An experimental procedure for stressing wipers such that the magnitude of the stresses are known, reproducible, and applied over a reasonable range, and such that the number of particles generated thereby is easily determined, is described. The stresses are administered by dragging weights of known mass and cross-sectional area across the surface of wetted wipers at known velocities and simultaneously measuring the resultant frictional forces. From these physical measurements, the frictional energy absorbed by the wipers is calculated. Plotting the number of particles generated versus this energy results in an empirical construction of the stress-strain curves.
Data and stress-strain curves are presented for a variety of wiping materials. The shapes of the curves are interpreted in terms of the physical characteristics of the wipers. The fact that the curves are independent of the rate with which energy is administered (i.e., the power) is discussed.
In an earlier presentation (1989 Annual Meeting of the Fine Particle Society, Boston, Massachusetts), a method for estimating the potential of wiping materials to contribute particles to clean environments was described. The research was predicated on the hypothesis that a wiper both releases particles already present on its surface and generates particles that do not yet exist but, in response to an applied mechanical stress, are created in some proportion to that stress. Also hypothesized was the existence of stress-strain curves for wiping materials, such that the number of particles released and generated per unit area of wiper is a function of the applied stress per unit area of wiper. The y-intercepts of these stress-strain curves, then, are interpretable as the number of particles released from a wiper under conditions of zero (or near-zero) mechanical stress. The authors gave a detailed description of a methodology for determining these y-intercepts and speculated on possible techniques for empirically determining the shape of the stress-strain curves.