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Auswahl der wissenschaftlichen Literatur zum Thema „Weld plasticity“
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Zeitschriftenartikel zum Thema "Weld plasticity"
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Malushin, N. N., D. V. Valuev, A. V. Valueva und A. Serikbol. „Kinetic Study of the Effect of Plasticity and its Role in Stress Relaxation in the Weld Speed Steel during the Martensitic Transformation“. Applied Mechanics and Materials 682 (Oktober 2014): 58–63. http://dx.doi.org/10.4028/www.scientific.net/amm.682.58.
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It is shown that in the weld metal of the type of high-speed steels observe the effect of kinetic plasticity and he owns a defining role in stress relaxation. It is shown that the kinetic effect of plasticity can be used to control the stress in the weld details.
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Oddy, A. S., J. A. Goldak und J. M. J. McDill. „Transformation Plasticity and Residual Stresses in Single-Pass Repair Welds“. Journal of Pressure Vessel Technology 114, Nr. 1 (01.02.1992): 33–38. http://dx.doi.org/10.1115/1.2929009.
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Prediction of the residual stresses caused by welding is important when post-weld stress relief is not feasible. Phase changes and transformation plasticity have a significant effect on the residual stresses generated by welding and heat-treatment of some alloys. Transformation plasticity occurs when the stresses generated by the transformation of individual grains interact with the macroscopic stress state to produce plastic strains. Heuristic methods requiring empirical constants have been used in the past. A method based on the fundamental laws of plasticity and basic material properties is proposed to incorporate transformation plasticity in a finite element program. The transformation plasticity which occurs depends on the stress state. During any increment the stress state can change substantially. If the step size is too large, the analysis may become unstable. A method which allows larger steps while eliminating the instability and improving the convergence is presented. A three-dimensional (3D) analysis of a short longitudinal pipe weld in a typical pressure vessel steel is shown. The significance of this phenomenon in welds is demonstrated by comparing the residual stress states predicted with and without transformation plasticity.
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Cho, Jae Hyung, Suk Hoon Kang, Kyu Hwan Oh, Heung Nam Han und Suk Bong Kang. „Friction Stir Weld Modeling of Aluminum Alloys“. Advanced Materials Research 26-28 (Oktober 2007): 999–1002. http://dx.doi.org/10.4028/www.scientific.net/amr.26-28.999.
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Friction stir welding (FSW) process of aluminum alloys was investigated using a two-dimensional Eulerian formulation coupling viscoplastic flow and heat transfer and strain hardening. The thermal equation for the temperature was modified to stabilize temperature distribution using a Petrov-Galerkin method. The evolution equation for strength was calculated using a streamline integration method. Predicted strength was compared with experiments. Based on crystal plasticity, texture evolution was predicted during FSW of AA6061.
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Zhang, Tian Hui, Hong Cai Fu, Wen Min Liu, Yun Chun Cheng und Ren Ping Xu. „Influence of Weld Heat Input on Weld Joint between B610CF and 16MnR Steel“. Advanced Materials Research 154-155 (Oktober 2010): 421–24. http://dx.doi.org/10.4028/www.scientific.net/amr.154-155.421.
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The influence of weld heat input on weld joint between B610CF and 16MnR steel using shielded metal arc welding method was investigated by metallographic experiment and mechanical properties experiment. Metallographic experimental results show that in welded metal with the increasing of weld heat input the quantity of bainite is decreased and crystalline grain is larger; but in both B610CF and 16MnR steel heat affected zone, with the increasing of weld heat input there is no distinct difference in microstructure. Mechanical property experimental results show that in weld metal with the increasing of weld heat input the impact toughness decreases, but in both B610CF and 16MnR heat affected zone, there is less difference in impact toughness; and there is no distinct difference in tensile strength and plasticity of weld joint, which is consistent with the metallographic experiment results.
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Jang, Gab Chul, Kyong Ho Chang und Chin Hyung Lee. „Effect of Residual Stress and Weld Metal on Hysteretic Behavior of a Welded Tubular T-Joint“. Key Engineering Materials 353-358 (September 2007): 2077–80. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.2077.
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During the welding process to make welded joints, residual stress is inevitably generated and weld metal is used. Welding Residual stress is influenced on the behavior of welded joints under monotonic and cyclic loading. And the weld metals used in welding process have different mechanical characteristics than structural steels. Therefore, to accurately predict the hysteretic behavior of welded joints, the effect of residual stress and weld metal must be investigated. In this paper, the residual stress distribution in a welded tubular T-joint was investigated by carrying out three-dimensional non-steady heat conduction analysis and three-dimensional thermal elastic-plastic analysis. To consider a effect of base metal(SM490) and weld metal(E71T-1), a cyclic plasticity model was formulated based on monotonic and cyclic loading tests. And the formulated model was applied to three-dimensional elastic-plastic finite element analysis. The effect of residual stress and weld metal on hysteretic behavior of a welded tubular T-joint was investigated by carrying out numerical analyses considering residual stress and cyclic plasticity model of base metal and weld metal respectively.
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Jiang, Xiao Xia, Shang Cai Fei, Shuai Zhang, Hua Ji und Liang Zhu. „Failure Analysis of the Laser-Welded Web-Core Steel Sandwich Panel with Narrow Weld Width T-Joints“. Applied Mechanics and Materials 863 (Februar 2017): 311–16. http://dx.doi.org/10.4028/www.scientific.net/amm.863.311.
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Static three-point bending test of the laser welded Web-core steel sandwich panel was performed. The deformation and failure of the sandwich panel with narrow weld width T-Joints were investigated. The results indicate that the deformation undertakes the following three stages: elastic deformation, plasticity deformation and T-joints cracking. The initial yield load is 25 kN, The maximum bending load is 54 kN. The high strength rate characteristic not be fully reflected. The finite simulation result shows the whole structure has no chance to reach the designed maximum value when the T-joints formed plasticity rings. Then the plastic region was developing till the weld cracked. We considered that the T-joint’s cracking is a new failure mode for the web-core steel sandwich panel. Thus, the laser welded T-joints with narrow weld width are the weakest location for the total structure. It is very necessary to consider the T-joint’s geometrical and mechanical properties for the total structural design.
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Lazzarin, P., und P. Livieri. „Welded joints: Limits on criteria for plasticity zones located at weld toes“. Welding International 14, Nr. 10 (Januar 2000): 806–10. http://dx.doi.org/10.1080/09507110009549272.
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Zhao, Li, Fu Ju Zhang und Shao Hua Feng. „Microstructure and Mechanical Properties of Weld in 980MPa Grade Steel by Ultra-Narrow Gap Welding“. Advanced Materials Research 322 (August 2011): 263–66. http://dx.doi.org/10.4028/www.scientific.net/amr.322.263.
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980MPa grade high strength low alloy steel was welded by ultra-narrow gap welding. Observed by optical metalloscope, there were large majority of equiaxial crystals in weld centers, which was the weld cross-section of 18.3%. Each weld could be compartmentalized into original microstructure zone, over heated zone and normalizing zone under next weld thermal cycle, in which the microstructures were almost the same. Through quantificational metallographic analysis, it was found there was more than 98.9% of acicular ferrite in weld metal, and other microstructures were fine. Mechanical test indicated that the strength of weld metal was higher than body material, and had outstanding plasticity. What is more, the toughness of weld metal was better than solder wire.
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Muránsky, Ondrej, Cory J. Hamelin, Mike C. Smith, Phillip J. Bendeich und Lyndon Edwards. „The Role of Plasticity Theory on the Predicted Residual Stress Field of Weld Structures“. Materials Science Forum 772 (November 2013): 65–71. http://dx.doi.org/10.4028/www.scientific.net/msf.772.65.
