Morphology of Surface Integrity as Effect of Cold Forging of Aluminum Alloy

Aluminum and its alloys represent a common raw material for components released through a cold machining routine (i.e., forging, cold heading, and rolling processes). They offer easy manufacturing and high plastic strength, together with light weight, long life span, and easy recycling and are heavily used in the transport industry (P. M. G. P. Moreira, et al. (1 Moreira, P. M. G. P., de Jesus, A. M. P., Ribeiro, A. S., and de Castro, P. M. S. T. (2008), “Fatigue Crack Growth in Friction Stir Welds of 6082-T6 and 6061-T6 Aluminium Alloys: A Comparison,” Theoretical and Applied Fracture Mechanics, 50, pp 81–91.[Crossref], [Web of Science ®] , [Google Scholar]), Theoretical and Applied Fracture Mechanics, 50, pp 81–91, 2008; H. Yoshimura and K. Tanaka (2 Yoshimura, H., and Tanaka, K. (2000), “Precision Forging of Aluminum and Steel,” Journal of Materials Processing Technology, 98, pp 196–204.[Crossref], [Web of Science ®] , [Google Scholar]), Journal of Materials Processing Technology, 98, pp 196–204, 2000). However, during processing, the sample–tool interfaces can generate sticking mechanisms that result in an increase in friction values and high wear rates, leading to irreversible damage to the workpiece surface. The surface morphology provides characteristics that allow detection of the damage amplitude. The hard contact between asperities causes nucleation and the formation of adhesive wear. The normal load and lubrication conditions may further affect the quantity of wear elements (A. Hase and H. Mishina (3 Hase, A., and Mishina, H. (2009), “Wear Elements Generated in the Elementary Process of Wear,” Tribology International, 42, pp 1684–1690.[Crossref], [Web of Science ®] , [Google Scholar]), Tribology International, 42, pp 1684–1690, 2009). Optical nondestructive observations permit the detection of the quantity of wear elements as per material transfer from one side (specimen surface) to the other side (contactor surface).

This article presents the mechanisms of the adhesive layer and material transfer that are directly proportional to the new roughness stature. A robust finite element method analysis was embedded to establish a relationship between time, plastic deformation, friction coefficients, and surface defects.     

AN AUTOMATED SPECIATION ANALYSER OF ORGANOMETALLIC COMPOUND CONTENT

This paper presents the design of an automated measurement device developed for speciation studies of organometallic compounds in samples of a complex and varying composition matrix.

The instrument automates three essential steps in a typical speciation analysis procedure: isolation of analytes, their enrichment, and time-resolved introduction into a detector. Analytes are extracted by purging from post-sample dissolution/digestion mixture, in the form of volatile derivatives, with their simultaneous enrichment on a capillary cryotrap. Before introduction into a detector, they are rapidly (ca. 0.5 min.) separated on a multi-capillary gas chromatographic column operating in isothermal mode.

The construction of the automated speciation analyser (ASA) makes it practically independent of a kind of the detector used (it was tested with MIP-AED,[1] Pereiro, I. R., Wasik, A. and ?obński, R. 1998. Purge-and-Trap Isothermal Multicapillary Gas Chromatographic Sample Introduction Accessory for Speciation of Mercury by Microwave-Induced Plasma Atomic Emission Spectrometry. Anal. Chem., 70: 4063 [Google Scholar] ICP—MS,[2] Wasik, A., Pereiro, I. R., Dietz, Ch., Szpunar, J. and ?obński, R. 1998. Speciation of Mercury by ICP-MS After On-Line Capillary Cryofocusing and Ambient Temperature Multicapillary Gas Chromatography. Anal. Commun., 35: 331 [Google Scholar] and AAS detectors) and gives the freedom of choice of sample preparation procedure. The only requirement to the latter is that analytes should be in a form of volatile compound in an aqueous matrix.     

