessel Steel ◽  
Local Approach ◽  
Vessel Steel

An unjustified simplification of the local quantitative criterion regarding cleavage nucleation is a key problem in the utilisation of the Local Approach to Fracture (LA), particularly to predict the fracture toughness within the ductile-to-brittle transition (DBT) region. The theoretical concept of the effect of both temperature and the plastic strain value on the crack nuclei (CN) generation rate in iron and ferritic steels is presented. It is shown how the plastic strain and temperature affect CN formation rate and, as a consequence, govern the shape of the temperature dependence of fracture toughness KJc and its scatter limits. Within the framework of the microscopic model proposed, dependences of the CN bulk density on the plastic deformation value and temperature are predicted. Convenient approximation dependences for incorporating this effect into the LA are suggested. The experimental data of reactor pressure vessel steel and cast manganese steel demonstrate that the use of these dependences enables one to predict, with sufficient accuracy, the effect of temperature on the value of fracture toughness and its scatter limits over the DBT region. It is shown that accounting for both the temperature and strain dependence of CN bulk density gives rise to the invariance of parameters of the Weibull distribution to temperature.

Experimental Study on the Cleavage Fracture Behavior of an ASTM A285 Grade C Pressure Vessel Steel

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Rafael G. Savioli ◽  
Claudio Ruggieri
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Pressure Vessel ◽  
Fracture Behavior ◽  
Pressure Vessels ◽  
Experimental Results ◽  
Pressure Vessel Steel ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Vessel Steel

This work addresses an experimental investigation on the cleavage fracture behavior of an ASTM A285 Grade C pressure vessel steel. One purpose of this study is to enlarge previously reported work on mechanical and fracture properties for this class of steel to provide a more definite database for use in structural and defect analyses of pressurized components, including pressure vessels and storage tanks. Another purpose is to determine the reference temperature, T0, derived from the Master curve methodology which defines the dependence of fracture toughness with temperature for the tested material. Fracture toughness testing conducted on single edge bend SE(B) specimens in three-point loading extracted from an A285 Grade C pressure vessel steel plate provides the cleavage fracture resistance data in terms of the J-integral and crack tip opening displacement (CTOD) at cleavage instability, Jc and δc. Additional tensile and conventional Charpy tests produce further experimental data which serve to characterize the mechanical behavior of the tested pressure vessel steel. The experimental results reveal a strong effect of specimen geometry on Jc and δc-values associated with large scatter in the measured values of cleavage fracture toughness. Overall, the present investigation, when taken together with previous studies, provides a fairly extensive body of experimental results which describe in detail the fracture behavior of an ASTM A285 Grade C pressure vessel steel.

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