• Journal of Aerospace System Engineering
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• v.17 no.2
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• pp.1-8
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• 2023

Power transmission shafts in rotary wing aircraft use a hollow shaft to reduce weight. We can apply linear elastic fracture mechanics to predict crack propagation behavior. This paper predicted crack growth life of a hollow shaft with a circumferential through-type crack by finite element analysis. A 2D finite element model was created by applying a torsion and forming elements considering cracks. We defined the initial crack length and performed the finite element analysis by increasing the crack length to derive stress intensity factor at crack tips. We defined the length just prior to the stress intensity factor exceeding the fracture toughness as the crack limit length. We calculated the crack limit length using a handbook and numerically integrated the crack growth rate equation to derive growth life of each crack. The growth life of each crack was compared to verify the proposed finite element analysis method.

• Journal of the Korean GEO-environmental Society
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• v.12 no.5
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• pp.59-63
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• 2011

Ground dynamic parameter such as shear elastic modulus and damping ratio is a very important variable in design of ground-structure with repeated load and dynamic load. Shear elastic modulus and damping ratio on small strain below linear limit strain is constant regardless of strain. Shear elastic modulus as the maximum shear elastic modulus and damping ratio as the minimum damping ratio were considered. As a lot of experiment related to the maximum shear elastic modulus, which is in dynamic deformation characteristics, have been conducted, many factors including voiding ratio, over consolidation ratio(OCR), confining pressure, geology time, PI, and the number of load cycle affect to dynamic soil characteristic. However, the research of ground dynamic characteristic improved with grout is absent such as underground continuous wall construction, deep mixing method, umbrella arch method. In order to investigate the dynamic soil characteristics improved with grout, in this study, resonant column tests were performed with changing water content(20%, 25%, 30%) and injection ratio of grout(5%, 10%, 15%), cure time(7th day, 28th day) As a result, shear elastic modulus and damping ratio, which are ground dynamic parameter, are affected by the injection ratio of milk grout, cure time and water content.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.8 s.251
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• pp.931-940
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• 2006

Defect assessment of a weld zone is important in fitness-for-service evaluation of plant components. Typically a J and $C^*$ estimation method for a defective homogeneous component is extended to a mismatched component, by incorporating the effect due to the strength mismatch between the weld metal and the base material. The key element is a mismatch limit load. For instance, the R6/R5 procedure employs an equivalent material concept, defined by a mismatch limit load. A premise is that if a proper mismatch limit load solution is available, the same concept can be used for any defect location (either a weld centre defect or a heat affected zone (HAZ) defect) and for any material combination (either two-material or multi-material combinations; either similar or dissimilar joints). However, validation is still limited, and thus a more systematic investigation is needed to generalise the suggestion to any geometry, any defect location and any material combination. This paper describes the effect of structural geometry on the $C^*$ integral for defective similar welds, based on systematic elastic-creep 2-D and 3-D finite element (FE) analyses, to attempt to elucidate the questions given above. It is found that the existing 'equivalent material' concept is valid only for limited cases, although it provides conservative estimates of $C^*$ for most of cases. A modification to the existing equivalent material concept is suggested to improve accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1379-1386
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• 2013

The present work reports the mismatch limit loads for a V-groove welded pipe for a circumferential crack using finite element (FE) analyses. To integrate the effect of groove angles on mismatch limit loads, one geometry-related slenderness parameter was modified by relevant geometric parameters including the groove angle, crack depth, and root opening based on plastic deformation patterns in the theory of plasticity. Circumferential through-wall cracks are located at the centre of the weldments with two different groove angles ($45^{\circ}$, $90^{\circ}$). With regard to the loading conditions, axial (longitudinal) tension and bending are applied for all cases. For the parent and weld metal, elastic-perfectly plastic materials are considered to simulate and analyze under- and over-matching conditions in plasticity. The overall results from the proposed solutions are found to be similar to the FE results.

• Structural Engineering and Mechanics
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• v.39 no.6
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• pp.795-812
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• 2011

Estimation of damage probability of buildings under a future earthquake is an essential issue to ensure the seismic reliability. Fragility curves are useful tools for showing the probability of structural damage due to earthquakes as a function of ground motion indices. The purpose of this study is to compare the damage probability of R/C buildings with low and high level of strength and ductility through fragility analysis. Two different types of sample buildings have been considered which represent the building types mentioned above. The first one was designed according to TEC-2007 and the latter was designed according to TEC-1975. The pushover curves of sample buildings were obtained via pushover analyses. Using 60 ground motion records, nonlinear time-history analyses of equivalent single degree of freedom systems were performed using bilinear hysteretic model and peak-oriented hysteretic model with stiffness - strength deterioration for each scaled elastic spectral displacement. The damage measure is maximum inter-story drift ratio and each performance level considered in this study has an assumed limit value of damage measure. Discrete damage probabilities were calculated using statistical methods for each considered performance level and elastic spectral displacement. Consequently, continuous fragility curves have been constructed based on the lognormal distribution assumption. Furthermore, the effect of hysteresis model parameters on the damage probability is investigated.

