Bibliografie tematiche / Critical stress intensity factor

Letteratura scientifica selezionata sul tema "Critical stress intensity factor"

Autore: Grafiati
Pubblicato: 24 agosto 2024

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Articoli di riviste sul tema "Critical stress intensity factor"

1

Dharmarajan, N., e C. Vipulanandan. "Critical stress intensity factor of epoxy mortar". Polymer Engineering and Science 28, n. 18 (settembre 1988): 1182–91. http://dx.doi.org/10.1002/pen.760281808.

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2

Daud, M. A. M., Zainuddin Sajuri, Mohd Zaidi Omar e Junaidi Syarif. "Critical Stress Intensity Factor Determination for AZ61 Magnesium Alloy". Key Engineering Materials 462-463 (gennaio 2011): 1121–26. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.1121.

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Abstract (sommario):
A stress intensity factor K was used as a fracture parameter to determine the plane strain fracture toughness KIC of AZ61 magnesium alloy using a single edge notch bend (SENB) specimen in accordance to ASTM E399 testing method. Five different specimen thicknesses of 2 to 10 mm were used in the test. A sharp fatigue pre-crack was initiated and propagated to half of specimen width at a constant crack propagation rate of about 1 x 10-8 m/cycle before the specimen was loaded in tension until the fracture stress is reached and then rapid fracture occurred. The fracture toughness KC values obtained for different thicknesses showed that KC value decreased with increasing specimen thickness. The highest KC value obtained was 16.5 MPa√m for 2 mm thickness specimen. The value of KC became relatively constant at about 13 MPa√m when the specimen thickness exceeds 8 mm. This value was then considered as the plane strain fracture toughness KIC of AZ61 magnesium alloy. Calculation of the minimum thickness requirement for plane strain condition and the size of the shear lips of the fracture surface validate the obtained KIC value.
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Zarzycki, J. "Critical stress intensity factors of wet gels". Journal of Non-Crystalline Solids 100, n. 1-3 (marzo 1988): 359–63. http://dx.doi.org/10.1016/0022-3093(88)90046-4.

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4

Zheng, Heng Xiang, e Cai Ying Chen. "Research on Interface Critical Fracture of Different Materials Based on Critical Fracture Curve". Applied Mechanics and Materials 204-208 (ottobre 2012): 3090–93. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.3090.

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In order to get the interface fracture curve of different materials under the four-point loading test pieces, firstly the displacement of fracture interface was obtained based on the finite element method. Then the first and second stress intensity factors of two different materials interface cracks in a beam specimen were calculated by the extrapolation method. Comprehensively considered the type of fracture specimen and the relative proportions between first and second section stress intensity, the variables K' , the first and second stress intensity factor were calculated according to the observed values of fracture load when the fissure appeared. By regression analysis of a six-groups of rock-concrete specimens with prefabricated fissure, the interface fracture criterion of different materials was got which was the interface fracture curve of rock-concrete samples. At last the calculated results of this method were compared and verified with the other related research results.
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SATO, Kiyoshi, Hisato YAMAMOTO, Atsushi TAYA e Hiroyuki OKUYAMA. "Influence of Moisture Content on Critical Stress Intensity Factor of Wood." Journal of the Society of Materials Science, Japan 49, n. 4 (2000): 365–67. http://dx.doi.org/10.2472/jsms.49.365.

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Meriem-Benziane, Madjid, Gadi Ibrahim, Zahloul Hamou e BelAbbes Bachir-Bouiadjra. "Stress intensity factor investigation of critical surface crack in a cylinder". Advances in Materials and Processing Technologies 1, n. 1-2 (3 aprile 2015): 36–42. http://dx.doi.org/10.1080/2374068x.2015.1111702.

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7

Yoshihara, Hiroshi. "Simple estimation of critical stress intensity factors of wood by tests with double cantilever beam and three-point end-notched flexure". Holzforschung 61, n. 2 (1 marzo 2007): 182–89. http://dx.doi.org/10.1515/hf.2007.032.

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Abstract (sommario):
Abstract Simple equations are proposed for calculation of critical stress intensity factors by tests using double cantilever beam (DCB) and three-point end-notched flexure (3ENF). The calculation modes are named here as modes I and II and are based on the beam theory and 95 previously published data on the elasticity properties of woods. The validity of the data was examined on specimens of western hemlock wood with various crack lengths. The influence of the elastic properties is more significant on the stress intensity factor calculated in mode I than that calculated in mode II. Further work is needed, particularly for measuring the mode I stress intensity factor. However, it is obvious from the experiments with western hemlock that the critical stress intensity factors can be determined by the equations proposed here.
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Anam, Khairul, e Chih Kuang Lin. "Thermal Stress Intensity Factors of Crack in Solid Oxide Fuel Cells". Applied Mechanics and Materials 493 (gennaio 2014): 331–36. http://dx.doi.org/10.4028/www.scientific.net/amm.493.331.

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Structural durability is the main focus of solid oxide fuel cells (SOFCs) development which is affected by the thermal stress caused by considerable CTE mismatch between components and thermal gradient. In this paper we investigate the thermal stress intensity factor for mode I, mode II and mode III of positive electrode-electrolyte-negative electrode (PEN) at room temperature and steady stage for an initial crack size of 10 μm. A commercial finite element analysis (FEA) was used to find the highly stressed regions in PENs and calculate the thermal stress intensity factors. The stress distributions are calculated at uniform room temperature and at steady stage with a non-uniform temperature profile. The thermal stress intensity factors are calculated for various principal directions at the location having the greatest maximum principal stress at room temperature and steady stage. The critical stress regions are identified based on the maximum principal stress at room temperature and steady stage. The maximum principal stress is of 53.45 MPa and 45.12 MPa in principal direction of-43.97° and-42.37° at room temperature and steady stage, respectively. The mixed-mode stress intensity factor including mode I, mode II, and mode III is calculated due to multi-axial thermal stresses. However, the stress intensity factor for mode I have a highest value compared to those for modes II and III. The principal direction has an effect on the thermal stress intensity factor for the critical region with the greatest maximum principal stress. All the calculated stress intensity factors in the present study are less than the corresponding fracture toughness given in the literature, ensuring the structural integrity for the given planar SOFC stack.
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Abuzaid, Ahmed, Meftah Hrairi e Mohd Sultan Dawood. "Mode I Stress Intensity Factor for a Cracked Plate with an Integrated Piezoelectric Actuator". Advanced Materials Research 1115 (luglio 2015): 517–22. http://dx.doi.org/10.4028/www.scientific.net/amr.1115.517.

