Dynamic Mechanical Analyzer
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Dynamic Mechanical Analyzer

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Dynamic Mechanical Analyzer Dynamic Mechanical Analyzer Presentation Transcript

  • DYNAMIC MECHANICAL ANALYZER (DMA)
    BY
    DAVID 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.
  • Construction of DMA
    Movable frame (main unit)
    Fixed frame or base
    Temperature control
    DMA+450 MODEL
  • Upper part of DMA
    DMA+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……
  • Tension jaws for film
    Tension jaws for bars
    Compression plates
    Tension jaws for bars
    Plane shear for films
    Plane shear
    Shear for liquid
    Shear for pasty material
    Dual cantilever
    Three point bending
    DMA+450 MODEL
  • Theoretical basis for DMA
    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
  • 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
    DMA+450 MODEL
    Correspondence between specimen holder and material of specimen
    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
    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
    Bar
    Test
    Compression test
    Specimen holder
    Compression plates
  • Glass transition temperature
  • Thank you