Download - Dynamic Mechanical Analyzer
DYNAMIC MECHANICAL ANALYZER (DMA)
BYDAVID SEHGAL
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.
Movable frame (main unit)
Fixed frame or base
Temperature control
DMA+450 MODEL
Construction of DMA
Upper part of DMADMA+450 MODEL
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.
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….
Mechanical testing
Configuration of specimen and specimen holder for different tests in DMA
Contd……
Compression platesTension 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 bendingDMA+450 MODEL
Viscoelasticity :- Viscoelastic materials exhibit characteristics of both viscous and elastic materialsEx.- 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 motionFlow TemperatureDefinition: point at which heat vibration is enough to break bonds in crystal lattice
Theoretical basis for DMA
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’
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
Working of DMA
Contd……
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
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
Continued…..
Correspondence between specimen holder and specimen shape
DMA+450 MODEL
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
Result
50 100 150 200 250 30010
100
1000
Temperature/oC
Sto
rage
Mod
ulus
/MPa
Loss
Mod
ulus
/MPa
Tan
Del
ta
10
100
Tg=213oC
0.0
0.1
0.2
0.3
0.4
0.5
DMA Graph
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
Testing of elastomer by DMA Specimen material Elastomer Specimen shape BarTest Compression testSpecimen holder Compression plates
Glass transition temperature
Thank you