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Constitutive plasticity theory is commonly applied to the numerical analysis of welds in one of three ways: using an isotropic hardening model, a kinematic hardening model, or a mixed isotropic-kinematic hardening model. The choice of model is not entirely dependent on its numerical accuracy, however, as a lack of empirical data will often necessitate the use of a specific approach. The present paper seeks to identify the accuracy of each formalism through direct comparison of the predicted and actual post-weld residual stress field developed in a three-pass 316LN stainless steel slot weldment. From these comparisons, it is clear that while the isotropic hardening model tends to noticeably over-predict and the kinematic hardening model slightly under-predict the residual post-weld stress field, the results using a mixed hardening model are quantitatively accurate. Even though the kinematic hardening model generally provides more accurate results when compared to an isotropic hardening formalism, the latter might be a more appealing choice to engineers requiring a conservative design regarding weld residual stress.
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Chen, Yun Chun, Wen Min Liu, Hou Sen Yang, Tian Hui Zhang und Pei Jun Yan. „Influence of Weld Parameter on Penstock Joint of B610CF-16MnR Steel“. Advanced Materials Research 675 (März 2013): 270–74. http://dx.doi.org/10.4028/www.scientific.net/amr.675.270.
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Weld parameter is an important factor affecting micrographic structure and mechanical properties of weld joints. It was investigated by metallographic experiments and mechanical property experiments for the influence of weld heat input on dissimilar steel weld joint of penstock using B610CF and 16MnR steel in water conservancy and hydropower engineering using shielded metal arc welding method and mixed active gas arc welding method. Metallographic experimental results show that in weld metal with the increase of weld heat input the quantity of bainite decreases and crystalline grain is larger when using the same welding method; but in both B610CF and 16MnR steel heat affected zone, there is no distinct difference in microstructure. Mechanical property experimental results show that in weld metal with the increase of weld heat input the impact toughness decreases when using the same welding method, but in both B610CF and 16MnR heat affected zone, there is less difference in impact toughness; and there is no distinct difference in tensile strength and plasticity of weld joint. So moderate weld heat input is recommended.
Dissertationen zum Thema "Weld plasticity"
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Kutil, Petr. „Studium plasticity svaru hlubokotažných plechů svařených technologií Laser-TIG“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443205.
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This thesis is focused on laser welding and hybrid laser-TIG welding. The first part contains a brief theoretical description of these technologies. Standard quality and plasticity tests of welded joint are also mentioned. The second, experimental part, centres on the study of plasticity of tailored blanks (made of different types of HSLA steel), that are welded with laser and laser-TIG technology. The aim of the thesis is to assess process parameters effect on weld suitability for following deep drawning operation. Based on the calculated and measured figures obtained from the experiment, the most suitable welding parameters were chosen.
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Boåsen, Magnus. „Modeling framework for ageing of low alloy steel“. Licentiate thesis, KTH, Hållfasthetslära (Inst.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-246036.
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Ageing of low alloy steel in nuclear applications commonly takes the form as a hardening and an embrittlement of the material. This is due to the evolution of the microstructure during irradiation and at purely thermal conditions, as a combination or separate. Irradiation introduces evenly distributed solute clusters, while thermal ageing has been shown to yield a more inhomogeneous distribution. These clusters affect the dislocation motion within the material and results in a hardening and in more severe cases of ageing, also a decreased work hardening slope due to plastic strain localization into bands/channels. Embrittlement corresponds to decreased fracture toughness due to microstructural changes resulting from ageing. The thesis presents a possible framework for modeling of ageing effects in low alloy steels.In Paper I, a strain gradient plasticity framework is applied in order to capture length scale effects. The constitutive length scale is assumed to be related to the dislocation mean free path and the changes this undergoes during plastic deformation. Several evolution laws for the length scale were developed and implemented in a FEM-code considering 2D plane strain. This was used to solve a test problem of pure bending in order to investigate the effects of the length scale evolution. As all length scale evolution laws considered in this study results in a decreasing length scale; this leads to a loss of non-locality which causes an overall softening at cases where the strain gradient is dominating the solution. The results are in tentative agreement with phenomena of strain localization that is occurring in highly irradiated materials.In Paper II, the scalar stress measure for cleavage fracture is developed and generalized, here called the effective normal stress measure. This is used in a non-local weakest link model which is applied to two datasets from the literature in order to study the effects of the effective normal stress measure, as well as new experiments considering four-point bending of specimens containing a semi-elliptical surface crack. The model is shown to reproduce the failure probability of all considered datasets, i.e. well capable of transferring toughness information between different geometries.Åldring av låglegerade stål i kärntekniska användningsområden framträder typiskt som ett hårdnande och en försprödning av materialet. Detta på grund av utvecklingen av mikrostrukturen under bestrålning och under rent termiska förhållanden. Bestrålning introducerar jämt fördelade kluster av legeringsämnen. Termisk åldring har däremot visats ge upphov till en mer ojämn fördelning. Klustren hämmar dislokationsrörelsen i materialet och ger därigenom upphov till en ökning av materialets sträckgräns, vid en mer påtaglig åldring det även leda till ett sänkt arbetshårdnande på grund av lokalisering av plastisk töjning i s.k. kanaler/band. Försprödning är en sänkning av materialets brottseghet som en följd av de mikrostrukturella förändringar som sker vid åldring. Arbetet som presenteras i den här avhandlingen har gjorts i syfte till att ta fram ett möjligt ramverk för modellering av låglegerade stål.I Artikel I, används en töjningsgradientbaserad plasticitetsteori för att kunna fånga längdskalebeteenden. Längdskalan i teorin antas vara relaterad till dislokationernas medelfria väg och den förändring den genomgår vid plastisk deformation. Flera utvecklingslagar för längdskalan har analyserats och implementerats i en finita element kod för 2D plan deformation. Denna implementering har använts för att lösa ett testproblem bestående av ren böjning med syfte att undersöka effekterna av utvecklingen hos längdskalan. Alla de utvecklingslagar som presenteras i artikeln ger en minskande längdskala, vilket leder till vad som valt att kallas förlust av icke-lokalitet. Fenomenet leder till ett övergripande mjuknande vid fall där den plastiska töjningsgradienten har stor inverkan på lösningen. Resultaten är i preliminär överenstämmelse med de typer av lokalisering av plastisk töjning som observerats i starkt bestrålade material.I Artikel II utvecklas ett generaliserat spänningsmått i syfte att beskriva klyvbrott, här benämnt effektivt normalspänningsmått. Detta har använts i samband med en icke-lokal svagaste länk modell, som har applicerats på två experimentella studier från den öppna litteraturen i syfte att studera effekterna av det effektiva normalspänningsmåttet. Utöver detta presenteras även nya experiment på ytspruckna provstavar under fyrpunktsböj. I artikeln visas att modellen återskapar sannolikheten för brott för alla undersökta experimentuppställningar, d.v.s. modellen visas vara väl duglig för att överföra brottseghet mellan geometrier.
QC 20190312
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Kotsou, Ilios. „Emotional plasticity: the impact of the development of emotional competence on well-being. Conditions, effects and change processes“. Doctoral thesis, Universite Libre de Bruxelles, 2017. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/246651.
