Aftermarket Composite Wheels Made of Matrix Material and Fiber Reinforcement Intended for Normal Highway Use - Test Procedures and Performance Requirements
This SAE Recommended Practice provides minimum performance requirements and uniform procedures for fatigue and impact testing, electrical resistance, and maximum operating temperature (MOT) of wheels intended for normal highway use on passenger cars, light trucks, and multipurpose vehicles.
This is a recommended practice for validating and assuring structural quality of composite wheels. Wheels made of matrix material and fiber reinforcement are termed composite wheels. These wheels can optionally have a metallic center section, which is termed hybrid composite wheel. These wheels have fasteners that secure the center section to the rim section that is termed functional fasteners.
Material characterization of composites, similar to that of low carbon steels, A356-T6 and 6061-T6, are not widely published. Additionally, steels and aluminums used previously in wheels are isotropic. Conversely, the fiber orientation to the stress is paramount in composites, thus unique to a wheel design. Thus, a fully processed wheel must be validated in its most service-like manner, i.e., the SAE J2562 biaxial wheel fatigue test.
It has been found that composite materials degrade over service that would include millions of cycles and exposure to sun, moisture, etc.; therefore, the wheel manufacturer and/or the vehicle manufacturer must provide a strength reduction factor that accounts for expected degradation of strength and/or fatigue life over the intended service life of the wheel.
The matrix materials of composite wheels have a property referred to as glass transition temperature above which the matrix materials diminish stiffness. The maximum operating temperature (MOT) should be below the glass transition temperature.
Road potholes and debris above road surface cause flange denting, which is exacerbated by the presence of lower aspect ratio tires. Flange damage is dominantly found on the inboard flange, yet it can affect both flanges depending on the shape of the pothole or debris.
A methodology is developed for measuring and comparing to assess the wheel reduction of stiffness as found on a cornering fatigue machine. This test defines a change of stiffness that can precede the end of service life of wheel, similar to a crack in steel and aluminum wheels. A 20% increase of deflection has been used for the acceptance criteria of steel and aluminum wheels.
A wheel design validation procedure is provided that uses biaxial fatigue per SAE J2562 with some allowances for material differences. A wheel design structural assurance procedure is provided for ongoing quality assurance testing with less costly equipment and in less time.
Electrical static charges on a motor vehicle need to be dissipated through a wheel/tire assembly. Electrical resistance inversely measures the ability of the wheel/tire assembly to dissipate static charge from the vehicle. A test of electrical resistance of tire/wheel assembly has been developed.