Mechanism-Based Evaluation of Thermal Ratcheting due to Traveling Temperature Distribution

2000 ◽  
Vol 122 (2) ◽  
pp. 130-138 ◽  
Author(s):  
Toshihide Igari ◽  
Hiroshi Wada ◽  
Masahiro Ueta
Keyword(s):  
Temperature Distribution ◽  
Structural Design ◽  
Evaluation Method ◽  
Stress Condition ◽  
Membrane Stress ◽  
Primary Stress ◽  
Ratcheting Strain ◽  
Axial Temperature ◽  
Thermal Ratcheting ◽  
New Type

Recently, structural design against a new type of thermal ratcheting under a null-primary-stress condition has been required. The representative case is the thermal ratcheting of a hollow cylinder caused by a traveling temperature distribution. In this paper, the mechanism of this ratcheting is proposed, and the evaluation method of ratcheting strain is shown based on this mechanism. The proposed evaluation method is basically based on the hoop-membrane stress due to the axial temperature distribution, and considers the influence of axial bending stress and traveling distance of temperature distribution. Predicted results by this method correspond to numerical results by FEM and can conservatively estimate the experimental results with several kinds of traveling distance, stress levels, and two types of temperature hold for types 316 and 316FR stainless steels. [S0094-9930(00)01102-1]

Proposal of the Screening Method for Prevention of the Accumulation of the Ratcheting Strain Derived From the Movement of the Temperature Distribution

2014 ◽  
Author(s):  
Satoshi Okajima ◽  
Takashi Wakai ◽  
Masanori Ando ◽  
Yasuhiro Inoue ◽  
Sota Watanabe
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Finite Element ◽  
Evaluation Method ◽  
Equivalent Stress ◽  
Plastic Region ◽  
Screening Method ◽  
Second Step ◽  
Ratcheting Strain ◽  
Thermal Ratcheting

The prevention of excessive deformation by thermal ratcheting is important in the design of high-temperature components of fast breeder reactors (FBR). This includes evaluation methods for a new type of thermal ratcheting caused by a traveling temperature distribution. Igari et al. [1] proposed a mechanism-based evaluation method to evaluate thermal ratcheting caused by temperature distributions traveling long and short distances. In this paper, we simplify the existing method and propose a screening method to prevent thermal ratcheting strain in the design of practical components. The proposed method consists of two steps to prevent the continuous accumulation of ratcheting strain. The first step is to determine whether all points through the wall thickness are in the plastic state. This is based on an equivalent stress, which comprises the primary stress, the thermal membrane stress, and the thermal bending stress. When the equivalent stress is less than the yield strength of the cylinder material, overall plastic deformation through the wall thickness does not occur. When the equivalent stress exceeds the yield strength in some regions of the cylinder, the ranges of these regions are measured for the second step. To prevent the acceleration of the plastic deformation due to creep, we define the upper limit of the equivalent stress based on the relaxation strength, Sr. The second step is to determine whether the accumulation of the plastic strain saturates (i.e. if shakedown occurs). For this purpose, we define the screening criteria for the range of the plastic region. When the range of the plastic region is sufficiently small, residual stress is generated in the direction opposite to the plastic deformation direction. As a result of residual stress, further accumulation of the plastic deformation is suppressed, and finally shakedown occurs. If the range of the plastic region exceeds the defined criteria, a more detailed evaluation method (e.g. inelastic finite element analysis) may be used for the component design. To validate the proposed method, we performed a set of elasto-plastic finite element method (FEM) analyses, with the assumption of elastic perfectly plastic material.

A Screening Method for Prevention of Ratcheting Strain Derived From Movement of Temperature Distribution

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Satoshi Okajima ◽  
Takashi Wakai ◽  
Masanori Ando ◽  
Yasuhiro Inoue ◽  
Sota Watanabe
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Screening Method ◽  
Second Step ◽  
Plastic State ◽  
Membrane Stress ◽  
Primary Stress ◽  
Ratcheting Strain ◽  
Section Yield ◽  
Yield State

In this paper, we simplify the existing method and propose a screening method to prevent thermal ratcheting strain in the design of practical components. The proposed method consists of two steps to prevent the continuous accumulation of ratcheting strain. The first step is to determine whether all points through the wall thickness are in the plastic state. This is based on an equivalent membrane stress, which comprises the primary stress and the secondary membrane stress. When the equivalent stress exceeds the yield strength in some regions of the cylinder, the axial lengths of these regions are measured for the second step. The second step is to determine whether the accumulation of the plastic strain saturates. For this purpose, we define the screening criteria for the length of the area with full section yield state. When this length is sufficiently small, residual stress is generated in the direction opposite to the plastic deformation direction. As a result of residual stress, further accumulation of the plastic deformation is suppressed, and finally shakedown occurs. To validate the proposed method, we performed a set of elastoplastic finite element method (FEM) analyses, with the assumption of elastic perfectly plastic material. Not only did we investigate about the effect of the axial length of the area with full section yield state but also we investigated about effects of spatial distribution of temperature, existence of primary stress, and radius thickness ratio.

scholarly journals Stator Non-Uniform Radial Ventilation Design Methodology for a 15 MW Turbo-Synchronous Generator Based on Single Ventilation Duct Subsystem

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2760
Author(s):  
Ruiye Li ◽  
Peng Cheng ◽  
Hai Lan ◽  
Weili Li ◽  
David Gerada ◽  
...  
Keyword(s):  
Finite Element ◽  
Temperature Distribution ◽  
Design Methodology ◽  
Large Scale ◽  
Synchronous Generator ◽  
Axial Direction ◽  
Scale Model ◽  
Element Analysis ◽  
Axial Temperature ◽  
Ventilation Duct

