Effect of Corrosion Pit on the Structural Characteristics of Foil Journal Bearings

2021 ◽  
Author(s):  
Vishal Mourya ◽  
Skylab P. Bhore
Keyword(s):  
Crack Initiation ◽  
Structural Integrity ◽  
Structural Characteristics ◽  
High Stress ◽  
Fem Analysis ◽  
Pressure Loading ◽  
Material Loss ◽  
Foil Bearings ◽  
Corrosion Pit ◽  
And Performance

Abstract Due to corrosive environment, material loss in a localized area leads to formation of a corrosion pit. It diminishes the structural integrity and performance of product. To predict and analyze the effect of corrosion pit on the performance of gas foil bearings (GFBs), FEM analysis of bump-type GFBs is carried out. The effect of corrosion pit is investigated for three different shapes: circular, square and triangular. In this study, the FEM analysis of bump-type GFBs is performed in ANSYS software. Firstly, the influence of a corrosion pit is analyzed for various shapes under different pressure loading. These results show that the presence of a corrosion pit developed high-stress crack intensity, which can result in crack initiation in foil bearings. As pressure loading increased, the stress crack intensity in foil bearings increased. Among different pit shapes, the circular pit shape induces the maximum stress crack intensity in foil bearings, which shows that the crack initiation in foil bearings is observed for a circular pit. Then, the influence of a corrosion pit on the structural stiffness of foil bearings is evaluated for various foil materials under different friction coefficients. These results show that the influence of friction coefficient in foil bearings is increased within the presence of a corrosion pit.

GPS in Pioneering Dynamic Monitoring of Long-Period Structures

2002 ◽  
Vol 18 (1) ◽  
pp. 47-61 ◽  
Author(s):  
Mehmet Çelebi ◽  
Ahmet Sanli
Keyword(s):  
Structural Integrity ◽  
Structural Characteristics ◽  
Tall Building ◽  
Dynamic Monitoring ◽  
Long Period ◽  
Global Positioning ◽  
Continuous Dynamic Monitoring ◽  
Strong Winds ◽  
And Performance ◽  
Continuous Dynamic

Global Positioning System (GPS) technology with 10–20-Hz sampling rates allows scientifically justified dynamic measurements of relative displacements of long-period structures. The displacement response of a simulated tall building in real time and permanent deployment of GPS units at the roof of a building are described. To the authors’ best knowledge, this is the first permanent deployment of GPS units (in the world) for continuous dynamic monitoring of a tall building. Data recorded from the building during a windy day is analyzed to determine the structural characteristics. When recorded during extreme motions caused by earthquakes and strong winds, such measurements can be used to compute average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the structural integrity and performance by establishing pre-established thresholds. Such information can be used to secure public safety and/or take steps to improve the performance of the building.

Rate Dependent Constitutive Equations of Cyclic Softening

1985 ◽  
Vol 40 (7) ◽  
pp. 653-665
Author(s):  
J. S. Mshana ◽  
A. S. Krausz
Keyword(s):  
Stress Relaxation ◽  
Low Temperature ◽  
Constitutive Equations ◽  
Strain Softening ◽  
Structural Characteristics ◽  
High Stress ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Stress Softening

Constitutive equations of cyclic strain and stress softening for materials with low internal stress levels are derived from the rate theory. The study shows that over the high stress and low temperature range where the description of plastic flow in cyclic softening can be approximated with activation over a single energy barrier, cyclic strain softening is well related to stress relaxation process while cyclic stress softening is related to creep process. The material structural characteristics for cyclic strain softening, cyclic stress softening and stress relaxation are identical. Subsequently, it is shown that cyclic stress and strain softening within the high stress and low temperature range can be evaluated from the constitutive equations using the material structural characteristics measured from a simple stress relaxation test.

scholarly journals Design and Performance of Novel Self-Cleaning g-C3N4/PMMA/PUR Membranes

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 850 ◽  
Author(s):  
Ladislav Svoboda ◽  
Nadia Licciardello ◽  
Richard Dvorský ◽  
Jiří Bednář ◽  
Jiří Henych ◽  
...  
Keyword(s):  
Methylene Blue ◽  
Thin Layers ◽  
Photocatalytic Reaction ◽  
Potential Toxicity ◽  
Material Loss ◽  
Contaminant Control ◽  
Biological Contaminant ◽  
Self Cleaning ◽  
And Performance ◽  
Photocatalytic Applications

In the majority of photocatalytic applications, the photocatalyst is dispersed as a suspension of nanoparticles. The suspension provides a higher surface for the photocatalytic reaction in respect to immobilized photocatalysts. However, this implies that recovery of the particles by filtration or centrifugation is needed to collect and regenerate the photocatalyst. This complicates the regeneration process and, at the same time, leads to material loss and potential toxicity. In this work, a new nanofibrous membrane, g-C3N4/PMMA/PUR, was prepared by the fixation of exfoliated g-C3N4 to polyurethane nanofibers using thin layers of poly(methyl methacrylate) (PMMA). The optimal amount of PMMA was determined by measuring the adsorption and photocatalytic properties of g-C3N4/PMMA/PUR membranes (with a different PMMA content) in an aqueous solution of methylene blue. It was found that the prepared membranes were able to effectively adsorb and decompose methylene blue. On top of that, the membranes evinced a self-cleaning behavior, showing no coloration on their surfaces after contact with methylene blue, unlike in the case of unmodified fabric. After further treatment with H2O2, no decrease in photocatalytic activity was observed, indicating that the prepared membrane can also be easily regenerated. This study promises possibilities for the production of photocatalytic membranes and fabrics for both chemical and biological contaminant control.

