Type of load to find out fatigue life of a component

- April 29, 2020 at 11:58 am
  
  99siddharth99
  Subscriber
  
  I have a bent tube. One end is supposed to be fixed. A sinusoidally varying load is to be applied on the other end. I need to compute the fatigue life of the full component.
  
  I have a few doubts regarding applying the load. In my case, I am applying a remote force.The load should reverse from - to +. I have inserted the fatigue tool and defined fully reversed loading.
  
  The sinusoidally varying load function is 15000*sin(31.41592*time). The frequency of the load is 5Hz. The amplitude of the load is 15000N. Since I have already mentioned 'fully reversed' loading in the fatigue tool, which sort of load should I apply?
  
  (a) constant load with load amplitude of 15000N:
  
  or (b) function load 15000*sin(31.41592*time):
  
  Also, since my frequency of the fully reversed loading is 5Hz, I have defined under 'Life units' that 'units name' is 'seconds' and that 1 cycle is equal to 0.2 seconds (basically accounting for the 5Hz condition). Is this the right approach?
- April 30, 2020 at 2:32 pm
  
  99siddharth99
  Subscriber
  
  Sorry about the duplicate question. I'm new to the community and I will make sure I don't post such questions again.
- April 30, 2020 at 3:47 pm
  
  peteroznewman
  Subscriber
  
  In Static Structural, apply option a) 15000 N and in the Fatigue Tool, select fully reversed.
  
  You don't need a Mean Stress Theory, since the mean stress is zero.
  
  If the maximum stress at 15000 N is less than yield, the Analysis Type can be Stress Life in the Fatigue Tool.
  
  If the maximum stress at 15000 N is more than yield, the Analysis Type can be Strain Life in the Fatigue Tool.
  
  Those choices will only work if the required data is in the Engineering Material database for the selected material. See the Structural Steel example which has both.
- April 30, 2020 at 4:55 pm
  
  99siddharth99
  Subscriber
  
  In my case, the maximum stress at 15000N is lesser than yield. However I have Strain life material properties but not Stress life. So can I still proceed with using Strain Life analysis type even though my maximum stress is lesser than yield?
- April 30, 2020 at 5:01 pm
  
  peteroznewman
  Subscriber
  
  Yes, you can use Strain Life, it has a curve that spans both regimes.
- May 1, 2020 at 10:12 am
  
  99siddharth99
  Subscriber
  
  Also, is my frequency approach right? (i.e for a 5Hz load, I have stated that 1 cycle = 0.2 seconds)
- May 1, 2020 at 11:27 am
  
  peteroznewman
  Subscriber
  
  Yes, that should work.