Advances in Fracture and Strength

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Authors: Hyouk Ryeol Choi, Kwang Mok Jung, Ja Choon Koo, Jae Do Nam, Young Kwan Lee, Mi Suk Cho
Abstract: ElectroActive Polymers (EAPs) are emerging as new actuating means replacing the existing technologies such as piezoelectric, electrostatic, SMA etc. The dielectric elastomer actuator is regarded as the one of the most practically applicable actuators in the near future among the EAPs. In this paper, we introduce a new material capable of being employed as the dielectric elastomer actuator. The proposed material, which is a kind of the synthetic rubber, produces larger deformation as well as higher enegy efficiency, since it has a much higher dielectric constant compared to the previous ones. Beginning with the method of material synthesis, we give the description of its basic material properties by comparing with those of the existing materials for the dielectric elastomers. Also, the advantages of the proposed material as the actuating means are discussed with the several results of the experiments.
Authors: Kenichi Ohi, Jae Hyouk Choi
Abstract: This paper deals with shape memory alloy. As a first step to assess the applicability of this kind of alloy in a structural system, a tension bar made of this kind of alloy that exhibits pseudo-elasticity at room temperature is used herein as a passive bracing system. This paper describes sub-structure pseudo-dynamic tests on pseudo-elastic bracing system with hysteretic damper. A pseudo-elastic bracing system is better to be used with other hysteretic elements such as a hysteretic damper. A damper provides energy dissipation within small displacement levels, and a pseudo-elastic bracing system works in turn as a back-up/fail-safe system when an accidental failure of damper or damper interface occurs, and also it helps to pull back the structure to the original position by uninstalling the damper after earthquake.
Authors: Jae Hyouk Choi, Kenichi Ohi
Abstract: Effectiveness of steel bracing system installed with fully mechanical interfaces is experimentally demonstrated through a series of monotonic and cyclic loading tests. Also, substructuring pseudo-dynamic earthquake response tests are performed on a possible situation of a two-story braced frame upgraded by the proposed bracing system. An earthquake record and theoretical impulses are adopted as input excitations. The results show that an impulsive excitation acts more stringently on the occurrence of brace breaking.
Authors: Mi Suk Cho, Jae Do Nam, Hyouk Ryeol Choi, Ja Choon Koo, Young Kwan Lee
Abstract: The fabrication of dry type conducting polymer actuator was presented. In the preparation of actuator system, nitrile rubber (NBR) was used as a base material of the solid polymer electrolyte. Thin films of NBR (150-200μ m) were prepared by compression molding process. The conducting polymer, poly (3,4- ethylenedioxythiophene) (PEDOT) was synthesized on the surface of NBR by chemical oxidation polymerization technique, and the room temperature ionic liquid, 1-ethyl-3- methylimidazolium bis (trifluoromethyl sulfonyl) imide (EMITFSI) was introduced into the composite film. The ionic conductivity of new type solid polymer electrolyte as a function of the immersion time and the cyclic voltammetry responses and the redox switching dynamics of PEDOT in NBR/ionic liquid solid polymer electrolyte were studied. The displacement of actuator was measured by laser beam radiation.
Authors: Seung Bok Choi, Kyung Su Kim
Abstract: This paper presents experimental results of tensile and compressive behaviors of smart electrorheological (ER) materials. Two different ER materials ; chemically treated starch particles and polymethylaniline particles are synthesized followed by devising a sqreeze mode type apparatus associated with motion controller and data acquisition system. The field intensity, electrode velocity and initial gap are chosen as important test parameters that influence on the tensile and compressive characteristics. The maximum tensile stresses are evaluated at each condition and compared between two ER materials.
Authors: Yoshinobu Shimamura, Keiko Oda, Akira Todoroki, Hideo Kobayashi, Takaomi Inada
Abstract: Bolted joints are widely used for composite structures. As is well known, excessive bearing load gives rise to bearing failure at hole boundaries. Detecting bearing failure is important for assuring integrity of composite structures. Conventional nondestructive inspection methods are expensive, cumbersome, time-consuming, and not suitable for health monitoring, and a simple, low-cost inspection method for bearing failure must be developed. Authors have experimentally demonstrated detection bearing failure by an electrical resistance change method. In this study, detectablity of remote damage, which includes bearing failure, using an electric resistance change method is investigated analytically. The results show that fiber breaking and delamination induce permanent increase in the electric resistance of the bolted composite joints, and that the proposed method, which involves measuring electric resistance, is effective for detecting bearing failure.
