• Title/Summary/Keyword: Specimen shape

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Retardation Behavior and Crack-Through-Thickness of a Surface-cracked Specimen under Cyclic Load (피로하중을 받는 표면균열재의 관통거동 및 지연거동)

  • 남기우
    • Journal of Ocean Engineering and Technology
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    • v.5 no.1
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    • pp.88-96
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    • 1991
  • Fatigue life and retardtion behavior after through-thickness were examined experimentally by using a CT specimen and surface-cracked specimen. The material used was 3% Ni-Cr-Mo steel. The fatigue crack shape before through-thickness is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using the K value proposed by Newman-Raju. It is found that the crack growth behavior on the back side after through-ghickness is unique and can be divided into three stages a, b and c. A retardation parameter has been used successfully to predict the growth of cracks in specimen, and in this time, retardation factor is 4.3. By using the crack propagation rule considering on retardation state and the K value proposed by the authors, the remarkable crack growth behavior and the change in crack shape can be evaluated quantitatively.

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Experimental study on the Flexural Capacity of U-shape Composite Beam (U-형 복합보의 휨 성능에 관한 실험적 연구)

  • Ha, Sang-Su
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.23 no.3
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    • pp.143-149
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    • 2019
  • In this study, a U-shape composite beam was developed to be effectively used for a steel parking lot which is 8m or lower in height. When the U-shape composite beam was applied to a steel parking lot, essential considerations were story-height and long-span. In addition, due to the mixed structural system with reinforced concrete and steel material, the U-shape composite beam needed to have a structural integrity and reliable performance over demand capacity. The main objective of this study was to investigate the performance of the structure consisting of the reinforced concrete (RC) slab and U-shape beam. A U-shape composite beam generally used at a parking lot served as a control specimen. Four specimens were tested under four-point bending. To calculate theoretical values, strain gauges were attached to rebar, steel plate, and concrete surface in the middle of the specimens. As the results, initial yielding strength of the control specimen occurred at the bottom of the U-shaped steel. After yielding, the specimen reached the maximum strength and the RC slab concrete was finally failed by concrete crush due to compressive stress. The structural performance such as flexural strength and ductility of the specimen with the increased beam depth was significantly improved in comparison with the control specimen. Furthermore, the design of the U-shape composite beam with the consideration of flexural strength and ductility was effective since the structural performance by a negative loading was relatively decreased but the ductile behavior was evidently improved.

Elimination of the effect of strain gradient from concrete compressive strength test results

  • Tabsh, Sami W.
    • Computers and Concrete
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    • v.3 no.6
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    • pp.375-388
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    • 2006
  • Poor strength test results are sometimes not an indication of low concrete quality, but rather inferior testing quality. In a compression test, the strain distribution over the ends of the specimen is a critical factor for the test results. Non-uniform straining of a concrete specimen leads to locally different compressive stresses on the cross-section, and eventual premature breaking of the specimen. Its effect on a specimen can be quantified by comparing the compressive strength results of two specimens, one subjected to uniform strain and another to a specified strain gradient. This can be done with the help of a function that relates two parameters, the strain ratio and the test efficiency. Such a function depends on the concrete strength and cross-sectional shape of the specimen. In this study, theoretical relationships between the strain ratio and test efficiency are developed using a concrete stress-strain model. The results show that for the same strain ratio, the test efficiency is larger for normal strength concrete than for high strength concrete. Further, the effect of the strain gradient on the test result depends on the cross-sectional shape of the specimen. Implementation of the results is demonstrated with the aid of two examples.

Stress Distribution Study along Shear Test Specimen Shape for Bonding Strength Verification between Glass and Metal (금속-유리 간 접착강도 검증을 위한 전단시험 시편형상에 따른 응력분포 연구)

  • Kim, Hye-Sung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.50 no.7
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    • pp.455-463
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    • 2022
  • As the need for R&D for high reliability cameras, such as satellite cameras, increases, the reliability of the bonding strength properties between an opto-mechanical structure and an optical component has been secured through specimen tests. However, the widely used specimen shape is not suitable for the application of glass and glass-ceramic material, which is fragile, making it difficult to obtain accurate bonding properties due to stress concentration in glass parts before reaching the bonding strength limit. In this study, the stress distribution characteristics in the shear test condition for various specimen shapes were studied analytically, based on the test results of the glass material's own fracture. Through this, the shape characteristics capable of relieving the stress concentration of the glass part were derived, and the range of the bonding shear strength verifiable by the specimen test was improved.

Smoke Density Characteristics of the FRP to the variance of test method, resin type and specimen shape (FRP 복합재의 시험조건 변화에 따른 연기 위해성 평가)

  • 이덕희;정우성;김용기;김선옥
    • Proceedings of the KSR Conference
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    • 2002.05a
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    • pp.567-571
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    • 2002
  • In this study we reported the Smoke Density test method of interior panel of railroad passenger car and investigated the specific smoke density(Ds) by NBS smoke chamber to the variance of some test conditions. First we compared the result of Ds from ISO 5659-2 with that from ASTM E662 for same phenol FRP Secondary studied the Ds value to the variance of resin type and to the variance of specimen shape.

