Investigation of Laser Treatment as a Method for Fatigue Crack Growth Retardation in Aluminum Alloy 2198-T851

Among the third-generation Al-Li alloys, AA2198 stands out for its lower density, formability and increased stiffness, being suitable for use in aircraft fuselage sheets and other inner structures in order to reduce weight and improve performance. An important topic related to damage tolerant structures is the development of techniques to retard fatigue crack propagation, such as the localized heating by a laser source. The aim of the present work was to find the most suitable parameters for the production of laser heating lines in 2198-T851 alloy sheets in order to reduce the fatigue crack growth rate in this material. Laboratory tests using C(T) specimens under two loading conditions (R = 0.1 and 0.5) provided a useful dataset on the laser heated material. The experimental results indicate a 200 W laser beam power at treatment speeds of 1 and 10 mm/s was sufficient to retard crack growth in the current setup. The more expressive results were obtained for 200 W laser power with a speed of 1 mm/s and cyclic loading with stress ratio R = 0.1.

IHSI Effectiveness for Crack Propagation Observed at Hamaoka PLR Piping

Indications of Ultrasonic Testing (UT) of 4 weld joints in Primary Loop Recirculation (PLR) piping in Hamaoka unit-2 had been identified during the 20th outage (2004). Metallurgical investigation after cutting from 2 weld joins had been conducted because of its accessibility etc. The 4 weld joins had been welded at the plant construction (1978), operated and IHSI (Induction Heat Stress Improvement) had been performed during the 1st outage (1979). 25 years passed by until the metallurgical investigation. As a result of the investigation, crack growth retardation by the IHSI was confirmed since crack tip was round and plastically deformed.

Residual stress affecting environmental damage in 7075-T651 alloy

The role of tensile overload superimposed on a constant amplitude cycling results in compressive residual stresses at the crack tip that cause crack growth retardation. The degree to which this effect manifests depends on whether the tests are done at a constant driving force (Kmax) or at a constant crack growth rate (da/dN). It is observed that depending on the magnitude of the overload at a given applied base stress intensity, these residual stresses can have significant effect on the crack growth in both the inert (vacuum) and the chemical (NaCl) environments. In general, cracks will grow only if the total crack tip driving force Ktotal exceeds the long crack intrinsic threshold ${\rm{K*}}_{{\rm{max,th}}}^{}.$ The crack growth retardation results can be attributed to the combined effects of the crack tip chemical reaction rates and the overload compressive residual stresses.