Current Design Rules for Welding of Wind Energy Structures for Arctic Conditions

2019 ◽  
Vol 822 ◽  
pp. 452-458
Author(s):  
Sergey Lopaev ◽  
Pavel Layus ◽  
Paul Kah ◽  
Sergey Parshin
Keyword(s):  
Wind Energy ◽  
Structural Integrity ◽  
Structural Characteristics ◽  
Welding Process ◽  
Climatic Conditions ◽  
Welding Parameters ◽  
Reliable Operation ◽  
Arctic Conditions ◽  
Current Design ◽  
Standards And Guidelines

An article presents a review of current standards and guidelines in the field welding fabrication requirements for wind energy structures in arctic conditions. Extreme climatic conditions, such as Arctic, have a strong influence on the requirements for wind turbines structural characteristics, materials and fabrication methods. Special attention has to be paid for selecting steels with suitable mechanical properties, processing methods and delivery conditions. Additionally, it is highly important to select proper welding process and welding parameters, so that the structural integrity and reliable operation can be achieved.

A Statistical-Based Fatigue Crack Initiation Model for Axial Flaws in Zr-Nb Pressure Tubes

2014 ◽  
Author(s):  
Cheng Liu ◽  
Douglas Scarth ◽  
Alain Douchant
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Rise Time ◽  
Structural Integrity ◽  
Fatigue Crack Initiation ◽  
Mechanical Damage ◽  
Fuel Bundle ◽  
Test Parameters ◽  
Pressure Tubes ◽  
Criteria For Evaluation

Flaws found during in-service inspection of CANDU Zr-2.5Nb pressure tubes include fuel bundle scratches, debris fretting flaws, fuel bundle bearing pad fretting flaws, mechanical damage flaws and crevice corrosion marks. The CSA Standard N285.8 contains procedures and acceptance criteria for evaluation of the structural integrity of CANDU Zr-2.5Nb pressure tubes containing flaws. One of the requirements is to evaluate the flaws for fatigue crack initiation. There was a need to develop a statistical-based model of fatigue crack initiation at flaws for use in deterministic and probabilistic assessments of Zr-2.5Nb pressure tubes. A number of fatigue crack initiation experiments have been performed on notched specimens from irradiated and unirradiated Zr-2.5Nb pressure tube material with a range of hydrogen equivalent concentrations. These experiments were performed in an air environment and included temperature and load rise time as test parameters. The test data has been used to develop a statistical-based model of fatigue crack initiation at flaws that covers the effects of flaw root radius, load rise time and irradiation. This paper describes the development of the statistical-based model.

Recovery-Stress States of Professional Ballet Dancers During Different Phases of a Ballet Season

2021 ◽  
Author(s):  
Jana S. De Wet ◽  
Eileen Africa ◽  
Ranel Venter
Keyword(s):  
Mixed Model ◽  
High Stress ◽  
Recovery Stress ◽  
Total Recovery ◽  
Ballet Dancers ◽  
Training Adaptations ◽  
Stress States ◽  
Classical Ballet ◽  
And Performance ◽  
Negative Training

Ballet dancers are exposed to chronic high training and performance demands that are associated with overtraining syndrome and injury. Balancing high training loads with recovery to reduce the risk of negative training adaptations is critical. Moreover, the recovery-stress states of professional ballet dancers during training phases of a season are largely unknown. Professional dancers (n = 27) from one classical ballet company in South Africa were monitored for two 8-week phases of a ballet season. A recovery-stress questionnaire for Athletes (RESTQ-76 Sport) was completed weekly during the rehearsal phase (P1) and the performance phase (P2), which took place at the start and the end of the ballet season, respectively. Comparisons were calculated between phases, sexes, and levels of performance with a mixed-model ANOVA and between demographic variables with a one-way ANOVA. The performance phase was signified by lower total recovery (TR, p < 0.01) and higher total stress (TS, p < 0.01) for the group. Female dancers had significantly lower recovery scores than male dancers during P2 (p < 0.01). No differences between levels of performance were found. Subscales previously associated with overreaching and injury were identified in certain groups during P2. In conclusion, P2 was a critical period where dancers, especially females, experienced high stress and low recovery. This could increase the risk for injury and negative training adaptations.

