• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1332-1338
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• 2003

To estimate the true wear rate of polyethylene acetabular cups used in total hip arthroplasty, the dynamic compressive creep deformation of ultra-high molecular weight polyethylene (UHMWPE) was quantified as a function of time, load amplitude, and radial location of the specimen in the extruded rod stock. These data were also compared with the creep behavior of polyethylene observed under static loading. Total creep strains under dynamic loading were only 64％, 70％, and 61％ of the total creep strains under static loading at the same maximum pressures of 2 MPa,4 MPa, and 8 MPa, respectively. Specimens cut from the periphery of the rod stock demonstrated more creep than those cut from the center when they were compressed in a direction parallel to the extrusion direction (vertical loading) whereas the opposite was observed when specimens were compressed in a direction perpendicular to the extrusion direction (transverse loading). These findings show that creep deformation of UHMWPE depends upon the orientation of the crystalline lamellae.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.295-298
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• 2005

A minimum commitment method (MCM) was applied to predict the creep rupture life of type 316LN SS. For this purpose, a number of the creep rupture data for the type 316LN SS were collected through literature survey and experimental data of KAERl, Using the short-term creep rupture data under 2000 hr, the long-term creep rupture life above $10^5$ hour was predicted by means of the MCM. An optimum value of A, P and G function, used in the MCM equation, was determined respectively, and the creep rupture life with the A values in different temperatures was compared with the experimental data and the predicted curves.

• 전기의세계
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• v.23 no.2
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• pp.55-61
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• 1974

Nature of magnetic creep phenomena in low coercive force films(Ni 80%-Fe 20%) in form of narrow channels imbedded in high coercive force films is studied in this work. Aluminium is evaporated on the hot glass substrate and eched free in the shape of narrow channels by photoetoetching method. then, Permalloy(Ni 80%, Fe 20%) is deposited on these Aluminium substrate under the uniform field of 30(Oe) to introduce anisotropy. Permalloy film on Al has a high coercive force and one on the substrate devoid of Al has how coercive force. Magnetic revers domain which is introduced at the end of channel grows under the a.c field in hard axis direction, in spite of very weak d.c field in easy axis direction. This creeping is investigated as a function of external fields and channel widths. Permalloy film thickness is 500.angs.-900.angs. and channel widths are 40, 51, 65, 81, 115.mu. respectively. Creeping increases as external field increases while it decreases with channel width decrease. Creep velocity in channels depends on the a.c field along hard axis, d.c field along easy axis and channel widths and its range is 1-10cm/sec in this experiment. From study of dependence of creep velocity on channel width, it can be concluded that creep velocity is expressed in form of v=v$_{0}$ exp .alpha.(H-H$_{0}$) where .alpha. is a function of a.c field along hard axis and H is driving d.c field along easy axis, H$_{0}$ is not a coercive force of film as usuall expected but the d.c threshold field along easy axis which is a function of channel width. This characteristic is also confirmed by the study of dependence of creep velocity upon easy axis field strength. Value of .alpha. obtained is 1.3-2.3cm/sec We depending upon film charactor, hard axis field strength and frequency.uency.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.408-415
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• 1998

The analysis model is the power law creep material containing an elliptical rigid inclusion subjected to the arbitrarily directional stress on infinite boudary. The stress analysis is performed using the conformal mapping function and complex pseudo-stress function. The stress distributions near an elliptical rigid inclusion are obtained with various ellipse shapes, strain hardening exponents and directions of applied stress.

• International Journal of Automotive Technology
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• v.6 no.1
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• pp.45-52
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• 2005

Interrupted creep tests for investigating the structural degradation during creep were conducted for a Mod.9Cr-1Mo steel in the range of stress from 71 to 167 MPa and temperature from 873 to 923 K. The change of hardness and tempered martensitic lath width was measured in grip and gauge parts of interrupted creep specimens. The lath structure was thermally stable in static conditions. However, it was not stable during creep, and the structural change was enhanced by creep strain. The relation between the change in lath width and creep strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep LCR(life consumption ratio). Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep LCR. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.92-99
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• 2020

High-temperature mechanical behaviors of Type 316L stainless steel (SS), which is considered as one of the major structural materials of Generation-IV nuclear reactors, were investigated through the tension and creep tests at elevated temperatures. The tension tests were performed under the strain rate of 6.67×10^-4 (1/s) from room temperature to 650℃, and the creep tests were conducted under different applied stresses at 550℃, 600℃, 650℃, and 700℃. The tensile behavior was investigated, and the modeling equations for tensile strengths and elongation were proposed as a function of temperature. The creep behavior was analyzed in terms of various creep equations: Norton's power law, modified Monkman-Grant relation, damage tolerance factor(λ), and Z-parameter, and the creep constants were proposed. In addition, the tested tensile and creep strengths were compared with those of RCC-MRx. Results showed that creep exponent value decreased from n=13.55 to n=7.58 with increasing temperature, λ = 6.3, and Z-parameter obeyed well a power-law form of Z=5.79E52(σ/E)^9.12. RCC-MRx showed lower creep strength and marginally different in creep strain rate, compared to the tested results. Same creep deformation was operative for dislocation movement regardless of the temperatures.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1329-1339
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• 1993

Creep tests were performed to determine the nonlinear viscoelastic properties of apples and pears with the creep experiment apparatus designed in this study. Compressive creep characteristics of fruits were tested at two kinds of storage conditions, four periods of storage and three levels of initial stress. Ten replications were made at each treatment combination. The creep behavior of the fruits could be well described by the nonlinear viscoelastic model as a function of initial stress and time. however, for each level of initial stress applied, the compressive behavior of the samples was satisfactorily represented by Burger's model. For all sample fruits, the longer the samples was stored, the higher the instantaneous elastic strain was observed, and the creep progressed at a high rate. These phenomena were even more remarkable on the fruit stored at the normal temperature storage rather than at the low temperature storage.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.293-298
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• 2008

This paper attempts to quantify the effect of mismatch in creep properties on steady-state stress distributions for a welded branch vessel. A particular geometry for the branch vessel is chosen. The vessel is modeled by only two materials, the base and weld metal. Idealized power law creep laws with the same creep exponents are assumed for base and weld metals. A mismatch factor is introduced, as a function of the creep constant and exponent. Steady-state stress distributions within the weld metal, resulting from threedimensional, elastic-creep finite element (FE) analyses, are then characterized by the mismatch factor. We can find that average stresses in the weld can be characterized by the mis-match factor. And there is an analogy between elastic-creep and elastic-perfectly plastic.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.131-140
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• 1993

The activation energy for high temperature creep is associated with stresses, temperatures, straians And the creep strain appears to be a function of a temperature, compensated time, namely $te^{-}$.DELTA.H/RT/, and the stress. In fact this functional relation appears to be isomorphic to material structure by x-ray analyses. Applying this functional relation, the dependance of activation energy for A17075 creep was investigated. The activation energy for creep is insensitive to stress, temperature, structure, and strain. And phenomenological model agrees with experimental creep data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.4
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• pp.143-148
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• 1983

A general numerical procedure for the time dependent analysis of concrete structures due to the effects of creep, shrinkage, aging of concrete and temperature variations is presented. Creep is represented by a superposition integral, and is considered as dependent on concrete age and temperature. An efficient numerical formulation of creep is possible through the use of a special exponential form of specific creep function which forms the kernel function of the superposition integral. The accuracy of this method is demonstrated by a numerical example.