MSC fatigue 实例-组件的疲劳分析

Solution Parameters
Open the Solution Params... form. On this form leave all the defaults except:
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Set Up the Fatigue Analysis
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Problem Description
Problem Description
A simple bracket as shown has a design life of 7 years (61,320 hours). Loading occurs at the end of the short section which has been welded and the component is constrained at both ends of the main bar. Because failure is known to occur at the weld, the finite element modeling at the loading point and the stresses found there can be ignored for the purposes of this exercise. The load applied in the model was 900 lbs total. In service, the component experiences loading of 3000 lbs in the direction of the finite element load and 7000 lbs in the reverse direction. This occurs once every 30 minutes. Only a 4% failure rate is allowed.
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Geometry
Quantity to Maximum Principal. Click the Apply button and note the areas of high stress mostly around the applied load. This however, is not of concern to us. What we are interested in is the stress at Node 514 of around 2,690 PSI. This will be explained in more detail as we set up the material information. To rotate the model, press the middle mouse button or for a two button mouse, press both at the same time. When you are done, press the Results switch again to close down the Results application form.
Set Up the Fatigue Analysis
1. Analysis: S-N 2. Results Loc.: Node This simply means that the fatigue lives will be determined at the nodes of the model. 3. Nodal Ave.: Global Accept the default which simply means element nodal stresses will be averaged to the nodes. 4. F.E. Results: Stress S-N analyses require stresses; you do not have a choice. 5. Res. Units: PSI Model dimensions are inches and forces are in Pounds, therefore stress units are PSI. 6. Jobname: comp_sn 7. Title: Component S-N Analysis
View the Stress Results
Before moving on to the fatigue analysis, press the Results application switch or tab on the main form to view the stress results from the MSC Nastran analysis. Select Stress Tensor, from the listbox and set the
Objective
• To introduce the concept of a component S-N curve. • To learn how to enter materials data into the database manager. • To determine if the component achieves its design life. • To determine what level of loading can be achieve and what failure rate could be expected - a
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Component S-N Analysis

Problem Description Geometry 139

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Set Up the Fatigue Analysis Run the Fatigue Analysis Review the Results Concluding Remarks 159 164
Certainty of Survival: 96
As we learned in the last exercise, the S-N data can have significant scatter associated with it. We are asking MSC Fatigue to calculate a fatigue live with 96% certainty of survival based on the scatter in the S-N data. This corresponds to a 4% failure rate. Click the OK button to continue.
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Geometry
Geometry
Invoke MSC Patran as you did in the previous examples. The geometry can be found in the file bracket.op2. The results are from MSC Nastran. Copy the file to your working directory. Open a new database in a clean, empty work directory from the File | New menu. Give the name bracket to the database.
Import the Model and Results
Press the Analysis toggle switch or tab on the main form. When the form appears set the Action to Access Results, the Object to Read Output2, and the Method to Both (model and results) then press the Select Results File button and select the file bracket.op2 and click Apply. The model will then appear and you are ready to set up a fatigue analysis.
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Geometry
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Set Up the Fatigue Analysis
Set Up the Fatigue Analysis
To begin setup for a fatigue analysis, from the Tools pull-down menu in MSC Patran, select MSC Fatigue and then Main Interface. This will bring up the MSC Fatigue main form from which all parameters, loading and materials information, and analysis control are accessed.
Material Information
The component was tested under constant amplitude, fully-reversed conditions to produce S-N data. In the previous examples we have used S-N curves that are representative of the material and independent of geometry. They related local stress (σ) to life. Now we have a different situation where the actual component geometry itself as well as the material has been used in tests to create the S-N curve. This type of S-N curve is called a component S-N curve. These type of curves relate nominal stress (S) to life and are dependent on the geometry of the component. If you change the geometry, the curve will no longer