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Abstract (sommario):
The fracture performance of cracked structures is dominated by singular stress in the crack tip vicinity. In fracture mechanics most interest is focused on stress intensity factors, which describe the singular stress field ahead of a crack tip and govern fracture of structures when a critical stress intensity factor is reached. In the present work linear fracture mechanics is applied in order to obtain the fracture toughness parameters of a cracked plate integrated with piezoelectric actuator under mode I loading. Analytical model was derived to represent the relation between piezoelectric parameters and stress intensity factor and energy release rate. The results indicate that the stress intensity factor decreases linearly with the application of the different piezoelectric actuator voltages.
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Toribio, J., F. J. Ayaso, B. González, J. C. Matos, D. Vergara e M. Lorenzo. "Critical stress intensity factors in steel cracked wires". Materials & Design 32, n. 8-9 (settembre 2011): 4424–29. http://dx.doi.org/10.1016/j.matdes.2011.03.064.

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Tesi sul tema "Critical stress intensity factor"

1

Alkoles, Omar M. S. "Mechanical behaviour and fracture toughness of unfilled and short fibre filled polypropylene both drawn and undrawn. Experimental investigation the effect of fibre content and draw ratio on the mechanical properties of unfilled and short glass fibre filled polypropylene". Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5510.

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The goal of this research is to investigate the combined effects of glass fibre reinforcement and molecular orientation in polypropylene-short glass fibre composites. Specimens have been fabricated using the injection moulding process and drawn using a small die drawing rig. The effects of die drawing on the fibre composites are complex, with the drawing process orienting both the polymer molecules and the glass fibres. This may be accompanied by the creation of voids in the polymer matrix and their destruction in the compressive stress field thus restoring the interfacial contact area between fibre and matrix. Unfilled and short glass fibre filled polypropylene specimens, with fibre content 7% wt, 13%wt, 27%wt, and 55%wt, were injection moulded prior to the die drawing process. An experimental program of die drawing within an oven at elevated temperature was conducted for polypropylene filled to various levels and at different strain rates. The specimens drew to draw ratios in the range ¿=1.41 to ¿=5.6. Mechanical characterization of the test materials has been conducted by examining the tensile stress strain and fracture behaviour under uniaxial conditions. The influence of glass fibre content and drawing conditions (draw ratio) on the fracture toughness and crack propagation was investigated using the double edge notched fracture test. The notch lengths ranged from 1.5 to 2.5 mm for 10 mm wide specimens. The critical stress intensity factor increased as the fibre content increased up to a limiting filler level. The fracture toughness of both unfilled and fibre filled polypropylene were found to be highly dependent on draw ratio. The results were analysed to find out the optimal draw ratio and fibre content that yielded the maximum modulus, strength and fracture toughness. Data showed that, at a given draw ratio, modulus, strength and fracture toughness increased with increasing fibre content to a maximum and then decreased. The optimum material was obtained at a draw ratio of 2.5 and filler loading 13wt%.
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Alkoles, Omar M. "Mechanical behaviour and fracture toughness of unfilled and short fibre filled polypropylene both drawn and undrawn : experimental investigation of the effect of fibre content and draw ratio on the mechanical properties of unfilled and short glass fibre filled polypropylene". Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5510.

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Abstract (sommario):
The goal of this research is to investigate the combined effects of glass fibre reinforcement and molecular orientation in polypropylene-short glass fibre composites. Specimens have been fabricated using the injection moulding process and drawn using a small die drawing rig. The effects of die drawing on the fibre composites are complex, with the drawing process orienting both the polymer molecules and the glass fibres. This may be accompanied by the creation of voids in the polymer matrix and their destruction in the compressive stress field thus restoring the interfacial contact area between fibre and matrix. Unfilled and short glass fibre filled polypropylene specimens, with fibre content 7% wt, 13%wt, 27%wt, and 55%wt, were injection moulded prior to the die drawing process. An experimental program of die drawing within an oven at elevated temperature was conducted for polypropylene filled to various levels and at different strain rates. The specimens drew to draw ratios in the range γ=1.41 to γ=5.6. Mechanical characterization of the test materials has been conducted by examining the tensile stress strain and fracture behaviour under uniaxial conditions. The influence of glass fibre content and drawing conditions (draw ratio) on the fracture toughness and crack propagation was investigated using the double edge notched fracture test. The notch lengths ranged from 1.5 to 2.5 mm for 10 mm wide specimens. The critical stress intensity factor increased as the fibre content increased up to a limiting filler level. The fracture toughness of both unfilled and fibre filled polypropylene were found to be highly dependent on draw ratio. The results were analysed to find out the optimal draw ratio and fibre content that yielded the maximum modulus, strength and fracture toughness. Data showed that, at a given draw ratio, modulus, strength and fracture toughness increased with increasing fibre content to a maximum and then decreased. The optimum material was obtained at a draw ratio of 2.5 and filler loading 13wt%.
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Lammens, Bastien. "Caractérisation de la décohésion dynamique des matériaux composites à matrice organique (CMO)". Electronic Thesis or Diss., Ecole centrale de Nantes, 2024. http://www.theses.fr/2024ECDN0007.

