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程里 《理化检验(物理分册)》2014,(10):718-722
总结介绍了痕迹分析技术及其在机械失效分析中的应用,并根据痕迹特征将机械失效分析中的痕迹分为了机械损伤痕迹、腐蚀和污染痕迹、热损伤痕迹3大类,并分别举例进行了说明。实际案例分析结果表明,通过对机械失效件表面的宏观及微观痕迹进行分析,对于确定机械失效性质、查明机械失效原因具有重要意义。 相似文献
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《中国新技术新产品》2016,(9)
随着农村劳动力的转移以及劳动力成本的增加,蔬菜移栽作业环节逐渐由人工化向机械化转变,从而提高蔬菜移栽效率及质量。本文阐述了国内外蔬菜移栽机械现状,分析了我国蔬菜移栽机械的发展方向。 相似文献
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果品运输中的机械损伤机理及减损包装研究进展 总被引:23,自引:5,他引:18
果品在贮运过程中承受静载、挤压、振动、冲击等载荷形式的作用,形成了以塑性变形为主的现时损伤和以粘弹性变形为主的延时损伤.果品采后由于贮运引起的机械损伤和耐贮性的下降是果品采后损耗的主要原因.采用科学有效的措施减少果品采后机械损耗具有重要意义.文中综述了国内外这方面的研究成果,着重论述了果品的流变特性、运输过程中果品的损伤机理与规律、模拟试验技术以及减损包装技术. 相似文献
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开展了SiC(20vol%)-石墨(15vol%)/ZrB2复合材料室温及高温拉伸性能实验,发现高温时复合材料的拉伸强度和弹性模量有所降低,并且具有明显的非线性特征。引入热损伤来表征弹性模量随温度的衰减规律,利用强度统计分析方法确定单向应力状态下材料的机械损伤演化方程,建立了材料在热力耦合条件下的高温拉伸损伤非线性本构模型。分析表明:随着温度的升高,SiC-石墨/ZrB2复合材料的热损伤和机械损伤不断增加,延性增强,且脆性-延性破坏转变温度范围为1 250~1 350℃。 相似文献
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目的研究猕猴桃在运输过程中振动特性以及机械损伤的影响因素,为增强水果运输包装的防护性提供可靠的理论依据。方法通过扫频振动实验检测猕猴桃的共振频率;基于正交实验分析法进行猕猴桃的定频振动实验,分析振动加速度、包装缓冲材料、振动时间和堆码层数等因素对表面损伤指数和振动传递率的影响,从而获得造成猕猴桃机械损伤的敏感因子。结果当振动加速度为0.15g时,猕猴桃的共振频率为85.2Hz;采用纸屑作为缓冲材料的整体包装,猕猴桃的受损程度最小,其振动传递率也较小。结论对表面损伤指数和振动传递率影响最大的因子均为缓冲包装结构,纸屑衬垫和EPS衬垫的缓冲性能优于PET衬垫。振动传递率越大,表面损伤指数越大。 相似文献
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本文介绍了用磨角、择优腐蚀的方法显示和测试硅片表面的机械损伤层厚度的测试方法、原理和实验结果。 相似文献
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This article presents the mechanical characterization of an eco composite consisting of a thermoplastic matrix reinforced by flax fibres. Different configurations of specimens were tested with uniaxial tensile loading and their mechanical behaviours were discussed. Moreover, the acoustic emission technique was used to detect the appearance of damage mechanisms and to follow their evolution. In addition, a list of these mechanisms was established by means of macroscopic and microscopic observations. The acoustic emission records were post processed by the k-means unsupervised pattern recognition algorithm. Depending on the specimen configuration, three or four classes of events were obtained. The acoustic characteristics of these classes were compared. Then, a correlation between these AE events classes and the damage mechanisms observed was proposed. Their effects on the mechanical behaviour of the material were investigated by means of a variable called the Sentry Function. 相似文献
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复合材料π接头拉伸力学性能的试验和计算研究 总被引:1,自引:0,他引:1
《复合材料学报》2009,26(2):181-186
采用试验和数值模拟的方法对整体化复合材料π接头在拉伸载荷作用下的力学特性进行研究。在Instron 8803电液伺服材料试验机上进行了π接头试验件的拉伸试验,记录试验过程中损伤产生及破坏过程,记录初始失效载荷和最终失效载荷。试验结果表明,填料是π接头破坏的关键部位,需要进行深入研究。提出了复合材料π接头力学性能数值模拟的基本假设和方法,基于通用有限元商用软件,建立π接头三维力学分析模型,获得π接头各部位应力分布情况;基于基本假设,对最大应力失效准则进行修正,并给出π接头各部位损伤载荷的预测值。计算预测π接头的初始损伤部位与试验吻合,初始失效载荷计算值与5个试件试验数据均值相比误差为0.53%,表明了数值分析方法的可行性。 相似文献
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Amanda S. Lim Qi An Tsu-Wei Chou Erik T. Thostenson 《Composites Science and Technology》2011,71(5):616-621
The numerous structural applications of composites, coupled with their complex, rate-dependent mechanical behavior necessitate research into their mechanical response under dynamic loading scenarios. While the damage mechanisms of composites under dynamic compression loading are well-understood, measuring the occurrence of damage in a non-invasive manner is challenging. Toward this end, we investigate the electrical response of an embedded percolating carbon nanotube network in woven fabric/epoxy composites to dynamic compression loading. The percolating network is established through the use of a non-uniform dispersion of carbon nanotubes, achieved using a fiber sizing agent. The resulting conductive network is sensitive to delamination and damage occurring near the fiber surfaces. The dynamic mechanical response of the composite specimens is explored using Hopkinson bar methodology. Definite increases in baseline resistance of the conductive composite specimens are seen after repeated impacts demonstrating the ability of the carbon nanotube network of these conductively modified composites to respond electrically to damage induced during dynamic loading. 相似文献
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《Composites Science and Technology》2003,63(3-4):507-516
Since fiber reinforced composite materials have been used in main parts of structures, an accurate evaluation of their mechanical characteristics becomes very important. Due to their anisotropic nature and complicated architecture, it is very difficult to reveal the damage mechanisms of these materials from the results of mechanical tests. Therefore, there is a need to conduct reliable simulations and analytical evaluations. In this paper, the damage behavior of FRP is simulated by finite element analysis using an anisotropic damage model based on damage mechanics. The proposed procedure is applied to an example; the finite element analysis of microscopic damage propagation in woven fabric composites. Experimental tests have been conducted to evaluate the validity of the proposed method. It is recognized that there is a good agreement between the computational and experimental results, and that the proposed simulation method is very useful for the evaluation of damage mechanisms. 相似文献