EFFECT OF SOME MODIFICATIONS TO OXLEY'S MACHINING THEORY AND THE APPLICABILITY OF DIFFERENT MATERIAL MODELS

Oxley's machining theory has recently been extended[1] Adibi-Sedeh, A. H., Madhavan, V. and Bahr, B. 2002. Extension of Oxley's analysis of machining to use different material models. Submitted to ASME Journal of Manufacturing Science and Engineering [Google Scholar] to accept material property inputs in the form of widely used constitutive models such as the Johnson–Cook and MTS material models. In the process, additional modifications have been made to the model to improve its self-consistency. For instance, the shear force is obtained from the total work of deformation, thereby eliminating the unknown parameter η, and the hydrostatic pressure at the tool-chip interface is calculated considering the gradient in temperature in addition to the gradient in strain. This study is aimed at understanding the effect of these modifications separate from the changes due to the introduction of the new material models by comparing results obtained using Oxley's original model to that obtained with the above modifications. We also compare results obtained using different constitutive models for AISI 1045 to the experimental results of the “Assessment of Machining Models” effort.     

Study on rock reaction force depending on PDC cutter placement

The article focuses on the problem of polycrystalline diamond cutter (PDC) cutters' overlapping influence on rock reaction force. This study proposed a static force balance model, based on the model of Wojtanowicz and Kuru (1993 Wojtanowicz, A.K.; Kuru, E. (1993) Mathematical modeling of PDC bit drilling process based on a single-cutter mechanics. Journal of Energy Resources Technology-Transactions of the ASME, 115(4): 247–256.[Crossref], [Web of Science ®] , [Google Scholar]). The innovation of this model is considering two types of friction forces, acting on the contact frontal surface and the lateral surface of a PDC cutter, respectively. Additionally, the proposed model assumes a rock reaction force direction not orthogonal to the contact surface of a cutter but parallel to the crack propagation direction and similar to the rock heterogeneity direction.

Numerical study was provided for a new and a worn PDC cutter to define a rock reaction force depending on options of adjacent cutters' placement (cutters' shape, cutter sizes, bake rake angle, side rake angle, etc.). Two main tendencies were observed: increasing of lateral plot of a cutter decreases rock reaction force, and deviation between directions of cutting force and crack propagation is an extremely significant factor and affects rock reaction force magnitude.     

Starvation Behavior in Cold Rolling of Aluminum with Oil-in-Water Emulsion

Reich, et al. ( 1 Reich, R., Panseri, N. and Bohaychich, J. 2001. “The Effects of Lubricant Starvation in Cold Rolling of Aluminum Metal When Using on Oil-in-Water Emulsion,”. Lubrication Engineering, 57: 15–18.  [Google Scholar] ) reported that the rolling force for the cold rolling of aluminum increased when starvation occurred in the oil-in-water (O/W) emulsion used as the rolling fluid. They reported that the starvation occurrence was dependent on the emulsion concentration and the size of the oil droplets, but the thickness of a starved lubricant film was independent of the rolling speed. However, from their experimental results, the cause of the increase of the rolling force and the quantitative inlet oil film thickness at the entrance between the roll and the workpiece for the O/W emulsions cannot be understood. In this study, the aluminum rolling experiments using O/W emulsions with different concentrations were carried out in order to reproduce the increase of the rolling force. Experiments were carried out using a laboratory mill with two high rolls. The workpiece material was an aluminum A1050-H. Commercial rolling oil was used as base oil for the aluminum emulsion. The rolling force was measured during the rolling and the appearance of the workpiece after rolling was taken. Moreover, the effect of the surface roughness of the rolls on the increase of the rolling force was investigated. The increase of the rolling force was reproduced in the aluminum rolling with the O/W emulsion using the laboratory rolling mill. It was observed that the increase of the rolling force occurred after the oil starvation, and it depended on the oil starvation, the oil film thickness, the surface roughness of the roll, the rolling speed, and the reduction in thickness.     