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This thesis focuses on the acquisition of emotional competence (EC) skills in adults and its impact on well being. The first part of the thesis is dedicated to the definition of EC, including a review of EC in order to better understand and operationalize its main dimensions and correlates. We also present a systematic review of EC intervention studies on adult populations in order to assess their outcomes and make recommendations for the development and implementation of future interventions. We then provide a theoretical and practical framework for emotional competence (EC) based interventions. We describe the main components of an EC intervention, underline the important characteristics of the intervention pedagogy and discuss theoretical and practical implications of this framework.In a second part we investigate whether a sustainable improvement in emotional competencies is possible in adults, and what are the conditions and effects of this improvement on well-being (e.g. on mental and physical health and quality of interpersonal relationships). Results of three empirical studies confirm that EC can be significantly increased following an intervention (and compared to a control group) and that this intervention impacts favourably personal and interpersonal well-being as measured by psychological health, quality of relationship and employability.A last part of the thesis explores the mechanisms underlying this improvement of competencies and well-being. We focus on emotional acceptance, self-compassion, self kindness and behavioural flexibility. Because there was no scale measuring self-compassion or self kindness in French, we validate two scales and assess the relationships between these constructs and well-being.We then examined the possible benefits of emotional acceptance and behavioural flexibility in a randomized controlled study, showing how increasing emotional competence can enhance these change processes and how these processes can, in turn, enhance well-being.This research helps to further elucidate the role of active change processes in EC increase related to the promotion of well-being.Doctorat en Sciences psychologiques et de l'éducation
info:eu-repo/semantics/nonPublished
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O'Meara, Nicholas. „Developing material models for use in finite element predictions of residual stresses in ferritic steel welds“. Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/developing-material-models-for-use-in-finite-element-predictions-of-residual-stresses-in-ferritic-steel-welds(0f2cfa95-1d35-42be-b224-665252950efc).html.
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Nuclear reactor pressure vessels are constructed by welding low alloy steel forgings together. Welding processes can leave residual stresses which affect the RPV's resistance to fracture. Welding also induces microstructural changes and these changes have a number of associated consequences, including inelastic strains and altering mechanical properties. The extent to which these microstructural changes influence residual stress evolution during welding is not fully understood. The aim of this project is to characterise the microstructural and mechanical response of SA-508 Gr.3 Cl.1 pressure vessel steel to thermal cycles and develop representative models that can be used to determine how these effects influence stress predictions. There is insufficient materials data to inform the models used to predict how phase transformations influence residual stresses. Using the recently developed Gleeble thermo-mechanical simulator, previously unmeasured data characterising the response of the material to weld-like thermal cycles was generated. Variations in the kinetics of austenite formation and decomposition were investigated using dilatometry. It was found that when the steel is subjected to multiple thermal cycles that exceed the austenisation temperature, the behaviour during the first thermal cycle is different to that of subsequent cycles. In the subsequent thermal cycles, two observations were made: 1) the austenite formation rate increases on heating, and 2) for a given cooling rate, the austenite will decompose at lower temperatures into harder phases. It is explained how these changes in behaviour can affect the residual stress distribution in this thesis. Bainitic, austenitic and martensitic samples were generated. The stress-strain behaviour of these phases is presented and has been used to inform mechanical constitutive models. Finite element simulations of autogenous edge welded beams have shown how microstructural changes can affect the residual stress predictions. The extent of the transformed region of the HAZ and the yield stress of the material surrounding this region influences the location and magnitude of the peak tensile residual stress after a weld pass. Changes in mechanical properties induced by tempering bainitic and martensitic samples were quantified experimentally. The reductions in yield stress in bainite and martensite during short tempering heat treatments were found to be significant. A new approach to integrate the observed tempering behaviour into existing models is presented. The data and models presented in this thesis can provide guidance to structural integrity engineers and help produce more accurate and less conservative residual stress predictions for use in structural integrity assessments.
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Parkkali, Seija Anna. „The role of natural selection and adaptation versus phenotypic plasticity in the invasive success of Hieracium lepidulum in New Zealand“. Thesis, University of Canterbury. Biological Sciences, 2008. http://hdl.handle.net/10092/1799.
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Hieracium lepidulum is an invasive weed in New Zealand. It colonises a wide range of habitats including pine plantations, scrubland, native Nothofagus forest, and mid-altitude to alpine tussock grassland, where it is competing with indigenous species. Understanding the breeding systems and population genetic structure of H. lepidulum is important for biocontrol, and aids in the understanding of evolutionary colonisation processes. H. lepidulum is a triploid, diplosporous, obligate apomict. This type of reproduction through clonal seed does not involve meiosis or fertilisation, and theoretically populations should contain very low levels of genetic variation, the only source being somatic mutation. Common garden experiments and microsatellite markers were used to determine the population genetic structure of H. lepidulum populations in the Craigieburn Range, Canterbury. Both experiments revealed that populations, sampled from three replicate altitudes within three geographically-separated locations, contained no genetic variation; individuals all possessed the same microsatellite genotype. These results strongly suggest that the Craigieburn Range H. lepidulum individuals reproduce solely by apomixis and populations belong to the same clonal lineage. Populations were also examined for their response to two abiotic environmental ‘stresses’, drought and shade. H. lepidulum populations’ exhibited high drought tolerance, yet appeared to be shade-intolerant. Low levels of reproduction in light-limiting habitats will prevent the invasion of H. lepidulum into closed-canopy forest habitats. H. lepidulum appears to have overcome the reduction in fitness associated with apomictic reproduction by phenotypic plasticity, fixed heterozygosity and polyploidy – all associated with increased vigour, fitness, and the ability to occupy broader ecological niches. This study’s results are hopeful for the development of biocontrol programs involving genotype-specific pathogens but suggest that grazing management may not succeed. The data will be useful for future comparisons of genetic structure during the course of H. lepidulum invasions and will contribute to the management of this invasive weed.
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Behravesh, Seyed Behzad. „Fatigue Characterization and Cyclic Plasticity Modeling of Magnesium Spot-Welds“. Thesis, 2013. http://hdl.handle.net/10012/7651.
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The automotive industry is adopting lightweight materials to improve emissions and fuel economy. Magnesium (Mg) alloys are the lightest of engineering metals, but work is required to assess their structural strength, especially for spot-welded applications. In the present research, fatigue behavior of magnesium spot-welds was characterized and compared with steel and aluminum spot-welds. A fatigue model was proposed to predict the failure location and crack initiation life in magnesium structures.
The material under investigation, AZ31B-H24 Mg alloy, and its spot-welds were characterized from microstructural and mechanical perspectives. Microstructure and hardness of the base metal (BM) and different regions in the spot-welds were studied. Under cyclic loading, the BM had an asymmetric hysteresis loop. Cyclic behavior of magnesium spot-welds was measured using different specimen configurations, and the effect of geometrical factors on fatigue life was evaluated.
A constitutive model was developed to model the asymmetric hardening behavior of wrought magnesium alloys under cyclic loading. An algorithm for numerical implementation of the proposed model was developed. The numerical formulation was programmed into a user material subroutine to run with the commercial finite element software Abaqus/Standard. The proposed model was verified by solving two problems with available solutions.
A number of available fatigue models, as well as a new model proposed in this research were assessed by predicting fatigue life of magnesium spot-welds. The new model used a strain energy damage parameter. All models were evaluated by comparing the predicted and experimental fatigue lives for different Mg spot-welded specimens. The effect of considering the asymmetric hardening behavior of wrought magnesium alloys on the accuracy of the fatigue life prediction was not significant for the available experimental data. This was attributed to the limited experimental data on spot-welded specimens.
The proposed material model and fatigue damage parameter were verified by simulating a real-life structure manufactured and fatigue tested by the US Automotive Materials Partnership. The results obtained from the proposed asymmetric model were compared with available symmetric simulation results and experimental data. The asymmetric material model along with the proposed damage parameter resulted in more accurate prediction of fatigue failure location and life.