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Abstract (sommario):
Les matériaux composites stratifiés à matrice organique sont utilisés dans le domaine de l'aéronautique pour alléger la masse des structures. Cependant, lors d'un impact sur ce type de matériaux, différents mécanismes d'endommagements peuvent apparaître comme le délaminage. C'est un processus de décohésion macroscopique du milieu interlaminaire qui peut être caractérisé par GIC (ou KIC). La littérature montre une grande disparité dans les mesures du fait d’un découplageincomplet des effets du confinement de la résine par les fibres, des non linéarités de comportement et/ou des effets de vitesse. Ce travail propose d’élaborer un protocole expérimental de caractérisation de résine pure via mesures de champs pour étudier méthodiquement ces couplages. L’objectif est d’élucider l’impact de la vitesse de propagation de fissure et des effets de structure sur le comportement en fissuration et ainsi étendre l’approche de Griffith aux stratifiés. Différentes géométries d’éprouvette sont utilisées pour reproduire certains effets de structure. Des vitesses de fissuration allant du quasi-statique à la dynamique sont étudiées et l’ensemble des essais sont interprétés au travers de la mécanique élastique linéaire de la rupture et de l’étude des facies. Ce travail propose finalement une modélisation décrivant l'évolution de KIC, pour la résine HexplyM21 utilisée dans l'aéronautique, à partir des termes non-singuliers du champ de contraintes, le Tstress,B-stress et aussi de la vitesse ȧ dans les gammes [0 - 15] MPa, [-200 - 10] MPa.m-0.5 et [10-6, 600] m.s-1 respectivement
Organic matrix laminated composites are increasingly used in the aeronautical field to reduce the weight of structures. However, during an impact on this type of material, various damage mechanism can occur, such as delamination. This is a process of macroscopic decohesion of the interlaminar environment, which can be characterised by GIC (or KIC ). The literature shows a wide disparity in measurements due to incomplete decoupling of the effects of resin confinement by fibers, nonlinearitiesbehaviour and/or velocity effects. This work proposes to develop an experimental protocol to characterise pure resin usingfullfields measurements to methodically study these couplings. The goal is to evaluate the impact of the crack propagation speed and the structural effects on the fracture behaviour and in particular to extend Griffith's theory to laminated composites. Different specimen geometries are used to reproduce structural effects. Crack propagation speeds ranging from quasi-static to dynamic are studied and all the tests are analysed using linear elastic fracture mechanics and the fracture surfaces. Finally, this work proposes a model to describe the evolution of KIC for the resin HexplyM21 used in aeronautics field, from the non-singularterms of the stress field T-stress, B-stress and also the speed ȧ in the ranges [0 - 15] MPa, [- 200 - 10] MPa.m-0.5 et [10-6, 600] m.s-1 respectively
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Keller, Scott. "Stress Intensity Factor Dependence of HG-AL Liquid Metal Embrittlement". Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2220.

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Abstract (sommario):
When high strength aluminum alloys are subjected to liquid metals, physical and chemical reactions ensue resulting in what is known as liquid metal embrittlement (LME). A subset of environmentally-assisted cracking, LME is exhibited when a liquid metal, e.g. Hg or Ga, comes into intimate contact with a solid metal having significant susceptibility. As mechanical loads are applied, the interaction between the two metals results in a reduction in the flow properties of the solid metal. Several theories have been proposed to identify the underlying microstructural failure mechanism; however, none have been widely accepted, as failures can typically incorporate features common to several failure theories. In an effort to confirm, extend or replace the physically-based theories, fracture mechanics experiments on Al 7075-T651 in liquid mercury have been conducted. Experiments were conducted in a custom environmental chamber capable of exposing specimens to liquid environments while applying a mechanical load. Through both plane-strain fracture and stress intensity factor-dependent (SIF) tests, fracture toughness values along with incubation periods were analyzed and provided data for a load-based theory of LME. These mechanical test data, along with metallographic analysis, show that the phenomena of LME is both strongly time- and SIF-dependent.
M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME
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5

Teh, Lay Seong. "Library of geometric influences for stress intensity factor weight functions". Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566060.

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This research thesis reports the development of a novel concept for Linear Elastic Fracture Mechanics (LEFM) analysis - Composition Theory of Stress Intensity Factor Weight Functions (CToWF). A generic closed form composition model has been derived to generate Mode I SIFs for an edge crack propagating in a symmetrically loaded two-dimensional body. The CToWF concept has demonstrated, by verification with published solutions and Finite Element Analysis (FEA), that the SIF weight function for a new cracked body can be evaluated by isolating and combining appropriate constituent geometries. Being a unique property of crack and component geometry, the newly determined weight function enables rapid generation of SIFs for the same cracked component under different stress systems. Over two thousand Finite Element (FE) models were analysed to provide constituent geometrical configurations and to validate the SIFs calculated from the CToWF model where published solutions were not available. These are Mode I SIFs for edge cracks emanating from two-dimensional notches i. e. semi-elliptical, U- and V-notches in semi-infinite bodies along with their associated stress distributions. Hence, a comprehensive database has been established. Using the versatile composition model with the database, a large number of new SIF solutions for edge cracks from equivalent notches in finite bodies have been obtained. This `Library' of geometric influences, which are presented as weight function coefficients in tabular form, can now be composed by the CToWF approach to generate SIFs for modelling crack propagation through residual stress fields and other complex stress systems. In general, this universal approach, which is easy-to-implement yet maintaining high accuracy, has tremendous potential in allowing rapid assessment of defects prone to linear elastic fracture behaviour via the evaluation of SIFs. Further work to enhance the understanding of this novel concept is proposed to develop a broader practical use in real engineering applications.
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Arli, Sirisha Divya. "An Investigation on the Stress Intensity Factor of Surface Micro-cracks". Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1495620917553525.

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Finlayson, Eric F. "Stress Intensity Factor Distributions in Bimaterial Systems - A Three Dimensional Photoelastic Investigation". Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36504.

