Shielding interaction effects of two parallel edge cracks in finite thickness plates subjected to remote tension load is analyzed using a developed finite element analysis program. In the present study, the crack interaction limit is evaluated based on the fitness of service (FFS) code, and focus is given to the weak crack interaction region as the crack interval exceeds the length of cracks (b...

It is considered that the process of fatigue fracture could be arranged the three classes, i.e., crack initiation, crack propagation and fracture. Of these the second process is important from the following point of view. (1) As has so far been reported in many publications, the importance of crack propagation process in total fatigue life increases in proportion to the increase in the stress c...

In this work we describe a series of impact experiments performed on PMMA/4340 steel edge cracked bimaterial plates. Specimens were impacted at 20 m SK’ in a one point bend configuration using a high speed gas gun. Dynamic interfacial crack propagation was observed using the optical method of Coherent Gradient Sensing and high speed photography. Very high crack tip accelerations (IO’ m SF’) and...

In this study, an analytical model is developed to study crack breathing behavior under the effect of crack location and unbalance force. Crack breathing behavior is determined using effectual bending angle by studying the transient change in closed area of the crack. The status of the crack of a balanced shaft is symmetrical about shaft rotational angle and the duration of each crack status re...

OBJECTIVES To compare demographic, HIV risk behaviors, and health status characteristics of injection drug users (IDUs) who have injected "crack" cocaine with IDUs who have not. METHODS Nine hundred and eighty-nine IDUs were recruited in New Haven, CT, Hartford, CT and Springfield, MA from January 2000 to May 2002. Participants were administered a modified version of the National Institute on...

Cracks and craze lines are often observed in the enamel of human teeth, but they rarely cause tooth fracture. The present study evaluates fatigue crack growth in human enamel, and compares that to the fatigue response of sintered hydroxyapatite (HAp) with similar crystallinity, chemistry and density. Miniature inset compact tension (CT) specimens were prepared that embodied a small piece of ena...

Dynamic crack growth along a bimaterial interface under impact shear loading is analyzed numerically. The material on each side of the bond line is characterized by an isotropic hyperelastic constitutive relation. A cohesive surface constitutive relation is also speci®ed that relates the tractions and displacement jumps across the bond line and that allows for the creation of new free surface. ...

A study has been made of the fatigue-crack propagation properties of a series of laminated Nbreinforced Nb3Al intermetallic-matrix composites with varying microstructural scale but nominally identical reinforcement volume fraction (20 pct Nb). It was found that resistance to fatigue-crack growth improved with increasing metallic layer thickness (in the range 50 to 250 mm) both in the crack-divi...

Cracks are dangerous and frequently observed defects in steel structures. Therefore, the understanding of the mechanism of crack is very important to structure safety. Although the mechanism of static crack has been widely studied by researchers, the mechanism of dynamic crack has been left out and seldom been discussed. In this paper, a modeling method for acoustic emission (AE) source of dyna...

Despite decades of study, the atomic-scale mechanisms of fatigue crack growth remain elusive. Here we use the coupled atomistic–discrete dislocation method, a multiscale simulation method, to examine the influence of dislocation glide resistance on near-threshold fatigue crack growth in an aluminum alloy. The simulations indicate that the threshold increases with an increase in dislocation glid...