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In this paper, allowable bending moments for circumferential inner surface cracked pipes are evaluated. ASME Boiler and Pressure Vessel code Section XI, “Rules for Inspection of Nuclear Power Plant Components” provides analytical evaluation procedures. Analytical evaluation methods based on the failure mechanism are provided in nonmandatory Appendix C and those based on failure assessment diagram are given in nonmandatory Appendix H. Allowable bending moments are evaluated using both appendices and compared with experiments. Conservativeness is compared quantitatively between both methods by normalizing allowable bending moments with experimental maximum moments.

This paper presents the analysis and design of an active electromagnetic interference (EMI) filter (AEF) for the common-mode (CM) noise reduction of switching power converters. The features of the several types of AEFs are discussed and compared in terms of implementation. The feed-forward AEF with a voltage-sensing and voltage-cancellation (VSVC) structure is implemented for an LLC resonant converter to replace a multiple-stage passive EMI filter and thereby reduce CM noise. The characteristics and performance of the VSVC-type AEF are investigated through theoretical and experimental works.

In this article, a semi-analytical method to estimate elastic follow-up factor as input to estimate the transient creep C( t) parameter under secondary loading is presented and validated against finite element results for a cracked two-bar structure under constant displacement loading. Predicted values of C( t) agree well with the finite element results for both elastic-creep cases and for elastic-plastic cases with the same creep and plastic hardening exponents. For elastic-plastic-creep cases with different creep and plastic hardening exponents, the proposed method gives good predictions at long time but can under- or over-predict C( t) at short time.

The present study analyzes the elastic follow-up factor under various secondary loads in the piping with cracks through finite element analysis. The secondary loads being considered included axial tensile load caused by the displacement applied in form of uniform stress through thickness and the load due to the thermal gradient in the radial direction applied as bending stress. According to this study, under displacement control loads, elastic follow-up factor can increase greatly.

This paper proposes a method to determine the elastic follow-up factors for the -integral under secondary stress. The rate of creep crack growth for transient creep is correlated with the -integral. Elastic follow-up behavior, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the values of and creep crack growth increase as increasing elastic follow-up. An estimation solution for was proposed by Ainsworth and Dean based on the reference stress method. To predict the value of using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is needed. This paper proposed that the elastic follow-up factors for can be determined by elastic-plastic analyses using the plastic-creep analogy. Finite element analyses were performed to verify this method.

Maternal interaction behavior, language input and children's language of 34 multicultural families were compared with those of ordinary families. MLU's of multicultural mothers and their children were shorter than those of ordinary Korean mothers and children. Positive maternal interaction behaviors of multicultural mothers were significantly lower than those of ordinary mothers. Correlational analyses revealed that there were positive correlations among maternal interaction behaviors, mother's MLU and children' MLU in multicultural families. However, there were no such correlations in ordinary families. Findings suggest language education and support for multicultural mothers be an effective policy for their children's language development. Keywords : maternal interaction behahior, language input, young children, spontaneous utterance, multicultural families Ⅰ. 서론 1990년대 인력부족으로 인한 이주노동자들의 유입과 농촌에서 발생한 남녀 불균형 문제의 해결을 위한 이주여성의 급격한 증가는 한국사회를 다문화사회로 이행하는 계기를 마련하였다. 이로 인해 한국 사회는 더 이상 단일민족이 아닌 다인종․다문화 시대로 급속히 변하고 있다. 행정안전부에 따르면 2010년 5월 외국계주민의 수는 1,139,283명으로, 이는 주민등록인구의 2.3% 수준에 해당한다고 한다(Ministry of Administration and Security, 2010). 이러한 추세로 나간다면 외국인의 비율은 더욱 늘어나 2020년에는 전체 인구의 5%, 그리고 2050년에는 9.2%까지 증가할 것으로 예상된다. 또한 통계청의 2010년 자료에 의하면, 우리나라 총 혼인 건수 325,104건 중 국제결혼의 비율은 34,235(10.5%) 건이고 그 중 한국인 남성과 외국인 여성의 결혼은 26,274건으로 전체 국제결혼인구의 76.7%를 차지하고 있다(The Statistics Korea, 2010). 이와 같이 외국 인력 유입과 국제결혼의 증가, 세계화에 따른 가치관 변화 등의 이유로 우리나라의 다문화 가정은 더욱 늘어날 것으로 예측하고 있다.

