共查询到20条相似文献,搜索用时 31 毫秒
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0Introduction Thefracturepropertiesofconcreteandrockmaterials,suchasfracturetoughnessKICand strengthfthavebeenofgreatinterestsformanyyearsbecauseoftheirimportantroleincontrolling thestructuralintegrityofvariousengineeringstructures[1-27].Varioustestingtec… 相似文献
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Brittle fracture: Variation of fracture toughness with constraint and crack curving under mode I conditions 总被引:1,自引:0,他引:1
The effect of constraint on brittle fracture of solids under predominantly elastic deformation and mode I loading conditions
is studied. Using different cracked specimen geometry, the variation of constraint is achieved in this work. Fracture tests
of polymethyl methacrylate were performed using single edge notch, compact tension and double cantilever beam specimens to
cover a bread range of constraint. The test data demonstrate that the apparent fracture toughness of the material varies with
the specimen geometry or the constraint level. Theory is developed using the critical stress (strain) as the fracture criterion
to show that this variation can be interpreted using the critical stress intensity factorK
Cand a second parameterT orA
3,whereT andA
3are the amplitudes of the second and the third term in the Williams series solution, respectively. The implication of this
constraint effect to the ASTM fracture toughness value, crack tip opening displacement fracture criterion and energy release
rateG
Cis discussed. Using the same critical stress (strain) as the fracture criterion, the theory further predicts crack curving
or instability under mode I loading conditions. Experimental data are presented and compared with the theory. 相似文献
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混凝土断裂尺寸效应的研究进展 总被引:17,自引:1,他引:16
混凝土结构断裂破坏的尺寸效应问题是近几十年来一个十分重要的研究领域.本文分析了混凝土断裂参数产生尺寸效应的原因,讨论了断裂过程区的测试方法,对国内外提出的一些尺寸效应的分析方法进行了评述.在此基础上对混凝土断裂尺寸效应的研究提出了自己的看法 相似文献
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厚度与加载速率对铁素体钢断裂韧性影响的SP压杆法实验研究 总被引:1,自引:0,他引:1
采用SP压杆实验方法,在常温下研究小圆薄片断裂韧性的厚度效应及加载速率对断裂特性的影响.实验结果表明,随着厚度的增加,断裂变形能增加,断裂部分的外表面因双向应力状态表现出微突起,微突起四周存在微小裂纹;随着加载速度的增加,断裂变形能增加,剪切断裂表面表现出从密集韧窝到韧窝连接成片特征.考虑试件变形过程中不同部分的能量耗散,从SP试件的整体断裂变形能得到试件的断裂韧性的宏观表达,断裂韧性随着厚度的增加而增加,随着加载速度的增加而减少.采用临界塑性断裂应变作为裂纹起裂判据,单位面积的能量耗散率作为裂纹扩展和失效判据的断裂模型,用有限元方法对SP压杆实验进行模拟,得到与实验结果比较相符的模拟结果. 相似文献
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The influence of a rate sensitive effect of material for a propagating crack-tip field 总被引:2,自引:0,他引:2
Fan-Chun Li 《Acta Mechanica Solida Sinica》1992,5(2):183-192
The elastic-viscoplastic model proposed in [1] is used in this paper to analyze the quasi-statically growing crack field and dynamic propagating crack-tip field of mode III. By analysis, we obtained more reasonable results than those of an elastic-plastic material. When the effect of rate sensitivity of a material is considered, it is found that only the quasi-statically growing crack-tip field is the special case of dynamic propagating crack-tip field when Mach numberM approaches zero. 相似文献
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采用最近开发的三维岩石破裂过程分析软件RFPA3D模拟单边裂纹紧凑拉伸断裂过程。试验中五个不同尺寸的岩样具有相同的力学性质参数分布,模拟结果得到了裂纹扩展中的应力场、位移场和声发射的空间分布以及单边裂纹扩展贯通的过程。单边裂纹拉伸断裂的路径是一个复杂的空间三维曲面,三维裂纹比二维裂纹更为复杂。分析了岩石试样的峰值强度和试样尺寸之间的关系。随着岩样尺寸的增加,峰值强度逐渐减小,并且延性破坏特征更加明显,模拟结果满足岩石的尺寸效应规律。最后模拟了三组不同均匀性的试样拉伸破坏过程,结果表明细观上的非均匀性对岩石尺寸效应有很大影响,随着非均匀性的增加,岩石宏观强度随之提高,即使在均匀材料中一样存在尺寸效应。 相似文献
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金属薄膜/聚合物基底(尤其是温度敏感型的聚合物)结构在外力和加热影响下的力学性能变化直接影响到器件的功能和使用寿命。通过光学显微镜原位观察钛膜/有机玻璃基底结构在力-热(20~44℃)耦合作用下的薄膜表、界面响应。在外部轴向压力作用下,薄膜会发生垂直于加载方向的屈曲。保持试件的加载端边界位移不变,对其进行加热,薄膜会出现垂直于屈曲方向的横向裂纹。通过分析发现薄膜产生横向裂纹的原因为:力-热耦合作用促使聚合物基底在非加载端方向的拉应变增大。在不同长度的薄膜裂纹段上,较长裂纹段中心部位上受到基底传递的拉应力较大,产生再次断裂的可能性较高。 相似文献
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In this paper, the classical solution of the opening mode crack in the 90° layer of 0/90/0 laminates has been determined by
means of Fourier transformations and the procedure of Copson for a pair of dual integral equations. The fracture behavior
and the in situ transverse strength of the 90° layer have been quantitatively studied in graphite/epoxy laminates, based on
the solution obtained above.
