• Composites Research
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• v.19 no.6
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• pp.23-31
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• 2006

We measured mechanical properties, including Young's modulus, effective bending modulus and nominal fracture strength of nanohoneycomb structures using an Atomic Force Microscope(AFM) and a Nano-Universal Testing Machine(UTM). Anodic aluminum oxide(AAO) films are well suited as nanohoneycomb structures because of the simple fabrication process, high aspect ratio, self-ordered hexagonal pore structure, and simple control of pore dimensions. Bending tests were carried out for cantilever structures by pressing AFM tips, and the results were compared with three-point bending tests and tensile tests using a Nano-UTM. One side of the AAO films is clogged by harrier layers, and looks like a face material of conventional sandwich structures. Analysis of this layer showed that it did not influence the bending rigidity, and was just a crack tip. The present results can act as a design guideline in applications of nanohoneycomb structures.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.1
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• pp.27-33
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• 2010

Static analyses and buckling analyses were carried out for buried GFRP pipes by using finite element method. Vehicle loads, vertical and lateral soil pressures were considered as external loads, and supplying water pressure was considered as an internal load. Nine types of the factory-manufactured GFRP pipes were analyzed. Their maximum stresses and displacements were compared with the limit displacements and ultimate stress. Additionally, stress analysis on an enhanced flange, which was designed to reduce stress concentration, was performed. A cantilever analysis was carried out to know the maximum stress on the neck of the flange, which is the critical part. And a static analysis was carried for the buried flange. The test results showed that GFRP pipes were safe and stable against the external loads. And they showed that the enhanced flange decreased about 35% of the stress concentration.

• Journal of Ocean Engineering and Technology
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• v.29 no.5
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• pp.351-358
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• 2015

This paper presents an effective damage detection method using a meta model. A meta model is an approximation model that uses the relations between the design and response variables. It eliminates the need for repetitive analyses of computationally expensive models during the optimization process. In this study, a response surface model was employed as the meta model. The surface model was estimated using the correlation of the stiffness and natural frequencies of the structures. The locations and values of the damages were identified using a meta model-based damage detection method. Two numerical examples (a cantilever beam and jacket structure) were considered to verify the performance of the proposed method. As a result, the damages to the structures were accurately detected.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.603-605
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• 1995

We present a novel method. to fabricate surface micromachined structures without their sticking on the substrate. An anhydrous HF/$CH_3OH$ vapor-phase etching (VPE) of sacrificial $SiO_2$ layers was employed to release 0.5-2 {\mu}m$ thick polysilicon cantilevers. The fabricated structures were observed using scanning electron microscope and 3-dimensional optical microscope. The results show that we can successfully make cantilever beams up to 1200{\mu}m$ long without sticking. Annealing effects on residual stress of polysilicon microstructures were also investigated. Anneal ins at 1100$^{\circ}C$ for 1 hour was found to be effective to release the residual stress of the polysilicon microstructures. These VPE and anneal ins techniques will be useful in surface micromachining technologies.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.4 s.23
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• pp.130-135
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• 2005

This paper presents application possibility of Lightweight Piezoceramic Composite Actuator(LIPCA) to suppress vibration of dynamic structures as an actuator. LIPCA is composed of a piezoelectric layer, a carbon/epoxy layer and glass/epoxy layers. When compared to the bare piezoelectric ceramic(PZT), LIPCA has advantages such as high performance, durability and reliability. In this study, performances of LIPCA have been estimated in an active vibration control system. Experiments were performed on an aluminum beam with cantilever configuration. In this test, strain gages and single LIPCA are attached on the aluminum beam with epoxy resin. Digital ON-OFF control algorithm is applied into the system to exhibit performance of LIPCA as actuator in active vibration control system. First, we performed static actuation test of bare PZT and LIPCA in order to show the superiority of LIPCA. Secondly, we carried out beam vibration control test using LIPCA. The results showed LIPCA could suppress free vibration of the aluminum beam, which means that LIPCA can be applied as an actuator to control vibration of dynamic structures.

