Stability of undercut space in fragment orebody based on key block theory

Undercut is one kind of important spaces to place the mining blocks in the mass underground mining. This structure is also used as a compensation space during blasting. In the process of underground mining in the fragment orebody, it is important and critical to analyze the stability and blockage of the three-dimensional wedges created around the undercut space. The wedge stability is mainly controlled by factors including geometry （i.e., the size, shape and spatial location of the wedge and undercut）, the strength （shear and tensile） of the discontinuities that created the wedge, and the stress distribution within the rock mass. The Unwedge software was used to conduct the orthogonal simulation tests （three factors and five levels） that considered different cross sections, trends, and plunges of the undercut space. The results demonstrate that the control value of the safety factor of wedge is set to be 1.2. The optimal parameters are determined in the undercut space, such as the blasting fragmentation, orientation of the fluid flow, and the equipment gradeability;the wedge stability can be evaluated in the light of the block images and continuous falling;the stability of the key block meets the needs of the undercut space, the parameters gained are reasonable and optimal. Cross section is 27°, trend is from 315°to 325°（it is 320°at in-suit test） and plunge is 5°.

A356铝合金车轮Undercut减质量结构制造工艺及验证

为实现铝合金车轮轻量化,用Undercut减质量结构车轮制造工艺,以483 mm(19 inch)Undercut结构车轮为例,通过热处理、机加工及旋压工艺强化Undercut结构车轮的刚性和强度。通过车轮可靠性试验及弯曲仿真试验,验证车轮静刚性、应变及疲劳寿命。结果表明:Undercut结构车轮满足300万次车轮弯曲疲劳寿命要求;Undercut结构d_(2)>6.9 mm时,安全裕度稍差,所以d_(2)>6.9 mm,可保证Undercut结构车轮静刚性要求。Undercut结构车轮研究技术可推广至其它类型及尺寸车轮的优化设计。

Mechanical properties of silicon nanobeams with an undercut evaluated by combining the dynamic resonance test and finite element analysis

Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young＇s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper. Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process, which inevitably generates the undercut of the nanobeam clamping. In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut, dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L, which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data. By using a least-square fit expression including △L, we finally extract Young＇s modulus from the measured resonance frequency versus effective length dependency and find that Young＇s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon. This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.

Effect of undercut defect on deformation behavior TC4 titanium alloy laser welded butt joint under static tensile loading

By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation behavior of the laser welded joint specimens of TC4 titanium alloy. The results showed that for the unmodified specimens, the yield phenomenon occurs first in the region of the joint, but the undercut value has an effect on the stress and strain of starting to yield phenomenon, and a great effect on the plastic deformation behavior.When the undercut is less than a certain value, the large plastic deformation occurs in the base metal region and the plasticity of the specimen is comparable to that of the base metal, but the larger undercut defect results in a concentrated plastic deformation in the joint region and rapidly failed in this region. But the double-sided dressing specimen is significantly different. The physical yield is no longer concentrated in the joint region, but at the same time occurs in the several regions including joint and the base metal. And the plastic deformation mainly occurs in the base material area, similar to that of the base material.

Formative mechanism of the undercut defect in horizontal variable polarity plasma arc welding

Abstract Horizontal welding is important for heavy or huge welding structures. Keyhole mode variable polarity plasma arc welding of aluminum alloy plates with medium thickness was carried out in horizontal position. The characteristic of welding defects was introduced. Preliminary experiments indicated that the undercut defect could not be eliminated easily. The relationship between welding parameters and the undercut defect showed that this deject could be lessened by using higher heat input. The fluid flow of weld pool was observed by a high speed camera. The fluid flow in weld pool was not symmetric and much of molten metal gathered in the lower part. The fluid flow velocity in the lower part was bigger than that in the upper part. To this end, the formative mechanism of the undercut defect was proposed. The flowability of the molten metal was an influential factor for the undercut defect. A preheating method was designed to verify the formative mechanism.

