• Title, Summary, Keyword: dynamic loading

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Non-Linear dynamic pulse buckling of laminated composite curved panels

  • Keshav, Vasanth;Patel, Shuvendu N.
    • Structural Engineering and Mechanics
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    • v.73 no.2
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    • pp.181-190
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    • 2020
  • In this paper, non-linear dynamic buckling behaviour of laminated composite curved panels subjected to dynamic in-plane axial compressive loads is studied using finite element methods. The work is carried out using the finite element software ABAQUS. The curved panels are modelled with S4R element and the nonlinear dynamic equilibrium equations are solved using the ABAQUS/Explicit algorithm. The effect of aspect ratio, radius of curvature and thickness are studied. The importance of orientation of plies in the direction of loading is also reiterated in this study. Vol'mir's criterion is used to calculate the dynamic buckling loads. The panels are subjected to rectangular pulse load of various amplitude and durations and the responses are observed. For particular loading amplitude, a critical value of loading duration is observed beyond which the variation of dynamic buckling load is insignificant. It is also observed that, the value of dynamic bucking load reduces as the loading duration is increased though the reduction is not much after a particular loading duration.

Characteristics of Bearing Capacity and Reliability-based Evaluation of Pile-Driving Formulas for H Pile (H-pile의 지지력 특성 및 동역학적 공식의 신뢰도 평가)

  • 오세욱;이준대
    • Journal of the Korean Society of Safety
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    • v.18 no.1
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    • pp.81-88
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    • 2003
  • Recently, pile foundations were constructed in rough or soft ground than ground of well condition thus it is important that prediction of ultimate bearing capacity and calculation of proper safety factor applied pile foundation design. This study were performed to dynamic loading tests for the thirty two piles at four different construction sites and selected pile at three site were performed to static loading tests and then compare with measured value and value of static and dynamic loading tests. The load-settlement curve form the dynamic loading tests by CAPWAP was very similar to the results obtained from the static load tests. Based on dynamic and static loading tests, the reliability of pile-driving formula were analyzed and then suggested with proper safety factor for prediction of allowable bearing capacity in this paper.

Experiment of single screw piles under inclined cyclic pulling loading

  • Dong, Tian Wen;Zheng, Ying Ren
    • Geomechanics and Engineering
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    • v.8 no.6
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    • pp.801-810
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    • 2015
  • The ultimate pullout capacity under inclined dynamic loading is an important measure of the destruction degree of vertical screw piles (anchors) under dynamic actions. Based on the static and dynamic tests on two kinds of model screw piles, the ultimate bearing capacity was researched considering different distance-width ratio of blade (D/W) and preloading ratio. The results compared well with other experimental data available in the literature. This research reveals that D/W might determine the failure model of the piles (anchors), for example D/W = 3.14 or 5; a critical dynamic-static loading ratio (DSLR) existed in the experiments. The critical DSLR was reached under the conditions of 40%~60% preloading (D/W = 3.14) or 20%~40% preloading (D/W = 5), respectively.

REVIEW OF DYNAMIC LOADING J-R TEST METHOD FOR LEAK BEFORE BREAK OF NUCLEAR PIPING

  • Oh, Young-Jin;Hwang, Il-Soon
    • Nuclear Engineering and Technology
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    • v.38 no.7
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    • pp.639-656
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    • 2006
  • In order to apply the leak before break (LBB) concept to nuclear piping systems, the dynamic strain aging effect of low carbon steel materials has to be taken into account, in compliance with the requirements of the Korean Standard Review Guide (KSRG) 3.6.3-1. For this goal, J-R tests are needed for a range of various temperatures and loading rates, including dynamic loading conditions. In the dynamic loading J-R test, the unloading compliance method can not be applied to measure the crack growth and direct current potential drop (DCPD) method; this method also has a problem defining the crack initiation point. The normalization method is known as a very useful method to determine the J-R curve under dynamic loading because it does not need additional equipment or complicated loading sequences such as electric current or unloading. This method was accepted by the American Society for Testing and Materials (ASTM) as a standard test method E1820 A15 in 2001. However, it has not yet been clearly verified yet if the normalization method is sufficiently reliable to be applied to LBB. In this study, the basic background of the J-integral, LBB and dynamic loading J-R test are explained, and the current status for dynamic loading J-R test methods are reviewed from the view point of LBB for nuclear piping. In particular, the theoretical and historical background of the normalization method which has received attention recently, is summarized. Recent studies for this method are introduced and future works are suggested that may improve the reliability of LBB for nuclear piping.

