Mechanism of fatigue crack initiation was investigated in ultrafine-grained (UFG) magnesium alloy AZ91 processed by equal channel angular pressing (ECAP). Fatigue behaviour of UFG material was compared to the behaviour of material in an initial as-cast state. Focused ion beam technique (FIB) was applied to reveal the surface relief and early fatigue cracks. Two substantially different mechanism...

Titanium-alloy weldments have been extensively used in engineering structures, and accurate estimation of the fatigue life is beneficial for avoiding catastrophic failures in titanium-alloy structures. The weld pore is a common defect in these weldments that significantly influences the fatigue process. In this study, the weld-pore size and depth and its effect on the fatigue life of Ti-6Al-2Zr...

We analyze the initiation and propagation of a crack from a point on the surface of a circular notch-tip in an impact loaded prenotched plate. The material of the plate is assumed to exhibit strain hardening, strain-rate hardening, and softening due to the rise in temperature and porosity. The degradation of material parameters due to the evolution of damage in the form of porosity is considere...

Additive manufacturing technologies are in the process of establishing themselves as an alternative production technology to conventional manufacturing, such as casting or milling. Especially laser additive manufacturing (LAM) enables the production of metallic parts with mechanical properties comparable to conventionally manufactured components. Due to the high geometrical freedom in LAM, the ...

OBJECTIVE To assess the relationship between crack cocaine use and dimensions of quality of life and social functioning in young adults. METHODS This was a cross-sectional, population-based study involving 1,560 participants in Pelotas, Brazil. Crack cocaine use and abuse were investigated using the Alcohol, Smoking and Substance Involvement Screening Test (ASSIST) inventory. Outcomes of inte...

Recent experimental and computational work by Link and associates has demonstrated that relatively small (W = 150 mm) single edge notched tension specimens (SE(T)) can be used to obtain crack arrest data high in the ductile-to-brittle transition of ferritic structural steel using dynamic computational techniques if a thermal gradient is utilized to aid in the crack arrest. Testing has been repo...

The initiation of a crack in a sound body is a real issue in the setting of Griffith’s theory of brittle fracture. If one uses the concept of critical energy release rate (Griffith’s criterion), it is in general impossible to initiate a crack. On the other hand, if we replace it by a least energy principle (Francfort–Marigo’s criterion), it becomes possible to predict the onset of cracking in a...

α/β titanium alloys are choice materials for aeronautical and automotive industries due to their high performance to density ratio. For several applications, fatigue resistance is one of the critical design parameter. Particularly, initiation of fatigue crack plays a key role. Furthermore, hardly anything can be found in the literature on the fatigue crack initiation in multiphase microstructur...

In the short crack regime of the fatigue process, grain boundaries in steels are barriers against crack growth. In this paper, we use: (1) a method involving crack density; and (2) a method of dimensional analysis, to evaluate the effects of grain size and grain-boundary resistance on short crack behaviour and fatigue life. The results show that the fatigue life increases with a decrease in gra...

Modified dynamic three-point-bending and compact shearing test configurations based on Hopkinson pressure bar (HPB) and crack detection gage (CDG) (Vishay Intertechnology, Inc.) were used for the determination of the dynamic mode I and mode II delamination-initiation toughness of a unidirectional graphite-fiber/epoxy composite made of P7051S-20Q-1000 prepregs (Toray Composites America). The tra...