A calculation model to assess the crack propagation length of rock block in clastic flow

The primary cracks in the rock block undergo series of steps and finally disintegrate,during this procession,the radius affects the impact force of rock block in clastic flow.Therefore,it is essential to figure out the evolution mechanism of crack propagation for the design of engineering protection.In this study,based on fracture mechanics and Hertz contact theory,collision happened between rock block and slope surface is assumed to be elastic contact.Based on the above assumption,the critical impact force of crack propagation is obtained,and a model used to calculate the crack propagation length in a single collision is established.Besides,a rock fall site in Jiuzhai Valley was used to verify the calculation model.According to the model,several key factors were identified to influence crack propagation length including falling height,initial equivalent radius,and recovery coefficient of slope surface.Moreover,as a result of the orthogonal experiment,the influence of those factors on the crack propagation length was ranked,normal recovery coefficient>initial radius>initial falling height.In addition,the kinetic energy of the rock block in the compression stage is transformed into elastic deformation energy,angular kinetic energy,and dissipated energy of crack propagation.Due to the increase of collisions,the kinetic energy is gradually transformed into angular kinetic energy,and the dissipated energy of crack propagation weights is reduced.In conclusion,the crack propagation in rock block is a complicated progress,which is affected by multiple factors,especially falling height,initial equivalent radius,and recovery coefficient of slope surface.Our study may provide guidance for the design of protective structure of clastic flows.

Vegetative propagation of Dalbergia sissoo:effect of growth regulators,length,position of shoot and type of cuttings on rooting potential in stem cuttings

The effect of auxins （IAA or IBA at 100, 200, 500 mg.L J） on rooting and sprouting parameters differed significantly （p 〈 0.05）. Rooting and sprouting percentages were higher in some treatments while other parameters were significantly higher in other treatments. The results of the present study revealed that rooting was significantly （p 〈 0.05） affected by the length of cuttings, as well as the position of shoots and type of cuttings. On average, 86.0 per cent rooting was observed in the 30-cm long cuttings com- pared to the other two lengths of cuttings, i.e., 20 and 25 cm, irrespective of any auxin treatment. In a control set, without any auxin treatment, a maximum of 60.0% rooting was recorded in the 30-cm long cuttings and a minimum of 40.0% of the cuttings rooted in the 20-cm long cuttings. Similarly, cuttings collected from the lower and upper portions of shoots resulted in 72.5 and 52.5 per cent rooting respectively, irrespective of auxin treatments. Maximum rooting was observed in the lower portion （40.0%） of cutting com- pared to the upper portion （30.0%） in the control set without auxin treatment. Leafless branches produced maximum （72.0%） rooting compared to the leafy cuttings （35.0%）, irrespective of the auxin treatment. The leafy cuttings produces a minimum of 15.0% sprout- ing and rooting in the control set.

Experimental Observation of Cumulative Second-Harmonic Generation of Circumferential Guided Wave Propagation in a Circular Tube

The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle.

Influence of Microstructures and Residual Stress on Fatigue Crack Propagation Rate of High Carbon Steels

The cold-work tool steels T10A and GCr15 have been studied with regard to the influence of austenitization temperature, tempering temperature and the residual stress on the crack propagation rate and the critical crack length. The kinds of fracture morphology have been studied too. The crack propagation rate is dependent strongly on the austenitization temperature, the tempering temperature and the surface compressional residual stress in specimens.

Propagation of surface magnetoplasmon polaritons in a symmetric waveguide with two-dimensional electron gas

The properties of surface magnetoplasmon polaritons(SMPPs)in a symmetric structure,composed of two semi-infinite regions of high-density two-dimensional electron gas(2DEG)separated by a thin film in Voigt configuration,are investigated.The normal and absorption dispersion relations for the transverse magnetic polarization are derived by correlating Maxwell’s equation and the boundary conditions.It is demonstrated that the features of SMPPs are greatly influenced by the external magnetic field,collision frequency of 2DEG,the dielectric constant,and the thickness of the thin film,suggesting that the locations and propagation lengths of SMPPs can be governed accordingly.It is shown that the symmetry of the physical geometry preserves the symmetry of the dispersion relations of SMPPs.Furthermore,it is discovered that as the external magnetic field increases,the penetration depth of SMPPs decreases,while their energy loss reduces,implying that plasmons can propagate for longer distances.Additionally,it is observed that SMPPs in the symmetric configuration have a longer lifetime than those in the asymmetric configuration.