In this paper, the effect of multi-axial stress states on the elastic follow-up behaviour of creeping structures is investigated by deriving analytical elastic follow-up factor solutions for two examples; power-law creeping square and cruciform plates under bi-axial displacement-controlled loading. The validity of the analytical solutions is checked against results from finite element analyses. The agreement is found to be good even for large amounts of stress relaxation. Based on the solutions developed, the effects of stress biaxiality, geometry and creep exponent on elastic follow-up are discussed.

This paper compares published experimental plastic collapse loads for 90° elbows with existing closed-form solutions. A total of 46 experimental data are considered, covering pure bending (in-plane closing, in-plane opening and out-of-plane bending) and combined pressure and bending loads. The plastic collapse load solutions considered are from the ASME code, the Ductile Fracture handbook of Zahoor, by Chattopadhyay and co-workers, and by Y.-J. Kim and co-workers. Comparisons with the experimental data shows that the ASME code solution is conservative by a factor of 2 on collapse load for in-plane closing bending, 2.3 for out-of-plane bending, and 3 for in-plane opening bending. The solutions given by Kim and co-workers give the least conservative estimates of plastic collapse loads, although they provide slightly non-conservative estimates for some data.

Approximate limit and plastic collapse load solutions for un-reinforced mitred bends under internal pressure and under bending are proposed in this paper, based on three-dimensional finite element analysis and approximate solutions for smooth bends. Solutions are given for single- and multi-mitred bends (mainly for single and double segmented bends) with the pipe mean radius-to-thickness ratio ( r/t ) ranging from r/t = 5 to r/t = 50, and the bend radius-to-mean radius ratio ( R/r ) from R/r = 2 to R/r = 4. Internal pressure, in-plane bending and out-of-plane bending loads are considered, but not their combination. It is found that the essential features of limit and plastic collapse loads for mitred bends are similar to those for smooth bends, and thus existing solutions for smooth elbows can be used to construct limit loads and plastic collapse for mitred bends.

This paper presents approximate closed-form plastic limit load solutions for branch junctions under out-of-plane bending and under combined pressure and out-of-plane bending, based on three-dimensional finite element limit analyses for an elastic-perfectly plastic material. When bending is applied to the branch pipe, the plastic limit loads for out-of-plane bending are shown to be lower than those for in-plane bending. However, for bending to the run pipe, the opposite trend is found. For combined pressure and out-of-plane bending, either the circular interaction or the parabolic interaction rule can be used, depending on the bending location and the branch geometry. Comparison with published experimental plastic limit load data shows that the predictions agree relatively well with the test data.

In our previous paper, it was found that the mis-match effect in creep on steady-state stresses within the weld metal for a large bore branch junction could be uniquely quantified by the mis-match factor defined as a function of the creep stress exponent and the ratio of creep constants for the base and weld materials. Furthermore ratios of section-averaged (effective and maximum principal) stresses for the mis-matched case to those for the even-matched case were linearly dependent on the mis-match factor. Above results were obtained for a specific branch geometry under single loading. This paper extends our previous analysis to other branch geometries and to combined loading. It is found that above conclusions can be applied to general branch components under combined loading.

