Discretization—Based analysis of structural electrodynamics

This paper experimentally confirms the fundamental dynamic properties of an electrodynamic structure. The discretization effects are examined for the conversion of continuous properties such as mass, stiffness and surface charge into discrete quantities. In the systems considered, the linearized characteristics are well-matched with the nonlinear systems in the sense that the linearized effects dominate over the high-order nonlinear terms. A conductive strip experiment is conducted in order to improve our understanding of the fundamental characteristics of the electrodynamic structure from discrete systems to continuous systems. The measured equilibrium positions agree with the analytically predicted equilibrium positions up to some small errors.     

Failure analysis of gas turbine generator cooling fan for 14° and 19° — blades angle of attack

In gas turbine power plants, a fan is used as a cooling system to dissipate generated heat in coils (copper conductors) and generator electric circuits at the end sides of its rotor. In some cases, fracture of blades causes short circuit between rotor and stator and consequently generator explosion and made lot of financial problems. The fracture of cooling fan blades has been occurred five times at the turbine side of the generator in our case of study, just 100 hr after resuming operation after overhaul. Using numerical analysis as well as laboratory investigation — includes visual inspections, metallography and SEM — can help better finding failure problems that cause blade failures. A series of numerical analysis was performed to diagnose the cause of failure possibility. CFD analysis is used to study the airflow distribution in order to observe probable separation phenomenon and pressure forces that they are imposed to fan blades due to operation. A finite element method was utilized to determine the stresses and dynamic characteristics of the fan blade (natural frequencies, stresses and vibrations).     

Effectiveness of structural–parametric synthesis of metal-cutting systems

The effectiveness of structural–parametric synthesis of metal-cutting systems is assessed in comparison with the traditional design approach.     

Electric conductance method for the assessment of liquid–gas injection into a large gas–solid fluidized bed

Liquid injections are applied widely in fluidized bed reactors such as Fluid Cokers, fluid catalytic crackers and polymerization reactors. In such industrial processes, it is necessary to optimize the contact between the injected liquid and the bed solids as it has a significant effect on product yields and quality, and reactor operability.     

Micro-drilling of Ti–6Al–4V alloy: The effects of cooling/lubricating

This paper presents a series of experimental investigations of the effects of various machining conditions [dry, flooded, minimum quantity lubrication (MQL), and cryogenic] and cutting parameters (cutting speed and feed rate) on thrust force, torque, tool wear, burr formation, and surface roughness in micro-drilling of Ti–6Al–4V alloy. A set of uncoated carbide twist drills with a diameter of 700 μm were used for making holes in the workpiece material. Both machining conditions and cutting parameters were found to influence the thrust force and torque. The thrust force and torque are higher in cryogenic cooling. It was found that the MQL condition produced the highest engagement torque amplitude in comparison to the other coolant–lubrication conditions. The maximum average torque value was obtained in the dry drilling process. There was no substantial effect of various coolant–lubrication conditions on burr height. However, it was observed that the burr height was at a minimum level in cryogenic drilling. Increasing feed rate and decreasing spindle speed increased the entry and exit burr height. The minimum surface roughness values were obtained in the flood cooling condition. In the dry drilling process, increased cutting speed resulted in reduced hardness on the subsurface of the drilled hole. This indicates that the surface and subsurface of the drilled hole were subject to softening in the dry micro-drilling process. The softening at the subsurface of drilled holes under different cooling and lubrication conditions is much smaller compared to the dry micro-drilling process.     

Application of the Jacobian–torsor theory into error propagation analysis for machining processes

The Jacobian–torsor theory is used to provide mathematical models of tolerance analysis, establishing a mathematical relationship between the open loop and closed loop of tolerances. The model allows additional chain of torsors joining them. So it is easy to model new ones. Therefore, the ability to calculate the end tolerance of assembly is useful in error propagation analysis. This paper formulates the error propagation model based on the Jacobian–torsor theory. With this theory, workpiece, fixtures, machine tool, and tool are regarded as an assembly. As a result, error sources can be grouped in a sequential manner and described by the parameters of the small displacement torsor. Moreover, the corresponding error propagation model can consider nonpunctual contacts of the fixture assembly, overcoming the limitation of the 3-2-1 layout. An experiment was conducted to demonstrate the model application and verify the effectiveness of the proposed methodology.     

Optimization of pulsed laser atom probe (PLAP) for the analysis of nanocomposite Ti–Si–N films

Laser-assisted atom probe tomography was used to investigate the nanostructure and composition of high-performance, ultra-hard Ti–Si–N nanocomposite films. However, the quality of data is heavily dependent on analysis conditions. In order to obtain reliable data from these, and other ‘less conducting’ specimens, the analysis parameter space was thoroughly investigated to optimize the mass resolution and hit multiplicity obtained in atom probe tomography. Geometric factors including tip radius and shank angle were found to play a significant role in mass resolution but had no apparent effect on the number of multiple hits observed. Increased laser energy led to a gradual increase in the number of single hits, but a modest improvement in mass resolution. The influence of other instrumental factors including detection rate and base temperature was investigated separately. Preliminary PLAP results are presented, and correlated with TEM analysis of the microstructure of the film.     

