The pendulum rig or “Pendulum Slip Resistance Meter” (pictured below) measures surface friction using an energy loss principle as used in the Charpy Impact test. As the pendulum strikes a surface energy is lost, which can be translated into a friction coefficient. The pendulum rig was designed in the 1940's and is widely used today as a road surface friction assessing tool in the cases of accidents or experimental road surfaces . Today the rig is also used as a standard method of assessing slip resistance of flooring .
On the end of the pendulum is a rubber slider, which is spring mounted so that a constant normal force is present through the entire contact (typically 12mm). The rig uses two different types of rubber pad; Four-s and TRL. The harder Four-s type rubber represents the heel of the average shoe and the TRL (softer pad) represents the heel of a foot. Rubber hardness is measured using the International Rubber Hardness Degrees, IRHD system. The harder rubber has an IRHD value of 96, and the softer 55 . The hardness test used in the IRHD differs from hardness tests on other materials such as metals and ceramics, which measure the ability of the material to withstand plastic deformation i.e. indentation. Instead it measures the modulus of the rubber using a spherical indenter and observing the depth of indentation with a given force . The IRHD scale ranges from 0 (no modulus) to 100 (infinite modulus).
- BS EN 13036-4:2003, Road and airfield surface characteristics. Test methods. Method for measurement of slip/skid resistance of a surface. The pendulum test
- AS/NZS 4586:2004, Slip resistance classification of new pedestrian surface materials
- BS 7976-1:2002, Pendulum Testers: Part 1 - Specification
- BS ISO 48:2007, Rubber, vulcanized or thermoplastic. Determination of hardness (hardness between 10 and 100 IRHD).