사고를 미연에 방지하기 위해서 감육에 대한 평가법 개발이 필요하다. 피더관 직관부에 발생한 감육에 대한 소성 붕괴 평가법은 개발되어 있으나, 현재 곡관Key Words : CANDU(캐나다형 중수로), feeder pipe(피더관), limit load(한계하중), circular wall-thinning(원형감육), bending(굽힘하중), internal pressure(내압) 초록: 캐나다형 중수로에서 피더관은 가동 중에 유동 가속 부식에 의해 감육이 발생한다. 피더관에 감육이 발생하면 배관 건전성이 떨어진다. 본 논문은 원형 감육이 발생한 피더관에서의 기기신뢰성 평가를 위한 한계 하중을 연구하였다. 유한요소 해석을 통하여 면내 굽힘 하중과 내압을 받는 경우에 대하여 연구하였다. 재료는 대변형 효과를 고려하고 탄성-완전소성 재료로 가정하였다. 원형 감육이 발생한 피더관에 대하여 내압과 닫힘 방향, 열림 방향 굽힘 하중에 대하여 한계하중해를 제시하였다. Abstract: Flow Accelerated Corrosion (FAC) occurring during in-service conditions results in localized wall-thinning in the feeder pipes of CANDU. The wall-thinning of the feeder pipes is the main degradation mechanisms affecting the integrity of piping systems. In this paper, we assess the integrity of wall-thinned feeder pipes by limit load analysis. The limit loads for wall-thinning feeder pipes subjected to in-plane bending and internal pressure were determined on the basis of finte element limit analyses. The limit loads are determined from the results of limit analyses of elastic-perfectly-plastic materials using the large geometry change. Closed-form approximations of limit load solutions for wall-thinning feeder pipes subjected to in-plane bending and pressure are proposed.

일반적으로 압력용기는 설계, 제작 그리고 용접을 거친 뒤 사용하게 된다. 입력용기의 설계, 제작 및 용접은 반드시 관련 기관 혹은 산업체가 허용하는 코드에 따라 수행되어야 하며, 미국의 기계학회 보일러 및 압력용기 코드(ASME BPV; American Society of Mechanical Engineers Boiler and Pressure Vessel Code) 등 다양한 코드가 있다. 이러한 Construction코드들은 주로 압력용기의 설계와 용접 및 제작에 관련된 기술기준을 제공하며, 미국 ASME BPV 코드의 Sec XI과 같이 가동 중 압력용기의 검사와 관련된 기준을 때로는 제시하기도 한다. 하지만 가동 중인 압력용기의 적절한 관리(Maintenance)는 설계와 제작만큼 중요한 문제이고 최근 대두되는 설비수명연장과 효율적인 관리 측면에서 상당히 중요한 문제로 취급되고 있다. 따라서 가동 중 압력용기의 효율적인 관리를 위해 다양한 기술과 기법이 제시되었고 이를 토대로 최근 다양한 Post-construction코드가 제시되고 있다. 설비의 효율적인 관리와 설비 수명연장을 통해 비용을 절감하고 산업의 경쟁력을 극대화할 수 있는 Post-construction코드는 가동 중인 압력용기의 검사 및 진단, 결함 및 구조 건전성 평가, 운전 및 운영과 관련된 방대한 기술을 취급해야 하므로 다양한 형태의 코드로 제시된다. 주로 가동 중인 압력용기의 위험도를 기반으로 관리하는 기법을 제시하는 Risk-Based Inspection(RBI), Risk-Based Maintenance(RBM), Risk-Centered Maintenance(RCM)등이 있으며, 가동 중인 압력용기에 발견된 결함에 대해 결함이 발견될 시 구조 건전성 평가를 수행하여 계속 운전이 적절한 가를 판단하고 나아가서 잔여수명을 평가할 수 있는 사용적합성(Fitness-For-Service; FFS)코드가 제시되어 있다. 일반적으로 가동 중 압력용기에서 결함이 발생하면 설계코드의 개념에서는 해당요소를 일괄적으로 교체하거나 보수하여야 한다. 그러나 사용적합성 평가의 개념에서는 균열과 같은 결함이 구조물의 건전성에 미치는 영향을 파악하여 계속 사용 여부 또는 보수 및 교체를 판단할 있으며, 이를 동해 보수적으로 설계된 설비의 수명을 연장하고 효율적으로 설비를 관리할 수 있을 것이다. 따라서 사용적합성 평가의 가장 큰 특징은 결함을 반영하여 설비의 건전성 및 수명을 평가한다는 점이다. 압력용기의 설계 시에는 용기에 요구되는 성능과 관련된 해석과 더불어 사용 시 예상되는 파손기구들(failure mechanisms, 예 침/부식, 피로, 파괴)을 고려하여 역학적 구조해석을 통해 용기의 재료, 형상 및 두께 그리고 수명을 결정한다. 특별한 경우 설계 시 가상결함을 고려하여 건전성평가를 수행하는 경우도 있으나 기본적으로는 설계 시에는 결함을 반영하지 않는다. 결함평가를 수행해야 하는 사용적합성평가에서는 비선형 해석 및 파괴역학 등과 같은 기법을 사용하지만 기본적으로는 설계와 같은 개념을 가지나, 사용목적이 상이함에 따라 설계코드와 사용적합성코드는 적용 시 차별성이 존재한다. 본 고에서는 사용적합성평가를 위한 기존 코드들을 간략히 소개한 뒤 적용 시 설계코드와의 차별성과 관련된 몇 가지 사항을 정리하고자 한다.

