Home About us Contact
|
Home About us Contact | ||
|
|
||
Cracking
Kinds of Cracking Terms modified by Cracking Selected AbstractsCracking the Incremental Paradigm of Japanese CreativityCREATIVITY AND INNOVATION MANAGEMENT, Issue 4 2004Tony Proctor This paper points out the differences between incremental and paradigm shift approaches to creativity in management that exists between Japanese and Western schools of thought. A number of examples are used to illustrate how a systematic incremental process that places emphasis on continuous improvement is key to Japanese creativity in management. A framework that captures the cornerstones of Japanese creativity is outlined. The paper concludes by discussing the contribution of this research and outlines a plan for further work. [source] Cracking the code: the genesis, use and future of the Code of ConductDISASTERS, Issue 4 2005Peter Walker Abstract This paper reflects on the genesis of the Code of Conduct for the International Red Cross and Red Crescent Movement and Non-Governmental Organizations (NGOs) in Disaster Relief, on the tenth anniversary of its adoption. The origins, usage and future of the code are examined with respect to three debates, current at the time of its inception, namely: the debate about the core content of humanitarianism; the debate about coherence and the consensual nature of the humanitarian community; and the debate about the need for, and the ability to demonstrate, accountability. The paper concludes that although the Code of Conduct was very much a product of its time, its content remains relevant today. However, its future application hinges on the capacity of those who purport to follow it to realise true accountability, and on proving that the code, written essentially for natural disasters, is relevant to contemporary complex emergencies. [source] Dichotic listening and school performance in dyslexiaDYSLEXIA, Issue 1 2008Turid Helland Abstract This study focused on the relationship between school performance and performance on a dichotic listening (DL) task in dyslexic children. Dyslexia is associated with impaired phonological processing, related to functions in the left temporal lobe. DL is a frequently used task to assess functions of the left temporal lobe. Due to the predominance of the contralateral neuronal pathways, a right ear advantage in the DL task reflects the superior processing capacity for the right ear stimulus in the left hemisphere (Kimura, 1963). Previous studies using DL in dyslexia are, however, inconclusive, and may reflect degree of severity of dyslexia. The aim of the present study was therefore to investigate lateralized processing in two sub-groups of dyslexia, differing in symptom severity. Two groups of dyslexic 12-year-old children and an age-matched control group were tested with a consonant,vowel DL task. The two dyslexia groups differed in severity through how they responded to training efforts being made in their schools, while otherwise being matched for age, IQ and diagnosis. The D1 (respondent group) group showed a DL performance pattern similar to the control group, i.e. a right ear advantage, while the D2 (non-respondent) group failed to show a right ear advantage on the DL task. The performance on the DL task by the two dyslexia groups may provide better insight as to the degree of reading and writing impairment in dyslexia. ,Cracking the code' and acquiring automatized literacy skills may seem harder for the D2 group children compared to the D1 children. Also, the present study points to the use of DL as a valid assessment tool in clinical work to improve differential diagnoses, particularly in relation to measures of school performance. Copyright © 2007 John Wiley & Sons, Ltd. [source] Stress Corrosion Cracking and Hydrogen Diffusion in Magnesium,ADVANCED ENGINEERING MATERIALS, Issue 8 2006A. Atrens Evaluation of recent data for hydrogen (H) diffusion in magnesium (Mg) yielded a new equation for the diffusion coefficient of H in Mg. This indicates that there can be significant H transport ahead of a stress corrosion crack in Mg at ambient temperature and that H may be involved in the mechanism of stress corrosion cracking in Mg. [source] Effects of Fiber Architecture on Matrix Cracking for Melt-Infiltrated SiC/SiC CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2010Gregory N. Morscher The matrix cracking behavior of slurry cast melt-infiltrated SiC matrix composites consisting of Sylramic-iBN fibers with a wide variety of fiber architectures were compared. The fiber architectures included 2D woven, braided, 3D orthogonal, and angle interlock architectures. Acoustic emission was used to monitor in-plane matrix cracking during unload,reload tensile tests. Two key parameters were found to control matrix-cracking behavior: the fiber volume fraction in the loading direction and the area of the weakest portion of the structure, that is, the largest tow in the architecture perpendicular to the loading direction. Empirical models that support these results are presented and discussed. [source] Cracking the Code: A Decode Strategy for the International Business Machines Punch Cards of Korean War SoldiersJOURNAL OF FORENSIC SCIENCES, Issue 3 2006Erin M. Mitsunaga B.A. ABSTRACT: During the Korean War, International Business Machines (IBM) punch cards were created for every individual involved in military combat. Each card contained all pertinent personal information