This paper presents the fracture analyses conducted on the FAA/NASA stiffened and unstiffened panels using the STAGS (STructural Analysis of General Shells) code with the critical crack-tip-opening angle (CTOA) fracture criterion. The STAGS code with the “plane-strain” core option was used in all analyses. Previous analyses of wide, flat panels have shown that the high-constraint conditions aro...

Fracture toughness resistance curves describe a material's resistance against crack propagation. These curves are often used to characterize biomaterials like bone, nacre or dentin as these materials commonly exhibit a pronounced increase in fracture toughness with crack extension due to co-acting mechanisms such as crack bridging, crack deflection and microcracking. The knowledge of appropriat...

Although fatigue damage in bone induced by cyclic loading has been recognized as a problem of clinical significance, few fracture mechanics based studies have investigated how incipient cracks grow by fatigue in this material. In the present study, in vitro cyclic fatigue experiments were performed in order to quantify fatigue-crack growth behavior in human cortical bone. Crack-growth rates spa...

Quantitative understanding of the parameters which control composite fracture is imperative to the implementation of fail safe design and inspection of critical load bearing structures. For isotropic materials, fracture is essentially controlled by a single parameter, e.g., the fracture toughness or the stress-intensity factor. This one dimensional nature lends itself to experimental quantifica...

The influence of tubule orientation on the transition from fatigue to fatigue crack growth in human dentin was examined. Compact tension (CT) and rectangular beam specimens were prepared from the coronal dentin of molars with three unique tubule orientations (i.e., 0 degrees , 45 degrees and 90 degrees). The CT specimens (N=25) were used to characterize fatigue crack initiation and steady-state...

The results of a numerical study of the nonlinear response of thin unstiffened aluminum cylindrical shells with a longitudinal crack are presented. The shells are analyzed with a nonlinear shell analysis code that accurately accounts for global and structural response phenomena. The effects of initial crack length on the prebuckling, buckling and postbuckling responses of a typical shell subjec...

We report the first atomistic determination of the minimum energy path for a series of bond ruptures to advance a crack front. Saddle-point configurations on (111) cleavage planes in Si reveal a steplike distribution of atomic displacements, implying a kink mechanism which is known to control dislocation mobility. Manifestations of lattice trapping and directional cleavage anisotropy are furthe...

In 2004, a team comprised of researchers and service providers launched the Safer Crack Use, Outreach, Research and Education (SCORE) project in the Downtown Eastside of Vancouver, British Columbia, Canada. The project was aimed at developing a better understanding of the harms associated with crack cocaine smoking and determining the feasibility of introducing specific harm reduction strategie...

A new method for detection and sizing of closed crack is described which uses transient waveform of subharmonics with half input frequency in ultrasonic nondestructive evaluation. In analogy to the resonant characteristics of vibration of bubbles in liquids, we formulate an equation for resonant excitation of subharmonics at partially closed cracks. The equation has been partially verified by c...