Learning Forum

[kncujo]

Hi everyone,

I have a question about fatigue analysis with bolt preload and a constant amplitude load.

To get results with Ansys Fatigue Tool I proceeded in this way.

I divided the simulation into two steps:

1. Static simulation with only bolt preload on the structure

2 I add a torque load on the structure.

3 Solution combination between this two steps, I subtract the results of the first step from the results of the second step

Now i want to use the fatigue tool and assign a constant amplitude load for the solution combination and a constant load for the bolt pretension, or, at least, only the constant ampitude load for the solution combination to evaluate the demage on my tructure.

Is this a good approach?

I want to use the same method using Ncode design life, but I have a problem, when connecting "static structural" with "ncode" the combined results obtained with solution combination are not passed to ncode.

How can I import the combination in Ncode?

Thanks very much for any help.

[Dragana Jandric]

You will not be able to pass stress combinations from Mechanical to nCode. nCode has duty cycles under load mapping for the load step combinations. You can read more about it in the nCode help and there are also examples in the nCode practice guide. Here are few slides to get you started.

[danielshaw]

Ansys nCode DesignLife cannot read results from a Mechanical Solution Combinations because they are not stored in the results file (file.rst).They are calculated on-the-fly in Mechanical.However, you do not need to use Solution Combinations with Ansys nCode DesignLife to evaluate fatigue life for a bolted closure with a preload.
You can use a duty cycle, but it is not necessary for this loading.You can simulate the described loading using a Constant Amplitude Load Mapper.If you connect a Constant Amplitude DesignLife system to the solution cell of Mechanical, DesignLife will automatically import the 2 result sets (preload and torque). Inside the load mapper, set the min and max values for the preload case to both be 1.0 (load does not alternate), and set the min and max values for the torque case to be whatever you want (e.g., 1.0 and -1.0 for fully reversing or rratio = -1).

[kncujo]

Thanks for the answers.
This is exactly what I want to do but in the first result set i have only pre-load, in the second result set there are both pre-load (lock) and the torque. So with the approach that you described the pre-load stress will double, am I wrong?.

[Anand Kumar]

Hi , have you got the answer for substracting preload from torque in ncode ?