查看更多>>摘要：Tool wear has an important impact on the machining process. During machining, except for the wear accumulation in time, the tool path and posture directly influence the wear spatial distribution characters. In this study, the influence of tool path and posture on tool wear distribution is introduced by describing the shape and posture of the undeformed cutting unit under different tool path and posture. Three dimensional wear matrix ergodic method is proposed to describe the spatial distribution characteristics of tool wear under arbitrary tool path, posture and machined surface. Then, the wear spatial distribution model of ball end milling tool is built based on work theory and verified by ruled surface milling of semi-open impeller. Finally, related simulation and discussion are made based on the model.
查看更多>>摘要：Wear of multi-asperity interfaces remains difficult to predict from first principles, in part because improvements are required in our ability to quantify and track wear across the micro-to nanometer scale. In this work, we developed a 6° of freedom topographical difference method based on large atomic force microscopy (AFM) measurements, up to 90 × 90 μm~2 in size. We detect wear volumes as small as 1.6 × 10~(-11) ± 3.7 × 10~(-12) mm~3 (0.016 μm~3), beyond the sensitivity of many existing techniques for the quantification of wear at multi-asperity interfaces. We show that our wear detection technique can be combined with 100 mN normal force ball-on-flat friction experiments to track nanoscale wear across the entire area of apparent contact.
查看更多>>摘要：Twin-disc tests were carried out between two discs of rail steel (fully pearlitic and spheroidized microstructures) to investigate the effect of the flash-butt welded rail HAZ microstructure. The spheroidized cementite micro-structure was obtained by heat-treating simulating the HAZ softer region. Ten tests were performed for each condition, considering maximum Hertz pressure of 1100 MPa, rotation speed of 400 rpm and slip of 0% and 1%. The results showed that the spheroidized cementite discs (with less hardness) presented more significant surface hardness due to deformation, more clearly for the tests carried out with 1% slip. This factor led to a cracking process for both heat-treated discs and counter-discs with a completely pearlitic microstructure. The number of cycles for the beginning of contact fatigue between the specimens compared to the untreated pairs proved to be statistically equal in the tests carried out with 1% slip. In tests without slip, however, this phenomenon did not occur, as the spheroidized discs showed a significant decrease in the number of cycles before the beginning of contact fatigue. Plastic deformation was observed around the fatigue cracks (even in the spheroidized micro-structure's discs), and the presence of inclusions influenced the cracking process.
查看更多>>摘要：Wear behaviour of quenched and tempered (QT) hot work tool steels (Uddeholm QRO90) was investigated against SAE 52100 grade bearing steel balls after gas nitriding using a dedicated laboratory scale impact-sliding wear test rig. Gas nitriding was employed in a fluidised bed reactor under two alternative regimes: i. "High Temperature Nitriding (HTN)" carried out at 510℃ and ii. "Low Temperature Nitriding (LTN)" carried out at ≤ 400℃. The HTN process resulted in the formation of ～2 μm thick external compound layer, whereas the LTN processed steels were free of any surface compound layer formation. After the impact-sliding wear tests employed at room temperature (RT), the prevailing wear mechanisms of the examined steels were assessed as tribo-oxidation and fatigue wear. The testing at 600℃ induced different wear mechanisms for the HTN and the LTN steels. While tribo-oxidation and fatigue wear were preserved for the HTN steel, plastic deformation dominated the wear that progressed on the compound layer free surface of the LTN steel. Impact-sliding wear testing at 600℃ showed that the wear rate of LTN > HTN steels, as opposed to the wear rate at RT where wear rate of HTN > LTN.
查看更多>>摘要：Traditional lubricants fail to meet the trend of green development. Consequently, eco-friendly hybrid nano lubricants are synthesized by incorporating 0.5 wt% 3D hierarchical porous graphene (3D HPG) and 0.7 wt% multi-walled carbon nanotubes (MWCNT) nanoparticles to castor oil. The performances of nano lubricants are determined by linear reciprocating wear test, and the obtained wear marks on steel balls and plates are evaluated by depth-of-field microscopy, scanning electron microscopy, energy dispersive spectrometer and Raman spectroscopy. The results of steel balls and steel plates wear analyses are highly consistent. Characterization results for steel plates show that the 3D HPG: MWCNT (0.5:0.7) achieves a reduction in friction coefficient and wear volume up to 26% and 48% at low speed and heavy load conditions (4 Hz - 20 N, 2.7 GPa), respectively. The mechanism of friction-reducing and anti-wear at low speed and heavy load is that 3D HPG is torn into 2D graphene nanosheets due to its easy shear performance, which forms a 2D graphene nanosheets/MWCNT/2D graphene nanosheets sandwich structure to be further involved in lubrication. This rolled bearing-like synergistic effect can further reduce friction and wear. All in all, the environmentally friendly nano lubricants consisting of 3D HPG/MWCNT hybrid nanoparticles and castor oil have sufficient potential for application in the field of heavy machine parts.
Theresa TrummlerSteffen J. SchmidtNikolaus A. Adams
14页
查看更多>>摘要：We numerically investigate the erosion potential of a cavitating liquid jet by means of high-resolution finite volume simulations. As thermodynamic model, we employ a barotropic equilibrium cavitation approach, embedded into a homogeneous mixture model. To resolve the effects of collapsing vapor structures and to estimate the erosion potential, full compressibility is considered. Two different operating points featuring different cavitation intensities are investigated and their erosion potential is estimated and compared. Different methods are used for this purpose, including collapse detection (Mihatsch et al., 2015), maximum pressure distribution on the wall, and a new method of generating numerical pit equivalents. The data of numerical pit equivalents is analyzed in detail and compared with experimental data from the literature. Furthermore, a comprehensive grid study for both operating points is presented.
