Determining role of heterogeneous microstructure in lowering yield ratio and enhancing impact toughness in high-strength low-alloy steel

Here we present a novel approach of intercritical heat treatment for microstructure tailoring,in which intercritical annealing is introduced between conventional quenching and tempering.This induced a heterogeneous microstructure consisting of soft intercritical ferrite and hard tempered martensite,resulting in a low yield ratio(YR)and high impact toughness in a high-strength low-alloy steel.The initial yielding and subsequent work hardening behavior of the steel during tensile deformation were modified by the presence of soft intercritical ferrite after intercritical annealing,in comparison to the steel with full martensitic microstructure.The increase in YR was related to the reduction in hardness difference between the soft and hard phases due to the precipitation of nano-carbides and the recovery of dislocations during tempering.The excellent low-temperature toughness was ascribed not only to the decrease in probability of microcrack initiation for the reduction of hardness difference between two phases,but also to the increase in resistance of microcrack propagation caused by the high density of high angle grain boundaries.

Deformation-softening behaviors of high-strength and high-toughness steels used for rock bolts

In deep ground engineering,the use of high-strength and high-toughness steels for rock bolt can significantly improve its energy absorption capacity.However,the mechanisms and effects of rock loading conditions on this kind of high energy-absorbing steel for rock bolt remain immature.In this study,taking Muzhailing highway tunnel as the background,physically based crystal plasticity simulations were performed to understand the effect of rock loading rate and pretension on the deformation behaviors of twinning induced plasticity(TWIP)steel used for rock bolt.The material physical connecting to the underlying microscopic mechanisms of dislocation glide and deformation twinning were incorporated in numerical modeling.The rock loading conditions were mimicked by the real-time field monitoring data of the NPR bolt/cable equipment installed on the tunnel surrounding rock surface.The results indicate that the bolt rod exhibits pronounced deformation-softening behavior with decrease of the loading rate.There is also a sound deformation-relaxation phenomenon induced by the dramatic decrease of loading rate after pre-tensioning.The high pretension(>600 MPa or 224 k N)can help bolt rod steel resist deformation-softening behavior,especially at low loading rate(<10~(-1)MPa/s or 10~(-2)kN/s).The loading rate was found to be a significant factor affecting deformation-softening behavior while the pretension was found to be the major parameter accounting for the deformation-relaxation scenario.The results provide the theoretical basis and technical support for practical applications.

An experimental study of a yielding support for roadways constructed in deep broken soft rock under high stress

A rationally designed support for deep roadways excavated in broken soft rock under high stress was investigated. The deformation and failure characteristics and the mechanism of ''yielding support'' was studied for anchor bolts and cables. The rail roadway of the 2-501 working face in the Liyazhuang Mine of the Huozhou coal area located in Shanxi province was used for field trials. The geological conditions used there were used during the design phase. The new ''highly resistant, yielding'' support system has a core of high strength, yielding bolts and anchor cables. The field tests show that this support system adapts well to the deformation and pressure in the deep broken soft rock. The support system effectively controls damage to the roadway and ensures the long term stability of the wall rock and safe production in the coal mine. This provides a remarkable economic and social benefit and has broad prospects for fur- ther application.

Principle and practice of coupling support of double yielding shell of soft rock roadway under high stress

In order to ensure the safety and stability of the soft rock roadway under high stress, based on the characteristics of the surrounding rock deformation and failure, this paper presented the support technology‘‘coupling support of double yielding shell'', then gave the design method of inner and outer shells and analyzed the principle and requirements of the support technology by taking the -850 m east belt roadway of Qujiang coal mine as the background. The field application results show that the support technology can control the soft rock roadway deformation better under high stress. The displacement between roadway sides was 851 mm, the displacement of the roof was 430 mm, and the displacement of the floor was 510 mm.

High-resistance controlled yielding supporting technique in deep-well oil shale roadways

In order to avoid the deep-well oil shale roadway being deformed, damaged, or difficult to maintain after excavating and supporting in Haishiwan coal mine, this paper has analyzed the characteristics of the deformed roadway and revealed its failure mechanism by taking comprehensively the methods of field geological investigation, displacement monitoring of surrounding rock, rock properties and hydration properties experiments and field application tests. Based on this work, the high-resistance controlled yielding supporting principle is proposed, which is: to ‘‘resist'' by high pre-tightening force and high stiffness in the early stage, to ‘‘yield'' by making use of the controlled deformation of a yielding tube in the middle stage, and to ‘‘fix'' by applying total-section Gunite in the later stage. A high-resistance controlled yielding supporting technique of ‘‘high pre-tightening force yielding anchor bolt + small-bore pre-tightening force anchor cable + rebar ladder beam + rhombic metal mesh + lagging gunite'' has been established, and industrial on site testing implemented. The practical results show that the high-resistance controlled yielding supporting technique can effectively control the large deformation and long-time rheology of deep-well oil shale roadways and can provide beneficial references for the maintenance of other con-generic roadways.

