Evaluation of Prestraining and Dynamic Loading Effects on the Fracture Toughness of Structural Steels by the Local Approach

2001 ◽  
Vol 123 (3) ◽  
pp. 362-372 ◽  
Author(s):  
Fumiyoshi Minami ◽  
Kazushige Arimochi
Keyword(s):  
Fracture Toughness ◽  
Dynamic Loading ◽  
Temperature Shift ◽  
Steel Structures ◽  
Structural Steels ◽  
Unstable Fracture ◽  
Virgin Material ◽  
Local Approach ◽  
Loading Effects ◽  
Weibull Stress

On the occasion of recent great earthquakes, great concern is focused on the prevention of unstable fracture of steel structures against the seismic loading. This paper employs the local approach for the evaluation of prestraining and dynamic loading effects, experienced during an earthquake, on the fracture toughness of structural steels. The prestraining and dynamic loading lead to a similar result: increasing the yield stress and tensile strength and decreasing the fracture toughness. It is shown, however, that the combined effects of prestraining and dynamic loading is not equivalent to the sum of each individual effect. The analysis using the local approach demonstrates that the critical Weibull stress at brittle fracture initiation is independent of prestraining and dynamic loading. Based on the Weibull stress fracture criterion, the prestraining and dynamic loading effects on the fracture toughness can be predicted from static toughness results of the virgin material. As an engineering application, a simplified method is proposed for the estimation of fracture toughness under the seismic condition. This method uses a reference temperature concept: the dynamic fracture toughness at the service temperature T with prestrain is displaced by the static toughness of the virgin material at a lower temperature T−ΔTPD, where ΔTPD is a temperature shift of the fracture toughness caused by prestraining and dynamic loading. The temperature shift ΔTPD is provided as a function of the flow stress elevation in the seismic condition.

Recent Developments and Challenges of Cleavage Fracture Modelling in Steels: Aspects on Microstructural Mechanics and Local Approach Methods

2019 ◽  
Author(s):  
Quanxin Jiang ◽  
V. M. Bertolo ◽  
V. A. Popovich ◽  
Carey L. Walters
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Structural Integrity ◽  
State Of The Art ◽  
Structural Steels ◽  
Ferritic Steels ◽  
Local Approach ◽  
Microstructural Parameters ◽  
Recent Developments ◽  
Size Scales

Abstract Offshore activity in low-temperature areas requires the use of analysis methods that are capable of reliably predicting cleavage (brittle) fracture of ferritic steels in order to guarantee the structural integrity during service. Cleavage fracture is controlled by physical events at different size scales and is influenced by the multiple microstructural parameters of the material. The prediction of fracture toughness of steels based on the microstructure has received great attention, and relevant techniques have been continuously developed. This paper is aimed at reviewing the recent development of cleavage fracture modelling in steels and identifying the existing challenges to inspire further research. The paper contains three parts aimed at explaining how methods are developed and utilized to predict fracture toughness of steel from its microstructures. (1) The complex multiparametric nature of the microstructures of ferritic steels and its influence on cleavage fracture is introduced. (2) A review is given on the main perspectives and models in micromechanisms of cleavage fracture in steels. (3) Discussion is contributed to the link between micromechanisms and the local approach in cleavage fracture modelling. As a result, the paper gives a state of the art on microstructural mechanics and local approach methods of cleavage fracture modelling in structural steels.

Theoretical Underpinning of the Constraint Effect Between Deeply Cracked C(T)- and SEN(B) Specimens

2005 ◽  
Author(s):  
Michael Ludwig
Keyword(s):  
Fracture Toughness ◽  
Standard Test ◽  
Test Method ◽  
Reference Temperature ◽  
Small Scale ◽  
Reference Solution ◽  
Constraint Effect ◽  
Local Approach ◽  
Transition Range ◽  
Weibull Stress

In the standard test method for the determination of the reference temperature T0 in the transition range, ASTM E 1921-03 [1], the remark is given that different specimen types could lead to discrepancies in the calculated T0 values. Especially C(T) and SEN(B) specimens indicate by experimental evidence that a 10 °C to 15 °C difference in T0 has been observed. In the course of the European research project VOCALIST [2] a ferritic RPV steel has been investigated by conducting numerous fracture toughness experiments as well as intensive numerical studies. A local approach model based on the Weibull stress has been developed and calibrated for this material [3]. For the calculation of the constraint effect between SEN(B) and C(T) specimens with a crack to ligament ratio of approx. 0.5 the model has been applied to predict the constraint effects on fracture toughness and the resulting theoretical difference in the reference temperature T0. For this purpose the according specimens have been calculated by several finite element models and a reference solution in the small scale yielding space allowed for the calculation of the “constraint free” reference transition temperature T0. By means of theoretical constraint functions derived from the Weibull stress model, the difference for each specimen compared to the reference solution could be calculated. From the results a theoretical difference of ΔT0 = 10°C between SEN(B) (lower value) and C(T) specimens (higher value) caused by the different crack tip constraint has been obtained. This value confirms the experimental observations.

