An apparatus for testing the fatigue of a sample of cord or filament (12) by bending it over a fixed surface (19). The apparatus comprises a tensioner (14), a fixed bending surface (19) and a driving mechanism (24), whereby the driving mechanism (24) causes a non-twisting bending of cord or filament (12) over bending surface (19) while tensioner (14) maintains a constant tension on cord or filament (12). In a method of the invention, a cord or filament (12) is attached to a tensioner (14), the cord or filament (12) is mounted on fixed bending surface (19) and attached to non-stationary roller (20), and driving mechanism (24) is activated to cause a back and forth movement of roller (20), thereby causing filament or cord (12) to bend back and forth over fixed bending surface (19) until it breaks. This process is repeated using different stress increase rates on the cord or filament (12) by adjusting the tensioner (14) and a linear regression equation is used to determine the fatigue stress limit of the material.