STUDY ON MODULAR FAULT TREE ANALYSIS TECHNIQUE WITH CUT SETS MATRIX METHOD

A new fault tree analysis (FTA) computation method is put forth by using modularization technique in FTA with cut sets matrix, and can reduce NP (Nondeterministic polynomial) difficulty effectively. This software can run in IBM PC and DOS 3.0 and up. The method provides theoretical basis and computation tool for application of FTA technique in the common engineering system

Effects of Different Matrix Formulations and NAA Concentrations on Rosemary Cuttings

[Objective] The effects of different matrix formulations and NAA concentra-tions on the growth of roots and survival rate of rosemary cuttings were investigat-ed. [Method] The randomized block design was adopted. There were 9 formulations of matrix and 4 concentrations of NAA in the test. The survey and determination data was analyzed by Excel. [Result] For rosemary cuttings, the roots of Treatment 7 （turfy soil∶perlite=3∶2） had the best growth with the highest survival rate of nearly 100%. The roots of rosemary cuttings had the best growth for 150 mg/L of NAA with the highest survival rate of 88.9%. [Conclusion] For rosemary cuttings, the op-timal matrix formulation was turfy soil∶perlite=3∶2, and the optimal NAA concentration was 150 mg/L.

DATA TRANSFORMATION OF FAULT TREE BY USING MATRIX OPERATION

On the base of study of the correlation of fault tree's main data-minimum cutsets, minimum path sets, non-intersect minimum cut sets and non-intersect minimum path sets,transformation method among main data are found, i.e. the transformation can be realized by theoperation of cut sets matrixes. This method provides anew way to reduce 'NP' difficulty and simplifyFTA.

Super-Shuffle Product and Cut-Box Coproduct on (0,1)-Matrices

In 2014, Vargas first defined a super-shuffle product and a cut-box coproduct on permutations. In 2020, Aval, Bergeron and Machacek introduced the super-shuffle product and the cut-box coproduct on labeled simple graphs. In this paper, we generalize the super-shuffle product and the cut-box coproduct from labeled simple graphs to (0,1)-matrices. Then we prove that the vector space spanned by (0,1)-matrices with the super-shuffle product is a graded algebra and with the cut-box coproduct is a graded coalgebra.

Dynamic modeling of ultra-precision fly cutting machine tool and the effect of ambient vibration on its tool tip response

The dynamic performances of an ultra-precision fly cutting machine tool(UFCMT)has a dramatic impact on the quality of ultra-precision machining.In this study,the dynamic model of an UFCMT was established based on the transfer matrix method for multibody systems.In particular,the large-span scale flow field mesh model was created;and the variation in linear and angular stiffness of journal and thrust bearings with respect to film thickness was investigated by adopting the dynamic mesh technique.The dynamic model was proven to be valid by comparing the dynamic characteristics of the machine tool obtained by numerical simulation with the experimental results.In addition,the power spectrum density estimation method was adopted to simulate the statistical ambient vibration excitation by processing the ambient vibration signal measured over a long period of time.Applying it to the dynamic model,the dynamic response of the tool tip under ambient vibration was investigated.The results elucidated that the tool tip response was significantly affected by ambient vibration,and the isolation foundation had a good effect on vibration isolation.

MACHINING OF METAL MATRIX COMPOSITES

Two types of aluminium-based composites reinforced respectively with 20 vol short fibre alumina and with a hybrid of 15 vol SiC particle and 5 vol short alumina fibre are machined with different tool materials:cemented carbide,ceramic,cubic boron nitride(CBN)and polycrystalline diamond(PCD).The analysis on tool wear shows that the various tool materials exhibite different tool wear behaviours,and the tool wear mechanisma are discussed.Apparently,PCD tools do not necessarily guarantee dimensional stability but they can provide the most economic means for machining all sorts of composites.Consequently,a suitable tool material is suggested for machining each metal matrix composite(MMC) from the standpoints of tool wear and machined surface finish.

