The development of bio-derived cutting fluids that combine dispersion stability and effective lubrication is an important direction toward more sustainable manufacturing. In this study, two zirconium-based bio-derived materials, MIP-202 metal–organic framework (bio-MOF) and a zirconium/organic-acid-assisted bio-aerogel, were investigated as nano-additives for jatropha-oil-based cutting fluids, while Gum Arabic and Vitamin E were evaluated as natural stabilizing agents. The additives were characterized by XRD, SEM, TEM, and EDX, and the formulations were assessed through UV–Vis spectroscopy, wettability, viscosity, oxidation stability, and ball-on-disc friction testing. Bio-MOF showed better kinetic dispersion persistence than bio-aerogel. The selected formulation containing jatropha oil, 0.10 wt.% MIP-202, and 0.10 wt.% Vitamin E reduced the contact angle from 22.29° to 18.10°, increased RPVOT from 28 to 39 min, and decreased the coefficient of friction from 0.0813 to 0.0366. Machining performance was then evaluated in AISI 304 turning using a randomized Taguchi L27 design comparing dry cutting, plain jatropha-oil MQL, and Bio-MOF nano-MQL. Bio-MOF nano-MQL reduced mean surface roughness by 16.9% and 16.1%, and flank wear by 35.2% and 15.4%, relative to dry cutting and plain MQL, respectively. The results demonstrate the potential of the designed bio-derived nano-MQL formulation for improving lubrication and machining performance of AISI 304.
Hemiarthroplasty is a partial joint replacement where one half of the joint is replaced, resulting in a cartilage-on-artificial-material articulation. With the development of novel joint replacement materials and coatings, there is a need to develop and standardise test methods to assess materials tribologically for use in hemiarthroplasty applications prior to implantation. Several different protocols and approaches with differing levels of complexity have been developed to study materials for use in hemiarthroplasty applications, but to date, no consensus has been reached as to the most appropriate method, or suite of methods, to use. The aim of this review article was to assimilate and critique published methods for tribologically evaluating hemiarthroplasty materials, to discuss advantages and limitations of the methods used, to highlight the variables that should be considered when developing new test methods and to identify gaps in the current literature. There is clearly a need to study materials and implants specifically for use in hemiarthroplasty applications and much research has been carried out in the field. However, for protocols to be standardised, there is a need for experts to converge on the most appropriate methodologies.
The dynamic support characteristics of hydrostatic spindles have an important influence on precision grinding stability and surface quality. However, existing grinding surface-generation models usually prescribe spindle motion as a known input and rarely establish a direct transfer relationship from hydrostatic-bearing dynamics to spindle vibration and subsequent surface formation. To address this issue, a sequential analysis framework is developed for a precision grinding spindle supported by conical hydrostatic bearings. The complete three-dimensional stiffness and damping matrices of the conical bearings are obtained from the oil-film force responses to small displacement and velocity perturbations and are assembled into a spatial rotor dynamic model to calculate the grinding-wheel-end vibration response. The calculated normal vibration displacement is then introduced into the abrasive grain trajectory model to predict the generated surface topography and roughness. The results show that the bearing dynamic support characteristics significantly affect the spindle response. In particular, increasing the average oil-film thickness from 30 μm to 40 μm increases the RMS grinding-wheel-end normal displacement by 79.82%, whereas the effects of eccentricity ratio and cone half-angle are comparatively smaller within the investigated ranges. Incorporating the calculated spindle-vibration response also improves the agreement between predicted and measured surface roughness. Single-crystal silicon grinding experiments show that the mean relative errors of Ra and Rq decrease from 28.40% and 33.45% to 23.61% and 28.54%, respectively. Although the model still tends to underestimate the measured roughness, it reproduces the overall variation tendency under different grinding conditions and clarifies the sequential transfer relationship from hydrostatic-bearing dynamics to spindle vibration and grinding surface formation.
Conventional Four-Ball extreme-pressure (EP) testing determines lubricant transitions through short tests at discrete force levels, combined with post-test wear scar evaluation. This study presents a continuous ramp load procedure in which the contact is run-in at 392 N and 1760 rpm for 60 s before normal force is increased linearly while measured force, friction and speed are recorded. Validation of the method uses a broad set of ASTM proficiency-testing and independently established reference fluids. Interrupted tests link the first significant friction transition to the onset of seizure-related surface damage. A central requirement is preservation of the measured normal-force trajectory during the event; on the pneumatically controlled system used here, the ramp remains near-linear through major friction and displacement changes without a corresponding seizure-induced drop in load. The precision of this ramp linearity has been found to be less than 10 N throughout regime transitions. To reduce operator dependence, an algorithm is used to identify the onset of frictional transitions. The basis for the algorithm is Savitzky–Golay polynomial filtering, which suppresses high-frequency noise while retaining local transition shape, followed by derivative-based event detection and an operator qualification step, to identify the onset of physically meaningful transitions. The continuous-test results remain closely anchored to the conventional Four-Ball load framework, such as the Last Non-Seizure Load (LNSL) and weld load (WL), while resolving these transition loads on a continuous scale instead of the discrete steps. A close correlation is found between the friction transitions and LNSL/WL for a set of nine oils with known ASTM results, either from ASTM PTP oils and greases investigated or other commercially available reference fluids, with a Pearson coefficient, r, of 0.955.
The electrification of mechanical systems imposes new demands on lubricants, which must simultaneously ensure effective tribological performance and adequate dielectric strength. This study investigates the combined influence of zinc dialkyldithiophosphate (ZDDP) and carbon nanotubes (CNTs) on the thermal, dielectric, and tribological behavior of a PAO6 base oil. Four lubricant samples were evaluated: neat PAO6, PAO6 + 1 wt% ZDDP, PAO6 + 0.1 wt% CNTs, and PAO6 + 1 wt% ZDDP + 0.1 wt% CNTs. Differential Scanning Calorimetry revealed additive-dependent thermal features, including a ZDDP-related transition that shifted to lower temperature in the presence of CNTs, indicating modified thermal activation behavior. Dielectric Breakdown Voltage (BDV) measurements at 21 °C and 75 °C showed that CNT addition markedly reduces dielectric strength due to conductive pathway formation, while ZDDP decreases BDV at elevated temperature, likely associated with increased molecular mobility and the formation of polar species. The combined formulation exhibited the lowest BDV, evidencing a clear trade-off between dielectric robustness and additive functionality. Tribological performance was assessed using electrified and non-electrified four-ball tests under 0 and 1.5 A, DC conditions. While the coefficient of friction remained largely unaffected, wear behavior was strongly formulation-dependent. The ZDDP-containing formulations exhibited lower mean wear volumes than the ZDDP-free samples under both electrical conditions. For PAO6 + CNTs, the mean wear volume decreased under electrical loading, although substantial between-test variability was observed. The combined formulation exhibited the lowest mean wear volume under electrical loading. Suspension stability and CNT redistribution during testing were not directly characterized; therefore, the wear response cannot be attributed to electrically induced deagglomeration. The results highlight the need to assess tribological performance and dielectric strength jointly in electrically loaded lubricated contacts.