• Structural Engineering and Mechanics
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• v.61 no.1
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• pp.15-29
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• 2017

The recently introduced index Ratio Of Torsion (ROT) quantifies the base shear amplification due to torsional effects on shear cantilever types of building structures. In this work, a theoretical proof based on the theory of elasticity is provided, depicting that the ratio of torsion (ROT) is independent of the forces acting on the structure, although its definition stems from the shear forces. This is a particular attribute of other design and evaluation criteria against torsion such as center of rigidity and center of strength. In the case of ROT, this evidence could be considered as inconsistent, as ROT is a function solely of the forces acting on structural members, nevertheless it is proven to be independent of them. As ROT is the amplification of the shear forces due to in-plan irregularities, this work depicts that this increase of internal shear forces rely only on the structural topology. Moreover, a numerical verification of this theoretical finding was accomplished, using linear statistics interpretation and nonlinear neural networks simulation for an adequate database of structures.

• Smart Structures and Systems
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• v.7 no.5
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• pp.417-432
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• 2011

The present paper is devoted to vibration canceling and shape control of piezoelastic slender beams. Taking into account the presence of electric networks, an extended electromechanically coupled Bernoulli-Euler beam theory for passive piezoelectric composite structures is shortly introduced in the first part of our contribution. The second part of the paper deals with the concept of passive shape control of beams using shaped piezoelectric layers and tuned inductive networks. It is shown that an impedance matching and a shaping condition must be fulfilled in order to perfectly cancel vibrations due to an arbitrary harmonic load for a specific frequency. As a main result of the present paper, the correctness of the theory of passive shape control is demonstrated for a harmonically excited piezoelelastic cantilever by a finite element calculation based on one-dimensional Bernoulli-Euler beam elements, as well as by the commercial finite element code of ANSYS using three-dimensional solid elements. Finally, an outlook for the practical importance of the passive shape control concept is given: It is shown that harmonic vibrations of a beam with properly shaped layers according to the presented passive shape control theory, which are attached to an resistor-inductive circuit (RL-circuit), can be significantly reduced over a large frequency range compared to a beam with uniformly distributed piezoelectric layers.

• Structural Engineering and Mechanics
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• v.25 no.6
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• pp.717-732
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• 2007

A formula to approximate the fundamental period of a fixed-free mass-spring system with varying mass and varying stiffness is formulated. The formula is derived mainly by taking the dominant parts from the general form of the characteristic polynomial, and adjusting the initial approximation by a coefficient derived from the exact solution of a uniform case. The formula is tested for a large number of randomly generated structures, and the results show that the approximated fundamental periods are within the error range of 4% with 90% of confidence. Also, the error is shown to be normally distributed with zero mean, and the width of the distribution (as measured by the standard deviation) tends to decrease as the total number of discretized elements in the system increases. Other possible extensions of the formula are discussed, including an extension to a continuous cantilever structure with distributed mass and stiffness. The suggested formula provides an efficient way to estimate the fundamental period of building structures and other systems that can be modeled as mass-spring systems.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.1
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• pp.42-47
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• 2021

Recently, many structures using lightweight materials have been developed. This study was conducted by using Al6061-T6 and carbon fiber reinforced plastic (CFRP), two common lightweight materials. In addition, the failure characteristics of an interface bonded between a single material and a heterogeneous bonding material were analyzed. The specimens bonded with CFRP and Al6061-T6 were utilized by the combination of the heterogeneous bonding material. The specimens had a double cantilevered shape and the bonding between the materials was achieved by applying a structural adhesive. The experiments were conducted in opening mode: the lower part of the samples was fixed, while their upper part was subjected to a forced displacement of 3 mm/min by using a tensile tester. Under the tested amount of strength, energy release rate, and considering the specimens' fracture characteristics in opening mode, the specimen "CFRP-Al" presented the maximum stress, followed by "Al" and "CFRP". We can hence conclude that the inhomogeneous material "CFRP-Al" is useful for the construction of lightweight structures bonded with structural adhesive.

• Computers and Concrete
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• v.28 no.5
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• pp.487-495
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• 2021

The use of prestressed concrete box girder bridges built by segmentally balanced cantilevers has bloomed in the last decades due to its significant structural and construction advantages in complex topographies. In Colombia, this typology is the most common solution for structures with spans ranging of 80-200 m. Despite its popularity, excessive deflections in bridges worldwide evidenced that time-dependent effects were underestimated. This problem has led to the constant updating of the creep and shrinkage models in international code standards. Differences observed between design processes of box girder bridges of the Colombian code and Eurocode, led to the need for a validation of in-service status of these structures. This study analyzes the long-term behavior of the Tablazo bridge with data scarcity. The measured leveling of this structure is compared with a finite-element model that consider the most widely used creep and shrinkage models in the literature. Finally, an adjusted model evidence excessive deflection on the bridge after six years. Monitoring of this bridge typology in Colombia and updating of the current design code is recommended.