about the individual and was utilized to keep track of all soldiers involved. However, at present, all of the information known about these punch cards reveals only their format and their significance; there is little to no information on how these cards were created or how to interpret the information contained without the aid of the computer system used during the war. Today, it is believed there is no one available to explain this computerized system, nor do the original computers exist. This decode strategy is the result of an attempt to decipher the information on these cards through the use of all available medical and dental records for each individual examined. By cross-referencing the relevant personal information with the known format of the cards, a basic guess-and-check method was utilized. After examining hundreds of IBM punch cards, however, it has become clear that the punch card method of recording information was not infallible. In some cases, there are gaps of information on cards where there are data recorded on personal records; in others, information is punched incorrectly onto the cards, perhaps as the result of a transcription error. Taken all together, it is clear that the information contained on each individual's card should be taken solely as another form of personal documentation. [source] Confocal Examination of Subsurface Cracking in Ceramic MaterialsJOURNAL OF PROSTHODONTICS, Issue 7 2009MMedSc, Maged K. Etman DDS Abstract Purpose: The original ceramic surface finish and its microstructure may have an effect on crack propagation. The purpose of this study was to investigate the relation between crack propagation and ceramic microstructure following cyclic fatigue loading, and to qualitatively evaluate and quantitatively measure the surface and subsurface crack depths of three types of ceramic restorations with different microstructures using a Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM). Materials and Methods: Twenty (8 × 4 × 2 mm3) blocks of AllCeram (AC), experimental ceramic (EC, IPS e.max Press), and Sensation SL (SSL) were prepared, ten glazed and ten polished of each material. Sixty antagonist enamel specimens were made from the labial surfaces of permanent incisors. The ceramic abraders were attached to a wear machine, so that each enamel specimen presented at 45 degrees to the vertical movement of the abraders, and immersed in artificial saliva. Wear was induced for 80K cycles at 60 cycles/min with a load of 40 N and 2-mm horizontal deflection. The specimens were examined for cracks at baseline, 5K, 10K, 20K, 40K, and 80K cycles. Results: Twenty- to 30-,m deep subsurface cracking appeared in SSL, with 8 to 10 ,m in AC, and 7 ,m close to the margin of the wear facets in glazed EC after 5K cycles. The EC showed no cracks with increasing wear cycles. Seventy-,m deep subsurface cracks were detected in SSL and 45 ,m in AC after 80K cycles. Statistically, there was significant difference among the three materials (p < 0.05). Bonferroni multiple comparison of means test confirmed the ANOVA test and showed that there was no statistical difference (p > 0.05) in crack depth within the same ceramic material with different surface finishes. Conclusions: The ceramic materials with different microstructures showed different patterns of subsurface cracking. [source] Criterion for the Avoidance of Edge Cracking in Layered SystemsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004M. Y. He When fabricating multilayers with brittle constituents, a prevalent design strategy is to choose fabrication conditions and thermal expansion coefficients that impose in-plane compression on the brittle layers. In such designs, a small zone of out-of-plane tension is induced at the edges that can cause cracks to form and extend, especially along the midplane. The associated stresses and energy release rates have been analyzed, revealing a fail-safe criterion, attributed to the existence of a maximum possible energy release rate, Gmax. Equating this maximum to the toughness defines a fail-safe parameter expressing the influence of the layer thickness, the misfit stress, and the toughness. When fail-safe designs cannot be realized, thin interlayers can be interposed in a manner that diminishes Gmax, broadening accessibility. The roles of misfit stress and interlayer thickness in attaining this condition are derived. [source] Stress-Corrosion Cracking of Silicon Carbide Fiber/Silicon Carbide CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Russell H. Jones Ceramic-matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements have been made in the creep resistance of SiC fibers and, hence, in the high-temperature properties of SiC fiber/SiC (SiCf/SiC) composites; however, more must be known about the stability of these materials in oxidizing environments before they are widely accepted. Experimental weight change and crack growth data support the conclusion that the oxygen-enhanced crack growth of SiCf/SiC occurs by more than one mechanism, depending on the experimental conditions. These data suggest an oxidation embrittlement mechanism (OEM) at temperatures <1373 K and high oxygen pressures and an interphase removal mechanism (IRM) at temperatures of ,700 K and low oxygen pressures. The OEM results from the reaction of oxygen with SiC to form a glass layer on the fiber or within the fiber,matrix interphase region. The fracture stress of the fiber is