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Stress-freezing photoelastic experiments are conducted using two different sets of photoelastic materials to investigate stress intensity behavior near to and coincident with bimaterial interfaces. Homogeneous, bonded homogeneous, and bonded bimaterial single edge-cracked tension specimens are utilized throughout the investigation for comparative purposes. The first series of tests involves machined cracks obliquely inclined to the direction of far field tensile loading. Mixed-mode stress intensity factors are observed and quantified using a simplified analytical algorithm which makes use of experimentally measured data. In this series of tests, the bimaterial specimens consist of a photoelastic material bonded to the same material containing a moderate quantity of aluminum powder (for elastic stiffening purposes). Moderate yet similar increases in stress intensity factors are observed in bonded homogeneous and bonded bimaterial specimens, suggesting the presence of bondline residual stresses (rather than elastic modulus mismatch) as the primary contributing factor. The second series of tests involves the bonding of mutually translucent photoelastic materials whose elastic module differ by a ratio of approximately four to one. Cracks are placed both near and coincident to the bimaterial interfaces. Mode-mixity and increases in stress intensity are found only in bimaterial specimens whose cracks are placed close to the bondline. Using the materials from the first series of tests it is shown that the increases in these near-bondline experiments are due to thermal mismatch properties (incurred during the stress freezing cycles) rather than mechanical mismatch properties.
Master of Science
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Ventura, Antunes Fernando Jorge. "Influence of frequency, stress ratio and stress state on fatigue crack growth in nickel base superalloys at elevated temperature". Thesis, University of Portsmouth, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285929.

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Garrido, F. A. Díaz. "Development of a methodology for thermoelastic investigation of the effective stress intensity factor". Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412241.

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Azeez, Ahmed. "Effect of dwell time on stress intensity factor of ferritic steel for steam turbine applications". Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-148283.

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In the transition from conventional to green energy production resources, steam turbines are used to satisfy the lack of energy during peaks in the demand times and the limited access of renewable resources. This type of usage for steam turbines makes them operate on a flexible schedule, which leads to unpredictable issues related to shorter component life and faster crack propagation. Thus, the steam turbine components must be examined to determine their specific life period. This will help set proper maintenance intervals and prevent unexpected failures. For that, thermo-mechanical fatigue (TMF) testing is used, where a specimen made of the same material as the turbine component is subjected to both temperature and load variation. The specimen is pre-cracked to investigate the crack propagation behavior, which is the focus of this study. This thesis work concentrates on simulating the TMF cycle for the steam turbine casing component. The material is 9%-10%Cr ferritic steel. The aim is to understand the material behavior during crack propagation and to predict a useful testing parameter. The method provided in this work discusses two cases, both are out-of-phase (OP) TMF tests with strain control. The maximum and minimum temperatures for the cycle are 600 ˚C and 400 ˚C respectively, while the maximum and minimum strain levels are 0 and  respectively. The study will investigate different , which is the maximum compressive strain level. Case 1 has a dwell time at the maximum temperature only, while case 2 has dwell times at both maximum and minimum temperatures. The method utilizes the stress intensity factor (SIF) to characterize the crack tip conditions. Also, it uses Paris' law to estimate the duration of the tests. For simplification, only the elastic behavior of the material is considered. The results obtained show no effect of using different pre-crack lengths due to the strain control condition. Minor effects can be observed by using different dwell times, however very short dwell times must be avoided to produce reliable results. A recommended dwell time of 5 minutes could be used, since longer dwell times will make the test prohibitively time-consuming. The compressive strain levels used in the work shows large effects on the results. Using low compressive strain values will produce a very long time for the tests, while very high compressive strains produce large plasticity. Thus, high compressive strains must be avoided since the SIF describes cracks for only elastic or near elastic cases. Also, small compressive strain levels in case 2 should not be used since it will lead to results like case 1. This is due to the small creep effect at the minimum temperature. Finally, compressive strain levels of 0.6 %, 0.5 % and 0.4 % are recommended for case 1, while only 0.6 % compressive strain level is recommended for case 2. This thesis contributes to the fields of solid mechanics, fracture mechanics and the use of TMF testing, where a recommended set of testing parameters are provided.
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Libri sul tema "Critical stress intensity factor"

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United States. National Aeronautics and Space Administration., a cura di. Determination of stress intensity factor distributions for "interface" cracks in incompressible, dissimilar materials: Summary report : reporting period - 8/15/94 - 12/31/97 : grant no. NAG-1-1622-Supl. 1-5*. [Washington, DC: National Aeronautics and Space Administration, 1997.

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1932-, Carlsson Janne, a cura di. Weight functions and stress intensity factor solutions. Oxford: Pergamon Press, 1991.

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3

S, Raju I., Newman J. C e Langley Research Center, a cura di. Stress-intensity factor calculations using the boundary force method. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1987.

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S, Raju I., Newman J. C e Langley Research Center, a cura di. Stress-intensity factor calculations using the boundary force method. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1987.

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S, Raju I., Newman J. C e Langley Research Center, a cura di. Stress-intensity factor calculations using the boundary force method. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1987.

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Heppler, G. R. Stress intensity factor calculation for designing with fiber-reinforced composite materials. [S.l.]: [s.n.], 1985.

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Pook, L. P. Keyword scheme for a proposed computer-based bibliography of stress intensity factor solutions. Glasgow: National Engineering Laboratory, 1986.

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Noblett, J. E. A stress intensity factor solution for root defects in fillet and partial penetration welds. Cambridge: TWI, 1996.

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Pang, H. L. J. A literature review of stress intensity factor solutions fora weld toe crack in a fillet welded joint. East Kilbride: National Engineering Laboratory, 1991.

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k, Kokula Krishna Hari, a cura di. FEA Analysis for Investigation of Stress Intensity Factor (SIF) for a Plate with Hole and Patches: ICIEMS 2014. India: Association of Scientists, Developers and Faculties, 2014.

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Capitoli di libri sul tema "Critical stress intensity factor"

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Gdoutos, Emmanuel E. "Critical Stress Intensity Factor Fracture Criterion". In Fracture Mechanics, 131–65. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-35098-7_5.

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Gdoutos, Emmanuel E. "Critical Stress Intensity Factor Fracture Criterion". In Fracture Mechanics, 117–51. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-015-8158-5_5.

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Gdoutos, E. E. "Experimental Determination of Critical Stress Intensity Factor KI". In Problems of Fracture Mechanics and Fatigue, 155–60. Dordrecht: Springer Netherlands, 2003. http://dx.doi.org/10.1007/978-94-017-2774-7_34.

