• Computers and Concrete
• /
• v.7 no.4
• /
• pp.317-329
• /
• 2010

The paper describes localization of deformation in a bar under tensile loading. The material of the bar is considered as non-linear viscous elastic and the bar consists of two symmetric halves. It is assumed that the model represents behavior of the quasi-brittle viscous material under uniaxial tension with different loading rates. Besides that, the bar could represent uniaxial stress-strain law on a single plane of a microplane material model. Non-linear material property is taken from the microplane material model and it is coupled with the viscous damper producing non-linear Maxwell material model. Mathematically, the problem is described with a system of two partial differential equations with a non-linear algebraic constraint. In order to obtain solution, the system of differential algebraic equations is transformed into a system of three partial differential equations. System is subjected to loadings of different rate and it is shown that localization occurs only for high loading rates. Mathematically, in such a case two solutions are possible: one without the localization (unstable) and one with the localization (stable one). Furthermore, mass is added to the bar and in that case the problem is described with a system of four differential equations. It is demonstrated that for high enough loading rates, it is the added mass that dominates the response, in contrast to the viscous and elastic material parameters that dominated in the case without mass. This is demonstrated by several numerical examples.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.225-228
• /
• 2008

In case of nonlinear analysis for reinforced concrete structure, the characteristics of the failure, which are depend on loading conditions, such as tension splitting, compression crushing and shear distortion should be considered. On the analytical evaluation for the failure behavior of these, the finite element techniques is the most widely used. After the maximum load, however, an analytical results by finite element technique are depending on the size of the element. In this study, integral nonlocal model which is one of those study for overcoming the element sensitivity and dependancy, used for the failure analysis of box culvert specimen. Comparing on the experimental and analytical results, validity and reliability of integral nonlocal model are investigate.

• Proceeding of KASS Symposium
• /
• 2005.05a
• /
• pp.116-124
• /
• 2005

The recent large-spatial structures are frequently made from light-weight structural system and it has a good mechanical efficiency and uses new materials. The large space is made by light-weight structural system using tension members mainly, and generally it is called a soft structure. The cable dome structures which are a soft structures are very flexible, the stresses and nodal coordinates of other members are changed when we control the stress of one member. Therefore, we have to do two kind of works for effective and accurate construction of the cable dome structures. The first work is making a working scenario to complete the final objective form and the second is revising constructional errors occurred in process of the actual works. These works are called constructional analysis. At this time, we have to consider geometric nonlinearity to reflect the sensitivity by the initial stresses of cable dome structures, and constructional analysis comes down to a nonlinear problem after all. In this study, we try to approach the constructional analysis of the cable dome structures using the numerical method, and then verify it.

• Smart Structures and Systems
• /
• v.1 no.4
• /
• pp.355-368
• /
• 2005

Large and complex structures are being built now-a-days and, they are required to be functional even under extreme loading and environmental conditions. In order to meet the safety and maintenance demands, there is a need to build sensors integrated structural system, which can sense and provide necessary information about the structural response to complex loading and environment. Sophisticated tools have been developed for the design and construction of civil engineering structures. However, very little has been accomplished in the area of monitoring and rehabilitation. The employment of appropriate sensor is therefore crucial, and efforts must be directed towards non-destructive testing techniques that remain functional throughout the life of the structure. Fiber optic sensors are emerging as a superior non-destructive tool for evaluating the health of civil engineering structures. Flexibility, small in size and corrosion resistance of optical fibers allow them to be directly embedded in concrete structures. The inherent advantages of fiber optic sensors over conventional sensors include high resolution, ability to work in difficult environment, immunity from electromagnetic interference, large band width of signal, low noise and high sensitivity. This paper brings out the potential and current status of technology of fiber optic sensors for civil engineering applications. The importance of employing fiber optic sensors for health monitoring of civil engineering structures has been highlighted. Details of laboratory studies carried out on fiber optic strain sensors to assess their suitability for civil engineering applications are also covered.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.7 no.2 s.17
• /
• pp.100-108
• /
• 2004