J and CTOD Based Tensile Strain Capacity Prediction for Pipelines with a Surface Crack in Girth Weld

2021 ◽  
Author(s):  
Youn-Young Jang ◽  
Nam-Su Huh ◽  
Ik-Joong Kim ◽  
Young-Pyo Kim
Keyword(s):  
Crack Initiation ◽  
Internal Pressure ◽  
Surface Crack ◽  
Driving Force ◽  
Tensile Strain ◽  
Structural Integrity ◽  
Accurate Estimation ◽  
Long Distance ◽  
Crack Driving Force ◽  
Girth Welding

Abstract Long-distance pipelines for the transport of oil and natural gas to onshore facilities are mainly fabricated by girth welding, which has been considered as a weak location for cracking. Pipeline rupture due to crack initiation and propagation in girth welding is one of the main issues of structural integrity for a stable supply of energy resources. The crack assessment should be performed by comparing the crack driving force with fracture toughness to determine the critical point of fracture. For this reason, accurate estimation of the crack driving force for pipelines with a crack in girth weld is highly required. This paper gives the newly developed J-integral and crack-tip opening displacement (CTOD) estimation in a strain-based scheme for pipelines with an internal surface crack in girth weld under axial displacement and internal pressure. For this purpose, parametric finite element analyses have been systematically carried out for a set of pipe thicknesses, crack sizes, strain hardening, overmatch and internal pressure conditions. Using the proposed solutions, tensile strain capacities (TSCs) were quantified by performing crack assessment based on crack initiation and ductile instability and compared with TSCs from curved wide plate tests to confirm their validity.

Features Testing of Stud Material Under Low Constraint Ductile Tearing

2017 ◽  
Author(s):  
P. James ◽  
M. Jackson ◽  
P. Birkett ◽  
C. Madew
Keyword(s):  
Structural Integrity ◽  
High Stress ◽  
Crack Tip ◽  
Pressure Vessels ◽  
Materials Testing ◽  
Screw Thread ◽  
Surface Point ◽  
Defect Tolerance ◽  
Material Response ◽  
Crack Tip Constraint

Defect tolerance assessments are carried out to support the demonstration of structural integrity for high integrity components such as nuclear reactor pressure vessels. These assessments often consider surface-breaking defects and assess Stress Intensity Factors (SIFs) at both the surface and deepest points. This can be problematic when there is a high stress at the surface, for example due to the stress concentration at the root of a screw thread. In the past this has led to the development of complex and costly 3D finite element analyses to calculate more accurate SIFs, and still resulting in small apparent limiting defect sizes based on initiation at the surface point. Analysis has been carried out along with supporting materials testing, to demonstrate that the increased SIF at the surface point is offset by a reduction in crack-tip constraint, such that the material exhibits a higher apparent fracture toughness. This enables a more simplistic assessment which reduces the effective SIF at the surface such that only the SIF at the deepest point needs to be considered. This then leads to larger calculated limiting defect sizes. This in turn leads to a more robust demonstration of structural integrity, as the limiting defect sizes are consistent with the capability of non-destructive examination techniques. The high SIF at the surface location, and the concomitant reduction in crack-tip constraint, meant that it was not possible to demonstrate the material response with conventional tests, such as those using shallow-notched bend specimens. Instead it was necessary to develop modified specimens in which semielliptical defects were introduced into a geometry which replicated the notch acuity at the root of a screw thread. These feature tests were used to demonstrate the principle, prior to testing with more conventional specimens to fit more accurately the parameters required to represent the material response in a defect tolerance assessment. Margins in defect tolerance assessments are usually measured against the initiation of tearing, even though the final failure for the material may occur at a higher load following stable crack extension. This work measured and assessed the benefit of reduced crack-tip constraint on both the point of initiation and on the development of the tearing resistance curve. This demonstrated that the effect of constraint was valid with tearing for this material and that there was additional margin available beyond the onset of tearing. The feature test geometry also provided evidence of the tearing behaviour at the surface and deepest points of a surrogate component under representative loading. This paper provides an overview of the range of tests performed and the post-test interpretation performed in order to provide the R6 α and k constraint parameters.

scholarly journals PERFORMANCE BASED COUPLED CFD-FEM ANALYSIS OF 3-BAY HIGH INDUSTRIAL HALL UNDER NATURAL FIRE

2016 ◽  
Author(s):  
Michal Malendowski ◽  
Adam Glema ◽  
Wojciech Szymkuc
Keyword(s):  
Heat Exposure ◽  
Fem Analysis ◽  
Structural Elements ◽  
Fire Load ◽  
Natural Fire ◽  
Standard Fire ◽  
Complex Approach ◽  
Main Emphasis ◽  
Low Probability ◽  
And Performance

In this paper, the main emphasis is put into showing differences between standard fire design of structural elements and performance based approach, that takes into account analysis of structure under natural fire. The exemplary structure is a 3-bay 65,0x110,0 m in plane and 22,0 m high industrial hall with heavy cranes. Because of the significant volume with respect to fire load, there is a low probability that the fully developed fire can occur, nonetheless regarding technological process, a significant local fire could take place and affect the neighbour structure. The most complex approach used in this work is based on coupled CFD-FEM analysis of influence of local fire onto structure.Fire exposure of structural elements is calculated by the coupling scripts, taking into account real heat exposure of section by using adiabatic surface temperature approach.

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