• 대한기계학회논문집A
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• 제27권2호
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• pp.239-246
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• 2003

This paper proposes engineering estimation equations of elastic-plastic J and COD fur axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length. and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a reformulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.421-428
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• 2004

Various type of welded joints of the ship structure have been examined numerically and experimentally under bending and tensional cyclic constant-amplitude loading. Cyclic loading on structures can produce failures not readily predicted by conventional static analysis. The aim of a benchmark study is achieved with a generalization of the reference stress concept. Also different methods and procedures exist for the computation of the welded structure hot-spot stress a welded joints. These are either based on the extrapolation of stresses at certain reference points on the plate surface (or edge) close to the weld toe-as known from experimental investigations- or on the linearization of stresses in the through-thickness direction. In the present paper, the different methods are reviewed and applied to four different details in order to compare the methods with each other and to illustrate the differences.

• 대한기계학회논문집A
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• 제25권3호
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• pp.548-553
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• 2001

A new method to estimate the elastic-plastic J-integral and the crack tip opening displacement (COD) for circumferential through-wall cracked pipes under tension and under bending is proposed for Leak-Before-Break (LBB) analysis. Being based on the reference stress method with further modifications, the proposed method is simple to use and easy to be generalised in practice. Comparison of the CODs, predicted using the proposed method with published pipe test data show overall excellent agreement.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1235-1241
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• 2001

An engineering estimation equation for the crack opening displacement(COD) is proposed for a complex cracked pipe, based on the reference stress approach. To define the reference stress, a simple plastic limit load analysis for the complex cracked pipe subjected to combined bending and tension is performed considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results.

• 대한기계학회논문집
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• 제4권3호
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• pp.113-118
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• 1980

Stresses were calculated for finite-width orthotropic laminates with a circular hole and remote uniaxial loading using a two-dimensional finite-element analysis with both uniform stress and uniform displacement boundary conditions. Five different laminates were analyzed: quasi-isotropic [0.deg./.+-.45.deg./90.deg.].$\_$s/, 0.deg., 90.deg., [0.deg./90.deg.]$\_$s/, and [.+-.45.deg.]$\_$s/, Computed results are presented for selected combinations of hole diameter-sheet-width ratio d/w and length-to width ratio L/w. For small L/w values, the stress-concentration factors K$\_$tn/ were significantly different for the uniform stress and uniform displacement boundary conditions. Typically, for the uniform stress conditions, the K$\_$tn/ values were much larger than for the infinite-strip reference conditions; however, for the uniform displacement conditon, they were only slighty smaller than for this reference. The results for long strips are also presented as width-correction factor. For d/w.leg.33, these width-correction factors are nearly equal for all five laminates.

• 대한기계학회논문집A
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• 제27권4호
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• pp.638-646
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• 2003

This paper presents experimental validation of the enhanced reference stress based J estimates for circumferential through-wall cracked pipes. recently proposed by authors. Using the pipe test data for circumferential through-wall cracked pipes, the predicted fracture initiation and maximum moments according to the proposed enhanced reference stress method are compared with experimental ones as well as predictions from the R6 method. The results show that both the R6 method and the proposed method give conservative estimates of initiation and maximum moments for circumferential through-wall cracked pipes, compared to experimental data. For longer cracks, the proposed method reduces conservatism embedded in estimated J according to the R6 method, and the resulting predictions are less conservative, compared to those from the R6 method. For shorter cracks, on the other hand, the proposed method reduces possible non-conservatism embedded in estimated J according to the R6 method, and the resulting predictions are slightly more conservative.

• 대한기계학회논문집A
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• 제25권4호
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• pp.741-747
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• 2001

Three-dimensional, elastic-plastic finite element analyses for circumferential through-wall cracked pipes are performed using actual tensile data of stainless steels, for two purposes. The first one is to validate the recently-proposed enhanced reference stress (ERS) method to estimate the J-integral and COD for circumferential through-wall cracked pipes. The second one is to compare those results with the GE/EPRI estimations. It is found that the J-integral and COD estimations according to the GE/EPRI method can be very sensitive to how the stress-strain data are fitted using the Ramberg-Osgood relation. Moreover, no tendency can be found regarding the most appropriate fitting range for the Ramberg-Osgood fit. On the contrary, the J-integral and COD estimations based on the ERS method give more accurate results than the GE/EPRI estimation. The present results provide confidence in applying the proposed method to the Leak-Before-Break(LBB) analysis.

• Structural Engineering and Mechanics
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• 제12권6호
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• pp.685-698
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• 2001

In this paper, a general method for the automatic search for Strut-and-Tie (S&T) models representative of possible resistant mechanisms in reinforced concrete elements is proposed. The representativeness criterion here adopted is inspired to the principle of minimum strain energy and requires the consistency of the model with a reference stress field. In particular, a highly indeterminate pin-jointed framework of a given layout is generated within the assigned geometry of the concrete element and an optimum truss is found by the minimisation of a suitable objective function. Such a function allows us to search the optimum truss according to a reference stress field deduced through a F.E.A. and assumed as representative of the given continuum. The theoretical principles and the mathematical formulation of the method are firstly explained; the search for a S&T model suitable for the design of a deep beam shows the method capability in handling the reference stress path. Finally, since the analysis may consider the structure as linear-elastic or cracked and non-linear in both the component materials, it is shown how the proposed procedure allows us to verify the possibilities of activation of the design model, oriented to the serviceability condition and deduced in the linear elastic field, by following the evolution of the resistant mechanisms in the cracked non-linear field up to the structural failure.

• 항공우주시스템공학회지
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• 제9권4호
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• pp.31-36
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• 2015

The fatigue analysis for cutout panel used for the weight reduction of aircraft has been conventionally performed through the open hole concept using the reference stress and stress concentration factor (Kt). However, in the actual structure cases, the goal of weight reduction might be less meaningful due to the conservative approach induced by the difficulties of extracting the confident reference stress from FE-Analysis in the complicated loading behavior. Therefore a new approach is proposed in order to secure the effectiveness of weight reduction and validate the confidence of the analysis results using the interaction of max-min principal stress at the critical location of open hole edge line.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1824-1829
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• 2007

In the present paper, limit pressures for axial surface cracked pipe are proposed, and a reference stress based J estimation method is also provided based on the proposed limit pressure solutions. Employed cracks are assumed to be constant-depth, internal surface cracks, and wide ranges of variables are considered.