Milling Machinability of TiC Particle and TiB Whisker Hybrid Reinforced Titanium Matrix Composites

The milling machinabilities of titanium matrix composites were comprehensively evaluated to provide a theoretical basis for cutting parameter determination. Polycrystalline diamond （PCD） tools with different grain sizes and geometries, and carbide tools with and without coatings were used in the experiments. Milling forces, milling temperatures, tool lifetimes, tool wear, and machined surface integrities were investigated. The PCD tool required a primary cutting force 15 % smaller than that of the carbide tool, while the uncoated carbide tool required a primary cutting force 10% higher than that of the TiA1N-eoated tool. A cutting force of 300 N per millimeter of the cutting edge （300 N/mm） was measured. This caused excessive tool chipping. The cutting temperature of the PCD tool was 20%-30% lower than that of the carbide tool, while that of the TiA1N-coated tool was 12% lower than that of the uncoated carbide tool. The cutting temperatures produced when using water-based cooling and minimal quantity lubrication （MQL） were reduced by 100 ~C and 200 ~C, compared with those recorded with dry cutting, respectively. In general, the PCD tool lifetimes were 2--3 times longer than the carbide tool lifetimes. The roughness Ra of the machined surface was less than 0.6μm, and the depth of the machined surface hardened layer was in the range of 0.15-0.25 mm for all of the PCD tools before a flank wear land of 0.2 mm was reached. The PCD tool with a 0.8 mm tool nose radius, 0% rake angle, 10% flank angle, and grain size of （30＋2） μm exhibited the best cutting performance. For this specific tool, a lifetime of 16 rain can be expected.

Analysis of the Machining Characteristics on Surface Roughness of a Hybrid Aluminium Metal Matrix Composite (Al6061-SiC-Al₂O₃)

Aluminium metal matrix composites are finding increased applications in many areas. Adding of the third element to the metal matrix make the composite hybrid. This paper presents the study on the surface roughness characteristics of a hybrid aluminium metal matrix (Al6061-SiC-Al2O3) composites. The experimental studies were carried out on a lathe. The composites were prepared using the liquid metallurgy technique, in which 3, 6 and 9 wt % of particulates SiC and Al2O3 were dispersed in the base matrix. The obtained cast composites were carefully machined. The characteristics that influence the surface roughness such as feed rate, depth of cut and cutting speed were studied, which made the analysis come to a conclusion that the surface roughness is increases with the increase of feed rate and it reduces the surface roughness with the increase of cutting speed.

Steam as coolant and lubricant in turning of metal matrix composites

Green cutting has become focus of attention in ecological and environmental protection. Steam is cheap, poilution-free and eco-friendly, and then is a good and economical coolant and lubricant. Steam generator and steam feeding system were developed to generate and feed steam. Comparative experiments were carried out in cutting AA6061-15 vol.% SiC （25 p.m particle size）, with cubic boron nitride （CBN） insert KB-90 grade under the conditions of compressed air, oil water emulsion, steam as coolant and lubricant, and dry cutting, respectively. The experimental results show that, with steam as coolant and lubricant, gradual reduction in the cutting force, friction coefficient, surface roughness and cutting temperature values were observed. Further, there was reduction in built up edge formation. It is proved that use of water steam as coolant and lubricant is environmentally friendly.

From the new Austrian tunneling method to the geoengineering condition evaluation and dynamic controlling method

The new Austrian tunneling method （NATM） is widely applied in design and construction of underground engineering projects. When the type and distribution of unfavorable geological bodies （UGBs） associated with their influences on geoengineering are complicated or unfortunately are overlooked, we should pay more attentions to internal features of rocks grades IV and V （even in local but mostly controlling zones）. With increasing attentions to the characteristics, mechanism and influences of engineering construction-triggered geohazards, it is crucial to fully understand the disturbance of these geohazards on project construction. A reasonable determination method in construction procedure, i.e. the shape of working face, the type of engineering support and the choice of feasible procedure, should be considered in order to mitigate the construction-triggered geohazards. Due to their high sensitivity to groundwater and in-situ stress, various UGBs exhibit hysteretic nature and failure modes. To give a complete understanding on the internal causes, the emphasis on advanced comprehensive geological forecasting and overall reinforcement treatment is therefore of more practical significance. Compre- hensive evaluation of influential factors, identification of UGB, and measures of discontinuity dynamic controlling comprises the geoengineering condition evaluation and dynamic controlling method. In a case of a cut slope, the variations of UGBs and the impacts of key environmental factors are presented, where more severe construction-triggered geohazards emerged in construction stage than those predicted in design and field investigation stages. As a result, the weight ratios of different influential factors with respect to field investigation, design and construction are obtained.

