Dom intro
- 1. A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR Machine Design What is the importance of Machine Design for engineers? What is Machine Design? Creation of new and better machines AND Improving existing ones So that it is economical in the cost of production and operation.
- 8. A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR 3. Selection of MATERIALs Physical properties: Density, Melting point, Elec/thermal properties Mechanical properties: • STRENGTH – resist externally applied loads without breaking or yielding • STIFFNESS – resist deformation under stress • ELASTICITY – regain original shape once the force is removed • PLASTICITY – property which retains deformation (required for forging etc) • DUCTILITY – ability to be drawn into a wire by a tensile force • BRITTLENESS – sudden breaking with minimum distortion • TOUGHNESS – resist fracture due to high impact load • CREEP – deformation under stress and high temperature • FATIGUE – ability to withstand cyclic stresses • HARDNESS – resistance to wear, scratching, deformation, machinability etc Metal Non-metal Ferrous Non-ferrous
- 18. A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR Theoretical stress concentration factor, Kt Maximum stress at the discontinuity Nominal stress, max stress with no discontinuity Kt is used for normal stresses and Kts for shear stresses.
- 19. A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR Consider an elliptical hole in an infinitely large plate loaded in uniform tension. Using the theory of elasticity the theoretical stress concentration factor is given by the equation below. Elliptical hole 2b 2a • For a circular hole Kt = 3 • The equation can be applied to a longitudinal crack where b << a
- 20. Guidelines for design. Abrupt changes in cross-section should be avoided. Fillet radii or stress-relieving groove should be provided. Fig. 11.3(d) Slot and grooves should be provided with generous run-out radii and with fillet radii in all corners. Fig. 11.3(b) Stress relieving grooves or undercut should be provided at the end of threads and splines. Fig. 11.3(c) Sharp internal corners and external edges should be avoided Weakening features like bolt and oil holes, identification marks, and part number should not be located in highly stressed areas. Weakening features should be staggered to avoid the addition of their stress concentration effects, Fig. 11.3(d) Stress Concentration A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR