ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Air crazes have been grown from indentor “crack” tips in polystyrene films of thicknesses 0.11, 0.57 and 1.2μm. Quantitative transmission electron microscopy is used to measure craze thickness and fibril volume fraction profiles. From these, profiles of craze fibril extension ratio, λ(x), craze surface displacement,w(x), and craze surface stress,S(x), have been computed. For all thicknesses of film, the λ(x) profiles prove that the craze thickens by drawing more material into the fibrils from the craze-matrix interface, rather than by fibril creep. The form ofS(x) is also similar for all thicknesses of film, with a maximum at the craze tip and a minimum approximately half way along the craze. The extension ratio profiles also show a maximum at the craze tip. The midrib, which develops in the high stress region behind the craze tip as the craze propagates, has a value of λ comparable to that found at the stationary craze tip. When an isolated craze grows in an initially homogeneous stress field the midrib is observed to be of constant thickness. In contrast the midribs of crazes grown from crack tips decrease in thickness to a constant value with distance from the crack tip. All these observations are explained by the surface drawing mechanism of craze thickening. The computed values of λ and the fibril stress,σ t, for the thinnest film, are significantly lower than for the thicker two films. These changes are attributed to the absence of plastic constraint in the thinnest film, which decreases the fibril true stress necessary for surface drawing.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02402785
Permalink