Syed7777777
Mechanical
- Apr 2, 2024
- 3
Hi Everyone,
I'm trying to do a "Random Vibration Fatigue Analysis" on a bracket assembly that is mounted on the headboard of a pickup truck.
BACKGROUND:
The bracket assembly is mounted on the headboard of the truck using 2xbolts (1 per each mount). The truck regularly travels on a rough rocky terrain that causes a lot of vibrations. The bracket assembly has been failing before its expected life.
I'm trying to simulate this in FEA to identify the weak spots, compare the life suggested by FEA to what we're actually getting, modify the design accordingly, and then re-do the analysis.
HERE'S WHAT I'VE DONE SO FAR:
We bought a couple of tri-axial accelerometers and fixed them at the two(and only) mounts of the bracket assembly. Drove the truck through the rough terrain and recorded the vibration time-history data of both mounts in x, y and z directions.
After that, I converted each of the six 85-minute long time histories into FFTs and then converted FFTs to PSDs using DewesoftX.
Then using Abaqus, in the first step I ran a frequency analysis and extracted natural frequencies and mode shapes of the bracket assy. In steps 2-4 I ran 3x steady-state dynamic(modal) analyses in x, y and z directions with a "Unit Load Curve" of 9.81 amplitude to represent gravity.
I also selected the outputs for "Generalised Displacements and Phase Angles" which are used by Fe-safe.
I then imported the odb file in Fe-safe using the option of "Open Finite Element Model for PSD Analysis", imported the PSD file, and selected Polar(degrees).
After defining the materials to the groups, you get an option to define "length per repeat in seconds".
QUESTIONS:
1. Should I put 85x60= 5100 seconds in length per repeat?
2. If yes, then how do I relate or extrapolate that to get the actual(total) life of the bracket assembly if the truck travels through that terrain(represented by the 85-minute time history) 5 times a day, every day of the year?
3. Am I doing everything correctly?
4. Is there an easier/ better alternative to what I'm trying to achieve?
I would really appreciate elaborate and easy-to-understand answers without jargon.
Thanks.
I'm trying to do a "Random Vibration Fatigue Analysis" on a bracket assembly that is mounted on the headboard of a pickup truck.
BACKGROUND:
The bracket assembly is mounted on the headboard of the truck using 2xbolts (1 per each mount). The truck regularly travels on a rough rocky terrain that causes a lot of vibrations. The bracket assembly has been failing before its expected life.
I'm trying to simulate this in FEA to identify the weak spots, compare the life suggested by FEA to what we're actually getting, modify the design accordingly, and then re-do the analysis.
HERE'S WHAT I'VE DONE SO FAR:
We bought a couple of tri-axial accelerometers and fixed them at the two(and only) mounts of the bracket assembly. Drove the truck through the rough terrain and recorded the vibration time-history data of both mounts in x, y and z directions.
After that, I converted each of the six 85-minute long time histories into FFTs and then converted FFTs to PSDs using DewesoftX.
Then using Abaqus, in the first step I ran a frequency analysis and extracted natural frequencies and mode shapes of the bracket assy. In steps 2-4 I ran 3x steady-state dynamic(modal) analyses in x, y and z directions with a "Unit Load Curve" of 9.81 amplitude to represent gravity.
I also selected the outputs for "Generalised Displacements and Phase Angles" which are used by Fe-safe.
I then imported the odb file in Fe-safe using the option of "Open Finite Element Model for PSD Analysis", imported the PSD file, and selected Polar(degrees).
After defining the materials to the groups, you get an option to define "length per repeat in seconds".
QUESTIONS:
1. Should I put 85x60= 5100 seconds in length per repeat?
2. If yes, then how do I relate or extrapolate that to get the actual(total) life of the bracket assembly if the truck travels through that terrain(represented by the 85-minute time history) 5 times a day, every day of the year?
3. Am I doing everything correctly?
4. Is there an easier/ better alternative to what I'm trying to achieve?
I would really appreciate elaborate and easy-to-understand answers without jargon.
Thanks.