decreased if this layer is thicker than a critical value (d > dc) and the temperature below a critical value (T < Tg), such that a sharp crack can be sustained in the layer. The IRM results from the oxidation of the interfacial layer and the resulting decrease of stress that is carried by the bridging fibers. Interphase removal contributes to subcritical crack growth by decreasing the fiber-bridging stresses and, hence, increasing the crack-tip stress. The IRM occurs over a wide range of temperatures for d < dc and may occur at T > Tg for d > dc. This paper summarizes the evidence for the existence of these two mechanisms and attempts to define the conditions for their operation. [source] Cracking the Nutshell Differently.LANGUAGE LEARNING, Issue 2006Commentary on Mueller First page of article [source] Cracking the atom of civic powerNATIONAL CIVIC REVIEW, Issue 2 2005Harris Wofford First page of article [source] A Heart Close to Cracking: Preachers Resurrecting the Body in a Roman Catholic Crisis of PlausibilityNEW BLACKFRIARS, Issue 984 2003Gregory Heille OP First page of article [source] Detecting sub-surface cracking in laminated membranes using infrared imagingPOLYMER COMPOSITES, Issue 6 2001Thomas J. Mackin This paper presents a new experimental method that utilizes the thermoelastic effect to detect sub-surface cracks in a laminated polymer membrane. A highly accurate infrared camera is used to measure the thermoelastic and dissipational heat signatures associated with bi-axial fatigue loading of membranes. Changes in these thermal signatures arise whenever cracks form in any layer of the laminate, including fully embedded layers, thereby providing a novel method for experimentally measuring the initiation and growth of damage in sub-surface layers. The proposed method is illustrated using a model 3-layer system of EVOH sandwiched between two polyurethane layers. Bi-axial fatigue loading was used to initiate cracking in the central EVOH layer without damaging the outer polyurethane layers. Cracking in the central layer resulted in a distinct thermal signature that was plainly visible using the proposed method. [source] Cracking up: faulting on Earth and MarsASTRONOMY & GEOPHYSICS, Issue 4 2003Joyce Vetterlein No abstract is available for this article. [source] IVUS: Cracking the "Code" in the wall,CATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 6 2008Robert M. Schainfeld DO No abstract is available for this article. [source] A Practical Method to Estimate the Bed Height of a Fluidized Bed of Fine ParticlesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2008M. Zhang Abstract Knowledge of both dense bed expansion and freeboard solids inventory are required for the determination of bed height in fluidized beds of fine particles, e.g., Fluidized Catalytic Cracking (FCC) catalysts. A more accurate estimation of the solids inventory in the freeboard is achieved based on a modified model for the freeboard particle concentration profile. Using the experimentally determined dense bed expansion and the modified freeboard model, a more practical method with improved accuracy is provided to determine the bed height both in laboratory and industrial fluidized beds of FCC particles. The bed height in a fluidized bed can exhibit different trends as the superficial gas velocity increases, depending on the different characteristics of the dense bed expansion and solids entrainment in the freeboard. The factors that influence the bed height are discussed, showing the complexity of bed height and demonstrating that it is not realistic to determine the bed height by a generalized model that can accurately predict the dense bed expansion and freeboard solids inventory simultaneously. Moreover, a method to determine the bed height, based on axial pressure fluctuation profiles, is proposed in this study for laboratory fluidized beds, which provides improved accuracy compared to observation alone or determining the turning points in the axial pressure profiles, especially in high-velocity fluidized beds. [source] The Study of Molecular Modeling for Heavy Oil Thermal CrackingCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2007L. Yan Abstract The tighter specifications for refining products have gradually led refineries to focus on the molecular modeling of petroleum processing. In this work, a systematic methodology is presented for the molecular modeling of heavy oil thermal cracking (HOTC). This research which is based on a microscopic understanding provides a basis to achieve better design, management, optimization, and control of HOTC. The molecular information of HOTC product streams is represented in the form of a MTHS (molecular type homologous series) matrix. From consideration of the complexity of structural isomers in heavy petroleum fractions, the heavy molecules in a homologous series are grouped to reduce the dimension of the MTHS matrix. Transformation correlations are developed to capture the molecular properties of each homologous series in the MTHS matrix and to interrelate the molecular composition and bulk properties of the product streams. The HOTC process model was built on the basis of the molecular representation provided by the MTHS matrix and the transformation correlations. Two case studies are illustrated for validation of the proposed model and methodology. [source] A Risk-Cost Optimized Maintenance Strategy for Corrosion-Affected Concrete StructuresCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2007Chun-Qing Li It is also observed that some severely deteriorated concrete structures survive for many years without maintenance. This raises the question of why and how to maintain corrosion-affected concrete structures, in particular in the climate of an increasing scarcity of resources. The present article attempts to formulate a maintenance strategy based on risk-cost optimization of a structure during its whole service life. A time-dependent reliability method is employed to determine the probability of exceeding a limit state at each phase of the service life. To facilitate practical application of the formulated maintenance strategy, an algorithm is developed and programmed in a user-friendly manner with a worked example. A merit of the proposed maintenance strategy is that models used in risk assessment for corrosion-affected concrete structures are related to some of the design criteria used by practitioners. It is found in the article that there exists an optimal number of maintenances for cracking and delamination that returns the minimum total cost for the structure in its whole life. The maintenance strategy presented in the article can help structural engineers, operators, and asset managers develop a cost-effective management scheme for corrosion-affected concrete structures. [source] A Possibilistic Petri Net Model for Diagnosing Cracks in RC StructuresCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2003Kevin F. R. Liu PPN integrates Petri nets with possibilistic reasoning and maintains the advantages of both formalisms. Two major features of PPN include the possibilistic token to carry information to describe an object and its corresponding possibility and necessity measures, and four types of possibilistic transitions,inference, duplication, aggregation, and aggregation-duplication. A reasoning algorithm, based on possibilistic Petri nets, is also developed to execute PPN. The PPN model and the reasoning algorithm are further used to diagnose possible causes of cracking in RC structures, and three basic cases are considered to demonstrate the applicability of the approach. The reliability of the results is increased by explaining the diagnostic process through the movement of tokens. Moreover, the confidence level associated with each possible cause of concrete cracking can be used to determine the relevance of the diagnosis. [source] Seismic performance of a 3D full-scale high-ductile steel,concrete composite moment-resisting frame,Part II: Test results and analytical validationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2008A. Braconi Abstract This paper presents the results of a multi-level pseudo-dynamic seismic test program that was performed to assess the performance of a full-scale three-bay, two-storey steel,concrete composite moment-resisting frame built with partially encased composite columns and partial-strength beam-to-column joints. The system was designed to develop a ductile response in the joint components of beam-to-column joints including flexural yielding of beam end plates and shear yielding of the column web panel zone. The ground motion producing the damageability limit state interstorey drift caused minor damage while the ultimate limit state ground motion level entailed column web panel yielding, connection yielding and plastic hinging at the column base connections. The earthquake level chosen to approach the collapse limit state induced more damage and was accompanied by further column web panel yielding, connection yielding and inelastic phenomena at column base connections without local buckling. During the final quasi-static cyclic test with stepwise increasing displacement,amplitudes up to an interstorey drift angle of 4.6%, the behaviour was ductile although cracking of beam-to-end-plate welds was observed. Correlations with numerical simulations taking into account the inelastic cyclic response of beam-to-column and column base joints are also presented in the paper together. Inelastic static pushover and time history analysis procedures are used to estimate the structural behaviour and overstrength factors of the structural system under study. Copyright © 2008 John Wiley & Sons, Ltd. [source] Shaking table tests of 1:4 reduced-scale models of masonry infilled reinforced concrete frame buildingsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2001Abstract Two models of masonry infilled reinforced concrete frame buildings were tested at the shaking table. Models were built in the reduced scale 1:4 using the materials produced in accordance to modelling demands of true replica modelling technique. The first model represented a one-storey box-like building and the second one the two-stories building with plan shaped in the form of a letter H. Models were shaken with the series of horizontal sine dwell motions with gradually increasing amplitude. Masonry infills of tested models were constructed of relatively strong bricks laid in weak mortar. Therefore, typical cracks developed and propagated along mortar beds without cracking of bricks or crushing of infill corners. Data collected from tests will be used in future evaluation, verification and development of computational models for prediction of in-plane and out-of-plane behaviour of masonry infills. The responses of tested models can be well compared with global behaviour of real structures using the