Fabrication of GaN-based LEDs with 22° undercut sidewalls by inductively coupled plasma reactive ion etching

We use a simple and controllable method to fabricate GaN-based light-emitting diodes （LEDs） with 22° undercut sidewalls by the successful implementation of the inductively coupled plasma reactive ion etching （ICP-RIE）. Our exper- iment results show that the output powers of the LEDs with 22° undercut sidewalls are 34.8 rnW under a 20-mA current injection, 6.75% higher than 32.6 mW, the output powers of the conventional LEDs under the same current injection.

Reduction of Undercuts in Fillet Welded Joints Using Taguchi Optimization Method

This project work focuses on the reduction of weld undercuts using the Taguchi method. The phenomenon of weld undercuts constitutes a major problem for the welding industry. When undercuts occur, and particularly when such cuts are deep, it has a negative impact on the weld as it lowers the integrity and quality of the weldment. Therefore, efforts are made globally to reduce the depth of such weld undercuts to the barest minimum. Several optimization methods have been adopted;however, in this study, the Taguchi method is applied. “The smaller the better components” of the Taguchi method is applied. From the results obtained from applying this Taguchi method, the optimum process parameters obtained are A2-B1-C2, which are a voltage of 20 V, a current of 180 A, and a welding speed of 130 mm/s, required to form an undercut of 0.03 mm. Whereas the existing process parameters used by the company are A1-B3-C, which make an undercut to a depth of 0.09 mm. It is concluded that the use of Taguchi method has been able to reduce the depth of undercut as shown in this study. A step-by-step approach is presented in the study.

Effect of Thermal Shrinkage of Extruded Sheet on Mouthguard Thickness: Influence of Model Undercut

The effectiveness and safety of the mouthguard are greatly affected by its thickness. The aim of this study was to investigate the effect of thermal shrinkage of the extruded sheet on the mouthguard thickness depending on the amount of undercut of the model. Mouthguard sheet was used a 4.0 mm thick ethylene-vinyl acetate resin manufactured by extrusion molding. The sheets were placed in the vacuum forming machine with the sheet extrusion direction either vertical (condition V) or parallel (condition P) to the model’s centerline. The working models were three hard plaster models trimmed so that the angles of the anterior teeth to the model base were 90?, 100?, and 110? (Models A, B, and C). The sheet was softened until it sagged 15 mm, and then suction was continued for 30 s. Measurement points of the mouthguard were the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface). The differences in the reduction rate of the thickness due to model form and extrusion direction were analyzed using two-way ANOVA and Bonferroni’s multiple comparison tests. Differences in thickness depending on the extrusion direction of the sheet were observed in Models B and C on the labial surface and in all models on the buccal surface, and the thicknesses obtained under condition P were significantly thinner than those obtained under condition V. The thicknesses of the incisal edge and the cusp were not affected by the extrusion direction. The result of this study was suggested that the labial and buccal thickness of the mouthguard was secured by placing the sheet in the extrusion direction vertical to the model’s centerline. Furthermore, it was clarified that the presence of the undercut of the model tends to increase the influence of the extrusion direction of the sheet on the thickness of the mouthguard.

Non-undercutting condition and parameter optimization for cycloid ball planetary transmission

The transmission performance of cycloid ball planetary transmission(CBPT) is affected by cycloid tooth undercutting directly, and the design of CBPT can be optimized by the non-undercutting condition. Firstly, the theoretical equation of cycloid tooth is given, and the curvature radius of cycloid tooth profile is derived. Secondly, according to the relationship between the curvature radius and the distribution circle of balls, the non-undercutting condition of cycloid tooth profile is established, and the non-undercutting critical condition is deduced. Finally, the validity of the non-undercutting critical condition is verified by simulation. The result shows that the non-undercutting critical condition can be used to optimize the design of CBPT.

Mechanical properties of silicon nanobeams with an undercut evaluated by combining the dynamic resonance test and finite element analysis

Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications.A numerical experimental method of determining resonant frequencies and Young’s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper.Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process,which inevitably generates the undercut of the nanobeam clamping.In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut,dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L,which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data.By using a least-square fit expression including △L,we finally extract Young’s modulus from the measured resonance frequency versus effective length dependency and find that Young’s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon.This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.

