Significance and Use
This test method is used by athletic footwear manufacturers both as a tool for development of midsole material systems and as a test of the general characteristics of the athletic footwear product (see 1.4-1.6.2 and Notes 1-6). Careful adherence to the requirements and recommendations of this test method shall provide results which can be compared between different laboratory sources.
Dynamic data obtained by these procedures are indicative of the shock attenuating properties (see 1.5) of the material systems under the specific conditions selected.
This test method is designed to provide force versus displacement response of materials systems for athletic footwear under essentially uniaxial compression conditions at impact rates, which are similar to that for heel strike in normal running movements.2 ,3 That is, peak forces of up to 2 kN (450 lb) in times of 10 to 20 ms.
The peak or maximum values of force, pressure, displacement, and strain are dependent on the maximum energy applied to the specimen. These values are normalized to provide comparative results for a reference maximum energy applied to the specimen of 5 J.
Shock attenuating characteristics are strongly dependent on specimen thickness and prior history of force application. Therefore, results should be compared only for specimens of essentially the same thickness and prior impact conditioning (see Notes 3-6). There are no currently acceptable techniques for normalizing results for specimen thickness variations.
Shock attenuating values (see 1.5) determined by this test method, for materials systems of athletic footwear, may not correlate with the similar values experienced by a runners heel or foot.
Scope
1.1 This test method covers the measurement of certain shock attenuating characteristics, rapid rate force-displacement relationships, of materials systems employed in the midsole of athletic footwear intended for use in normal running movements. This test method covers three different procedures for performance of the rapid rate force application: Procedure A for falling weight impact machines, Procedure B for compression force controlled machines, and Procedure C for compression displacement controlled machines.
1.2 The material system response for rapid rate force application may be different for each of the three procedures of this test method.
1.3 This test method is empirically based on the use of an 8.5-kg mass dropped from 50 mm (1.97 in.) to generate peak compressive forces which are comparable to that experienced by a midsole in heel strike tests for normal running movement., This requires the specimen to be rigidly supported and the energy to be delivered through a 45-mm (1.8-in.) diameter flat tup.
1.4 This test method imposes an impulse to generate a rapid rate compressive force-displacement hysteresis cycle and evaluates shock attenuating characteristics of the specimen. The maximum energy applied to the specimen occurs at peak displacement and must be within 10 % of a reference value that is used to normalize the data for comparative purposes.