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(8741097), Ritwik Bandyopadhyay. „ENSURING FATIGUE PERFORMANCE VIA LOCATION-SPECIFIC LIFING IN AEROSPACE COMPONENTS MADE OF TITANIUM ALLOYS AND NICKEL-BASE SUPERALLOYS“. Thesis, 2020.
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In this thesis, the role of location-specific microstructural features in the fatigue performance of the safety-critical aerospace components made of Nickel (Ni)-base superalloys and linear friction welded (LFW) Titanium (Ti) alloys has been studied using crystal plasticity finite element (CPFE) simulations, energy dispersive X-ray diffraction (EDD), backscatter electron (BSE) images and digital image correlation (DIC).
In order to develop a microstructure-sensitive fatigue life prediction framework, first, it is essential to build trust in the quantitative prediction from CPFE analysis by quantifying uncertainties in the mechanical response from CPFE simulations. Second, it is necessary to construct a unified fatigue life prediction metric, applicable to multiple material systems; and a calibration strategy of the unified fatigue life model parameter accounting for uncertainties originating from CPFE simulations and inherent in the experimental calibration dataset. To achieve the first task, a genetic algorithm framework is used to obtain the statistical distributions of the crystal plasticity (CP) parameters. Subsequently, these distributions are used in a first-order, second-moment method to compute the mean and the standard deviation for the stress along the loading direction (σ_load), plastic strain accumulation (PSA), and stored plastic strain energy density (SPSED). The results suggest that an ~10% variability in σ_load and 20%-25% variability in the PSA and SPSED values may exist due to the uncertainty in the CP parameter estimation. Further, the contribution of a specific CP parameter to the overall uncertainty is path-dependent and varies based on the load step under consideration. To accomplish the second goal, in this thesis, it is postulated that a critical value of the SPSED is associated with fatigue failure in metals and independent of the applied load. Unlike the classical approach of estimating the (homogenized) SPSED as the cumulative area enclosed within the macroscopic stress-strain hysteresis loops, CPFE simulations are used to compute the (local) SPSED at each material point within polycrystalline aggregates of 718Plus, an additively manufactured Ni-base superalloy. A Bayesian inference method is utilized to calibrate the critical SPSED, which is subsequently used to predict fatigue lives at nine different strain ranges, including strain ratios of 0.05 and -1, using nine statistically equivalent microstructures. For each strain range, the predicted lives from all simulated microstructures follow a log-normal distribution; for a given strain ratio, the predicted scatter is seen to be increasing with decreasing strain amplitude and are indicative of the scatter observed in the fatigue experiments. Further, the log-normal mean lives at each strain range are in good agreement with the experimental evidence. Since the critical SPSED captures the experimental data with reasonable accuracy across various loading regimes, it is hypothesized to be a material property and sufficient to predict the fatigue life.
Inclusions are unavoidable in Ni-base superalloys, which lead to two competing failure modes, namely inclusion- and matrix-driven failures. Each factor related to the inclusion, which may contribute to crack initiation, is isolated and systematically investigated within RR1000, a powder metallurgy produced Ni-base superalloy, using CPFE simulations. Specifically, the role of the inclusion stiffness, loading regime, loading direction, a debonded region in the inclusion-matrix interface, microstructural variability around the inclusion, inclusion size, dissimilar coefficient of thermal expansion (CTE), temperature, residual stress, and distance of the inclusion from the free surface are studied in the emergence of two failure modes. The CPFE analysis indicates that the emergence of a failure mode is an outcome of the complex interaction between the aforementioned factors. However, the possibility of a higher probability of failure due to inclusions is observed with increasing temperature, if the CTE of the inclusion is higher than the matrix, and vice versa. Any overall correlation between the inclusion size and its propensity for damage is not found, based on inclusion that is of the order of the mean grain size. Further, the CPFE simulations indicate that the surface inclusions are more damaging than the interior inclusions for similar surrounding microstructures. These observations are utilized to instantiate twenty realistic statistically equivalent microstructures of RR1000 – ten containing inclusions and remaining ten without inclusions. Using CPFE simulations with these microstructures at four different temperatures and three strain ranges for each temperature, the critical SPSED is calibrated as a function of temperature for RR1000. The results suggest that critical SPSED decreases almost linearly with increasing temperature and is appropriate to predict the realistic emergence of the competing failure modes as a function of applied strain range and temperature.
LFW process leads to the development of significant residual stress in the components, and the role of residual stress in the fatigue performance of materials cannot be overstated. Hence, to ensure fatigue performance of the LFW Ti alloys, residual strains in LFW of similar (Ti-6Al-4V welded to Ti-6Al-4V or Ti64-Ti64) and dissimilar (Ti-6Al-4V welded to Ti-5Al-5V-5Mo-3Cr or Ti64-Ti5553) Ti alloys have been characterized using EDD. For each type of LFW, one sample is chosen in the as-welded (AW) condition and another sample is selected after a post-weld heat treatment (HT). Residual strains have been separately studied in the alpha and beta phases of the material, and five components (three axial and two shear) have been reported in each case. In-plane axial components of the residual strains show a smooth and symmetric behavior about the weld center for the Ti64-Ti64 LFW samples in the AW condition, whereas these components in the Ti64-Ti5553 LFW sample show a symmetric trend with jump discontinuities. Such jump discontinuities, observed in both the AW and HT conditions of the Ti64-Ti5553 samples, suggest different strain-free lattice parameters in the weld region and the parent material. In contrast, the results from the Ti64-Ti64 LFW samples in both AW and HT conditions suggest nearly uniform strain-free lattice parameters throughout the weld region. The observed trends in the in-plane axial residual strain components have been rationalized by the corresponding microstructural changes and variations across the weld region via BSE images.
In the literature, fatigue crack initiation in the LFW Ti-6Al-4V specimens does not usually take place in the seemingly weakest location, i.e., the weld region. From the BSE images, Ti-6Al-4V microstructure, at a distance from the weld-center, which is typically associated with crack initiation in the literature, are identified in both AW and HT samples and found to be identical, specifically, equiaxed alpha grains with beta phases present at the alpha grain boundaries and triple points. Hence, subsequent fatigue performance in LFW Ti-6Al-4V is analyzed considering the equiaxed alpha microstructure.
The LFW components made of Ti-6Al-4V are often designed for high cycle fatigue performance under high mean stress or high R ratios. In engineering practice, mean stress corrections are employed to assess the fatigue performance of a material or structure; albeit this is problematic for Ti-6Al-4V, which experiences anomalous behavior at high R ratios. To address this problem, high cycle fatigue analyses are performed on two Ti-6Al-4V specimens with equiaxed alpha microstructures at a high R ratio. In one specimen, two micro-textured regions (MTRs) having their c-axes near-parallel and perpendicular to the loading direction are identified. High-resolution DIC is performed in the MTRs to study grain-level strain localization. In the other specimen, DIC is performed on a larger area, and crack initiation is observed in a random-textured region. To accompany the experiments, CPFE simulations are performed to investigate the mechanistic aspects of crack initiation, and the relative activity of different families of slip systems as a function of R ratio. A critical soft-hard-soft grain combination is associated with crack initiation indicating possible dwell effect at high R ratios, which could be attributed to the high-applied mean stress and high creep sensitivity of Ti-6Al-4V at room temperature. Further, simulations indicated more heterogeneous deformation, specifically the activation of multiple families of slip systems with fewer grains being plasticized, at higher R ratios. Such behavior is exacerbated within MTRs, especially the MTR composed of grains with their c-axes near parallel to the loading direction. These features of micro-plasticity make the high R ratio regime more vulnerable to fatigue damage accumulation and justify the anomalous mean stress behavior experienced by Ti-6Al-4V at high R ratios.
