Scratch loading

Fig. 20 Critical scratching load L, macro-indentation failure load F and residual stresses SiC in the triple layer system, e. corresponds to the thickness of the Ta interlayer.

Scrape and scratch loading techniques Scrape loading. By scrape loading, adherent cells are scraped off their substratum with a cell scraper in the presence of the macro-molecule(s) (up to 500 kD mol weight) to be loaded (McNeil et al 1984). Thus loaded cells are obtained in suspension, and have to be replated and allowed to spread before microscopic observation. 

Scratch loading. Scratch loading is a variation of the scrape loading technique (Swanson and McNeil, 1987). An artificial wound is made on a cell monolayer with a sharp instrument in the presence of a solution of the molecule(s) to be loaded (up to 150 kD mol weight). Cells lining the edge of the wound are loaded. 

Figure 5. Measured scratch width as a function of scratch load.

Figure 13. Raman peaks collected from the SiC particles present within and away from the scratch grooves. Note peak shift to lower wave numbers with increasing scratch load...

Raman spectroscopy of SiC particles within the scratch groove indicated development of tensile residual stress which increased with increasing scratch load. 

Individual scratch is often done with a constant loading rate (which includes constant load) and constant scratch rate. The scale of damage of interest varies from macroscopic features to those of nanometer scale. This renders comparisons between studies difficult. The recent concerted industry-university effort (6,7,44) has led to the development of a scratch test method and universal scratch testing equipment to facilitate good scratch test practices and fimdamental study of scratch behavior of polymers. Figure 4 presents the scratch tester that was developed. It aims to provide reasonable capability to vary experimental conditions for capturing the essential scratch characteristic of the materials with reliable and reproducible results. One unique feature of the tester is its ability to alter scratch load and velocity at a linear rate. This feature is foimd to be useful in understanding scratch behavior of polymers, to be presented in later sections. 

Although the on-load depth is lower on sample 4 this does not necessarily represent improved tribological performance in this case. Examination of the curves show that during the on-load scratch the probe is pushed out of the material by cracking (e.g. by uplift at the edge of the scratch track which helps to support the scratch load) which leads to a lower final depth. This material is pushed up over the scratch track as observed in the final topography as shown in the figure 2b. 

Figure 12.7 ALS vs. SLS 0.7-mm-thick ion-exchanged glass ring-on-ring load to failure as a function of scratch load or say damage induced by scratch (according to Gomez ef a ., 2011 Glaesemann eto/., 2012).

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