Authors: Hideaki Murayama, Kazuro Kageyama, Isamu Ohsawa, Makoto Kanai, Kiyhoshi Uzawa, Tsuyoshi Matsuo
Abstract: We have developed a novel fiber-optic vibration sensors and applied commercially available strain and temperature sensors to health monitoring of composite structures. In this study, we constructed an optical fiber network integrating four types of optical fiber sensor into a carbon reinforced plastic (CFRP) panel. These four sensors were the vibration sensor developed by our laboratory, two distributed sensors based on Brillouin and Raman backscattering and Fiber Bragg Grating (FBG) sensors. By dealing the data obtained from the measurement systems corresponding to these four sensors, strain/stress and temperature distributions throughout the panel can be monitored. Vibration and elastic waves transmitting on the panel are also detected at several sensing points. Furthermore, we will be able to determine damage locations and modes by processing the wave signals. To make the panel with the optical fiber sensor network more sensitive and smarter, we are developing some techniques that can improve the performance of the sensors and can assess the structural integrity by analyzing measurement results. In this paper, the development of the first generation of our smart composite panel with the optical fiber sensors is described and the techniques making the panel more sensitive and smarter are also described.
Authors: Ja Choon Koo, Hyouk Ryeol Choi, Min Young Jung, Kwang Mok Jung, Jae Do Nam, Young Kwan Lee
Abstract: Smart polymer based actuators have demonstrated various benefits over the traditional electromagnetic or piezoelectric-material actuators. One of the most significant contributions of the polymers is its soft actuation mechanisms. Hence morphological freedom for actuator construction benefits production of either small scale complex mechanisms or human-like applications. Although many actuation paradigms of polymer actuators are presented in various publications, no significant contributions are made for investigation of modeling and control methods of the material. In the present work, a smart polymer based actuator is constructed. It is then modeled and analyzed for feasible control scheme selection.
Authors: Jae Hwan Kim, Yu Keun Kang, Sung Ryul Yun
Abstract: This paper presents the characterization of Electro-active paper (EAPap). EAPap is a paper that produces large displacement with small force under electrical excitation. EAPap is made with a cellulose paper by constructing thin electrodes on both sides of the paper. When electrical voltage is applied to the electrodes the EAPap produces bending displacement. To be able to apply EAPap in many applications, characterization of EAPap is essential to understand and improve EAPap actuators. The characterization is done in terms of mechanical, electrical and physical tests. Mechanical strain and strength are investigated in sheet level and thermo-mechanical analysis is performed. Electrical resistance and admittance are analyzed to investigate the actuation mechanism. The actuation principle associated with piezoelectric effect is explained. EAPap has merits in terms of lightweight, dry condition, large displacement output, low actuation voltage and low power consumption. The most attractive characteristics of EAPap materials is their application potential for the development of biomimetic systems that are ultra-lightweight, low power, flexible, damage tolerant, noiseless, and agile.
Authors: Sang Il Lee, Dong Jin Yoon, Seung Seok Lee, Joung Man Park
Abstract: Cure monitoring and stress-strain sensing of single-carbon fiber composites were nondestructively evaluated by the measurement of electrical resistance. The difference of electrical resistance before and after curing increased highest when gauge length of the specimen was the smallest. As curing temperature increased, the electrical behavior of steel fiber was different from that of semi-conductive carbon and SiC fibers. Residual stress built in the fiber was the highest at the fiber axis direction. Whereas residual stress built in the matrix was relatively high at the fiber circumference and radius directions. Residual stress calculated from the experiment was consistent with the results from the finite element analysis (FEA). The strain at low curing temperature was larger than that of higher temperature until the load reached maximum value. The apparent modulus of the electrodeposited composites was higher than that of the untreated composites due to the improved interfacial shear strength (IFSS). The electrical resistance was responded quantitatively with stress-strain behavior during the test. Electrical resistance measurement can be feasible nondestructive techniques to evaluate cure monitoring and stress-strain sensing in the conductive fiber composites.

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