Experimental and Numerical Investigations on the Failure Behavior of Pressurized Components Containing Crack Fields

2018 ◽  
Author(s):  
Patrick Gauder ◽  
Xaver Schuler ◽  
Michael Seidenfuss
Keyword(s):  
Numerical Simulations ◽  
Damage Mechanics ◽  
Base Material ◽  
Pressure Vessels ◽  
Shear Loading ◽  
Current Status ◽  
Failure Behavior ◽  
Research Project ◽  
Ongoing Research ◽  
Numerical Investigations

During the 2012 outage of the Belgian nuclear power plants (NPP) Doel 3 and Tihange 2 non-destructive testing (NDT) measurements revealed a high quantity of indications in the upper and lower core shells of the reactor pressure vessels (RPV). A root cause analysis leads to the most likely hypothesis that the indications are hydrogen flakes in segregated zones of the RPV ferritic base material. The laminar and quasi-laminar orientation (0° – 15° inclination to the pressure retaining surface) of the hydrogen flakes, the interaction of several adjacent flakes and the mechanical loading conditions lead to a mixed-mode behavior at the crack tips. In the framework of an ongoing research project, experimental and numerical investigations are conducted with the aim to describe the failure behavior of such complex crack configurations. The experiments are carried out using two ferritic materials. One is a non-irradiated representative RPV steel (SA 508 Class 2) and the second material is a special lower bound melt of a modified 22NiMoCr3-7 steel (FKS test melt KS 07 C) containing hydrogen flakes. A material characterization is done for both materials including tensile specimens, notched round bars, shear-, torsion- and compact-tension-shear (CTS) - specimens to investigate different stress states. Furthermore, flat tensile specimens with eroded artificial crack fields are used to investigate the interaction between the cracks in different arranged crack fields. Numerical simulations are carried out with extended micromechanical based damage mechanics models. For the description of ductile failure an enhanced Rousselier model is used and an enhanced Beremin model to calculate the probability of cleavage fracture. To account the sensitivity for low stress triaxiality damage by shear loading, the Rousselier model was enhanced with a term to account for damage evolution by shear. The Beremin model will be enhanced with a term to account for different levels of triaxiality. For the numerical simulations in the transition region of ductile-to-brittle failure a coupled damage mechanics model (enhanced Rousselier and Beremin) will be used. In this paper, the current status of the ongoing research project and first results are presented.

Evaluation of the Crack Interaction and Failure Behavior of Components With Crack Fields Using a Damage Mechanical Approach

2019 ◽  
Author(s):  
Christian Swacek ◽  
Patrick Gauder ◽  
Michael Seidenfuss
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Base Material ◽  
Pressure Vessels ◽  
Failure Behavior ◽  
Multiple Cracks ◽  
Critical Crack ◽  
Ongoing Research ◽  
Integrity Assessment ◽  
Crack Tips

Abstract In 2012 non-destructive testing measurements (NDT) of the reactor pressure vessels (RPV) in the Belgian Nuclear Power Plants Doel 3 and Tihange 2 revealed a high quantity of indications in the upper and lower core shells. The most likely explanation is that the measured indications are hydrogen flakes positioned in segregated zones in the base material of the pressure vessels. These hydrogen flakes have a laminar and quasi-laminar orientation with an inclination up to 15° to the pressure retaining surface. Under internal pressure, the crack tips undergo predominantly mixed mode loading conditions, where the induced stress and strain fields of the single crack tips influence each other. The safety assessment of crack afflicted pressurized components is performed by fracture mechanical approaches. For the evaluation of multiple cracks in crack fields, state of the art codes and standards apply interaction criteria and grouping methods, to determine a representative crack, which has to be evaluated. In this paper, the interaction of cracks in crack fields is numerically and experimentally evaluated. Damage mechanical models based on the Rousselier- and the Beremin model are used to investigate numerically the interaction of cracks in crack fields. Experimental data from ferritic flat tensile specimens afflicted with cracks are used to verify the numerical results. The damage mechanical calculations reveal critical crack arrangements due to coalescence behavior and cleavage fracture probability. These results and ongoing research intends the derivation of interaction criteria for cracks in crack fields. The interaction criteria will be used for the definition of a representative flaw for a conservative integrity assessment of crack afflicted components.