Analysis of Thermal Stability of High-Performance Rolling–Sliding Contacts in Mixed Lubrication

Thermal instability has been considered by pioneer researchers to be one of the most promising lines for a fundamental investigation into the failure mechanisms of rolling–sliding contacts. This article uses a recently developed mixed lubrication model that integrates interrelated topographical, mechanical, thermal, and tribochemical aspects to study the thermal instability of high-performance rolling–sliding contacts. The effects of various system parameters on the relation between the system bulk temperature and the heat generation in the contact are analyzed. The parameters include surface roughness; contact component size; surface and lubricant mechanical, thermal, and tribochemical properties; and operating conditions. Key results and their implications to system design and operation considerations are summarized in the Conclusion section of the article in relation to enhancing the thermal stability of the contact, particularly under adverse lubrication conditions.     

Experimental–theoretical study of high-cycle failure of structural elements of VZh-159 alloy

The results of an experimental–theoretical investigation of high-cycle fatigue of a VZh-159 alloy at a temperature of 850°C are represented. A model and algorithm for the prediction of fatigue damages are proposed, which, with respect to relationships of damaged-medium mechanics, permit the simulation of processes of high-cycle structural failure subject to general factors affecting the cyclic strength of structural material. The results of the numerical simulation of high-cycle failure of structural elements are given that verify the working capacity of the proposed model, algorithms, and software environment developed based on it.     

A finite element methodology for wear–fatigue analysis for modular hip implants

Fretting of the stem-head joint in a prosthetic hip implant is investigated experimentally and computationally. An FE-based methodology for fretting wear-fatigue prediction in a prosthetic hip implant is developed. Tribological and profilometry tests are performed for two head/stem material combinations: Co–28Cr–6Mo/DMLS Ti–6Al–4V and Co–28Cr–6Mo/forged Ti–6Al–4V. The hardness and wear resistance of DMLS Ti–6Al–4V are shown to be superior to those of forged Ti–6Al–4V. The significance of wear in a hip joint for 10 years of service in a normal weight person for moderately intense exercise is predicted for both material combinations. Both material combination joints are shown to have excellent wear resistance which suggests that the wear debris emission will not be significant.     

A Spectral–Thermal Bench with a Special Fiber-Optic Probe–Objective for Measuring Diffuse-Reflection Spectra

The results of tests of a new fiber-optic probe–objective for measuring both IR diffuse-reflection spectra and other types of spectra of solids at various temperatures are presented. In comparison with the conventional devices, the new scheme for measuring diffuse-reflection spectra has such advantages as the minimum distortion of spectra by the specular and Fresnel diffuse components of the reflection from surface irregularities and the linearity of the concentration dependences. The use of a fiber-optic probe–objective provides the ability for the simultaneous analysis of the solid phase and outgoing gases with increasing temperature and calibration of the spectral methods using the thermogravimetric-analysis data. An example of monitoring the process of drying catalysts in laboratory studies when analyzing composite and other materials is used to consider the prospects for using the probe–objective.     

Calibrated Thermal Microscopy of the Tool–Chip Interface in Machining

This paper presents the results of calibrated, microscopic measurement of the temperature fields at the tool–chip interface during the steady‐state, orthogonal machining of AISI 1045 steel. The measurement system consists of an infrared imaging microscope with a 0.5 mm square target area, and a spatial resolution of less than 5 µm. The system is based on an InSb 128 × 128 focal plane array with an all‐reflective microscope objective. The microscope is calibrated using a standard blackbody source from NIST. The emissivity of the machined material is determined from the infrared reflectivity measurements. Thermal images of steady state machining are measured on a diamond‐turning class lathe for a range of machining parameters. The measurements are analyzed by two methods: 1) energy flux calculations made directly from the thermal images using a control–volume approach; and 2) a simplified finite‐difference simulation. The standard uncertainty of the temperature measurements is ± 52°C at 800°C.     

Hybrid time–frequency methods for non-stationary mechanical signal analysis

This paper presents a family of hybrid time–frequency methods to be used as a tool for transient signal analysis. These methods are based on autoregressive models of the signal, and on the maximum likelihood method. A classical Wigner–Ville distribution and a parametric time–frequency methods are used for comparison purposes. The characteristics, advantages and disadvantages, of non-parametric, parametric and hybrid methods are discussed and their performances are compared by analysing actual data. The superiority of time–frequency resolution of the hybrid methods is pointed out over that of the parametric and non-parametric ones. Three practical examples of transient signals illustrate the discussion: the vibration signal issued from a damaged gearbox, a signal from a pendular scratch test presenting beating phenomenon and the vibration signal measured in an electrical motor during start-up.     