A NEW MODEL FOR CALCULATING PROPAGATION PRESSURE AND INITIATION PRESSURE OF PIPELINES WITH A LOCAL DENT

An analytical model of a ring with six yield hinges and two deformable arc segments is presented for. the prediction of the buckle propagation pressure and initiation pressure in offshore pipelines. The configuration of a fully collapsed ring is considered as a real dumbbell shape with a line touch between two 'bells', instead of the dumbbell shape with a point touch of two diametrically opposite points. Calculations are performed assuming that the dominant effect on the plastic energy dissipation has the circumferential bending mode. For the linear strain-hardening materials it is found that theoretical predictions based on the above model for both propagation pressure and initiation nressure are in good agreement with experimental results of Kyriakides et al.

Impulse Creeping Streamer and Propagation Velocity in Vegetable and Mineral Oils with Pressboard Interface

This paper presents an experimental study on the creeping discharge propagating over the pressboard surface in two vegetable oils(PFAE(palm fatty acid ester)oil and CRS(crude rapeseed)oil)and commercial mineral oil under the quasi-square impulse voltage with any pulse width.The pressboard impregnated with the sample oil is immersed completely into the same oil.The tungsten needle electrode is installed in the pressboard surface with and without the counter electrode to generate a creeping discharge.The other side of pressboard has the thin copper rod as a back side electrode.A comparison of the shape and stopping length of positive and negative streamers,discharge current,emitted light signal,and temporal variation and velocity of streamer propagation is reported for all different oil-pressboard interfaces.It has been shown that the behavior of creeping streamers has unique characteristics and polarity effects,and the traveling mode and propagation velocity of streamers are greatly different depending on the type of oil.

Long-range surface plasmon polaritons with subwavelength mode expansion in an asymmetrical system

Long-range surface plasmon polariton （LRSPP） modes in an asymmetrical system, in which the thin metal film is sandwiched between a semi-infinite substrate and a high permittivity polymer film with a finite thickness, are theoret~ ically calculated and analyzed. Due to the high permittivity of the polymer film, at proper polymer film thicknesses, the index-matching condition of the dielectrics at both sides of the metal can be satisfied for supporting LRSPP modes, and the electromagnetic field above the metal can be localized well. It is found that these LRSPP modes have both long propagation lengths and subwavelength mode expansion above the metal at the optimal polymer film thickncsses. Furthermore, the requirements on the refractive index and the thickness of the polymer film to support LRSPP modes at the optimal thicknesses are found to be not critical.

Quantitative relationship between the maximum streamer length and discharge voltage of a pulsed positive streamer discharge in water

A linear relationship has been realized between the maximum streamer length and discharge voltage of a pulsed positive streamer discharge by measuring the streamer length in water with conductivity of 100 μS cm-1using high-speed photography. Based on Ohm＇s law, a quantitative equation has been derived for the dependence of the maximum streamer length on the discharge voltage of a pulsed positive streamer discharge in water. According to the equation, our results suggest that the streamers spontaneously stop propagating through water due to the voltage at the streamer head dropping below the ignition voltage of a pulsed positive streamer discharge.

The Effect of the Chain Length on MMA Free Radicl Polymerization

In the polymerization process of methyl methacrylate (MMA), the Arrhenius parameters (activation energy and frequency factor) of propagating reaction monotonically decrease with increasing monomer conversion. At the beginning and middle stage of the propagating reaction, the increase of radical chain length is the main reason of above mentioned change. And at the end stage, the sharp decrease of k(p) indicates that the activation energy is approximately incline to zero and the propagating reaction is controlled by molecular diffusion motion.