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Sglavo, Vincenzo M., David J. Green, Steven W. Martz e Richard E. Tressler. "Determination of Threshold Stress Intensity Factor for Sub-Critical Crack Growth in Ceramic Materials by Interrupted Static Fatigue Test". In Fracture Mechanics of Ceramics, 167–77. Boston, MA: Springer US, 1996. http://dx.doi.org/10.1007/978-1-4615-5853-8_13.

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Gooch, Jan W. "Stress-Intensity Factor". In Encyclopedic Dictionary of Polymers, 705. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_11281.

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Gdoutos, E. E. "Dynamic Stress Intensity Factor". In Problems of Fracture Mechanics and Fatigue, 359–63. Dordrecht: Springer Netherlands, 2003. http://dx.doi.org/10.1007/978-94-017-2774-7_78.

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Radaj, Dieter. "Extended Stress Intensity Factor Concepts". In Advanced Methods of Fatigue Assessment, 101–265. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-30740-9_2.

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Gdoutos, E. E. "Photoelastic Determination of Stress Intensity Factor KI". In Problems of Fracture Mechanics and Fatigue, 63–64. Dordrecht: Springer Netherlands, 2003. http://dx.doi.org/10.1007/978-94-017-2774-7_14.

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Kobayashi, A. S., e K. H. Yang. "Dynamic Stress Intensity Factor versus Crack Velocity Relation". In Advanced Materials for Severe Service Applications, 51–60. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3445-0_4.

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Lu, Xi. "Stochastic Boundary Element Analysis of Stress Intensity Factor". In Computational Mechanics ’88, 1401–2. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-61381-4_370.

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Atti di convegni sul tema "Critical stress intensity factor"

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JUN, HYUNKYU. "STRESS INTENSITY FACTOR CALCULATION ON CRITICAL POINTS OF RAILWAY BOGIE FRAME". In Proceedings of the International Conference on ANDE 2007. World Scientific Publishing Company, 2008. http://dx.doi.org/10.1142/9789812793034_0089.

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Lal, Achchhe, e Rakesh K. Kapania. "Stochastic Critical Stress Intensity Factor Response of Single Edge Notched Laminated Composite Plate". In 54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2013. http://dx.doi.org/10.2514/6.2013-1615.

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Sun, Rui, Zongwen An, Hong-Zhong Huang e Qiming Ma. "Stress Intensity Factor Calculation Using a Weight Function Method". In ASME 2007 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/detc2007-34736.

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Propagation of a critical unstable crack under the action of static or varying stresses is determined by the intensity of strain field at tips of the crack. Stress intensity factor (SIF) is an important parameter in fracture mechanics, which is used as a criterion to judge the unstable propagation of a crack and plays an important role in calculating crack propagation life. SIF is related to both geometrical form and loading condition of a structure. In the paper, a weight function method is introduced to study crack propagation of center through cracks and edge cracks in a finite-size plate. In addition, finite element method, linear regression, and polynomial interpolating technique are used to simulate and verify the proposed method. Comparison studies among the proposed and current methods are performed as well. The results show that the weight function method can be used to calculate SIF easily.
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Vaziri, A., e H. Nayeb-Hashemi. "Effective Stress Intensity Factor in Mode III Crack Growth in Round Shafts". In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-43478.

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Turbine-generator shafts are often subjected to a complex transient torsional loading. Such transient torques may initiate and propagate a circumferential crack in the shafts. Mode III crack growth in turbo-generator shafts often results in a fracture surface morphology resembling a factory roof. The interactions of the mutual fracture surfaces result in a pressure, and a frictional stress field between fracture surfaces when the shaft is subjected to torsion. This interaction reduces the effective Mode III stress intensity factor. The effective stress intensity factor in circumferentially cracked round shafts is evaluated for a wide range of applied torsional loadings by considering a pressure distribution in the mating fracture surfaces. The pressure between fracture surfaces results from climbing the rought surfaces respect to each other. The pressure profile not only depends on the fracture surface roughness (height and width (wavelength) of the peak and valleys), but also depends on the magnitude of the applied Mode III stress intensity factor. The results show that the asperity interactions significantly reduce the effective Mode III stress intensity factor. However, the crack surfaces interaction diminishes beyond a critical applied Mode III stress intensity factor. The critical stress intensity factor depends on the asperities height and wavelength. The results of these analyses are used to find the effective stress intensity factor in various Mode III fatigue crack growth experiments. The results show that Mode III crack growth rate is related to the effective stress intensity factor in a form of the Paris law.
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Faidy, Claude. "Stress Intensity Factor Handbook: Comparison of RSEM and ASME XI Codes". In ASME 2015 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/pvp2015-45199.

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For fracture mechanic applications at design level or during operation the basic parameter used is the elastic stress intensity factor K. This stress intensity factor can be evaluated through different methods: formulas, influence or weight functions or direct elastic finite element analysis of the cracked structure. After a brief review of available methods to develop elastic analysis of the fracture mechanic parameter K (stress intensity factor), this paper will compare French RSE-M Appendix 5 handbook and corresponding ASME-XI draft Appendix A-3000 handbook under development for cylindrical cracked structures (pipes or vessels) in a first step. In a future step, other structures (elbows, thickness variation…) and other crack types or locations will be considered. The cross reference validations and the technical white papers will be discussed in the paper. A short overview of plasticity corrections proposed by these 2 different Codes will be presented, compared and discussed in accordance with the validation analysis available. Finally, some differences between these 2 handbooks can have important safety consequences in their practical applications, some over-conservatism have to be better understand and will be discussed in term of consequences on different practical applications, like fatigue or corrosion crack growth, or critical crack size in brittle or ductile regime of nuclear components.
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Klingbeil, Nathan W., e Jack L. Beuth. "Free-Edge Stress Intensity Factors for Edge-Loaded Bimaterial Layers". In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0511.

