Applied Mechanics- Stress and Strain

STRESS STRAIN DIAGRAM MILD STEEL

The following salient points are observed on stress-strain curve: -. LIMIT OF PROPORT ONALITY(A) 2. ELASTIC LIMIT 3. UPPER YIELD POINT(B) 4. LOWER YIELD POINT (C) 5. ULTIMATE STRESS (D) 6. BREAKING POINT (E) TRUE CURVE UPPER YIELD 1 POINT ULTIMATE STRENGTH APPARENT CURVE FRACTURE prJA LOWER YIELD POINT ELASTIC LIMIT LIMIT OF PROPORTIONALITY STRAIN

Stress Strain Relation In Aluminum And High Strength Steel If loading is made within elastic limit, it follows a straight line parallel to the original straight portion as shown by F'F in the figure. Stress Thus, if it is loaded beyond elastic limit and the unloaded a permanent strain (OF) is left in the specimen Strength Rupture Yeild Strength This is called permanent set The strain p at which if unloading is made, there will be 0.2% permanent set is called 0.2% percent proof stress and this point is treated as yield point for all practical purposes. 0.002 Strain

STRESS STRAIN DIAGRAM FOR BRITTLE MATERIAL In brittle materials there is no appreciable change In the rate of strain. There is no yield point and no necking takes place. Ultimate point and breaking point are one or the Same The strain at failure is very small. STRAIN

HOOKE'S LAW Hooke's law states that, stress is directly proportional to strain upto elastic limit Let p be the stress and e be the strain, then p = Ee where, E = constant of proportionality of material called modulus of elasticity. ,p= and e- AB

ELASTIC CONSTANTS ELASTIC CONSTANTS FORMULA Modulus of Elasticity E= Modulus of Rigidity AV Bulk modulus ev Relationship between elastic constants E= 3K(1-28) 9KG 3K+G