• Journal of the Korean Society for Nondestructive Testing
• /
• v.37 no.2
• /
• pp.115-121
• /
• 2017

The nonlinear ultrasonic technique is a potential nondestructive method to evaluate material degradation, in which the ultrasonic nonlinearity parameter is usually measured. The ultrasonic nonlinearity parameter is defined by the elastic nonlinearity coefficients of the nonlinear Hooke's equation. Therefore, even though the ultrasonic nonlinearity parameter is not equal to the elastic nonlinearity parameter, they have a close relationship. However, there has been no experimental verification of the relationship between the ultrasonic and elastic nonlinearity parameters. In this study, the relationship is experimentally verified for a heat-treated aluminum alloy. Specimens of the aluminum alloy were heat-treated at $300^{\circ}C$ for different periods of time (0, 1, 2, 5, 10, 20, and 50 h). The relative ultrasonic nonlinearity parameter of each specimen was then measured, and the elastic nonlinearity parameter was determined by fitting the stress-strain curve obtained from a tensile test to the 5th-order-polynomial nonlinear Hooke's equation. The results showed that the variations in these parameters were in good agreement with each other.

• Journal of the Korean Ceramic Society
• /
• v.36 no.9
• /
• pp.923-929
• /
• 1999

The cause of optical nonlinearity induced in thermally poled silica glass is believed to be the space charge polarization. Since the second order optical nonlinearity (electro-optic effect) can be used in optical switches the optical nonlinearity in silica glass has drawn a large attention. Space charge polarization occurs when an ionic conducting material is subjected to dc electric field by the blocking electrode. Thermal poling performed to induce the optical nonlinearity in silica glass is basically identical to the process generating space charge polarization. As a first step to understand the mechanism of space charge polarization in silica glass hence the induced optical nonlinearity the absorption currents as functions of time were measured for various types of silica glasses and analyzed by the theory of space charge polarization. It was found that the electrical relaxation exhibited a step by the space charge polarization in the relatively long time range and dielectric loss peak showed a maximum at a specific temperature which is depending on type of silica glass. It was turned out that this relaxation might be a cause of nonlinearity in electrical conductivity of silica glass.

• Transactions of the Society of Information Storage Systems
• /
• v.10 no.1
• /
• pp.19-22
• /
• 2014

Optical nonlinear property is utilized to the wave generation, generating the beam at intended wavelength, and optical computing systems. The genetic material, which is the DNA with helical structure in nano-scale, is fascinating for optics communities due to artificially controllable sequence that determines the physical and chemical property. Nonlinearity of DNA was investigated by the four wave mixing experiment, which is with two incident beams located at 1550nm and 1650nm. The four output beams including incident beams are emitted from genetic material such as 1461nm and 1763nm by nonlinear characteristic. The 1461nm beam which is generated by four wave mixing phenomena was observed by optical spectrum analyzer.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.12
• /
• pp.2915-2925
• /
• 1993

A finite element program using degenerated shell element was developed to solve the geometric, material and combined nonlinear behaviors of composite laminated plates. The total Lagrangian method was implemented for geometric nonlinear analysis. The material nonlinear behavior was analyzed by considering the matrix degradation due to the progressive failure in the matrix and matrix-fiber interface after initial failure. The results of the geometric nonlinear analyses showed good agreements with the other exact and numerical solutions. The results of the combined nonlinear analyses considered both geometric and material nonlinear behaviors were compared to the experiments in which a concentrated force was applied to the center of the square laminated plate with clamped four edges.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1993.04a
• /
• pp.53-60
• /
• 1993

Nonlinear equation of motion due to material nonlinearity of structure is transformed to linear equation of motion by treating the nonlinear elastic force term as an applied force. The solution in a time step is carried out by iterative linear dynamic analysis. The present simple algorithm is varidated by several examples .The results show that this algorithm is and efficient.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2003.03a
• /
• pp.415-421
• /
• 2003

With the increasing possibility of earthquake occurrence, seismic safety of bridges has become one of the most important social issues in Korea. In this study, a nonlinear earthquake response analysis is carried out for a real bridge by incorporating soil-structure interaction and pier nonlinearity. The material nonlinearity of the bridge pier is realized by utilizing SAP2000 whereas the soil-structure interaction is analized in time domain by adapting KIESSI. The numerical results are compared to those of the models without considering the effects.

• Journal of Korean Association for Spatial Structures
• /
• v.18 no.4
• /
• pp.31-39
• /
• 2018

This paper analyse the mechanical characteristics of geometrical and material nonlinearity behavior of cylindrical shell roofs subjected to a concentrated load. The shell elements were modeled using 'NISA2016' software as 3D general shell element and 3D composite shell element. The 3D shell element includes deformation due to bending, membrane, membrane-bending coupling and shear perpendicular to the grain effects is suited for modeling moderately thick or thin general shells and laminated composite shells. And The 3D composite shell element consists of a number of layers of perfectly bonded anisotropic and orthotropic materials. The purpose of this research is to analysis the load-deflection curves considering the combined geometric and material nonlinearity of cylindrical shells. In a shallowed cylindrical shell, snap-through curve can be found.

• Smart Structures and Systems
• /
• v.22 no.6
• /
• pp.711-725
• /
• 2018

Most of the practical engineering structures exhibit nonlinearity due to nonlinear dynamic characteristics of structural joints, nonlinear boundary conditions and nonlinear material properties. Hence, it is highly desirable to detect and characterize the nonlinearity present in the system in order to assess the true behaviour of the structural system. Further, these identified nonlinear features can be effectively used for damage diagnosis during structural health monitoring. In this paper, we focus on the detection of the nonlinearity present in the system by confining our discussion to only a few selective time-frequency analysis and multivariate analysis based techniques. Both damage induced nonlinearity and inherent structural nonlinearity in healthy systems are considered. The strengths and weakness of various techniques for nonlinear detection are investigated through numerically simulated two different classes of nonlinear problems. These numerical results are complemented with the experimental data to demonstrate its suitability to the practical problems.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11b
• /
• pp.472-475
• /
• 2001

The electrical properties and stability of ZPCCY-based varistors composing of $ZnO-Pr_{6}O_{11}-CoO-Cr_{2}O_{3}-Y_{2}O_{3}$ ceramics were investigated with sintering time. As sintering time is increased, the nonlinear exponent decreased in the range of 51.19~26.70. Among varistors having above 30 in nonlinear exponent, for the varistor sintered for 1h, the nonlinearity was superior to the stability comparatively and, in the case of 2h, the stability was superior to the nonlinearity relatively. Consequently, it is estimated that the varistors sintered for 1~2h will be applied to various fields by trade-off between nonlinearity and stability.

• Structural Engineering and Mechanics
• /
• v.54 no.4
• /
• pp.809-827
• /
• 2015

In this paper, seismic energy response of inelastic steel structures under earthquake excitations is investigated. For this purpose, a numerical procedure based on nonlinear dynamic analysis is developed by considering material, geometric and connection nonlinearities. Material nonlinearity is modeled by the inversion of Ramberg-Osgood equation. Nonlinearity caused by the interaction between the axial force and bending moment is also defined considering stability functions, while the geometric nonlinearity caused by axial forces is described using geometric stiffness matrix. Cyclic behaviour of steel connections is taken into account by employing independent hardening model. Dynamic equation of motion is solved by Newmark's constant acceleration method in the time history domain. Energy response analysis of space frames is performed by using this proposed numerical method. Finally, for the first time, the distribution of the different energy types versus time at the duration of the earthquake ground motion is obtained where in addition error analysis for the numerical solutions is carried out and plotted depending on the relative error calculated as a function of energy balance versus time.