Determination of Turboprop Reduction Gearbox System Fatigue Life and Reliability

Two computational models to determine the fatigue life and reliability of a commercial turboprop gearbox are compared with each other and with field data. These models are (1 Zaretsky, E. V. 1992. “STLE Life Factors for Rolling Bearings,”, STLE SP–34 Park Ridge, IL: STLE.  [Google Scholar]) Monte Carlo simulation of randomly selected lives of individual bearings and gears comprising the system and (2 Weibull, W. 1939. “A Statistical Theory of the Strength of Materials,”. In Ingenioersvestenskapsakademiens. Handl. 151 [Google Scholar]) two-parameter Weibull distribution function for bearings and gears comprising the system using strict-series system reliability to combine the calculated individual component lives in the gearbox. The Monte Carlo simulation included the virtual testing of 744,450 gearboxes. Two sets of field data were obtained from 64 gearboxes that were first-run to removal for cause, were refurbished and placed back in service, and then were second-run until removal for cause. A series of equations were empirically developed from the Monte Carlo simulation to determine the statistical variation in predicted life and Weibull slope as a function of the number of gearboxes failed. The resultant L ₁₀ life from the field data was 5,627 h. From strict-series system reliability, the predicted L ₁₀ life was 774 h. From the Monte Carlo simulation, the median value for the L ₁₀ gearbox lives equaled 757 h. Half of the gearbox L ₁₀ lives will be less than this value and the other half more. The resultant L ₁₀ life of the second-run (refurbished) gearboxes was 1,334 h. The apparent load-life exponent p for the roller bearings is 5.2. Were the bearing lives to be recalculated with a load-life exponent p equal to 5.2, the predicted L ₁₀ life of the gearbox would be equal to the actual life obtained in the field. The component failure distribution of the gearbox from the Monte Carlo simulation was nearly identical to that using the strict-series system reliability analysis, proving the compatibility of these methods.     

SURFACE FINISH AND TOOL WEAR CHARACTERIZATION IN HARD TURNING USING A MATHEMATICAL CUTTING TOOL REPRESENTATION

The development of a general 3D model for a corner-radiused, chamfered, edge-honed cutting worn tool is elaborated. The surface of the cutting tool was constructed using one angular scalar specifying location on the corner radius and leading/trailing edges and another non-dimensional scalar for specifying location on the relief, edge-hone, chamfer and tool-top. Then, for given geometric parameters and cutting conditions, the angular extremities of contact on the corner radius and leading/trailing edges was obtained and validated. The kinematic surface finish on the workpiece surface including the Brammertz and sideflow effects was then simulated in typical hard turning. The model was expanded to allow wiper edges and flank wear. A simplified crater wear model was adopted for continuous hard turning to allow virtual cross-sectioning. Accurate estimation of flank and crater wear volume was also enabled. The model results for the fresh tool agreed with well-known trends from 2D modeling. Preliminary results indicate that there exists a geometric basis for higher R_a and R_t for a worn tool. The Brammertz effect simulation, though not in agreement with the data of Knuefermann (2003 Knuefermann , M.M.W. ( 2003 ) Machining surfaces of optical quality by hard turning, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire, UK . [Google Scholar]) corroborated the modification proposed therein.     

Numerical Aspects of Cone Beam Contour Reconstruction

We describe a method for directly calculating the contours of a function from cone beam data. The algorithm is based on a new inversion formula for the gradient of a function presented in Louis (Inverse Probl 32(11):115005, 2016. http://stacks.iop.org/0266-5611/32/i=11/a=115005). The Radon transform of the gradient is found by using a Grangeat type of formula, reducing the inversion problem to the inversion of the Radon transform. In that way the influence of the scanning curve, vital for all exact inversion formulas for complete data, is avoided Numerical results are presented for the circular scanning geometry which neither fulfills the Tuy–Kirillov condition nor the much weaker condition given by the author in Louis (Inverse Probl 32(11):115005, 2016. http://stacks.iop.org/0266-5611/32/i=11/a=115005).     

The Ingenious Structure of Scorpion Armor Inspires Sand-Resistant Surfaces

Erosion is so widespread and undesirable in various engineering applications such that it is so incumbent to find anti-erosion means to address it. In previous researches (Han et al. in J Bionic Eng 7(09):S50–S58, 2010; J Wuhan Univ Technol Mater Sci Ed 26(2):305–310, 2011; Langmuir 28(5):2914–2921, 2012; Adv Colloid Interface Sci 234:27–50, 2016; Surf Coat Technol 313:143–150, 2017; Zhang et al. in Adv Mater Sci Eng 2013(5):1–9, 2013), people found that the surface of desert scorpion Androctonus australis, which belonged to the parabuthus, had very complex microstructures that had the strong anti-erosion qualities in the blown sand environment. Here, through further research, a new microstructure, hexagonal pit structure, was firstly discovered on the back of desert scorpion. These microstructures were applied in the design of biomimetic samples, which were fabricated by 3D printer using EOS stainless steel GP1. These biomimetic samples were used to test the erosion rate under the impact of quartz sand of three different sizes. The experiment was carried out using a blasting jet machine with injection angle, velocity and time of 30°, 25 ms^?1 and 90 s, respectively, and the results showed that the biomimetic samples with different microstructures had better anti-erosion performance. The hexagonal pit structure, whose depth was 200–300 μm and the length was 200–500 μm, had also good anti-erosion performance. The physical model was established to express the mechanism of anti-erosion by controlling the motion direction and impacting velocity of the particles. The anti-erosion performance of all these biomimetic samples can be quantified by the erosion rate and improvement rate. On the whole, these microstructures all have good anti-erosion effect; hence, this paper research is of great practical significance.     