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Maas, Bea. „Birds, bats and arthropods in tropical agroforestry landscapes: Functional diversity, multitrophic interactions and crop yield“. Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-5E77-5.
Der volle Inhalt der QuelleBücher zum Thema "Weld plasticity"
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Schlaug, Gottfried. Music, musicians, and brain plasticity. Herausgegeben von Susan Hallam, Ian Cross und Michael Thaut. Oxford University Press, 2012. http://dx.doi.org/10.1093/oxfordhb/9780199298457.013.0018.
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This article reviews studies on the brains of musicians. Making music not only engages primary auditory and motor regions and the connections between them, but also regions that integrate and connect areas involved in both auditory and motor operations, as well as in the integration of other multisensory information. Professional instrumentalists learn and repeatedly practice associating hand/finger movements with meaningful patterns in sound, and sounds and movements with specific visual patterns (notation) while receiving continuous multisensory feedback. Learning to associate actions with particular sounds leads to functional but also structural changes in frontal cortices.
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Heimler, Benedetta, Francesco Pavani und Amir Amedi. Implications of Cross-Modal and Intramodal Plasticity for the Education and Rehabilitation of Deaf Children and Adults. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780190880545.003.0015.
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Exploring the environment without the auditory modality elicits wholesale reorganizations at both the behavioral and the neural levels throughout life. This chapter reviews changes in brain organization and behavior arising from early deafness. It depicts a multifaceted framework in both domains: the performance of deaf persons has been shown to be comparable to, better than, as well as worse than that of hearing participants. They also show brain modifications ascribable both to intramodal (within the visual system) and cross-modal plasticity (the recruitment of the deprived auditory cortex by intact sensory modalities). The authors discuss the implications of these results for sensory rehabilitation and highlight the benefits of multisensory systematic training programs to boost recovery.
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Poretti, Andrea, und Michael V. Johnston. Genetic Disorders and Stroke. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780199937837.003.0110.
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A variety of monogenic and polygenic genetic disorders have been linked to stroke, making it important for the clinician to keep up with the new discoveries and the potential to provide new gene-based therapies. Hematologic disorders such as sickle cell disease and thrombophilia due to mutations in prothrombin, factor V Leiden, and homocysteine metabolism are fairly well known, but mutations in mitochondrial metabolism and matrix metalloproteinases are less recognized. In addition, results of genome-wide association studies (GWAS) in stroke populations are revealing mutations that could predispose to stroke in specific ethnic populations. These studies are also revealing some crossover in mutations between stroke and familial hemiplegic migraine as well as mutations in growth factors such as brain derived neurotrophic factor (BDNF) that appear to influence the recovery from stroke by altering cortical plasticity.
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Stotz, Karola, und Paul Griffiths. A Developmental Systems Account of Human Nature. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198823650.003.0004.
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We argue here that to understand human nature is to understand the plastic process of human development and the diversity it produces. Drawing on the framework of developmental systems theory and the idea of developmental niche construction, we argue that human nature is not embodied in only one input to development, such as the genome, and that it should not be confined to universal or typical human characteristics. Both similarities and certain classes of differences are explained by a human developmental system that reaches well out into the ‘environment’. We point to a significant overlap between our account and the ‘life history trait cluster’ account of Grant Ramsey, and defend the developmental systems account against the accusation that trying to encompass developmental plasticity and human diversity leads to an unmanageably complex account of human nature.
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Markus, Hugh, Anthony Pereira und Geoffrey Cloud. Recovery and rehabilitation. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780198737889.003.0014.
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Life is never the same after stroke and the processes that can help go into picking up the pieces and returning to a pre-stroke life and lifestyle are outlined in this recovery and rehabilitation chapter. The principles of neuronal plasticity and stroke recovery are discussed as well as the rehabilitation process. Multidisciplinary team care is the cornerstone of treatment and the individual roles of team members are outlined. The common complications that can follow stroke are individually reviewed including immobility, spasticity, communication (aphasia and dysarthria) and swallowing difficulties (dysphagia), low mood (depression) and psychological sequelae, incontinence, pain syndromes, neglect, inattention, and visual loss (hemianopia). Post-stroke epilepsy is also reviewed in this chapter. The transitioning into life in a community setting including discharge planning and vocational rehabilitation is also included.
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Mazzolai, Barbara. Growth and tropism. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199674923.003.0009.
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Plants or plant parts, such as roots or leaves, have the capacity of moving by growing in response to external stimuli with high plasticity and morphological adaptation to the environment. This chapter analyses some plant features and how they have been translated in artificial devices and control. A new generation of ICT hardware and software technologies inspired from plants is described, which includes an artificial root-like prototype that moves in soil imitating the sloughing mechanism of cells at the root apex level; as well as innovative osmotic-based actuators that generate movement imitating turgor variation in the plant cells. As future directions, new technologies expected from the study of plants concern energy-efficient actuation systems, chemical and physical microsensors, sensor fusion techniques, kinematics models, and distributed, adaptive control in networked structures with local information and communication capabilities.
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Baz, Avner. The Alternative Conception of Language. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198801887.003.0006.
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Drawing on ideas of Wittgenstein’s and of Merleau-Ponty’s, this chapter presents a conception of language on which the method of cases—even after contextualist amendments—is fundamentally misguided and liable to lead us astray. The alternative conception combines context-sensitivity with pragmatist non-representationalism, or what Huw Price has called “functional pluralism,” while at the same time emphasizing the synchronic and diachronic plasticity of language. Following Wittgenstein and Merleau-Ponty, as well as Austin, it argues that the basic unit of linguistic sense is the speech act, an act wherein a speaker—drawing more or less creatively on the history of her language—positions herself significantly by means of words, in relation to others and in a world shared with others. This sort of positioning is precisely what we do not do—or even so much as simulate—when we give our answers to the theorist’s questions.
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Klimecki, Olga M., und Tania Singer. The Compassionate Brain. Herausgegeben von Emma M. Seppälä, Emiliana Simon-Thomas, Stephanie L. Brown, Monica C. Worline, C. Daryl Cameron und James R. Doty. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780190464684.013.9.
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This chapter focuses on the neuroscience of compassion and related social emotions such as empathy, empathic concern, or empathic distress. First, we review neuroscientific literature on empathy and relate empathy to similar social emotions. We then turn to neuroscientific research on caregiving and social connection before describing cross-sectional studies on the neural signatures of compassion. To investigate whether training of compassion can change neural functions, the neural “fingerprints” of compassion expertise were studied in both expert and inexperienced meditators. The latter included the comparison between functional plasticity induced by empathy for suffering as opposed to compassion training. These studies show that compassion training changes neural functions, and that the neural substrates related to empathy for suffering differ experientially as well as neuronally. This is in line with the observation of distinct behavioral patterns related to feelings of empathic distress and compassion, described towards the end of the chapter.
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Buetefisch, Cathrin M., und Leonardo G. Cohen. Use-dependent changes in TMS measures. Herausgegeben von Charles M. Epstein, Eric M. Wassermann und Ulf Ziemann. Oxford University Press, 2012. http://dx.doi.org/10.1093/oxfordhb/9780198568926.013.0018.
