August 27, Dr. Alagiriswamy A A, (M.Sc, PhD, PDF) Asst. Professor (Sr. Grade), Dept. of Physics, SRM-University, Kattankulathur campus, Chennai UNIT V Lecture 1 MECHANICS OF MATERIALS

August 27, Introduction Fundamental mechanical properties Stress-strain relation for different engineering materials Introduction to Ductile materials /Brittle material Outline of the presentation

August 27, 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.

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. Properties of Materials

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

August 27, 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” Manufacturing; “The Process of Converting Raw Materials Into Products”

August 27, 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 What Does our Experience Tell Us? When do materials deform/break? Why do they deform/break ? How do they?? Central Questions Why Do Materials Differ in Their Mechanical Response ???

August 27, Internal/External stress relaxation is the key

August 27, ENGINEERS NEED A WAY TO QUANTIFY THESE DIFFERENCES Why don’t you think in terms of the chemical bonds and chemical structures that are present A deeper approach

August 27, 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) Some Important Definitions

August 27, Different means of load applied

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 Quiz time

August 27, A close correlation/analogy Necking begins

August 27, 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)

August 27, 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. Some More terms Amount of energy absorbed by a material in the ELASTIC region Toughness CREEPING; deformation increases even under constant load E.g..- Rubber stretching, concrete bridge

To be Precise ; A compelling competition between elastic and plastic deformation August 27,

August 27, Stress-Strain Relation for Different Engineering Materials ferrous metals non - ferrous metals Brittle; don’t exhibit yielding before failure

August 27, All dim. in mm An another example Structural steel

August 27, Polyamide Yet another piece of information

August 27, A deeper look on stress-strain curves

August 27, A close comparison Original/actual area

August 27, The nominal stress σ n = P/A 0 where P is the force and A 0 the original area of cross section The nominal strain, ε n = (L-L 0 )/L 0 where L is the length of the original gauge length under force P, and L 0 is the original gauge length.  Engineering stress/strain diagrams - elastic range,  while true stress – strain diagrams plastic range.