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31.
The pulsed thermographic technique was used to detect flat-bottomed hole defects in CFRP sheet. Pulsed phase thermography (PPT) was used to extract the characteristic information of the thermal wave signal generated by thermal pulse. The difference of the phases between the sound and defective areas were analyzed. The defects’ edges were extracted by Fuzzy C-Means clustering algorithm. 相似文献
32.
33.
An experimental method for considering dispersion and attenuation in a viscoelastic Hopkinson bar 总被引:9,自引:0,他引:9
C. Bacon 《Experimental Mechanics》1998,38(4):242-249
An experimental method is developed to perform Hopkinson tests by means of viscoelastic bars by considering the wave propagation
attenuation and dispersion due to the material rheological properties and the bar radial inertia (geometric effect). A propagation
coefficient, representative of the wave dispersion and attenuation, is evaluated experimentally. Thus, the Pochhammer and
Chree frequency equation is not necessary. Any bar cross-section shapes can be employed, and the knowledge of the bar mechanical
properties is useless. The propagation coefficients for two PMMA bars with different diameters and for an elastic aluminum
alloy bar are evaluated. These coefficients are used to determine the normal forces at the free end of a bar and at the ends
of two bars held in contact. As an application, the mechanical impedance of an accelerometer is evaluated.
A part of this work has been performed in the Laboratoire Matériaux Endommagement Fiabilité of the Ecole Nationale Supérieure
des Arts et Métiers de Bordeaux. 相似文献
34.
35.
提出了一种新的基于Hopkinson杆实验技术的在102~103s-1高应变率下实现压剪复合加载的实验装置,并给出了相应的理论分析和数值模拟。为了获取材料在复杂应力下的本构关系,借助斜飞片冲击实验的思想,对Hopkinson杆进行改造,将入射杆的末端改进为截锥形,以便在试样中同时产生压缩和剪切应力。利用有限元分析软件LS-DYNA对试样中的应力波传播进行模拟计算,并利用改进装置进行了初步实验。计算和分析结果表明,利用所设计的装置可以实现对试样的动态压剪复合加载,获得材料在高应变率复杂应力加载下的本构响应,进而建立材料在复杂应力状态下本构行为的描述。 相似文献
36.
The present investigation aims at testing polymeric foam under impact loading using large diameter nylon Hopkinson bars and optical field measurements. Accurate average stress-strain relations can be obtained when soft large diameter polymeric pressure bars and the appropriate data processing are used. However, as there are generally no homogeneous strain and stress fields for polymeric foams, an optical field observation is needed. In contrast to quasi-static tests where the digital image correlation (DIC) measurement is commonly used, technical difficulties still remain for the reliable use of DIC under impact conditions. In this paper, an accurate synchronization method based on the displacement measurement of the end of pressure bars (calculated by a robust DIC algorithm) is preferred to conventional MCDL box time synchronization. Also, the bar end displacement measurement offers a complementary calibration method for the tension/strain conversion coefficient. Strain fields are obtained for tests on foam sample at impact velocities up to 20 m/s. The localized strain fields permit better understanding of the observed stress plateau from SHPB results. The relevance of the present method for establishing mechanical response of polymeric foam is then demonstrated. 相似文献
37.
石油钻井底部钻具组合大挠度三维分析 总被引:3,自引:0,他引:3
精确描述了石油钻井底部钻具组合在三维弯曲井眼中的变形约束条件及边界条件,应用加权余量法,对底部钻具组合静力大挠度问题进行了三维分析研究,并编写了相应的计算机分析程序。该程序可以在普通微机上运行,能迅速模拟计算底部钻具组合任一点的挠度、转角和内力,同时求得钻头对地层的机械作用力和偏转角。通过算例分析,本文初步阐明了井眼曲率及方程中的非线性项对钻头力学特性的影响效果。 相似文献
38.
Carbon fiber reinforced polymer (CFRP) after low-velocity impact is detected using infrared thermography, and different damages in the impacted composites are analyzed in the thermal maps.The thermal conductivity under pulse stimulation, frictional heating and thermal conductivity under ultrasonic stimulation of CFRP containing low-velocity impact damage are simulated using numerical simulation method. Then, the specimens successively exposed to the low-velocity impact are respectively detected using the pulse infrared thermography and ultrasonic infrared thermography. Through the numerical simulation and experimental investigation, the results obtained show that the combination of the above two detection methods can greatly improve the capability for detecting and evaluating the impact damage in CFRP. Different damages correspond to different infrared thermal images. The delamination damage, matrix cracking and fiber breakage are characterized as the block-shape hot spot, line-shape hot spot, and “” shape hot spot respectively. 相似文献
39.
A General and Mild Approach to Controllable Preparation of Manganese‐Based Micro‐ and Nanostructured Bars for High Performance Lithium‐Ion Batteries 下载免费PDF全文
Prof. Dr. Weixin Zhang Prof. Dr. Zeheng Yang Shulin Liu Dr. Xiaoming Fan Fei Chen Yuan Tian Weibo Zhang Prof. Dr. Shihe Yang Dr. Mei Li 《Angewandte Chemie (International ed. in English)》2016,55(11):3667-3671
One‐dimensional (1D) micro‐ and nanostructured electrode materials with controllable phase and composition are appealing materials for use in lithium‐ion batteries with high energy and power densities, but they are challenging to prepare. Herein, a novel ethanol–water mediated co‐precipitation method by a chimie douce route (synthesis conducted under mild conditions) has been exploited to selectively prepare an extensive series of manganese‐based electrode materials, manifesting the considerable generalizability and efficacy of the method. Moreover, by simply tuning the mixed solvent and reagents, transition metal oxide bars with differing aspect ratios and compositions were prepared with an unprecedented uniformity. Application prospects are demonstrated by Li‐rich 0.5 Li2MnO3?0.5 LiNi1/3Co1/3Mn1/3O2 bars, which demonstrate excellent reversible capacity and rate capability thanks to the steerable nature of the synthesis and material quality. This work opens a new route to 1D micro‐ and nanostructured materials by customizing the precipitating solvent to orchestrate the crystallization process. 相似文献
40.
为了得到碳纤维复合材料(Carbon Fiber-reinforced Polymer, CFRP)筋弯曲状态下的极限承载力, 开展了不同直径的CFRP筋在不同弯曲半径下抗拉极限承载力研究. 首先, 根据前人的理论公式, 分析CFRP筋直径和弯曲半径对弯曲抗拉强度的影响, 在此基础上建立CFRP筋在弯曲状态下极限承载力的理论计算模型; 其次, 利用建立的模型对2种不同直径的CFRP筋在3种不同弯曲半径下的弯曲极限承载力进行测试, 并将测试结果与理论模型计算结果进行对比, 验证理论模型的正确性; 最后, 通过CFRP筋弯曲状态下极限承载力理论计算模型, 对不同直径和弯曲半径的CFRP筋弯曲极限承载力进行预测. 结果表明 在相同弯曲半径下, CFRP筋的弯曲极限强度随其直径的增大而减小; 在相同直径下, CFRP筋的弯曲极限强度随其弯曲半径的增大而增大; 当弯曲半径大于5m时, 直径为10mm和12mm的CFRP筋的张拉效率均超过90%. 本文所建立的理论计算模型的计算结果与试验结果吻合较好, 可用于预测不同弯曲工况下CFRP筋的极限承载力. 相似文献