Biomedical subjects

Robert D Deegan

Publications and source records attributed to Robert D Deegan.

3 recordsLinked to original sources

PubMed2004

Persistent holes in a fluid.

We observe stable holes in a vertically oscillated 0.5 cm deep aqueous suspension of cornstarch. Holes appear only if a finite perturbation is applied to the layer for accelerations a above 10g. Holes are circular and approximately 0.5 cm wide, and can persist for more than 10(6) cycles. Above a approximately equal to 17g the rim of the hole becomes unstable, producing fingerlike protrusions or hole division. At higher acceleration, the hole delocalizes, growing to cover the entire surface with erratic undulations. We find similar behavior in an aqueous suspension of glass microspheres.

Journal Article↗

PubMed2003

Wavy and rough cracks in silicon.

Single-crystal silicon exhibits a strong preference to cleave along a few certain planes, but in experiments we observe wavy cracks with almost no evidence of a preferred fracture direction. Furthermore, we find that the fracture surface is an anisotropic and self-affine fractal over five decades in length scale in the direction of the crack with a roughness exponent of 0.78. In our experiments a 1-4 cm wide strip of single-crystal silicon is heated to 378 degrees C and lowered into a 20 degrees C water bath at speeds of 0.2-5 cm/s. The thermal gradient produces cracks that, depending on the speed, are straight, wavy with amplitude 0.1-0.5 cm and wavelength 0.3-1 cm, or multibranched. The transition from one mode of fracture to another is discontinuous and hysteretic.

Journal Article↗

PubMed2001

Oscillating fracture paths in rubber.

We have found an oscillating instability of fast-running cracks in thin rubber sheets. A well defined transition from straight to wavy cracks occurs as the amount of biaxial strain increases. Measurements of the amplitude and wavelength of the oscillation near the onset of this instability indicate that the instability is a Hopf bifurcation.

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