• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.765-772
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• 2011

The present study summarizes a series of compressive tests on concrete cylinder in order to examine the stressstrain relationship of alkali-activated (AA) slag concrete. The compressive strength and unit weight of concrete tested ranged from 8.6 MPa to 42.2 MPa and from $2,186kg/m^3$ to $2,343kg/m^3$, respectively. A mathematical equation representing the complete stress-strain curve was developed based on test results recorded from 34 concrete specimens. The modulus of elasticity, strain at peak stress, slopes of ascending and descending branches of stress-strain curves were generalized as a function of compressive strength and unit weight of concrete. The mean and standard deviation of the coefficient of variance between measured and predicted curves were 6.9% and 2.6%, respectively. This indicates that the stress-strain relationship of AA slag concrete is represented properly with more accuracy in the proposed model than in some other available models for ordinary portland cement (OPC) concrete.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.75-82
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• 2001

Static loadings on ship structure induced either by water pressure before service such as a tank test and ballasting or by cargo pressure during first laden voyage cause relatively much greater stress than dynamic loadings induced by wave. With these static pre-loadings, the initial residual stresses around welded joint, where fatigue strength is concerned(in most cases, where stress concentration occurs) are expected to be shaken-down in a great extent by the elasto-plastic deformation behavior of material. Therefore, it is more resonable to assess the fatigue strength of ship structure with S-N data which have taken into account the effect of shaken-down residual stresses(re-distributed stresses) on the fatigue strength. In this research work, the re-distribution of residual stresses by the tensile pre-loading is measured using an ordinary sectioning method for specimens of padding plate weldment. Fatigue tests are performed also to evaluate the fatigue strength of the both as-welded and pre-loaded specimens.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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• pp.35-44
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• 1999

In a view point of earth environmental protection and social requirement, adhesively bonded structures of aluminum alloys have become to be employed for the purpose of decreasing fuel ratio by weight reduction and to improve performance in various engineering fields such as aircrafts, automobiles, rolling stocks and so on. In spite of such wide applications in adhesively bonded structures of aluminum alloys, the quantitative fracture criterion and evolution method of its bonded strength have not been established yet. The objective of this paper is to establish fracture criterion considering stress singularity at interface edges in adhesively bonded structures of aluminum alloys. Through the analyses of boundary element method and static fracture experiments with three different types of specimens in the adhesively bonded joints of aluminum alloys, its fracture criterion was proposed and discussed about strength evolution of adhesively bonded structures.

• Tunnel and Underground Space
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• v.13 no.3
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• pp.180-186
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• 2003

The fracture processes under dynamic loading in tension were simulated using a proposed numerical approach and analyzed to determine dynamic tensile strength. The dynamic tensile strength and the scatter of the strength data decreased with increasing uniformity coefficients. The differences of static and dynamic tensile strength were due to the stress concentrations and redistribution mechanisms in the rock specimen. Although there were different mechanisms for the static and dynamic fracture processes, the static and dynamic tensile strengths were close to the mean microscopic tensile strength at high values of the uniformity coefficient. This paper shows that the rock inhomogeneity has an effect on dynamic tensile strength and is a factor that contributes to the different specimen strengths under dynamic and static loading conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2087-2096
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• 1996

Recentrly advantages in composite and light weight material techniques have led to the increased use of bonded dissimilar materials such as ceramics/metal bonded joints, IC package, brazing, coating and soldering in the various industries. It is required to analyze the evaluation method of fracture strength and design methodology of bonded joints in dissimilar materials. Stress singularity according to changes of scarf angles for bonded scarf joints in dissimilar materials was investigated by the boundary element method and static experiments. In this paper, effect of the stress singularity factors at the interface edges of scarf joints on various dissmilar materials combinations were investigated by analysis of its stress and stress singularity index using 2-dimensional elastic program of boundary element method. And the variations of stress singularity index by changes for Young's modulus ratios of materials and scarf angles were investigated. Also, it is found that stress singularities at bonded interface edges are disappeared for certain combination of scarf angle in a pair of bonded dissimilar materials. As the results, it is proposed that the strength evaluation by using stress singularity factors, $\Gamma$, considering stress singularity at the interface edges of bonded dissimilar materials, is very useful.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.701-713
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• 2000

In this study, the 4-point bending test been performed in order to estimate effect of grinding on fatigue characteristics quantitatively for as-welded specimen, grinding specimen & TIG-dressing specimen for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength at $2{\times}106$cycles of grinding specimen and TIG-dressing specimen has been increased compared with as-welded specimen and satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC. As a result of beachmark test, fatigue cracks on all specimens have occurred at several points where stress

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3035-3043
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• 2015

This study evaluates the thermal structural safety of the three-way catalyst(TWC) substrate for domestic passenger cars. Thermal-fluid boundary conditions on the TWC substrate were determined by D-optimal DOE. The thermal stresses on the TWC substrate were calculated by the temperature distribution obtained from the CFD results. The safety factors of the TWC substrate were determined by statistical strength and stress distributions and estimated to be 0.275. The thermal stresses for TWC substrate exceeded the strength of the material. Therefore, it is necessary to redesign the TWC substrate because it has much shorter service life than design life.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.305-314
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• 2012

This paper presents the quantitative damage assessment of granite taken from KAERI Underground Research Tunnel using acoustic emission (AE). The results determined showed the crack initiation and crack damage stress occurred at 48%, 72% of uniaxial compressive strength (UCS) and until the applied stress level was reached the crack damage stress, the damage degree was 0.06. When the applied stress exceeded 80%, 90% of UCS, the damage degree were 0.34, 0.06 and which were similar to those obtained from axial deformation modulus. The simply regression analysis was used to interpret the relationship of the two damage assessment techniques and the two were highly correlated ($R^2$=0.90). Therefore, damage degree based on the AE energy and mohr-coulomb failure criterion were adopted to predict the mechanical properties. As results, the axial deformation modulus, rock strength, internal friction angle, and cohesion of KURT rock were reduced 6%, 12%, 7%, and 3% until the applied stress was 70% of UCS. But when the applied stress reached 90% of UCS, the results were more reduced 69%, 72%, 62%, and 24%, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3121-3126
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• 2013

The integrity evaluation of pipes in nuclear power plant are essential for the safety of reactor vessel, and integrity must be assured when flaws are found. Accurate stress intensity analyses and crack growth rate data of surface-cracked components are needed for reliable prediction of their fatigue life and fracture strengths. Fatigue design and life assessment are the essential technologies to design the structures such as pipe, industrial plant equipment and so on. The effect of crack spacing on stress intensity factor K values was studied using three-dimensional finite element method (FEM). For the case of cylinder under internal pressure, a significant increase in K values observed at the deepest point of the surface crack. Also, this paper describes the fatigue analysis for cracked structures submitted to bending loads.

• Computational Structural Engineering
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• v.11 no.1
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• pp.153-160
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• 1998

A small break loss of coolant accident is postulated as a pressurized thermal shock accident in this study. From the temperature and pressure histories of coolant, distributions of the temperature and stress in a vessel wall are analytically calculated. The stress intensity factor and fracture toughness of the vessel wall are determined at the crack tip using the ASME code method and they are compared to check if cracking is expected to occur during the transient postulated. The maximum allowable reference nil-ductility transition temperatures are determined for various crack sizes and the results are discussed.