stretching is due to plastic deformation - SRJCsrjcstaff.santarosa.edu/~yataiiya/E45/LECTURE...

Strengthening mechanismsstretching is due to plastic deformation•

plastic deformation is due to Motion of dislocations•

to strengthen Materials, make it harder for dislocations to move.•

9-17-2014Wednesday, September 17, 2014 6:50 AM

ENGR45-strengthening mech

Example: Calculate 0 and Ky and estimate YS of a polyxrystalline brass with ASTM number 8

From interactive graph we find:

Solve:

Use M=1 and n=8, you get N=1.28x106

It means

•

So •


Effect of cold work on tensile stress-strain curve for low-carbon steel bars.

Pasted from <http://www.daldermaterialsconsulting.com/html/materials-engineering.html>

Work hardening, strain hardening, Cold working, more later

3)


http://www.daldermaterialsconsulting.com/html/materials-engineering.html

ppt hardening (or Age hardening)4)more Later.


Dislocations create Plastic deformation by "slip""SLIP" occurs as shear in slip system consisting of SLIP PLANE and SLIP DIRECTION.

In BCC, SLIP PLANE is (110) and SLIP DIRECTION is [111]In FCC, SLIP PLANE is (111) and SLIP DIRECTION is [110]

Both SLIP PLANE and SLIP DIRECTION are closed pack.

(6planes)*(2 directions) =12 systems


Slip system in FCC, (111) and [110)

(4 planes)*(3 directions) =12 systems


Schmid's factor


More on Cold working, Strain Hardening, work hardening.

Swaging

Extrusion

Forging

Sizing

Riveting

Staking

Coining

Peening

Burnishing

Heading

Hubbing

Thread rolling

Rolling

Angle bending

Roll bending

Draw and compression

Roll forming

Seaming

Flanging

Straightening

Bending

Slitting

Blanking

Piercing

Lancing

Perforating

Notching

Nibbling

Shaving

Trimming

Cutoff

Dinking

Shearing Tube drawingWire drawing•Spinning•Embossing•Stretch forming

•

Sheet metal drawing

•

Ironing•Superplastic forming

•

These are all examples of C.W:


*100


You are given a 2.5 mm diameter 70Cu-30Zn brass. It must a have a final diameter of 1mm with the following mechanical properties: T.S>450 Mpa, Hardness>75RB, and a minimum ductility of 10%. Describe a processing history to provide this results.

to have Hardness of more than 75 RB, the % C.W. should be more than 27%to have ductility of at least 10%, the %C.W should be less than 35%.

From Graph: to have T.S.>450Mpa, %C.W should be more that 20%.

So we should pick a %C.W. between 27 and 35. Lets decide on 30%C.W.If Final diameter has to be 1mm with 30%C.W., we can calculate the starting diameter:0.30 = (d2-12)/d2 solving for d: d=1.2 mmSo the process is: to cold work in several steps from 2.5 mm to 1.2 mm, followed by hot work, then cold work to final diameter of 1mm.OR: Hot work from 2.5 mm to 1.2 mm. Then cold work form 1.2 mm to 1 mm.

A Cu-Ni alloy is to be made with the following mechanical properties:T.S.>55 ksi, ductility of at least 42% and Y.S of approximately 28ksi.Suggest an alloy.

For T.S. to be more than 55ksi, the %Ni has to be between 45 to 85%.For ductility to be more than 42%, Ni has to be at least 50%.For the Y.S. to be 28 ksi, the Ni content has to be between 50 to 75 percentage.

ENGR 45, CW EXAMPLESA 3mm diameter brass wire of 85Cu-15Zn is cold worked 35%. What are the final diameter and the mechanical properties of the final product?Answer: 0.35 = (32-d2)/32 solving for d: d= 2.4 mmFrom graphs, the final product will have the following mechanical properties:Hardness = 73 RB, T.S. = 475 MPa, Ductility = 5%


For ductility to be more than 42%, Ni has to be at least 50%.For the Y.S. to be 28 ksi, the Ni content has to be between 50 to 75 percentage.

So to have all the listed mechanical properties, the overlapped %C.W is between 50 to 75% Ni. We will choose 75% Ni in order to have all the required properties and room for batch variation.NOTE: you also have to be aware of price of Ni!

CW example.

1-An 85-15 brass sheet (initial thickness = .5 “) is cold work to a thickness of 0.43”. What are the mechanical properties of the final products?

This is a take-home quiz. It will be emailed to you

Examples listed in the manual,

2- A 3.7” diameter brass rod (made from 70Cu-30Zn) is desired to be drawn into a 1.8” diameter rod with the following properties:

Hardness 70 RB, T.S 400MPa %EL 10%Is it possible to do this in one shot?If not, why and if yes, how? Show your reasoning.


NOTE: Cold-working followed by annealing is called Hot-Working


Formation of polygonized subgrains•Dislocation density is unchanged•Reduction in residual stress•Electrical resistivity decreases for AL and CU•Improvement in corrosion resistance•No change in grain size•

Initiated by Nucleation and Growth (N&G)•Results in smaller grains •Has important impact in welding•Rex temperature is between Tm/2 and Tm/3 depending on severity of CW.

•

Diffusion controlled (function of T and t)

Example:

Grain Growth:


Semester project from many moons ago

Note: t=24x60=1440 min.

Example:

Recovery RecrystallizationCrystal growth

Using n=2,a} calculate K and d0 at 600Cb} estimate grain diameter if sample is heated for 24 hrs at 600C


Semester project from many moons ago

Use of CW to improve fatigue properties: https://www.youtube.com/watch?v=_yOTga_3eTM1-Cold drawing tubes: https://www.youtube.com/watch?v=J3aLT2B2m3Y2-How it is made: nails and staples: https://www.youtube.com/watch?v=CUTTmtLKD2g3-Hot working steel sheet: https://www.youtube.com/watch?v=CUTTmtLKD2g4-

Extra resources:


https://www.youtube.com/watch?v=_yOTga_3eTM

https://www.youtube.com/watch?v=J3aLT2B2m3Y

https://www.youtube.com/watch?v=CUTTmtLKD2g

https://www.youtube.com/watch?v=CUTTmtLKD2g

stretching is due to plastic deformation - SRJCsrjcstaff.santarosa.edu/~yataiiya/E45/LECTURE...

Documents

Transcript of stretching is due to plastic deformation - SRJCsrjcstaff.santarosa.edu/~yataiiya/E45/LECTURE...