City Guilds Model Questions Vol1 2024 Engineering Question 5

In the Materials laboratory a student carries out a tensile test on a cylindrical brass rod of unknown grade. The rod has a measured length of 200 mm. Its diameter is measured at three equally spaced points along the length giving 12.1 mm, 11.9 mm and 12.0 mm. The average diameter is to be used for all calculations. The specimen is loaded in a universal testing machine and the following load (N) and corresponding extension (mm) are recorded: | Load (N) | Extension (mm) | |----------|----------------| | 0 | 0.00 | | 2000 | 0.15 | | 4000 | 0.30 | | 6000 | 0.46 | | 8000 | 0.63 | |10000 | 0.82 | |12000 | 1.05 | |14000 | 1.35 | |16000 | 1.78 | |18000 | 2.40 | Using the data above, answer the following: a) Determine the cross‑sectional area of the rod (expressed to two decimal places in mm²). b) From the linear portion of the load‑extension curve (the first five readings), calculate the stress and strain for each of those points, and determine the Young’s modulus (E) of the material in GPa. Show the method used and give the final value to two decimal places. c) Find the ultimate tensile strength (UTS) of the rod using the maximum load recorded. Express the UTS in MPa to one decimal place. d) Identify two possible sources of systematic error in this experiment and suggest one practical way to minimise each error.