A surface topography analysis of the curling stone curl mechanism.

The curling motion of the curling stone on ice is well-known: if a small clockwise rotational velocity is imposed to the stone when it is released, in addition to the linear propagation velocity, the stone will curl to the right. A similar curl to the left is obtained by counter-clockwise rotation. This effect is widely used in the game to reach spots behind the already thrown stones, and the rotation also causes the stone to propagate in a more predictable fashion. Here, we report on novel experimental results which support one of the proposed theories to account for the curling motion of the stone, known as the "scratch-guiding theory". By directly scanning the ice surface with a white light interferometer before and after each slide, we observed cross-scratches caused by the leading and trailing parts of the circular contact band of the linearly moving and rotating stone. By analyzing these scratches and a typical curling stone trajectory, we show that during most of the slide, the transverse force responsible for the sideways displacement of the stone is linearly proportional to the angle between these cross-scratches.

Onset of frictional sliding of rubber-glass contact under dry and lubricated conditions.

Rubber friction is critical in many applications ranging from automotive tyres to cylinder seals. The process where a static rubber sample transitions to frictional sliding is particularly poorly understood. The experimental and simulation results in this paper show a completely different detachment process from the static situation to sliding motion under dry and lubricated conditions. The results underline the contribution of the rubber bulk properties to the static friction force. In fact, simple Amontons' law is sufficient as a local friction law to produce the correct detachment pattern when the rubber material and loading conditions are modelled properly. Simulations show that micro-sliding due to vertical loading can release initial shear stresses and lead to a high static/dynamic friction coefficient ratio, as observed in the measurements.

Three Three-Axis IEPE Accelerometers on the Inner Liner of a Tire for Finding the Tire-Road Friction Potential Indicators.

Direct tire-road contact friction estimation is essential for future autonomous cars and active safety systems. Friction estimation methods have been proposed earlier for driving conditions in the presence of a slip angle or slip ratio. However, the estimation of the friction from a freely-rolling tire is still an unsolved topic. Knowing the existing friction potential would be beneficial since vehicle control systems could be adjusted before any remarkable tire force has been produced. Since accelerometers are well-known and robust, and thus a promising sensor type for intelligent tires, this study uses three three-axis IEPE accelerometers on the inner liner of a tire to detect friction potential indicators on two equally smooth surfaces with different friction levels. The equal roughness was chosen for both surfaces in order to study the friction phenomena by neglecting the effect of surface texture on vibrations. The acceleration data before the contact is used to differentiate the two friction levels between the tire and the road. In addition, the contact lengths from the three accelerometers are used to validate the acceleration data. A method to differentiate the friction levels on the basis of the acceleration signal is also introduced.

Optimal proportion of studded tyres in traffic flow to prevent polishing of an icy road.

Studded tyres can significantly wear the road surface and increase particle emissions from the road surface, which has a negative impact on air quality in urban areas. However, road wear might have a positive aspect by roughening the road surface and thus preventing polishing. As a consequence, other vehicles than the ones using studded tyres might also benefit from the usage of studded tyres. The impact of the proportion of studded tyres in the traffic flow on the tyre-ice friction coefficient was studied with a fleet of real cars in a closed environment under strict procedural control. The results show that a proportion of 25-50% studded tyres in the traffic flow is enough to prevent ice from developing in a manner that is critically slippery for non-studded winter tyres. It was also observed that the visual appearance of the ice surface does not indicate if the ice has become more slippery or not.

Vehicle lateral state estimation based on measured tyre forces.

Future active safety systems need more accurate information about the state of vehicles. This article proposes a method to evaluate the lateral state of a vehicle based on measured tyre forces. The tyre forces of two tyres are estimated from optically measured tyre carcass deflections and transmitted wirelessly to the vehicle body. The two remaining tyres are so-called virtual tyre sensors, the forces of which are calculated from the real tyre sensor estimates. The Kalman filter estimator for lateral vehicle state based on measured tyre forces is presented, together with a simple method to define adaptive measurement error covariance depending on the driving condition of the vehicle. The estimated yaw rate and lateral velocity are compared with the validation sensor measurements.