Materials

Aim; To give examples of different materials and describe their properties.

Task1.Make a list of;a) Materials b) Words used to describe a material’s properties

Learning Objectives• ALL will (Grade D) name the different categories of materials and give

examples define keywords

• MOST will (Grade C/B) explain what properties each category of material has separate materials into natural and synthetic

• SOME will make connections between what the material is used for and it’s properties (Grade A/A*)

Keywords

• Brittle• Ductile• Malleable• Hard• Stiff• Tough

To Do; Find out what each keyword means

Types of Materials

• Metals• Glasses• Ceramics• Polymers• Composites

To Do; Research each category. Find out;1.Examples of materials that fit into the category2.What properties the materials in the category have3.Whether the material is natural or synthetic4.Any information you think may be useful

Extension Work

• Using what you have learned, decide which group of materials should be used for each item and explain your choice.

1. Bike frame2. Surfboard3. Baking tray4. Shopping bag5. Dentures

Useful Websiteshttp://ceramics.org/learn-about-ceramics/structure-and-properties-of-ceramicshttp://www.keytometals.com/page.aspx?ID=MetalProperties&LN=EN# http://www.technologystudent.com/designpro/metals1.htmhttp://www.lenntech.com/glass.htm http://glasstalks.com/2011/03/16/physicalproperties/ http://www.pslc.ws/macrog/mech.htm http://www.science.org.au/nova/059/059key.html http://www.astarmathsandphysics.com/a_level_physics_notes/materials/

a_level_physics_notes_differences_between_malleable_ductile_tough_hard_strong_and_brittle.html

Testing Materials

Aim; To carry out different tests on a range of materials

Task1.What are the different categories of material?2.Define the following keywords; a) Brittleb) Ductile c) Malleable d) Hard e) Stiff f) Tough

Learning Objectives

• ALL will complete the experiments and tabulate their results (Grade C)

• MOST will compare and contrast their results from different materials (Grade B)

• SOME will use their results to assess the properties of the materials (Grade A/A*)

Experiments Activity 10E Tensile Testing; Getting a feel for materials 1Activity 20E Compressive Testing; Getting a feel for materials 2Activity 30E Hardness Testing; Getting a feel for materials 3Activity 40E Tear Testing; Getting a feel for materials 4Activity 50E Measuring Density; Getting a feel for materials 5

Carry out the experiments on the different materials and record your results in a table

Write Up

1. Group the materials you tested using your results. Give reasons for your choices.

2. Analyse the method you used during your experiment. What are the possible sources of error? How could you reduce these? How could you improve the method? How could you improve, reliability, accuracy and precision?

Extension

Read 100T; Introduction to materials selection charts

File 5L (Interactive materials selection charts) File 10D (Materials Database)

1. How can these charts be used?2. What do these charts tell us about materials?3. Why are they useful/important?

Hooke’s Law

Aim; To explain what Hooke’s Law is and use it in

calculations

Task1. How can we test the properties of materials?

Learning Objectives

• ALL will collect data, state Hooke’s Law and use it in calculations (Grade D/C)

• MOST will explain what the graph shows and distinguish between elastic and plastic deformation (Grade B)

• SOME will use the idea of spring constant to explain how stiff a spring is (Grade A/A*)

Hooke’s Law

Force, F (N) = Spring constant, k (Nm-1) x Extension, Δx (m)

• The extension is proportional to stretching force up to the elastic limit

Elastic and Plastic Deformation

• BEFORE the elastic limit the spring behaves elastically – it will go back to it’s original shape once the force is removed

• AFTER the elastic limit the spring behaves plastically – it has been permanently stretched and will not return to it’s original shape

Experiment

• Collect a spring• Measure the length of the spring and record• Add masses to the springs• Calculate the extension and record

To Do

1. Draw a graph of load (y axis) and extension (x axis) 2. Label the following points on your graph and explain

what they meana) Elastic Limitb) Plastic deformationc) Elastic deformation3. Calculate the spring constant (k) of your spring. If you had data for two springs how could you

tell which one was stiffer? Explain your answer (Use ideas about Hooke’s Law).

Stress and Strain

Aim; To define stress and strain and calculate them.

Task1.What is Hooke’s Law?

Learning Objectives

• ALL will define stress and strain and calculate it (Grade C)

• MOST will distinguish between compressive and tensile stress and strain (Grade B)

• SOME will use stress and strain to make connections between other properties of the material (Grade A/A*)

Stress

• A measure of how strong a material is. • How much pressure an object can withstand

before undergoing physical change• Stress occurs inside the solid

Stress, ơ = Force, F (N) ÷ Cross-sectional area, A (m2)

• Measured in Nm-2 or Pa

Strain

• A measure of how much a material has stretched

• Putting pressure (stress) on an object causes it to stretch

• A ratio between extension and original length which has no units

Strain, ɛ = Extension, Δx (m) ÷ Original Length, L (m)

Compressive Stress and Strain

• Compression means to be squashed

• Compressive stress causes the object to decrease in length

• Compressive strain is negative.