Numerical Study on the Stress–Strain Cycle of Thermal Self-Compressing Bonding

Thermal self-compressing bonding(TSCB) is a new solid-state bonding method pioneered by the authors. With electron beam as the non-melted heat source, previous experimental study performed on titanium alloys has proved the feasibility of TSCB. However, the thermal stress–strain process during bonding, which is of very important significance in revealing the mechanism of TSCB, was not analysed. In this paper, finite element analysis method is adopted to numerically study the thermal elasto-plastic stress–strain cycle of thermal self-compressing bonding. It is found that due to the localized heating, a non-uniform temperature distribution is formed during bonding, with the highest temperature existed on the bond interface. The expansion of high temperature materials adjacent to the bond interface are restrained by surrounding cool materials and rigid restraints, and thus an internal elasto-plastic stress–strain field is developed by itself which makes the bond interface subjected to thermal compressive action. This thermal self-compressing action combined with the high temperature on the bond interface promotes the atom diffusion across the bond interface to produce solid-state joints. Due to the relatively large plastic deformation, rigid restraint TSCB obtains sound joints in relatively short time compared to diffusion bonding.     

Temperature-mediated structural evolution of vapor–phase deposited cyclosiloxane polymer thin films for enhanced mechanical properties and thermal conductivity

Polymer-derived ceramic(PDC) thin films are promising wear-resistant coatings for protecting metals and carbon-carbon composites from corrosion and oxidation.However,the high pyrolysis temperature hinders the applications on substrate materials with low melting points.We report a new synthesis route for PDC coatings using initiated chemical vapor deposited poly(1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane)(pV₃D₃) as the precurs or.We investigated the changes in siloxane m...     

Transient Thermal Elastohydrodynamic Modeling of Cam–Follower Systems: Understanding Performance

This article deals with the lubrication of cam–follower contacts in automobile racing applications. Time-dependent thermal elastohydrodynamic line contact simulations are performed to analyze the contact performance achieved with a shear-thinning lubricant under highly dynamic conditions. Comparisons between different simulations are used to quantify the respective influence of shear thinning, thermal softening, and transient effects on friction and film thickness. Furthermore, this article highlights the formation and transport of a transient dimple responsible for an increase in lift close to the conditions where reversals of entrainment occur. Temperature distributions across the film thickness and pressure variations are reported to discuss the underlying phenomena.     

Wear resistance of cast Fe–Cr–C steels with various combinations of structural constituents at high velocities of sliding

The positive effect of the additional alloying of cast Fe–Cr–C steels on the formation of a secondary structure in the steels and their tribological characteristics under boundary friction has been shown. This effect leads to a decrease in the wear rate of the cast steel 1.2–5.2 times compared to that of the commercial 95Kh18 steel depending on the alloying system of the steels.     

Experimental analysis of coating layer behavior of Al–Si-coated boron steel in a hot bending process for IT applications

The utilization of high-strength steel for automotive structural parts has increased since the oil crisis in the 1970s owing to its high strength and potential for weight reduction. Because of the limited formability of high-strength steels, automotive components are increasingly produced through hot press forming. In some instances, high-strength steel sheets are coated with an Al–Si layer in order to prevent scaling of components during hot press forming, and this can increase their reliability with a view to the dimensional accuracy and stress distribution when they are in service. In this contribution, the coating degradation mechanisms of Al–Si-coated boron steel after the hot bending process are reported. The issues related to coating degradation during hot press forming are critically reviewed at different positions on a part that was subject to hot bending. In addition, the hardness and friction coefficient were tested by a nano-indenter at various positions. The relationship between the experimental parameters and coating layer properties is also reported. It is concluded that the bending deformation affected the coating layer behavior the most.     

In Situ Growth of Graphene on Carbon Fabrics with Enhanced Mechanical and Thermal Properties for Tribological Applications of Carbon Fabric–Phenolic Composites

ABSTRACT

Though the premature failures of wind turbine gearboxes are often attributed to bearing fatigue from overloading, there is compelling evidence that wear from underloading is a significant contributor. Here we attempt to gain insight into the relative contributions of over- and underloading by assessing planet bearing reaction forces from the Gearbox Reliability Collaborative (GRC) standard gearbox within a typical utility-scale wind turbine under realistic conditions. The results demonstrate that non-torque load sharing by the planetary stage increases and decreases planet bearing reaction forces at different locations within each rotor cycle regardless of wind speed. Planet bearing reaction forces exceeded the fatigue limit at wind speeds above 12 m/s and fell below the minimum load rating at wind speeds below 7 m/s. Based on analyses of published wind spectra from 10 U.S. sites, the expected fatigue life of the planet bearings ranged from 42 to 529 years even after accounting for non-torque load sharing. At the same 10 sites, planet bearings were underloaded (below 2% of the dynamic load rating) once per rotor cycle 40–70% of the time. Underloaded bearings are susceptible to surface damage when suddenly exposed to common transient events, such as yaw, wind gusts, braking, and grid faults. The resulting surface damage can initiate premature failure via wear (e.g., micropitting) or by reducing bearing fatigue life. The results suggest that carrier bearing clearance, non-torque load sharing, and planet bearing underloading are significant contributors to the premature failures of wind turbine planet bearings.