pwr pt science bridge gap materials

8/7/2019 Pwr Pt Science Bridge Gap Materials

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The Final Test

Before the opening ceremony in 1859, theVictoria Bridge underwent a safety test.

The test consisted of an 18 platform cart train filledto capacity with rocks crossed the bridge. The

train and load weighed about 1 ton/foot.

The two locomotives hired to pull the train across

were insufficient and a third was required.

In spite, of all this weight, the deflection (bending)

of the bridge was a little over 1 inch and returned

to normal as the load was removed.


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The Victoria BridgeA quick overview of the Tubular design


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Situation

The Victoria Bridge was a technological

marvel, yet the engineers in chargeknew less about materials than we do

today.

Justify which material you would have

chosen for the project.


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What to consider?

What should one consider before

selecting the construction materials?


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What to consider?

What are the stresses/external forces thematerial will undergo? (Constraints)

How do we want the material to react to suchstresses? (Deformation)

How will the material react? (Material

properties)

Will the material last a long time?(Degradation)


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Constraints

What external forces are at play?


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Constraints

A constraint is the effect external forces

have on a material/object/system.

Examples of constraints:

Pulling an elastic band

Squishing a sponge


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Types of Constraints

There are 5 main types of constraints

Compression

Tension Torsion

Deflection

Shearing

Using the definitions soon to be provided, can you give a

common everyday example for each of these constraints?


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Types of constraints

Compression:

When a material is subjected to forces that

tend to crush it

Tension

When a material is subjected to forces that

tend to stretch it


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Types of Constraints

Which constraints would a bridge most likely

be subjected? Explain your reasoning.

5 Constraint reminder:

Compression

Tension

Torsion

Shearing

Deflection


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Deformation

Ways that materials react to the

constraint


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Deformations

A material deformation is the change in

shape of a material based on the constraints

that are applied.

There are three main types of deformations

Elastic

Plastic Fracture

Using the definition soon to be provided, can you give a

common everyday example for each of these

deformations?


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Types of material deformation

Elastic:

When the constraint leads to a temporarychange in the shape or dimensions of thematerial.

When the constraint is removed, thematerial returns to its original form.


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Types of material deformation

Plastic:

The constraint leads to a permanent

change in the shape or dimensions of the

material.

Even when the constraint is removed, the

material remains deformed


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Types of Material Deformation

Fracture:

The constraint is so intense that it breaksthe material


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Types of Deformations

What are some of the deformations that

a bridge is likely to undergo?

Explain your reasoning.


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Properties

Characteristics that will help

determine how a given materialwill react to a constraint.


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Properties

The reaction of a material to constraints depends onits mechanical properties.

Types of Mechanical Properties: Hardness

Elasticity

Resilience

Ductility

Malleability

Stiffness

Which properties do you believe were considered inthe selection of the building material for the Victoria

Bridge?


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Definition of mechanical properties

Hardness

Ability to resist indentation

Elasticity:

Ability to return to their original shape

Resilience:

Ability to resist shocks


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Ductility:

Ability to be stretched without breaking

Malleability:

Ability to be flattened or bent withoutbreaking

Stiffness:

Ability to retain their shape when subjectedto many constraints

Definition of mechanical properties


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A material can also undergo chemical

changes, such as rusting and corrosion.

What kind of properties should a bridge

possess?


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Other properties

Resistance to corrosion:

Ability to resist the effects of corrosivesubstances which cause the formation of rust,

for example.

Electrical conductivity:

Ability to carry an electric current

Thermal conductivity:

Ability to transmit heat


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Degradation

How will a material age?


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Degradation

The degradation of a materials is the

decline in some of its properties due to

its environment or time


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Degradation of the Victoria Bridge

In 1897 the Victoria bridge was

renovated

To accommodate the increase in thedemand of transportation

To repair the degradation of the bridges

superstructure. The piers only required

minor changes.


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Common materials used in the

1800s


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Wood

Wood is a ligneous (fibrous) material whosebark has been removed.

The mechanical properties differ dependingon the type of wood

Two types of wood Hardwood (deciduous trees)

More resistant to wear and harder than softwood

Softwood (coniferous trees)


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Wood (general properties)

Hardness, elasticity, resilience

Low thermal conductivity

Easily shaped and assembled Light weight

Would these properties be useful duringthe construction of a bridge?


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Wood degradation

Due to its organic nature, fungus,

insects and micro-organisms can infest

the wood.

By varnishing, painting or treating the

wood, we can extend its lifetime.


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Metals

Metals are not usually used in their pure

form, but are combined with other

substances to improve their properties.

This mixture is called an alloy

(homogeneous mixture of two or more

metals)


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Metals (properties)

The properties vary on the metal used

Out of the list provided to you, which metal or alloywould you consider in the construction of the

Victoria Bridge. Justify your answer.


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Please keep in mind

The Victoria bridge is a Tubular Bridge

It is 6 592 feet in length

The superstructure alone weighed 9044 tons. That is 8 204 578.79 kg

Due to the use of the steam engine, temperatures

inside the tube could reach up to 125 F That is 52 Celsius


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Metals Description Properties Cost *

Aluminum White Malleability 2.508$/kg

Soft Lightness

Abundant in nature Resists corrosion

Very good electrical

conductor

Iron Silver in color Ductility 0.21$/kg

Can rust in the

presence of Oxygen

Malleability

Nickel Grey Hardness 1.43$/kg

Malleability

Resists Corrosion

Tin Silvery white Ductility 16.214$/kg

Malleability

Relatively low melting point

(239C)


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Alloys Description Properties Cost*

Cast iron (iron

and carbonmixture)

Made of more than 2%

carbon

Hardness 0.18$/kg

Steel (iron and

carbon

mixture)

Made of less than 1.5%

carbon

Hardness 0.52$/kg

Resilience

Malleability

Brass (copper

and steel)

Mixture of copper and steel

Color varies according to

mixture

Ductility 2.37$/kg

Malleability

Resists Corrosion

Excellent electrical

conductivity

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