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质砂作为一种建筑材料,近年来广泛应用于我国南海岛礁工程建设中。本文通过建立考虑钙质砂真实颗粒形状和颗粒破碎的胶结钙质砂离散元模型,研究了二维剪切条件下试样的宏微观力学行为,包括应力-应变行为、颗粒破碎、胶结破坏、位移场和裂纹随剪应变的演化规律,讨论了颗粒形状、颗粒粒径范围、颗粒强度和水泥胶结强度对胶结钙质砂力学行为的影响规律。结果表明,钙质砂颗粒粒径区间越宽,胶结钙质砂的强度越高。同一级配条件下,考虑真实颗粒形状的胶结钙质砂试样比圆颗粒试样的强度更高,试样总体颗粒破碎率也更高。钙质砂颗粒的强度越高,胶结钙质砂的性能越好。但是提高水泥的强度对胶结钙质砂力学性能的影响并不显著。本文的研究结果可为实际工程中钙质砂的加固提供理论依据。 相似文献
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基于接触面的宏、细观物理特征,建立了单调加载条件下钙质砂与结构接触面的弹塑性增量本构关系。从接触面的宏观条件上考虑,该模型将弹性模量取为法向压力的指数函数,采用非关联流动法则和Mohr-columb屈服函数,以及切向塑性功为硬化参量,适用于多数接触摩擦问题。在细观上将滑动面抽象为锯齿面,同时将摩擦系数取为塑性功的双曲线函数,以考虑钙质砂颗粒破碎对接触面力学特性的影响。模型概念简单、参数较少,通过理论计算与钙质砂拉拔试验结果比较,显示了模型的合理性。 相似文献
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开展了11组南海钙质砂和福建石英砂的分离式霍普金森压杆(SHPB)实验,试样相对密实度为90%,厚度分别为10、30和50 mm,得到了冲击荷载下钙质砂和石英砂的应变率时程曲线、应变时程曲线和应力应变关系。实验结果表明:通过严格装样技术可以减小实验设备产生的误差,改变试样厚度、子弹长度、整形器等是实现钙质砂应力平衡和恒应变率的主要手段。在相同的密实度和加载条件下,钙质砂的体积模量和剪切模量约为石英砂的10%,压缩强度和抗剪强度约为石英砂的30%。冲击荷载作用下钙质砂的动态力学性能与石英砂存在较大的差异,因此不能将已有石英砂的研究结果直接用于钙质砂。 相似文献
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开展了一系列钙质砂和石英砂的地面爆炸试验,主要对比分析了两种砂土介质中爆炸波的传播规律,包括峰值压力、弹塑性波速及升压时间、爆坑尺寸等。试验结果表明,爆炸波在钙质砂中的传播与在石英砂中存在较大差异:地面爆炸作用下钙质砂爆坑较石英砂爆坑的直径和深度更小,且成坑形状为两阶同心圆;钙质砂中弹性波速为236~300 m/s,石英砂中弹性波速为218~337 m/s,弹性波速和塑性波速均随炸药质量增加而增大;爆炸波在钙质砂中的升压时间随比例距离的增加而增加,而在石英砂中升压时间随比例距离变化不明显,且较钙质砂中升压更迅速;在地面爆炸作用下,低含水率钙质砂的衰减系数为2.86,石英砂为2.79。 相似文献
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岩石单颗粒压缩破碎试验研究 总被引:3,自引:0,他引:3
岩石颗粒结构复杂、形态不规则,很难用现有经典理论进行研究,分形理论可以从统计的角度研究颗粒破碎的强度。根据600颗大理岩单颗粒破碎试验,测量单颗粒破碎的应力与竖向应变关系曲线和破碎后的颗粒分布曲线,将颗粒破碎曲线按形态分为三种类型;根据颗粒破碎后的颗粒分布特性,建立了岩石颗粒破碎的分形模型,测得了大理岩颗粒破碎的分维D为2.48;根据颗粒破碎的分形模型,导出颗粒破碎强度的理论公式;将大理岩颗粒破碎强度的试验数据与理论公式预测结果进行比较,两者十分吻合,从而验证了颗粒破碎强度的分形理论。 相似文献
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以球形TNT药包作为爆源,在密实的非饱和钙质砂中进行了一系列大尺寸爆炸模型试验。主要研究在不同药包质量、埋深及砂土试样含水率条件下,密实钙质砂中爆炸波的主要基本参数随传播距离增加而变化的规律。试验结果表明爆炸波主要以弹塑性波的形式在密实钙质砂中传播,在干燥和潮湿试样中塑性纵波波速随试样初始密度的增大或含水率的降低而增大,且范围分别为250~282 m/s和302~339 m/s。集团装药情况下,非饱和钙质砂中封闭爆炸的临界比例埋深约为2.25 m/kg1/3。在试验范围内,密实钙质砂中爆炸波的法向应力峰值及法向比冲量的衰减均服从爆炸相似律。封闭爆炸时,干燥钙质砂中爆炸波的应力衰减指数在测点比例爆心距大于或小于0.75 m/kg1/3处分别为2.94或1.37;潮湿钙质砂中爆炸波的应力衰减指数随含水率升高而增大,其范围为1.39~1.79。法向比冲量衰减指数随试样含水率升高而减小,其范围为0.97~1.18。 相似文献
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Dr. A. Hettler 《Archive of Applied Mechanics (Ingenieur Archiv)》1984,54(5):321-327
Übersicht Eine Ähnlichkeitstheorie für trockenen Sand aus starren Körnern wird erweitert zur Erfassung von Kornbruch und Kapillarkohäsion. Für Kreisfundamente wird gezeigt, wie sich die Kapillarkohäsion auf die Verschiebungen in Abhängigkeit vom Fundamentradius auswirkt. Bei Kornbruch werden Entwurfsformeln entwickelt, mit denen die Ergebnisse von kleinmaßstäblichen Versuchen auf große Prototypen übertragen werden können. Die dargestellte Theorie wird durch Modellversuche sowie Sondertriaxialversuche geprüft und bestätigt.
