Section 1 Introduction

1.1.1 Fatigue testing can be divided into two main groups; testing of small specimens and testing of full-size crank throws. Testing can be made using the staircase method or a modified version thereof, which is presented in this document. Other statistical evaluation methods may also be applied.

1.2.1 For crankshafts without any fillet surface treatment, the fatigue strength can be determined by testing small specimens taken from a full size crank throw. When other areas near the fillets are surface treated, introducing residual stresses in the fillets, this approach cannot be applied.

1.2.2 One advantage of this approach is the rather high number of specimens which can be then manufactured. Another advantage is that the tests can be made with different stress ratios (R-ratios) and/or different modes e.g. axial, bending and torsion, with or without a notch. This is required for evaluation of the material data to be used with critical plane criteria.

1.3.1 For crankshafts with surface treatment, the fatigue strength can only be determined through testing of full-size crank throws. For cost reasons, this usually means a low number of crank throws. The load can be applied by hydraulic actuators in a 3- or 4- point bending arrangement, or by an exciter in a resonance test rig. The latter is frequently used, although it usually limits the stress ratio to R = -1.