Numerical Model Research on Rotational Performance of Beam-Column High-Strength Bolt Extension End-Plate Connection Node

The high-strength bolted end plate connection is widely used in the construction industry with its green environmental protection and excellent seismic performance. The joints of the joints are semi-rigid, the force performance is extremely complicated, and the experimental research cost is relatively high, and the cycle is very long. Therefore, the establishment of an efficient numerical model is of great significance for evaluating the force performance of high-strength bolt end plates. In this paper, the influence of different material models on the rotation performance of the joint is studied by numerical simulation, and the bending moment-rotation curve is obtained. The numerical simulation and the experimental results are in good agreement, so as to provide a reference for the design and application of this kind of joint.

锚栓屈服型可抬升柱脚节点抗震性能试验研究

为满足结构在震中安全且震后可修复使用的目的,设计了一种锚栓屈服型可抬升柱脚节点,该节点是一种半刚性节点,将柱脚锚栓的一部分作为节点的阻尼器,阻尼器为柱脚提供抗弯能力和可抬升能力,在地震时柱脚节点塑性变形主要集中在阻尼器上,震后通过更换阻尼器即可完成柱脚节点的修复。为此,设计一组普通外露式柱脚节点和锚栓屈服型可抬升柱脚节点进行对比试验,并通过拟静力试验,研究它们在低周往复荷载下的滞回特性、抗弯承载力、刚度退化、耗能能力等抗震性能,同时研究柱脚节点在更换阻尼器前后的抗震性能。研究结果表明:对比普通外露式柱脚节点,锚栓屈服型可抬升柱脚具有更好的耗能能力和变形能力,试件的损伤基本集中在可更换的阻尼器上,耗能模式和损伤机制较为合理。在进行修复后,除初期转动刚度略低于修复前试件外,整体抗震性能基本可恢复至震前水平。另外,该新型柱脚的阻尼器拆卸和更换较为简便。

基于泄漏率的垫片参数测试方法优化研究

垫片系数m和预紧比压y是法兰螺栓连接结构设计中的2个关键参数,ASMEⅧ.1卷和GB/T 150.3给出的都是基于结构强度的工程经验值,未与泄漏率关联。针对现有垫片参数测试方法不足之处进行优化调整,提出了一种更符合国内垫片标准体系和工程应用实际的垫片参数测试方法。通过与现有方法的试验比对,并对8类典型垫片产品进行验证测试,测试结果误差都在1%左右。使用多孔介质模型及Logistic模型对测试结果进行拟合,结果表明,该方法测试结果可靠,拟合情况良好,可供法兰螺栓连接结构设计参考使用。

深埋圆形隧道衬砌-锚杆支护结构弹塑性解答

文章采用等效材料法,基于Drucker-Prager屈服准则推导了具有衬砌-锚杆支护深埋隧道在不同施工阶段下的弹塑性解答,并进行FLAC3D数值模拟验证。结果表明:塑性区位于衬砌内部,锚杆的锚固作用对其塑性区扩展响应不明显,塑性区扩展到锚固区,软岩中锚杆锚固作用对抑制塑性扩展的响应较好;塑性区扩展到锚固区时,塑性区半径与锚杆的弹性模量呈负相关趋势,塑性区半径与锚杆的支护角度呈正相关趋势,软岩中锚杆锚固作用对抑制塑性区扩展的效果更为明显。

筒体悬挂结构若干问题分析

以菏泽博物馆新馆项目为背景,从计算方法、构件受力和设计、整体屈服机制等八个方面对筒体悬挂结构体系做了较全面的研究。结果表明:1)计算筒体悬挂结构水平地震作用时无需调整层质量;2)规范底部轴力法、振型分解反应谱法并不适用筒体悬挂结构竖向地震作用计算,考虑最小限值调整后的吊柱设计仍可能偏不安全;3)采用长孔螺栓节点设计能让筒体悬挂结构吊柱在各工况下处于理想轴向拉压受力状态;4)中高烈度区吊柱在大震组合作用下可能受压,有必要复核其受压稳定和承载力;5)吊柱受力在小震阶段为恒、活载控制,大震阶段其恒、活载占比降低,地震逐渐起控制作用;6)合理的吊柱布置除满足建筑条件外,还需兼顾核心筒顶受力,减小筒顶不平衡弯矩;7)核心筒顶上包与否均能实现与屋面悬挂桁架的有效刚性连接;8)合理的筒体悬挂结构屈服机制就是落地核心筒的延性破坏过程,即始于连梁开裂破损,终于筒底墙肢钢筋拉屈、混凝土压溃。