Nitramine-polymer composites suffer from a problem known as dewetting. Dewetting adversely affects the performance and the sensitivity characteristics of an explosive composition. Voids, which are generated between explosive particles and binder on dewetting, act as initiation sites. For a PBXs as well as propellants, where good adhesion and mechanical properties are of great importance, dewetting therefore must be prevented by strong adhesion between the filler and the binder. The surface energy of materials is measured by Wilhelmy plate and wicking method. The interfacial energy between the filler and the binder is calculated from the disperse phase and the polar phase of surface energy. Time dependent compressive properties of composite explosives have been determined by stress-strain curves obtained at different strain rates and temperatures. The interfacial state of the PBX was observed through SEM. It was found from the result that the interface between the explosive and the binder becomes better adhesion with decreasing interfacial tension and increasing work of adhesion. The result clearly shows that the castable PBX has good adhesion more than the pressable PBX.

• Geomechanics and Engineering
• /
• v.29 no.6
• /
• pp.627-643
• /
• 2022

Water-rock interactions have a significant influence on the mechanical behavior of rocks. In this study, uniaxial compression and tension tests on different water-treated sandstone samples were conducted. Acoustic emission (AE) monitoring and micro-pore structure detection were carried out. Water-rock interactions and their effects on rock mechanical behavior were discussed. The results indicate that water content significantly weakens rock mechanical strength. The sensitivity of the mechanical parameters to water treatment, from high to low, are Poisson ratio (𝜇), uniaxial tensile strength (UTS), uniaxial compressive strength (UCS), elastic modulus (E), and peak strain (𝜀). After water treatment, AE activities and the shear crack percentage are reduced, the angles between macro fractures and loading direction are minimized, the dynamic phenomenon during loading is weakened, and the failure mode changes from a mixed tensile-shear type to a tensile one. Due to the softening, lubrication, and water wedge effects in water-rock interactions, water content increases pore size, promotes crack development, and weakens micro-pore structures. Further damage of rocks in fractured and caved zones due to the water-rock interactions leads to an extra load on the adjoining coal and rock masses, which will increase the risk of dynamic disasters.

• Transactions of Materials Processing
• /
• v.32 no.2
• /
• pp.92-99
• /
• 2023

In this study, shear fracture specimens are designed using finite element analyses for the characterization of ductile fracture criteria of metal sheets. Many recently suggested ductile fracture criteria require experimental fracture data at the shear stress states in the model parameter identification. However, it is challenging to maintain shear stress states in tension-based specimens from the initial yield to the final fracture, and the loading path can be different for the different materials even with the same shear specimen geometries. To account for this issue, two different shear fracture specimens for low ductility/high ductility metal sheets are designed using the sensitivity tests conducted by finite element simulations. Priorly mechanical properties including the Hosford-Coulomb fracture criterion of the aluminum alloy 7075-T6 and DP590 steel sheets are used in the simulations. The results show that shear stress states are well-maintained until the fracture at the fracture initiation points by optimizing the notch geometries of the shear fracture specimens.