Tool wear mechanisms in axial ultrasonic vibration assisted milling in-situ TiB2/7050Al metal matrix composites

The in-situ TiB2 particle reinforced aluminum matrix composites are materials that are difficult to machine,owing to hard ceramic particles in the matrix.In the milling process,the polycrystalline diamond(PCD)tools are used for machining these materials instead of carbide cutting tools,which significantly increase the machining cost.In this study,ultrasonic vibration method was applied for milling in-situ TiB2/7050A1 metal matrix composites using a TiAIN coated carbide end milling tool.To completely understand the tool wear mechanism in ultrasonic-vibration assisted milling(UAM),the relative motion of the cutting tool and interaction of workpiecetool-chip contact interface was analyzed in detail.Additionally,a comparative experimental study with and without ultrasonic vibration was carried out to investigate the infuences of ultrasonic vibration and cutting parameters on the cutting force,tool life and tool wear mechanism.The results show that the motion of the cutting tool relative to the chip changes periodically in the helical direction and the separation of tool and chip occurs in the transverse direction in one vibration period,in ultrasonic vibration assisted cutting.I arge instantaneous acceleration can be obtained in axial ultrasonic vibration milling.The cutting force in axial direction is significantly reduced by 42%-57%,40%--57%and 44%-54%,at different cutting speeds,feed rates and cutting depths,respectively,compared with that in conventional milling.Additionally,the tool life is prolonged approximately 2--5 times when the ultrasonic vibration method is applied.The tool wear pattern microcracks are only found in UAM.These might be of great importance for future research in order to understand the cutting mechanisms in UAM of in-situ TiB2/7050A1 metal matrix composites.

Tool wear during high speed turning in situ TiC_p/TiB_w hybrid reinforced Ti-6Al-4V matrix composite

Chipping, adhesive wear, abrasive wear and crater wear are prevalent for both the polycrystalline diamond （PCD） and the carbide tools during high speed turning of TiCp/TiBw hybrid reinforced Ti-6Al-4V （TC4） matrix composite （TMCs）. The combined effects of abrasive wear and diffusion wear caused the big crater on PCD and carbide tool rake face. Compared to the PCD, bigger size of crater was found on the carbide tool due to much higher cutting temperature and the violent chemical reaction between the Ti element in the workpiece and the WC in the tool. However, the marks of the abrasive wear looked much slighter or even could not be observed on the carbide tool especially when low levels of cutting parameters were used, which attributes to much lower hardness and smaller size of WC combined with more significant chemical degradation of carbide. When cutting TC4 using PCD tool, notch wear was the most significant wear pattern which was not found when cutting the TMCs. However, chipping, adhesive wear and crater wear were much milder when compared to the cutting of titanium matrix composite. Due to the absence of abrasive wear when cutting TC4, the generated titanium carbide on the PCD protected the tool from fast wear, which caused that the tool life for TC4 was 6-10 times longer than that for TMCs.

AN EFFECTIVE CONTINUOUS ALGORITHM FOR APPROXIMATE SOLUTIONS OF LARGE SCALE MAX-CUT PROBLEMS

An effective continuous algorithm is proposed to find approximate solutions of NP-hard max-cut problems. The algorithm relaxes the max-cut problem into a continuous nonlinear programming problem by replacing n discrete constraints in the original problem with one single continuous constraint. A feasible direction method is designed to solve the resulting nonlinear programming problem. The method employs only the gradient evaluations of the objective function, and no any matrix calculations and no line searches are required. This greatly reduces the calculation cost of the method, and is suitable for the solution of large size max-cut problems. The convergence properties of the proposed method to KKT points of the nonlinear programming are analyzed. If the solution obtained by the proposed method is a global solution of the nonlinear programming problem, the solution will provide an upper bound on the max-cut value. Then an approximate solution to the max-cut problem is generated from the solution of the nonlinear programming and provides a lower bound on the max-cut value. Numerical experiments and comparisons on some max-cut test problems （small and large size） show that the proposed algorithm is efficient to get the exact solutions for all small test problems andwell satisfied solutions for most of the large size test problems with less calculation costs.