A hybrid cuckoo search and variable neighborhood descent for single and multiobjective scheduling problems

Cuckoo search (CS) is a relatively new meta-heuristic that has proven its strength in solving continuous optimization problems. This papers applies cuckoo search to the class of sequencing problems by hybridizing it with a variable neighborhood descent local search for enhancing the quality of the obtained solutions. The Lévy flight operator proposed in the original CS is modified to address the discrete nature of scheduling problems. Two well-known problems are used to demonstrate the effectiveness of the proposed hybrid CS approach. The first is the NP-hard single objective problem of minimizing the weighted total tardiness time ( \(1|| \sum {T_{w}}\) ) and the second is the multiobjective problem of minimizing the flowtime \(\overline {C}\) and the maximum tardiness T _{m a x} for single machine ( \(1|| (\frac {1}{n}\sum {C}, T_{max})\) ). For the first problem, computational results show that the hybrid CS is able to find the optimal solutions for all benchmark test instances with 40, 50, and 100 jobs and for most instances with 150, 200, 250, and 300 jobs. For the second problem, the hybrid CS generated solutions on and very close to the exact Pareto fronts of test instances with 10, 20, 30, and 40 jobs. In general, the results reveal that the hybrid CS is an adequate and robust method for tackling single and multiobjective scheduling problems.     

Study on optimization of the circumferential and axial wavy geometrical configuration of hydrodynamic journal bearing

This paper is focused on using GA genetic algorithm to find the optimal performance with respect to shape optimization in three dimensions for the hydrodynamic journal bearing. The mathematical model for film thickness was drawn using Fourier series function and axial waviness value ( $\bar \Delta $ ) D to represent the journal bearing in circumferential and axial direction, respectively. The objective was then to determine the Fourier coefficients and axial waviness value ( $\bar \Delta $ ) D that maximized the load capacity subjected to a given set of constraint. Optimized results show that the presence of cos wave in axial direction, with a positive dimensionless amplitude (+A) and waviness number m = 0.633, improves the load capacity by (8–10) % over the cylindrical plain bearing with the same arbitrary shape and size; in general, the increasing order of Fourier series (n), an axial dimensionless amplitude and L/D ratio cause the change in load capacity to become more evident.     

Tire–Road Contact Stiffness

When a rubber block is squeezed against a nominal flat but rough surface, the rubber bottom surface will penetrate into the substrate roughness profile. The relation between penetration depth \(w\) (or the average interfacial separation \(\bar{u}\) ) and the applied squeezing pressure \(p\) determines the (perpendicular) contact stiffness \(K=\hbox {d}p/\hbox {d}w=-\hbox {d}p/\hbox {d}\bar{u}\) , which is important for many applications. We have measured the relation between \(p\) and \(\bar{u}\) for a rubber block squeezed against 28 different concrete and asphalt road surfaces. We find a linear relation between \({\mathrm{log}}p\) and \(\bar{u}\) , in agreement with theory predictions. The measured stiffness values correlate rather well with the theory prediction.     

Magnetic Levitation Tribometer: A Point-Contact Friction

We developed a new magnetic levitation tribometer (MLT) to study point-contact friction via pendulum method. The device allows us to carry out fast and accurate point-contact measurement of friction between a pair of materials. The MTL parameters were found with the help of test experiments with the steel ball / glass plate pair. The friction coefficient values are coherent with the results known in the literature (Serway and Beichner in Physics for scientists and engineers, 5th edn, Saunders College Publishing, Orlando, 2000). The proposed MLT technique at loads lower than \(10^{-3}\) N is very promising for non-destructive investigation of frictional properties of organic monolayers.     