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The compressive mechanical properties of three dimensional (3D) braided composites are of key concern for design in actual engineering application. A representative volume cell (RVC) is chosen to study the uniaxial compressive mechanical properties of the braided composites with different braid angles by combing damage theory and finite element method. The fiber misalignment and longitudinal shear nonlinearity of braid yarn are considered in the computation model. And their influences on the compressive behavior of the braided composites are also evaluated. The damage development of constituents within the braided composites are obtained and analyzed. The main damage and failure modes and their interaction of braid yarn are provided as well. The numerical results are found that the compressive mechanical behavior of the braided composites with lower braid angle is sensitive to the fiber initial imperfection of braid yarn. The strength of the braided composites with different braid angle is controlled by the different microscopic failure modes. 相似文献
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Recent developments on damage modeling and finite element analysis for composite laminates: A review
Under complex environments such as continuous or cyclic loads, the stiffness degradation for the laminated composites such as the carbon fiber reinforced polymer matrix composites is an important physical and mechanical response to the damage and failure evolution. It is essential to simulate the initial and subsequent evolution process of this kind of damage phenomenon accurately in order to explore the mechanical properties of composite laminates. This paper gives a comprehensive review on the general methodologies on the damage constitutive modeling by continuum damage mechanics (CDM), the various failure criteria, the damage evolution law simulating the stiffness degradation, and the finite element implementation of progressive failure analysis in terms of the mechanical response for the variable-stiffness composite laminates arising from the continuous failure. The damage constitutive modeling is discussed by describing the evolvement of damage tensors and conjugate forces in the CDM theory. The failure criteria which interpret the failure modes and their interaction are compared and some advanced methods such as the cohesive theory which are used to predict the damage evolution properties of composites are also discussed. In addition, the solution algorithm using finite element analysis which implements progressive failure analysis is summarized and several applicable methods which deal with the numerical convergence problem due to singular finite element stiffness matrices are also compared in order to explore the whole failure process and ultimate load-bearing ability of composite laminates. Finally, the multiscale progressive failure analysis as a popular topic which associates the macroscopic with microscopic damage and failure mechanisms is discussed and the extended finite element method as a new finite element technique is expected to accelerate its practical application to the progressive failure analysis of composite laminates. 相似文献
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We highlight our recent experimental work on an efficient molecular nonlinear optical crystal, 3-methoxy 4-hydroxy benzaldehyde
(MHBA). Optical quality single crystals of MHBA were grown from mixtures of solvents and from melt. The overall absorption
and transparency window were improved by growing them in a mixture of chloroform and acetone. The grown crystals were characterized
for their optical transmission, mechanical hardness and laser damage. We have observed a strong correlation between mechanical
properties and laser induced damage. 相似文献
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An analytical model is developed for the mechanical degradation of asphalt cement and mastic under repeated loading. The model is derived by applying the strain decomposition principle to consider linear viscoelastic, nonlinear viscoelastic, and damage mechanisms. The experimental processes to isolate the behaviors and the analytical functions used to model each are described. It is found that the Schapery type damage approach is capable of modeling the fatigue process of these materials once appropriate consideration is taken for their nonlinear viscoelastic responses. Fatigue in asphalt mastics is also found to occur due to physical damage occurring in the asphalt cement. 相似文献
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Jandro L. Abot Yi Song Maruthi Sri Vatsavaya Sandeep Medikonda Zachary Kier Chaminda Jayasinghe Nathan Rooy Vesselin N. Shanov Mark J. Schulz 《Composites Science and Technology》2010
Laminated composite materials can reach high mechanical properties at low weight. Composite materials, however, are susceptible to damage due to their low interlaminar mechanical properties and poor heat and charge transport in the transverse direction to the laminate. Moreover, methods to inspect and ensure the reliability of composites are expensive and labor intensive. Recently carbon nanotube forests were spun into thread that is tough and electrically conductive. The thread was integrated into composite materials and used for the first time as a sensor to monitor strains and detect damage including delamination in the material. These self-sensing composites were found to be very sensitive to damage and will help to revolutionize the maintenance of composite structures, which will now be based on their condition and not their amount of use. 相似文献