双悬臂截割机器人相对动力学建模与力位混合控制研究

双悬臂截割机器人可解决传统单臂掘进机在截割大尺寸断面时效率低下的难题,但其与煤岩的动态交互影响控制性能。现有研究以双臂接触同一对象形成运动闭链为前提,无法满足双悬臂截割机器人双臂运动及末端截割头输出力的控制要求。针对该问题,设计了一种基于机器人相对动力学模型的力位混合控制系统。建立双悬臂截割机器人运动学和动力学模型,基于机器人的相对雅可比矩阵及虚位移与虚功原理推导出机器人的相对动力学模型,通过单一变量同时描述机器人双臂的运动状态,将机器人双臂独立的动力学模型整合为一个整体。基于机器人的相对动力学模型,设计了机器人双臂力位混合控制系统,通过李雅普诺夫函数验证了系统的稳定性和可行性。仿真结果表明:双悬臂截割工艺较单悬臂截割拥有更大的工作空间,具有一次性实现大断面截割的能力;双悬臂截割机器人力位混合控制系统能够完成对期望相对位置和期望相对力的同步跟踪,对截割头期望位置跟踪的绝对误差在0.3132 m以内,均方根误差为0.1447 m。

基于应变梯度理论的切削加工SiCp/Al表面创成机理分析

为了深入研究颗粒增强铝基复合材料的切削过程,对45%体积分数的SiCp/Al复合材料通过多相建模的方法建立了基于应变梯度的本构模型,并对软件ABAQUS进行了二次开发,用程序语言将所建本构模型以及描述断裂的B-W断裂准则编入用户子程序VUMAT,并导入ABAQUS进行仿真分析。结合切削实验和仿真分析结果,研究了在相同切削速度及不同切削深度下SiCp/Al复合材料加工表面温度、材料内部应力应变和位错的变化情况。研究结果表明,相较于传统Johnson-Cook模型,修正后的本构模型所得到的结果与实验结果更加吻合;切削深度增大会引发高温梯度;材料内部应力会在颗粒附近形成应力集中;在加工表面应变较大的区域出现大量位错,导致加工颗粒增强金属基复合材料的难度上升。

基质及IBA浓度对鲜食葡萄‘天工墨玉’硬枝扦插的影响

为促进鲜食葡萄品种的繁育及推广,以鲜食葡萄品种‘天工墨玉’为试材,探究了不同基质+不同浓度IBA对其硬枝扦插效果的影响。结果表明,采用珍珠岩为扦插基质,随着IBA浓度的升高,‘天工墨玉’硬枝扦插的生根率呈逐渐升高的趋势。在相同IBA浓度条件下,采用珍珠岩为扦插基质,‘天工墨玉’硬枝扦插的生根率最高;采用弹性基质为扦插基质,‘天工墨玉’硬枝扦插的生根率最低。采用珍珠岩和草炭土为扦插基质,IBA浓度为750和1000 mg·L^(-1)时,‘天工墨玉’硬枝扦插的根数在同一基质条件下无显著差异。综合考评‘天工墨玉’的叶片数量、根鲜重、根干重、叶片鲜重、叶片干重等指标,采用珍珠岩作为扦插基质,配以750 mg·L^(-1) IBA的效果较好。

