截割厚度与截线距对镐型截齿破岩力学参数的影响

基于对一种砂岩的直线截割试验,研究截割厚度和截线距对镐型截齿破岩力学参数的影响。单因素回归表明:截割力、法向力与截割厚度成正比,线性拟合和幂函数拟合均能很好地描述它们之间的统计学关系;随着截割厚度的增加,法向力截割力比值呈线性减小;随着截线距的增加,截割力和法向力呈线性增加,法向力截割力比值呈幂函数减小。载荷波动性系数随着截线距与截割厚度比值的增大呈线性减小。多元线性回归表明:截割力、法向力与截割厚度和截线距之间有极强的统计学关系;载荷波动性系数与截割厚度及截线距之间存在显著的统计学关系,且与截割厚度成正比,与截线距成反比。对比发现,Evans的理论模型较Roxborouth等、Goktan的改进模型对截割力有更好的预测性能。     

Nanometric cutting of copper: A molecular dynamics study

Molecular dynamics (MD) simulations were carried out to study the nanometric cutting of copper. In our approach, the many-body EAM potential was used for the atoms interaction in the copper workpiece. The effect of the tool geometry on the cutting process was investigated. It is observed that with negative rake angle, the chip becomes smaller due to the larger plastic deformation generated in the workpiece. It is shown that as the rake angle changes from −45° to 45°, the machined surface becomes smoother. Besides, both the cutting forces and the ratio of normal force to tangential force decrease considerably with the rake angle changing from negative to positive. In addition, MD simulations with the two-body Morse potential instead of the EAM potential were also carried out to study the effect of different potentials on the simulation results. It is found that there is no big difference in the simulated chip formation and the machined surface under the two different potentials. However, the Morse potential results in about 5–70% higher cutting forces than the EAM potential. It is recommended that the EAM potential should be used for the MD simulations of nanometric machining processes.     

A molecular dynamics simulation study on trapping ions in a nanoscale Paul trap

We found by molecular dynamics simulations that a low energy ion can be trapped effectively in a nanoscale Paul trap in both vacuum and aqueous environments when appropriate AC/DC electric fields are applied to the system. Using the negatively charged chlorine ion as an example, we show that the trapped ion oscillates around the center of the nanotrap with an amplitude dependent on the parameters of the system and applied voltages. Successful trapping of the ion within nanoseconds requires an electric bias of GHz frequency, in the range of hundreds of mV. The oscillations are damped in the aqueous environment, but polarization of water molecules requires the application of a higher voltage bias to reach improved stability of the trapping. Application of a supplemental DC driving field along the trap axis can effectively drive the ion off the trap center and out of the trap, opening up the possibility of studying DNA and other charged molecules using embedded probes while achieving a full control of their translocation and localization in the trap.     

Electronic processes in molecular dynamics simulations of nanoscale metal tips under electric fields

Electronic effects play a crucial role in the temperature evolution of metal parts which have electric currents running through them. The increase in temperature due to resistive heating can cause the melting of metal nanoscale wires creating damage in electric circuits. Likewise, electric currents are also present in sharp features on metal surfaces exposed to high electric fields. The destruction of such tips can lead to vacuum arcs, supplying the neutral species to build up plasma over the surface. To follow the temperature evolution caused by electric currents in such a tip, we developed a new model, based on an existing molecular dynamics code, to include resistive heating and electronic thermal conduction. The results given by the new simulation model are in good agreement with analytical predictions.     

Comparative study of the effect of surface texturing on cutting tool in dry cutting

Recent researches in the field of dry machining have indicated that surface texture has the potential to influence tribological conditions. Researchers have studied the application of controlled surface microtextures on cutting tool surfaces to improve machining performance by changing the tribological conditions at the interfaces of tool–chip and tool–work piece. An experiment to study the performance of the microtextured high-speed steel cutting implement within the machining of steel and aluminum samples was performed. Surface textures were introduced using Rockwell hardness tester, Vickers hardness tester, and by scratching with diamond dresser on the face of single point cutting tool. Machining in dry conditions was applied on mild steel (EN3B) and aluminum (AA 6351) samples using lathe machine with microtextured and traditional cutting tool for the constant range of feed, depth of cut, and for varying range of cutting speeds. Measurement of cutting force, cutting temperature, and surface roughness of the work surfaces after machining were made. The results showed reduction in cutting forces and cutting temperature with textured tools in comparison with those of the untextured tool. Chips collected from different samples were studied under a microscope and the results showed that textures created on the tool surface by various methods exhibited variations in chip formation. Cutting tools without texture and with texture were comparatively studied and the outcomes of the experimental study are presented in this paper.     

Stress-strain state in the grit-matrix system of a diamond tool under force disturbances

The stress-strain state in the grit-matrix system of carbide-bonded diamond tools has been studied by numerical simulation. A transition layer in contact with a diamond grit is shown to be the most heavily loaded portion of the bond. The behavior of stresses in this region has been clarified for variable cutting force directions, properties of the matrix, and the transition layer. Stresses have been analyzed for various extents of the grit embedding in the matrix; critical loading parameters have been determined for various grit shapes and Poisson ratios of the bond.     

