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DYN AMIC MECHANICAL AN ALYSIS I TESTING MODES & APPLICATIONS
Step Tests: Creep and Stress Relaxation
Step Tests, including Stress Relaxation and Creep Recovery, are so-named because the sample deformation or stress is applied in a step fashion. Both are highly sensitive tests for
measuring viscoelastic properties of materials. In creep and recovery, a constant stress is applied to the sample at tl and the resulting strain is measured over time. At t2 the stress is
removed and the recovery (recoil) strain is measured. The creep compliance, D(t), is calculated from the stress and time-dependent strain. In stress relaxation, an instantaneous strain
is applied to the sample and held constant. The resulting stress decay is measured as a function of time yielding relaxation modulus E(t) or G(t).
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Creep and Recovery
D
(t)
=
£
(t)/o
Time
Testing Modes and Applications
22
Stress Relaxation
E
(t)
=
0
(t)/E
Time