Cyclic Load Testing of Steel Bars

1
Cyclic Load Testing of Steel Bars

• By Laurel Chun, Paul Knutzen, and Cynthia Shen.
• Spring 2001 CE 334 Prof. Xiao

2
Discussion Topics

• Background on cyclic loading tests
• Original procedure
• Problems encountered
• Modified procedure
• Discussion of results

3
Cyclic Loading Behavior Of Real Materials

• What is Cyclic Stress-Strain?
• Cyclic Stress-Strain relationships (two types)
• Cyclic Hardening
• Cyclic Softening

4
Cyclic Stress-Strain Graphs

• Cyclic Hardening
• Stresses increase with increasing number of
  cycles
• Cyclic Softening
• Stresses decrease with increasing number of cycles

5
Original Procedure
6
Problems Encountered

• Strain gauges which snapped off of the specimen.
• SATEC machine is unable to apply cyclic loads
• Extensometer slippage
• Difficulty in determining strain in plastic region

7
Modified Procedure

• Monotonic loading to failure
• Cyclic loading
• 3 elastic cycles
• 4 plastic cycles
• 1 loading to failure

8
Monotonic Loading
9
Cyclic Loading Stress-Strain in Elastic Region

• Slope E
• Extensometer errors
• Instrumental errors

10
Cyclic Loading Compiled Results

• Consistent slope
• Resemble monotonic behavior
• Reduced maximum stress
• Increased ductility

11
Comparison Between Monotonic and Cyclic Loading
Behavior
12
Conclusion and Future Recommendations

• Establishing strain correlations from strain
  gauges, extensometer, and loading plate
  displacement
• Continuous cyclic testing experiments
• Development and use of linear potentiometer to
  measure strain