爆炸荷载作用下围岩累积损伤效应的数值分析

巷道爆破开挖推进过程中,循环爆破开挖的多次扰动作用使保留岩体产生累积损伤,导致岩体力学参数的弱化,从而造成工程岩体的宏观失效。利用ANSYS/LS-DYNA的重启动技术,通过损伤云图和损伤变量D的变化,对圆形巷道循环进尺过程中爆破作用下的岩体累积损伤效应进行研究。计算结果表明:随着掌子面推进爆破次数的增加,围岩的损伤程度加深,但影响深度变化较小;在装药量和爆心距不变的情况下,损伤量与爆破次数之间有很好的非线性关系,即爆破损伤的累积具有非线性特性。     

白鹤滩水电站地下厂房爆破累积损伤效应研究

结合白鹤滩水电站地下主厂房围岩超声波测试结果,研究了地下工程隧洞围岩在循环爆破荷载作用下的累积损伤效应。结果表明:隧洞围岩在爆破开挖作用下的松弛范围为0.8~1.6 m,并且随着爆破次数的增加而范围有逐渐扩大的趋势;随着爆破次数的不断增加,岩体声波速度逐渐降低,损伤度D呈现出非线性累积规律;随着与爆源距离的增大,岩体爆破损伤程度受爆破循环荷载作用的影响减小,累积损伤效应相对不明显;对比发现侧壁和拱顶测孔的测试结果存在较大差异,说明爆破作用下岩体损伤具有各向异性的特征。在Hoek-Brown强度准则的基础上,提出了更适用于损伤岩体的考虑累积损伤效应的岩体力学参数计算公式,并运用现场测试数据验证了公式的工程适用性及合理性。     

循环爆破荷载作用下小净距隧道围岩累积损伤特性研究

明确多循环爆破推进情况下小净距隧道围岩损伤演化特征有助于施工安全和围岩稳定.依托福州地铁2号线某区段小净距隧道工程,基于LS-DYNA完全重启动技术,结合现场中夹岩声波测试结果,研究循环爆破荷载作用下该区段小净距隧道5个开挖进尺内围岩的累积损伤演化过程.结果表明:围岩损伤范围和损伤程度随爆破加载次数增加而增加,每一循环爆破荷载下各段别均对围岩有不同程度损伤,MS7和MS9段爆破荷载对围岩损伤最大;实测和模拟结果表明在多次爆破后中夹岩体损伤沿测孔深度方向呈圆角的斜"L"形状,近爆破处岩体损伤较大于远爆破侧;在同一监测断面内围岩的累积损伤尤以段间爆破加载损伤程度最大,随着隧道开挖推进岩体的损伤范围逐渐趋于稳定,监测断面9m范围外的爆破扰动基本不再对监测部位围岩造成损伤.研究成果可为现场围岩的加固提供参考,也可为类似工程的提供理论依据.     

动态卸荷作用下节理围岩损伤过程研究

为了探明节理岩体中的巷道爆破开挖后的卸载机理,为实际工程提供理论依据,本文基于离散元数值模拟方法,分析了考虑爆破荷载深埋矩形巷道节理围岩的损伤过程。结果表明:高地应力条件下,爆破开挖会在节理围岩中诱发显著的松动效应,导致洞壁附近形成远大于静态塑性区的动态松动损伤区,使得最终屈服区以外的节理面强度和渗透性等力学参数发生劣化;受爆破荷载的影响,岩体的回弹将产生较大的振动速度,达到m/s量级,是洞壁附近节理面损伤的主要来源;节理的组合方式也会对节理松动产生较大的影响,当节理夹角接近60°时,围岩最容易破坏。     

地下洞室爆破开挖诱发围岩损伤特性及PPV阈值研究

地下洞室爆破开挖产生的围岩损伤主要由爆破荷载和地应力重分布共同作用引起。针对圆形隧洞全断面毫秒延迟爆破开挖过程,采用LS-DYNA有限元数值模拟研究了不同地应力水平下爆破开挖诱发围岩损伤的机理及爆破损伤PPV阈值变化规律。研究表明:地应力对爆破荷载产生的张拉损伤起抑制作用,高地应力条件下,爆破荷载产生的岩体损伤仅限于围岩表层,地应力重分布引起的岩体压剪破坏是围岩中大范围损伤区形成的主要原因;爆破过程中开挖面上地应力瞬态释放所产生的附加动应力也是影响围岩损伤的重要因素,相比于准静态卸荷,地应力瞬态卸荷产生的围岩损伤范围更大;随着地应力水平的提高,岩体爆破损伤的PPV阈值呈先增大后减小的变化趋势,地下洞室爆破安全振动控制标准应考虑地应力状态的影响。     

