deformatİon behavİour of polymerİc materials.pptx

7/30/2019 DEFORMATON BEHAVOUR OF POLYMERC MATERIALS.pptx

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Mechanical Behaviour Of

Materials

Deformation Behaviour of Ceramics and

Polymers

23.05.2013


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MECHANICAL AND DEFORMATION

BEHAVIOURS OF POLYMERIC

MATERIALS


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QUESTION 1

Explain how many type of polymeric materials

exist and what makes them different to each

other


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Types Of Polymers

Thermoplastic Elastomer Thermoset

Polymeric

Materials


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Types Of Polymers

Thermoplastics: Also known asa thermosofteningplastic, is a polymer thatbecomes pliable or moldable above a specifictemperature, and returns to a solid state upon

cooling. Most thermoplastics have ahigh molecular weight, whose chains associatethrough intermolecular forces; Thats mean thereis no crosslinking between chains, this property

allows thermoplastics to be remolded becausethe intermolecular interactions spontaneouslyreform upon cooling.


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Types Of Polymers

Thermosets: A type of plastic that is

permanently hardened by cooling.

Thermosets are heavily cross-linked.


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Types of Polymers

Elastomer: A formation of a thermoplastic or

thermoset that can stretch and then return to

its original shape without permanent

deformation. Elastomers are only slightly

cross-linked.


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Question 2

How many basic stress-strain curve can we see

for polymeric materials and explain what kind

of mechanical behaviours they will show.


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Stress- Strain Curves


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A: Glassy polymers (rigit region)

B: Amorf polymers (plastic region)

C: Elastomers


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Question 3

Expalin Maxwell, Voigt Models with your own

words. And scketch loading time graphic for

each model.


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Question 4

How many types polymeric structure can we

see and explain the deformation behaviour for

one of them.


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Polymeric structures

Amourphous: totally lacking positional order

on the molecular scale

Semicrystalline: containing both crystalline

and amorphous regions in the same sample


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Deformation behaviour of

Semicrystalline Polymers Firstly, the deformation is (visco-)elastic,which is caused by straining

the inter-lamellar amorphous domains

At yield, two lamellar deformation mechanisms occur, The firstmechanism is the chain slipthrough the lamellae, where after thesecond process of coarse slip of lamellae occurs

This intra-crystalline shear results in a fragmentation of the lamellae Subsequently, the lamellae disintegrate and their remains will be

transformed into a fibrillar phase coupled with the appearance ofvoids in the amorphous layers.

Upon further deformation, the fibrils stretch, causing the chains toalign and causing a lateral coalescation of voids, eventually resultingin a macroscopic crack due to breaking fibril


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Question 5

What is the shrink wrap? What is the material

of shrink wrap and what kind of polymer is

that? How can you explain the behaviour of

shrink wraps under heating via the changes of

microstructre


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Shrink wrap

Shrinkwrap, also shrinkwrap or shrinkfilm, is

a material made up of polymer plastic film.

When heat is applied, it shrinks tightly over

whatever it is covering. Heat can be applied

with a hand held heat gun (electric or gas) or

the product and film can pass through a heat

tunnel on a conveyor.


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Shrink Wrap

The most commonly used shrink wrap is polyolefin. It is available ina variety of thicknesses, clarities, strengths and shrink ratios. Thetwo primary films (polyethylene and polypropylen )can be eithercrosslinked, or non crosslinked. Other shrink films include PVC andseveral other compositions.

Polyethylene:

Polyproplene:


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Shrink Wrap

The molecules of a sheet or tube are randomly intertwinedlike a bowl of spaghetti. The molecules are coiled andtwisted and have no particular alignment. However when adraw force is imposed, the amorphous regions of the chainsare straightened and aligned to the direction of orientation.

By applying proper cooling, the molecules will be frozen inthis state until sufficient heat energy is applied to allow thechains to shrink back.

One can visualize this phenomenon by stretching a rubberband and dipping it into liquid nitrogen so as to freeze in

the stretched state. The band will remain in this state aslong as it is kept at sufficiently cold temperatures. However,when enough heat energy is applied, the rubber band willshrink back to its original relaxed state.


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deformatİon behavİour of polymerİc materials.pptx

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