7) Mechanical properties of solids and tissues Flashcards

(37 cards)

1
Q

Interactions between molecules of solids

A

Molecules of solids interact through Van Der Waals forces

The spacing of molecules is 10^-10

Density of solids is larger

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2
Q

Spatial arrangements of molecules of solids

A

Determined by interaction forces between molecules

Most stable has minimum potential energy of interaction forces

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3
Q

Crystal lattice

A

An arrangement of points repeating periodically in three dimensions

They consist of identical unit class that fill the space of the lattice

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4
Q

Lattice order

A

Long range order
-arrangement of unit cells is continuous and unbroken

Short range order
-the crystal like structure is unbroken only for short distances

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5
Q

Single crystal

A

The crystal lattice is continuous and unbroken in the whole body

Single crystals are anisotropic 
-properties are directionally dependent 
. Mechanical strength 
.thermal conductivity 
.velocity of light
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6
Q

Polycrystals

A

Polycrystals- bodies made out of smaller monocrystals with random orientation

Polycrystals are isotropic- they’re homogenous in all directions

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7
Q

Amorphous bodies

A

No repeating structures

Isotropic in all their properties

No definite boundary between solid and liquid states =supercooled liquids

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8
Q

Classification of crystal lattices

A

230 space groups
32 classes
7 system

Polymorphism when a solid material can exist in more than one form of crystal lattice

Eg:carbon in graphite and diamond

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9
Q

Classification of crystal lattice 2

A

Ionic
Metallic
Molecular
Network (atomic)

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10
Q

Ionic crystal lattice

A

Salts have ionic crystal lattice

DRAWING
NACL

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11
Q

Metallic lattice

A

A sea of delocalised electrons around positive charge

.high electrical conductivity
.high thermal conductivity

Eg: zinc

DRAWING

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12
Q

Network crystal lattices

A

Elements in group 14 of the periodic table have network crystal lattices

eg:carbon

DRAWING

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13
Q

Molecular crystal lattice

A

Crystal lattice is made by interaction of weak Van Der Waals forces

Eg: ice, co2 bromine and iodine

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14
Q

Polymers

A

Long chains composed of repeating units called monomers

Protein is a naturally occurring polymer

Eg:cotton and skin

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15
Q

Properties of polymers

A

Strong and capable of large elastic deformations

Very viscous

Don’t exist in gaseous state

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16
Q

Conformations of polymers

A

Thermal motion and external forces cause reconfiguration of the polymer

17
Q

Liquid crystals

A

Liquid crystals

  • can flow
  • are anisotropic

Have narrow temp range

Properties are determined by structure or by shape

18
Q

Types of liquid crystals

A

Nematic
Smectic
Cholesteric

19
Q

Nematic

A

Long range orientational order

No positional order

20
Q

Smectic

A

Long range orientational order

Long range positional order In one direction

21
Q

Cholesteric

A

Arranged in layers

Orentiation is rotated by small angle from one layer to the next

Sensitive to external factors

22
Q

Deformation

A

Change in the size and shape of the body due to applied force

Mechanical properties of solids depend on their ability to resist deformation

23
Q

Types of deformation

A

Elastic
Then body recovers to its original shape and size

Plastic
Permanent deformation occurs

24
Q

Types of deformations 2

A
Classification:
Tensile 
Compression 
Bending 
Shear 
Twisting 

Examples
Muscles: stretching and compressing
Bones: stretching, bending and twisting

25
Mechanism of elastic deformation
The distance between molecules change Internal elastic forces arise trying to restore initial state
26
Mechanical stress
Ó= F/S F is deforming force S is area of cross section
27
Hooke’s Law
Applied stress ó and strain ę are directly proportional Ó= Eę E is Young’s modulus Strain ę=🔺L/L
28
Modulus of elasticity
E is Young’s modulus and is a temperature dependant constant Equal strain means higher stress in materials
29
Deformation is crystalline solids
DRAWING C is strength B is elastic limit A is proportional limit
30
Other mechanical properties
Plasticity and brittleness Hardness is determined by material resistance to scratching Strength is determined by ultimate strength
31
Deformation of polymers
Wrapping of long molecular chains is changed by deformation forces Tensile force strengthens chain
32
Elasticity of polymers
Rubber can experience strain of 300% without breaking but steel breaks at 0.3%strain
33
Creep
Is the time dependant time stress and strain Drawing x 3 F ę Ó
34
Bone tissue
Made from hydroxyapatite and collage in ration 2:1 Fast deformation due to hydroxypatite and collages due to creep
35
Skin
Main components Collagen 75% and elastin 4% Elastin stretches up to 300 Collage up to 10
36
Muscles
Built of elastin and collagen Deformation due to straightening of collagen molecules
37
Walls of blood vessels
High collagen means less elasticity and higher strength Elastin: collagen 2: 1 in carotid artery 1: 2 in the femoral artery