Endurance Tests

Machine endurance tests were conducted with Green '012' spines and with the mechanical ankle locked, which is a worse case situation because the artificial spine is straight during the flutter return stroke (while the mechanical ankle is locked). A cost versus benefit analysis concludes that Truefin should survive at least 1,000,000 kicks at 60 kicks per minute in the test tank apparatus so Truefin may offer a lifetime warranty of the spines while utilizing the lowest cost spine materials. A first endurance test utilizing 3D printed '012 links (SLS material mineral filled, tensile strength 7,050 in one direction and 4,500 psi in the other direction – white vertebra in photo below), and TP4050 (8200 psi tensile) - blue vertebra in photo below), where this combination lasted 800,000 cycles at 40 kicks/minute before failure at the base of the neck of base link 10000. This combination was not intentional, but simply happened to be the links available at the time of the test. As of this writing an endurance test (1,000,000 kick cycles @ 60 kicks/minute) of injection molded glass filled nylon 21,000 psi tensile Green '012 links has not been performed (update website). Injection molded links are far superior to 3D printed links, so such links are expected to pass this endurance test. Also, Blue '412 spines are stressed less than Green '012 spines due to the allowable flex of the fin blade in the 'toe up' direction while the test apparatus mechanical ankle is locked, so the machine endurance test stresses the links beyond the stresses which a human could create.

Link 10000 and link 20012 below (white links) were 3D printed links, so the break which occurred at 800,000 @ 40 kicks/min is not a surprise. The blue links in the photo below are actually '012 links, where normally '012 links are colored green. Also note, link 10000 (base link) as well as the blue links in the photo below have been geometrically strengthened since this endurance test.