Within large turboalternators, the excessive local temperatures and spatially distributed temperature differences can accelerate the deterioration of electrical insulation as well as lead to deformation of components, which may cause major machine malfunctions. In order to homogenise the stator axial temperature distribution whilst reducing the maximum stator temperature, this paper presents a novel non-uniform radial ventilation ducts design methodology. To reduce the huge computational costs resulting from the large-scale model, the stator is decomposed into several single ventilation duct subsystems (SVDSs) along the axial direction, with each SVDS connected in series with the medium of the air gap flow rate. The calculation of electromagnetic and thermal performances within SVDS are completed by finite element method (FEM) and computational fluid dynamics (CFD), respectively. To improve the optimization efficiency, the radial basis function neural network (RBFNN) model is employed to approximate the finite element analysis, while the novel isometric sampling method (ISM) is designed to trade off the cost and accuracy of the process. It is found that the proposed methodology can provide optimal design schemes of SVDS with uniform axial temperature distribution, and the needed computation cost is markedly reduced. Finally, results based on a 15 MW turboalternator show that the peak temperature can be reduced by 7.3 ∘C (6.4%). The proposed methodology can be applied for the design and optimisation of electromagnetic-thermal coupling of other electrical machines with long axial dimensions.

scholarly journals Influence of CFRC Insulating Plates on Spark Plasma Sintering Process

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 393
Author(s):  
Alexander M. Laptev ◽  
Jürgen Hennicke ◽  
Robert Ihl
Keyword(s):  
Temperature Distribution ◽  
Spark Plasma Sintering ◽  
Energy Demand ◽  
Composite Powders ◽  
Fem Method ◽  
Plasma Sintering ◽  
Axial Temperature ◽  
Spark Plasma ◽  
Power And Energy ◽  
The Impact

Spark Plasma Sintering (SPS) is a technology used for fast consolidation of metallic, ceramic, and composite powders. The upscaling of this technology requires a reduction in energy consumption and homogenization of temperature in compacts. The application of Carbon Fiber-Reinforced Carbon (CFRC) insulating plates between the sintering setup and the electrodes is frequently considered as a measure to attain these goals. However, the efficiency of such a practice remains largely unexplored so far. In the present paper, the impact of CFRC plates on required power, total sintering energy, and temperature distribution was investigated by experiments and by Finite Element Modeling (FEM). The study was performed at a temperature of 1000 °C with a graphite dummy mimicking an SPS setup. A rather moderate influence of CFRC plates on power and energy demand was found. Furthermore, the cooling stage becomes considerably longer. However, the application of CFRC plates leads to a significant reduction in the axial temperature gradient. The comparative analysis of experimental and modeling results showed the good capability of the FEM method for prediction of temperature distribution and required electric current. However, a discrepancy between measured and calculated voltage and power was found. This issue must be further investigated, considering the influence of AC harmonics in the DC field.

Analysis and Suggestions on Leakage of Boiler Low Temperature Reheater

2013 ◽  
Vol 341-342 ◽  
pp. 341-344
Author(s):  
Xue Xia Xu ◽  
Yan Ting Feng ◽  
Hao Ke ◽  
Xiao Guang Niu ◽  
Qing Wang
Keyword(s):  
Low Temperature ◽  
Structural Design ◽  
Stress Condition ◽  
Comprehensive Analysis ◽  
Composition Analysis ◽  
Weak Zone ◽  
Welding Seam ◽  
Microstructure Examination ◽  
Pipeline Vibration ◽  
Metallurgical Microstructure

Leakage causes of boiler low temperature reheater were discussed by means of macroscopic inspection, chemical composition analysis, metallurgical microstructure examination, SEM and EDS fracture analysis. Results showed that the reheater leakage occurred for cracks originating from the fillet seam of ear plate. The main causes lie in improper structural design of the ear plate welding directly on the reheater elbow where suffered from complicated stress condition, wall thinning and out-of-round. In addition, as a weak zone, heat effect zone of the fillet welding seam was more likely to crack under fatigue stress for frequent unit start and stop and pipeline vibration. Installation stress existed between the ear plate and support block also contributed to the cracking. Suggestions were provided to avoid similar accident based on the comprehensive analysis of leakage causes.

Influence of Thermal Ratcheting on the Creep and Mechanical Properties of High-Density Polyethylene

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Rahul Palaniappan Kanthabhabha Jeya ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Creep Strain ◽  
High Density Polyethylene ◽  
Coefficient Of Thermal Expansion ◽  
Creep Property ◽  
High Density ◽  
Steady Creep ◽  
Thermal Cycles ◽  
Ratcheting Strain ◽  
Thermal Ratcheting ◽  
The Impact

Abstract The objective of this research is to describe the consequence of thermal ratcheting on the long-term creep property of the high-density polyethylene (HDPE) material. The thermal ratcheting phenomenon increases significantly the creep strain of HDPE. The magnitude of the creep strain of HDPE increases by 8% after just 20 thermal cycles between 28 and 50 °C. The creep modulus, which is inversely proportional to the creep strain, depletes further under thermal ratcheting. Both the properties change significantly with the number of thermal cycles. The coefficient of thermal expansion (CTE) of HDPE varies with the applied compressive load, with successive thermal cycles, and with the thermal ratcheting temperature. The impact of thermal ratcheting diminishes with an increase in initial steady creep exposure time period, but still the magnitude cumulative deformation induced is noteworthy. The magnitude of growth in creep strain drops from 8% to 2.4% when thermal ratcheting is performed after 1 and 45 days of steady creep, respectively. There is a notable change in the thickness of the material with each heating and cooling cycle even after 45 days of creep; however, the thermal ratcheting strain value drops by 80% in comparison with the thermal ratcheting strain after 1 day of creep and under similar test conditions.

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