基于离散元法三裂纹岩石裂纹扩展特征的试验与数值研究

为研究三裂纹岩石的静力学破坏特征,采用离散元数值模拟软件PFC2D和模型试验方法,分析三裂纹岩石的峰值应力、应力—应变曲线及裂纹扩展特性,验证离散元数值模拟方法的可行性。通过改变岩石的水平围压和裂纹长度,分析单轴压缩载荷作用下三裂纹岩石的力学响应机制。研究结果表明:中间横向裂纹对裂纹岩石的峰值应力影响较大,中间竖向裂纹对裂纹岩石的峰值应力影响较小;加载过程中裂纹尖端最先出现应力集中现象,最后形成2条约70°的主裂纹贯通3条预制裂纹;随着围压的增大,三裂纹岩石的峰值应力先增大后减小;随着裂纹长度的增加,三裂纹岩石的峰值应力不断减小。

缺口对悬臂板裂纹扩展和固有频率演变的仿真分析

选取不同初始缺口长度的悬臂板为研究对象,对其裂纹扩展和固有频率演变进行数值研究。首先,建立一种基于ABAQUS-FRANC 3D的联合仿真分析方法,ABAQUS用于结构的有限元分析,FRANC 3D基于ABAQUS的数值结果进行裂纹扩展仿真。其次,评估了初始缺口长度对裂纹扩展行为与固有频率演变的关系。研究表明,悬臂板初始缺口长度越大,固有频率随裂纹扩展长度的衰减速度越快,且固有频率变化率随着裂纹扩展长度的增加可分为3个阶段:缓慢增加,匀速增加和快速增加;固有频率变化率与应力强度因子呈对数线性关系,与裂纹扩展速率曲线相似。最后,评估了缺口带来的应力集中系数对悬臂板疲劳寿命的影响,发现其对寿命的影响规律符合指数函数模型。

缺口对悬臂板裂纹扩展和固有频率演变的仿真分析

本文选取不同初始缺口长度的悬臂板为研究对象,对其裂纹扩展和固有频率演变进行数值研究。首先,建立一种基于ABAQUS-FRANC 3D的联合仿真分析方法,其中ABAQUS用于结构的有限元分析,FRANC 3D基于ABAQUS数值结果进行裂纹扩展仿真。其次,评估了初始缺口长度与裂纹扩展行为和固有频率演变的关系。研究表明,悬臂板初始缺口长度越大,固有频率随着裂纹扩展长度的增加衰减速度越快,固有频率变化率随着裂纹扩展长度的增加可分为3个阶段:缓慢增加、匀速增加和快速增加阶段;固有频率变化率与应力强度因子呈对数线性关系,与裂纹扩展速率曲线相似。最后,评估了缺口应力集中系数对悬臂板疲劳寿命的影响,影响规律符合指数函数模型。

填塞长度对岩体爆破损伤效果的影响研究

采用数值模拟方法建立单孔装药的爆破模型,采取不同填塞长度模拟并利用Otsu算法进行阈值分割后,提取岩体的破裂面积比、孔隙分形维数、块度数据等进行对比分析,研究填塞长度对深孔爆破损伤效果的影响。结果表明,分形维数和破裂面积比随填塞长度增加呈现先增后降的变化趋势,填塞长度3.0 m时分形维数达到最大值,填塞长度1.7 m时破裂面积比达到极大值。填塞长度2.2 m左右时碎块数量取得最大值,填塞长度2.0 m时碎块平均面积为最小,填塞长度2.0~2.2 m时可达到较优的岩石破碎效果。随着填塞长度增加,抛出的岩石从小块为主转向大块,位移距离降低。研究成果对爆破作业填塞参数选取具有一定参考价值。

网络舆论主题的周期长度对主题热度的影响及预测

网络平台中舆论主题演化、起伏的周期与节律是否以及如何影响到主题的热度,是具有困惑度和缺乏研究的问题,探索该问题对于研究主题周期功能、主题演化机制等具有重要意义。本文基于今日头条平台帖子样本,探索主题的周期长度对主题热度的作用及可预测模型。采取功率谱分析计算主题周期长度,使用逻辑回归与决策树检验主题周期长度对主题热度的预测效果。结果表明:1)多数主题具有1周、1/3周、1/2周这三种周期,可称为平台三大“主频”,“主频”对主题热度起到抑制作用;2)对主题热度起到抑制作用的还有1/2周左右的“波长”集群、1周左右的“波长”集群;3)[2.6天,3天]区段(α区段)、[5.2天,6天]区段(β区段)内的周期长度,对主题热度起正向作用,它们主要是处于6天长度内的“快频率”和短波长,且在三大“主频”的抑制区波长以外;4)α区段约处于1/2周和1/3周的这2个主频中间,β区段约处于1/2周和1周这2个主频中间,且α区段与β区段之间有近似的2倍关系。上述周期长度的特征,可对主题热度起到一定的预测作用。