Avoiding Local Brittle Zones in Offshore Pipeline Girth Welds for Reeling Installation Involving Large Plastic Strain

2013 ◽  
Author(s):  
Jens P. Tronskar ◽  
Vebjørn Andresen
Keyword(s):  
Fracture Toughness ◽  
Plastic Strain ◽  
Strain Curve ◽  
Structural Steels ◽  
Coarse Grained ◽  
Unstable Fracture ◽  
Large Plastic Strain ◽  
Acceptance Criteria ◽  
Offshore Pipeline ◽  
Girth Welds

Pipelines for reeling are designed to tolerate the large plastic strain associated with the reeling installation process based on widely accepted strain based design principles for subsea pipelines as described in Det Norske Veritas (DNV) Offshore Pipeline Code OS-F101: 2012 [1]. Engineering Critical Assessment (ECA) to develop flaw acceptance criteria for automatic ultrasonic testing (AUT) for girth welds subject to large plastic strain shall according to DNV-OS-F101: 2012 [1] and DNV RP-F108 [2] be carried out in accordance with BS 7910 [3], at assessment Level 3B, with amendments and adjustments described in Appendix A of DNV-OS-F101 for strain-based loading. This is a tearing analysis using the material specific failure assessment diagram (FAD), the material stress-strain curve and the fracture resistance J-R curve (or CTOD-R curve) for the HAZ or WM. It is therefore essential that the pipeline girth welds exhibit maximum load behavior and large tearing capacity to enable development of workable and practical flaw acceptance criteria for the girth welds on the stalks. Welds in offshore structural steels are known from the early 80s introduction of low carbon-manganese micro-alloyed steels, to occasionally exhibit low fracture toughness associated with so-called local brittle zones (LBZ) in the HAZ. Similarly, in the 90s LBZs were found in pipeline seam welds welded at high arc energies. Presence of such microstructures may have a dramatic effect on the coarse grained HAZ CTOD fracture toughness properties causing unstable fracture in the CTOD tests and CTOD values below 0.1 mm at test temperatures of 0°C and below. Recently low CTOD critical fracture toughness values due to pop-ins and unstable fracture initiation in the HAZ have been experienced for pipeline girth welds for reeling and investigation confirmed these were caused by LBZs. This paper makes a comparison with the situation experienced earlier for welds in structural steels and pipeline seam welds, to understand the factors influencing the LBZ formation, and to show how such problems can be avoided. To avoid LBZs formation in the girth welds is imperative for reeling installation, where the large plastic strain associated with reeling installation affects every girth weld.

scholarly journals Dynamic Fracture Toughness Evaluation of Structural Steels Based on the Local Approach

1998 ◽  
Vol 1998 (184) ◽  
pp. 453-464 ◽  
Author(s):  
Fumiyoshi Minami ◽  
Tomoyuki Hashida ◽  
Masao Toyoda ◽  
Jun Morikawa ◽  
Takeshi Ohmura ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Dynamic Fracture ◽  
Dynamic Fracture Toughness ◽  
Structural Steels ◽  
Local Approach ◽  
Toughness Evaluation ◽  
Fracture Toughness Evaluation

TIMES: An International Project on Transferability of Fracture Toughness Values for Irradiated RPV Steels

2007 ◽  
Author(s):  
Matthias Huemmer ◽  
Elisabeth Keim ◽  
Harald Hoffmann
Keyword(s):  
Fracture Toughness ◽  
Yield Strength ◽  
Temperature Dependence ◽  
Input Parameter ◽  
Base Material ◽  
Temperature Shift ◽  
Failure Behavior ◽  
Local Approach ◽  
Recent Developments ◽  
Material State

The prediction of specimen or component failure behavior can be attained by the use of local approach (LA) models based on Weibull stresses. Over the last years recent developments have been achieved, and the predictive capabilities of these models have been improved significantly. In this paper a concept, which is based on a LA model, will be proposed for the prediction of fracture toughness for different specimen types made of ferritic base and weld metal in the unirradiated as well as in the irradiated state. The only necessary input parameter will be the yield strength of the material at one temperature (preferably room temperature). The LA model under consideration is tuned for its temperature dependence using a ferritic base material in the unirradiated material state. The outcome of the tuning are the Weibull parameters m, • •u, • •th, • •p,0. The parameters m, • •th, • •p,0 are kept constant over temperature and for variation of materials and fluences. To model the temperature dependence over the transition region, local events like plastic shielding, blunting or arrest of micro cracks have to be considered. These events are modeled via an increase of • •u over temperature. The temperature shift, • •T, in • •u, is obtained by using a correlation between the yield strength of the tuned material and the material under investigation. In order to validate this concept, a large number of computations, which includes different temperatures, specimen types, loading ratios, weld and base metal in unirradiated and irradiated conditions are conducted. They lead to the prediction of a median fracture toughness curve for each material and specimen type. All numerical investigations are compared with experimental results. It could be shown that the predictions made by this approach are in good agreement with the experiments. This is encouraging for further application to other materials and irradiation conditions.

