City Guilds Model Questions Vol1 2017 Engineering Question 5

A student is carrying out a tensile test on a cylindrical steel specimen using a universal testing machine. The specimen has a gauge length of 100 mm and an original diameter of 10 mm. The machine records the applied load (N) against the extension (mm) at intervals of 0.5 mm up to fracture. The recorded data are shown below. | Extension (mm) | Load (N) | |----------------|----------| | 0.0 | 0 | | 0.5 | 1500 | | 1.0 | 3000 | | 1.5 | 4400 | | 2.0 | 5600 | | 2.5 | 6600 | | 3.0 | 7200 | | 3.5 | 7500 | | 4.0 | 7700 | | 4.5 | 7800 | | 5.0 | 7850 (fracture) | Using the data above, answer the following: a) Determine the load at the proportional limit of the specimen by applying the 0.2 % offset method. Show clearly how the offset line is constructed and identify the corresponding load. b) Using the load obtained in (a), calculate: i) the engineering stress (in MPa) at the proportional limit, ii) the engineering strain at the proportional limit, iii) the Young’s modulus (in GPa) assuming the stress–strain relationship is linear up to the proportional limit. c) After fracture the final diameter of the broken specimen is measured as 8.0 mm. Calculate the percentage reduction in area. d) Identify two possible sources of systematic error in this tensile test and suggest one practical way to minimise each error.