Long-term performance properties of polyurethane elastomers for shoe soles.

For polyurethane soling materials (Bayflex® Footwear), abrasion resistance and resistance to alternating dynamic loads are key quality criteria. There are various methods for testing the latter – some of them developed with a specific industry in mind and some created in house.

Alternating flexural tests

For every phase of product development, there is a special testing method, but with all of them crack formation and/or cut growth is measured as a function of the number of flexures. Predefined conditions for the flexing frequency, flexing angle and flexing radius are used.

a) Rossflex method – the material determines the result.

	Strip specimens
	Temperature range -30 °C to room temperature; up to 60,000 cycles
	Measurement of cut growth

b) PFI method – material and sole design determine the result.

	Strip specimens or complete shoe soles
	Temperature range: -25 °C to room temperature; up to 60,000 cycles
	Measurement of cut growth, assessment of overall damage

c) Myrenne unit – soling material, sole design and overall shoe construction determine the result.

	Specimen strips, shoe soles or complete shoes
	Kinematics developed in-house (up to 90,000 cycles)
	Measurement of cut growth, evaluation of overall damage

Test method to simulate walking

The long-term performance properties of shoes (particularly wear comfort) are influenced by the fatigue behavior of the materials. To measure this parameter, a method has been developed for simulating the motion of walking. It can be used both in the development of polyurethane mid-sole materials and in the testing of complete shoes.

The walking simulation test is performed on a servo-hydraulic machine with a heel-like element exerting pressure. In the heel region, the shoe is subjected to a power-controlled dynamic pressure load with up to 200,000 load cycles (to simulate the individual steps). The tests furnish data on the cushioning/damping behavior and the compressive strain on the sole as a function of the number of load cycles.