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366 Fracture Mechanics: Fundamentals and Applications

(a)

(b)

FIGURE 8.8 Effect of specimen thickness on fracture toughness of plastics: (a) rigid PVC and (b) polycar-
bonate. Taken from Cayard, M., “Fracture Toughness Testing of Polymeric Materials.” Ph.D. Dissertation,
Texas A&M University, College Station, TX, 1990.

For common test specimens such as the compact and bend geometries, J is typically inferred
from the area under the load vs. load-line displacement curve:
η ∆
J = ∫ Pd∆ (8.26)
Bb 0
No
where
B = net thickness (for side-grooved specimens)
N
b = initial ligament length
o
η = dimensionless parameter that depends on geometry