Under the Guidance of:

Dr. Pradip K. Maji

Dynamic Mechanical Analysis

Or

DMA

What is it and what’s it all about?

Dynamic mechanical analysis (abbreviated DMA, also known as dynamic mechanical spectroscopy) is a technique used to study and characterize materials.

Dynamic Mechanical Analysis measures the mechanical properties of materials as a function of time, temperature, and frequency.

The DMA lets you relate

MATERIALBEHAVIOUR

Product PropertiesMolecular Structure

ProcessingConditions

Hmm…Seems Interesting..

let’s know about itmore deeply

What are Dynamic Mechanical Properties ?

Dynamic mechanical properties refer to the response of a material as it is subjected to a periodic force. These properties may be expressed in terms of a dynamic modulus, a dynamic loss modulus, and a mechanical damping term. Typical values of dynamic modulus for polymers range from 106 -1012 dyne/cm2 depending upon the type of polymer, temperature, and frequency.

DYNAMIC MECHANICAL ANALYZER

ButHow to analyze these properties ?

>> 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 STRAIN

how itworks???

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.

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

Configuration of specimen and specimen holder for different

tests in DMA

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

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

THEORITICAL

BASIS

Viscoelasticity :- Viscoelastic materials exhibit

characteristics of both viscous and elastic materials

Ex.- Elastomers, polymers etc.

Glass Transition TemperatureDefinition: Transition from bond stretching to long range molecular motion

Theoretical basis for DMA

Elastic vs ViscoelasticViscosity resistance to flow (damping)Elasticity ability to revert back to original shape

Flow TemperatureDefinition: point at which heat vibration is enough to break bonds in crystal lattice

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’

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

Determination of different

Moduli And their application

Let’s see and understandWhat are Storage Modulus, Loss Modulus and Tan δ……

Oscillation and response of a linear-viscoelastic material; δ = phase angle, E = tensile modulus, G = shear modulus, K = bulk compression modulus, L = uniaxial- strain modulus

F The complex modulus E* is the ratio of the stress amplitude to the strain amplitude and represents the stiffness of the material. The magnitude of the complex modulus is

These are dynamic elastic characteristics and are material-specific; their magnitude depends critically on the frequency as well as the measuring conditions and history of the specimen.

the storage modulus E´ represents the stiffness of a visco- elastic material and is proportional to the energy stored during a loading cycle. It is roughly equal to the elastic modulus for a single, rapid stress at low load and reversible deformation.

the loss modulus E´´ is defined as being proportional to the energy dissipated during one loading cycle. It represents, for example, energy lost as heat, and is a measure of vibrational energy that has been converted during vibration and that cannot be recovered.modulus values are expressed in MPa, but N/m2 are sometimes used.

The phase angle δ is the phase difference between the dynamic stress and the dynamic strain in a viscoelastic material subjected to a sinusoidal oscillation. The phase angle is expressed in radians (rad).

The loss factor tan is the ratio of loss modulus to storage modulus.It is a measure of the energy lost, expressed in terms of the recover-able energy and represents mech-anical damping or internal friction in a visco-elastic system. The lossfactor tan is expressed as a dimensionless number. A high tan value is indicative of a material that has a high, non elastic strain component, while a low value indicates one that is more elastic.

In a purely elastic material the stress and deformation are in phase ( = 0), that is, the complex modulus E* is the ratio of the stress amplitude to the deformation amplitude and is equivalent to the storage modulus E´ ( = 0, therefore cosine 0 = 1; sine 0 = 0, therefore E* = E´). Steel is an example of an almost purely elastic material. In a purely viscous material, such as a liquid, the phase angle is 90°. In this case, E* is equal to the loss modulus E´´, the viscous part.

Determining the glass transition temperature from the maximum loss tangent is fairly straightforward. Furthermore, the value agrees well with the temperature given by DMA step evaluation (linear plot, half height). Problems can arise, however, if the loss modulus maximum is not sufficiently accentuated.

In summary, it may be said that different methods of determining Tg yield different values for Tg. When a glass transition temperature is stated, therefore, it is absolutely vital to indicate the method of evaluation in addition to the experimental parameters.

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:

PolymersElastomersCompositesMetals and alloysCeramics, glassAdhesives

BitumenPaint and varnish Cosmetics OilsBiomaterials Leather, skin hair….

APPLICATIONS

OF

D.M.A.

Measurement of the glass transition temperature of polymers

Varying the composition of monomers

Effectively evaluate the miscibility of polymers

To characterize the glass transition temperature of a material

This table shows which DMA characteristics can be used to describe quality defects, processing flaws, and other parameters.

Application

Charachteristic

Example

Regions in which state is dependent on temperature

E‘ Energy and entropy-elastic region, start of melting

Temperature-dependent stiffness

E´, E´´, Tg , tan δ Elastic and non elastic response

Thermal limits on use Tg Start of softening or embrittlement

Frequency and temperature dependent

damping

tan δ (f) Response of damping elements

Application

Charachteristic

Example

Blend of constituents difficult to identify by DSC

Tg Impact-modification of Polyamid 6 through butadiene rubber

Influence of fiber reinforcement on mechanical

parameters

E´, E´´, tan G Anisotropic stiffness

Recycling, repeated processing, aging

T g1 , Tg2 Shift in butadiene Tg from ABS to higher temperatures

State of aging (conditioning) Tg Water content of PA

Degree of curing, postcuring Tg Tg rises, tan G falls, modulus rises

Thermal degradation Tg Tg falls

Thank you!Source: MAC.IASTATE.EDU GUIDE WWW.WIKIPEDIA.ORG TAINSTRUMENTS DMA+450 MODEL GUIDE WWW.PERKINELMER.COM WWW.SCHOLAR.LIB.VT.EDU DMA: A PRACTICAL INTRODUCTION by Hevin P. Menard