Modelling the fatigue behaviour of sandwich beams under monotonic, 2-step and block-loading regimes

FRP composite sandwich materials are being increasingly used in high-perfor mance structural applications because of their high stiffness and low weigh t characteristics. At present, relatively little is known about the long-te rm performance of such structures, especially under multi-step loading cond itions. The aim of this paper is to address such fatigue behaviour by using a fatigue model verified by experimentation. The fatigue model is based on the fatigue modulus concept (degradation of stiffness) which is proposed f or core-dominated behaviour. Two non-linear cumulative damage models derive d from the chosen stiffness degradation equation are examined in context wi th the linear Miner's damage summation and compared with available experime ntal data for 2-step loading. The models are then applied to examine the in fluence of 2-step block loading. Finally, conclusions are drawn regarding t he aptness of the chosen models. (C) 1999 Elsevier Science Ltd. All rights reserved.