2. What is DMA?
DMA is a measuring instrument which is used to determine the
dynamic characteristics of materials.
It applies a dynamic oscillating force to a sample and analyze the
material’s response to that cyclic force.
Basically, DMA determines changes in sample properties resulting
from changes in five experimental variables: temperature, time,
frequency, force, and strain.
3. Movable frame (main unit)
Fixed frame or base
Temperature control
DMA+450 MODEL
Construction of DMA
5. How does DMA work?
The basic principle of this instrument is to exert a dynamic
excitation of known amplitude and frequency to a specimen of
known dimensions.
The measurement of strains and dynamic forces yields the
specimen's stiffness.
From the known geometry, one can derive mechanical properties
of the material, such as modulus and loss factor or damping.
The presence of the thermal chamber allows us to perform test at
different temperatures and thus determining materials' glass
transition temperature.
6. Which materials can be analyzed with DMA?
DMA instrument can be used to characterize mechanical and/or thermal properties of a
great numbers of materials:
Polymers
Elastomers
Composites
Metals and metallic alloys
Ceramics, glass
Adhesives
Bitumen (solid and pasty)
Paint and varnish (gels or films)
Cosmetics (gels, spray….)
Oils
Biomaterials
Leather, skin hair….
8. Compression plates Tension jaws for film Tension jaws for bars Tension jaws for bars
Plane shear for films Plane shear Shear for liquid Shear for pasty material
Dual cantilever Three point bending
Grips for Testing on MetraviB DMA
9. Viscoelasticity :-
Viscoelastic materials exhibit characteristics of both viscous and elastic materials
Ex.- Elastomers, polymers etc.
Viscosity resistance to flow (damping)
Elasticity ability to revert back to original shape
Elastic vs viscoelastic response
Glass Transition Temperature (Tg)
Definition: Transition from bond stretching to long range molecular motion
Flow Temperature
Definition: point at which heat vibration is enough to break bonds in crystal lattice
Theoretical basis for DMA
10. Continued….
sinusoidally applied stress
measured strain
phase lag between applied stress and measured strain
Complex dynamic modulus (E*)
• Ratio of applied stress to measured strain
E* = E’ + iE” = SQRT(E’2+ E”2)
Storage modulus (E’)
• Energy stored elastically during deformation
• “Elastic” of “viscoelastic”
• E’= E* cos
Loss modulus (E’’)
• Energy loss during deformation
• “Visco” of “viscoelastic”
• E” = E* sin
Loss tangent (tan ) or damping or loss factor
• shows the ability of material to dissipate the energy
• Tan = E’’/E’
11. Continued….
If phase lag is zero
then E*= E’ material is purely elastic
If phase lag is 90 degree
then E* = E” material is purely viscous
If phase lag is between 0 90 degree
then E* = E’ + iE” material is viscoelastic
12. 1. Preparation of specimen
Depending on the material to analyze, the specimen can be prepared in different ways: Molding, Cutting
As a general rule, common specimen dimensions range from a few millimeters to a few centimeters.
The use of a caliper is then advised. The use of a micrometer is preferred to measure film thickness.
Cutting
Venire caliper micrometer
Working of DMA
13. 2. Selection of specimen holder
On the basis of
- The nature of the material
- specimen shape
Correspondence between specimen holder and material of specimen
DMA+450 MODEL
Materials specimen holder
Elastromer (cylinder or bar) compression plates, plane shear
Elastomer (band) tension jaws for bars, tension jaws for films,
shear jaws for films
Polymer compression plates, tension jaws for bars, three
point bending, dual cantilever bending,
plane shear, shear jaws for films
Polymers (films) tension jaws for films, shear jaws for films
Polymers (fibers) tension jaws for fibers
Pasty bitumen shear for pasty material, shear for liquid materials
Metals, metallic alloys, ceramics three point bending, dual cantilever bending
15. 3. Installation of the selected specimen holder
4. Installation of the prepared specimen into the specimen holder
inside thermal chamber
5. Start temperature, finish temperature, and step
6. Application of dynamic excitation (stress or strain) on the specimen by
dynamic shaker through entire temperature range
7. Then DMA records the response of specimen and
determines: E’, E”, Tan
8. Identify transition temperatures based on noticeable changes in
curves
16. Typical Data from DMA
50 100 150 200 250 300
10
100
1000
Temperature/
o
C
StorageModulus/MPa
LossModulus/MPa
TanDelta
10
100
Tg
=213
o
C
0.0
0.1
0.2
0.3
0.4
0.5
Storage modulus (E’):elastic property
Loss modulus (E”) :viscous property
Loss tangent (tan )
A typical response from a DMA shows both modulus and Tanδ. As the material goes through its glass
transition, the modulus reduces and the Tanδ goes through a peak.
Tg indicated by major change in curves: Large drop in log E’ curve and Peak in Tanδ curve