modelling rules. The similarity of local behaviour of structural elements, e.g. reinforced concrete joints, is less reliable due to limitations in modelling of steel reinforcement properties. The model responses showed that buildings designed according to Eurocodes are able to sustain relatively high dynamic excitations due to a significant level of structural overstrength. Copyright © 2001 John Wiley & Sons, Ltd. [source] Waterponding: Reclamation technique for scalded duplex soils in western New South Wales rangelandsECOLOGICAL MANAGEMENT & RESTORATION, Issue 3 2008Ray Thompson Summary Building on previous trials initiated in the 1960s, a demonstration programme involving 18 landholders was established at Nyngan, New South Wales Australia; in the mid-1980s to refine ,waterponding' techniques used to rehabilitate scalded claypans. The waterponding technique involves building horseshoe shaped banks (about 240 m in length) to create ponds of about 0.4 ha each. Each pond retains up to 10 cm of water after rain which leaches soluble salts from the scald surface. This improves the remaining soil structure, inducing surface cracking, better water penetration and allows entrapment of wind-blown seed. Consequently, niches are formed for the germination of this (and any sown) seed and recovery of a range of chenopod native pasture species occurs on the sites, which can be supplemented by direct seeding. What started as a project continues now as a standard rangeland rehabilitation process for reclaiming bare, scalded semi-arid areas of New South Wales and turning them back into biodiverse and productive rangelands. Since 1985, further modifications have been made to the method and the ongoing programme has surveyed, marked out and built approximately 56 700 waterponds within the Marra Creek waterponding district. [source] Amperometric Nitrite Sensor Based on PVP-Os Entrapped in Titania Sol-Gel MatrixELECTROANALYSIS, Issue 19 2004Yancai Li Abstract A novel nitrite sensor was developed based on the immobilization of a partially quaternized poly(4-vinylpyridine) complexed with [Os(bpy)2Cl]+/2+ (PVP-Os) in a porous TiO2 sol-gel matrix by a vapor deposition method. The preparation process simplified the traditional sol-gel process and prevented the cracking of conventional sol-gel derived glasses. Electrochemical behavior of the sensor was characterized by cyclic voltammetry and shows excellent electrocatalytic response for the reduction of nitrite. Effect of operating potential on electrochemical responses of the sensor was explored for optimum analytical performance by using the amperometric method. The stability of the sensor was also evaluated. [source] In Situ Synthesis, Characterization of SiPMo-X, and Different Catalytic Properties of SiPMo-X and SiPW-XEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2006Chunfeng Shi Abstract SBA-15 frameworks with encapsulated Keggin type heteropolyacids (HPAs) were synthesized in situ under strongly acidic conditions (pH,<,0). During the hydrolysis of tetraethyl orthosilicate (TEOS), a P- and a Mo source were added into the initial sol,gel system to form Keggin type HPAs. The texture of the final products was studied by the N2 adsorption,desorption isotherms and transmission electron microscopy (TEM), and their structure was systematically characterized by X-ray diffraction (XRD), UV/Vis diffuse reflectance- (DRS), infrared- (IR), and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Characterization results suggest that the samples show very ordered hexagonal mesostructure, and the HPAs that are incorporated into the framework of meso-silica are insoluble during catalysis. Results of catalytic tests indicate that the materials demonstrated catalytic activity comparable with or even surpassing those of the bulk HPAs in catalytic tests implementing chemical reactions of bulky molecules (1,3,5-triisopropylbenzene cracking, esterification of benzoic acid with tert -butyl alcohol, and 2,3,6-trimethylphenol hydroxylation with H2O2). Additionally, some other properties, such as easy separation and stability when recycled, ensure their potential applications in the chemical industries. Here, we report not only the in situ synthesis and characterization of SiPMo-X, but also the difference in the catalytic properties of SiPMo-X and SiPW-X. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Modeling of Hot Ductility During Solidification of Steel Grades in Continuous Casting , Part I,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Dieter Senk The present paper gives an overview of the simultaneous research work carried out by RWTH Aachen University and ThyssenKrupp Steel Europe AG. With a combination of sophisticated simulation tools and experimental techniques it is possible to predict the relations between temperature distribution in the mould, solidification velocity, chemical steel composition and, furthermore, the mechanical properties of the steel shell. Simulation results as well as experimentally observed microstructure parameters are used as input data for hot tearing criteria. A critical choice of existing hot tearing criteria based on different approaches, like critical strain and critical strain rate, are applied and developed. The new "damage model" is going to replace a basic approach to determine hot cracking susceptibility in a mechanical FEM strand model for continuous slab casting of ThyssenKrupp Steel Europe AG. Critical strains