Extension of a similarity theory to sand with capillary cohesion and grain crushing
Summary A theory of similarity for dry sand with rigid grains is extended to sand with capillary cohesion and grain crushing. The influence of capillary cohesion on the displacements of circular foundations is discussed. For sand with grain crushing the model laws are outlined describing the force-displacement relationship. The theory is checked and verified by model tests and special element tests.相似文献
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《International Journal of Solids and Structures》1999,36(29):4367-4396
The in-plane compression and crushing of honeycombs is known to be closely related to the crushing behavior of the broader class of space filling cellular solids. Previously, the authors conducted an extensive study of uniaxial crushing of a polycarbonate honeycomb with circular cells. In this paper the same honeycomb is crushed biaxially. The crushing was performed in a custom testing facility between rigid platens which can be moved independently in two orthogonal directions. The facility allows testing at various biaxiality ratios and volume reductions as high as 95%. The facility was used to conduct several series of biaxial crushing experiments on nearly square honeycomb specimens (18×21 cells) . In each experiment we recorded the true stress–displacement responses in the x- and y-directions as well as full field views of the deformation using a video camera. Biaxial crushing is quite complex and the prevalent mechanisms of collapse depend on the biaxiality ratio (γ) . As is the case in uniaxial crushing, the onset of collapse involves localized instabilities, however, the extent of localized deformation varies with γ. The energy absorption capacity of the material depends on γ. The highest energy is required when the specimen is crushed at the same rates in the two directions. 相似文献
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《International Journal of Non》2005,40(2-3):373-380
This note reexamines Biot's model for the propagation of acoustic waves in a material such as cohensionless sand, infused with a fluid, within the context of mixture theory. Instead of the standard entropy equation that is used in mixture theory, an inequality for the viscous dissipation is employed here due to a conceptual difficulty that one encounters in applying the standard equation to a mixture of sand and a fluid. The wave equations are reformulated by taking the velocity field, instead of the displacement, for the fluid as a primary quantity. By recognizing and thereby exploiting the dependence of the stored energy of the sand on the pore fluid pressure and choosing an appropriate form for the rate of dissipation, a set of governing equations are obtained which are equivalent to those derived by Biot [J. Acoust. Soc. Am. 28(1956) 168, 179; J. Appl. Phys. 33(1962) 1482]. A differential equation for the pore fluid pressure is derived and the effects of drag and virtual mass are dealt with in a unified fashion. The procedure allows us to develop generalizations to Biot's equations in a rational manner. 相似文献
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Amin Ajdari Hamid Nayeb-Hashemi Ashkan Vaziri 《International Journal of Solids and Structures》2011,48(3-4):506-516
The in-plane dynamic crushing of two dimensional honeycombs with both regular hexagonal and irregular arrangements was investigated using detailed finite element models. The energy absorption of honeycombs made of a linear elastic-perfectly plastic material with constant and functionally graded density were estimated up to large crushing strains. Our numerical simulations showed three distinct crushing modes for honeycombs with a constant relative density: quasi-static, transition and dynamic. Moreover, irregular cellular structures showed to have energy absorption similar to their counterpart regular honeycombs of same relative density and mass. To study the dynamic crushing of functionally graded cellular structures, a density gradient in the direction of crushing was introduced in the computational models by a gradual change of the cell wall thickness. Decreasing the relative density in the direction of crushing was shown to enhance the energy absorption of honeycombs at early stages of crushing. The study provides new insight into the behavior of engineered and biological cellular materials, and could be used to develop novel energy absorbent structures. 相似文献
