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Mica Grujicic B. Pandurangan W. C. Bell S. Bagheri 《Journal of Materials Engineering and Performance》2012,21(2):167-179
The propagation of uniaxial-stress planar shocks in granular materials is analyzed using a conventional shock-physics approach.
Within this approach, both compression shocks and decompression waves are treated as (stress, specific volume, particle velocity,
mass-based internal energy density, temperature, and mass-based entropy density) propagating discontinuities. In addition,
the granular material is considered as being a continuum (i.e., no mesoscale features like grains, voids, and their agglomerates
are considered). However, while the granular material is treated as a (smeared-out) continuum, it is recognized that it contains
a solid constituent (parent matter), and that the structurodynamic properties (i.e., Equations of State (EOS) and Hugoniot
relations) of the granular material are related to its parent matter. Three characteristic shock loading regimes of granular
material are considered and, in each case, an analysis is carried out to elucidate shock attenuation and energy dissipation
processes. In addition, an attempt is made to identify a metric (a combination of the material parameters) which quantifies
the intrinsic ability of a granular material to attenuate a shock and dissipate the energy carried by the shock. Toward that
end, the response of a typical granular material to a flat-topped compressive stress pulse is analyzed in each of the three
shock loading regimes. 相似文献
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M. Grujicic R. Yavari J. S. Snipes S. Ramaswami 《Journal of Materials Engineering and Performance》2013,22(5):1268-1283
In this article, an attempt is made to construct a soil-material model which can be used over a wide range of soil densities. To construct such a model, an existing purely continuum-type soil material model (used in the high-density regime), within which the granular structure of the soil is neglected, is combined with an existing discrete-type soil material model (used in the low-density regime) within which soil is treated as an assembly of interacting particles. In order to enable it to be used in conventional transient, nonlinear dynamics, and finite element analyses, the new soil material model is cast using a continuum-type framework. Thus, while in the low-density regime soil behavior is fully dominated by the discrete-type soil-material model, soil has been treated as a continuum constituent properties of which are governed by particle geometrical parameters and particle-particle interaction laws. To demonstrate the utility and fidelity of the new soil material model, a series of uniaxial strain computational tests involving rectangular, parallelepiped-shaped soil-slug normal impact onto a rigid, fixed, flat surface is carried out. While these tests are of a one-dimensional character, they are generally considered as being representative of the loading and deformation histories experienced by mine-blast-ejected soil during its impact with the target structure. The results obtained using the newly proposed soil material model, in the low-density regime, are found to be fully consistent with their discrete-particle modeling and simulation counterparts, suggesting that the new model can be used in transient nonlinear dynamics, finite element simulations involving low-density soil. 相似文献
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1Cr18Ni9不锈钢夹紧带断裂原因分析 总被引:1,自引:1,他引:0
夹紧带在进行振动试验时焊点处发生断裂,对断裂的夹紧带进行了断口的宏观、微观形貌观察、化学成分分析、金相组织分析、硬度测试和焊点质量检验。结果表明,焊接工艺控制不当造成热影响区组织过热以及焊点压痕深度过大是导致夹紧带脆性断裂的主要原因;另外,原材料强度偏高,导致焊接性能和断裂韧性下降,增加了脆断倾向。通过采用较低强度的冷作硬化状态钢带进行焊接加工,改善焊接工艺,优化焊接接头参数,产品经过振动试验未发生断裂失效。 相似文献
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Al-Cu-Li合金搅拌摩擦焊接头的微观组织和力学性能 总被引:3,自引:1,他引:3
采用搅拌摩擦焊方法对2mm厚的Al-Cu-Li合金轧制板进行了焊接.接头内形成了焊核区、热机影响区和热影响区.焊核区由细等轴再结晶组织构成;热机影响区内的组织发生较大的弯曲变形,并在热循环的作用下发生了回复反应;热影响区形成了粗大的板条状组织.实验结果表明:在200mm/min的焊接速度下,接头的拉伸强度最高,达到393MPa,断裂形式为韧性和脆性的混合型断裂;在500mm/min的焊接速度下,接头强度为267.7MPa,断裂形式为脆性断裂. 相似文献
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基于弹性导波的部分平面波分析方法,对复合固体层中兰姆波的声场分布问题进行了研究。在对称的复合固体层中传播的兰姆波模式可以是对称的或反对称的;在非对称的复合固体层中传播的兰姆波模式是非对称的。针对常见的固体层-粘结层-固体层结构中兰姆波的色散关系及声场分布等进行了数值分析,所得结果对兰姆波应用于复合固体层的无损评价具有实际意义。 相似文献
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大型轧机用滚动轴承绝大部分都采用柱销焊接保持架结构,其具有承载大等优点,但在使用过程中,早期失效往往发生在保持架焊接部位。本文对典型失效轴承进行了宏观检查、断口分析、低倍检验、金相分析及轴承的运动状态分析。结果表明,焊接工艺失控导致柱销焊接端存在焊接未融合等缺陷是引起此类轴承早期失效的主要原因,并提出了在大型柱销焊接式保持架轴承的结构设计、柱销材料的选择以及焊接工艺质量控制等方面的改进建议。 相似文献
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Fracture at high temperature has become a critical problem for such high temperature components as those used in power plants
or oil refinery plants, because both high operating temperature and pressure are required for better thermal efficiency. Therefore,
it is very important to approach such problems from the viewpoint of high temperature material properties. Since fatigue and
