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DYN AMIC MECHANICAL AN ALYSIS I TESTING MODES & APPLICATIONS
Dynamic Mechanical Analysis, DMA
DMA is the most common test type for measuring viscoelastic properties of materials. Both elastic and viscous characteristics of the material can be studied by imposing a sinusoidal
strain (or stress) and measuring the resultant sinusoidal stress (or strain) along with the phase difference between the two sinusoidal waves (input and output). The phase angle is
zero degrees for purely elastic materials and 90° for purely viscous materials. Viscoelastic materials exhibit a phase angle anywhere between these two ideal cases depending on the
rate of deformation. The figures below show these sinusoidal responses along with the variety of rheological parameters obtained. The viscoelastic parameters can be measured as a
function of deformation amplitude, frequency, time, and temperature and examples of each important experiment are provided.
Purely Elastic and Viscous Behavior
Strain
Stress
I
I
I
1
00% Elastic Behavior
Stra i n
Stress
1 00% Viscous Behavior
Testing Modes and Applications
16
Viscoelastic Behavior and Parameters
0·<11<90·
Strain
E"
E'
Stress
Rheological Parameters
•
E *
=
Stress * IStrain
•
E'
=
E *
•
cos /)
•
E"
=
E*
•
sin
/)
Viscoelastic Behavior
•
tan
/)
=
E" IE'