A Study of the Effects of Scaling on Structural Integrity Assessment and Feasibility of Physical Validation

2016 ◽  
Author(s):  
Paulo Orrock ◽  
Christopher E. Truman
Keyword(s):  
Scaling Laws ◽  
Structural Integrity ◽  
Driving Forces ◽  
Stress Fields ◽  
Complex Nature ◽  
Statistical Nature ◽  
Integrity Assessment ◽  
And Performance ◽  
Scaled Models ◽  
Random Nature

For nuclear welded components the complex nature of the stresses involved means it is often advantageous to produce mock-ups in order that the structural integrity and performance may be assessed. The weight and size of these components can make the production of mock-ups prohibitively expensive and impractical, and so the use of scaled models is considered here. The scaling laws encountered affecting the applied loads, residual stresses and crack driving forces that are of interest are investigated using numerical analyses and finite element simulations. Of particular interest is the physical validation of these laws and the statistical difficulties that may be encountered. The scaling of applied loads required to obtain the same residual stress fields and stress intensity factors are investigated using simulated four point bends. The statistical nature of fracture introduces uncertainty into fracture measurements which this paper takes into consideration in preparation for physical validation, ensuring that the random nature of fracture will not make the described laws impractical to validate.

A Study of the Effects of Scaling on Structural Integrity Assessment

2015 ◽  
Author(s):  
Paulo Orrock ◽  
David J. Smith ◽  
Christopher E. Truman
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Scaling Laws ◽  
Structural Integrity ◽  
Driving Forces ◽  
Scaling Law ◽  
Stress Fields ◽  
Complex Nature ◽  
Integrity Assessment ◽  
And Performance

For nuclear welded components the complex nature of the residual stresses involved means it is often advantageous to produce mock-ups in order that the structural integrity and performance may be assessed. The weight and size of these components can make the production of mock-ups prohibitively expensive, and so the use of scaled models is considered here. Numerical analysis and finite element simulations have been carried out to investigate the scaling laws encountered affecting the applied loads, stress fields and crack driving forces that are of interest in the full sized component. To illustrate the effects of scaling we consider the introduction of a residual stress through prior plastic deformation in rectangular beams of different sizes. A simple scaling law provides the loads required to introduce the same magnitude and distribution of residual stresses in different sized specimens. This is pertinent to uncracked beams. In contrast, if a crack is introduced this scaling law is no longer applicable and the stress intensity factor associated with residual and applied stresses differ for different sized specimens. Alternatively, to create the same crack driving force in different sized specimens different initial residual stress fields are required. The implications of these findings are discussed in the context of future work.

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.

Residual Stress Effects on Ductile Tearing

2006 ◽  
Author(s):  
A. H. Sherry ◽  
M. R. Goldthorpe ◽  
J. Fonseca ◽  
K. Taylor
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Structural Integrity ◽  
Driving Forces ◽  
Internal Stresses ◽  
Engineering Structures ◽  
Numerical Work ◽  
Crack Driving Force ◽  
Integrity Assessment

Residual stresses are internal stresses generated during the fabrication and/or operation of engineering structures. Such stresses can provide the major element of the driving force for crack initiation and growth. Structural integrity assessment procedures, provide guidance for the assessment of defects located within regions of high residual stress. However, such guidance may be conservative where the defect develops progressively during service. This paper describes recent experimental and numerical work aimed at quantifying such conservatisms and providing improved guidance for undertaking more realistic analyses. The results demonstrate that pre-loaded compact-tension specimens provide a useful means for studying the behaviour of cracks within residual stress fields. The magnitude of calculated crack driving forces due to residual stresses is influenced by the approach used to introduce cracks into the stress field, with progressive cracks providing lower levels of crack driving force than instantaneously introduced cracks. The J R-curve associated with cracks under primary or combined primary + secondary loading can apparently be rationalized when the total crack driving force is calculated using methods that take proper account of the influence of prior plasticity on the J-integral. However, it is noted that due to differences in the form of the crack-tip stress and strain fields for static and growing cracks, such values of J may be path dependent and influenced by the magnitude of the growth increment.

scholarly journals A New Characterization Parameter of out-of-plane Constraint for C(T) Specimens

2018 ◽  
Vol 179 ◽  
pp. 02006
Author(s):  
Zhao Lingyan ◽  
Cui Yinghao ◽  
Yang Fuqiang
Keyword(s):  
Structural Integrity ◽  
Three Dimensional ◽  
Equivalent Plastic Strain ◽  
Crack Tip ◽  
Stress Fields ◽  
Integrity Assessment ◽  
Out Of Plane ◽  
Dimensional Finite Element ◽  
Material Fracture ◽  
Three Dimensional Finite Element

As the resistance of structures against the crack-tip plastic deformation, constraints has attracted much attention in the research of material fracture behaviour. In order to increase the accuracy of structural integrity assessment, many characterization parameters of in-plane and out-of-plane constraints have been considered and proposed in the last few decades. Three-dimensional finite element analyses have been conducted for five C(T)50 specimens with different out-of-plane constraint. The distributions of four constraint parameters (σ22/σ0, Tz, h and Dp) along crack fronts were calculated. To characterize the out-of-plane constraint, the capability of constraint parameters such as σ22/σ0, Tz, h and Dp were analyzed and compared. Results show that, compared with the three constraint parameters (σ22/σ0, Tz and h) based on crack-tip stress fields, the parameter Dp based on crack-tip equivalent plastic strain is more sensitive to out-of-plane constraint, and may effectively characterize the out-of-plane constraint.