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Adult brains maintain the ability to reorganize throughout life. Cortical reorganization or plasticity includes modification of synaptic efficacy as well as neuronal networks that carry behavioural implications. Transcranial magnetic stimulation (TMS) allows for the study of primary motor cortex reorganization in humans. Motor-evoked potential (MEP) amplitudes change in response to practice. This article gives information about the effect of practice on TMS measures such as motor-evoked potential amplitudes, motor maps, paired-pulse measures, and behavioural measures. These changes may be accompanied by down-regulation of activity in nearby body part representations within the same hemisphere and in homonymous regions of the opposite hemisphere, mediated by interhemispheric interactions. There is evidence pointing towards the influence of practice on a distributed network of cortical representations within regions of cerebral hemispheres. This has lead to the formulation of intervention strategies to enhance the training effects by cortical or somatosensory stimulation in health and disease.
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Zanto, Theodore P., und Adam Gazzaley. Attention and Ageing. Herausgegeben von Anna C. (Kia) Nobre und Sabine Kastner. Oxford University Press, 2014. http://dx.doi.org/10.1093/oxfordhb/9780199675111.013.020.
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This chapter addresses how normal ageing may affect selective attention, sustained attention, divided attention, task-switching, and attentional capture. It is not clear that all aspects of attention are affected by ageing, especially once changes in bottom-up sensory deficits or generalized slowing are taken into account. It also remains to be seen whether deficits in these abilities are evident when task demands are increased. Age-based declines have been reported during many tasks with low cognitive demands on various forms of attention. Fortunately, the older brain retains plasticity and cognitive training and exercise may help reduce negative effects of age on attention. Although no single theory of cognitive ageing may account for the various age-related changes in attention, many aspects have been taken into account, such as generalized slowing, reduced inhibitory processes, the retention of performance abilities via neural compensation, as well as declines in performance with increased task difficulty.
Buchteile zum Thema "Weld plasticity"
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Saimoto, Akihide. „Analysis of Weld Induced Plasticity by BFM“. In Mechanics and Model-Based Control of Smart Materials and Structures, 153–62. Vienna: Springer Vienna, 2010. http://dx.doi.org/10.1007/978-3-211-99484-9_17.
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Amirthalingam, Murugaiyan, M. J. M. Hermans, R. M. Huizenga, S. E. Offerman, J. Sietsma und I. M. Richardson. „In Situ Phase Transformation Studies on a Transformation Induced Plasticity Steel Under Simulated Weld Thermal Cycles Using Synchrotron Diffraction“. In In-situ Studies with Photons, Neutrons and Electrons Scattering, 133–48. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-14794-4_9.
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Azuma, K., Y. Kurobane und Y. Makino. „Evaluation of beam-to-column connections with weld defects based on CTOD design curve approach“. In Structural Failure and Plasticity, 495–500. Elsevier, 2000. http://dx.doi.org/10.1016/b978-008043875-7/50209-4.
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Nguyen, N. T. „Analytical Solution for Semi-Infinite Body Subjected to 3D Moving Heat Source and Its Application in Weld Pool Simulation“. In Structural Failure and Plasticity, 819–26. Elsevier, 2000. http://dx.doi.org/10.1016/b978-008043875-7/50260-4.
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Pircher, M., und R. Q. Bridge. „The Influence of Residual Stresses in the Vicinity of Circumferential Weld-Induced Imperfections on the Buckling of Silos and Tanks“. In Structural Failure and Plasticity, 419–24. Elsevier, 2000. http://dx.doi.org/10.1016/b978-008043875-7/50198-2.
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Koch, Christof. „Synaptic Plasticity“. In Biophysics of Computation. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195104912.003.0019.
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Animals live in an ever-changing environment to which they must continuously adapt. Adaptation in the nervous system occurs at every level, from ion channels and synapses to single neurons and whole networks. It operates in many different forms and on many time scales. Retinal adaptation, for example, permits us to adjust within minutes to changes of over eight orders of magnitude of brightness, from the dark of a moonless night to high noon. High-level memory—the storage and recognition of a person's face, for example—can also be seen as a specialized form of adaptation (see Squire, 1987). The ubiquity of adaptation in the nervous system is a radical but often underappreciated difference between brains and computers. With few exceptions, all modern computers are patterned according to the architecture laid out by von Neumann (1956). Here the adaptive elements—the random access memory (RAM)—are both physically and conceptually distinct from the processing elements, the central processing unit (CPU). Even proposals to incorporate massive amounts of so-called intelligent RAM (IRAM) directly onto any future processor chip fall well short of the degree of intermixing present in nervous systems (Kozyrakis et al., 1997). It is only within the last few years that a few pioneers have begun to demonstrate the advantages of incorporating adaptive elements at all stages of the computation into electronic circuits (Mead, 1990; Koch and Mathur, 1996; Diorio et al.,1996). For over a century (Tanzi, 1893; Ramón y Cajal, 1909, 1991), the leading hypothesis among both theoreticians and experimentalists has been that synoptic plasticity underlies most long-term behavioral plasticity. It has nevertheless been extremely difficult to establish a direct link between behavioral plasticity and its biophysical substrate, in part because most biophysical research is conducted with in vitro preparations in which a slice of the brain is removed from the organism, while behavior is best studied in the intact animal. In mammalian systems the problem is particularly acute, but combined pharmacological, behavioral, and genetic approaches are yielding promising if as yet incomplete results (Saucier and Cain, 1995; Cain, 1997; Davis, Butcher, and Morris, 1992; Tonegawa, 1995; McHugh et al., 1996; Rogan, Stäubli, LeDoux, 1997).
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Reinsch, Jennifer, Anna Zdunczyk, Tarik Alp Sargut, Maren Denker, Melina Engelhardt, Peter Vajkoczy, Thomas Picht und Nora Dengler. „Factors of Cortical Plasticity in Brachial Plexus Injury“. In Brachial Plexus Injury [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.98822.
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Cortical plasticity is the brain’s capability of decoding new information through growth and reorganization over our whole life spam. It is the basis for good outcomes after reinnervation and for rehabilitation of adult and obstetric brachial plexus injury. Knowledge about cortical reorganization is crucial to reconstructive surgeons and physiotherapists that aim to give their patients a reasonable prognosis. This chapter intends to present and summarize the current literature on how to detect and quantify cortical plasticity and how research on factors that influence cortical plasticity, mainly in relation to peripheral nerve and more precise brachial plexus injury progresses. Peculiarities of adult and obstetric brachial plexus injuries and their treatment are given. We present techniques that visualize and quantify cortical plasticity with focus on functional imaging like fMRI and nTMS as well as molecular aspects. Future research is needed to understand mechanisms of how molecular changes on a synaptic level of a neuron influence the macroscopic plasticity, to improve rehabilitative resources, to understand the exact prognostic value of nTMS in brachial plexus injury and to investigate the therapeutic capability of rTMS.
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Karambizi, David, und Nikos Tapinos. „The Dynamic m6A Epitranscriptome in Glioma Stem Cell Plasticity and Function“. In CNS Malignancies [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96792.
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Glioblastoma multiforme is one of the most aggressive tumors of the central nervous system. The current standard-of-care includes maximal resection followed by chemotherapy, radiation and more recently, tumor treating fields (TTFs). Despite this multimodal approach, glioblastoma remains refractory to therapy. Glioblastoma resistance, recurrence and malignancy are believed to be driven by a subpopulation of glioma stem cells (GSCs) within the tumor bulk which are characterized by the retention of self-renewal potential as well as the capacity to recapitulate tumor heterogeneity. Within the dynamic intratumoral niche, GSCs demonstrate a high degree of cellular plasticity, reversibly interconverting between stem-like states and more differentiated states as a result of environmental cues/signaling fluctuations. Such plastic adaptive properties are mostly driven by multiple dynamic, reversible epigenetic modifications. We posit that reversible post-transcriptional methylation of RNA transcripts at the m6A position may be one such regulatory mechanism employed by GSCs to efficiently maintain plasticity and adaptive phenotypic transitions. In this section, we discuss the concept of cellular plasticity, introduce dynamic m6a epitranscriptomic mechanisms as potential key regulators of GSC plasticity and finally propose epigenetic based therapeutics as a mean of attenuating glioblastoma plasticity to improve patient outcome.
