Abstract

The effective temperature in rotor type curemeters is — according to DIN 53529 — controlled using an unfilled EPDM compound with dicumylperoxide as cross‐linking agent. The rate of DCP decomposition has a well‐known temperature dependence. This rate is also in all practical cases the same as the rate of cross‐linking. Therefore, the measured rate of cross‐linking indicates the effective temperature in the reaction cavity. The rotor in common curemeters is clamped. Because it can not be heated directly, this rotor is a heat sink in the cavity. The effect is a temperature gradient in the cavity depending on the heat conductivity of the tested compound. This temperature gradient in rotor type curemeters is compared to rotorless curemeters. It is shown that using the unfilled EPDM/DCP compound for temperature calibration leads to a too high effective temperature for filled compounds.

Abstract

Material property data used in finite element and other models for tire applications have often been obtained under static or low strain rate conditions at room temperature. In the latter case Williams‐Landel‐Ferry (WLF) shifts are assumed in order to relate the data to strain rates and temperatures typical of actual tire operation. However, such shifts may not always be appropriate for the highly loaded, diverse elastomer blends used in tires today unless one wishes to go to the trouble of generating the WLF constant for each compound.

Data are presented to show that one can directly and easily obtain high quality stress or strain energy density results over wide ranges of strain rates, strain levels, and temperature using techniques developed for fatigue characterization. Thus, material properties can be obtained as a by‐product of fatigue testing with little added work, or they can be obtained straightforwardly and quickly if fatigue testing is not required. These data are generated in a dynamic, pulsed loading mode which is especially relevant for those modeling applications which deal with the rolling tire.

Results from a high performance tire tread, a sidewall, and an innerliner are presented to illustrate the wide range of compounds that can be accommodated. The primary mode of deformation employed is pure shear. Also, limited data from static simple extension and pulsed simple extension tests are shown for comparison.

The pulsed pure shear and simple extension data, obtained over a wide strain range, are an excellent source of basic information on a given compound to fit empirical models, generate Mooney‐Rivlin constant, or define material constants for more generalized nonlinear models such as Ogden, Peng, or Peng‐Landel. The latter material models are now becoming available in commercial finite element codes to allow studies of tire deformations, rolling resistance, and failure properties under realistic operating conditions.

Abstract

It is shown that in the strain range from 30% compression to 60% tension, the elastic potential of filled rubber compounds can be described with sufficient accuracy as a polynomial of the fourth degree with three independent constants. Methods to experimentally determine these constants are pointed out. A method for the calculation of mechanical losses in rubber compounds in a complex stressed state is suggested using the measurement data for simple modes of loading.

Abstract

A brief review of tire critical speeds is given using the beam under tension as a physical model. In its most common form, this model visualizes the critical speed as that speed just sufficient to sustain a continuous sinusoidal bending wave in the tire tread band. A number of studies have been published modifying this concept by the introduction of material damping, centrifugal effects, and other characteristics, some of which aid in explaining the fact that the wave pattern observed experimentally is local and decays rapidly away from the contact patch. This paper presents a different view of the wave pattern needed for a critical speed to exist, namely that a naturally occurring local wave can arise independent of material damping and that as a practical fact, material damping may have little to do with the onset of the phenomenon. A discussion on the effect of tire design variables on critical speed is given based on the expressions derived here.