BACKGROUND Individual and sociocultural factors may pose significant barriers for drug abusers seeking treatment, particularly for African-American crack cocaine abusers. However, there is evidence that pretreatment interventions may reduce treatment initiation barriers. This study examined the effects of a pretreatment intervention designed to enhance treatment motivation, decrease crack use, ...

A turbine blade root contains notches that locate into a “fir-tree” root fixing in the turbine disc. Fatigue initiation in these stress concentrating features is of some concern. When a turbine blade is cast, the primary orientation along the blade is controlled (usually in the <001> direction) to within certain limits, however the secondary orientation (i.e. the orientation of any notches) is ...

Porosity has been shown to affect the fatigue life of bone cements, but, although vacuum mixing is widely used to reduce porosity in the clinical setting, results have been mixed and the effects of porosity are not well understood. The aim of this study was to investigate the effects of porosity using stress analysis and fracture mechanics techniques. The stress concentrations arising at voids ...

We report on the in situ, time resolved, observation of solidification cracking in a thin sample of an Al-15wt%Sn alloy at ESRF BM05. During the experiment, solidification cracking was seen to occur during natural cooling of the sample at a solid fraction of ∼95%, between directionally agglomerated dendritic networks. Through detailed analysis, three stages of crack growth were observed: crack ...

Fracture of ceramic materials has been one of the most frequently reported complications for all-ceramic restorations. The aim of the study was to analyze the fracture features of hot-pressed ceramic crowns in order to evaluate areas susceptible to crack initiation and crack propagation correlated with stress areas. The crowns were inspected visually to determine the shape and orientation of th...

Ambientto elevated-temperature fracture and fatigue-crack growth results are presented for five MoMo3Si-Mo5SiB2–containing -Mo matrix (17 to 49 vol pct) alloys, which are compared to results for intermetallic-matrix alloys with similar compositions. By increasing the -Mo volume fraction, ductility, or microstructural coarseness, or by using a continuous -Mo matrix, it was found that improved fr...

A puzzling question in dynamic fracture has been why cracks in amorphous brittle materials always travel at velocities smaller than the Rayleigh wave speed. The answer is that the energy per length needed for the crack to propagate depends strongly on velocity. As the energy flux to the crack tip increases, the crack chooses new modes of dissipation such as micro-cracking and the creation of su...

We investigate initiation, growth, and healing of wing cracks in confined silica glass by molecular dynamics simulations. Under dynamic compression, frictional sliding of precrack surfaces nucleates nanovoids which evolve into nanocrack columns at the precrack tip. Nanocrack columns merge to form a wing crack, which grows via coalescence with nanovoids in the direction of maximum compression. L...

We investigate the feasibility of cohesive theories of fracture, in conjunction with the direct simulations of shear-load dominated fracture, to numerically reproduce the inter-sonic crack propagation in unidirectional graphite-epoxy composite plates [1]. The particular configuration contemplated in this study refers to the experiments performed by Coker and Rosakis [2, 3]. The numerical simula...

In this paper, we report on an experimental study of spontaneous, mixed-mode, crack propagation in weakly bonded similar and dissimilar materials. A unique experimental configuration is proposed to induce spontaneous crack growth events along the interfaces. The cracks nucleate from tiny circular holes and are triggered by an exploding wire. They subsequently propagate under the action of a con...