Nickel-base superalloys have been used extensively in power generation applications due to their high strength at temperatures up to 1093°C. When the material is subjected to complex mechanical loading superimposed with thermal loading, fatigue interacts with either creep and/or oxidation. Directionallysolidified (DS) materials are often used in place of polycrystalline (PC) materials since the...

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...

The unexpected failures of structural materials in very high cycle fatigue (VHCF) regime have been a critical issue in modern engineering design. In this study, the VHCF property of a Cr-Ni-W gear steel was experimentally investigated under axial loading with the stress ratio of R = -1, and a life prediction model associated with crack initiation and growth behaviors was proposed. Results show ...

The role of elastic mismatch in determining critical conditions for indentation fracture in brittle coatings on substrates of unlike modulus was investigated. A model transparent trilayer system, consisting of a glass coating layer bonded to a thick substrate of different glass or polymer by a thin layer of epoxy adhesive, facilitated in situ observations of crack initiation and propagation. A ...

Crack initiation and growth behaviour of an austempered ductile iron (ADI) austenitised at 800C and austempered at 260C has been assessed under three point bend fatigue conditions. Initiation sites have been identified as carbides remaining from the as cast ductile iron due to insufficient austenisation. The number of carbides cracking on loading to stresses greater than 275 MPa is critical in ...

Ultrasonic methods have been implemented for in situ sizing of fatigue cracks near fastener holes. These techniques, however, only provide an estimate at the time of the measurement and cannot predict the remaining life of the structure. In contrast, statistical crack propagation approaches model the expected fatigue life based on worst-case fatigue process assumptions. The authors have recentl...

The goal of the work presented here is to study dynamic crack initiation in ductile steels "NiÐCr steel and 293 stainless steel# at di}erent loading rates and to establish appropriate dynamic failure criteria[ A variety of infrared and visible optical methods and high!speed photography are used in this study[ Precracked steel specimens are subjected to dynamic three!point bend loading by impact...

Analyses of dynamic crack growth along interfaces are discussed. The material on each side of the bond line is characterized by an elastic constitutive relation. A cohesive surface constitutive relation that allows for the creation of new free surface is also specified across the bond line. The resistance to crack initiation and the crack speed history are then predicted without invoking any ad...

In order to investigate the properties of Y-shaped cracks of brittle materials under compression, compression tests by using square cement mortar specimens with Y-shaped crack were conducted. A true triaxial loading device was applied in the tests, and the major principle stresses or the critical stresses were measured. The results show that as the branch angle θ between the branch crack and th...

A phase-field model based on a modified form of the regularized formulation Griffith’s fracture theory is presented to investigate intergranular and transgranular crack propagations in polycrystalline brittle materials. Grains grain boundaries are incorporated initiation propagation for growth, which elastic anisotropy varies orientation angle, boundary energy related misorientation angle adjac...