水布垭电厂水轮机顶盖分瓣面螺栓加工标准变更的可行性分析

水布垭电厂机组扩修更换顶盖分瓣面螺栓,发黑处理过的新螺栓在设计拉伸压力出现无法达到规定拉伸值的情况。厂家通过现场对比试验,判断因顶盖分瓣面M80×6螺栓拉伸量过大致螺纹发生破坏,螺栓拉伸后剩余伸长量过小,导致螺母和法兰之间存在间隙,拉伸力撤走后这部分间隙造成了回弹量过大超标,是使圆螺母卡涩无法转动的具体原因。并分析将螺栓加工标准更改为DIN2510的可行性。

慈林山煤业沿空掘巷让压支护技术应用

为解决小煤柱沿空掘巷煤柱支承应力较大以及采空区顶板坚硬岩层断裂产生动载破坏围岩支护的问题,对慈林山煤矿15208工作面运输顺槽沿空掘巷支护存在的问题进行分析,开展单泡让压管和双泡让压管抗压试验,同时优化锚杆、锚索的施工。结果表明让压管能够提高锚索的延伸率,在压力显现时能够吸收围岩传递的能量,保证锚杆、锚索的有效性;在此基础上对帮锚索的优化能保证支护强度的同时还能提高生产效率并降低支护成本。

Numerical and analytical simulation of the structural behaviour of fully grouted cable bolts under impulsive loading

Designing reliable yielding support system to mitigate the effect of the kinetic energy in burst-prone conditions in mining and tunneling excavations is one of the challenges for geotechnical engineers. A combination of the support elements can be used to increase rock strength and minimise the displacement of unstable rock mass. It is important to understand how the support system works to ensure the stability of underground excavations. Cable bolts have been commonly used as an effective underground support system and an element of reinforcement to improve rock stability. Cable bolts are usually considered to be subjected to static loads under relatively low stress environments, however, in burst-prone conditions, they might be subjected to dynamic loads. Cable bolts as well as other support elements are used in burst-prone conditions to absorb the kinetic energy of the removed rock to avoid sudden and violent failures. This paper develops numerical and a novel analytical simulation technique for cable bolts to assess their structural behaviour under static and dynamic loading conditions. The numerical and analytical models are then validated against experimental observations reported in the literature, which demonstrates the reliability of the proposed models.

Influence of anchorage length and pretension on the working resistance of rock bolt based on its tensile characteristics

In coal mining roadway support design,the working resistance of the rock bolt is the key factor affecting its maximum support load.Effective improvement of the working resistance is of great significance to roadway support.Based on the rock bolt’s tensile characteristics and the mining roadway surrounding rock deformation,a mechanical model for calculating the working resistance of the rock bolt was established and solved.Taking the mining roadway of the 17102(3)working face at the Panji No.3 Coal Mine of China as a research site,with a quadrilateral section roadway,the influence of pretension and anchorage length on the working resistance of high-strength and ordinary rock bolts in the middle and corner of the roadway is studied.The results show that when the bolt is in the elastic stage,increasing the pretension and anchorage length can effectively improve the working resistance.When the bolt is in the yield and strain-strengthening stages,increasing the pretension and anchorage length cannot effectively improve the working resistance.The influence of pretension and anchorage length on the ordinary and high-strength bolts is similar.The ordinary bolt’s working resistance is approximately 25 kN less than that of the high-strength bolt.When pretension and anchorage length are considered separately,the best pretensions of the high-strength bolt in the middle of the roadway side and the roadway corner are 41.55 and 104.26 kN,respectively,and the best anchorage lengths are 1.54 and 2.12 m,respectively.The best anchorage length of the ordinary bolt is the same as that of the high-strength bolt,and the best pretension for the ordinary bolt in the middle of the roadway side and at the roadway corner is 33.51 and 85.12 kN,respectively.The research results can provide a theoretical basis for supporting the design of quadrilateral mining roadways.

A review on the performance of conventional and energy-absorbing rockbolts

This is a review paper on the performances of both conventional and energy-absorbing rockbolts manifested in laboratory tests. Characteristic parameters such as ultimate load, displacement and energy absorption are reported, in addition to load-displacement graphs for every type of rockbolt. Conventional rockbolts refer to mechanical rockbolts, fully-grouted rebars and frictional rockbolts. According to the test results, under static pull loading a mechanical rockbolt usually fails at the plate; a fully-grouted rebar bolt fails in the bolt shank at an ultimate load equal to the strength of the steel after a small amount of displacement; and a frictional rockbolt is subjected to large displacement at a low yield load. Under shear loading, all types of bolts fail in the shank. Energy-absorbing rockbolts are developed aiming to combat instability problems in burst-prone and squeezing rock conditions. They absorb deformation energy either through ploughing/slippage at predefined load levels or through stretching of the steel bolt. An energy-absorbing rockbolt can carry a high load and also accommodate significant rock displacement, and thus its energy-absorbing capacity is high. The test results show that the energy absorption of the energy-absorbing bolts is much larger than that of all conventional bolts. The dynamic load capacity is smaller than the static load capacity for the energy-absorbing bolts displacing based on ploughing/slippage while they are approximately the same for the D-Bolt that displaces based on steel stretching.

