fatigue: strain-life workshop a12-2. workshop supplement fatigue module: workshop 12a-2 august 26,...

Fatigue: Strain-Life

Workshop A12-2

August 26, 2005Inventory

#002266WSA12.2-2

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement

Fatigue Module: Workshop 12A-2

Goals

• Goal: – In this workshop, a fatigue

analysis will be performed using the strain-life approach.

– A solid bracket, shown on the left, is constrained on one end and loaded on the other end.• A load of 1000 N is applied on

one end

• For fatigue calculations, 3000 N will be assumed

– Fatigue calculations using the strain-life approach is performed on the part.• A design life of 1e5 cycles is

considered


#002266WSA12.2-3

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Start Page

• From the launcher, start Simulation

• Change “Open” to “Workbench Projects,” and click on [Browse]

• Select the Workbench database “strain-based.wbdb” and click on [Open]


#002266WSA12.2-4

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Start Page

• The Workbench Project page will appear. Double-click on the Simulation icon (highlighted) to open the existing Simulation database– A stress analysis has already been set-up and solved for the bracket.

Only fatigue-specific steps will be covered in this workshop.


#002266WSA12.2-5

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Review Static Analysis Results

1. Review the mesh by selecting the “Mesh” branch– Note that a fine mesh is

specified at four corners of the bracket in anticipation of areas of high stress concentration

2. Inspect the loads and supports by selecting the “Environment” branch– One end is constrained while a

force of 1000 N is applied on the other end

3. View the static analysis results.– For example, select the

“Equivalent Stress” branch to view von Mises stress results

1.

2.

3.


#002266WSA12.2-6

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Review Fatigue Material Properties

4. Select “Solid” under the “Geometry” branchIn the Details view, click on the tab next to “Material: Structural Steel” and select “Edit Structural Steel…”– The “Engineering Data” module will appear (next)

4.


#002266WSA12.2-7

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Review Fatigue Material Properties

5. Select the curve icon next to “Strain Life Parameters”– The Strain-Life data will appear, as shown on the right, with the

following data:• “Strength Coefficient” is 920 MPa

• “Strength Exponent” is –0.106

• “Ductility Coefficient” is 0.213

• “Ductility Exponent” is –0.47

5.


#002266WSA12.2-8

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Review Fatigue Material Properties

– Under the “Display Curve Type” pull-down menu, “Cyclic Stress Strain” can be selected to plot the stress-strain curve, which uses the following data:• “Cyclic Strength Coefficient” is 1000 MPa

• “Cyclic Strain Hardening Exponent” is 0.2

– Note: In reality, although there are six parameters, only four are independent: n’ = b/c and H’ = ’f/(’f b/c)However, it is common practice to derive all six constants from test data and only satisfy this constraint approximately• -0.106/-0.47 = 0.2255 ≈ 0.2

• 920/(0.213^-0.106/-0.47) = 1303 ≈ 1000


#002266WSA12.2-9

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Specify Fatigue Options

6. Select the “Solution” branch and, from the Context toolbar, add “Tools > Fatigue Tool”

7. In the newly-added “Fatigue Tool” Details View, make the following changes:– Change “Type” to “Zero-Based”

– Change “Scale Factor” to “3”• This multiplies all static analysis results by a specified factor. While the initial

linear static analysis was carried out with a load of 1000 N, the fatigue calculations will be based on an applied load of 3000 N.

• This feature allows users to scale loads without having to re-run the static analysis, which may be more computationally intensive than the fatigue calculations.

– Change “Analysis Type” to “Strain Life”

– Leave “Mean Stress Theory” to “None”• For the first run, no modification of strain-life

based on mean stress will be accounted for.

– Change “Stress Component” to “Signed von Mises”

– Leave “Infinite Life” to “1e9”

7.


