Effect of reinforcement on plastic limit loads of branch junctions

Kim, Y.J.,Myeong, M.S.,Yoon, K.B. Applied Science Publishers ; Elsevier Science Ltd 2009 The International journal of pressure vessels and Vol.86 No.8

This paper provides effects of reinforcement shape and area on plastic limit loads of branch junctions under internal pressure and in-plane/out-of-plane bending, via detailed three-dimensional finite element limit analysis assuming elastic-perfectly plastic material behaviour. It is found that reinforcement is most effective when (in-plane/out-of-plane) bending is applied to the branch pipe. When bending is applied to the run pipe, reinforcement is less effective when bending is applied to the branch pipe. The reinforcement effect is the least effective for internal pressure.

Three-dimensional finite element welding residual stress analysis of penetration nozzles: I - Sensitivity of analysis variables

Bae, H.Y.,Kim, Y.J.,Kim, J.H.,Lee, S.H.,Lee, K.S.,Park, C.Y. Applied Science Publishers ; Elsevier Science Ltd 2014 The International journal of pressure vessels and Vol.114 No.-

This paper investigates effects of variables related to 3-D finite element welding residual stress analyses of penetration nozzles on residual stresses. Five variables are considered; (i) number of elements in the circumferential direction, (ii) number of beads in the circumferential direction, (iii) kinematic boundary conditions, (iv) circumferential modelling angle in 3-D finite element models and (v) detailed weld shape. Based on sensitivity analysis results, guidelines for 3-D finite element welding residual stress analyses of penetration nozzles are provided.

Evaluation of stress intensity factors due to welding residual stresses for circumferential cracked pipes

Oh, C.Y.,Kim, Y.J.,Oh, Y.J.,Kim, J.S.,Song, T.K.,Kim, Y.B. Applied Science Publishers ; Elsevier Science Ltd 2013 The International journal of pressure vessels and Vol.105 No.-

To investigate the applicability of existing methods to estimate stress intensity factors due to welding residual stresses, comparisons with finite element (FE) solutions are made for two types of generic welding residual stress profiles, generated by simulating repair welds. It is found that fitting residual stresses over the crack depth using third-order polynomials gives good estimates of stress intensity factors but fitting over the entire thickness can result in inaccurate estimates even with fourth-order polynomials. Noting that welding residual stresses are often determined from FE analyses, linearization of residual stresses to estimate stress intensity factors is proposed. Comparison with FE solutions shows good agreements.

Effect of hydrocolloid coatings on the heat transfer and oil uptake during frying of potato strips

Kim, D.N.,Lim, J.,Bae, I.Y.,Lee, H.G.,Lee, S. Applied Science Publishers ; Elsevier Science Ltd 2011 Journal of food engineering Vol.102 No.4

The effect of the hydrocolloid coatings (gellan gum and guar gum) of a food matrix on the heat transfer during a frying process was investigated and correlated with the oil uptake. While the potato strips coated with the hydrocolloid solutions were fried at 170<SUP>o</SUP>C, the hydrocolloid coatings significantly reduced the heat transfer coefficients as well as oil uptake which became more apparent at higher concentrations. Thus, the oil uptake was found to have a good polynomial correlation (R<SUP>2</SUP>>0.99) with heat transfer coefficients, suggesting that a rapid heat transfer led to an increase in the oil content of the fried samples.

Evaluation of fracture toughness characteristics for nuclear piping using various types of specimens

Park, S.,Yoo, S.S.,Min, J.K.,Koo, J.M.,Seok, C.S. Applied Science Publishers ; Elsevier Science Ltd 2012 The International journal of pressure vessels and Vol.90 No.-