A combined method of molecular dynamics with micromechanics improved by moving the molecular dynamics region successively in the simulation of elastic--plastic crack propagation

Molecular dynamics is applicable only for a small region of simulation. To simulate a large region it is necessary to combine molecular dynamics with continuum mechanics. Previously we proposed a new model in which molecular dynamics was combined with micromechanics. A molecular dynamics model was applied to the crack tip region and a micromechanics model to the surrounding region. In that model, however, crack propagation simulation must be stopped when the crack tip reaches the boundary of the two regions. In this paper the previous model is improved by moving the molecular dynamics region successively with crack propagation. The improved model may be applied to simulate limitless crack propagation. In order to examine the validity of the improved model, we simulate α-iron. The calculation cost with the improved model is less than a tenth of that of the previous model although the results are equal to each other. The crack tip opening displacement calculated with this model is almost equal to the analytical solution derived by Rice. This revised version was published online in July 2006 with corrections to the Cover Date.     

A molecular dynamics study on the nucleation of calcium phosphate regulated by collagen

Molecular dynamics (MD) simulations have been used to study calcium phosphate formation regulated by collagen in solution. In this study, a collagen-like peptide molecule has been mixed with different types of ions for simulations of the early stage of biomineralization. We have compared one system containing calcium ions, and hydrogen phosphate ions to the other system containing calcium ions, phosphate ions and hydroxy ions in a water box containing a peptide molecule (1CAG) in the center. After the simulations, the radical distance function and coordination number profiles show that calcium ions and phosphate ions attract each other and form stable clusters in both systems studied. The hydroxy ions are attracted by calcium ions and the distance between them is close to that in hydroxyapatite, which is considered to play important roles in the formation of hydroxyapatite. The current results provide a useful approach to study the scenario of mineralizing collagen using MD methods.     

Vibrational study of a molecular device using molecular dynamics simulations

A Potential scenario for the implementation of molecular electronic systems is introduced by applying digital signal processing techniques to results from classical molecular dynamics simulations of a molecular system interconnected by nanosize gold clusters. Under this new scenario, signals can be introduced, processed, and read through interactions with the internal vibrational modes of the small molecular unit. We use modulation operations intrinsically inherent to any molecular system as a concept proof. As an example of this type of analysis, we focus on the individual oscillations between C-H and C-C bonds and cluster-cluster displacements.     

制动力作用下车辆—车站结构耦合系统分析

研究制动力作用下车辆—结构耦合系统的分析方法。以刚体动力学方法建立车辆子系统模型,以振型叠加法建立结构子系统模型,以给定的制动加速度时程、简化的Kalker蠕滑理论和轮轨密贴假定分别定义纵向、横向和竖向轮轨间相互作用力,采用时程积分和时间步内的力—运动状态迭代方式求解运动方程。作为算例,研究了深圳地铁4号线、6号线列车制动于深圳北站时车辆—结构动力耦合系统的动力响应,并对车站结构关键部位的振动状态做出了分析和评价。     

小波分析在K24铣削力研究中的应用

通过正交试验对镍基铸造高温合金K24的铣削力进行了研究,将小波分析运用于铣削力的信号处理。运用小波分析对铣削力进行去噪处理,并且对刀具不同磨损状态下的铣削力信号进行了小波分解,能量检测。结果证明,随着刀具磨损量的增加,各尺度频段的信号振动加剧,而且能量也对应地增加。     

Dynamic response of a beam on elastic foundation of finite depth under a moving force

Summary In this paper, dynamic response of an infinitely long beam resting on a foundation of finite depth, under a moving force is studied. The effect of foundation inertia is included in the analysis by modelling the foundation as a series of closely spaced axially vibrating rods of finite depth, fixed at the bottom and connected to the beam at the top. Viscous damping in the beam and foundation is included in the analysis. Steady state response of the beam-foundation system is obtained. Detailed numerical results are presented to study the effect of various parameters such as foundation mass, velocity of the moving load, damping and axial force on the beam. It is shown that foundation inertia can considerably reduce the critical velocity and can also amplify the beam response.List of symbols b width of the beam - C _b coefficient of viscous damping for the beam - C _f coefficient of viscous damping for the foundation - E Young's modulus - f frequency - H foundation depth - I moment of inertia - i =(–1)^0,5 - K, k indexing variables - k _f foundation modulus - m mass per unit length of the beam - N total number of frequency points in Eqs. (25) and (26) - n indexing variable - P moving force - Q axial force on the beam - q(x, t) foundation pressure per unit length of the beam - q() foundation pressure in the moving co-ordinate system - t time variable in sec. - U _j () generalized coordinate in Eq. (4) - U _j ^*(f) Fourier transform ofU _j - u(y, t; x) axial displacement in the foundation at a particularx value - u(y, ) foundation displacement in the moving coordinate system - , nondimensionalized foundation deflection - v velocity in meters/sec. - v _cr critical velocity corresponding to massless foundation - w(x, t) beam deflection - w() beam deflection in the moving coordinate system - =w()/L nondimensionalized beam deflection - Fourier transform of - x, y coordinate axis - velocity parameter - _cr critical velocity parameter - mass parameter - moving coordinate - _b beam damping parameter - _f foundation damping parameter - (y, t, x) vertical stress in the foundation - () Dirac delta function - foundation mass per unit depth per unit length of the beam     

