Stephanie Kahms

The aircraft tire is the link between the aircraft and the runway and transmits forces and moments within the contact area. During ground maneuvers, the tire is exposed to a wide range of operating conditions. The tires support the weight of the aircraft, they ensure safe rolling during taxiing, and they transfer the required forces to the runway during takeoff and landing. Temperature development during these maneuvers is of great importance because temperature can affect both material stiffness and friction behavior as well as wear characteristics. Heat is generated inside the tire due to energy dissipation caused by the cyclic loading of the tire during rolling. In addition, heat is generated due to friction in the tire–runway contact. Experimental measurements of the temperature distribution in the entire tire are not yet possible. The tire temperatures can only be determined at selected critical spots. Simulation models can help to obtain a better understanding of the overall tire temperature distribution during transient maneuvers. In this work, the transient thermomechanical processes of a rolling aircraft tire, e.g., directly following the touchdown process or during taxiing, are modeled based on a simple physical tire model. An extended brush model is used to simulate the contact forces. The tire temperature is determined via the transient heat conduction equation in radial and circumferential directions. The mechanical and thermal models are coupled via the coefficient of friction and the sliding velocities in contact. The free model parameters are parameterized using experimental data, and the overall model is validated by measurements on the whole tire. The validated thermomechanical tire model is used for simulations or the analysis of different driving maneuvers to get a better understanding of the temperature development in the aircraft tire.

The ability to interact safely with the environment is known as one of the major advantages of soft robots (SRs). Due to their low material stiffness, these continuously deformable robots offer inherent flexibility. These advantages make them suitable for application that involve human-robot collaboration in industrial settings as well as medical application such as minimally invasive surgery. To date only few research groups have analyzed the contact and frictional behavior of soft robots. In fact, the contact behavior is often oversimplified or neglected. Motivated by the idea to bridge this gap, this work presents measurements and the resulting coefficient of friction (COF) for silicone rubbers that are widely used in the field of SRs and different contact partners which depend on contact pressure and ambient temperature. From these measurements, a more representative contact model is established and used to more accurately simulate soft material robots’ frictional contact behavior. Moreover the influence of friction and therefore the need to implement frictional behavior is demonstrated for a typical application of a SR.

Not only in the automotive sector, but also in the field of aircraft tires, the topic of abrasion is of great importance. The aircraft tire manufacturers provide criteria for the permissible degree of wear. If these limits are exceeded, the tire must be replaced or retreaded. By this time, the tire should withstand as many takeoff and landing cycles as possible. Abrasion models should help to predict the wear behavior in preflight modeling. At the Institute of Dynamics and Vibration Research, quasi-steady abrasion tests are performed using tread block samples from an aircraft tire. For various pressures and sliding speeds, the abrasion is determined by recording the mass loss of the rubber sample. Based on these measurement data, a wear model is derived as a function of coefficient of friction, contact pressure, and sliding speed for different ambient temperatures. The well-known brush model forms the basis for the wear simulations. With parameters validated on the aircraft tire, such as contact length, stiffness, and friction coefficient, the resulting mechanical forces within the contact area are calculated. Finally, the classic brush model is extended by the abrasion calculation. The tire wear is determined during unsteady load and slip conditions by use of the quasi-steady wear maps derived from our experiments. Within a measurement campaign on the complete tire, the tread depth is measured after various driving maneuvers and is in good agreement with the simulation results.