不同类型基质和生长调节剂对橡胶草根扦插生根的影响

创建橡胶草新的无性繁殖技术体系,能为今后橡胶草的良种繁育及有效利用提供新的技术支撑,本研究以当年生橡胶草根部为试验材料,试验方法采用L9(34)正交试验设计,分别对植物生长调节剂的种类、浓度、处理时间以及不同扦插基质对橡胶草根扦插生根的影响进行试验研究。试验结果表明,通过对9种处理进行统计分析,橡胶草根生根率间存在显著差异,其中在8号处理条件下的橡胶草生根率最高,达到88.9%;与清水对照处理相比较,植物生长调节剂可对橡胶草根的扦插生根率达到显著影响,但不同种类的植物生长调节剂,在不同浓度以及处理时间下,对橡胶草根扦插苗不同生长指标的影响在统计学上无显著差异;三种不同类型的扦插基质处理下的橡胶草根生根率差异水平达到了极显著,其中以草炭土:珍珠岩=3:1配比条件下的橡胶草根平均生根率最高,为71.2%;8号处理条件下的隶属函数值最高。由此可得相应结论:扦插基质配比为草炭土:珍珠岩=3:1,植物生长调节剂采用ABT1号生根粉,浓度为300 mg/L,处理时间为0.5 min,是适合橡胶草根扦插的最佳处理组合。

大丽花扦插繁殖影响因子研究

为研究大丽花扦插影响因子,完善大丽花扦插技术体系,以大丽花"樱花"品种为试验材料,研究了不同扦插时期、不同插穗规格、不同基质、不同生长调节剂及其浓度对扦插生根的影响。研究结果表明,不同扦插时期对扦插生根效果有显著影响,以5月扦插的生根率、生根数和根系效果指数显著好于其他时期;基质种类、生长调节剂种类及浓度对生根效果均有显著影响,以处理6(1000 mg/L IBA+珍珠岩)扦插生根效果最好,其存活率、生根率、生根数、最大根直径和根系效果指数分别为95.00%、80.00%、9.54条、4.25 mm和41.93,均高于其他处理,且生根率、生根数和根系效果指数显著优于其他所有处理;插穗粗度相同时,8 cm长的插穗在多个指标上均显著好于5 cm长的插穗,而长度相同时,4~6 mm粗的插穗在最大根长和最大根直径上显著好于2~4 mm,因此插穗规格以S3(长8 cm粗4~6 mm)扦插生根效果最好。综合而言,以5月份用长8 cm粗4~6 mm的插穗经1000 mg/L IBA处理30 s后在珍珠岩扦插其生根情况最好。

不同处理对百合鳞片扦插诱导小鳞茎的影响

为丰富百合扦插繁殖技术体系,筛选出合适的扦插处理组合,以百合新品种“骄阳”为试验材料,探究不同基质配比和肥料处理组合、植物生长调节剂种类和浓度、鳞片位置对其鳞片扦插的影响。结果表明,纯珍珠岩更有利于小鳞茎的生成,纯蛭石有利于小鳞茎发育和后期根系生长,复合肥作底肥并不适用于其扦插繁殖;最优基质配比+肥料组合为纯蛭石+水溶肥处理,其所生成小鳞茎较多,且小鳞茎直径最大、生根数量最多、根长最长;外层鳞片有利于小鳞茎生成,中外层鳞片利于小鳞茎发育和后期根系生长;IBA的扦插生根效果优于NAA;最优鳞片位置+生长调节剂组合为中层鳞片+IBA 200 mg/L,其所生成小鳞茎较多,所产生的小鳞茎直径较大,且生根数量最多、生根较长,研究结果为百合新品种“骄阳”的种球繁育奠定了技术基础。

激光辅助切削CNTs/AL的数值模拟及参数优化

针对碳纳米管铝基复合材料(CNTs/AL)加工过程中加工性差、刀具磨损大等特点,提出采用激光辅助加工的方法进行改善。使用ABAQUS有限元仿真软件进行,对CNTs/AL复合材料的表面损伤形式、亚表面残余应力分布及切削力进行仿真研究,以完成对激光辅助加工CNTs/AL的可行性验证。基于响应曲面实验分析切削力与加工参数的关系,并建立了拟合程度良好的切削力模型。结果表明,使用激光辅助加工可以有效减小切削力和表面质量,平均切削力降低34%,但会稍微增大残余应力;3个工艺参数对切削力影响强弱依次为:激光功率、切削速度和切削深度。