Unit 27: Static Mechanical Principles Tutorial 6 Axial Stress & Strain 1. A bar of material with cross section area 60mm is subject to a tensile force of 180N, what is the tensile stress? 2. What is the percentage strain if a material of length 80mm is stretched to a length of 80.75mm? 3. A bar OD diameter 30mm and 50mm long is subject to a force of 120N and extends by 0.05mm, i) What is the direct stress? ii) What strain is the bar under? 4. A square section steel bar with side 30mm has a tensile strength of 600 M Pa. What is the maximum force it will withstand? 5. Polypropylene has a tensile modulus of 1.3 GPa. What strain will be produced by a stress of 4MPa? 6. A length of extruded PVC 3m long is extended 200mm by a force of 1.5x103 N. The tensile modulus for PVC is 3.1 GPa what is the cross sectional area of the material? 7. Steel has an elongation of 20 %, Cast Iron has an elongation of 1 %. If two identical bars one of steel & one cast iron (both 1.5m long) are stretched, what is the difference in their extensions? 8. A round, steel tube OD 50mm & ID 30mm is subjected to a tensile force of 1kN. What is the stress in the tube? (Area of a circle = r where r is radius) 9. A sample of carbon steel has a tensile strength of 400 M Pa and an elongation of 35%. A sample of Aluminium alloy has a tensile strength of 140 M Pa and an elongation of 10%. What does this tell you about the mechanical behaviour of the material (hint sketch graphs for stress-strain)? P ==stress A &===normal strain L P = Force Direct stress L= original length = Extension E = Strain E = Young's Modulus or Tensile Modulus