窄腔内倒扣产品多次顺序抽芯注塑模设计

针对塑件正面窄腔内5个倒扣、背面2个窄腔内环形倒扣、四周侧17个倒扣,背面7个倒扣的结构难点,创新提出了隧道楔紧块、滑块运动方向与侧型芯垂直的吊挂侧型芯式抽芯方法,实现窄腔内倒扣抽芯。设计了4类抽芯机构,通过4次顺序抽芯成功实现窄腔内复杂倒扣产品的脱模。第一次抽芯解决正面窄腔内5个倒扣抽芯难题,由顺序定距分型机构控制抽芯顺序;第二次抽芯解决四周侧17个倒扣抽芯难题;第三次抽芯解决背面7个倒扣抽芯难题;第四次抽芯解决背面2个窄腔内环形倒扣抽芯难题,创新设计了弹簧式快速二次推出机构控制抽芯顺序。经试模验证,该模具结构合理、工作可靠。

水轮机转轮根切现象研究及预防

混流式水轮发电机组生产制造过程中,需手工打磨转轮叶片与上冠、下环之间的焊缝。在打磨焊缝过程中,易产生根切现象影响工件质量。本文对混流式转轮根切现象进行了全面的分析及研究,特别针对根切的预防措施做了详细介绍,极大程度减少了根切现象的产生,具有积极的指导意义及推广价值。

超声骨刀辅助下单侧入路对侧潜行减压治疗退变性重度腰椎管狭窄症的临床疗效

目的:探讨超声骨刀辅助下单侧入路对侧潜行减压治疗退变性重度腰椎管狭窄症的效果和安全性。方法:收集2018年6月~2021年6月超声骨刀辅助下单侧入路对侧潜行减压治疗退变性重度腰椎管狭窄症患者174例[单侧入路双侧减压(对侧潜行减压)经椎间孔腰椎椎间融合术(transforaminal lumbar interbody fusion,TLIF)组,A组],对比同期行双侧经椎间孔减压患者129例(双侧小切口TLIF组,B组),比较两组之间切口长度、手术时间、术中出血量、术后引流量、住院时间等围手术期参数,行肌酸磷酸激酶(creatine phosphokinase,CPK)检查评估肌肉破坏情况,术后采用疼痛视觉模拟量表(visual analogue scale,VAS)评分以及Oswestry功能障碍指数(Oswestry disability index,ODI)评估术后疗效,并比较两组之间术后并发症和融合情况。结果:两组间比较,两侧切口平均长度和住院时间无明显差异(P>0.05),而手术时间、术中出血量及术后引流量A组较B组明显减少,差异有统计学意义(P<0.05)。两组患者术前CPK值差异无显著性意义(P>0.05),术后1d、3d时B组明显高于A组,差异具有显著性(P<0.05),术后5d两组比较差异无显著性(P>0.05)。术后3d、1个月、3个月、12个月,两组患者的VAS评分和ODI较术前均显著改善,术后3d、1个月、3个月、12个月时VAS评分和ODI两组均无明显差异(P>0.05),术后12个月时A组ODI和VAS评分均优于B组,但无统计学意义(P>0.05)。术后出现硬膜撕裂、切口脂肪液化、脑脊液漏、术后感染等并发症两组之间无明显差异。术后出现下肢麻木加重,和臀部/下肢症状反跳的患者比例,单侧入路双侧减压TLIF组均小于双侧小切口TLIF,差异有统计学意义(P<0.05)。术后1年时,单侧入路双侧减压TLIF组有12例尚未融合,双侧小切口TLIF组有8例未融合,两组患者的植骨融合情况差异无统计学意义(P>0.05)。结论:与双侧小切口TLIF手术相比,超声骨刀辅助下单侧入路对侧潜行减压治疗退变性重度腰椎管狭窄症亦可取得较好疗效,具有创伤小,对脊柱稳定性影响小,手术时间短,术中出血少等临床优势,值得临床推广。