A large-scale test of reinforced soil railway embankment with soilbag facing under dynamic loading

  • Liu, Huabei;Yang, Guangqing;Wang, He;Xiong, Baolin
    • Geomechanics and Engineering
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    • v.12 no.4
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    • pp.579-593
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    • 2017
  • Geosynthetic reinforced soil retaining walls can be employed as railway embankments to carry large static and dynamic train loads, but very few studies can be found in the literature that investigate their dynamic behavior under simulated wheel loading. A large-scale dynamic test on a reinforced soil railway embankment was therefore carried out. The model embankment was 1.65 meter high and designed to have a soilbag facing. It was reinforced with HDPE geogrid layers at a vertical spacing of 0.3 m and a length of 2 m. The dynamic test consisted of 1.2 million cycles of harmonic dynamic loading with three different load levels and four different exciting frequencies. Before the dynamic loading test, a static test was also carried out to understand the general behavior of the embankment behavior. The study indicated the importance of loading frequency on the dynamic response of reinforced soil railway embankment. It also showed that toe resistance played a significant role in the dynamic behavior of the embankment. Some limitations of the test were also discussed.

A Case Study on the Dynamic Loading Tests of Large Diameter - Long Drilled Shafts into Weathered Rock (풍화암에 근입된 장대 현장타설말뚝의 동재하시험 사례연구)

  • Seok, Jeong-Woo;Cho, Chun-Whan;Ji, Wan-Goo;Park, Min-Cheul;Yoon, Jeoung-Seob
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.486-493
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    • 2006
  • This paper deals with the procedure and the results on the dynamic loading tests of two large diameter - long drilled shafts (diameter=2.0m, length=75m) which were embedded into weathered rocks through thick soft marine clays and sandy gravels. Prior to the real dynamic loading test, the numerical simulation for the test procedure was performed to check the structural stability of the main pile body using equivalent static elastic analysis and the application of the hammer system using WEAP (Wave Equation Analysis of Pile Driving). Through these preliminary analyses the dynamic loading tests on large diameter - long drilled shafts have been successfully achieved.

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Dynamic Deformation Behavior of Aluminum Alloys Under High Strain Rate Compressive/Tensile Loading

  • Lee, Ouk-Sub;Kim, Guan-Hee;Kim, Myun-Soo;Hwang, Jai-Sug
    • Journal of Mechanical Science and Technology
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    • v.17 no.6
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    • pp.787-795
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    • 2003
  • Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as seismic loading are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, dynamic deformation behaviors of the aluminum alloys such as A12024-T4, A1606 IT-6 and A17075-T6 under both high strain rate compressive and tensile loading conditions are determined using the SHPB technique.

Research on Secure Coding and Weakness for Implementation of Android-based Dynamic Class Loading (안드로이드 동적 클래스 로딩 기법을 이용한 개발단계에서의 보안약점 및 시큐어 코딩 연구)

  • Kim, Hyunjo;Choi, Jin-Young
    • Journal of Korea Multimedia Society
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    • v.19 no.10
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    • pp.1792-1807
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    • 2016
  • Android application is vulnerable to reverse engineering attack. And by this, it is easy to extract significant module from source code and repackage it. To prevent this problem, dynamic class loading technique, which is able to exclude running code from distributed source code and is able to load running code dynamically during runtime can be used. Recently, this technique was adapted on variety of fields and applications like updating pre-loaded android application, preventing from repacking malicious application, etc. Despite the fact that this technique is used on variety of fields and applications, there is fundamental lack on the study of potential weakness or related secure coding. This paper would deal with potential weaknesses during the implementation of dynamic class loading technique with analysing related international/domestic standard of weaknesses and suggest a secure way for the implementation of dynamic class loading technique. Finally, we believe that this technique described here could increase the level of trust by decreasing the weakness related to dynamic class loading technique.

EFFECT OF STRENGTH MISMATCH AND DYNAMIC LOADING ON THE DUCTILE CRACK INITIATION FROM NOTCH ROOT

  • An, Gyn-Baek;Yoshida, Satoshi;Ohata, Mitsuru;Toyoda, Masao
    • Proceedings of the KWS Conference
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    • pp.145-150
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    • 2002
  • It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal, elastic-plastic, dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.

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In Situ Mechanical Response of Bovine Humeral Head Articular Cartilage in a Physiological Loading Environment (생리학적인 하중 조건에서 소 상완골 연골의 기계적 특성)

  • Park, Seong-Hun
    • Journal of the Korean Society for Precision Engineering
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    • v.25 no.1
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    • pp.145-150
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    • 2008
  • One of the unresolved questions in articular cartilage biomechanics is the magnitude of the dynamic modulus and tissue compressive strains under physiological loading conditions. The objective of this study was to characterize the dynamic modulus and compressive strain magnitudes of bovine articular cartilage at physiological compressive stress level and loading frequency. Four bovine calf shoulder joints (ages 2-4 months) were loaded in Instron testing system under load control, with a load amplitude up to 800 N and loading frequency of 1 Hz, resulting in peak engineering stress amplitude of ${\sim}5.8\;MPa$. The corresponding peak deformation of the articular layer reached ${\sim}27%$ of its thickness. The effective dynamic modulus determined from the slope of stress versus strain curve was ${\sim}23\;MPa$, and the phase angle difference between the applied stress and measured strain which is equivalent to the area of the hystresis loop in the stress-strain response was ${\sim}8.3^{\circ}$. These results are representative of the functional properties of articular cartilage in a physiological loading environment. This study provides novel experimental findings on the physiological strain magnitudes and dynamic modulus achieved in intact articular layers under cyclical loading conditions.