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Kil-Sung Lee Yong-Jun Yang Sun-Kyu Kim In-Young Yang 《Acta Mechanica Solida Sinica》2008,21(4):383-388
An experimental investigation was carried out to study the energy absorption characteristics of thin-walled square tubes subjected to dynamic crushing by impact loading to develop the optimum structural members. Here, the controller is introduced to improve and control the absorbed energy of thin-walled square tubes in this paper. When the controller were used, the experimental results of crushing of square tubes controlled by the controller's elements showed a good candidate for a controllable energy absorption capability in impact crushing. 相似文献
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《International Journal of Solids and Structures》2007,44(9):2837-2851
An analytical model to study the impact process of a spherical projectile penetrating at high velocity into a carbon/epoxy plain woven laminate is developed in this work. The model is based on an energy balance, where the kinetic energy of the projectile is absorbed by the laminate by three different mechanisms: laminate crushing, linear momentum transfer and tensile fiber failure. A non-homogeneous differential equation is obtained. A subsequent simplification using regular perturbation analysis gives a closed-form solution that allows the approximative calculation of the residual velocity and hence the ballistic limit. The model is validated with the results of experimental tests in which the residual velocity is measured by means of high speed cameras. 相似文献
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为研究开剖面复合材料薄壁吸能结构的吸能特性,基于高速液压伺服试验系统,开展了开剖面复合材料薄壁结构轴向压缩试验,分析了截面构型、截面长宽比、触发模式及加载速度对其吸能特性的影响,揭示了其在压溃过程中的失效及吸能机理。研究结果表明,复合材料薄壁结构压溃过程中主要通过材料弯曲、分层、剪切破坏以及压溃区之间的摩擦吸能。截面构型对其吸能特性影响显著,其中,帽形及Ω形试件的平均压溃载荷较C形试件分别高出14.1%和14.6%,比吸能较C形试件分别高出14.3%和14.8%;截面长宽比对复合材料薄壁结构吸能特性的影响不如截面构型明显;触发模式主要影响吸能结构的初始压溃阶段,在降低峰值载荷方面,C形试件采用45°倒角触发效果更好,帽形试件采用15°尖顶触发效果更好;当加载速度从0.01 m/s提高到1 m/s时,C形、帽形及Ω形试件的平均压溃载荷分别下降了6.1%、10.9%和6.1%,比吸能分别下降了6.2%、11.0%和6.2%。 相似文献
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通过在连续-非连续单元法(CDEM)中引入考虑应变率效应的断裂能本构以及能量统计算法,实现了球体冲击破碎过程中损伤破裂程度及能量演化的定量分析。计算结果表明,冲击破碎过程分为接触蓄能阶段、损伤破碎阶段和碎块飞散阶段。首先,颗粒的部分动能转化为单元弹性变形能,随后这部分变形能和动能迅速转化为摩擦消耗、阻尼消耗及弹簧断裂能,破碎基本完全后碎块继续飞散。不同冲击速度下,颗粒分别出现了反弹、开裂、破碎和粉碎的现象。随冲击速度的增加,D50的变化速率逐渐放缓,破碎块度逐渐趋于稳定;破裂度、损伤度以及平均损伤因子的变化速率先增加后放缓,颗粒破坏以拉伸破坏为主。以上结论可为脆性材料冲击破碎工艺的优化设计提供依据。 相似文献
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An analytical model is developed to study the crushing behavior and energy absorption capability of a single elliptical tube impacted by two parallel rigid plates, with and without consideration of the strain hardening effect. The four-hinge collapse mechanism is used, and the governing equation is derived from Lagrange equations of the second kind. The numerical simulation of the dynamic response of the elliptical tube under impact using the finite element explicit code LS-DYNA is performed. The reaction force-displacement curve and displacement-time curve of the plate obtained from the two methods are in good agreement. 相似文献
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Crushing of particles in idealised granular assemblies 总被引:1,自引:0,他引:1
Adrian R. Russell David Muir Wood 《Journal of the mechanics and physics of solids》2009,57(8):1293-1313
Four idealised assemblies of equally sized spherical particles are subjected to a range of macroscopic compressive principal stresses and the contact forces on individual particles are determined. For each set of contact forces the stress fields within individual particles are studied. A failure criterion for brittle materials is imposed and indicates that crushing (or rupture) occurs when the maximum contact force reaches a threshold particle strength value, irrespective of the presence and magnitude of other lesser contact forces acting on the particle and the material properties of the particle. Combining the crushing mechanism with an assembly instability mechanism enables failure surfaces to be drawn in the three-dimensional stress space. A simple spatial averaging technique has been applied to the failure surfaces to remove the effects of assembly anisotropies. Sections of the failure surfaces on π planes have similarities to those commonly used in sand modelling. 相似文献