  Static and dynamic analysis of the fracture tests of fiber composites in
hydraulically servo-controlled testing machines currently in use shows that
their grips are much too soft and light for observing the postpeak softening.
Based on static and dynamic analysis of the test setup, far stiffer and heavier
grips are proposed. Tests of compact-tension fracture specimens of woven
carbon-epoxy laminates prove this theoretical conclusion. Sufficiently stiff
grips allow observation of a stable postpeak, even under load-point
displacement control. Dynamic stability analysis further indicates that stable
postpeak can be observed under CMOD control provided that a large mass is
rigidly attached to the current soft grips. The fracture energy deduced from
the area under the measured complete load-deflection curve with stable postpeak
agrees closely with the fracture energy deduced from the size effect tests of
the same composite. Previous suspicions of dynamic snapback in the testing of
composites are dispelled. So is the previous view that fracture mechanics was
inapplicable to the fiber-polymer composites.
