Stribeck curves have long been used for understanding the lubricating behaviour of oils and greases, and in the recent years for applications ranging from ball point inks to synovial fluids. In the current work, an attempt is made to show as to what one can read from Stribeck curves of food samples such as chocolate spread, sauce etc. Additionally, the effect of salivahuman and artificialon the frictional behaviour has also been studied. The tests were carried out on an MCR Tribometer with a ball-on-three-pin configuration. Polydimethylsiloxane and glass were used to simulate soft contact conditions that exist in the human mouth. Results from the tribological tests are plotted in the form of extended Stribeck curves, wherein, the friction coefficient is plotted as a function of rotational speed. Since the tribometer is capable of speeds as low as a few nanometres per second, it is also possible to observe the build-up of static friction and its transition into the kinetic regime of friction. Results indicate that certain aspects of the Stribeck curve can offer an insight into the correlation between the frictional behaviour of food to their sensory feel.

This study compares two methods for model scale testing of ferrous/non-ferrous tribocouples under large area conformal contact condition, the kind existing in engine components such as journal bearings. Results show that the ring-on-disc method is better suited to visualise the performance of such tribosystems compared with the pin-on-plate method. The former offers greater sensitivity to minor changes in coefficient of friction and contact potential and is able to determine the thermal stability of the tribosystem under given conditions. Post-test surface characterisation revealed protective phosphorus-rich tribofilms on the surface of the steel counterparts from both test methods.

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The aim of this work was to examine relations between instrumental and sensory parameters in a texture modified food matrix, with and without saliva. Nine pureed carrot samples (eight thickened and a control) were developed with starch (0.4 and 0.8% wt/wt), xanthan (0.2 and 0.4% wt/wt) or starch–xanthan blends that met International Dysphagia Diet Standardisation Initiative (IDDSI) Level 4 guidelines using fork and spoon tests. Rheological and tribological tests were conducted on the food and simulated bolus prepared by adding fresh stimulated saliva to the food (1:5, saliva:food) to mimic oral processing. Perceived sensory properties were identified using a temporal dominance of sensations (TDS) test (n = 16) where panelists were given a list of nine attributes. The area under the curve was extracted from TDS curves for each attribute/sample and this was correlated with rheological (viscosity at 10 s−1, G′, G″, and tan δ at 1 Hz) and tribological (friction coefficient in three regimes) data. The viscosity of the control sample decreased after adding hydrocolloids (except Starch_0.8%) and with saliva incorporation. G′ and G″ either increased or were similar for xanthan and blends and decreased for starch‐thickened samples. Hydrocolloid addition increased friction for all samples and was higher with saliva addition. Sensory results showed that samples with starch were perceived as thick and grainy while xanthan was perceived as smooth and slippery. A greater number of sensory attributes correlated with viscoelastic parameters compared to friction coefficients. Correlations were highest with the saliva added samples, further highlighting the importance of including saliva during instrumental testing.

The layer-forming properties of different lubricants on technically used tribosystems were investigated. The experiments were carried out on a ring-on-disc test set-up on Fe/Fe-and Fe/Cu-based systems. Three different lubricants were used viz. base oil with detergents (Oil-A), oil with ZnP-based additives (Oil-B) and oil with P-based additives (Oil-C). We measured the electrical resistance between the rubbing surfaces. Surface characterisation (light microscopy, SEM/EDX and XPS) and tribometric results show differences in wear and friction properties. Oil-B showed profound layer formation on steel counterparts and correlation in the amount of Zn and S, P and O, respectively; whereas, none of the above was observed with Oil-A. Oil-C, however, showed thin but tribologically effective layer formation on ferrous system and a superior performance for the Fe/Cu system.