The leak-before-break (LBB) concept is based on the fracture resistance curve obtained by J-R tests for various types of specimens. But fracture toughness data of various types of specimens are different. For example, the estimates for fracture toughness of standard specimens are conservative when compared to the fracture toughness of real pipes because of the difference of the constraint effect between real pipes and standard specimens. Therefore, to estimate the integrity of real pipes based on elastic-plastic fracture mechanics, we have to first establish the relations among real pipes, standard CT specimens and curved CT specimens. In this study, we perform fracture toughness tests of nuclear piping materials using various types of specimens. And each J-R curve considered in the constraint effect is compared. The experimental results showed that a curved CT specimen is similar to the cases of pipes with small crack angles (60<SUP>o</SUP> and 120<SUP>o</SUP>) and a CT specimen is similar to the case of pipes with the crack length of 180<SUP>o</SUP>. Also, the Q-stress for curved CT specimens is higher than that of pure bending pipe specimens and lower than that of CT specimens.

Analysis of residual stress relief mechanisms in post-weld heat treatment

Dong, P.,Song, S.,Zhang, J. Applied Science Publishers ; Elsevier Science Ltd 2014 The International journal of pressure vessels and Vol.122 No.-

This paper presents a recent study on weld residual stress relief mechanisms associated with furnace-based uniform post-weld heat treatment (PWHT). Both finite element and analytical methods are used to quantitatively examine how plastic deformation and creep relaxation contribute to residual stress relief process at different stages of PWHT process. The key contribution of this work to an improved understanding of furnace based uniform PWHT can be summarized as follows:(1)Plastic deformation induced stress relief during PWHT can be analytically expressed by the change in material elastic deformation capacity (or elastic deformation limit) measured in terms of material yield strength to Young's modulus ratio, which has a rather limited role in overall residual stress relief during furnace based uniform PWHT. (2)The most dominant stress relief mechanism is creep strain induced stress relaxation, as expected. However, a rapid creep strain development accompanied by a rapid residual stress reduction during heating stage before reaching PWHT temperature is shown to contribute to most of the stress relief seen in overall PWHT process, suggesting PWHT hold time can be significantly reduced as far as residual stress relief is concerned. (3)A simple engineering scheme for estimating residual stress reduction is proposed based on this study by relating material type, PWHT temperature, and component wall thickness.

Separation of fine organic particles by a low-pressure hydrocyclone (LPH)

Applied Science Publishers ; Elsevier Science Ltd 2014 Aquacultural engineering Vol.63 No.-

The separation performance of a low-pressure hydrocyclone was tested using fine organic particles from 1 to 700μm. The dimensions of the low-pressure hydrocyclone were an inflow diameter of 30mm, a cylinder length of 575mm, an overflow diameter of 60mm, an underflow diameter of 50mm, a cylinder diameter of 335mm and a cone angle of 68<SUP>o</SUP>. The low-pressure hydrocyclone was operated with a lower inlet pressure (average 1.38-5.56kPa) that could be maintained under water level differences that ranged from 17.5 to 53.5cm between the water surface of the feeding mass cylinder and the middle of the inlet pipe of the low-pressure hydrocyclone. By varying the inflow rate, underflow ratio and feed concentration, the separation performance of the low-pressure hydrocyclone was affected. The separation performances were determined from total separation efficiency and grade efficiency. Separation performances were determined according to the different inflow rates of 400, 600, 800 and 1000mls<SUP>-1</SUP> and their respective underflow ratios that ranged from 5% to 30%. The maximum total separation efficiencies for each inflow rate were 41%, 46% and 46% at 400, 800 and 1000mls<SUP>-1</SUP> inflow rates, respectively, and at underflow rates of 30% of the inflow rates. In addition, a total separation efficiency of 46% was employed at 600mls<SUP>-1</SUP> of inflow rate and with an underflow rate of 25% its inflow rate. As the feed concentration increased from 25 to 150mgl<SUP>-1</SUP>, the separation performances were gradually decreased. For the fine particles ranging 1-200μm, the grade efficiency was higher at the higher inflow rate (higher than 600mls<SUP>-1</SUP>) and higher underflow rate. However, for the coarse particles ranging 400-700μm, the grade efficiency was higher at the lower inflow rate (lower than 600mls<SUP>-1</SUP>) and higher underflow rate. The cut-point (d<SUB>50</SUB>) values ranged from 30 to 200μm for a feed size range of 1-700μm. The Response Surface Method (RSM) model predicted an optimum operating inflow rate and underflow ratio of 721mls<SUP>-1</SUP> of inflow rate and 30%, respectively, for the low-pressure hydrocyclone at a maximum total separation efficiency. Based on these findings, further design and operating adaptation of low-pressure hydrocyclones used for fine solids removal in recirculating aquaculture systems is expected.

