Fatigue crack growth analysis in cylinders under simultaneous tensile and bending loads with constant internal pressure.

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Fatigue crack growth analysis in cylinders under simultaneous tensile and bending loads with constant internal pressure.

ارائه دهنده: Provider: Abolfazl Afshar

اساتید راهنما: Supervisors: Dr Rahman Seifi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr Hashem Mazaheri and dr Mahdi Shaban

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: 55

چکیده: Abstract: Cylinders are widely used in various industries such as aerospace, automotive, and fluid transmission systems, and their long-term performance under complex loading conditions is of great importance. Therefore, studying the behavior of fatigue cracks in cylinders and pipes is of particular significance. The Paris–Erdogan relation and the stress intensity factor are among the fundamental parameters in fracture mechanics, used to estimate fatigue life and predict crack propagation. In this research, the growth of a semi-elliptical surface crack in a cylinder subjected to simultaneous tensile load, bending moment, and constant internal pressure has been investigated using both numerical and experimental methods. The fatigue life was calculated based on the Paris law and the differential form of the stress intensity factor. Furthermore, the effects of various parameters such as the crack length-to-depth ratio, crack depth-to-cylinder thickness ratio, bending load, and internal pressure on crack propagation and fatigue life were analyzed. The tested cylinder material was AL-6061, and the validity of the numerical method was verified through comparison with experimental results. The findings of this study indicate that increasing the crack length-to-depth ratio leads to an increase in the stress intensity factor, resulting in a reduction in fatigue life. It was also observed that for semi-elliptical surface cracks with a length-to-depth ratio greater than one, the maximum crack growth occurred at the deepest point of the crack front, whereas for semi-circular cracks, it occurred at the crack surface. The effect of the bending fatigue load plays a critical role in the fatigue crack growth rate and the overall fatigue life of the cylinder, as its increase significantly reduces fatigue life. The influence of constant internal pressure on the fatigue life of cracked cylinders was found to be less significant than that of the bending load, while increasing crack depth had a direct effect on reducing the fatigue life of the cylinder. . Key Words: Crack Growth, Stress Intensity Factor, Semi-Elliptical Crack, Fatigue Life, Bending Moment