Numerical Investigations on the Interaction of Cracks in Quasi-Laminar Crack Fields

2018 ◽  
Author(s):  
Christian Swacek ◽  
Xaver Schuler ◽  
Michael Seidenfuss
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Base Material ◽  
Pressure Vessels ◽  
Loading Conditions ◽  
Critical Crack ◽  
Ongoing Research ◽  
Specific Loading ◽  
Mechanical Methods ◽  
Crack Tips

Non-destructive testing measurements in the Belgian nuclear power plants Doel 3 and Tihange 2 revealed a high quantity of indications in the upper and lower core shells of the reactor pressure vessels. The most likely explanation is that the indications are hydrogen flakes positioned in segregated zones of the base material of the pressure vessel. These hydrogen flakes have a laminar and quasi-laminar orientation to the pressure retaining surface. Under mechanical loading the crack tips undergo predominantly mixed mode loading conditions, where the induced stress and strain fields of the single crack tips influence each other. Due to these specific loading conditions, the assumptions for classical standardized fracture mechanical methods are not met. Currently, there is no verified concept for the evaluation of such kind of crack fields. Therefore the mechanical behavior of components with laminar crack fields and the interaction of cracks in such crack fields are investigated in an ongoing research project. Relevant parameters to describe crack fields in terms of crack size, crack location and crack orientation are derived from literature and own nondestructive measurements. Damage mechanical approaches are used in finite element calculations to investigate the interaction of cracks. Advanced damage mechanical models will be used to investigate crack initiation, crack growth and coalescence of cracks in crack fields. According to the results, representative parameters for crack fields will be derived and critical crack formations determined. The results will be evaluated and compared with state of the art approaches and standards.

Information Needs of Microenterprise Owners in Louisiana

2013 ◽  
Author(s):  
Tao Jin
Keyword(s):  
Information Needs ◽  
Wide Spectrum ◽  
Research Project ◽  
Ongoing Research ◽  
Industrial Sectors

This presentation will report on an ongoing research project about the information needs of microenterprise owners in Louisiana. Microenterprises are those businesses with fewer than five employees or sole proprietorships with no employees. They exist across all industrial sectors and incorporate a wide spectrum of information needs.Cette communication présente un projet de recherche en cours s'intéressant aux besoins informationnels des propriétaires de microentreprises de la Louisiane. Les microentreprises comptent moins de cinq employés, y compris celles à propriétaire unique sans employé, et sont présentes dans tous les secteurs d'activités. Les besoins informationnels varient donc grandement.

Chinese Television in Africa

2021 ◽  
pp. 026327642110120
Author(s):  
Alessandro Jedlowski
Keyword(s):  
Soft Power ◽  
The Political ◽  
Power Dynamics ◽  
Economic Factors ◽  
Research Project ◽  
Chinese Media ◽  
Ongoing Research ◽  
The Media ◽  
Chinese Television ◽  
Media Company

On the basis of the results of an ongoing research project on the activities of the Chinese media company StarTimes in Nigeria and Côte d’Ivoire, this paper analyses the fluid and fragmentary dimension of the engagements between Chinese media and African publics, while equally emphasizing the power dynamics that underlie them. Focusing on a variety of ethnographic sources, it argues for an approach to the study of Chinese media expansion in Africa able to take into account, simultaneously, the macro-political and macro-economic factors which condition the nature of China–Africa media interactions, the political intentions behind them (as, for example, the Chinese soft power policies and their translation into specific media contents), and the micro dimension of the practices and uses of the media made by the actors (producers and consumers of media) in the field.