• The Korean Journal of Pharmacology
• /
• v.27 no.1
• /
• pp.45-52
• /
• 1991

The inhibitory effects of GS354 and GS389 on cytosolic $Ca^{2+}$ level ($[Ca^{2+}]_{1}$; measured with fura-2 fluorescence) and muscle tension in vascular smooth muscle of rat thoracic aorta were investigated. Both GS354 and GS389 inhibited the contractions induced by high $K^+$ or by norepinephrine. The vasodilator effect of GS354 was accompanied by a decrease in $[Ca^{2+}]_{1}$. The inhibitory effect on high $K^+-stimulated$ $[Ca^{2+}]_{1}$ was antagonized by a $Ca^{2+}$ channel activator, Bay K8644. However, the inhibitory effect on muscle tension was not antagonized by Bay K8644. These results suggest that GS354 inhibits $Ca^{2+}$ channels to decrease $[Ca^{2+}]_{1}$ and also decreases $Ca^{2+}$ sensitivity of contractile elements. The inhibitory effects of GS389 was accompanied by the increase in tissue fluorescence. This increment was not due to fura-2 fluorescence but to endogeneous pyridine nucleotides, suggesting that GS389 has an effect to inhibit mitochondrial function. Because of this interference, effects of GS389 on $[Ca^{2+}]_{1}$ was obscured. However, since sequential addition of Bay K8644 in the presence of GS389 further increased the fluorescence but not muscle tension, this compound seems to have the effects to inhibit $Ca^{2+}$ channels and to decrease $Ca^{2+}$ sensitivity of contractile elements.

• Korean Journal of Psychosomatic Medicine
• /
• v.11 no.1
• /
• pp.15-24
• /
• 2003

Objectives: The object of this study was to compare perceived stress and quality of life among patients with HIV infection, patients with pulmonary tuberculosis and normal controls. Methods: Stress response inventory(SRI) and Symptom checklist 90-Revised(SCL-90-R) were used to measure perceived stress responses and psychopathology. Smithklein Beecham quality of life scale was used to measure quality of life. Results: Patients with HIV infection scored significantly higher on scores of tension, anger, depression, fatigue and frustration subscale of the SRI than those with pulmonary tuberculosis and normal controls. Scores of the SCL-90-R, somatization, depression, anxiety, hostility, phobic anxiety, paranoid ideation and psychoticism subscale were also significantly higher in patients with HIV infection than those with pulmonary tuberculosis and normal controls. Patients with HIV infection scored significantly lower in quality of life than those with pulmonary tuberculosis. In patients with HIV infection, age had a significantly negative correlation with scores of somatization, obsessive-compulsive, interpersonal sensitivity, phobic anxiety, paranoid ideation and psychoticism subscale of the SCL-90-R. but the level of education had a significantly positive correlation with somatization, obsessive-compulsive, interpersonal sensitivity, phobic anxiety, paranoid ideation and psychoticism subscale of the SCL-90-R. Conclusion: The results suggest that patients with HIV positive were likely to have higher levels of perceived stress response and psychopathology, and lower quality of life than those with pulmonary tuberculosis and normal controls.

• Korean Journal of Psychosomatic Medicine
• /
• v.10 no.2
• /
• pp.120-129
• /
• 2002

Objectives : The object of this study was to compare perceived stress and quality of life among patients with HIV infection, patients with pulmonary tuberculosis and normal controls Methods: Stress Response Inventory(SRI) and Symptom checklist 90-Revised(SCL-90-R) were used to measure perceived stress responses and psychopathology. Smithklein Beecham quality of life scale was used to measure quality of life. Results : Patients with HIV infection scored significantly higher on scores of tension, anger, depression, fatigue and frustration subscale of the SRI than those with pulmonary tuberculosis and normal controls. Scores of the SCL-90-R, somatization, depression, anxiety, hostility, phobic anxiety, paranoid ideation and psychoticism subscale were also significantly higher in patients with HIV infection than those with pulmonary tuberculosis and normal controls. Patients with HIV infection scored significantly lower in quality of life than those with pulmonary tuberculosis. In patients with HIV infection, age had a significantly negative correlation with scores of somatization, obsessive-compulsive, interpersonal sensitivity, phobic anxiety, paranoid ideation and psychoticism sub scale of the SCL-90-R. but the level of education had a significantly positive correlation with somatization, obsessive-compulsive, interpersonal sensitivity, phobic anxiety, paranoid ideation and psychoticism sub scale of the SCL-90-R. Conclusion : The results suggest that patients with HIV positive were likely to have higher levels of perceived stress response and psychopathology, and lower quality of life than those with pulmonary tuberculosis and normal controls.