Tensile Stress and Strain

• When an object is stretched

• Tensile stress causes the object to increase in length

• Tensile strain is positive.

Experiment

Compressive Stress and Strain• Make a cylinder with paper • Measure the original length • Calculate the cross-

sectional area• Add masses to it• Measure the length of the

cylinder• Record in a table• Calculate the stress and the

strain

Tensile Stress and Strain• Use an elastic band• Measure the original length• Calculate the cross-

sectional area• Add masses to it• Measure the length of the

band• Record in a table• Calculate stress and strain

1. a) Plot a graph for each of your results b) Do paper and elastic bands obey Hooke’s Law? c) What are the limitations of these experiments? d) How could you improve them?2. a) Compare and contrast the tensile strength of elastic

to the compressive strength of paper b) Using your results to assess what other properties

paper could have3. Look at the stress strain graph below. a) What properties do these materials have?b) What category of materials could they be?

ơ ơ

ɛɛ

Young’s Modulus

Aim; To calculate the Young’s Modulus of a material.

Task1.What is the definition and formula fora)Stress b) Strain2. What is the difference between tensile stress

and compressive stress?

Learning Objectives• ALL will complete the experiment, plot a graph

and use it to calculate Young’s Modulus (Grade D/C)

• MOST will explain what the graph shows in detail and explain why Young’s Modulus is a measure of stiffness (Grade C/B)

• SOME will explain the differences between stress strain graphs of ductile and brittle materials (Grade A/A*)

To Do

Activity 150E Good Measurements of Stiffness and Strength

1. Complete the experiment and record your results2. Plot a graph of stress (Y axis) against strain (X axis)

Young’s Modulus

• A measure of how stiff a material is• Can be found in the elastic region of a stress

strain graph

Young’s Modulus, E (Nm-2)= Stress, ơ (Nm-2) ÷ Strain, ɛ

Stress = F÷A Therefore E = FL ÷ AΔxStrain = Δx÷L

Before the limit of proportionality the material obeys Hooke’s Law and behaves elastically. At the limit of proportionality the graph starts to bend, but the material would return to it’s original shape if the stress was removed. After the limit of proportionality is the elastic limit. At the elastic limit the object begins to behave plastically and would not return to it’s original shape.

At the yield point the material begins to stretch without any extra load. The yield point is the stress at which a large amount of plastic deformation occurs.

The ultimate tensile strength/stress is the maximum amount of stress the material can withstand. Necking occurs after this point and cross-sectional area decreases.

At the fracture point or breaking stress, the atoms separate completely and the material breaks

Ductile Only

• Brittle materials do not plastically deform• UTS and Breaking Stress are the same

1. Plot a Stress (y)/Strain (x) graph and use it to calculate Young’s Modulus of your material

2. Label your graph OR sketch a diagram of your graph and label the following points and explain what they mean.

a) Elastic Region b)Limit of Proportionalityc) Elastic Limit d) Plastic Regione) Yield Point f) Ultimate Tensile Stressg) Breaking Stress3. Use diagrams to explain why Young’s Modulus is a

measure of stiffness3. Explain the differences you would see between a

stress strain graphs for brittle and ductile materials

4. Explain why a longer wire is better for finding the Young’s Modulus of a material.

5. Find out which materials are a)Strong in compression but weak in tensionb)Strong in tension but weak in compression

Strength and Toughness

Aim; To explain how the strength and toughness of a material is calculated.

Task1.How is Young’s Modulus calculated?2.Sketch a stress strain graph for;a) ductile materialb) Brittle material

Learning Objectives• ALL will use a graph to calculate the strength and

toughness of a material (Grade C)

• MOST will explain why the area under a stress strain graph indicates how tough a material is (Grade B)

• SOME will derive the equation for energy stored per unit volume using the equations for stress, strain and Young’s Modulus (Grade A/A*)

Strength

• The ability of a material to withstand stress• The points at which strength is measured are;

Yield Stress – Point at which plastic deformation begins

Breaking Stress – Point at which the material breaks

Breaking stress looks lower on a stress strain graph because the original cross-sectional area (CSA) is used to calculate strain. As the material is necking CSA is decreasing and stress increases.

Complete Q1 – 5 pg 87 Advancing Physics Textbook

Toughness

• A measure of how much energy the material can absorb before it breaks.

• Energy stored per unit volume can be found by calculating the area under a stress strain graph

Low energy per unit volume = brittle material

High energy per unit volume = tough material

Stress = Force ÷ AreaStrain = Extension ÷ Original Length

Area under graph = Stress x Strain = Force x Extension Area x Original Length

= Work Done Jm-3

Volume

Work done = Energy stored = Force x Distance

To Do

1. Calculate the energy stored per unit volume for the piece of wire you plotted a stress strain graph for

2. Complete Q6a) – c) on the print out pg 324 Advanced Physics 4U