Materials lecture 2

Materials lecture 2

1. Physical properties-melting point,density, conductivity, magnetic properties=determined by atomic structure, little affect by alloying

2. chemical properties= oxidation,corrosion

   • metals=combine=oxygen
     • altered by alloying,alloys=protective layer

3. mechanical properties-strength,hardness,ductility,malleability, stiffness, toughness

   • affect by:alloying,temperature,heat treatment, previous working

4. types of loading:torsion,shear,tension,compression, bending

5. TT

   • standard specimen-12.8mm diameter,50mm gauge length
   • elongate=constant rate,measure load+extension
     • stress= force acting/cross sectional area=N/m^2=Pa
     • strain=factional amount of deformation
   • Elastic def-regain exact shape=unloaded.
     • elas def=stiffness
       • linearly proportional behaviour=Hookes law=E(ym)=constant
         • Materials stiffness
           • little affect by alloying, all steel=similar YM.
   • plas def-permanent def after unloading
     • plas def=planes=slide over each other=dislocation movement.
     • yield stress, work hardening, UTS=change by HT or alloying

6. types of yielding

   • continuous- Cu, Al, Ni- no unique yield point-proof stress= used
     • Proof stress= intercept=stress Vs strain curve=line offset 0.002 from elastic line
     • volume=constant in plas def=specimen=uniformly longer+narrower
     • necking
   • Discontinuous(mild steel)- UYS/LYS, UPY-too irreproducible, LYS- Very reproducible=taken as yield stress
     • Luders bands occur at UYS then spread at LYS-subsequent def by work-hardening then necking
   • Work hardening=starts at yield stress

7. Ductility

   • withstand plas def=no rupture=tension
   • low ductility=deform little after yield point
   • Measured-%elongation or %reduction in area
   • decreases as its deformed at low Temps, =cold working-head to DBTT. Raise temp=significantly increases, impurities reduce ductility, grain size reduces too, extremely fine grains=converse=true

8. Malleability- shaping under compression=with out breaking=increased by heating