workshop 1: fatigue : stress- ?· 1 © 2015 ansys, inc. ansys fatigue module training – ws 1...

Download Workshop 1: Fatigue : Stress- ?· 1 © 2015 ANSYS, Inc. ANSYS Fatigue Module Training – WS 1 16.0…

Post on 26-Jun-2018

232 views

Category:

Documents

9 download

Embed Size (px)

TRANSCRIPT

  • 1 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    16.0 Release

    The Fatigue Module of ANSYS Mechanical

    Workshop 1: Fatigue : Stress-Life

  • 2 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Goal: In this workshop our goal is to perform a Stress-Life analysis of the

    connecting rod model (ConRod.x_t) shown here. Specifically, we will analyze two load environments: 1) Constant Amplitude Load of 4500 N, Fully Reversed and 2) Random Load of 4500N.

    Goals

  • 3 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Start Page

    1. From Analysis System, select Static Structural

    2. Import the Geometry:

    a. RMB on Geometry >Import Geometry>Browse

    b. Browse to the file ConRod.x_t to open it

  • 4 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Preprocessing [1]

    4. Set the working unit system:

    Units > Metric (m, kg, N, C, s, V, A

  • 5 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Preprocessing [2]

    6. Apply loads to the model:

    a. Highlight the connection rod surface shown b. RMB > Insert > Force c. Change Components and enter a magnitude of -

    4500N for the Z Component

    a.

    c.

  • 6 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Preprocessing [3]

    7. Add supports to the model:

    a. Highlight the bolt holes shown b. RMB > Insert > Cylindrical Support c. Set Radial = Fixed, Axial = Free, Tangential = Free d. Highlight the face on the connecting rod shown e. RMB > Insert > Fixed Support

    a.

    c. d.

  • 7 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Solution / Results

    8. Solve the model:

    Click Solve View the Results : a. Highlight the Solution branch b. RMB > Insert > >Deformation >Total c. RMB > Insert > Stress > Equivalent (Von-Mises)

  • 8 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Fatigue Tool [1]

    9. Insert the Fatigue Tool:

    a. Highlight the Solution branch b. RMB > Insert > Fatigue > Fatigue Tool

    10. Specify fatigue details :

    a. Specify a Fatigue Strength Factor (Kf) of 0.8 (material data represents a polished specimen and the in-service component is cast).

    b. Specify fully reversed loading to create alternating stress cycles.

    c. Specify a stress-life fatigue analysis (No mean stress theory needs to be specified since no mean stress will exist fully reversed loading).

    d. Specify that Von Mises stress will be used to compare against fatigue material data.

  • 9 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Fatigue Tool [2]

    11. Add results to the Fatigue Tool:

    a. Highlight the Fatigue Tool branch b. RMB > Insert > Safety Factor. c. From the Details of Safety Factor window, set the

    Design Life to 1e6 cycles.

    d. RMB > Insert > Fatigue Sensitivity e. Under the Details of Fatigue Sensitivity window,

    specify the following:

    Lower variation of 50% (an alternating stress of 2250N)

    Upper variation of 200% (an alternating stress of 9000N).

    f. RMB > Insert > Biaxiality Indication

    12. Click Solve to view results.

    c.

    e.

  • 10 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [1]

    Safety Factor

  • 11 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    13. Highlight and plot the Fatigue Sensitivity result for a minimum base load variation of 50% and a maximum base load variation of 200%.

    Results [2]

  • 12 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [3]

    14. Find the sensitivity of available life with respect to loading for a maximum base load variation of 400%. Note : must re-solve to obtain the new Fatigue Sensitivity results.

  • 13 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [4]

    15. Highlight and plot the Biaxiality Indication result. Note : The stress state near the critical location is not far from uniaxial (.1~.2), which gives an

    added measure of confidence since the material properties are uniaxial. Recall, a biaxiality of zero corresponds to uniaxial stress, a value of 1 corresponds to pure shear, and a value of 1

    corresponds to a pure biaxial state.

  • 14 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Fatigue Tool [1]

    16. Analyze a random load of 4500N: Note : Assume that we have strain gauge results that were collected

    experimentally from the component and that we know that a strain gauge reading of 200 corresponds to an applied load of 4500N

    a. Highlight the solution branch. b. RMB > Insert > Fatigue > Fatigue Tool.

    17. Specify fatigue details:

    a. Specify a Fatigue Strength Factor (Kf) of .8 (material data represents a polished specimen and the in-service component is cast).

    b. Change Loading Type to History Data c. Click inside History Data Location to open

    SAEBracketHistory.dat containing strain gauge results over time

    a.

    b.

    c.

  • 15 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Fatigue Tool [2]

    d. Define the scale factor to be .005 (we must normalize the load history so that the FEM load matches the scale factors in the load history file)

    e. Specify Goodman theory to account for mean-stress effects.

    f. Specify that a signed Von Mises stress will be used to compare against fatigue material data (use signed since Goodman theory treats negative and positive mean stresses differently).

    g. Specify a bin size of 32 (Rainflow and Damage matrices will be of dimension 32x32).

    005.gaugestrain 200

    load FEM 1

    gaugestrain 200

    1000

    1000

    load FEM 1

    lbs

    lbs

  • 16 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Fatigue Tool [3]

    18. Add results to the Fatigue Tool 2:

    a. RMB > Insert > Life b. RMB > Insert > Safety Factor c. Set the Design Life to 1000 cycles. d. RMB > Insert > Fatigue Sensitivity e. In the Details window for Fatigue Sensitivity,

    specify :

    Lower Variation of 50% (an alternating stress of 2250N)

    Upper variation of 200% (an alternating stress of 9000N)

    f. RMB > Insert > Biaxiality Indication g. RMB > Insert > Rainflow Matrix h. RMB > Insert > Damage Matrix i. From the Details of Damage Matrix window, set

    the Design Life to 1000 blocks

    19. Solve

  • 17 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [1]

    20. View Results:

    a. Highlight and plot the Life result.

  • 18 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [2]

    b. Highlight and plot the Safety Factor result for a design life of

    1000 cycles.

    If the loading history corresponded

    to the loading experienced by the

    part over a month time, the

    damage and FS will be at a design

    life of 1000 months. Note that

    although a life of only 77 loading

    blocks is calculated, the needed

    scale factor (since FS @ 1000=.60)

    is only .60 to reach a life of 1000

    blocks.

    Note, the scale factor (FS) is the

    scale factor for the loading to make

    it meet the life of 1000 months.

  • 19 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [3]

    c. Highlight and plot the Fatigue Sensitivity result for a minimum base load variation of 50% and a maximum base load variation of 200%.

  • 20 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [4]

    d. Highlight and plot the Biaxiality Indication result.

  • 21 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Results [5]

    e. Highlight and plot the Rainflow Matrix result.

    Here, one can see from the

    rainflow matrix that the

    majority of the cycle counts

    are for low mean stress and

    low stress amplitude (range).

  • 22 2015 ANSYS, Inc. ANSYS Fatigue Module Training WS 1

    Highlight and plot the Damage Matrix result.

    Results [6]

    Although, from the previous

    slide, one saw that most of

    the counts were for the low

    mean and range bins,

    these do not cause the

    most damage at the critical

    location, as shown in this

    damage matrix. Instead,

    the 'medium' stress

    amplitude cycles cause the

    most damage at the critical

    location.

Recommended

View more >