effect of strain rate and control method on the behavior of three aluminum alloys l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Effect of strain rate and control method on the behavior of three aluminum alloys PowerPoint Presentation
Download Presentation
Effect of strain rate and control method on the behavior of three aluminum alloys

Loading in 2 Seconds...

play fullscreen
1 / 30

Effect of strain rate and control method on the behavior of three aluminum alloys - PowerPoint PPT Presentation


  • 261 Views
  • Uploaded on

Effect of strain rate and control method on the behavior of three aluminum alloys. Rich Brazill Bob Sirkoch Alcoa Technical Center. Field problems. - Commissioning of new tensile testing equipment - 7175-T6511 extrusion material. Field problems. Field problems.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Effect of strain rate and control method on the behavior of three aluminum alloys' - daniel_millan


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
effect of strain rate and control method on the behavior of three aluminum alloys

Effect of strain rate and control method on the behavior of three aluminum alloys

Rich Brazill

Bob Sirkoch

Alcoa Technical Center

2007 May 21

field problems
Field problems

- Commissioning of new tensile testing equipment

- 7175-T6511 extrusion material

2007 May 21

field problems3
Field problems

2007 May 21

field problems4
Field problems

Problem likely related to improper PID control parameters.

2007 May 21

materials
Materials
  • Three sheet alloys:
    • 2024-T3
      • 0.094 in. thick
      • Medium strength, high elongation
    • 7075-T6
      • 0.016 in. thick
      • high strength, low elongation
    • 5182-O
      • 0.050 in. thick
      • low strength, very high elongation
      • exhibits discontinuous straining

2007 May 21

materials6
Materials
  • These aluminum alloys not usually considered strain rate sensitive, although discontinuous straining behavior is known to be influenced by strain rate.

2007 May 21

properties tabulated
Properties tabulated
  • Yield strength
  • Initial elastic slope
  • Stress rate during elastic deformation
  • Strain rate during elastic deformation
  • Strain rate at yield
  • Stress rate at yield
  • Time to reach yield
  • Machine stiffness at yield
  • UTS
  • Elongation at fracture*

2007 May 21

equipment
Equipment
  • Instron 4486 test machine, 60-kip capacity
  • 10-kip piggybacked load cell
  • Instron 2630-114, 2-in. 10% extensometer
  • Instron Series IX software (Bluehill did not have strain control module)
  • Instron universal joint
  • Alcoa Templin self-acting wedge grips
  • Load train diameter ~3/4-1 in.
  • Total load train length about 30 in.

2007 May 21

notes
Notes
  • Post-yield rate set to switch at 2% total strain.
  • Up to that point, strain is read from extensometer.
  • After that point, machine uses crosshead position to calculate an effective strain.
  • Elongation at fracture calculated from these data.
  • Force, strain, and time collected at 15 readings per second.

2007 May 21

strain rate control with series ix
Strain rate control with Series IX
  • From help files, we learned
    • Strain rate control is implemented as an outer control loop on crosshead speed, not actually direct strain rate control.
    • For strain rate control, you must tell the software at what stress you want to change to strain rate control.
    • Strain rate control will commence within 2 seconds of the test achieving the specified stress.
  • Apparently, up to that point, the system is gathering information about the specimen behavior in order to set up for strain control.

2007 May 21

strain rate control with series ix11
Strain rate control with Series IX
  • This makes sense because there are no operator-settable parameters for PID control to account for widely varying system stiffness due to different specimen and grip configurations.
  • It took us three tries to get the parameters set for the 5182 material. However, it seemed to control strain rate surprisingly well considering the discontinuous yielding behavior exhibited by this alloy.

2007 May 21

specimen
Specimen
  • 0.500 in. tapered-width sheet specimen
  • Parallel length: 2.25 in.
  • Overall length: 9 in.

2007 May 21

three control modes
Three Control Modes

Three duplicate specimens tested for each condition on each material

2007 May 21

slide14

Initial elastic slope

2024-T3

7075-T6

5182-O

2007 May 21

slide15

Strain rate during elastic loading

2024-T3

7075-T6

5182-O

2007 May 21

slide16

Stress rate during elastic loading

2024-T3

7075-T6

5182-O

2007 May 21

slide17

Yield strength

Trend to lower yield strength with strain rate control for all three alloys

2024-T3

7075-T6

5182-O

2007 May 21

slide18

Strain rate at yield

2024-T3

7075-T6

5182-O

Note SRC not at 0.015

2007 May 21

slide19

Stress rate at yield

2024-T3

7075-T6

5182-O

Note negative stress rates

2007 May 21

slide20

Time to yield

2024-T3

7075-T6

5182-O

2007 May 21

slide21

Apparent machine stiffness Km at yield

2024-T3

Machine stiffness at yield depends on material

7075-T6

5182-O

2007 May 21

slide22

UTS

2024-T3

7075-T6

5182-O

2007 May 21

slide23

Elongation at fracture

2024-T3

7075-T6

5182-O

2007 May 21

slide24

2024-T3

SRC

1

2

3

2007 May 21

slide25

7075-T6

SRC

1

2

3

2007 May 21

slide26

5182-O

SRC

1

2

3

2007 May 21

slide27

2024-T3

Std

SRC

Exp

2007 May 21

slide28

7075-T6

Std

SRC

Exp

2007 May 21

slide29

Note effect of strain rate on discontinuous yielding behavior

5182-O

Std

SRC

Exp

2007 May 21

conclusions
Conclusions
  • Strain rate control tests produced yield and ultimate results that were slightly lower on all three alloys than when using our “standard” constant crosshead speed based on stress rate.
  • Strain rate control changed the character of the discontinuous yielding exhibited by 5182-O material.
  • Strain rate control on 5182-O material worked better than expected even though it exhibits discontinuous yielding. However strain rate as we measured it went outside the limits in the yield region.
  • Machines improperly set up can produce undesirable results (like the observed drop in stress in yield region).
  • Because it doesn’t consider machine stiffness, use of the proposed crosshead rate based on 0.015 /min is too slow (5-7 times slower to get to yield) and should be discarded.
  • The “stress rate” method in the current standard was intended to account for machine stiffness problem with the previous point.
  • I believe that the stress rate method is misinterpreted by many users (ie, comments received during last ballot).

2007 May 21