Dr. Alagiriswamy A A , (M.Sc, PhD, PDF) Asst. Professor (Sr. Grade),

1. Dr. Alagiriswamy A A, (M.Sc, PhD, PDF) Asst. Professor (Sr. Grade), Dept. of Physics, SRM-University, Kattankulathur campus, Chennai MECHANICS OF MATERIALS UNIT V Lecture 1

2. Outline of the presentation • Introduction • Fundamental mechanical properties • Stress-strain relation for different engineering materials • Introduction to Ductile materials /Brittle material

3. Types of Materials Ferrous Metals: iron and steel. Nonferrous Metals and Alloys: aluminum, magnesium, copper, nickel, titanium, super-alloys, beryllium, zirconium, low-melting alloys, precious metals. Plastics: thermoplastics, thermosets, elastomers. Ceramics: glass, graphite, diamond. Composite materials: reinforced plastics, metal-matrix and ceramic-matrix composites, honeycomb structures.

4. Materials Properties of Materials • Mechanical Properties: strength, toughness, ductility, hardness, elasticity, fatigue, creep, Brittleness, toughness, stifness, resilience, endurance etc. • Behavior Under Loading: tension, compression, bending, torsion, shear. • Physical Properties: density, specific heat, thermal expansion, thermal conductivity, melting point, electrical and magnetic properties. • Chemical Properties: oxidation, corrosion, degradation, toxicity, flammability.

5. Manufacturing Processes for Metals • Casting: expendable mold and permanent mold. • Forming and Shaping: rolling, forging, extrusion, drawing, sheet forming, powder metallurgy, molding • Machining: turning, boring, drilling, milling, planning, shaping, broaching, grinding, ultrasonic machining, chemical machining, electrical discharge machining (EDM), electrochemical machining, high-energy beam machining • Joining: welding, brazing, soldering, diffusion bonding, adhesive bonding, mechanical joining • Finishing: honing, lapping, polishing, burnishing, deburring, surface treating, coating, plating

6. Manufacturing a Product: General Considerations • Material Selection • Processing Methods • Final Shape and Appearance • Dimensional and Surface Finish • Economics of Tooling • Design Requirements • Safety and Environmental Concerns Manufacturing; “The Process of Converting Raw Materials Into Products”

7. Why Do Materials Differ in Their Mechanical Response ??? What Does our Experience Tell Us? • Bricks and glass do not deform and break easily. • Rubber bands deform a lot but return to their original shape • A paper clip easily deforms but does not easily return to its original shape • The thicker something is, the more force we have to exert to get it to break Central Questions • When do materials deform/break? • Why do they deform/break ? • How do they??

8. Internal/External stress relaxation is the key

9. A deeper approach Why don’t you think in terms of the chemical bonds and chemical structures that are present ENGINEERS NEED A WAY TO QUANTIFY THESE DIFFERENCES

10. Some Important Definitions Isotropy ; physical properties – direction independent. • Ex: Aluminum, steels/cast irons Anisotropy; direction dependent, • Ex: Various composite materials, wood and laminated plastics Elasticity; • able to regain its original shape/size after the deformation within the elastic limit (Hooke’s law) • Stress is linearly proportional to strain Plasticity; • able to permanently deform, after the stress is removed • Stress and strain no longer linearly related Yield strength (an important ENGINEERING parameter); • defines the stress at which plastic DEFORMATION begins (Al -370 Mpa, Steel-1500 Mpa, Cu 490 Mpa)

11. Different means of load applied

12. Quiz time • When a metal stretches, but does not break under a certain load, this point is called the _________ Point. A: yield B: tensile C: stretch D: ultimate strength

13. A close correlation/analogy Necking begins

14. Some terminology of the term “Strength” Elastic Strength; The strength value of a material , it s’ behavior changes from elastic to plastic regime Plastic Strength; plastic to rupture regime Tensile Strength; Ultimate strength corresponds to maximum load Compressive Strength; The value of load applied to break-off by crushing. Shear Strength; The value of load applied (specifically tangential load) Torsional Strength; The value of load applied (specifically twisting load)

15. Toughness Some More terms Resilience • property- stores energy and resists shocks or impacts Toughness Amount of energy absorbed by a material up to the fracture Endurance • property - withstand varying stresses or repeated application of stress. CREEPING; deformation increases even under constant load E.g..- Rubber stretching, concrete bridge Amount of energy absorbed by a material in the ELASTIC region

16. To be Precise ; A compelling competition between elastic and plastic deformation

17. Stress-Strain Relation for Different Engineering Materials ferrous metals Brittle; don’t exhibit yielding before failure non - ferrous metals

18. An another example Structural steel All dim. in mm

19. Yet another piece of information Polyamide

20. A deeper look on stress-strain curves

21. A close comparison Original/actual area for copper

22. The nominal stress σn = P/A0 where P is the force and A0 the original area of cross section • The nominal strain, εn = (L-L0)/L0 where L is the length of the original gauge length under force P, and L0 is the original gauge length. • Engineering stress/strain diagrams - elastic range, • while true stress – strain diagrams • plastic range.