共查询到16条相似文献,搜索用时 156 毫秒
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为研究蒸汽养护对再生骨料混凝土断裂过程损伤特征的影响,开展了再生骨料混凝土三点弯断裂试验,并采用声发射技术对损伤过程进行了监测分析。结果表明,蒸养降低了再生骨料混凝土断裂峰值荷载,断裂过程中声发射信号强度低于标准养护试件。声发射振铃计数、撞击数、b值等参数能够准确反映再生骨料混凝土断裂过程损伤演变规律。加载上升阶段,声发射信号活动性很低,试件内以微裂纹的形成为主,加载至荷载峰值,声发射振铃计数累计值增长呈现平缓阶段,混凝土内微裂缝的聚合会持续一段时间。峰值后荷载迅速降低阶段声发射信号最活跃,为裂缝迅速发展的过程。峰后荷载缓慢降低的过程,声发射信号活跃性降低,裂缝扩展至试件顶部区域,主要是宏观裂缝的开展,不再产生新的裂缝。 相似文献
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利用声发射技术监测受载混凝土裂缝发展特征的首要任务是对声发射源的准确定位。为了解混凝土中声发射波速特性,提高声发射源定位精度,该文开展了一系列室内试验,构建了考虑衰减现象的声发射波速修正模型,优化建立了基于修正波速的区域穷举定位法。结果表明:水灰比越小,基准波速越大,波速随距离的衰减越大。骨料粒径越大,基准波速越大,波速随距离的衰减越大。直线距离小于500 mm时,可采用对数函数描述声发射波速与距离的定量关系,以此构建的波速修正模型满足工程精度要求。采用修正波速的区域穷举定位法对单轴压缩试验产生的裂缝进行定位时,定位点比时差定位法更接近裂缝实际位置,有效提高了定位精度。 相似文献
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用埋入式光纤传感器探测建筑结构中的声发射 总被引:5,自引:0,他引:5
声发射技术已经应用于金属和混凝土结构中,作为探测内部裂缝的一种无损检测方法。目前用的技术都是由压电换能器来采集声发射信号。讨论了基于用光纤技术的声发射传感器的开发和测量方法。它是用埋入式光纤传感器来监测类似桥梁、高速公路、隧道和房屋建筑等混凝土结构中的开裂信号。 相似文献
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为探讨掺入聚丙烯塑料颗粒(PP)对混凝土疲劳损伤的影响,以不同塑料颗粒掺量Wf (0、10%和20%)混凝土为研究对象,采用声发射技术,开展一系列三点弯曲疲劳试验。试验结果表明:掺入塑料颗粒后,混凝土疲劳寿命增大,断裂能增大,可承受的最大荷载降低,但挠度增大,塑性变形能力增强;AE(Acoustic Emission)定位的损伤源主要集中在跨中,首次峰值荷载前,AE事件偏少,AE定位可识别的内部疲劳损伤点较少,当接近疲劳破坏阶段,AE信号源急剧增加,且随着Wf越大,AE事件数量明显减少,AE事件主要出现在循环荷载波谷处;掺入塑料颗粒后,声发射信号次数显著降低,持续时间更短,且随着Wf的增加,声发射信号次数进一步降低。掺入PP塑料颗粒有助于缓解混凝土内部疲劳损伤,延长其疲劳寿命。 相似文献
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为研究BFRP筋与混凝土粘结-滑移过程中的损伤特征,对BFRP筋混凝土粘结试件进行了加载速度为0.1 mm/s的拔出试验。采用声发射技术对损伤过程的特点进行了研究,并且针对破坏预警指标的有效表征进行了深入分析。结果表明,声发射能量、撞击数、振铃计数等参数能够真实反映BFRP筋混凝土粘结受载情况,并得到250 kHz~300 kHz频段的声发射事件百分比及声发射b值范围可以作为粘结应力达到峰值时的预警指标,为BFRP筋混凝土粘结-滑移破坏预警提供了依据。 相似文献
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《高压物理学报》2020,(1)
为了研究钢筋混凝土墙在冲击荷载作用下的动态响应,借助ANSYS/LS-DYNA建立钢筋混凝土墙的有限元模型。冲击体质量为2 t,冲击速度为3 m/s,分析了轴压比、墙宽和边缘构件对钢筋混凝土墙抗冲击性能的影响。在此基础上,分析了墙体在极限荷载作用下经历的3个阶段,提出了一种在极限荷载作用下墙体破坏失效的判别准则;利用所提出的判别准则分析了在极限荷载作用下轴压比、墙宽和边缘构件的影响。结果表明:在一定范围内,随着轴压比的增加,墙体抗冲击性能提高,有轴压的墙体损伤区域较为集中;增加墙宽和加入边缘构件均能有效增强墙体的抗冲击性能;在极限荷载作用下,冲击质量一定时,随着轴压比的增加,结构破坏失效所需的冲击能变小。 相似文献
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混凝土内部在断裂时会产生相应的声发射信号,通过这一信号,混凝土内部损伤断裂区域可以被定位。然而,混凝土是一种多相非均匀材料,而声发射定位算法是基于均匀介质假设进行计算的,因此采用该算法对其定位会产生一定的误差,有必要从细观的角度研究混凝土非均匀性对定位精度的影响。该文基于随机骨料模型以及时差定位算法(基于遗传算法),建立了一种用于估计混凝土声发射定位误差的定量估算模型。采用该模型定量估算分析了混凝土细观组分对其声速的影响,并在该分析结构的基础上继续分析了骨料含量以及声速取值偏差对定位精度的影响。结果表明,在正常骨料含量变化范围内,骨料含量对定位精度影响不大,而声速取值偏差对定位精度的影响远大于骨料含量对其的影响。 相似文献
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采用声发射技术,对四种不同晶粒度20~#钢试件的单轴拉伸过程进行监测,探究不同晶粒度对于金属材料损伤过程中声发射特性的影响。试验结果表明:声发射信号的幅值、能量和撞击计数等特征参数能够很好地描述材料不同晶粒度大小对材料拉伸过程中声发射特性的影响。细晶粒试件声发射信号数较少,强度较低,随着试件晶粒度的增大,声发射信号的强度和活性呈现明显增加的趋势。说明粗晶粒试件力学性能劣化严重,拉伸过程极易损伤,因此,试验结果也反映了金属材料微观损伤过程中声发射与材料内部的损伤演化密切相关。 相似文献
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The influence of a prolonged rest at room temperature on the activity of acoustic emission upon microindentation of preliminarily deformed MgO single crystals is investigated. It is found that the number of acoustic emission signals after the specimens have rested increases at low loads P (~50 g) applied to an indenter and decreases at high loads P (~200 g). The change observed in the activity of acoustic emission depends on the degree of preliminary deformation. It is assumed that the observed effects are associated with the difference between the sources of acoustic pulses: the main contribution to the activity of acoustic emission comes from the breakaway of dislocation pileups at low loads P and from the formation of microcracks and macrocracks at high loads. 相似文献
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Effect of the state of internal boundaries on granite fracture nature under quasi-static compression
E. E. Damaskinskaya I. A. Panteleev A. G. Kadomtsev O. B. Naimark 《Physics of the Solid State》2017,59(5):944-954
