• Geomechanics and Engineering
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• v.14 no.2
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• pp.203-209
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• 2018

Reliable estimation of compressive as well as tensile in-situ stresses is critical in the design and analysis of underground structures and openings in rocks. Kaiser effect technique, which uses acoustic emission from rock specimens under cyclic load, is well established for the estimation of in-situ compressive stresses. This paper investigates the Kaiser effect on marble specimens under cyclic uniaxial compressive as well as cyclic uniaxial tensile conditions. The tensile behavior was studied by means of Brazilian tests. Each specimen was tested by applying the load in four loading cycles having magnitudes of 40%, 60%, 80% and 100% of the peak stress. The experimental results confirm the presence of Kaiser effect in marble specimens under both compressive and tensile loading conditions. Kaiser effect was found to be more dominant in the first two loading cycles and started disappearing as the applied stress approached the peak stress, where felicity effect became dominant instead. This behavior was observed to be consistent under both compressive and tensile loading conditions and can be applied for the estimation of in-situ rock stresses as a function of peak rock stress. At a micromechanical level, Kaiser effect is evident when the pre-existing stress is smaller than the crack damage stress and ambiguous when pre-existing stress exceeds the crack damage stress. Upon reaching the crack damage stress, the cracks begin to propagate and coalesce in an unstable manner. Hence acoustic emission observations through Kaiser effect analysis can help to estimate the crack damage stresses reliably thereby improving the efficiency of design parameters.

• International Journal of Concrete Structures and Materials
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• v.10 no.4
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• pp.435-450
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• 2016

Experimental studies were conducted on 36 grouted splices to investigate their mechanical performance under four loading schemes: (1) incremental tensile loading, (2) repeated tensile loading, (3) cyclic loading at high stress, and (4) cyclic loading at large strain. Load-deformation responses of the grouted splices under cyclic loadings were featured with pinching effect and stiffness degradation compared to those responses under tensile loadings. The shape of the hysteresis loops of load-deformation curves was similar to that under incremental tensile loading. For the purpose of structural analysis, stress-strain relationships were presented for grouted splices under various loadings.

• Journal of Biomedical Engineering Research
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• v.19 no.5
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• pp.495-502
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• 1998

A mathematical model of viscoelasticity on the material property of human pharyngeal tissue utilizing Y.C. Fung's Quasi-linear viscoelastic theory is proposed based on cyclic load, stress relaxation, incremental load, and uniaxial tensile load tests. The material properties are characterized and compared with other biological materials' results. The mathematical model is proposed by combining two characteristic functions determined from the stress relaxation and uniaxial tensile load tests. The reduced stress relaxation function G(t) and elastic response function S(t) are obtained from stress relaxation test and uniaxial tensile load test results respectively. Then the model describing stress-time history of the tissue is implemented utilizing two functions. The proposed model is evaluated and validated by comparing the model's cyclic behaviour with experimental results. The model data could be utilized as an important information for constructing 3-dimensional biomechanical model of human pharynx using FEM(Finite Element Method).

• Journal of Welding and Joining
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• v.34 no.4
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• pp.28-33
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• 2016

The purpose of this study is to evaluate the redistribution of transverse residual stress in the multi-pass FCA butt weld of YP47 in the hatch coaming top plate of ultra large size containership under the tensile cyclic load. In order to do it, the configuration of modified H type specimen including restraint length was first designed to simulate the restraint condition of the butt weld in hatch coaming top plate. FE analysis procedure for evaluating the transverse residual stress was verified by comparing the calculated mean and surface residual stresses with the measured results in the test specimen. After that, the effect of the cyclic load on the redistribution of transverse residual stress was evaluated by comprehensive FEA. From the results, it was found that although the maximum transverse residual stress decreased with an increase in the applied maximum load, the effect of the cyclic load on the mean residual stress is small enough to be negligible. It is because the maximum stress of the ship corresponding to the probability of 10E-8 is less than 70% of yield stress of the weld.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.868-880
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• 2020

One of the main concerns in the structural integrity of offshore pipelines is mechanical damage from external loads. Pipelines are exposed to fatigue failure in welded joints due to geometric discontinuity. In addition, fatigue loads such as currents, waves, and platform motions may cause significant plastic deformation and fracture or leakage within a relatively low-cycle regime. The 2007 ASME Div. 2 Code adopts the master S―N curve for the fatigue evaluation of welded joints based on the mesh-insensitive structural stress. An extension to the master S―N curve was introduced to evaluate the low-cycle fatigue strength. This structural strain method uses the tensile properties of the material. However, the monotonic tensile properties have limitations in describing the material behavior above the elastic range because most engineering materials exhibit hardening or softening behavior under cyclic loads. The goal of this study is to extend the cyclic stress-strain behavior to the structural strain method. To this end, structural strain-based procedure was established while considering the cyclic stress-strain behavior and compared to the structural strain method with monotonic tensile properties. Finally, the improved prediction method was validated using fatigue test data from full-scale girth-welded pipes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1446-1455
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• 2000