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Abstract Structures composed of bonded layers of dissimilar materials are common in a variety of applications. Designing such structures to resist debonding at free edges is often of critical importance. In this work, the problem of initiation of free-edge debonding is considered for use in designing debond-resistant layered structures. It is well known that the local elastic stress fields near the free edge of bonded dissimilar quarter planes can exhibit singular behavior, with the power of the stress singularity determined by the material mismatch. A fracture mechanics-type approach is adopted here which assumes that the local interface tractions governing initiation of debonding can be characterized by the power of the stress singularity and a suitably defined stress intensity factor. The global problem considered in this study is that of a bimaterial strip composed of isotropic layers with a uniform edge pressure applied to the top layer. A dimensionless free-edge stress intensity factor is introduced from which stress intensity factors can be derived for either uniform edge or thermal loadings applied to either or both of the layers. Finite element results are presented for the dimensionless free-edge stress intensity factor over a wide range of material mismatches and relative layer thicknesses. Trends in the dimensionless stress intensity factor are used to identify strategies for designing debond-resistant bimaterials. Finally, the trends are shown to be well approximated by the analytically calculated stress resultants transmitted across the interface, which suggests a simplified approach for designing debond-resistant multilayer structures.
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Johnston, Carol, e Tyler London. "Development of a Stress Intensity Factor Solution for Mechanically Lined Pipe". In ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/omae2022-78559.

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Abstract Mechanically lined pipe (MLP) is a lower cost alternative to clad pipe, and is used to carry corrosive fluids in oil and gas applications. The pipe includes a liner which is made from corrosion resistant alloy (CRA). The liner is fixed at both ends using seal welds and a length of weld overlay. This results in a junction between the backing steel, weld overlay and liner, which is called the transition point or the triple point. When lined pipe is subjected to fatigue loading, the triple point has been shown to be location where fatigue cracks initiate. Flaws present at the triple point will grow in service. When a flaw breaches the liner, the backing steel will be exposed to the corrosive fluid, limiting the remaining life of the pipeline. It is therefore of interest to perform fracture mechanics calculations to understand fatigue crack growth from the triple point, so that the operational service life of MLP can be calculated if a flaw is present at the triple point. In order to do this, a stress intensity factor, K, is needed which describes the stress intensity at a crack tip at the triple point. However, owing to the unique geometry of this location, no stress intensity factor solution currently exists for the triple point location. To overcome this challenge, parametric finite element models were developed to calculate stress intensity factors for triple point crack-like flaws. This paper presents results from a work package from a joint industry project whose aim was to understand the fatigue performance of mechanically lined pipe. Finite element analysis was used to develop K solutions for the triple point in mechanically lined pipe by developing geometry-specific Y-factors for the MLP triple point geometry. An engineering critical assessment was then performed. The calculated fatigue life agreed well with results from full scale resonance fatigue tests and demonstrates the value of using FEA to derive geometry-specific K solutions for this geometry.
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Brückner-Foit, A., P. Hülsmeier, M. Sckuhr e H. Riesch-Oppermann. "Limitations of the Weibull Theory in Stress Fields With Pronounced Stress Gradients". In ASME Turbo Expo 2000: Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/2000-gt-0663.

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The Weibull theory for brittle fracture of ceramic materials has to be modified for stress fields with pronounced spatial inhomogeneities, e.g. for severe thermal shock or for material joints. This is due to the fact that the stress intensity factor determining the failure behavior of the natural flaws is affected by the stress gradients. This leads to a rather involved relationship between critical flaw size and applied stress and affects the strength.
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Keller, Scott G., e Ali P. Gordon. "Stress Intensity Incubation Periods for the Al-Hg Coupled Subjected to LME". In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-38921.

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When in the presence of liquid metal environments, structural materials can potentially lose the ability to deform and plastically flow. In the case of a ductile material, the result of this reduction in flow ability is a transition from ductile to brittle behavior, resulting in a brittle-like failure. This phenomenon is known as liquid metal embrittlement (LME) and is a subset of the more commonly known family of environmentally assisted cracking (EAC). Both EAC and LME have a significant negative impact on structural materials that are designed to behave elastically. Previous research in all facets of EAC, including stress corrosion cracking (SCC), corrosion fatigue (CF) and LME, has revealed that structural materials subjected to loading will generate and propagate cracks at stresses and stress intensities well below the critical values for that material. Additionally, crack tip velocities have been predicted and observed to be orders of magnitude greater than in ambient environments, with velocities in the range of tens to hundreds of centimeters per second. A variety of experimental routines have been used to characterize the interaction and develop microstructural failure mechanism in LME; however, uncertainty still surrounds the true failure mechanism. In a novel experimental approach, the dependence of the stress intensity factor (SIF) on crack propagation in the presence of a liquid metal was observed. Fracture mechanics specimens machined from Al7075-T651 in the S-L orientation were fatigue pre-cracked and incubated under load while submersed in liquid mercury. The result was the observation of rupture times over a range of stress intensity factors. It was noted that any stress concentration could provide the necessary criterion for crack initiation and propagation, regardless of the presence of a crack. Critical stresses and critical microstructural orientations dictated rupture paths more so than a pre-formed fatigue crack. Further experimentation, involving original and novel methods, has been conducted to determine the relationship between the stress intensity factor, stress concentration and microstructural orientation. Ultimately, the goal to confirm, extend or reject current microstructural failure mechanisms can be achieved through continued experimental routines.
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Cheng, Wing, e Shigeru Itoh. "Stress Intensity Factors for Defects in Two Common Weld Joints". In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93348.

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Defects are commonly in weld joints depending on the process condition and workmanship of the welding process. Under good control environment, the amount and size of the defects can be very small and do not compromise the integrity of the weld joints. In other cases, the amount and size of the defects in the weld joints can be large and, therefore, can limit the integrity of the structure. Determination of critical flaw sizes of the welds requires accurate calculation of stress intensity factors of cracks of various lengths at different locations for their use in crack growth evaluation under cyclic loading. Two commonly used welded joints, namely butt and corner weld joints, were investigated. Three crack configurations for each of the two welded joints were considered. Finite element method was used in conjunction of the M-integral to obtain the stress intensity factors for various lengths of the cracks. Results were then used to perform the fitness-for-purpose assessment of these welds under spectral loading. Methodology and results of the stress intensity factor calculation for the above-mentioned cracks are covered in this paper.
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Rapporti di organizzazioni sul tema "Critical stress intensity factor"

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Semiga, Vlad. PR-214-174517-WEB Sleeve End Fillet Weld Stress Intensity Factor Solutions. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), agosto 2019. http://dx.doi.org/10.55274/r0011612.

