mbrook
Mechanical
- Dec 12, 2013
- 4
Hi everyone,
I'm relatively new to Abaqus and am having a lot of fun and trouble at the same time. I am trying to model a 3D multi-body mechanism using beam elements (for now) connected with a combination of hinge and flexion torsion elements. The end goal is to see the resulting stresses in the beams as displacement boundary conditions are applied to either end of the mechanism.
I have determined that I am limited to using implicit dynamic analysis steps. Static steps simply will not converge. Explicit dynamic steps prohibits me from using elbow beam elements. The boundary condition displacement rate is very low, so I am using large step times like 3600 seconds to minimize inertial effects. I am trying to use either moderate dissipation or quasi-static procedures with no initial acceleration, and ramping loads boundary conditions.
I have no problems when using only hinge elements in single or multi-body studies. The solution time is quick and the results are what I would expect.
The problem comes in when I try to use flexion torsion elements in either single or multi-body studies. I feel that flexion torsion elements best represent the behavior of ball joints since connector moments can be defined separately for flexion (relative angle between shaft tangential vectors), and torsion (relative rotation about the "shaft" axes). What want to define is rigid-perfectly plastic behavior separately for both flexion and torsion. The reason being that I have manufacturer bench test flexion and torsion break torque values. Would you agree that I should be using flexion torsion elements, or is there another more appropriate connector element that I should be using?
In terms of defining the flexion torsion element I have done the following based on my interpretation of the user manuals:
[ul]
[li]The coordinate system for the nodes in a flexion torsion element should have the 3rd (z) axis aligned with the respective connected beam tangential vector. I see no requirements for the direction of the other two coordinate system axes. Is that correct?[/li]
[li]Flexion directions and moments are defined as UR1 and M1 respectively in the connector section editor. Therefore I have defined elasticity behavior to be rigid for UR1, and plasticity behavior to be uncoupled isotropic hardening with a single yield force/moment of X at 0 plastic motion for M1.[/li]
[li]Torsion direction and moments are defined as UR2 and M2 respectively. Therefore I have defined elasticity behavior to be rigid for UR2, and plasticity behavior to be uncoupled isotropic hardening with a single yield force/moment of X at 0 plastic motion for M2.[/li]
[li]The sweep direction and moments are defined as UR3 and M3 respectively. I believe that I can completely neglect sweep parameters, so I have not specified any behaviors for UR3 and M3. I’m not so sure that assumption is accurate. Any comments?[/li]
[/ul]
Out of a total step time of 3600 seconds, the Abaqus Standard aborts the analysis after a step time of approximately 5e-5 seconds. What’s deal?
Any help you more experienced guys can provide me with would be greatly appreciated!
Thanks,
Matthew
I'm relatively new to Abaqus and am having a lot of fun and trouble at the same time. I am trying to model a 3D multi-body mechanism using beam elements (for now) connected with a combination of hinge and flexion torsion elements. The end goal is to see the resulting stresses in the beams as displacement boundary conditions are applied to either end of the mechanism.
I have determined that I am limited to using implicit dynamic analysis steps. Static steps simply will not converge. Explicit dynamic steps prohibits me from using elbow beam elements. The boundary condition displacement rate is very low, so I am using large step times like 3600 seconds to minimize inertial effects. I am trying to use either moderate dissipation or quasi-static procedures with no initial acceleration, and ramping loads boundary conditions.
I have no problems when using only hinge elements in single or multi-body studies. The solution time is quick and the results are what I would expect.
The problem comes in when I try to use flexion torsion elements in either single or multi-body studies. I feel that flexion torsion elements best represent the behavior of ball joints since connector moments can be defined separately for flexion (relative angle between shaft tangential vectors), and torsion (relative rotation about the "shaft" axes). What want to define is rigid-perfectly plastic behavior separately for both flexion and torsion. The reason being that I have manufacturer bench test flexion and torsion break torque values. Would you agree that I should be using flexion torsion elements, or is there another more appropriate connector element that I should be using?
In terms of defining the flexion torsion element I have done the following based on my interpretation of the user manuals:
[ul]
[li]The coordinate system for the nodes in a flexion torsion element should have the 3rd (z) axis aligned with the respective connected beam tangential vector. I see no requirements for the direction of the other two coordinate system axes. Is that correct?[/li]
[li]Flexion directions and moments are defined as UR1 and M1 respectively in the connector section editor. Therefore I have defined elasticity behavior to be rigid for UR1, and plasticity behavior to be uncoupled isotropic hardening with a single yield force/moment of X at 0 plastic motion for M1.[/li]
[li]Torsion direction and moments are defined as UR2 and M2 respectively. Therefore I have defined elasticity behavior to be rigid for UR2, and plasticity behavior to be uncoupled isotropic hardening with a single yield force/moment of X at 0 plastic motion for M2.[/li]
[li]The sweep direction and moments are defined as UR3 and M3 respectively. I believe that I can completely neglect sweep parameters, so I have not specified any behaviors for UR3 and M3. I’m not so sure that assumption is accurate. Any comments?[/li]
[/ul]
Out of a total step time of 3600 seconds, the Abaqus Standard aborts the analysis after a step time of approximately 5e-5 seconds. What’s deal?
Any help you more experienced guys can provide me with would be greatly appreciated!
Thanks,
Matthew