Assessment on Strain-Based and Stress-Based Design Strategies for Components at Elevated Temperatures: A Comparative Study

Geometrical discontinuities (such as holes and grooves) widely exist in many components, which operate at elevated temperatures. Creep assessment of the geometrical discontinuities is essential for the safe operation of the system. In general, creep evaluations are conducted from the stress-based and strain-based strategies, but comparative studies on the extent of conservatism of these two design strategies are rarely included. In this work, creep test data of the notched components made of 9–12% Cr steel conducted by authors and that of 9Cr–1Mo steel collected from published works are employed for comparative evaluations. Results indicate that strain-based and stress-based strategies are both relatively conservative for notches in metal materials, and the conservatism of the assessment strategies increases with the notch acuity ratio of the component. The differences of the conservatism for strain-based and stress-based strategies are dependent on the notch acuity ratio and the ductility of the materials. For a blunt notch, the strain-based strategy is more conservative than the stress-based strategy for materials mentioned, while the dominant assessment strategy is dependent on stress redistribution performances of components with a sharp notch.

Fatigue crack growth in 2017A-T4 alloy subjected to proportional bending with torsion

The paper presents the results of tests on the fatigue crack growth for a constant moment amplitude under combined bending with torsion in the aluminium alloy AW-2017A-T4. The tests were performed under different values of the load ratio R. Plane specimens with stress concentrators in form of the external one-sided sharp notch were tested. A non-uniform fatigue cracks growth on both lateral surfaces of specimens was observed during experimental tests. Fatigue cracks were developing in the specimens in two stages; quarter-elliptic edge cracks were observed at the beginning, then evolving into through cracks.

On the Contact Stresses at the Indenting Edge of a Shaft-Hub Interference Fit Subject to Bending and Shear Forces

The contact stress field is addressed that is developed at the indenting edge of a keyless shaft-hub interference fit, in the case that both bending and shear forces are applied, and in the absence of friction. The combined effect of a set of elementary load cases is assessed for the sharp notch case in terms of a generalized stress intensity factor, with the aid of Finite Elements and for a class of shaft-hub geometries. In fact, linearity is preserved in the case of a sharp edged bore up to the incipient detachment condition; such event, which may occur as a result of e.g. excessive bending loads, may be forecast based on the proposed framework. Contact stresses in the case of rounded edge may be subsequently predicted by scaling an appropriate local solution; fatigue analysis may then be performed in the case of rotating or fluctuating loads. An exhaustive design table is finally compiled to assist the designer in dimensioning an interference fit in the presence of an arbitrary combination of time varying bending and shear forces.