自然崩落法拉底参数对矿岩初始与持续崩落的影响机制

矿岩自然崩落过程中初始崩落与持续崩落的作用机制影响崩落时空演化规律。为了研究拉底方向与拉底高度对自然崩落法矿山初始与持续崩落过程的影响,采用FLAC3D数值模拟,开展斑岩型厚大铜矿拉底推进方向垂直或平行于最大主应力方向、拉底高度8~12 m条件下的初始崩落条件、持续崩落条件、崩落体形态、崩落矿量的规律研究。结果表明,累积拉底面积与崩落高度呈二次函数关系;在发生初始崩落后,累积拉底面积与累积崩落矿量呈指数函数关系。当拉底方向一定时,崩落高度随着拉底高度的增大而增大,且拉底高度大时有利于提早诱发初始崩落与持续崩落,累积崩落矿量整体呈增长趋势。拉底方向垂直最大主应力时比平行于最大主应力时更易诱发初始崩落、持续崩落。研究结果揭示了拉底参数对矿岩初始与持续崩落的影响机制,可为硬岩矿山自然崩落法的基础研究提供依据。

不同设计的聚醚醚酮卡环固位及疲劳性能研究

目的增加聚醚醚酮(PEEK)卡环臂进入倒凹的比例,并探究这一改变对PEEK卡环固位力和疲劳性能的影响,提出并验证一种可以提高PEEK卡环性能的设计方式。方法设计并加工3组PEEK三臂卡环(n=10/组),分别令其固位臂的末端1/3、末端2/3以及全部固位臂进入0.75 mm深度的倒凹;一组钴铬合金卡环(n=10),令其固位臂末端1/3进入0.25 mm深度的倒凹作为对照组。在对卡环进行初始固位力测量后,在体外进行15000次摘戴的疲劳循环,每经过1500次循环再测量一次卡环的固位力。使用光学扫描与软件偏差分析,通过均方根(RMS)比较疲劳前后卡环的形变量。使用扫描电子显微镜观察疲劳前后卡环臂内表面的变化。结果固位臂全进入倒凹区的PEEK卡环平均固位力(9.24±1.78)N,在3组PEEK卡环中最高;但仍略低于钴铬合金卡环(11.88±2.05)N。经过疲劳循环,各组卡环的固位力均发生了下降,其中钴铬合金卡环固位力的下降率最高(38.38%)。三组PEEK卡环的RMS没有统计学差异(P=0.111),且都低于钴铬合金卡环的RMS(105.47±10.82)μm。在扫描电子显微镜成像下,所有组卡环臂内表面都观察到了磨损的痕迹,并且主要发生在卡环臂进入倒凹的部分。结论增加PEEK卡环固位臂进入倒凹的比例能够有效提高卡环的固位力,并且在经过体外疲劳循环后,具有优于钴铬合金卡环的固位力稳定性,可以满足临床要求。初步验证了通过增加PEEK卡环臂进入倒凹的比例来提高卡环性能的可行性。

周向超前割缝辅助碟形滚刀楔裂破岩性能

碟盘滚刀基于底切破岩模式而具有较好的硬岩破碎性能,为进一步提高煤矿井下硬岩巷道机械化掘进效率,以碟盘滚刀为对象,探究了周向超前割缝预裂岩石辅助碟盘滚刀楔裂破岩性能。通过碟形滚刀楔裂破岩实验,明确了碟形滚刀楔裂破岩机理,揭示了周向超前割缝对岩石断裂特性的影响机制,并以滚刀载荷、岩石破碎体积和破岩比能耗为指标综合评价了切削参数和割缝参数对滚刀破岩性能的影响,采用正交试验得到了各因素对破岩性能的影响显著性及滚刀最优破岩性能时对应的参数匹配关系。结果表明:根据滚刀载荷波动和岩石断裂造成的声发射振铃变化特征可将碟形滚刀楔裂破岩过程划分为3个阶段,即压密阶段、应力积聚阶段和崩落阶段;相同切削厚度条件下,与无割缝条件相比,割缝深度和割缝宽度分别为16 mm和3 mm时碟形滚刀破岩载荷和滚刀应力分别降低40%和20%。基于三因素四水平正交试验得到的破岩性能最优条件下切削厚度、割缝深度和割缝宽度的匹配关系为30、16和3 mm,其中切削厚度对碟形滚刀破岩性能的影响最为显著,割缝深度次之,割缝宽度的影响程度最小。滚刀破岩载荷和岩石破碎体积均与切削厚度呈正相关关系,破岩比能随着切削厚度的增加先减小后增大,在30 mm切削厚度下得到最小值;各指标随着割缝深度的增加均呈现出先减小后增大的变化规律,最佳割缝深度为16 mm;当割缝宽度超过3 mm时,各指标受缝宽的影响不显著。周向超前割缝预裂岩石对提高碟形滚刀楔裂破岩性能具有较好提升效果,同时益于改善碟形滚刀受载条件、延长刀具服役寿命,进而为碟形滚刀掘进装备的设计提供一定的指导和参考。