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Lee, James J., und Jessica L. Imanaka. „Theorizing Virtuality in Enterprise Social Systems“. In Entrepreneurship, Collaboration, and Innovation in the Modern Business Era, 102–20. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-5014-3.ch005.
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This chapter has built on research on today's modern organizations to lay the foundations for a comprehensive and systematic theorization of enterprise social systems. Theorizing virtuality marks a fundamental transformation in space-time parameters in communications. This is especially so in the context of rapid current advancements in IT such as cloud computing, as well as numerous other technological fronts. Current IT trends show that increased spatio-temporal plasticity heightens the effectiveness and the efficiency of modern enterprise social systems. In particular, subject-oriented asynchronous communications experience greater inferred plasticity and event-oriented synchronous communications experience greater referred plasticity. Finally, enterprise social systems vary in their degree of virtuality based on the perspective of the relevant stakeholder group considered.
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Lee, James J., und Jessica L. Imanaka. „Theorizing Virtuality in Enterprise Social Systems“. In Research Anthology on Digital Transformation, Organizational Change, and the Impact of Remote Work, 1081–99. IGI Global, 2021. http://dx.doi.org/10.4018/978-1-7998-7297-9.ch054.
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This chapter has built on research on today's modern organizations to lay the foundations for a comprehensive and systematic theorization of enterprise social systems. Theorizing virtuality marks a fundamental transformation in space-time parameters in communications. This is especially so in the context of rapid current advancements in IT such as cloud computing, as well as numerous other technological fronts. Current IT trends show that increased spatio-temporal plasticity heightens the effectiveness and the efficiency of modern enterprise social systems. In particular, subject-oriented asynchronous communications experience greater inferred plasticity and event-oriented synchronous communications experience greater referred plasticity. Finally, enterprise social systems vary in their degree of virtuality based on the perspective of the relevant stakeholder group considered.
Konferenzberichte zum Thema "Weld plasticity"
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Muránsky, Ondrej, Cory J. Hamelin, Minh Tran, Chedly Braham und Michael C. Smith. „Assessment of Welding-Induced Plasticity in Austenitic Steel Weldments“. In ASME 2016 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/pvp2016-63358.
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Historically, weld residual stresses (WRS) have been used as the primary validation parameter for welding simulations, largely due to the importance of predicting WRS for structural integrity assessments. However, the extent of welding-induced plasticity (WIP) caused by the plastic flow of near-weld material is also an important characteristic affecting weld performance. WIP has been shown to negatively affect weld integrity, since the associated accumulation of defects (dislocations) in the material will accelerate the nucleation of macro-scale defects that lead to component failure. Information on WIP is particularly important when attempting to validate the constitutive models used for weld simulation, and can assist with the proper definition of material yield strength. The present study highlights two approaches to assess WIP in welded structures. The first approach involves the development of a micro-hardness correlation to infer the level of WIP across the near-weld region. The second approach uses electron backscatter diffraction (EBSD) data to directly calculate the average crystal misorientation in the region of interest, which is proportional to the amount of geometrically necessary dislocations present. The dissimilar approach to determine WIP between the two characterization methods allows a degree of confidence in the results obtained, therefore providing an accurate dataset for weld model validation. To exemplify this point, the two approaches are used to characterize WIP across a three-pass slot weld in AISI 316 steel (NeT TG4 specimen), and the results are compared to weld modelling predictions.
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Zhou, Daowu, und Ali Mirzaee-Sisan. „Plasticity Induced Residual Stress in Pipes“. In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-83530.
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An analytical model for predicting residual stress introduced in a pipe (away from girth weld) by plastic bending is examined. Stresses for a specific case where the pipe is bent, reverse bent and straightened are compared with results from a non-linear finite element analysis. The analytical model is then used to determine the through-thickness plasticity induced residual stress in the axial direction for a wide range of pipe geometries which are typically used offshore. It is found that the magnitude of extreme axial residual stress depends significantly on the ratio of pipe diameter to wall thickness. A simplified formula for estimating the extreme fibre tensile residual stress is derived and presented.
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Mochizuki, Masahito, und Yoshiki Mikami. „Prediction of SCC Initiation in Weld Components by Multi-Scale Analysis Incorporating Crystal Plasticity“. In ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/pvp2010-25899.
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A multi-scale analysis method of microscopic stress is proposed to predict the occurrence of stress corrosion cracking (SCC) in the welded components in power plants. The method includes a macroscopic model and microscopic models. Calculation of the stress was first performed in the macroscopic model. Subsequent to this calculation, simulation of the microscopic model was conducted to evaluate the microscopic stress on the scale of the grains and microstructure. Then, the nodal temperatures and nodal displacements were transferred from the macroscopic model to the microscopic model as boundary conditions. The proposed multi-scale analysis was used to evaluate the weld residual stress of a bead-on-plate weld model to demonstrate the validity of the method. Good agreement was obtained between the macroscopic and microscopic models in nodal temperature, nodal displacement, and in the residual stress distribution. Following the bead-on-plate model, the multi-scale analysis method was applied to the model of an SCC test specimen of type 600 Nickel-based alloy. Crystal plasticity and inhomogeneous grain shapes were introduced into the microscopic model to consider the effect of crystal orientation. The crystal orientation was measured by electron backscattering pattern (EBSP) technique and applied to the microscopic model. The stress concentration at the grain boundaries was shown by the multi-scale analysis. In the simulated SCC tests, cracks were observed in the grain boundaries. The locations where microscopic stress concentrations occurred in the multi-scale analysis were in good agreement with the locations of cracks observed in the SCC test. The proposed multi-scale analysis method of microscopic stress distribution is thus applicable to the prediction of the locations of stress corrosion cracks.
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Dai, H., R. Moat, A. F. Mark und P. J. Withers. „Investigation of Transformation Induced Plasticity and Residual Stress Analysis in Stainless Steel Welds“. In ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/pvp2010-25325.
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The aim of this paper is to investigate the implications for weld residual stresses of martensitic transformation induced plasticity (TRIP) in stainless steel filler metal. The TRIP strains occurring during cooling under different uniaxial load levels have been obtained using digital image correlation (DIC) for a residual stress relieving low transformation temperature weld filler known to show little variant selection on cooling as a function of stress. In order to investigate the efficacy of current FE transformation plasticity models of different levels of sophistication in simulating TRIP strains, a finite element model, incorporating the so-called Greenwood-Johnson effect was used to simulate these constrained dilatometry measurements. To assess the implications of the different approaches to modelling TRIP for weld residual stresses, the TRIP coefficients determined from the above experiments were incorporated into an FE model simulating the residual stresses that are generated when a single weld bead is deposited on to a stainless steel base plate. It was found that including TRIP had a significant influence on the weld stresses, while the differences between the models were much smaller.
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Leen, S. B., M. Li, R. A. Barrett, S. Scully, D. Joyce und P. E. O’Donoghue. „High Temperature, Multi-Material, Cyclic Plasticity of a P91 Welded Branch-Header Connection Under Cyclic Pressure“. In ASME 2015 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/pvp2015-45605.