This paper reports steady-state stress distributions within the weld metal in a welded branch component, via detailed three-dimensional elastic-creep finite element analyses. The creep exponent and constants for the base and weld metal are systematically varied to simulate under-matching, even-matching and over-matching conditions in creep. Various loading conditions are also considered to see the effect of the loading mode. It is found that the mismatch effect in creep on steady-state stresses within the weld metal can be uniquely quantified by the mismatch factor, defined as a function of creep exponent and constant. Ratios of section-averaged (effective and maximum principal) stresses for the mismatched case to those for the even-matched case are linearly dependent on the mismatch factor.

This paper quantifies the effect of the yield strength-to-elastic modulus ratio on twice-elastic-slope plastic loads for 90-degree elbows under in-plane and out-of-plane bending. Based on extensive and systematic finite element limit analyses using elastic-perfectly plastic materials, simple regression equations between the yield strength-to-elastic modulus ratio and twice-elastic-slope plastic loads for elbows under in-plane closing, in-plane opening and out-of-plane bending are proposed, and validated against published experimental data. Applicability of the proposed equations to circumferential cracked elbows under in-plane bending is also investigated.

This technical note extends the validity of limit load solutions for thin-walled branch junctions, previously proposed by the current author, to thick-walled cases. It is achieved simply by re-normalizing the thin-wall expressions by the limit loads of thick-walled tubes instead of those of thin-walled tubes. Comparison with finite element results shows overall good agreement.

The authors have previously proposed plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on finite element (FE) limit loads resulting from three-dimensional (3-D) FE limit analyses using elastic–perfectly plastic materials [Kim YJ, Lee KH, Park CY. Limit loads for thin-walled piping branch junctions under internal pressure and in-plane bending. Int J Press Vessels Piping 2006;83:645–53]. The solutions are valid for ratios of the branch-to-run pipe radius and thickness from 0.4 to 1.0, and for the mean radius-to-thickness ratio of the run pipe from 10.0 to 20.0. Moreover, the solutions considered the case of in-plane bending only on the branch pipe. This paper extends the previous solutions in two aspects. Firstly, plastic limit load solutions are given also for in-plane bending on the run pipe. Secondly, the validity of the proposed solutions is extended to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparisons with FE results show good agreement.

This paper provides plastic limit and TES (twice-elastic-slope) plastic load solutions for 90° pipe bends under combined pressure and out-of-plane bending, via three-dimensional non-linear FE analyses using elastic-perfectly plastic materials. Without internal pressure, a closed-form approximation is given. For combined pressure and out-of-plane bending, tabulated data are given, from which TES plastic loads can be interpolated. It is found that TES plastic loads for pipe bends under out-of-plane bending are lower than those under in-plane opening bending, but are higher than those under in-plane closing bending. It suggests that the in-plane closing bending mode is the most critical loading mode for 90° pipe bends, which is fully consistent to existing findings.