爆破扰动松软煤层对巷道围岩稳定性的影响EI北大核心CSCD

随着煤矿采掘深度的增加,爆破技术在煤矿井下的应用越来越广泛,但因爆破扰动松软煤层诱发的煤与瓦斯突出事故也不容忽视。为研究爆破扰动松软煤层的力学特征以及爆破震动效应对巷道围岩稳定性的影响,以巷道掘进爆破扰动松软煤层诱发煤与瓦斯突出为工程背景,根据相似理论在实验室搭建了爆破模拟试验系统,通过超动态应变仪监测爆破载荷作用下试样的力学特性,结合理论分析和数值模拟探讨爆破对巷道稳定性的影响。研究发现,当爆破孔从岩层进入松软煤层,在该试验条件下产生了类似突出的破碎抛掷过程;爆破裂纹扩展是导致巷道围岩破坏的根本原因,而松软煤层的存在会加剧巷道围岩的破坏程度,促使巷道围岩的裂隙进一步扩展发育,在煤矿井下一次爆破装药量大,炮孔数目多和需要多次爆破的情况下,爆破振动的累积损伤会最终影响到巷道的稳定。研究成果对揭示井下爆破扰动构造带煤岩诱导煤与瓦斯突出的发生机理具有重要的理论价值。     

爆破扰动松软煤层对巷道围岩稳定性的影响

随着煤矿采掘深度的增加,爆破技术在煤矿井下的应用越来越广泛,但因爆破扰动松软煤层诱发的煤与瓦斯突出事故也不容忽视。为研究爆破扰动松软煤层的力学特征以及爆破震动效应对巷道围岩稳定性的影响,以巷道掘进爆破扰动松软煤层诱发煤与瓦斯突出为工程背景,根据相似理论在实验室搭建了爆破模拟试验系统,通过超动态应变仪监测爆破载荷作用下试样的力学特性,结合理论分析和数值模拟探讨爆破对巷道稳定性的影响。研究发现,当爆破孔从岩层进入松软煤层,在该试验条件下产生了类似突出的破碎抛掷过程;爆破裂纹扩展是导致巷道围岩破坏的根本原因,而松软煤层的存在会加剧巷道围岩的破坏程度,促使巷道围岩的裂隙进一步扩展发育,在煤矿井下一次爆破装药量大,炮孔数目多和需要多次爆破的情况下,爆破振动的累积损伤会最终影响到巷道的稳定。研究成果对揭示井下爆破扰动构造带煤岩诱导煤与瓦斯突出的发生机理具有重要的理论价值。     

饱和水岩体中大断面巷道群的爆破安全研究

利用爆破振动作为信号源,运用3种不同的计算和测试方法,对爆破施工现场地下饱和含水巷道群的矿山法施工安全进行了计算和安全评价。结合现场岩石条件,对含饱和水、不含水2种工况进行了模拟计算,比较了计算结果,围岩充水时岩体内部受力情况劣化,内部应力增大约13%~15%;通过对爆破振动的现场测量,结合测点几何坐标,计算出了巷道围岩在爆破时产生的振动附加力,对隧道围岩的稳定性进行了评价,为现场支护的时间安排提供了指导意见。另外,结合地震勘探的方法,进一步求出了围岩的品质因子,细化了围岩在受到爆破振动时的衰减规律,为区域隧道群的合理、安全开挖提供了工程参考。     

多次爆破对大跨度硐室围岩的损伤累积及松动圈范围研究

为探究多次爆破作用下,损伤累积效应对大跨度硐室围岩松动圈的影响规律,结合某大跨度硐室爆破工程,采用声波法和钻孔窥视法对其爆破开挖过程中硐室围岩松动圈进行监测,利用现场试验结果分析大跨度硐室围岩损伤累积及松动圈变化规律。结果表明：随着爆破次数的增加,超声波波速不断减小;围岩损伤值增大,但增长速率不断降低,最后逐渐趋于稳定。多次爆破作用后,硐室围岩松动圈半径由原来的2.8 m逐步扩大为3.2 m,且硐室顶部的松动圈对比边墙处较大。因此,在大跨度硐室施工中应重点考虑硐室顶部的围岩稳定性,且在围岩支护和安全防护时应充分考虑多次爆破造成的围岩损伤累积效应对围岩松动圈半径变化的影响。     

基于损伤累积的爆破振动传播规律试验研究

为进一步揭示基于损伤累积的爆破振动波传播与衰减规律,设计混凝土试块进行损伤累积及爆破振动测试试验。结果表明,测点损伤值随爆破次数增加持续增大,中远区测点损伤有初期缓增及后期突增两阶段;测点单次爆破振动速度随距离增大而减小,近区测点振动速度减小较中、远区测点快;测点爆破振动速度随爆破次数增加总体减小,且爆源近区减小较快,中远区呈小幅度缓慢减小;随爆破次数继续增大各测点振动速度存有突增过程,且衰减系数 增加缓慢, 值减小,两者均存在小幅度畸变过程;多次爆破时确定振动安全阈值及爆破振动波传播衰减规律( 、 值)时应充分考虑损伤累积效应。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...