Papers by Keyword: Stress Intensity Factor Range

Abstract: When fatigue crack growth rate da/dN = 0, the stress intensity factor range ΔK_I is a threshold and it is expressed by ΔK_I = ΔK_th. The threshold ΔK_th is important for design, repair/replacement, particularly, trouble shooting for cracked components. However, the thresholds were not well codified. Authorized and consensus ΔK_th are required. This paper introduces the current thresholds provided by fitness-for-service codes and the definition of ΔK_th under negative stress ratio R is discussed. Finally, the threshold ΔK_th for aluminum alloys in air environment is proposed for fitness-for-service codes.

Abstract: An experimental campaign was developed to evaluate fatigue crack growth in Haynes 230. The effects of plasticity induced crack closure were investigated with Digital Image Correlation. In particular, crack opening levels were measured with the digital extensometer technique, which allowed the evaluation of crack flanks relative displacements. Experimental results were compared with a reference da/dn – ΔK_eff curve and with the data of a previous study, which analyzed single crystal propagation. It was found that the adoption of crack closure local measurements provided an accurate estimation of crack propagation driving forces, since all the experimental points from single crystals and polycrystals collapse onto the da/dn – ΔK_eff curve.

Abstract: The paper presents the results of tests on the fatigue crack growth rate for a constant moment amplitude under combined bending with torsion in the aluminium alloy AlCuMg1. The tests were performed under different values of the stress ratio R. Plane specimens with stress concentrators in form of the external one-sided sharp notch were tested. The results of experiments were described on graphs of the fatigue crack growth rate versus changes of the stress intensity factor range ΔK. A non-uniform fatigue cracks growth on both lateral surfaces of specimens was observed during experimental tests.

Abstract: This paper studies the evaluation of the proper stress intensity factor ranges in the fracture mechanics-based fatigue analysis of the rib-to-deck welded joints of orthotropic steel decks. It is pointed out in the paper that the stress intensity factor ranges used in Paris law for the fatigue crack growth at a rib-to-deck welded joint can not be taken as a value proportional to the corresponding stress ranges since the compressive stresses are the dominant transverse stresses in the cyclic stresses under the action of truck traffics. The proper fatigue design loads to characterize the standard truck loading for the accurate calculation of the tensile transverse stresses at the rib-to-deck joints is also discussed in the paper. It is shown that the loads from two neighboring wheel-axles of heavy trucks have to be taken into account.

Abstract: The objective of this study is to investigate the effect of the low or high strain rate on the impact fatigue properties of the nickel foam material and to understand the lifetime of this material which is subjected to the repeated impacts at different energy levels. Failures of foam materials under single and repeated impacts analogous to fatigue are essential to designers and users in military and aerospace structures. The material failure induced by repeated impact loading becomes a critical issue because of significant loss of stiffness and compressive strength in the foam material. Testing methods to study impact(that is, high strain rate) fatigue are quite numerous; no single standard testing procedure is defined for studying the impact fatigue property of a material. The increasing application of foam material in aerospace structures, owing to high specific stiffness and strength has attracted a great concern about the high sensitivity to impact damage introduced during manufacture or in service, and the effects of such damage on structural degradation. To investigate this issue, this study sets up an experimental procedure to determine the impact fatigue properties of nickel foam material. This study performs both experimental and numerical investigations to catch the impact fatigue behavior of nickel foam with open type. Design life and probability of failure or survival at specified life can be calculated so that the fatigue life of nickel core material subjected to repeated impact loading is predicted.

Abstract: The purpose of this study was making evident the overload effect in a spectre with constant amplitude cycles. The crack growth simulation was made on cracked specimen and was studied for four loading cases. Fatigue crack growth rate was calculated applying NASGRO equation and the crack growth retardation analyzed.