This paper quantifies the effect of a bend angle of a pipe bend on plastic loads, via small strain and large strain finite element (FE) limit analyses using elastic–perfectly plastic materials. To consider the effect of the attached straight pipe, two limiting cases are considered. One case corresponds to the pipe bend without the attached straight pipe, and the other to that with a sufficiently long attached straight pipe. For the former case, the FE results suggest that the limit load is not affected by the bend angle for both in-plane bending and internal pressure. For the latter case, however, the bend angle affects plastic loads. An interesting finding is that the plastic load smoothly changes from the limit load of the straight pipe when the bend angle approaches zero to the plastic load of the 90 ∘ pipe bend when the bend angle approaches 90 ∘ . Based on such observations, closed-form plastic load solutions are proposed for the pipe bend with an arbitrary bend angle under in-plane bending and internal pressure.

The present work presents plastic limit load solutions for branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) FE limit analyses using elastic-perfectly plastic materials. The proposed solutions are valid for a wide range of branch junction geometries; ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0.

The present work presents plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic–perfectly plastic materials. To assure reliability of the FE limit loads, modelling issues are addressed first, such as the effect of kinematic boundary conditions and branch junction geometries on the FE limit loads. Then the FE limit loads for branch junctions under internal pressure and in-plane bending are compared with existing limit load solutions, and new limit load solutions, improving the accuracy, are proposed based on the FE results. The proposed solutions are valid for ratios of the branch-to-run pipe radius and thickness from 0.4 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 10.0 to 20.0.

Degraded steam generator tubing can affect its safety functions. Therefore, its integrity should be maintained for each degradation form and all detected degradation must be assessed to verify that if adequate integrity is retained. Determination of tube integrity limits includes identifying acceptable structural parameters such as flaw length, depth, and amplitude of signals. If we consider just single-cracked tubes, short and deep flaws are not likely to threaten structural integrity of tubes. But if it has multiple-cracks, we have to consider interaction effects of multiple adjacent cracks on its burst pressure. Because adjacent multiple cracks can be merged due to the crack growth then it can challenge against the structural performance limit. There are some studies on the interaction effects of adjacent cracks. However, existing works on the interaction effect consider only through-wall cracks. No study has been carried out on the interaction effects of part-through cracks. Most cracks existing in real steam generator tubing are not through-wall cracks but part-through cracks. Hence, integrity of part-through cracks is more practical issue than that of through-wall cracks. This paper presents experimental burst test results with steam generator tubing for evaluation of interaction effects with axial oriented two collinear and parallel part-through cracks. The interaction effect between two adjacent cracks disappeared when the distance exceeds about 2 mm.

This paper proposes a method to determine the elastic follow-up factors for C(t)-integral under secondary stress. The rate of creep crack growth for transient creep is correlated with C(t)-integral. The elastic follow-up behaviour, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the value of C(t) and creep crack growth increase with an increasing elastic follow-up. An estimation solution for C(t) has been proposed by Ainsworth and Dean based on the reference stress method. In order to predict the value of C(t) using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is required. This paper proposes that the elastic follow-up factors for C(t) can be determined by elastic-plastic analyses by using the plastic-creep analogy. Finite element analyses have been performed to verify this method.Copyright © 2012 by ASME

This paper describes steady-state stress on welded branch components using detailed three dimensional elastic creep finite element analyses. In our previous paper [1], it was found that the mismatch effect in creep on steady-state stresses within the weld metal for a various branch junction could be uniquely quantified by the mis-match factor, defined as a function of creep exponent and constant. In actual branch components, the branch junction contains the heat-affected zone (HAZ) when the branch pipe is welded. Thus, additional mismatch factor for HAZ should be presented. This paper deals with not only the mismatch effect for weld metal but also that for HAZ. The creep exponent and constant for the base and weld metal as well as HAZ were systematically varied to analyze under-matching, even-matching and over-matching conditions in creep. In order to investigate the effect of the loading mode, FEA was carried out under internal pressure and in-plane bending to the branch pipe. Two geometries such as large bore branch and medium bore branch were considered. It was found that steady-state creep stresses within HAZ can be quantified as mismatch factor with specific characteristics.