#002266WSA12.2-10

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Request Fatigue Contour Results

8. From the Context Toolbar, add the following fatigue results from “Contour Results”:– Life

– Damage

– Safety Factor

– Biaxiality Indication

8.


#002266WSA12.2-11

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Request Fatigue Contour Results

9. Select the “Damage” object and, in the Details view, change “Design Life” to “1e5”

10. Select the “Safety Factor” object and, in the Details view, change “Design Life” to “1e5”

9. and 10.


#002266WSA12.2-12

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Request Fatigue Graph Results

11. From the Context Toolbar, add the following fatigue results from “Graph Results”:– Fatigue Sensitivity

– Hysteresis

– Hysteresis

– Hysteresis

Request Hysteresis three times. In the Object Tree, there should be “Hysteresis,” “Hysteresis 2,” and “Hysteresis 3”

11.


#002266WSA12.2-13

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Request Fatigue Graph Results

12. Select “Hysteresis 2” and, in the Details view, change “Geometry” to the fillet shown on the bottom– Also change “Points per Segment” to “100”

12.


#002266WSA12.2-14

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Request Fatigue Graph Results

13. Similarly, select “Hysteresis 3” and, in the Details view, change “Geometry” to the fillet shown on the bottom– Also change “Points per Segment” to “100”

13.


#002266WSA12.2-15

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Perform Fatigue Calculations

14. Click on the “Solve” icon to initiate the fatigue analysis– Since the linear static analysis has already been completed, only the

fatigue calculations need to be run

15. Review fatigue results. – Plots of “Damage” using isolines is shown on the bottom.

• Note that the amount of damage present on the top and bottom fillets are close. This is because although the load is Zero-Based, there is no correction made for tensile vs. compressive stresses

• Both “Damage” and “Safety Factor” show that the current design life of 1e5 cycles will not be met.


#002266WSA12.2-16

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Review Fatigue Results

– “Hysteresis 2” and “Hysteresis 3” show the cyclic stress-strain behavior at the top and bottom fillets, respectively. As is apparent from the curves, the top fillet is in compression while the bottom is in tension. If “Signed Von Mises” were not used, both results would be the same since “Equivalent (von Mises)” is always positive.

Top Fillet Bottom Fillet


#002266WSA12.2-17

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Rerun Fatigue Calculations

16. Select the “Fatigue Tool” and change “Mean Stress Theory” to “SWT”– Mean stress correction will be accounted for both tensile and

compressive mean stresses

17. Rerun the fatigue calculations by clicking on the “Solve” icon

16.


#002266WSA12.2-18

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


Review New Fatigue Results

18. Review “Damage”– This example shows the difference of using no mean stress

correction with using SWT.

– Note that unlike the case with no stress correction, the top and bottom fillets report different amounts of damage. This is because the top is in compression and the bottom is in tension. With the SWT mean stress correction, compressive mean stresses increase life while tensile mean stresses decrease it.

Top Fillet Bottom Fillet


#002266WSA12.2-19

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Review New Fatigue Results

19. Select “Biaxiality Indication”– Select the “Legend” icon on the Context toolbar. The Legend dialog

box will appear, as shown on the right.

– Change “Max” value to “1” and “Min” value to “-1”

– Change the number of middle colors (+/-) to “3”

– Click on “OK”. The contour plot will be modified as shown on the next slide.

19.


#002266WSA12.2-20

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

AN

SY

S W

ork

ben

ch

- Sim

ula

tion

Workshop Supplement


… Review New Fatigue Results

– Values of “0” correspond to uniaxial stress, “1” indicates biaxial state of stress, and “-1” relates to pure shear state. This helps users to determine what the stress state is in different regions since the fatigue tests are done assuming a particular state of stress. For this example, the critical fillet regions report values near zero (green), so the fatigue assumptions may be valid if the fatigue testing was done on uniaxial specimens.

fatigue: strain-life workshop a12-2. workshop supplement fatigue module: workshop 12a-2 august 26,...

Documents