Effect of Seedling Quality on Growth,Yield and Quality of Angelica sinensis

[Objectives]Aiming at the problems of high bolting rate,low yield and poor quality traits in the production of Angelica sinensis in Qinghai Province,this study investigated the effect of seeding quality on the growth,yield and quality of A.sinensis.[Methods]Field experiments were carried out in five aspects,including different seedling shapes,different seedling sizes,different seedling ages,different seedling raising methods,and different seedling sources.The effect of seedling quality on the survival rate,bolting rate,main quality traits(root length,root fresh weight,root head thickness,root head length)and yield of A.sinensis was investigated.[Results]The seedlings,0.2-0.5 cm in diameter,100-110-d old,raised from three-year-old provenance in cultivated land by conventional method,were more preferable,and their survival rate was high,bolting rate was low,yield is high,and quality traits performed well.[Conclusions]The seedlings,0.2-0.5 cm in diameter,100-110-d old,raised from three-year-old provenance in cultivated land by conventional method,were more preferable,and their survival rate was high,bolting rate was low,yield is high,and quality traits performed well.

栽培方式对前胡生长状况及其品质影响研究

目的:考察生态种植模式下前胡生长状况和品质影响,优化生态种植方法。方法:考察不同成熟度种子、播种时间、海拔、摘薹、遮阴条件对前胡出苗率、抽薹率、产量和品质等的影响。采用高效液相色谱法同时测量白花前胡甲素、白花前胡乙素和白花前胡素E含量,进行前胡品质表征。结果:建立了前胡生态种植模式下质优高产的栽培方法,其要点可概括为选择1年生青黄色种子,在12月中下旬、海拔较高、遮阴度达到60%的地块条播,待3—5月抽薹时摘薹,同时进行必要的田间维护与管理。结论:本栽培方法能有效地减少前胡抽薹,提高有效成分含量,提升前胡栽培药材的品质,创造更高的经济和社会效益。

Hydrogen-induced delayed fracture of Cu-containing high-strength bolt steel

The hydrogen-induced delayed fracture(HIDF)behavior of a 1300-MPa-grade high-strength bolt steel 42CrMoV containing 0.42 wt.%Cu was investigated by constant load tensile test in a pH 3.5 Walpole solution.It is shown that the addition of Cu is beneficial to enhance the HIDF resistance by~13%.The observation of the fracture surface revealed that the area fraction of brittle crack initiation zone decreased remarkably for the Cu-added steel.Both the corrosion pit depth and the corrosion rate of the Cu-added steel in the Walpole solution are notably decreased,which is primarily because of the formation of a Cu-rich protective compact rust layer and slightly higher corrosion potential.As a result,the absorbed hydrogen content in that solution was also decreased by~21%.It is concluded that the improvement in the HIDF resistance of the tested steel is primarily due to the increase in corrosion resistance and resultant decrease in the absorbed diffusible hydrogen content in the acidic condition.

某动力总成悬置胶垫螺栓松动的设计改进

螺栓松动作为汽车可靠性问题中的一个难题,经常困扰着汽车设计人员。文章将针对一款动力总成悬置胶垫螺栓松动问题,通过与紧固件厂家技术合作,对螺栓预紧力、安装扭矩和接触面屈服强度进行计算校核。并针对计算发现的悬置支架接触面存在的屈服压溃风险及螺栓预紧力不足等问题,分别制定了相应的整改方案,最终确定了此悬置紧固螺栓的安装扭矩范围,满足悬置胶垫紧固预紧力要求。根据文章计算方法确定的安装扭矩进行定扭后,通过紧固件横向振动试验和越野路路试,动力总成悬置胶垫紧固螺栓未再出现松动现象,可以看出文中螺栓松动计算校核和改进方案有效。文中案例通过对螺栓预紧力、安装扭矩和接触面屈服强度等进行符合性计算校核和改进,为汽车螺栓松动问题整改提供了一个非常好的解决思路和方法。

煤矿框架式高强度液压支架让锚装置设计与应用

为保证高水充填沿空留巷顶板的完整性,保护锚杆、锚索在使用中不被液压支架移架时破坏,提高顶板支护强度,以沿空留巷高冲水充填作为切入点,设计了一种液压支架让锚装置。从支架让锚装置的组成、让锚装置部件尺寸的确定、工字钢及内外钢板的选取、固定连接方式等方面进行阐述。此装置的成功投运,在保护锁具的同时保护了支护结构,为大采高综采工作面无煤柱连续开采提供了有力保障。