Tearing force-time curves

The most convenient way to distinguish between the two types of tear process is to do tear measurements at a constant rate separation using a trouser test-piece. The fluctuations of tearing force with rate will reflect the nature of the tear process. Typical tearing force-time curves for this type of tear measurement are illustrated in Figure 5.3. 

Figure 5.3 Schematic tearing force-time curves for constant rate of separation of trouser test-piece (a) steady (smooth) tearing, (b) stick-slip tearing, (c) knotty tearing.

There is another type of tear failure known as knotty tear, where the tear tends to deviate from the intended tear path and circles around almost perpendicularly, as shown in Figure 5.4. The tearing force-time chart corresponds to curve (c) in Figure 5.3. 

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