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Presented Thursday, September 5, 2019 PRESENTER: Vlad Semiga HOST: Rober Lazor, TC Energy MODERATOR: Thomas Marlow, PRCI Expected Benefits/Learning Outcomes: - Attendees will be given an overview of the sleeve end fillet weld stress intensity factors (SIFs) software, which provides a simplified means of estimating the SIFs for a single scenario or for an unlimited number of scenarios defined using a standard batch file format; - the presentation will also include the results of a sensitivity study illustrating the general trends in terms of the SIFs versus the range of inputs used to define an assessment scenario; - and the use of the SIFs in a standard integrity assessment (engineering critical assessment of fitness-for-service assessment) will also be demonstrated. Target Audience: - Pipeline design engineers - Welding specialists and engineers - Integrity management personnel Recommended pre-reading: Project final report: PR-214-174517-Z01 Development of Sleeve End Fillet Weld Stress Intensity Factor Calculator
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Dinovitzer, Aaron. PR-214-114504-R01 Development of Sleeve End Fillet Weld Fitness for Service Assessment. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), aprile 2020. http://dx.doi.org/10.55274/r0010989.

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Full encirclement repair sleeves with fillet-welded ends are often used as permanent repairs on pipelines to reinforce and develop pressure retaining repairs on areas with defects, such as cracks, dents, or corrosion. In-service failures have occurred at pressure retaining sleeves as a result of defects associated with the sleeve welds, such as hydrogen-induced cracks, undercut at the fillet welds and inadequate weld size. Currently, there are no reliable methods to carry out a quantitative fitness for service assessment for a sleeve fillet weld with a weld fault because: - The stresses at the sleeve end fillet weld roots and toes are not easily determined; - Stress intensity factor solutions are not available for the sleeve fillet weld geometry; and - Ccurrent inspection procedures cannot effectively define the size of weld defects. Following completion of a sleeve fillet weld it is currently common practice to carry out a visual inspection and magnetic particle inspection (MPI) to determine whether weld toe defects exist. With continuing advances in nondestructive examination (NDE) technologies, the ability to not only inspect for toe and root flaws but also to size these cracks is becoming a reality. The current project has developed a flaw acceptance criteria which will fill gaps in the available engineering critical assessment procedures for sleeve repairs on all grades of pipelines.
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Turnbull, A., e L. Crocker. Finite element calculation of stress intensity factor for cracks developing from corrosion pit. National Physical Laboratory, gennaio 2021. http://dx.doi.org/10.47120/npl.mat95.

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Underwood, John H. Stress Intensity Factor and Load-Line Displacement Expressions for the Round Bar Bend Specimen. Fort Belvoir, VA: Defense Technical Information Center, giugno 1994. http://dx.doi.org/10.21236/ada285669.

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Dinovitzer, Aaron. PR-214-174517-Z01 Development of Sleeve End Fillet Weld Stress Intensity Factor Calculator. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), maggio 2019. http://dx.doi.org/10.55274/r0011588.

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The objective of the project documented in the following report was to simplify the use and further demonstrate the application of the complex formulation developed for the stress intensity solutions developed in the previous project. The primary output of the project is a set of software tools (i.e. a Microsoft Excel based tool and a standalone executable software tool) that allows for the rapid calculation of the stress intensity factor solutions along with a set of sample calculations illustrating the use of the software tools. Additionally, a set of sensitivity analyses have been performed that illustrate the effect of various parameters on the SIFs.
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Kapp, J. A. Wide Range Stress Intensity Factor and Crack-Mouth-Opening Displacement Expressions Suitable for Short Crack Fracture Testing with Arc Bend-Chord Suppport Samples. Fort Belvoir, VA: Defense Technical Information Center, gennaio 1990. http://dx.doi.org/10.21236/ada218395.

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Dinovitzer, Aaron. PR-214-114504-R02 Development of Sleeve End Fillet Weld Fitness for Service Assessment Tools. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), maggio 2016. http://dx.doi.org/10.55274/r0010890.

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Pipeline defects such as cracks, dents and corrosion often require permanent pressure retaining repairs. Full encirclement metallic repair sleeves with fillet-welded end connections to the pipe-line are often used for this purpose. In-service failures have occurred at pressure retaining sleeves as a result of defects associated with the sleeve welds, such as hydrogen-induced cracks, undercut at the fillet welds and inadequate weld size. At present, accurate quantitative fitness for service assessments for circumferential defects in sleeve fillet welds are difficult to carry out due to a lack of detailed stress intensity factor solutions for finite length cracks. The primary objective of the project was to improve the assessment of circumferential defects in sleeve fillet welds through the development of more accurate stress intensity factors and plastic collapse solutions for finite length sleeve-end fillet weld toe and root cracks. The stress intensity factors were estimated using detailed finite element analysis. These factors were then used to develop simplified parametric equations which are suitable for carrying out defect assessments on a wide range of pipe and sleeve geometries. These equations can be used in the assessment of fatigue crack growth and/or fracture using failure assessment diagram methods at sleeve end fillets alongside the results developed for other structural geometries in national standards.
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Gould, Melissa, Bill Bruce e Vince Arnett. PR-186-113600-R01 Grinding Limits for Repair of SCC on Operating Pipelines. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), marzo 2018. http://dx.doi.org/10.55274/r0011473.