查看更多>>摘要：Austempered ductile irons (ADIs) are used in applications commonly exposed to severe contact conditions, and as a consequence wear damage frequently followed by failure of components. Hence, wear resistance of the material governs the final life time of a component. In the present work, the sliding wear resistance of two ausferritic spheroidal graphite ductile irons ADI1 and ADI2 used commonly in mining and construction equipment was investigated. ADI1 and ADI2 were heat treated to a similar strength, the volume fraction of the carbon-rich austenite in ADI1 and ADI2 was around 30% and 16%, respectively, and they both contained 10 - 13% nodular graphite. The wear tests were performed using a slider-on-flat-surface (SOFS) tribometer. Case-hardened steel plates made of a high strength steel, 22NiCrMo12-F, were used as the counterface. The wear tests were conducted under lubricated sliding contact at normal loads of 50, 100, 200 and 300 N, and at each load level sliding at 100, 200 and 300 m. The friction force between contacting surfaces was continuously monitored during sliding. The lubrication used in the present investigation was a mineral-oil-based paste commonly used in applications where high frictional heating is generated. Wear mechanisms of the tested specimens were investigated by means of optical and scanning electron microscopy and X-ray diffraction, and the wear damage was quantified using a 3D-profile optical interferometer. The main wear mechanisms, severe plastic deformation and surface delamination, were discussed concerning test conditions and material properties. The ADI1 grade with the higher volume of carbon-rich austenite displayed better resistance to sliding wear at high normal loads. The higher normal loads promoted larger deformation at and beneath the contact surface and initiated austenite transformation into hard martensite. Thus, it was concluded that the increase of wear resistance in ADI1 was due to the formation of marteniste. On the other hand, the ADI2 grade with higher silicon content showed lower wear resistance at high normal loads. This was associated with cracking of the proeutectoid ferrite presented in ADI2.
Balaganesan HariprasadS. Joyson SelvakumarD. Samuel Raj
17页
查看更多>>摘要：The effect of cutting edge radius (30-55 μm) during milling Ti-6Al-4V under minimum quantity cooling lubrication (MQCL) conditions is studied. A trial study is conducted to compare the performance of dry, wet, and MQCL using unprepared tools with edge radius of 30 μm alone. Subsequently, inserts having initial radius of 30 μm are prepared to 40-55 μm radius using drag finishing and milling of Ti-6Al-4V under MQCL is studied for different edge radii. Rounded edge tools are found to produce thinner and more curvilinear chips resulting in easier chip removal from the machining zone. The chip thickness and curl radius were up to 54% and 47% lower for the larger edge radius tools as compared to the 30 μm edge radius tool. This improves the penetration of the MQCL aerosol jet into the cutting zone thus producing better tribological results. The better penetration of MQCL aerosol into the cutting zone for larger edge radius tools results in lowering the resultant process forces (up to 16%), tool-chip interface temperature (15%), tool wear (40%) and surface roughness (30%) for the 48 μm radius tool as compared to the unprepared (30 μm) tool. There is deterioration in process forces, tool wear and surface integrity for the 55 μm tool possibly suggesting the existence of an optimum edge radius closer to 48 μm.
查看更多>>摘要：Three types of differently shaped lasered microtextures (microdimples) were produced on the surface of a U75V hot-rolled rail roller with a TY-FM-20S laser marking machine. Wheel flange/rail gauge lubrication starvation tests of four kinds of rail samples running against CL60 wheel samples were carried out, and the friction properties of the wheel/rail steels were studied. The results indicate that the injection of lubricating grease dominates the friction coefficient reductions and that the lubricating effects are closely related to the shapes of the lasered microtextures; for instance, the rectangular and rhombic textures show a better lubricating effect. Furthermore, the wear rates depend on the wear mechanism of the wheel/rail steel; for example, delamination and spalling always result in severe wear while peeling results in mild wear. The materials from the rolling-sliding surface to the matrix region of the wheel/rail materials can be divided into three parts: the plastic deformation region, transition region and undeformed matrix region. The average crack length and angle values of the textured rail and coupled wheel steels are much smaller than those of the untextured rail and coupled wheel steels; thus, the textured rail and coupled wheel steels exhibit better rolling contact fatigue (RCF) resistance. The effects of the lasered microtextures shapes on the wear and fatigue damage are determined based on the fluid dynamic pressure on the microtexture. Notably, rhombic lasered microtextures can be adopted to improve the grease storage capacity, thereby reducing wear and fatigue damage.
查看更多>>摘要：A set of nanolubricants was prepared by varying concentrations of Boehmite nanoparticles (0.25,0.5,0.75,1 wt%) in synthetic base oil (PAO-6) with a fixed concentration of dispersant (PIBSA). This is the first study exploring Boehmite mineral for its antiwear and extreme pressure performance. Nanolubricants showed excellent colloidal stability for over 30 days without any sedimentation and improved viscosity index by 4.35% at 1 wt% concentration. Four ball tribometer was used for exploring the tribological performance of Boehmite nanolubricants. A significant 24% wear reduction over base oil was observed for optimum NPs concentration of 0.5 wt% beyond that performance deteriorated. On the other hand, increased NPs concentration enhanced load-bearing capacity for EP test and the highest enhancement of 40% was observed for 0.75 and 1 wt% concentrations. Based on surface characterization techniques, we confirm dehydration of Boehmite NPs into Aluminium oxide (Al_2O_3) under tribostress. We further confirm regenerative, sacrificial protective tribofilm composed of tribosintered Al_2O_3 along with oxide film on the rubbing surfaces.
NSTL
Elsevier