A FAD-Based Procedure for Defect Assessments of Welded Structures Including Effects of Weld Strength Mismatch: Micromechanics Approach and Application to Pipeline Girth Welds

2008 ◽  
Author(s):  
Gustavo H. B. Donato ◽  
Claudio Ruggieri
Keyword(s):  
Structural Integrity ◽  
Driving Forces ◽  
Pipeline Steel ◽  
Crack Tip ◽  
Weld Strength ◽  
Homogeneous Material ◽  
Fracture Parameter ◽  
Integrity Assessment ◽  
Girth Welds ◽  
Assessment Problems

ECA procedures of crack-like defects based upon the FAD philosophy have undergone extensive developments in the past decade to form the basis for industrial codes and guidelines for structural integrity assessments. However, the application of these procedures in welded structural components with mismatch in tensile properties between the weld and base metal remains a potential open issue. Weld strength mismatch may significantly alter the crack-tip driving forces, such as J and CTOD, thereby producing crack-tip stresses quite different than the fields that arise in corresponding homogeneous material. Weld strength mismatch also affects the plastic collapse load for the structural component which further complicates the interplay between fracture and plastic instability before gross yield section takes place. This work describes the development of a microme-chanics-based FAD methodology building upon a local fracture parameter, characterized by the Weibull stress (σw), to incorporate the effects of weld strength mismatch on crack-tip driving forces. As a further refinement, the study also addresses an exploratory application of a limit load analysis including effects of weld strength mismatch to correct the loading trajectory incorporated into the FAD procedure. Fracture testing of girth welds obtained from an API X80 pipeline steel provide the data needed to validate the proposed modified FAD procedure in failure predictions. Such an application serves as a prototype for a wide class of integrity assessment problems involving the effects of weld strength mismatch.

scholarly journals Relating Competitive Golfers’ Perceived Emotions and Performance

2021 ◽  
pp. 003151252110059
Author(s):  
Erik Lundkvist ◽  
Henrik Gustafsson ◽  
Gunilla Björklund ◽  
Paul Davis ◽  
Andreas Ivarsson
Keyword(s):  
Perceived Control ◽  
Performance Outcomes ◽  
Skill Level ◽  
Complex Nature ◽  
Moderating Effects ◽  
Dynamic Relationship ◽  
And Performance ◽  
Player Skill ◽  
Task Oriented ◽  
The Relationship

The present study examined relationships between golfers’ self-perceived emotions (e.g., irritability, nervousness, tension), task-oriented coping, perceived control, and performance during a golf competition. We implemented a process-oriented golf analysis in which competitors rated these variables hole-by-hole in a competitive golf round. Within a two-level Bayesian multivariate autoregressive model, we showed that (a) within persons, emotions and task-oriented coping were reactions that stemmed from performance on the previous hole; and (b) between persons, player skill level predicted both better scores and the ability to limit the influence of negative affect on performance. These findings highlight the complex nature of the relationship between emotions and performance. Future studies might use a similarly ecologically valid research design to more precisely measure aspects of time and potentially moderating effects of player skill level and personality. An increased understanding of the dynamic relationship between emotions and performance can promote the development of effective psychological interventions for optimal performance outcomes.

Effects of water deficiency on preference and performance of an insect herbivore Ostrinia furnacalis

2021 ◽  
pp. 1-10
Author(s):  
M.Y. Duan ◽  
H. Zhu ◽  
H. Wang ◽  
S.Y. Guo ◽  
H. Li ◽  
...  
Keyword(s):  
Driving Forces ◽  
Oviposition Preference ◽  
Precipitation Pattern ◽  
Ostrinia Furnacalis ◽  
Oviposition Choice ◽  
Offspring Performance ◽  
Corn Borer ◽  
Limited Mobility ◽  
Offspring Fitness ◽  
And Performance

Abstract With further climate change still expected, it is predicted to increase the frequency with plants will be water stressed, which subsequently influences phytophagous insects, particularly Lepidoptera with limited mobility of larvae. Previous studies have indicated that oviposition preference and offspring performance of Lepidoptera insects are sensitive to drought separately. However, the integration of their two properties is not always seen. Here, we evaluated changes in oviposition selection and offspring fitness of a Lepidoptera insect under three water-stressed treatments using a model agroecosystem consisting of maize Zea mays, and Asian corn borer Ostrinia furnacalis. Results found that female O. furnacalis preferred to laying their eggs on well-watered maize, and then their offspring tended to survive better, attained bigger larvae mass, and developed more pupae and adults on the preferred maize. Oviposition selection of O. furnacalis positively correlated with height and leaf traits of maize, and offspring fitness positively related with water content and phytochemical traits of hosts. Overall, these results suggest that oviposition choice performed by O. furnacalis reflects the maximization of offspring fitness, supporting preference–performance hypothesis. This finding further highlights that the importance of simultaneous evaluation of performance and performance for water driving forces should be involved, in order to accurately predict population size of O. furnacalis under altered precipitation pattern.

Sign in / Sign up

Export Citation Format

Share Document