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Grinding is an accepted repair method for stress corrosion cracking (SCC) on buried pipelines. Grinding is routinely performed while the pipeline remains in service (i.e., pressurized and flowing). When grinding on a live pipeline, there is a risk that the pipe wall will rupture, either by reducing the wall thickness to below that which is appropriate for the operating pressure or by causing the cracking that is being removed to become 'critical' or unstable as the result of increased local stresses, etc. This project involved a review of current limits, practices, and previous work relevant to this topic. A full-scale experimental program was carried out in an effort to validate the premise that, during the removal of a crack or crack colony by grinding, there is a reduction in stress intensity as grinding proceeds and that the reduction in stress intensity more than compensates for the reduction in wall thickness. The project objective was to provide confidence for those who perform an SCC repair by grinding on an operating pipeline; while the experimental program produced some unexpected results, industry experience indicates that, with an appropriate pressure reduction prior to repair, this practice can be safe.
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Cialone, H., D. N. Williams e T. P. Groeneveld. L51621 Hydrogen-Related Failures at Mechanically Damaged Regions. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), settembre 1991. http://dx.doi.org/10.55274/r0010313.

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Leaks attributed to hydrogen-stress cracking (HSC) initiating in regions of mild mechanical damage have been reported in cathodically protected pipe lines constructed from high-strength, microalloyed, controlled-rolled steels. The hydrogen is believed to be present in service from the cathodic potential applied. Laboratory studies were initiated to determine the factors that contributed to those unexpected failures. Strain aging at ambient temperatures as a result of deformation introduced during the mechanical damage, was found to be a significant factor. Smooth-bar specimens that were strained and then aged failed by HSC within one week, whereas specimens that were not strain aged did not fail by HSC. Result: The findings of this research indicate a potential sequence of events which may lead to hydrogen-related failures in regions of mild mechanical damage: (1) Following the damage, ambient-temperature strain aging which promotes sensitivity to HSC takes place in the mechanically damaged region, in a surface layer of the pipe wall which has been subjected to a critical level of strain. The time period for this step would be on the order of several years. (2) Electrochemical conditions which promote hydrogen charging develop at the pipe surface from the cathodic current applied (or possibly corrosion). (3) Local stresses in the mechanically damaged region are elevated above the threshold stress for HSC by the moderate stress concentration provided by the mechanical damage. For the X70 pipe studied, the stress elevation should be at least 20 percent above the nominal hoop stress. (4) An HSC crack initiates and grows in the strain-aged surface layer. (5) The crack propagates further by HSC, through the non-strain-aged portion of the wall, as a result of the high stress concentration at the crack tip. (6) When the crack grows to a critical depth, it propagates rapidly through the wall by overload and causes a leak.
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Horwitz, Benjamin A., e Barbara Gillian Turgeon. Fungal Iron Acquisition, Oxidative Stress and Virulence in the Cochliobolus-maize Interaction. United States Department of Agriculture, marzo 2012. http://dx.doi.org/10.32747/2012.7709885.bard.

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Our project focused on genes for high affinity iron acquisition in Cochliobolus heterostrophus, a necrotrophic pathogen of maize, and their intertwined relationship to oxidative stress status and virulence of the fungus on the host. An intriguing question was why mutants lacking the nonribosomal peptide synthetase (NRPS) gene (NPS6) responsible for synthesis of the extracellular siderophore, coprogen, are sensitive to oxidative stress. Our overall objective was to understand the mechanistic connection between iron stress and oxidative stress as related to virulence of a plant pathogen to its host. The first objective was to examine the interface where small molecule peptide and reactive oxygen species (ROS) mechanisms overlap. The second objective was to determine if the molecular explanation for common function is common signal transduction pathways. These pathways, built around sensor kinases, response regulators, and transcription factors may link sequestering of iron, production of antioxidants, resistance to oxidative stress, and virulence. We tested these hypotheses by genetic manipulation of the pathogen, virulence assays on the host plant, and by following the expression of key fungal genes. An addition to the original program, made in the first year, was to develop, for fungi, a genetically encoded indicator of redox state based on the commercially available Gfp-based probe pHyper, designed for animal cell biology. We implemented several tools including a genetically encoded indicator of redox state, a procedure to grow iron-depleted plants, and constructed a number of new mutants in regulatory genes. Lack of the major Fe acquisition pathways results in an almost completely avirulent phenotype, showing how critical Fe acquisition is for the pathogen to cause disease. Mutants in conserved signaling pathways have normal ability to regulate NPS6 in response to Fe levels, as do mutants in Lae1 and Vel1, two master regulators of gene expression. Vel1 mutants are sensitive to oxidative stress, and the reason may be underexpression of a catalase gene. In nps6 mutants, CAT3 is also underexpressed, perhaps explaining the sensitivity to oxidative stress. We constructed a deletion mutant for the Fe sensor-regulator SreA and found that it is required for down regulation of NPS6 under Fe-replete conditions. Lack of SreA, though, did not make the fungus over-sensitive to ROS, though the mutant had a slow growth rate. This suggests that overproduction of siderophore under Fe-replete conditions is not very damaging. On the other hand, increasing Fe levels protected nps6 mutants from inhibition by ROS, implying that Fe-catalyzed Fenton reactions are not the main factor in its sensitivity to ROS. We have made some progress in understanding why siderophore mutants are sensitive to oxidative stress, and in doing so, defined some novel regulatory relationships. Catalase genes, which are not directly related to siderophore biosynthesis, are underexpressed in nps6 mutants, suggesting that the siderophore product (with or without bound Fe) may act as a signal. Siderophores, therefore, could be a target for intervention in the field, either by supplying an incorrect signal or blocking a signal normally provided during infection. We already know that nps6 mutants cause smaller lesions and have difficulty establishing invasive growth in the host. Lae1 and Vel1 are the first factors shown to regulate both super virulence conferred by T-toxin, and basic pathogenicity, due to unknown factors. The mutants are also altered in oxidative stress responses, key to success in the infection court, asexual and sexual development, essential for fungal dissemination in the field, aerial hyphal growth, and pigment biosynthesis, essential for survival in the field. Mutants in genes encoding NADPH oxidase (Nox) are compromised in development and virulence. Indeed the triple mutant, which should lack all Nox activity, was nearly avirulent. Again, gene expression experiments provided us with initial evidence that superoxide produced by the fungus may be most important as a signal. Blocking oxidant production by the pathogen may be a way to protect the plant host, in interactions with necrotrophs such as C. heterostrophus which seem to thrive in an oxidant environment.
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