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Fatigue crack propagation (FCP) under constant and variable amplitude loading in base metal (BM), weld metal (WM) and heat affected zone (HAZ) of longitudinal welded joints of an API X-70 pipeline steel was investigated. Constant amplitude loading tests were performed at R = 0.1 and 0.5, whereas for variable amplitude testing single peak tensile overloads (OLs) alternating between 75 and 100% of maximum load were applied at 2.5 mm intervals in crack growth. Results of SE(B) specimens tested under constant and variable amplitude loading revealed that BM, WM and HAZ regions subjected to R = 0.5 and low Δ K-values presented the highest crack growth rates. At higher Δ K values FCP rates in all the studied regions were similar and the R effect on FCP rate was no more observed. Crack growth retardation due to OLs was observed at the three studied regions, showing a decrease on the FCP delay with a decreasing on Δ K. [ABSTRACT FROM AUTHOR]

Fibre-metal laminates (FMLs) are structural composites designed with the aim of producing very low fatigue crack-propagation rate, damage-tolerant and high-strength materials, if compared to aeronautical Al alloys. Their application in aeronautical structures demands a deep knowledge of a wide set of mechanical properties and technological values, including both fracture toughness and residual strength. The residual strength of FMLs have been traditionally determined by using wide centre-cracked tension panels M(T). The use of this geometry requires large quantities of material and heavy laboratory facilities. In this work, fracture toughness ( JC) of some unidirectional FMLs laminates was measured using a recently proposed methodology for critical fracture toughness evaluation on compact tension C(T) and single-edge bend SE(B) specimens. Additionally, residual strength values of wider M(T) specimens with different widths ( W from 150 to 200 mm) and several crack to width ratios (2 a/W) were experimentally obtained. Some experimental residual strength values of M(T) specimens ( W from 150 to 400 mm and different 2 a/W ratios) of Arall were also obtained from the bibliography. Based on JC results from C(T) and SE(B) specimens, and either using or not using crack-tip plasticity corrections, the residual strengths of the M(T) specimens were predicted and compared to the experimental ones. The results showed good agreement, especially when crack-tip plasticity corrections were applied. [ABSTRACT FROM AUTHOR]

Objective: Consider the efficacy of glass infiltration etching (SIE) treatment as a procedure to modify the zirconia surface resulting in higher interfacial fracture toughness., Methods: Y-TZP was subjected to 5 different surface treatments conditions consisting of no treatment (G1), SIE followed by hydrofluoric acid treatment (G2), heat treated at 750°C (G3), hydrofluoric acid treated (G4) and airborne-particle abrasion with alumina particles (G5). The effect of surface treatment on roughness was evaluated by Atomic Force Microscopy providing three different parameters: R a , R sk and surface area variation. The ceramic/resin cement interface was analyzed by Fracture Mechanics K I test with failure mode determined by fractographic analysis. Weibull's analysis was also performed to evaluate the structural integrity of the adhesion zone., Results: G2 and G4 specimens showed very similar, and high R a values but different surface area variation (33% for G2 and 13% for G4) and they presented the highest fracture toughness (K IC ). Weibull's analysis showed G2 (SIE) tendency to exhibit higher K IC values than the other groups but with more data scatter and a higher early failure probability than G4 specimens., Significance: Selective glass infiltration etching surface treatment was effective in modifying the zirconia surface roughness, increasing the bonding area and hence the mechanical imbrications at the zirconia/resin cement interface resulting in higher fracture toughness (K IC ) values with higher K IC values obtained when failure probability above 20% was expected (Weibull's distribution) among all the experimental groups., (Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)