The results show that the stress intensity factor of this kind of laminates, which is different from that of a single unidirectional
90° layer, decreases with the increase in thicknessb, or modulusE
L orG
LT of the 0° layer and also decreases with the decrease in the thickness of the 90° layer. So the lamination effect manifests
itself and thein situ transverse strength of the 90° layer is thereby enchanced. The theoretical calculations agree with the experimental data
presented by D.L. Flaggs.
Supported by National Natural Science Fundation of China. 相似文献
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岩石动态断裂韧度的尺寸效应 总被引:1,自引:0,他引:1
采用两种圆孔裂缝平台巴西圆盘试件(一种为直径分别为42、80、122、155 mm的几何相似试件,另一种为直径80 mm、仅裂缝长度不同的单一尺寸试件)对岩石动态断裂韧度的尺寸效应进行了研究。给出了在霍普金森压杆系统上对试件进行径向撞击产生的应变波形和断裂模式。实验结果表明,对于几何相似试件,动态断裂韧度的测试值随着尺寸的增大而增大,而对于单一尺寸试件,其测试值随着中心裂缝长度的增加呈现先增大后减小的趋势。裂缝前端的断裂过程区长度和孕育时间是岩石动态断裂韧度测试值表现为尺寸效应的主要原因,为了减小尺寸效应,建立了考虑这两个参数在空间-时间域对动态应力强度因子的分布进行积分后再平均来确定岩石动态断裂韧度的方法。 相似文献
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Tienchong Chang 《Acta Mechanica Solida Sinica》2011,24(4):318-325
Theoretical studies have been extensively performed to reveal the mechanism of the biological adhesive structure with a flat head.However,most biological adhesive structures have a big head.Here we investigate the effect of the head shape on the adhesion capability of a mushroomlike adhesion structure based on a finite element model.We show that a mushroom-like head produces significant adhesion enhancement.We investigate also the effect of the elastic modulus of the adhesive structure on the adhesion.Our results are consistent with existing experimental results. 相似文献
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Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading frequency (20 kHz) were investigated and compared with the results under conventional loading of rotating bending (50 Hz). The growth of a crack retarded at about 500 µm in surface length under ultrasonic loading, while at about 20 µm under rotating bending. Although striations being a typical fracture mechanism were observed under conventional loading, most of fracture surface was covered with many facets under ultrasonic loading. These facets were also observed under rotating bending in nitrogen gas. The difference in growth mechanism depending on the loading frequency and the retardation of a crack growth under ultrasonic loading may be caused by the environment at the crack tip due to high crack growth rate under ultrasonic loading. 相似文献
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J. Najar V. V. Silberschmidt M. Müller-Bechtel 《Archive of Applied Mechanics (Ingenieur Archiv)》2000,70(1-3):145-157
Summary Enhanced fracture energy losses at spalling and the temperature dependence of the spalling strength of alumina ceramic bars
are analysed on the basis of the experimental tests conducted both in room temperature and within the temperature range up
to 1500°C at strain rates of some 500 s−1. The experimental method and the measurements are first shortly outlined. The mechanical response of ceramic bars is modelled
then as a heterogeneous distribution of brittle-elastic mesoelements undergoing continuum damage at the known strain history,
corresponding to that registered in the experiments. The mesoelements are characterised by the values of initial damage randomly
fluctuating within a given band-width superposed on a deterministic distribution, which corresponds to the fabrication conditions
of the ceramic bars. The model has been tested in the evaluation of room-temperature experiments, its parameters: the average
value of the initial damage, Young's modulus of the undamaged material and the energy absorption capacity in continuum damage
are taken from the calibration fitting the experimental data. The registered energy losses at spalling, which exceed the static
values of fracture energy by almost an order of magnitude, can be explained thus by the enhancement of the dissipation due
to bulk damage, which is computed on the basis of the above parameters. The temperature change of the Young's modulus of the
matrix material is taken as corresponding to the measured change of the uniaxial wave velocity in the bar, and corrected by
the temperature change of the mass density. The analysis of the model shows that the drop in the spalling strength of the
specimens with the increase of the temperature is phenomenologically related to the falling energy absorption capacity within
the continuum damage mechanism. An explanation of this phenomenon is attempted, based on the grain-size-related mechanisms
of the microfracture from pre-existing intergranular flaws distributed over the bulk of ceramics.
Received 7 May 1999; accepted for publication 14 June 1999 相似文献
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Scale effects on strength of geomaterials, case study: Coal 总被引:1,自引:0,他引:1
Scale effects on the strength of coal are studied using a discrete element model. The key point of the model is its capability to discriminate between the “strictly sample size” effect and the “Discrete Fracture Network (DFN) density” effect on the mechanical response. Simulations of true triaxial compression tests are carried out to identify their respective roles. The possible bias due to the discretization size distribution of the discrete element model is investigated in detail by considering low-resolution configurations. The model is shown to be capable of quantitatively reproducing the dependency of the maximum strength on the size of the sample. This relationship mainly relies on the DFN density. For all given sizes, as long as the DFN density remains constant with a uniform distribution or if discontinuities are absent in the considered medium, the maximum strength of the material remains constant. 相似文献