• Journal of Welding and Joining
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• v.13 no.2
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• pp.60-67
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• 1995

The factors affecting on the fatigue strength of spot_welded specimens have been studied. The influence of initial overloads on the fatigue life of spot_welded tensile_shear specimens is investigated by considering fatigue crack initiation and crack propagation. The change of strain range and the influence of initial overload are correlated on the basis ol strain results. The results of this study are as follows. l) The initial absolute strain range decreased with initial overloads increase, and absolute strain range decreased before transformation of waveform of strain, but increased after transformation of waveform of strain. 2) In case of subsequent point of inflection of offset strain, the increment of this strain decreased with initial overload increase. 3) As initial overloads increase, the deformation behavior of spot welded parts is restricted after overloading.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1192-1202
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• 1994

Fatigue behavior and life prediction were presented for thermal-mechanical and isothermal low cycle fatigue of 12Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test at 350 to 600.deg. C and isothermal low cycle fatigue test at 600.deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Cyclic softening behavior was observed regardless of thermal-mechanical and isothermal fatigue tests. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. The difference in fatigue lives was dependent upon the magnitudes of inelastic strain ranges and mean stresses. Increase in inelastic strain range showed a tendency of intergranular cracking and decrease in fatigue life, especially for out-of-phase thermal-mechanical fatigue. Thermal-mechanical fatigue life prediction was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase thermal-mechanical fatigue lives, which was quite improved conservatively by a proposed strain range partitioning method.

• Korean Journal of Microbiology
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• v.10 no.1
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• pp.9-28
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• 1972

1. To get the suitable yeasts for the tratment of waste liquor from pulp and paper industries, the 162 yeasts were isolated from the waste liquor, decayed trees and sewage (1, 7, 8, 9, 1971). 17 species were chosen by its ability to assimilate the carbon compounds and indentified. 2. All of the strain was increased its growing ability by agitation. In particular, the strain 912, strain 613, strain 100, strain 732 showed excellent high productive ratio(A/$A_{0}$). 3. The optimum temperature of the strains rangel $27^{\circ}C$ and $30^{\circ}C$. 4. Most of the strain was grown actively in 10C/5N-composition and strain 113, strain 432, strain 735, strain 936, and strain 912 showed its optimum growing in 15C/5N-composition and 5C/5N-composition, respectively. 5. The optimum pH of the strains lay within range pH 4.5-6. Effect of the variation of pH on the growth was nearly negligible within this range. 6. The strain 912, strain 100, strain 613, strain 311, strain 235, and strain 732 were expected for the utilization to the treatment of the waste liquor from pulp and paper industries.

• Journal of Welding and Joining
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• v.12 no.1
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• pp.73-79
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• 1994

Low cycle fatigue test was performed by companion specimens method to compare the properties of cyclic strain for the weldments of controlled rolling steel CR60 and welding structural steel SM58Q. And the result does not showed any difference of low cycle fatigue life between weldments. Especially, the values of coefficient of cyclic plastic strain $C_{p}$ and exponent of cyclic plastic strain $K_{p}$ of heat affected zones of CR60 steel and SM58Q steel were same. And $C_{p}$ and $K_{p}$ of CR60 steel were equal to the values of weld it means a good combination between the base metal, the heat affected zone and the weld of CR60 steel.eel.eel.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.5
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• pp.793-801
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• 1990

A single mode fiber-optic Mach-Zehnder interferometer for the measurement of strain is described. A fiber-optic strain gauge with great resolution and wide measurement range is realized. In order to varify the dynamic response, the measurements of strain below 1涅 with frequency range 5-50Hz are compared with a semiconductor strain gauge. We report theoretical evaluation for mechanical analysis, PZT-plate, the phase change in a fiber-optic strain gauge and a semiconductor strain gauge. The dynamical characteristics of a fiber-optic strain gauge and a semiconductor strain gauge output siganl show equivalent behavior. This result is shown in very good usage as the dynamical measurement of the low strain below 1涅 by this system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1856-1863
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• 2003

Overlay model had several advantages to describe hysteretic behavior of material and showed good capability for many engineering materials. However, this model is only applicable to material obeying Masing postulate. Some materials such as 316L stainless steel do not follow Masing postulate and show cyclic hardening(or softening) and strain range dependence. Low cycle fatigue tests of 316L stainless steel at 600$^{\circ}C$ were performed to investigate the characteristics of cyclic behavior of non-Masing material. From all tests cyclic softening was observed. There were differences in elastic limit of hysteresis loop according to applied strain range. To consider these features, modified overlay model was developed. Yield stresses of subelements were divided into isotropic and anisotropic part to describe the non-Masing behavior. The plastic strain range memorization was introduced to consider the strain range dependence. The prediction using modified overlay model showed a good accordance to actual hysteresis loops.