Design of undercuts and dipole stabilizer rods for the CPHS RFQ accelerator

As part of the design and machining of the RFQ accelerator in the Compact Pulsed Hadron Source （CPHS） project at Tsinghua University, the design process of the undercuts and dipole stabilizer rods is presented in this paper. In particular, the relationship between the inter-vane voltage slope and the local frequency of the undercut section is described quantitatively. With the identification of modes existing in the cavity, the specific parameters are optimized by the SUPERFISH and MAFIA codes. In addition, the water-cooling requirement of the dipole stabilizer rods is briefly discussed.

正交面齿轮传动的两类界线

为了建立系统的正交面齿轮传动啮合界线与曲率干涉界线理论,本文通过求解非线方程组获得了两类界线的数值解。证明了啮合界线在小轮齿面上是渐开线;其共轭线也是渐开线。发现干涉界线一般有2条,近齿面干涉界线存在于面齿轮内端附近,大致沿齿高走向。近齿面干涉界点存在平凡解,是干涉界线和啮合界线共轭线的交点,位于传动副瞬时相对转动轴上。基于近齿面干涉界线,建立了面齿轮无根切内径公式,通过数值迭代可以获得内径准确值;还导出了无根切内径估算公式,便于设计中应用。

阀体偏心沉割槽对滑阀阀芯径向不平衡力的影响

滑阀流道呈现一种非对称且变化的复杂流道,阀内形成湍流流动,致使阀芯表面受到不均匀压力作用,形成不平衡力,导致阀芯出现倾斜,增加阀芯卡滞的风险,影响滑阀正常工作。针对这个问题,研究了阀体偏心沉割槽对滑阀阀芯径向不平衡力的影响。首先,简化了滑阀流道模型,采用数值模拟方法建立了滑阀瞬态流动分析模型;然后,基于伯努利效应,分析了不同偏心沉割槽时阀芯表面不均匀压力分布规律;最后,获取了不平衡力计算公式,研究了不同沉割槽偏心距对阀内流动特性、阀芯表面受力及径向不平衡力的影响。研究结果表明:采用偏心沉割槽结构减缓了出口段阀芯下表面区域的湍流程度,有效降低了阀芯径向不平衡力的大小;沉割槽偏心距为1.92 mm时,阀芯受到的不平衡力最小,相对于无偏心沉割槽,径向不平衡力在开度为0.5 mm时减小了77.63%,开度为1.5 mm时减小了50.18%,有效减缓了阀芯的倾斜程度。该研究结果对阀体沉割槽设计及阀芯不平衡力抑制方法的研究具有一定参考价值。

多期次河谷下切重力应力场分布特征研究

河谷下切的卸荷应力分布特征一直是水电工程关注的焦点之一。通过Geo-studio模拟多期次河谷下切后重力应力场的分布特征,分析认为河谷下切过程中仅距坡面一定深度范围内发生明显的应力重分布,主要表现为主应力方向的偏转和量值变化,而河谷及坡体深部主应力量值基本不随河谷下切过程而发生变化,河谷表层稍有卸荷现象,但程度很低。同时,软弱夹层的存在会使得夹层内岩体应力明显松弛,而在相邻硬岩中出现应力增高,但对远处岩体影响不大。