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This paper presents a study on high temperature cyclic plasticity of a welded P91 T-joint under cyclic internal pressure, in the context of high temperature low cycle fatigue (HTLCF) performance of such connections. In the present work, attention is focused on the development of a multi-material model for high temperature cyclic plasticity, including the effects of the different weld-related material zones, namely, parent metal, weld metal and heat-affected zone. The cyclic plasticity behaviour of the three zones is identified from previously-published high temperature, low cycle fatigue test results on uniaxial test specimens, including parent metal, weld metal and cross-weld specimens, obtained from a specially fabricated pipe girth weld, using ex-service P91 material. The cyclic plasticity material model includes the effects of kinematic hardening and cyclic softening. A three-dimensional finite element model of the welded T-joint is developed, incorporating the three sets of identified cyclic plasticity constants. The study is limited to isothermal conditions of 500°C, with a view to understanding the complex effects of multiple material zones with inhomogeneous cyclic plasticity behaviour. The heat affected zone is shown to play a key role in the development of plastic strains and localised stresses. The particular T-joint geometry is the subject of an investigation due to premature failure in a combined cycle gas turbine plant.
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Puliyaneth, Manu, Haofeng Chen und Weiling Luan. „Creep Fatigue Damage Assessment of V-Butt Weld Pipe With an Extended Direct Steady Cycle Analysis“. In ASME 2018 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/pvp2018-84568.
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One of the methods to increase the efficiency of power plants is by increasing their operating temperature, this can lead to various damage mechanisms due to creep-cyclic plasticity interactions such as creep ratcheting, cyclically enhanced creep and creep enhanced plasticity. In the presence of welds, their assessments are complicated due to the presence of different material zones, namely parent metal, weld metal and heat affected zone which exhibit different properties. This paper aims at investigating the creep-fatigue damage of a V-butt welded pipe under a constant mechanical load and a cyclic temperature load, considering full interaction between creep and cyclic plasticity using the extended Direct Steady Cycle Analysis (eDSCA) within the Linear Matching Method Framework (LMMF). The impact of applied load level and creep dwell on the failure mechanism and location is investigated. Influence of hoop to axial stress ratio and groove angle is studied comprehensively by choosing ranges covering majority of common pipe configurations. Further validation of results is carried out by using detailed step-by-step inelastic analyses in ABAQUS, thereby demonstrating the accuracy and efficiency of LMM eDSCA in predicating the remaining life of multi-material components such as a welded pipe, combining with appropriate creep and fatigue damage models.
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Sarzosa, Diego F. B., und Claudio Ruggieri. „Experimental and Numerical Investigation of Plasticity-Induced Fatigue Crack Closure in Overmatched Welds“. In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-66076.
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This work provides a numerical and experimental investigation of fatigue crack growth behavior in steel weldments including crack closure effects and their coupled interaction with weld strength mismatch. A central objective of this study is to extend previously developed frameworks for evaluation of crack closure effects on fatigue crack growth rates (FCGR) to steel weldments while, at the same time, gaining additional understanding of commonly adopted criteria for crack closure loads. Very detailed non-linear finite element analyses using 3-D models of compact tension C(T) fracture specimens with square groove, weld centerline cracked welds provide the evolution of crack growth with cyclic stress intensity factor which is required for the estimation of the closure loads. Fatigue crack growth tests conducted on plane-sided, shallow-cracked C(T) specimens provide the necessary data against which crack closure effects on fatigue crack growth behavior can be assessed. Overall, the present investigation provides additional support for estimation procedures of plasticity-induced crack closure loads in fatigue analyses of structural steels and their weldments.
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Sriskandarajah, T., Graeme Roberts und Daowu Zhou. „Effect of Reeling Installation on Weld Residual Stress in Pipeline Girth Welds“. In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-11502.
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A characteristic of pipeline installation by the reeling technique is the generation of high plastic strain around the majority of the pipeline’s circumference as it is spooled onto a drum, under displacement controlled conditions. It is well-known that the application of sufficiently high amounts of mechanical or thermal energy will “anneal” (relax) weld residual stresses and, therefore, under the gross plasticity experienced during reeling it should be expected that initial girth weld residual stresses will be entirely relaxed during the first reel cycle. The residual stress state needs to be taken into account in Engineering Critical Assessment (ECA) procedures of girth welds when predicting allowable defect dimensions. ECA codes such as DNV-OS-F101 and BS7910 assume the welding residual stress to be equal to the yield strength of the parent material and relaxation of welding residual stress under overload is allowed. However, the treatment specified in DNV is established from load-controlled scenarios and may result in un-realistic allowable defect dimensions in displacement-controlled situations such as reeling. Welding residual stress in reeling ECA is concerning to the subsea pipeline industry. By performing reeling simulations with 3D finite element analyses (FEA), this paper examines the welding residual stress before and after reeling and assesses the extent of residual stress relaxation. It was found that reeling axial strain causes significant relaxation of the weld residual stress at the pipe intrados and extrados. At the saddle points there is a slight disruption to the residual stress field. The full weld residual stress is relaxed from a value equal to the material yield stress, and is replaced by a plastic deformation induced stress of much lower magnitude, typically in the order of 100 MPa or less. The plastic deformation stress is of equal magnitude whether or not the pipe section contains initial weld residual stress and, therefore, it is concluded that weld residual stress can be ignored following the first reel cycle.
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Kim, Sang-Hyun, Jae-Jun Han und Yun-Jae Kim. „Mismatch Limit Loads of Circumferential Cracked Pipes With V-Groove Welds“. In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-98127.
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The present work reports mis-match limit loads for V-groove welded pipe for a circumferential crack using finite element (FE) analyses. In our previous paper [14], closed-form solutions of mis-match limit loads were proposed for idealized butt weld configuration as a function of the strength mis-match ratio with only one geometry-related slenderness parameter. To integrate the effect of groove angles on mis-match limit loads, the geometry-related slenderness parameter has to be modified by relevant geometric parameters including groove angle, crack depth and root opening based on plastic deformation patterns in theory of plasticity. Circumferential through-wall cracks are located at the centre of the weld considering two different groove angles (45°, 90°). With regards to loading conditions, axial (longitudinal) tension is applied for all cases. For the parent and weld metal, elastic-perfectly plastic materials are used to simulate under-matching and over-matching conditions in plasticity. The overall results from the proposed solutions agree well with FE results.
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Scheel, Jeremy E., Douglas J. Hornbach und Paul S. Prevey. „Mitigation of Stress Corrosion Cracking in Nuclear Weldments Using Low Plasticity Burnishing“. In 16th International Conference on Nuclear Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/icone16-48597.
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Stress corrosion cracking (SCC) has been observed for decades in austenitic alloy weldments such as type 304 stainless steel as well as in Ni based alloy weldments including Alloy 600 and 690. SCC continues to be a primary maintenance concern for many components in both pressurized water reactors (PWR) and boiling water reactors (BWR). SCC is understood to be the result of a combination of susceptible material, exposure to a corrosive environment, and tensile stress above a threshold. Tensile residual stresses developed by prior machining and welding can accelerate SCC. A surface treatment is needed that can reliably produce deep compressive residual stresses in austenitic and Ni based alloy weldments in order to prevent SCC. Post-weld surface enhancement processing via low plasticity burnishing (LPB) can be used to introduce deep compression into tensile fusion welds thereby mitigating SCC. LPB has been developed as a rapid and inexpensive surface enhancement method adaptable to existing CNC machine tools or robots. Deep compressive residual stresses produced by LPB are designed to reduce the surface, and near surface stress state to well below the SCC threshold. Residual stress results are shown for 304 stainless steel, Alloy 22 and Alloy 718. SCC test results comparing LPB treated and un-treated 304 stainless steel weldments are presented. Results show that the deep compression produced by LPB eliminates SCC in austenitic weldments.