Current Status, Design and Performance Trends for the Regenerative Flow Compressors and Pumps

2002 ◽  
Author(s):  
Mukarrum Raheel ◽  
Abraham Engeda
Keyword(s):  
Performance Improvement ◽  
Current Status ◽  
Ongoing Research ◽  
Performance Trends ◽  
The Family ◽  
Working Principle ◽  
Low Specific Speed ◽  
And Performance ◽  
Number Of Publications ◽  
Regenerative Flow

Regenerative flow compressors and pumps, hereafter called RFC/RFP have found many applications in industry; still they are the most neglected turbomachines in the family of dynamic compressors. The number of publications existing in literature is very small compared to the large number of papers about the centrifugal and axial turbocompressors. This paper gives a detail discussion of fundamentals and working principle of regenerative turbomachines. Regenerative compressors are compared with centrifugal compressors and the importance of regenerative turbomachines in low specific speed range is emphasized. The major findings of available literature on regenerative turbomachine are summarized. The current status, limitations and some of the challenges faced by RFC/RFP are assessed in context of performance improvement. The paper concludes with an overview of ongoing research and future directions to be followed for performance improvement of this neglected class of turbomachines.

scholarly journals Evaluation of Stiffness and Dynamic Properties of a Mine Shaft Steelwork Structure through In Situ Tests and Numerical Simulations

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 664
Author(s):  
Jacek Jakubowski ◽  
Przemysław Fiołek
Keyword(s):  
Numerical Simulations ◽  
Dynamic Properties ◽  
Vertical Motion ◽  
Load Test ◽  
Mode Shapes ◽  
Dynamic Amplification Factor ◽  
In Situ Tests ◽  
Mine Shaft ◽  
Numerical Investigations

A mine shaft steelwork is a three-dimensional frame that directs the vertical motion of conveyances in mine shafts. Here, we conduct field and numerical investigations on the stiffness and dynamic properties of these structures. Based on the design documentation of the shaft, materials data, and site inspection, the steelwork’s finite element model, featuring material and geometric non-linearities, was developed in Abaqus. Static load tests of steelwork were carried out in an underground mine shaft. Numerical simulations reflecting the load test conditions showed strong agreement with the in situ measurements. The validated numerical model was used to assess the dynamic characteristics of the structure. Dynamic linear and non-linear analyses delivered the natural frequencies, mode shapes, and structural response to dynamic loads. The current practices and regulations regarding shaft steelwork design and maintenance do not account for the stiffness of guide-to-bunton connections and disregard dynamic factors. Our experimental and numerical investigations show that these connections provide considerable stiffness, which leads to the redistribution and reduction in bending moments and increased stiffness of the construction. The results also show a high dynamic amplification factor. The omission of these features implicates an incorrect assessment of the design loads and can lead to over- or under-sized structures and ultimately to shortened design working life or failure.

scholarly journals Welcome Intrusions: Capturing the Unexpected in Translators’ Prefaces to Dante’s Divine Comedy

2018 ◽  
Vol 6 (1) ◽  
pp. 1-10
Author(s):  
Marella Feltrin-Morris
Keyword(s):  
Divine Comedy ◽  
Source Text ◽  
Research Project ◽  
Ongoing Research ◽  
Authentic Voice

As part of an ongoing research project, this essay examines a number of translators’ prefaces to Dante’s Divine Comedy, summarizing recurring patterns and then focusing on deviations from the norm. The majority of these prefaces tend to follow a script, particularly in the case of retranslations of classical texts, which require an acknowledgment of past translations, a homage to the authority of the source text and a display of the translator’s expertise. However, occasional detours from the predictable constellation of themes deserve closer scrutiny, since they give a more authentic voice to the individuals who engaged with the text in its deepest form, not merely within the confines of a prescriptive formula, but expanding the potential of this unique space towards new avenues of discovery.

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