Stress–Strain Explorer

Aim: To investigate whether all materials stretch and break in the same way.

Specimen: gauge length 100 mm (0.100 m), cross-sectional area 1.0 × 10−4 m².

Specimen Material

Load

Press and hold to increase the force. Release to pause the test and take a reading.

Data Table

# Material Force, F (kN) Extension, x (mm) Stress (Pa) Strain Clear

Aim: To investigate whether all materials stretch and break in the same way.

Part A — Does every material behave the same way under load?

  1. Fit the mild steel specimen. Hold Load in short bursts, reading and recording the force and extension each time you pause, until the specimen fails.
  2. Repeat for copper, glass and rubber, recording at least four force–extension pairs for each material before it fails.
  3. Look at how each specimen actually failed. Did it neck, shatter, or snap? Are all four failures the same?

Part B — What does the loading behaviour of a material depend on?

  1. For each material, work out the stress and strain for every row in your table and sketch a rough stress–strain shape for each material, based on your own numbers.
  2. Which materials show a long stretch before they fail, and which fail suddenly with little warning?
  3. Based on your sketches, what property of a material seems to determine whether it fails suddenly or gradually?

Part C — How do the four materials compare quantitatively?

  1. For each material, use the straight-line part of your stress–strain data to find its gradient. What physical quantity does this gradient represent?
  2. From your table, identify — for each material — the stress at which your graph stops being straight (the limit of proportionality) and, where the specimen has one, the highest stress it reached before failure (the ultimate tensile stress).
  3. Rank the four materials from stiffest to least stiff, and from strongest to weakest, using your own figures.

Part D — What are the practical implications of these differences?

  1. Glass shows no plastic region at all before it fails. What does this mean for how safe glass is to use in a structure that might accidentally be overloaded?
  2. Mild steel and copper both neck visibly before they fracture. Why might this visible warning matter in engineering design, compared with a material like glass?
  3. Suggest one application where you would deliberately choose rubber's stretching behaviour, and one where you would deliberately avoid a material that gives no warning before it fails.