The results of full-size pressure vessel tests are summarized and used to demonstrate the validity of design procedures developed by others. In particular, design for low cycle (plastic) fatigue strength and fracture safety are investigated. The results justify the design stress recommendations made by PVRC to ASME and confirm the NRL fracture analysis diagram procedure hypothesis. It is emphasized that full advantage can be taken of high strength materials only by improvement of fabrication and inspection procedures.

Fatigue crack propagation studies were conducted on three new high-strength structural steels: 9Ni–4Co–0.20C quenched-and-tempered, 10Ni–2Cr–1Mo–8Co dual-strengthened, and 13Cr–8Ni–2Mo precipitation-hardened stainless. The yield strengths of these steels ranged from 176 to 193 ksi. Notched cantilever-bend specimens of each steel were cycled zero-to-tension in two environments, room air and 3.5 percent NaCl salt water. Fatigue crack growth rates were measured experimentally and correlated with the crack tip stress-intensity factor range. The results indicate that these new steels possess greater resistance to fatigue crack propagation and less sensitivity to environment than previously studied steels of comparable strength.

No abstract

The impact forces and specimen bending moments generated during the NRL dynamic tear test are interpreted in terms of the dynamics of the system and the fracture characteristics of the material. It is shown that the impact forces and bending moments up to the time of crack initiation can be predicted using a simple analysis based on Timoshenko’s treatment of transverse beam impact problems. This implies the possibility of using this analysis for dynamic KIc determinations.

Fatigue-crack growth is a potential failure mechanism that can be strongly influenced by a salt-water environment. This paper discusses fatigue-crack-propagation studies performed on three high-strength structural steels: 9Ni-4Co-0.25C, 12Ni 180-grade maraging, and 18Ni 200-grade maraging. Each steel underwent a program of fatigue cycling in two environments, a “dry” environment consisting of ambient room air and a “wet” environment consisting of 3.5 percent NaCl salt water. Relationships for fatigue-crack-growth rates as a function of the fracture mechanics stress-intensity factor (K) were obtained experimentally for each steel in both environments. The engineering significance of these relationships is presented in terms of stress levels and flaw sizes relevant to the steels under investigation. The results of this work indicate that, in an air environment, the fatigue-crack-growth rate correlates with the stress-intensity-factor range according to the power-law relationship, da/dN = C (ΔK)m. Fatigue-crack growth in each of the steels was accelerated by the salt-water environment. However, the environmental response varied significantly, depending upon the material and the ΔK level. The lower-toughness steel was less affected by environment, and environmental effects in all the steels diminished with increasing ΔK levels. No correlation was observed between fatigue-crack-growth behavior in the salt-water environment and the stress-corrosion-cracking parameter (K Iscc) obtained on the same materials.