Based on an analysis of the spatial distribution of hypocenters of acoustic emission signal sources and an analysis of the energy distributions of acoustic emission signals, the effect of the liquid phase and a weak electric field on the spatiotemporal nature of granite sample fracture is studied. Experiments on uniaxial compression of granite samples of natural moisture showed that the damage accumulation process is twostage: disperse accumulation of damages is followed by localized accumulation of damages in the formed macrofracture nucleus region. In energy distributions of acoustic emission signals, this transition is accompanied by a change in the distribution shape from exponential to power-law. Granite water saturation qualitatively changes the damage accumulation nature: the process is delocalized until macrofracture with the exponential energy distribution of acoustic emission signals. An exposure to a weak electric field results in a selective change in the damage accumulation nature in the sample volume. 相似文献
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Neutron emission measurements, by means of 3He devices and bubble detectors, were performed during two different kinds of compression tests on brittle rocks: under monotonic and cyclic loading. The material used for the tests was Green Luserna Granite, with different specimen sizes and shapes, and consequently with different brittleness numbers. Since the analyzed material contains iron, our conjecture is that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure. Some studies have been already conducted on the different forms of energy emitted during the failure of brittle materials. They are based on the signals captured by acoustic emission measurement systems, or on the detection of electromagnetic charge. On the other hand, piezonuclear neutron emissions from very brittle rock specimens in compression have been discovered only very recently. In this paper, the authors analyse this phenomenon from an experimental point of view. 相似文献
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A. N. Nikitin R. N. Vasin A. M. Balagurov G. A. Sobolev A. V. Ponomarev 《Physics of Particles and Nuclei Letters》2006,3(1):46-53
The results of combined application of the neutron diffraction and acoustic emission methods for investigation of the physical properties of synthetic quartz and natural quartzite in a temperature range of α-β transition are given. In experiments, the quartzite sample was exposed to heating and uniaxial compression. Changes of the lattice spacings in quartzite were measured in a temperature range 540–620°C. On the basis of these measurements, the inner inner stresses are evaluated and found to exceed the applied stresses by several times. It is found that after the phase transition is finished, short bursts of acoustic emission (AE) occur which are two orders of magnitude more intense than the acoustic emissions produced by thermal cracking of the sample while the sample is heating up to the transition temperatures. An assumption is made that the anomalous behavior of the physical properties of quartz-containing rocks under relatively low pressures near the transition temperature can cause the formation of strong concentrators of local stresses comparable with the breaking point of the material, thereby initiating microcracking. 相似文献
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E. E. Damaskinskaya I. A. Panteleev D. R. Gafurova D. I. Frolov 《Physics of the Solid State》2018,60(7):1363-1367
Accumulation of defects at various stages of the deformation of a structurally inhomogeneous material (granite) has been studied using two nondestructive methods: acoustic emission (AE) and X-ray computer microtomorgaphy (CT). The quasi-static testing of cylindrical samples of a Westerly granite was carried out under uniaxial compression. The control of the defect formation was realized using the real-time monitoring of acoustic emission. For each sample under study, several steps of the loading and tomographic imaging have been performed. We have found that an exponential or power-law function of the energy distribution of the AE signals makes it possible to select a sample region, in which the system of defects has transited into a self-organized criticality state and large cracks have been formed. This result coincides with the data of the X-ray tomography Computer Microtomography. 相似文献