## General Mechanical

#### Fatigue test

• Venugopal_thk
Subscriber

I have been working on the fatigue analysis of one of the three parts assembly with aluminum and steel materials.where I have to do calculation using the unit load with elastic materials and after that fatigue testing to be done.Load spectra with single Frequency.step1. N= 597, fact.Ampl. 6.060(6.000 kN)step1. N= 5, fact.Ampl. 12.9(12.9 kN) where survival probabilty is 90% .

• peteroznewman
Subscriber
I'm confused by the abbreviations you use: step1. fact.Ampl
Please state the load history completely and plainly. Define what one cycle is. For example is the load 0 kN, 6 kN, -6 kN, 0 kN, which is a fully reversed cycle, or is it 0 kN, 6 kN, 0 kN which is not a reversing load.
When you say a unit load, is one unit 1 kN or 1 N?
• Venugopal_thk
Subscriber
step 1: N= 597, fact.Ampl. 6.060(6.000 kN)
step2: N= 5, fact.Ampl. 12.9(12.9 kN)
where survival probabilty is 90% .
• peteroznewman
Subscriber
You didn't explain the meaning of the term: fact.Ampl.
So one cycle of fatigue loading will be (step 1 then step2) and that cycle will be repeated on the assembly until it fails.
You mention that you have a three part assembly and that the parts are made of steel and aluminum. Are the three parts held together with fasteners? Can you insert an image of this assembly in your reply?
What material data do you have for the steel and aluminum? Do you have Yield Strength and Ultimate Tensile Strength? Do you have S-N curves for each material? Do you have the Endurance Limit or Fatigue Limit strength values for each material?
When you apply 12.9 kN to the assembly, what is the maximum Equivalent Stress in each part? What is the maximum Max Principal Stress in each part?
Where is the maximum stress in each part? Can you insert an image of each part and show the location of the maximum stress?
• Venugopal_thk
Subscriber
Dear Peteroznewman The term Fact Amplitude is Max load .
Three part assembly looks like Tie rod held together by Nut and below is the Image As attached.I dont havethe information now and myself taking the default AL and Steel from Ansys workbench material data base. Yield Strength and Ultimate for AL is 280 MPaand 320 MPa. while for Steel as 600 and 780 MPa.
When I apply 12.9KN to the assembly I`m getting around 0.35MPa.MaxEquivalent Stress In each part is 0.35MPa and 0.2E-7 In other part. Max Principal occuring on the Outer side of Al Outer ball joint.
• danielmccusker
Subscriber
Dear Peteroznewman I am trying to simulate pedaling forces and the fatigue life of a pedal crank. It's is a simplified model but it is just about me getting used to how it works. I have rigid links representing the pedals and 2 forces at an angle.
However, I am having trouble simulating the pedal forces happening at different moments, as the two pedaling forces wouldn't act at the same time. One test cycle consists of the application and removal of the two test forces. I have set the fatigue loading type to zero-based, as the force would need to start at 0, go to its maximum, then back to 0. Then, once this first force returns to 0, the other one would start. Is there any advice you could give? Each end of the cylindrical pipe are fixed.
The above picture illustrates how the rigid links have been set up. This represents the pedals, and allows them to be modeled without actually modelling the parts. 2 downward forces (angled) have been applied at D and H.