• Transactions of Materials Processing
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• v.12 no.8
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• pp.744-749
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• 2003

The effect of tempering temperatures on microstructures and mechanical properties was studied in a low carbon steel. The disappearance of continuous yielding and the formation of an extended region in engineering stress-strain curves at tempering temperatures ranging from 673 to 873K was caused by the reduction of mobile dislocations during tempering and dynamic recovery during tensile deformation. In addition, the occurrence of discontinuous yielding in the sample treated at the tempering temperatures above 923K was attributed to the formation of new strain-free polygonal ferrite grain.

• Computers and Concrete
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• v.20 no.4
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• pp.469-481
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• 2017

This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.

• Korean Journal of Agricultural Science
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• v.12 no.2
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• pp.309-323
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• 1985

The Paper describes the observed behaviour in the undrained triaxial condition of marine clays remoulded at various different levels of factors, to find out the effects of restricted factors on the stress-strain characteristics. The conventional triaxial compression tests $({\sigma}1>{\sigma}2={\sigma}3)$ were carried out on the 50mm in diameter and 100mm long cylindrical specimens of Gun-san bay mud under controlled various moisture content, density, axial strain rate and passing on No. 200 sieve. Significant conclusions from this study are; 1. The compressible deviator stress at failure of pure marine clay was observed to increase with the decrease of moulding moisture content. 2. The compressible deviator stress at failure increased with the increasing of moulding dry density. 3. The interaction between moisture content and density on the stress-strain characteristics of marine clay was remarkedly significant, as the result of factorial experimental method. 4. The effect of axial strain rate on stress-strain behaviour was unsignificant in marine clay and but the secant moduli could be pronounced on a slight decreasing with increase of the strain rate. 5. With the increasing of the passing on No. 200 sieve, the deviator stress increased regularly. 6. The multiple regression equation could be modeled for the prediction of stress or strain and the comparison with experimental results relatively proved the accuracy.

• Geomechanics and Engineering
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• v.8 no.1
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• pp.1-15
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• 2015

This paper presents a series of conventional undrained triaxial compression tests conducted to determine the effect of both tire crumbs and cement addition on Narli sand specimens. The tire crumb contents and cement contents were 3%, 7%, 15%; and 1%, 3%, 5% by dry weight of the sand specimens respectively. Specimens were prepared at about 35% relative density, cured during overnight (about 17 hours) for artificially bonding under a 100 kPa effective stress (confining pressure of 500 kPa with a back pressure of 400 kPa), and then sheared. Deviatoric stress-axial strain, pore water pressure-axial strain behavior, and Young's modulus of the specimens at various mixture ratios of tire crumb/cement/sand were measured. Test results indicated that the addition of tire crumb to sand decreases Young's modulus, deviatoric stress and brittleness, and increase pore water pressure generation. The addition of cement to sand with tire crumbs increases deviatoric stress, Young's modulus, and changes its ductile behavior to a more brittle one. The results suggest that specimen formation in the way used here could reduce the tire disposal problem in not only economically, and environmentally, but also more effectively beneficial way for some geotechnical applications.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.127-132
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• 2003

In a today industry, the welding is doing a many portion in structure manufacture. This study is simulated heat of heat-effected zone and researched a mechanical properties and ultrasonic characteristic in used the SS400 and the STS304. As the result mechanical properties of steel that become drawing decreased because of remaining stress by strain gardening according as simulated heat temperature rises, but according as temperature rises in material that do simulated heat after have done annealing, mechanical propensity was improved. The velocity and attenuation become different by effect of remaining stress than effect of material internal microstructure in ultrasonic wave test. In the case of STS304, there was change in mechanical properties by effect that is by strain hardening, but there was no change in material that simulated heat after annealing. When become drawing in ultrasonic waves test, according as simulated heat temperatures rise, change of attenuation coefficient is looked, but material that simulated heat after annealing was no change almost both the volocity and attenuation.

• Computers and Concrete
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• v.1 no.2
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• pp.115-130
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• 2004

The flexural ductility of solid rectangular reinforced concrete beams has been studied quite extensively. However, many reinforced concrete beams are neither solid nor rectangular; examples include T-, ${\Gamma}$-, ${\Pi}$- and box-shaped beams. There have been few studies on the flexural ductility of non-rectangular reinforced concrete beams and as a result little is known about the possible effect of sectional shape on flexural ductility. Herein, the effect of sectional shape on the post-peak flexural behaviour of reinforced normal and high-strength concrete beams has been studied using a newly developed analysis method that employs the actual stress-strain curves of the constitutive materials and takes into account the stress-path dependence of the stress-strain curve of the steel reinforcement. It was revealed that the sectional shape could have significant effect on the flexural ductility of a concrete beam and that the flexural ductility of a T-, ${\Gamma}$-, ${\Pi}$- or box-shaped beam is generally lower than that of a solid rectangular beam with the same overall dimensions and the same amount of reinforcement provided. Based on the numerical results obtained, a simple method of ensuring the provision of a certain minimum level of flexural ductility to non-rectangular concrete beams has been developed.

• Transactions of Materials Processing
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• v.15 no.2 s.83
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• pp.118-125
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• 2006

API steel is used for line-pipe to transport the oil and natural gas. As the recent trends in the development of API steel are towards the use of larger diameter and thicker plate, many researches have been studied to achieve higher strength, higher toughness and lower yield ratio in API steel. However, the strength of API steel after pipe forming is changed depending on the competition of the Bauschinger effect and work hardening which are affected by the strain history during pipe forming process. So, the purpose of this study is to investigate the influence of microstructure on the Bauschinger effect for API steel. To change the microstructure of API steel we have changed the hot rolling condition and the amounts of V and Cu addition. The compression-tensile test and the microstructure observation by OM and TEM were conducted to investigate the yield strength drop and the correlation between the Bauschinger effect and microstructure of API steel. The experimental results show that the increase of polygonal ferrites volume fraction increases the Baushcinger effect due to the back stress which comes from the increase of mobile dislocation density at polygonal ferrite interior during the compressive deformation. The hot rolling condition was more effective on the Bauschinger effect in API steel than the small amount of V and Cu addition.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.377-382
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• 2004

The dynamic material characteristics on some mild steel sheets were observed. The dynamic tests were conducted on the ESH servo-hydraulic test machine. It was observed that the mechanical properties of mild steel are highly sensitive to the value of strain rate. The well known Cowper-Symonds constitutive equation was used to generalize the strain rate sensitivity effect. Modified constitutive equations were suggested to couple the strain hardening to the strain rate sensitivity. The dynamic stress-strain relationships for the mild steel sheets used in the present study were reasonably predicted using these modified constitutive equations.

• Journal of the Korean Society of Safety
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• v.5 no.2
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• pp.58-65
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• 1990

The purpose of this study is to consider the effects of strain rate on the stress-strain behavior of sheet metal at instability. The results and conclusions obtained as follows ： 1. As the strain rate increases, the fracture pressure increases and the polar height at fracture decreases. 2. The effect of strain rate on forming limit diagram produces a general lowering of the diagram with increasing strain rate but changes according to materials and strain paths. 3. The forming limit diagram predicted by swift instability theory is comparatively inconsistent with the experimental result at high strain rates, because there is inevitable gap between them.

• Advanced Composite Materials
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• v.16 no.2
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• pp.167-180
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• 2007

The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress-strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai-Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the above failure criterion under dynamic loading conditions.