smjanows
Mechanical
- May 18, 2012
- 1
I am trying to perform a bolted joint analysis on a tuning fork, but first just trying to get the hang of bolted joints in general in Workbench 14. From what I've read I thought I had the correct contacts, etc., but apparently not.
I modeled a simple case of two plates with four screws in Inventor 2012. I have tried both content center screws and manually created dumbed down ones which have better contact geometry. In both cases I am having problems. There must be a disconnect with my understanding of how ANSYS is treating this.
In the attached image you can see my setup:
1. The top plate is called Clearance Holes
2. The bottom plate is called Tapped Holes
I have the following contacts:
1. No separation between the four faces between the top and bottom plates.
2. Bonded contact between the top face of the clearance holes plate and the mating surface of the screw head.
3. Bonded contact between the cylinders of threaded portion of the screws, and the tapped hole cylinders: One surface per fastener and hole. I modeled the fasteners with a nominal diameter shank, and a minor diameter thread to match the tapped hole size. The clearance hole is bigger than the shank diameter.
4. There is a frictionless constraint between the screw shank and the clearance hole. The results were the same with this suppressed.
Constraints:
1. The two symmetric outer holes are pinned on the top surface (part of the clearance holes plate). The tangential direction is free on both, and axial is free on one.
2. The center hole has a load in the direction that would pull the parts apart.
3. The shank of the fasteners has a bolt pretension applied - this is what is causing problems.
Solution:
With no bolt pretension, the plates pull apart (more so in the center) as expected with the load.
With the bolt pretension applied, all goes to hell. The displacements instead of being near 0 as expected are extremely large. This occurs whether the bolt preload is 1000 lbs or just 1 lbs. What am I missing? Are my contacts incorrect?
I am also concerned about a rigid body motion warning. I replaced one of the pinned supports with a fixed support and still get the same results. I think it's showing a rigid body warning due to the large deflection.
Anyone has any ideas as to what is going on and why?
Thanks,
Sebastian
I modeled a simple case of two plates with four screws in Inventor 2012. I have tried both content center screws and manually created dumbed down ones which have better contact geometry. In both cases I am having problems. There must be a disconnect with my understanding of how ANSYS is treating this.
In the attached image you can see my setup:
1. The top plate is called Clearance Holes
2. The bottom plate is called Tapped Holes
I have the following contacts:
1. No separation between the four faces between the top and bottom plates.
2. Bonded contact between the top face of the clearance holes plate and the mating surface of the screw head.
3. Bonded contact between the cylinders of threaded portion of the screws, and the tapped hole cylinders: One surface per fastener and hole. I modeled the fasteners with a nominal diameter shank, and a minor diameter thread to match the tapped hole size. The clearance hole is bigger than the shank diameter.
4. There is a frictionless constraint between the screw shank and the clearance hole. The results were the same with this suppressed.
Constraints:
1. The two symmetric outer holes are pinned on the top surface (part of the clearance holes plate). The tangential direction is free on both, and axial is free on one.
2. The center hole has a load in the direction that would pull the parts apart.
3. The shank of the fasteners has a bolt pretension applied - this is what is causing problems.
Solution:
With no bolt pretension, the plates pull apart (more so in the center) as expected with the load.
With the bolt pretension applied, all goes to hell. The displacements instead of being near 0 as expected are extremely large. This occurs whether the bolt preload is 1000 lbs or just 1 lbs. What am I missing? Are my contacts incorrect?
I am also concerned about a rigid body motion warning. I replaced one of the pinned supports with a fixed support and still get the same results. I think it's showing a rigid body warning due to the large deflection.
Anyone has any ideas as to what is going on and why?
Thanks,
Sebastian