Fatigue crack initiation and propagation behavior under cyclic biaxial loading has been investigated using thin-walled tubular specimen with a hole. Two types of biaxial loading system, i.e. cyclic tensile loading with super-imposed static torsional load and cyclic torsional loading with superimposed static tensile load, with various values of the biaxial loading ratio, $\tau$ s/ $\sigma$ max (or $\tau$ max/ $\sigma$s) were employed. Fatigue tests show that fatigue crack near the hole initiates and propagates at 900 and 450 direction to the longitudinal direction of the specimen under cyclic tensile and torsion loading with static biaxial stress, respectively, and the static biaxial stress doesn't have any great influence on fatigue crack initiation and growth direction. Stress analysis near the hole of the specimen shows that the crack around the hole initiates along the plane of maximum tangential stress range. Fatigue crack growth rates were evaluated as functions of equivalent stress intensity factor range, strain energy density factor range and crack tip opening displacement vector, respectively. It is shown that the biaxial mode fatigue crack growth rates can be relatively consistently predicted with these cyclic parameters.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.239-248
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• 2002

A constitutive model unifying plasticity and crack damage mode)s was developed to address the cyclic behavior of reinforced concrete planar members. The stress of concrete in tension-compression was conceptually defined by the sum of the compressive stress developed by the strut-action of concrete and the tensile stresses developed by tensile cracking. The plasticity model with multiple failure criteria was used to describe the isotropic damage of compressive crushing affected by the anisotropic damage of tensile cracking. The concepts of the multiple fixed crack damage model and the plastic flow model of tensile cracking were used to describe the tensile stress-strain relationship of multi-directional cracks. This unified model can describe the behavioral characteristics of reinforced concrete in cyclic tension-compression conditions, i.e. multiple tensile crack orientations, progressively rotating crack damage, and compressive crushing of concrete. The proposed constitutive model was implemented to finite element analysis, and it was verified by comparison with existing experimental results from reinforced concrete shear panels and walls under cyclic load conditions.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1784-1787
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• 2008

Molecular dynamics (MD) simulations are used to analyze behavior of copper nanowires under cyclic loading. The embedded atom method (EAM) potential is employed to represent atomic interaction. Cyclic load is applied in two ways (Forward Tension / Reverse Compression and Forward Compression / Reverse Tension). The results show that dislocations are piled up as a result of plastic deformation during alternate tensile and compressive loading. After cyclic loading with a change of direction, yield stress decreases in consequence of the effect by the dislocation pileups. On the other hand, under FC/RT cyclic load, phase transformation represent associated with mechanical twinning. And copper nanowire can return to almost former undeformed condition during tensile loading at 300K.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1970-1981
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• 1999

The low-cycle fatigue behaviour of a SiC-particulate-reinforced Al-Si cast alloy with two different volume fractions has been investigated from a series of strain-control led fatigue tests with zero and nonzero tensile mean strains. The composites including the unreinforced matrix alloy, exhibited cyclic hardening behaviour, with more pronounced strain-hardening for the composites with a higher volume fraction of the SiC particles. For the tensile mean strain tests, the initial high tensile mean stress relaxed to zero for the ductile Al-Si alloy, resulting in no influence of the tensile mean strain on the fatigue life of the matrix alloy. However, tensile mean strain for the composite caused tensile mean stresses and reduced fatigue life. The pronounced effects of mean strain on the low-cycle fatigue life of the composite compared to the unreinforced matrix alloy were attributed to the initial large prestrain and non-relaxing high tensile mean stress in the composite with very limited ductility and Cyclic plasticity. Fatigue damage parameter using strain energy, density efficiently accounted for the mean stress effects. Predicted fatigue life using the damage parameter correlated fairly well with the experimental life within a factor of 3. Also, the fatigue damage parameter indicated the inferior life in the low-cycle regime and superior life in the high-cycle regime for the composite, compared to the unreinforced matrix alloy.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1422-1430
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• 1995

Al6061 alloy reinforced with 15 volume% of Saffil fibers was fabricated by squeeze infiltration method. Uniform distribution of reinforcements and good bondings between reinforcements and matrix alloy were found in the microstructure of composites. Comparing with A16061 matrix alloy, tensile strength and elastic modulus of $Al_{2}$O$_{3}$/Al composites were increased up to 26% and 31%, respectively. Cyclic deformation and fatigue behavior of $Al_{2}$O$_{3}$/Al metal matrix composites were studied. The specimens were cycled using tension-tension(R=0.1) loading and under load controlled fatigue test. Cyclic stress-displacement curve through fatigue test was obtained. Fatigue strength of $Al_{2}$O$_{3}$/Al composites was about 200 MPa, i.e.0.55 of applied stress level(q). During fatigue test, $Al_{2}$O$_{3}$/Al composites displayed cyclic hardening at all applied stress levels. The most of resultant displacement due to permanent plastic deformation occurred in less than the first 5% of fatigue life. Displacement-to-failure of the fatigue test was smaller than that of the tensile test because of accumulative damage by cumulative plastic deformation.