Inglis (1913) vs. Griffith (1921)
I have updated my notes on the Griffith paper. I added more description on the experimental determination of surface tension of solids. Griiffith himself determined the surface tension of glass by an experimental setup. Udin et al (1949) described a setup based on the same principle. This setup is now known as the zero creep experiment.
In class today Chao Chen asked me to compere Inglis theory and Griffith theory, which I did at the very end of the notes. The two theories give the same prediction:
the strength times the squre-root of the crack length is a material constant.
In the Inglis theory, the constant involves atomic strength and atomic size. In the Griffith theory, the constant involves Young’s modulus and surface energy. If we adopt any simple-minded atomic model, we can show that the two constants are essentially the same.
Both theories work well for silica glass. Neither works for steel. Both theories survived to this day, in somewhat different forms. In general terms, the Inglis theory has evolved into the stress approach to fracture, and the Griffith theory has evolved into the energy approach. The two approaches are, of course, equivalent. We will talk more about both approaches in coming lectures.