Approximate J estimates for combined primary and secondary stresses with large elastic follow-up

Song, T.K.,Oh, C.Y.,Kim, Y.J.,Ainsworth, R.A.,Nikbin, K. Applied Science Publishers ; Elsevier Science Ltd 2013 The International journal of pressure vessels and Vol.111 No.-

This paper proposes the V-factor for approximate J estimates under combined primary and secondary stresses with large elastic follow-up within the failure assessment diagram approach. The elastic follow-up is characterized by three parameters. The first two are the relative magnitudes of the primary load and of the secondary stress, β. The third parameter is the initial slope of the Vo-β curve where Vo is the value of V for zero primary load. Elastic follow-up effects are more pronounced for contained yielding, smaller β and a larger initial slope of the Vo-β curve. An approximate expression for V/V<SUB>o</SUB> is proposed, showing good agreements with finite element solutions.

Identification of inelastic material parameters for modified 9Cr-1Mo steel applicable to the plastic and viscoplastic constitutive equations

Koo, G.H.,Kwon, J.H. Applied Science Publishers ; Elsevier Science Ltd 2011 The International journal of pressure vessels and Vol.88 No.1

In this paper, the material parameters of plastic and viscoplastic constitutive equations for modified 9Cr-1Mo steel are developed for various isothermal conditions to support inelastic analysis for a sodium-cooled fast reactor. To do this, the material parameters related with the elastoplastic behaviour are identified with uniaxial cyclic test data by performing computer simulations, which use the combined Chaboche model including the kinematic hardening rule and the isotropic softening rule. The viscous parameters are identified from uniaxial stress relaxation test data through computer simulations with the pre-determined elastoplastic material parameters. Sensitivity studies are performed for the material parameters to investigate cyclic inelastic behaviour and stress relaxation during a hold time. From the comparison between the tests and the simulations, it is expected that the identified material parameters of the plastic and viscoplastic constitutive equations can accurately express the material characteristics of modified 9Cr-1Mo steel sufficiently well to be used for inelastic analysis.

Generation of plastic influence functions for J-integral and crack opening displacement of thin-walled pipes with a short circumferential through-wall crack

Park, J.S.,Choi, Y.H.,Im, S. Applied Science Publishers ; Elsevier Science Ltd 2014 The International journal of pressure vessels and Vol.117 No.-

Fracture mechanics parameters such as the J-integral and crack opening displacement (COD), are necessary for Leak-Before-Break (LBB) evaluation. The famous two estimation methods, the GE/EPRI and the Reference Stress Method (RSM), have their applicability limit with regard to the ratio of a pipe mean radius to thickness (R<SUB>m</SUB>/t). In order to extend their applicability limit to a thin walled pipe, several finite element analyses are performed for the J-integral and COD, and then new plastic influence functions are developed for thin-walled pipes with a short circumferential through-wall crack. With the newly generated plastic influence functions, the GE/EPRI and the RSM give closer results with those obtained from detailed finite element analyses. In addition, C*-integral and COD rate are estimated by using the new plastic influence functions and they are well matched with elastic-creep finite element analysis results under the power-law creep condition. Since the LBB concept can be applied to a piping system in a Korean Sodium-cooled Fast Reactor (SFR) which is designed to have thin-walled pipes and to operate in high temperature enough to cause creep, this paper can be applied for the LBB assessment of thin-walled pipes with a short through-wall crack in the SFR.