• Structural Engineering and Mechanics
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• v.11 no.2
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• pp.199-210
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• 2001

Axially compressed circular cylinders repeat symmetry-breaking bifurcation in the postbuckling region. There exist stable equilibria with all symmetry broken in the buckled configuration, and the minimum postbuckling strength is attained at the deep bottom of closely spaced equilibrium branches. The load level corresponding to such postbuckling stable solutions is usually much lower than the initial buckling load and may serve as a strength limit in shell stability design. The primary concern in the present paper is to compute these possible postbuckling stable solutions at the deep bottom of the postbuckling region. Two computational approaches are used for this purpose. One is the application of individual procedures in computational bifurcation theory. Path-tracing, pinpointing bifurcation points and (local) branch-switching are all applied to follow carefully the postbuckling branches with the decreasing load in order to attain the target at the bottom of the postbuckling region. The buckled shell configuration loses its symmetry stepwise after each (local) branch-switching procedure. The other is to introduce the idea of path jumping (namely, generalized global branch-switching) with static imperfection. The static response of the cylinder under two-parameter loading is computed to enable a direct access to postbuckling equilibria from the prebuckling state. In the numerical example of an elastic perfect circular cylinder, stable postbuckling solutions are computed in these two approaches. It is demonstrated that a direct path jump from the undeformed state to postbuckling stable equilibria is possible for an appropriate choice of static perturbations.

• Steel and Composite Structures
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• v.18 no.1
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• pp.165-185
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• 2015

The suspended zipper bracing system is suggested to reduce the flaws of ordinary zipper braced and concentric inverted V braced frames. In the design procedure of suspended zipper bracing systems, columns and top story truss elements are strengthened. This bracing system show different performances and characteristics compared with inverted V braced and ordinary zipper frames. As a result, a different response modification factor for suspend zipper frames is needed. In this research paper, the response modification factor of suspended zipper frames was obtained using the incremental dynamic analysis. Suspended zipper braced frames with different stories and bay lengths were selected to be representations of the design space. To analyze the frames, a number of models were constructed and calibrated using experimental data. These archetype models were subjected to 44 earthquake records of the FEMA-P695 project data set. The incremental dynamic analysis and elastic dynamic analysis were carried out to determine the yield base shear value and elastic base shear value of archetype models using the OpenSEES software. The seismic response modification factor for each frame was calculated separately and the values of 9.5 and 13.6 were recommended for ultimate limit state and allowable stress design methods, respectively.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.583-591
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• 2005

The ship plating is generally subjected to combined in-plane load and lateral pressure loads. In-plane loads include axial load and edge shear, which are mainly induced by overall hull girder bending and torsion of the vessel. Lateral pressure is due to water pressure and cargo. These load components are not always applied simultaneously, but more than one can normally exist and interact. Hence, for more rational and safe design of ship structures, it is of crucial importance to bitter understand the interaction relationship of the buckling and ultimate strength for ship plating under combined loads. Actual ship plates are subjected to relatively small water pressure except for the impact load due to slamming and panting etc. The present paper describes an accurate and fast procedure for analyzing the elastic-plastic large deflection behavior up to the ultimate limit state of ship plates under combined loads. In this paper, the ultimate strength characteristics of plates under axial compressive loads and lateral pressure loads are investigated through ANSYS elastic-plastic large deflection finite element analysis with varying lateral pressure load level.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.4 s.247
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• pp.420-427
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• 2006

The structural and leakage integrity of steam generator tubes should be sustained against all postulated loads even if a crack is present. During the past three decades, most of the efforts with respect to integrity evaluation of steam generator tubes have been focused on limit load solutions but, recently, the applicability of elastic-plastic fracture mechanics was examined cautiously due to its effectiveness. The purpose of this paper is to introduce a testing method to estimate fracture resistance characteristics of steam generator tubes with a through-wall crack. Due to limited thickness and diameter, inevitably, the steam generator tubes themselves were tested instead of standard specimen or alternative ones. Also, a series of three dimensional elastic-plastic finite element analyses were carried out to derive closed-form estimation equations with respect to J-integral and crack extension for direct current potential drop method. Since the effectiveness of $J_{IC}$ as well as J-R curves was proven through comparison with those of standard specimens taken from pipes, it is believed that the proposed scheme can be utilized as an efficient tool for integrity evaluation of cracked steam generator tubes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6521-6526
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• 2013

Elastic and nonlinear ultimate strength analyses were conducted to examine the effects of the stiffness and slenderness of flat-type stiffeners on ultimate in-plane strengths of a stiffened plate system. Although it is not feasible to consider local buckling in the stiffeners in elastic analysis, it was confirmed that the in-plane strengths of the stiffened plate system can be achieved by antisymmetric buckling mode when a certain level of stiffness in the stiffeners is provided. Nonlinear ultimate strength analysis, in which initial imperfection and residual stress are incorporated, showed that the ultimate strengths are sensitively affected by the mode shapes for initial imperfections. The slenderness limit for flat-type stiffeners in KHBDC (Korean Highway Bridge Design Code) was evaluated as conservative compared to the analysis results.