3 11 MECHANICS OF MATERIALS F03 Lecture 33 Professor Christine Ortiz OFFICE 13 4022 PHONE 452 3084 WWW http web mit edu cortiz www IMPACT TESTING OF MATERIALS SUMMARY LAST LECTURE Multiaxial Yield Criterion Yielding takes place in 1D when Y where Y yield stress in uniaxial tension Define equivalent stress f p1 p2 p3 Yielding takes place in 3D when Y 1 Tresca or Maxmimum Shear Stress Criterion TRESCA 2 max p1 p3 Y 2 Von Mises Criterion 2 2 2 1 VM p1 p3 p2 p3 p3 p1 Y 2 VM 2 D p12 p1 p 2 p 2 2 Y Yield Locus YIELDED I UNYIELDED VI II V III IV TRESCA polygon VM ellipse Some More on Metal Plasticity http www msm cam ac uk doitpoms tlplib BD3 results1 php uniaxial tension Some More on Metal Plasticity uniaxial tension Some More on Metal Plasticity uniaxial tension Some More on Metal Plasticity Work hardening The process of plastically deforming a sample by rolling or drawing the material at low temperatures less than half the melting temperature Tm which increases the number of dislocations and the amount that they are entangled resulting in reduced ductility and increased hardness and strength Annealing is a heat treatment process that brings about a softer or more relaxed state in worked materials with an increased grain size IMPACT RESISTANCE AND TESTING BASIC DEFINITIONS SPEEDS Miles Hour Light 670 57 million Bullet 818 2727 Concorde 1336 Speed of Sound in Air 758 Boeing 747 566 World Fastest Helicopter 250 High Speed Bullet Train 170 Fastest Bird peregrine 100 200 falcon Car 100 Cheetah 70 Fastest fish sailfish 68 Fastest insect dragonfly 35 Snail 0 03 Pendulum Impact Tests Charpy Pendulum Impact Tests Charpy Pendulum Impact Tests The energy absorbed is equal to the loss in potential energy of the system according to Potential energy lost MgH sin 1 90 cos 2 Charpy Pendulum Impact Tests Drop Weight Impact Tests Drop Weight Physics Instrumented Impact Tests
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