CRACK TIP STRESS SHIELDING AND CRACK CLOSURE ON FERRITIC-PEARLITIC STEEL USING IN-SITU SEM METHOD

• Main Author: Jeremy Ishak, Elkan
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/71866
• Institution: Institut Teknologi Bandung

Fracture toughness is one of the material properties. Fracture toughness can be maxed out to its limit with crack tip stress shielding. Crack tip stress shielding acts as a barrier for a fatigue crack to propagate. Thus, fatigue crack is slowed down. Crack tip stress shielding yields from the steel's second hard phase, i.e. pearlite. Branching and interlocking are the most common phenomena from crack tip stress shielding. From previous studies, microstructure plays a vital role in inhibiting fatigue crack growth. In this paper, crack tip stress shielding will be explored from the microscopic perspective by analyzing crack opening displacement from an SEM image and its correlation with the macroscopic crack tip stress shielding. Low-carbon ferritic-pearlitic steel with variations in microstructure morphology was used. Fatigue crack growth tests were carried out along with in-situ SEM. Fatigue crack propagation was observed through the optical microscope and SEM. To identify the crack tip stress shielding microscopically, crack openings under variations of loading stress were observed using SEM. Results show that crack tip stress shielding phenomena were observed on lowcarbon steel with microstructure morphology variations. In-situ SEM observation shows branching and interlocking as the crack tip stress shielding phenomena. Branching occurs when a crack propagates through a pearlite band. Crack interlocking occurs on a distributed ferrite-pearlitic microstructure. Observations on in-situ SEM crack opening show that crack opening was not increasing together with the increase of load. It was observed that a decrement in crack opening happened at some loading points.