CRACK PROPAGATION IN PLAIN CONCRETE UNDER FATIGUE LOADING

Abstract

Concrete exhibits different behaviour under various loading when compared with various materials used in civil engineering like steel, aluminum etc. due to varying nature of material, methods and workmanship. Concrete behaviour is different from ideal brittle materials as concrete exhibits non linear response before peak load and develops large size inelastic zone called fracture process zone (FPZ) ahead of crack tip. The primary aim of the study is to determine, analyse and compare the various fracture parameters of plain concrete under static as well as in fatigue loading on Geometrically similar notched beams have been constructed for various specimens 3-point bend test experiment. In this study, analysis of Load-CMOD and Load-Displacement curves is done and compares it with work of fracture. Various fracture parameters namely fracture energy, critical crack length, brittleness number, characteristic length, crack tip opening displacement (CTOD) and stress intensity factor etc are obtained using two parameter model, size effect model and work of fracture method. It is observed that fracture energy increase with increase in specimen size. Brittleness number result incorporates the non linear fracture mechanics (NEFM) analysis. Compliance approach is used to calculate crack propagation under fatigue loading. Variation of crack growth rate has been calculated as function of change in stress intensity factor range for all beam sizes. It is observed that fatigue growth rate incorporates two stages: a deceleration stage in which crack growth rate decreases with crack length increase, followed by an acceleration stage in which crack growth rate is increased with steady rate. It is observed that crack length and flexural stiffness follows S-shaped trend with increasing load cycle. The fatigue life is recorded as 2260, 4875 and 9017 cycles for small medium and large specimens respectively