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Experimental characterization of a smart material via DIC

  • Casciati, Sara;Bortoluzzi, Daniele;Faravelli, Lucia;Rosadini, Luca
    • Smart Structures and Systems
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    • v.30 no.3
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    • pp.255-261
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    • 2022
  • When no extensometer is available in a generic tensile-compression test carried out by a universal testing machine (for instance the model BIONIX from Material Testing Systems (MTS)), the test results only provide the relative displacement between the machine grips. The test does not provide any information on the local behaviour of the material. This contribution presents the potential of an application of Digital Image Correlation (DIC) toward the reconstruction of the behaviour along the specimen. In particular, the authors test a Ni-Ti shape memory alloys (SMA) specimen with emphasis on the coupling of the two measurement techniques.

Focused Ion Beam-Based Specimen Preparation for Atom Probe Tomography

  • Lee, Ji Yeong;Ahn, Jae-Pyoung
    • Applied Microscopy
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    • v.46 no.1
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    • pp.14-19
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    • 2016
  • Currently, focused ion beams (FIB) are widely used for specimen preparation in atom probe tomography (APT), which is a three-dimensional and atomic-scale compositional analysis tool. Specimen preparation, in which a specific region of interest is identified and a sharp needle shape created, is the first step towards successful APT analysis. The FIB technique is a powerful tool for site-specific specimen preparation because it provides a lift-out technique and a controllable manipulation function. In this paper, we demonstrate a general procedure containing the crucial points of FIB-based specimen preparation. We introduce aluminum holders with moveable pin and an axial rotation manipulator for specimen handling, which are useful for flipping and rotating the specimen to present the backside and the perpendicular direction. We also describe specimen preparation methods for nanowires and nanopowders, using a pick-up method and an embedding method by epoxy resin, respectively.

Small-size Specimen's Effectiveness That is Used to Mortar Layer of Slab (Heavy-weight Floor Impact Sound) (슬래브 상부 몰탈층에 사용된 작은시편의 유효성 검토(중량충격음을 중심으로))

  • Chung, Jin-Yun
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.19 no.2
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    • pp.184-191
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    • 2009
  • This study examined small-size specimen's effectiveness that is used to evaluate floor impact sound performance. Floor impact sound level of small-size specimen is higher than full-size. This is due to excessive impact power of Bang machine. Impact hammer that has small impact power relatively can solve this problem. But, according to the size of specimen, mode shape and frequency that influence to structural borne sound is changed. Slab mode of full-size specimen was changed to frequency design of resilient materials. But in case of small-size specimen, there is no change of vibration mode by resilient materials change, Vibration mode of small-size specimen is the same. Therefore, it is not proper that use small-size specimen in floor impact sound estimation.

Effects of Specimen Geometry on Stress Distribution in Sandwich Specimen Under Combined Loads (복합하중을 받는 샌드위치 시편의 응력분포에 미치는 시편 형상의 영향)

  • Park, Su-Kyeong;Hong, Sung-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.11
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    • pp.1587-1592
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    • 2010
  • The effects of specimen geometry and loading conditions on the stress distribution in a sandwich specimen under combined loads are investigated by elastic finite element analysis. A commercial software NASTRAN is used in plain-strain two-dimensional finite element analysis of sandwich specimens; the analysis was performed for three different specimen shape factors and four different combined displacement conditions. The results of computational analysis suggest that the effect of the combined displacement angle, which is defined as the ratio of the shear displacement to the normal displacement, on the size of the non-homogeneous stress distribution is observed only in the case of the shear stress and von Mises stress. Also as the combined displacement angle increases, the size of the nonhomogeneous stress distribution decreases in the case of the shear stress and increases in the case of the von Mises stress. In addition, as the specimen shape factor, which is defined as the ratio of the specimen length to the height, increases, the size of the non-homogeneous stress distribution under combined displacement conditions decreases significantly.

Variation of Notch Shape on the Delamination Zone Behavior in Al/AFRP Laminates (노치형태 변화에 따른 Al/AFRP 적층재의 층간분리거동)

  • Song, Sam-Hong;Kim, Cheol-Woong
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.278-285
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    • 2001
  • Aluminum/Aramid Fiber Reinforced Plastic(Al/AFRP) laminates are applied to the fuselage-wing intersection. The main objective of this study was to evaluate the delamination zone behavior of Al/AFRP with a saw-cut and circular hole using average stress criterion and the effect of notch geometry. Mechanical tests were carried out to determine the cyclic-bending moment and delamination zone observed ultrasonic C-scan pictures. In case of Al/AFRP containing saw-cut specimen, the shape and size of the delamination zone formed along the fatigue crack. However, in case of Al/AFRP containing circular hole specimen, the shape and size of delamination zone formed two types. first type, delamination zone formed along the fatigue crack. Second type, not observed fatigue crack. Therefore, delamination zone was formed dependently of the circular hole shape.

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