Learning Forum

[javat33489]

Hi all.

I've done a fatigue test and have questions.

I model a tungsten carbide drill tip that drills an SPG die, with a ring of solid body around the die for securing. The material of the die and ring is Mora-Columba concrete.

 

 

The units I use are: GPa, mm, ms.

The rotation of the drill is set at a speed of rad/ms.

 

I did a short calculation (2 hours), the drill rotated about 30 degrees during this time (the total solution to the problem was 60 hours).

I checked the d3plot file. Adequate stress:

 

Next, I decided to do a fatigue analysis to check what it would look like.

I got inadequate results:

 

 

 

1. The cumulative damage ratio is too high.

2. Expected Fatigue Life - too small, the elements will only last 235 seconds under load? But they drill with such a drill for many hours or even the whole day. Tungsten carbide is a very durable material with high density.

3. Expected fatigue cycles are generally empty. Why?

Help me understand the results, what could I have done wrong?

I also apply some basic fatigue tinctures:

 

SN curve for drill:

 

I also got this warning when I increased the starting point in the SN curve, I got the following results:

 

The damage has become less, it is gone, but the lifespan is still short.

 

PS. To reduce calculation time, I increased the density of the die, ring and drill by 4e10, can this make a difference? 

Please, help. Thank you.

[javat33489]

Colleagues.

I figured out one question regarding "1. The cumulative damage ratio is too high". The problem was in the material, I specified the compressive strength and removed the tangential modulus, because... it is unknown and the value was tested in detail.

 

But problems 2 and 3 remain:

2.Expected Fatigue Life - too small.

3.Expected fatigue cycles are generally empty.

 

 

 

Why is Expected Fatigue Life so small? Tungsten carbide is a very durable material. Compressive strength 6 GPa. The maximum stress according to calculations (d3plot) is 1 GPa.

There are no Expected fatigue cycles at all, why? Am I missing something?

Please, help.

[javat33489]

HELP PLEASE

[javat33489]

Guys, I decided everything again and transferred it, look, there are no cycles because the life is very small at the very bottom! why is that?

[igandiko]

Hello, how do the element stress results compare to the S-N curve? Do the elements showing low fatigue life have higher stresses/high damage ratio? 

The expected fatigue life is computed as exposure time (in time domain, it is defined by termination time by *CONTROL_TERMINATION, also see texpo paramter) divided by cumulative damage ratio.

Regarding your question 3, expected fatigue cycles are computed as "expected fatigue life" times “zero-crossing frequency with positive slope”. For d3ftg generated in a time domain fatigue analysis, only cumulative damage ratio and expected fatigue life are provided. There is no “zero-crossing frequency” so no “expected fatigue cycle” is provided.

[javat33489]

Hello, how do the element stress results compare to the S-N curve? Do the elements showing low fatigue life have higher stresses/high damage ratio?

 

- Sir, I have modified and simplified the SN curve for the test in this way, from the tensile strength of the material:

 

Mises stress:

 

 

*CONTROL_TERMINATION, also see texpo parameter

- Sir, there is no such parameter

 

 

Regarding your question 3, expected fatigue cycles are computed as “expected fatigue life” times “zero-crossing frequency with positive slope”. For d3ftg generated in a time domain fatigue analysis, only cumulative damage ratio and expected fatigue life are provided. There is no “zero-crossing frequency” so no “expected fatigue cycle” is provided.

 

- I understand sir, there will be no cycles. How then can I check the load, for example, for a task I will drill 10 mm, but I need to check the strength at 1000, how can I scale this? what maps or settings?

 

___

PS

 

Maybe I can upload a K-file here? Can you watch it?

[javat33489]

HELP PLEASE!