creep are closely related to such components failures, the fracture behavior in high temperature components must be evaluated
through fatigue and creep crack growth tests, and based on these results, better operating conditions can be determined. In
this study, recently developed P92 (9Cr-2W) alloy steel, which is a high strength material for high temperature use, is investigated
and its fatigue crack growth has been characterized by Paris law. A series of high temperature fatigue tests were carried
out at 400, 500, 550, 600, 625, 650, and 700°C to verify the temperature effect. The results indicated that the Paris exponent
remained at approximately the same value up to a certain temperature. From 600 to 700°C, creep rupture tests were conducted
in order to investigate the creep behavior with temperature. Further analysis has also been carried out to investigate the
effect of temperature on fracture mode shift, dimple formation, and its role in crack growth rate and deformability at high
temperature. 相似文献
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为研究加载速率和高温对岩石动态断裂韧性的影响,利用分离式霍普金斯压杆对4种温度状态下的中心直裂纹半圆盘试样进行动态断裂试验。采用试验和解析方法研究杆中温度梯度对应力波的影响,并利用高速摄像机观察试样的破坏特征。结果表明:杆上的温度梯度不会使应力波的波形发生明显的变形;即使在400℃条件下,试样也能达到应力平衡。在25~400℃的温度条件下,岩石动态断裂韧度随着加载率的增加线性增长,且高温对岩石断裂韧度具有强化作用。 相似文献
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Thermally sprayed coatings are frequently subjected to impacts by small solid particles which induce surface erosion. To identify the physical mechanisms associated with such a material removal process, experimental tests as well as detailed computational analyses of porous coatings containing multiple phases are performed. In the experiments, a gas jet erosion test is conducted to measure material loss of coatings with different mixtures of brittle and ductile phases. The results show higher erosion resistances with small volume fractions of metal phase added to predominantly brittle coatings. Following this outcome, the study is directed toward elucidating the physical mechanisms behind the increased erosion resistance. Here, solid particle impacts are simulated with dynamic finite element analyses where material removals and coating's energy absorption behaviors are closely monitored. Furthermore, parametric study is carried out to quantify effects of cracking resistances and plastic dissipation on the erosion rate. The results reveal synergistic effects of fracture energy and plastic deformation. The combined mechanisms allow greater energy absorptions and enhanced erosion resistance in coatings with mixture of ductile phase. These assessments should offer insights into tailoring coatings with optimized composition of ductile phase to increase their performances. The results are also valuable in understanding foreign object damage (FOD) of coatings. 相似文献
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利用电子光学仪器(扫描电镜、透射电镜、电子探针和Auger能谱仪)对钢中白点的晶体取向和元素偏析进行了综合研究。结果表明:白点断口以晶内的准解理和沿晶的波状撕裂条纹的混合断裂形态为特征;白点断裂面的晶体学取向主要是沿铁素体{112}晶面的准解理断裂,显徽空隙内枝晶表面为{111}自由面;白点断口上有P和Cr,Mo,Mn的正偏析,其中以P最为明显。 相似文献
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The aim of the present work is the classification of the characteristics of elastic waves, which are generated by fibre failures during quasi-static tensile fibre bundle tests and captured by the use of acoustic emission (AE) method. In addition, elastic waves generated out of the fibre bundle gauge length and propagated through the bundle at different stages of the loading process using an acousto-ultrasonic (AU) technique are also classified. To this target, a large number of tests were conducted on organic, ceramic and carbon fibre bundles according to DIN 53942. An in-house developed analysis and quantification methodology of the captured AE and AU waveforms is proposed in order to identify the frequency content of the fibre failure event, to characterize the medium of propagation and to investigate the effect of the acquisition system on the monitored signals. In fact, the application of the proposed analysis on the results of the conducted mechanical tests leads to the development of a useful database, concerning the ranges of AE features and the representative sets of frequency values that correspond to fibre fracture. Furthermore, the proposed database offers valuable knowledge for the role of material parameters, such as fibre structure and properties, on the characteristics of the recorded waveforms, constituting in this way a valuable tool that enables a better understanding of elastic waves initiation and propagation through continuous fibres. 相似文献
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采用国家标准GB4161-2007对高速列车承载底架焊接结构材料A7N01P-T5铝合金型材的断裂韧度KC进行了测试和分析,测试了3种厚度母材的KC,基于能量理论和线弹性力学提出A7N01P-T5铝合金断裂韧度随试样厚度变化关系KC(B)的解析公式,并进一步采用国家标准GB21143-2007的CTOD试验对其进行验证.结果表明,该公式具有较高的精度和普适性,可用于确定不同板厚材料的KC,将公式应用于不同壁厚条件下的焊接结构的完整性评定,以此节省人力物力,并大幅度缩短焊接结构完整性评定及结构剩余寿命的计算周期.同时为各种金属材料的KC获取提供通用性的方法和参考准则. 相似文献