• Korean Journal of Materials Research
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• v.6 no.6
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• pp.561-567
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• 1996

The grain size effect on grain boyndary cracking in Pb-Sn eutectic during isothermal fatigue was investigated. Fatigue experiments were confined to two conditions : (1) 0.4% total strain range(approximetely 0.2% plastic strain range), 1.67$\times$10$^{-3}$/s frequency; and (2) 1.5% total strain rante(approximately 1.2% plastic strain range), 8.33$\times$10$^{-4}$/s frequency. Fatigue specimens were cross-sectioned to monitor the depth of crack growth continuosly and then, the maximum crack depths in units of the number of boundaries were plotted as functions of number of cycles for these two different strain ranges. The results revealed that the rate of crack growth(per cycle at fixed rate of crosshead motion) can be expressed as dc/dN=($\Delta$$\varepsilon$$_p$)$^n$c where n is typically 2, c is the crack length, $\Delta$$\varepsilon$$_p$ is the plastic strain range, and A is a "constant" that depends on whether the crack is deeper or shallower than its first triple point of the grain boundary, A decrdases by about a factor of three after the crack hits the first triple point, indecating that the fatigue crack is trapped at the triple point of the grain boundaries.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.1022-1025
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• 2001

This paper presents the characteristics of TaN thin-film as high-temperature strain gauges, which were deposited on Si substrate by DC reactive magnetron sputtering in an argon-nitrogen atmosphere(Ar-(4∼20%)N$_2$). The electrical and mechanical characteristics of these films investigated with the thickness range 1650∼1870${\AA}$ and room temperature resistivities in the range 178.3 ${\mu}$$\Omega$cm to 3175.7 ${\mu}$$\Omega$cm. The TaN thin-film strain gauge deposited in Ar-(20%)N$_2$atmosphere is obtained a temperature coefficient of resistance(TCR), 0∼-1357 ppm/$^{\circ}C$ in the temperature range 25∼275$^{\circ}C$ and a high temporal stability with a longitudinal gauge factor, 2.92∼3.47. Because of their high resistivity, low TCR and linear gauge factor, these cermet thin-film may allow high-temperature strain gauges miniaturization.

• Korea-Australia Rheology Journal
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• v.18 no.2
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• pp.67-81
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• 2006

Using a strain-controlled rheometer, the dynamic viscoelastic properties of aqueous xanthan gum solutions with different concentrations were measured over a wide range of strain amplitudes and then the linear viscoelastic behavior in small amplitude oscillatory shear flow fields was investigated over a broad range of angular frequencies. In this article, both the strain amplitude and concentration dependencies of dynamic viscoelastic behavior were reported at full length from the experimental data obtained from strain-sweep tests. In addition, the linear viscoelastic behavior was explained in detail and the effects of angular frequency and concentration on this behavior were discussed using the well-known power-law type equations. Finally, a fractional derivative model originally developed by Ma and Barbosa-Canovas (1996) was employed to make a quantitative description of a linear viscoelastic behavior and then the applicability of this model was examined with a brief comment on its limitations. Main findings obtained from this study can be summarized as follows: (1) At strain amplitude range larger than 10%, the storage modulus shows a nonlinear strain-thinning behavior, indicating a decrease in storage modulus as an increase in strain amplitude. (2) At strain amplitude range larger than 80%, the loss modulus exhibits an exceptional nonlinear strain-overshoot behavior, indicating that the loss modulus is first increased up to a certain strain amplitude(${\gamma}_0{\approx}150%$) beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (3) At sufficiently large strain amplitude range (${\gamma}_0>200%$), a viscous behavior becomes superior to an elastic behavior. (4) An ability to flow without fracture at large strain amplitudes is one of the most important differences between typical strong gel systems and concentrated xanthan gum solutions. (5) The linear viscoelastic behavior of concentrated xanthan gum solutions is dominated by an elastic nature rather than a viscous nature and a gel-like structure is present in these systems. (6) As the polymer concentration is increased, xanthan gum solutions become more elastic and can be characterized by a slower relaxation mechanism. (7) Concentrated xanthan gum solutions do not form a chemically cross-linked stable (strong) gel but exhibit a weak gel-like behavior. (8) A fractional derivative model may be an attractive means for predicting a linear viscoelastic behavior of concentrated xanthan gum solutions but classified as a semi-empirical relationship because there exists no real physical meaning for the model parameters.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.4
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• pp.161-172
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• 2020

The tensile property of A5082 and A6060 aluminium wrought alloys was investigated, in terms of the strain rate sensitivity on alloy conditions by heat treatment and bake hardenability on pre-strain prior to strain ageing. The tensile test was carried out in a range of strain rate of 4.17 × 10^-5 s^-1 ~ 4.17 × 10^-5 s^-1 in room temperature and the nominal range of pre-strain was 3.0 ~ 10.5%. The tensile deformation of A5082 alloys is characterized as typical case of dynamic strain ageing with negative strain rate sensitivity for all conditions, and the tensile strength indicates a similar level regardless of alloy conditions, except only in full annealed condition. The stress-relief annealing on A6060 alloys can induce practical decrease in strength level of over approximately 100 MPa without any ductility loss, compared to as-rolled condition, while a full annealed and aged condition leads remarkable strengthening effect with the decrease of tensile elongation. Additionally, the bake hardenability of A5082 alloy by strain ageing indicates a negative dependence upon the increase of pre-strain, while A6060 alloy exhibits a positive sign even in low level relatively compared with conventional SPCC.