填塞长度对单孔爆破轴向损伤分布影响研究

为研究在爆破过程中填塞长度对圆柱岩样爆破效果的影响,通过数值模拟方法建立了分区域圆柱岩样单孔装药的三维模型。通过改变填塞长度,对爆破过程中填塞物及圆柱岩样的损伤情况、位移变化和裂纹扩展进行了对比分析。结果表明:数值模拟结果与圆柱岩样实验室爆破裂纹扩展与损伤情况相一致,验证了爆破模型可有效模拟岩石爆破过程。在填塞长度为炮孔长度的23.7%内,填塞长度的增加可显著抑制填塞物冲出炮孔程度,而超过此区间后,单位抑制效应微弱。填塞长度从炮孔长度的7.9%到39.5%,岩柱表面裂纹网络复杂程度逐渐降低,但裂隙宽度显著增加。在炸药引爆后岩柱中部区域的损伤值最高,在填塞长度为炮孔长度的23.7%时取得最高值为0.75。在岩柱上部区域,损伤随填塞长度呈现凹形变化,差值为0.054 3;而五种填塞长度在岩柱中部区域的损伤差值最大,为0.067 9;对岩柱下部区域的损伤影响较小,变动幅度为0.009 9。填塞长度的合理选取为实现精确区域爆破和提高爆破效果提供了新的途径。

柔度法测算三点弯曲试样疲劳裂纹长度的影响因素

使用柔度法对不同厚度三点弯曲试样的疲劳裂纹长度进行测算,结合有限元仿真分析方法,研究了试样厚度、柔度函数关系式的适用条件、材料的弹性模量、裂纹前缘弯曲程度、引伸计标距等因素对柔度法测算裂纹长度准确性的影响。结果表明:归一化实际裂纹长度不小于0.3是保证柔度法测算结果准确性的必要条件;用有限元方法模拟平直的贯穿型裂纹,归一化模拟裂纹长度不小于0.3时,柔度函数关系式与模拟结果的吻合程度较高;当试样厚度不大于40 mm时,在柔度函数关系式中使用材料的弹性模量可以获得较为准确的测算结果;随着试样厚度的增加,裂纹前缘圆弧角度增大,裂纹平直度降低,导致测算裂纹长度比实际裂纹长度偏小。

微细通道内火焰传播及淬熄过程研究

为研究阻火器阻火单元微细通道内火焰传播与淬熄的过程,基于Fluent建立了平板狭缝通道内火焰传播的数值模型。将仿真结果与之前的实验值进行了对比,发现仿真结果与实验值的误差最大值仅为6.5%,数值计算模型准确性及仿真结果可靠度均较高。提取火焰在微细通道内的温度变化数据可知,微细通道内火焰逐渐拉伸,最终形成“尖状”,同时传播速度呈先增大后减小的趋势。分析OH自由基的浓度分布情况可知,OH自由基的浓度分布也呈先增大后减小的趋势。其次分析火焰的淬熄过程可知,入口火焰速度、孔隙高度均是影响淬熄长度的重要因素,但温度变化对淬熄长度的影响程度较低。

基于DLS曲线的探伤车伤损检测能力评估方法

为研究探伤车检测能力评估方法,提出了钢轨伤损埋藏深度(Depth)、超声波走波距离(Length)和伤损尺寸(Size)的DLS曲线建模方法,结合探伤车判伤最小走波距离,提出了探伤车对不同埋藏深度、不同尺寸钢轨伤损的检测能力的评估方法。以钢轨横孔为研究对象,采用仿真计算方法得到了不同埋藏深度和尺寸的钢轨横孔走波距离与回波幅值,绘制出钢轨横孔DLS曲线。通过比较钢轨伤损的走波距离比与最小走波距离比,可评估钢轨伤损是否被有效检出。

不同因素对闽楠嫩枝扦插生根的影响

为了研究不同因素对闽楠嫩枝扦插的影响,以多年生母株上当年生半木质化枝条及当年实生苗茎段作插穗,分别探讨不同插穗、生根促进剂质量浓度、插穗浸泡时间3种因子对闽楠嫩枝扦插生根率及幼根生长的影响。结果表明:此3种因子对闽楠嫩枝扦插生根率及根长均有显著影响;试验最佳组合为当年实生苗茎段,浸泡于质量浓度为200mg/L的ABT-1#溶液中9 h,扦插后60 d生根率可达93.3%,平均根长为4.9 mm。