Yield Stress Σ0 Research Articles

Fatigue fracture toughness of maraging steel.

High-cycle fatigue tests, low-cycle fatigue tests, and static tensile tests on notched specimens of a maraging steel were conducted. not only is the fatigue fracture toughness Kfc approximately constant for high-cycle and low-cycle fatigue, regardless of applied stresses and strains, but also Kfc is approximately equal to the static fracture toughness KIC;Kfc<cong>KIC<cong>36 MPa·m1/2. Moreover, for its high tensile strength (yield stress σ0.2=2440 MPa, tensile stress σB=2490 MPa), the maraging steel has an extremely small value of KIC in comparison with other low-and medium-strength steels. Considering that the crack propagation period occupies only 20-30% of total life in high-cycle fatigue and also that the crack lengths at final fracture in low-cycle fatigue are very small in comparison with specimen size, the fatigue life prediction method on the basis of the integral of crack growth rate equation is inadequate and should not be applied to high-strength steels such as maraging steels. Instead, Kfc will be useful to predict the final fracture of maraging steels.

On the Break‐Up of Shaped Charge Jets

AbstractIt is shown from dimensional arguments that the semi‐empirical jet break‐up formula of Hirsch(1) is consistent with physical models characterized by ideal plasticity (yield stress σ0), the material initial density (ϱ0), strain rate (η0), and jet radius (r0). Similar arguments applied to a one‐dimensional jet stretching model yields the existence of a maximum unstable perturbation wavelength, and fixes its value to within a numerical constant. Within the class of physical models considered the plastic velocity appearing in the Hirsch formula, the incremental velocity between successive fragments of a particulated jet, and the velocity (σ0/ϱ0)1/2 are all related, as originally conjectured by Hirsch.

Pressure distribution in gaskets of high pressure devices

The values of the coefficient of internal friction μ and the yield stress σ0 of materials which are used in gaskets of high pressure devices, are given. The mathematical expressions, based on the analysis of the real pressure distribution in the gasket of Bridgman anvils enables one to calculate the gasket geometry and the forces acting on the pistons of the high pressure devices.

Pressure dependence of the yield stress of potassium at low homologous temperature

Tensile stress-strain curves for polycrystalline potassium were obtained at liquid-nitrogen temperature (T=0.23Tm) and up to a pressure of 5.15 kbar. Pressure shifts the stress-strain curve upward. The yield stress versus pressure was measured. Theoretical dislocation models for the effect of pressure on the yield stress are reviewed herein. It is shown that the effect of pressure on the yield stress owes its origin to the effect of pressure on the effective elastic constant only. The present experimental results for the yield stress σ0 as a function of pressure P are in excellent agreement with the equation σ0=σ00[1+(Ce′0/C0) P], where σ00 is the yield stress at zero pressure, Ce0 is the value of the elastic constant Ce=G/(1−ν) at zero pressure, and Ce′0 is the value of the pressure derivative of the elastic constant Ce at zero pressure. Here G is the bulk shear modulus and ν is Poisson’s ratio. If Ce′0/C0 is replaced by E′0/E0 (where E is Young’s modulus) or G′0/G0 the agreement is also within experimental error. In this study, the yield stress was found to increase by 42% at 5.15 kbar.

High-temperature strength and ductility increases of Ti-Mo-Al alloys by step aging

Step-aging programs, based on principles of particle-dislocation interactions, were developed systematically to obtain increases in the high-temperature strength and ductility properties of Ti-7 at. pct Mo-Al alloys. A triple-step aging program applied to Ti-7 Mo-16 Al produced a yield stress σ0.2 = 1,500 MN/m2, elongation to fracture e F = 4 pct at room temperature, and σ0.2 = 900 MN/m2, e F = 12 pct at 600°C. A two-step aging program resulted in σ0.2 = 1,350 MN/m2, e F = 5 pct at room temperature; σ0.2 = 800 MN/m2, e F = 20 pct at 600°C.