Internal mold bulging test and circumferential fracture toughness of small blunt-cracked thick-walled cylinders

Aiming at the problems of complex preparation and high cost of fatigue pre-cracks in the circumferential fracture toughness testing of small-caliber thick-walled cylinders, an innovative testing method based on electrical discharge machining (EDM) notches and elastic internal mold bulging tests is proposed. By establishing a stress intensity factor calculation model for thick-walled cylinders under internal pressure and introducing the stress concentration factor correction theory, accurate estimation of the fracture toughness of EDM blunt notch specimens is realized. Tests were carried out on 45# steel and 30SiMn2MoVA materials. The results show that this method effectively avoids the traditional fatigue pre-cracking process, and the test results are in good agreement with literature values, verifying the fracture mechanics rationality of the simplified method. By eliminating the requirement for fatigue pre-cracking, the present approach establishes a low-cost and engineering-viable alternative for circumferential fracture toughness assessment of thick-walled cylinders.