This paper derives analytical solutions of the elastic follow-up factor for power-law creeping cruciform plates under bi-axial displacements to investigate the effect of multi-axial stress states on elastic follow-up behaviors. Validity of the proposed solutions is checked against the results from finite element analyses using power-law creep material. Based on proposed solutions, effects of the biaxiality, geometry, Poisson’s ratio and creep exponent on elastic follow-up factors are discussed. Present results show that the elastic follow-up factor for structure with structural discontinuity can be significantly affected by the multi-axial stress states.Copyright © 2011 by ASME

Finding plastic (limit) loads for elbows under various loading conditions such as in-plane bending and out-of-plane bending is not an easy task due to complexities involved in plastic analyses. Considering complexities involved in plastic limit analysis of elbow, deriving analytical solutions of plastic loads for elbows would be extremely difficult. So, recently the limit analysis using finite element program has been widely adopted. Based on extensive and systematic FE limit analyses using elastic-perfectly plastic materials, closed-form solutions of plastic loads for defect-free elbows under in-plane closing, in-plane opening and out-of-plane bending were presented. This paper summarizes the well-known criteria for finding plastic (limit) loads proposed by ASME BPVC Sec.III [1], Zahoor [4], Chattopadhyay et al. [17] and Kim et al. [19] The purpose of this paper is to integrate and improve the proposed solutions by Kim et al. Also, comparison results with published experimental data are presented. From these results, the pros and cons of each criterion for finding plastic (limit) loads for elbows are discussed.Copyright © 2011 by ASME

In this paper, a prediction of V-factor, the correction factor for the plasticity interaction between the primary stress and secondary stress, for the cracked pipe under combined mechanical and thermal stresses with significant elastic follow-up is presented. Recently, present authors suggested enhanced V-factor solution using failure assessment curve, which is less conservative than R6 code. However, this solution is limited to weak elastic follow-up condition. The degree of elastic follow-up is related to the variations of Vo with β according to this study. Based on this observation, a prediction solution for the V-factor which can be applied to the crack assessment ranging from weak elastic follow-up condition to strong elastic follow-up condition is proposed.Copyright © 2010 by ASME

This paper describe steady state stress distribution into the weld metal of welded branch components using detailed three dimensional elastic creep finite element analyses. In order to show the effect of the loading mode, this research is carried out under various loading conditions such as internal pressure, in-plane bending to the branch pipe and out-of-plane bending to branch pipe. Also, to generalize the unique aspect, three geometries of branch components including welded large bore branch, medium bore branch, and trunnion are considered. It is a well-known fact that the creep strain rate of welds material is faster than that of parent material. Therefore, the creep exponent and constants for the parent and weld metal are systematically varied to analyze under-matching, even-matching and over-matching conditions in creep. It can be shown that mismatch effect can be quantified as mismatch factor with specific characteristics.Copyright © 2010 by ASME

This paper quantifies the effect of the yield strength-to-elastic modulus ratio (yield strain) on plastic loads (defined by the twice-elastic-slope according to the ASME code) for 90° elbows under in-plane and out-of-plane bending. Results are based on extensive and systematic FE limit analyses assuming elastic-perfectly plastic materials. Based on FE results, a simple approximation of plastic loads of pipe bends, incorporating the yield strength-to-elastic modulus ratio effect, is proposed. To validate the proposed approximation, predicted plastic moments are compared with published full-scale pipe test data, showing that the proposed approximation gives overall lower than the FE results and close to experimental values.Copyright © 2008 by ASME

The present work presents plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) FE limit analyses using elastic-perfectly plastic materials. The proposed solutions are valid to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparison with FE results shows good agreement.Copyright © 2007 by ASME

This paper proposes a method to determine the elastic follow-up factors for C(t) -integral under secondary stress. To estimate values of C(t) for secondary stress based on the reference stress method, elastic follow-up factors of cracked structure are needed. The present paper proposes a method to estimate elastic follow-up factors of cracked structure under pure secondary loading. The elastic follow-up factors for plasticity and creep are identical due to Hoff‘s plastic-creep analogy. Thus elastic follow-up factors for C(t) can be determined by elastic-plastic finite element (FE) analyses. To verify this method, FE analyses for circumferential internal axisymmetric cracked pipe under thermal loading was performed. The Proposed approach gives good agreement with FE result.