for hot cracking in continuous casting were investigated by in situ tensile tests for four steel grades with carbon contents in the range of 0.036 and 0.76,wt%. Additionally to modeling, fractography of laboratory and industrial samples was carried out by SEM and EPMA and the results are discussed. [source] Modelling of Hot Ductility during Solidification of Steel Grades in Continuous Casting , Part II,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Bernd Böttger In continuous casting, the probability of hot cracks developing strongly depends on the local solidification process and the microstructure formation. In ref. 1, an integrative model for hot cracking of the initial solid shell is developed. This paper focuses on solidification modelling, which plays an important role in the integrated approach. Solidification is simulated using a multiphase-field model, coupled online to thermodynamic and diffusion databases and using an integrated 1D temperature solver to describe the local temperature field. Less-complex microsegregation models are discussed for comparison. The results are compared to EDX results from strand samples of different steel grades. [source] Stress Corrosion Cracking and Hydrogen Diffusion in Magnesium,ADVANCED ENGINEERING MATERIALS, Issue 8 2006A. Atrens Evaluation of recent data for hydrogen (H) diffusion in magnesium (Mg) yielded a new equation for the diffusion coefficient of H in Mg. This indicates that there can be significant H transport ahead of a stress corrosion crack in Mg at ambient temperature and that H may be involved in the mechanism of stress corrosion cracking in Mg. [source] Numerical simulation of rotating bending process for U-tubes in heat exchangersFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2009H.-S. KIM ABSTRACT Heat exchangers comprise thousands of tubes having U-shaped portions. Rotating bending method has been widely utilized to make U-bends. Although this method shows an excellent performance, cracks have been frequently detected in the U-bends due to residual stresses induced by bending. In this paper, the bending process is simulated based on elastic,plastic finite element analyses in order to investigate the magnitude and distribution of the residual stresses including the effects of operating pressure. Analyses results show that the residual stress increases as the radius of U-bend decreases and that operating pressure has a detrimental effect in terms of stress corrosion cracking at the intrados of U-bend. It is thought that these results can be utilized for the estimations of fracture mechanics parameters such as limit load, stress intensity factor and J-integral, prevention of the cracking, and establishment of the optimum inspection strategy for the heat exchanger tubes. [source] The effect of laser power density on the fatigue life of laser-shock-peened 7050 aluminium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2007Q. LIU ABSTRACT Laser shock peening (LSP) is an innovative surface treatment method that can result in significant improvement in the fatigue life of many metallic components. The process produces very little or no surface profile modification while producing a considerably deeper compressive residual stress layer than traditional shot peening operations. The work discussed here was designed to: (a) quantify the fatigue life improvement achieved by LSP in a typical high strength aircraft aluminium alloy and (b) identify any technological risks associated with its use. It is shown that when LSP conditions are optimal for the material and specimen configuration, a ,three to four times increase in fatigue life over the as-machined specimens could be achieved for a representative fighter aircraft loading spectrum when applied at a representative load level. However, if the process parameters are not optimal for the material investigated here, fatigue lives of LSP treated specimens may be reduced instead of increased due to the occurrence of internal cracking. This paper details the effect of laser power density on fatigue life of 7050-T7451 aluminium alloy by experimental and numerical analysis. [source] A meso-level approach to the 3D numerical analysis of cracking and fracture of concrete materialsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2006A. CABALLERO ABSTRACT A meso-mechanical model for the numerical analysis of concrete specimens in 3D has been recently proposed. In this approach, concrete is represented as a composite material with the larger aggregates embedded in a mortar-plus-aggregates matrix. Both continuum-type components are considered linear elastic, while the possibilities of failure are provided with the systematic use of zero-thickness interface elements equipped with a cohesive fracture constitutive law. These elements are inserted along all potential crack planes in the mesh a priori of the analysis. In this paper, the basic features of the model are summarized, and then results of calculations are presented, which include uniaxial tension and compression loading of 14-aggregate cubical specimen along X, Y and Z axes. The results confirm the consistency of the approach with physical phenomena and well-known features of concrete behaviour, and show low scatter when different loading directions are considered. Those cases can also be considered as different specimens subjected to the same type of loading. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||