Use of Au Nanoparticle-Filled PTFE Films to Produce Low-Friction and Low-Wear Surface Coatings

Polytetrafluoroethylene (PTFE) possesses exceptional lubricating properties; however, its uses are limited due to its high susceptibility to wear. In an effort to overcome this shortcoming, a great deal of focus is placed on creating PTFE composites that exploit the strengths of PTFE and also reduce or eliminate its weaknesses. This investigation explores the use of Au nanoparticle-filled PTFE films to produce low-friction and low-wear surface coatings. PTFE + Au nanoparticle composite films were produced by dip coating stainless steel substrates into a mixture of colloidal PTFE and Au nanoparticles. Tribological tests showed that the composite film has a wear life that is twice that of pure PTFE and possesses an average coefficient of friction that is up to 50 % lower. PTFE suffers delamination as a result of poor adhesion of the film to the substrate and tearing resulting from a dominant adhesive wear mode. PTFE + Au, on the other hand, shows no sign of delamination or adhesive wear. This change in wear mode caused by the addition of Au nanoparticles significantly increases the wear resistance and durability of PTFE.     

Boundary Layer Behaviour in Circular EHL Contacts in the Elastic-Piezoviscous Regime

The solution of elastohydrodynamically lubricated contacts at high loads and/or low speeds can be described as a Hertzian pressure with inlet and outlet boundary layers: zones where significant pressure flow occurs. For the soft lubrication regime (elastic-isoviscous), a self-similar solution exists in the boundary layers satisfying localized equations. In this paper, the boundary layer behaviour in the elastic-piezoviscous regime is investigated. The lengthscale of the boundary layers and the scaling of pressure and film thickness are expressed in non-dimensional parameters. The boundary layer width scales as \(1/\sqrt{M}\) (equivalent to \({\bar{\lambda }}^{3/8}\) ), the maximum pressure difference relative to the Hertzian solution as \(1 / \root 3 \of {M}\) (equivalent to \({\bar{\lambda }}^{1/4}\) ) and the film thickness as \(1/\root 16 \of {M}\) (equivalent to \({\bar{\lambda }}^{3/64}\) ) with \(M\) the Moes non-dimensional load and \({\bar{\lambda }}\) a dimensionless speed parameter. The Moes dimensionless lubricant parameter \(L\) was fixed. These scalings differ from the isoviscous-elastic (soft lubrication) regime. With increasing load (decreasing speed), the solution exhibits an increasing degree of rotational symmetry. The pressure varies less than 10 % over an angle less than 45 degrees from the lubricant entrainment direction. The results provide additional fundamental understanding of the nature of elastohydrodynamic lubrication and give physical rationale to the finding of roughness deformation depending on the “inlet length”. The findings may contribute to more efficient numerical solutions and to improved semi-analytical prediction methods for engineering based on physically correct asymptotic behaviour.     

Wear resistance of composites based on ultrahigh molecular weight polyethylene filled with graphite and molybdenum disulfide microparticles

Tribological characteristics of ultrahigh-molecular-weight polyethylene (UHMWPE)-based compositions with graphite and molybdenum disulfide are studied under conditions of dry friction, boundary lubrication, and abrasive wear. It is shown that, under dry sliding friction, the wear rate of UHMWPE-graphite and UHMWPE-MoS2 polymer compositions is halved as compared to that of pure UHMWP, while their mechanical characteristics change only slightly. Under the conditions of abrasive wear, the wear resistance of these composites increases by 1.3–1.5 times. Concentrations of the fillers, which are optimum for improving the wear resistance, are determined. The supramolecular structure and the topography of worn surfaces of the UHMWPE compositions with various concentrations of the fillers are examined. A comparative analysis of the wear resistance of the composites under conditions of dry friction and lubrication is carried out. Mechanisms of the wear of the UHMWPE-graphite and UHMWPE-MoS₂ polymer compositions under conditions of dry sliding friction and abrasive wear are discussed.     

On calculation of contact temperatures arising at rotation of ball in spherical bearing

The heat conduction problem for a spherical bearing with a spherical insert is considered. The constant coefficient κ ₁ ^′ from the formula of the average ball temperature in the contact region has been determined.