A tree-search method for solving a cutting stock assignment problem

Many production environments such as carpet or flat glass manufacturing have linked operations that perform completely different activities. In this paper, we consider a two-stage manufacturing process involving a cutting operation, followed by an assignment operation. Raw material is cut to meet product demand with minimum trim loss, and assignments are made to minimize resource requirements. This cutting stock assignment problem is formulated as a large-scale, mixed-integer nonlinear programming problem. We propose a solution methodology based on decomposition and tree search heuristic strategies. We report on extensive computational experiments on a wide range of problems, and apply statistical techniques to determine significant factors. For all small-size problems tested, our method found the exact optimal solution. For practical-size problems, our method was about two orders of magnitude faster and produced solutions that were one-third better than tabu search.     

Effect of hydrogen adsorption by 40Kh steel on the force parameters of cutting, stresses in a tool, and its wear resistance

We established that a decrease in the components of cutting forces owing to electrolytic hydrogen adsorption by blanks does not yet guarantee a positive effect of hydrogen treatment on the durability of cutting tools. The approach based on the determination of local force parameters of cutting, such as the tangential and normal stresses at the tool working surfaces, is more promising. We established the effect of hydrogen adsorption on the durability of cutting toolsK _{v 20} andK _{v 60}. The speedv ₂₀ orv ₆₀ that corresponds to a durability of 20 or 60 min, respectively, served as a durability index. The coefficient of the effect of hydrogen adsorption on the durability of the cutting tool (K _{v 20} andK _{v 60}) was calculated as the ratio between the values ofv ₂₀ orv ₆₀ for cutting of hydrogenated and original blanks. The durability of cutting tools of high-speed steel and hard alloy increases when using comparatively soft modes of hydrogen adsorption (the current density is less than 0.1 kA/m²). For harder modes, a negative effect of the treatment is already observed, despite a decrease in the components of cutting forces. Hydrogen-adsorption technologies have better prospects as applied to tools of hard alloys. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 6, pp. 95–100, November–December, 1999.     

Sintering of aluminum nanoparticles: A molecular dynamics study

Molecular-dynamics simulations have been used to study the consolidation of nanopartictes of aluminum. We have studied two- and three-particle sintering as it is influenced by temperature, particle size and crystallographic orientation. We have elucidated the dominant transport mechanisms by measuring the shear stresses that develop in the contact regions and the mobilities of the surface and core atoms during sintering. Our studies demonstrate that increasing the particles size slows down the sintering kinetics. The extent of interpenetration of the particles is independent of the particle size and is afunction of the temperature of the particles.     

A molecular dynamics study of hydrocarbons adsorbed in silicalite

A molecular dynamics study reproducing the vibrational spectra of a series of flexible hydrocarbon molecules adsorbed in silicalite yields very satisfactory structural and diffusional data. The form selectivity appears clearly when the molecules are compared. The influence of molecular flexibility on the calculated diffusional data is not obvious. The influence of adsorption on the molecular geometry is not very important.     

System for control of wear and diagnosis of a cutting tool

Translated from Izmeritel'naya Tekhnika, No. 8, pp. 35–36, August, 1990.     

一种圆锥形变幅杆弯曲振动固有频率的计算方法

提出了一种圆锥形变幅杆弯曲振动固有频率的计算方法。先忽略剪切变形和惯性矩作用,基于Euler-Bernoulli杆理论求解出固有频率初值,再计入二者的作用进行弯曲振动固有频率的修正。应用有限元分析法和模态实验测试对该方法进行了验证,理论结果与实验结果相吻合,误差在5%以内。基于该方法编写了程序,实现了弯曲振动变幅杆结构的主动设计。     

A study of the CEN test method for measurement of the carbonation depth of hardened concrete

This paper reports on the effect of an enhanced test method for the recently drafted CEN method for measuring the depth of carbonation of hardened concrete which was aimed at reducing the known variability of the test. Variations in environmental factors that may have led to a poor precision have been identified, for example the assumption that natural ventilation will provide the required level of carbon dioxide and relative humidity has been shown to be incorrect. This lead to the development of an environmental control system the actively controls the storage atmosphere. In addition to this, a two stage normalisation process of test data is proposed comprising the use of two additional mixes along with the mix being tested. Results from the assessment of the repeatability of a limited series of 10 mixes carried out by one operator of a 37 N/mm² PC/30% PFA concrete mix indicated that a significant improvement could be achieved following this type of control and normalisation.