November 16, 2018 at 8:20 amsaimaaz786Subscriber
I have a bean which is given time series data of force ( Amplitude is not constant with time) for fatigue analysis. When i expand the fatigue tool for rain flow matrix ,it ask for History data. Now my is question, what is this History data ?? Is is it the applied time vs force data or some thing else??? Kindly help me.Thanking you
November 16, 2018 at 6:45 pmSandeep MedikondaAnsys Employee
Hi, From the manual:
Maximum Data Points To Plot
November 17, 2018 at 1:45 ampeteroznewmanSubscriber
Here is a relevant discussion.
November 17, 2018 at 6:23 amsaimaaz786Subscriber
Dear Sir ,
First of all I would like to thank you for giving me your precious time.I got some idea about that but still confused. Once again i would like to explain my problem .I have a cantilever beam which is subjected to Aerodynamic load at the free end . This force was applied in the form of table (Time vs Force ,Rows =6000 ,Column =2) under the transient in order to evaluate the fatigue damage. Problem arises when I try to get damage matrix/rain flow matrix as for that History data is needed. Sorry i am asking very stupid question , From where i will get this History data??? Is it the time history of force??? or tabular load(TIME Vs Force ) which was applied to the free end of cantilever ???
November 17, 2018 at 6:25 amsaimaaz786Subscriber
November 17, 2018 at 4:12 pmpeteroznewmanSubscriber
The History data is the time history of the 6000 rows of applied force. What are the units used in the table of force? Let's assume they are in kN.
Build a Static Structural model and apply a 1 kN force to this model. This represents a unit force. Solve it. ANSYS now knows the stress for a unit force. Import the 6000 rows of force data in kN. Each row in the table will be a scale factor on the stress result for the unit force of 1 kN. So if the table has a 2.2 in it then the stress will be for 2.2 kN and if the table has a 0.42 kN value, the stress will be multiplied by 0.42 to represent that row of the table. The Fatigue Tool will assemble the damage matrix/rainflow matix by binning the 6000 rows of scaled stress into a smaller number of bins.
I hope this makes sense.
November 18, 2018 at 7:11 amsaimaaz786Subscriber
I followed your instruction as follow : (Please correct me if I am wrong )
Step 1 : I built static Structural model and applied a 1 kN force to the free end of the beam and ran the simulation.
Step 2: I Imported table (Time Vs Force history ) and applied to the free end of the beam and ran the simulation
Step 3: After step 2 , I opened fatigue tool for evaluating damage matrix /rainflow matrix .Here, under History data I attached Time history (Only) in the form of a text file and than reevaluated results.
November 18, 2018 at 4:03 pmpeteroznewmanSubscriber
Delete Step 2.
The results from Step 1 which has the 1 kN end load are used in Step 3 by the Fatigue Tool, along with a table of values of force in kN imported into the Fatigue Tool to compute the damage matrix / rainflow matrix.
November 19, 2018 at 6:56 pmsaimaaz786Subscriber
Dear Sir ,
Thank you Very much sir for your generous support. However, another sets of problems have emerged now. Sir, suppose I have a two different tables each having time force history and these tables are applied on the beam at the two different points. Now for computing damage matrix , which table shall i select for History data?? Because Under History data ,Its allowed to upload only one table.
Apart from this another questions is ,Is it possible to compute damage matrix/rain flow matrix in Mechanical APDL (Ansys 15.0) ??.
November 19, 2018 at 7:50 pmpeteroznewmanSubscriber
The Fatigue Tool is intended to simplify common calculations. You are describing an uncommon calculation that the Fatigue Tool was not designed to accommodate.
You should perform a Transient Dynamics simulation instead. Now both forces can be acting at the two locations over the duration of the test. You can output stress from as many locations as you want and perform a Fatigue Damage computation on each location.
Do you have matlab? There is a very useful and free GUI package called vibrationdata that includes Fatigue Damage calculations on time-history data.
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