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4 TESTING MATERIALS Properties of materials

4 TESTING MATERIALS Properties of materials. Classify and explore mechanical and electrical properties of materials Explain the meaning of the term intensive property , with examples Appreciate the need for log scales for representation of properties. Classifying materials.

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4 TESTING MATERIALS Properties of materials

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  1. 4 TESTING MATERIALSProperties of materials • Classify and explore mechanical and electrical properties of materials • Explain the meaning of the term intensive property, with examples • Appreciate the need for log scales for representation of properties

  2. Classifying materials • Look at the vast range of solid materials used in objects around you. • What general classes of material do they fall into? • Can you describe the internal structure of materials in these classes?

  3. Investigating breaking stress • Measure the breaking force and breaking stress for a material • Use “plot and look” to identify outliers

  4. Starter • How can we compare how strong/stiff different metals are when the wire samples we have are of different diameters for different metals? • Similarly, how can you compare how elastic/stretchy different metals are when the wire samples we have are of different lengths for different metals?

  5. Force extension graphs and Young’s modulus • Record and interpret a load-extension graph for copper • Make an accurate and precise measurement of the Young’s Modulus of a material, estimating the uncertainties involved

  6. Starter A wire of Material A fractures under a load of 100 N, while a wire of Material B fractures under a load of 10 N. Q1. What, if anything, can you conclude about the strengths of the materials A and B? Q2. What further information would you need in order to make a valid comparison between materials A and B?

  7. Stress, strain and Young’s Modulus • Define and then calculate these from experimental measurements

  8. Olympus Mons imaged by Mars Reconnaissance Orbiter, September 2009

  9. Measuring Young’s Modulus • Make an accurate and precise measurement of the Young’s Modulus of a material, estimating the uncertainties involved

  10. Stress strain curves • Describe and explain the stress-strain curves for metals, ceramics and polymers

  11. Note: Elastic limit and yield point are often very close to each other

  12. STRONG HARD TOUGH STIFF

  13. A These are microscope images of the fracture cross sections of rods of two different materials. A A B Which one has undergone ductile fracture, and which one brittle fracture? Explain your answer.

  14. Electrical properties of materials • Investigate the relationship between material dimensions and resistance • Derive equations linking resistance, conductance, resistivity and conductivity

  15. Measuring resistivity • Make an accurate and precise measurement of the resistivity of a material, estimating the uncertainties involved Starter: Write down the equation for working out the resistance R of a wire of length L and area A. Compare with the equation of a straight line. What should you measure and plot in order to determine the resistivity of the metal?

  16. Making measurements • Review key considerations relating to experimental measurement

  17. Uncertainty and Error How do they apply in this experiment? Random uncertainties • Identify sources of measurement uncertainty and quantify them. • Which contributes the most to the uncertainty in the final answer? Systematic errors • Identify limitations in the design of the experiment and explain how they could either be eliminated or reduced in effect.

  18. Accuracy and precision • Accuracy: how close your measurement is to the accepted value • Precision: what range of values does your measurement span? Accepted value = 110 • 108 +/- 4 • 125 +/- 2 • 111 +/- 9 • 85 +/- 40

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