Significance of Fracture Toughness of Laser Welds for Structural Steels and Fracture Performance Assessment by Weibull Stress Criterion

2007 ◽  
Vol 25 (1) ◽  
pp. 149-158 ◽  
Author(s):  
Fumiyoshi MINAMI ◽  
Mitsuru OHATA ◽  
Akihiko TANIZAWA ◽  
Yukito HAGIHARA ◽  
Susumu TUKAMOTO ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Performance Assessment ◽  
Structural Steels ◽  
Stress Criterion ◽  
Laser Welds ◽  
Fracture Performance ◽  
Weibull Stress

Physical and Mechanical Aspects of Radiation Embrittlement of RPV Steels

2008 ◽  
Author(s):  
B. Margolin ◽  
V. Shvetsova ◽  
A. Gulenko ◽  
V. Nikolaev ◽  
D. Lidbury ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Yield Stress ◽  
Critical Stress ◽  
Temperature Shift ◽  
Irradiation Damage ◽  
Irradiation Embrittlement ◽  
Local Approach ◽  
Mechanical Factor ◽  
Multi Scale ◽  
Physical Mechanisms

A multi-scale approach to brittle fracture of irradiated RPV steels has been developed within the EURATOM FP6 Integrated Project PERFECT, and the EC-sponsored ISTC Project 3072: “Modelling of Brittle and Ductile Fracture and Prediction of Irradiation Damage Effects on Fracture Toughness Properties of Steels for Reactor Pressure Vessels on the Basis of Local Approach”. In the present paper, the physical and mechanical aspects of the irradiation embrittlement phenomenon are analysed on the basis of a multi-scale approach that includes the physical mechanisms of irradiation damage, the physical mechanisms of nucleation and propagation of cleavage microcracks, formulation of a local approach criterion and calculation of fracture toughness. It has become clear from the study performed that irradiation embrittlement is not only due to the hardening of material as traditionally considered. Damage features such as irradiation-induced lattice defects, element precipitation and impurity segregation also affect cleavage microcrack nucleation, although they do not appreciably change the critical stress for microcrack propagation. It is shown that irradiation embrittlement of RPV steels is connected both with the increase of yield stress (mechanical factor) and the decrease of the critical stress for microcrack nucleation (physical factor). This finding allows an interpretation of the experimental observations, showing that for some cases there is no simple one-to-one relationship between the brittle-to-ductile transition temperature shift ΔTtr and the corresponding increase in yield stress ΔσY. For example, this explains why irradiation-induced phosphorus segregation may significantly increase the transition temperature shift ΔTtr but does not result in a significant increase in yield stress. Calculation of the KJC(T) curves has shown that the contributions of mechanical and physical factors in irradiation embrittlement may differ for various steels. So, for low-alloy, low-strength steel the mechanical factor predominates, while for RPV steels both of these factors control irradiation embrittlement. The results obtained have been interpreted with reference to a local cleavage fracture criterion.

Comparison of Global and Local Approaches to Predicting Warm Pre-Stress Effect on Cleavage Fracture of Ferritic Steels

2004 ◽  
Vol 261-263 ◽  
pp. 69-74 ◽  
Author(s):  
Saeid Hadidi-Moud ◽  
A. Mirzaee-Sisan ◽  
Christopher E. Truman ◽  
David John Smith
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Type Model ◽  
Ferritic Steels ◽  
Stress Effect ◽  
Loading History ◽  
Global Approach ◽  
Local Approach ◽  
Global And Local ◽  
Weibull Stress

Potentially both global and local approaches may be used to predicting the effect of loading history on cleavage fracture toughness distribution of ferritic steels. In this paper the dramatic increase in the apparent lower shelf fracture toughness of A533B steel following warm pre-stressing (WPS) has been predicted using these approaches. Extensive experimental evidence suggesting significant enhancement in fracture toughness of ferritic steels within the lower shelf temperatures following WPS are used to verify and compare the applicability and the extent of validity of the models. The global approach is based on the distribution of toughness data described by Wallin statistical model in conjunction with the Chell model for WPS effect. The local approach on the other hand is a Beremin type model that uses the Weibull stress to predict the WPS effect. Weibull stresses would essentially reflect the WPS effect on redistribution of stress-state around the crack tip. Predictions for apparent toughness using the two approaches are discussed in the light of the suggestion that residual stresses are the main cause of the enhancement, at least for the material and geometry used in this study.

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