## General Mechanical

#### Defining Fatigue Load in SMART crack growth simulation

• Sai Abhinav Jammi
Subscriber

Hi,

I have been trying to simulate the propogation of a premeshed crack in a spur gear using the 'SMART Crack Growth' module in ANSYS Mechanical. The problem I am facing is that, I cannot find where I can input the frequency of the cyclic loading that I want to apply.

Image 1 attached shows the definition of the load amplitude (Line Pressure) but it is taking as a constant load and not accepting tabular data. So I tried in Transient Structural, but the SMART Crack Growth is not supported in Transient structural. We don't have control over the number of cycles. Moreover, Number of cycles is obtained from the 'Number of cycles' probe.

I would greatly appreciate if someone could help me define this fatigue load properly by inputting the frequency.

Many Thanks,

Abhinav.

• peteroznewman
Subscriber

Hi Abhinav,

SMART crack growth for fatigue uses Paris’ Law to compute crack growth for a single cycle. SMART then tracks the growth and the number of cycles through the simulation.

If you set the Crack Growth Option property to Fatigue, your structure is subject to constant amplitude cyclic load.

A Stress Ratio of 0 means the load goes from 0 to 100%, which in your case is 600 N/mm. Your load graph shows a peak of 36000 N so I hope your tooth width is 60 mm wide.

SMART tells you how many cycles have occurred to get to a specific crack extension. Your load graph shows 2.5 cycles/sec or 2.5 Hz. That is not an input to SMART.  If you want to know how much time has elapsed for a specific number of cycles, divide the cycles by 2.5 to get the number of seconds.

For example, if the SMART probe on number of cycles shows 1e6 cycles, your load profile gets there in 1e6/(2.5*3600) = 111 hours.