FLEX BODY SIMULATION OF LOWER CONTROL ARM FOR SLA FRONT SUSPENSION SYSTEM
Aim- To determine the Maximum and Minimum Stress and Strain values acting on the Flex body converted from Rigid body for Lower control arm on both left and right sides of the Front steering Wheel mechanism.
Points that are taken into consideration-
1. Analysis Type- Static Ride Analysis
2. Analysis model- SLA Front wheel suspension system
While designing a suspension system for a vehicle, one should often not ignore the loads that suspension linkages take up during rebound. Finite Element Analysis wouldn\'t be sufficient to analyze displacement, stress and strain acting on the linkages since it does not take into account the collective behaviour of the suspension system.
Moreover, Finite Element models have a very high number of degrees of freedom which is difficult for MBD solvers to handle. In such a case Flex-Body simulations come into play that allows the engineer to test the strength of linkages without isolating them from the geometry. A Flex-Body is obtained from the Rigid Body conversion with the help of the Flexprep Tool in the Motionview User interface.
A Flexbody is a modal representation of the Finite Element model, approximation of a deformable structure for CAE analysis. It is based on the concept of modal superposition and is therefore very efficient for solvers that need to model structures as non-rigid.
The MBD solver calculates the coefficients for the various deflection modes calculated in the Component Mode Synthesis method which when added together produce the deformed shape. Flexbodies connect to the MBD system through the interface nodes.
After importing the FEM model in the Hypermesh, there is an option to convert RBE3 spiders to RBE2 spider. As shown-
Furthermore, we used CRAIG-BRAMPTON method for as a synthesis type. And the highest mode of a degree set to the default value along with the units.
RBE is basically rigid body elements. RBE2 elements rigidly connect an independent FEA node to one or more dependent nodes. Most often for MBD flexible bodies, the RBE2 elements are “rigid spiders” that have the independent node at the centre of a hole and the dependent nodes along with the circumference modelling bolts or other connection hardware.
The independent node of the rigid spider becomes an interface node of the flexible body that allows the body to connect to other elements like joints or forces in the MBD model. RBE3 - On the other hand, for the RBE3 element, the dependent node is in the centre and the independent nodes are along the circumference.
The interface nodes are specified as 4887+4888+4890. The node ID\'s of the RBE2/ RBE3 central nodes will be the interface nodes which are obtained from Hypermesh when we import the model.
The solver mode is chosen as Lanczos which is the default algorithm in OptiStruct.
After importing the model to the Hypermesh interface we now, check for the existence of RBE3 spiders in order to convert them into the RBE2 spiders.
There were already existing RBE2 spiders at the CG of the Control arm as well as one of the knuckles of the arm.
Whereas, the other knuckle opposite to that had RBE3 spider, as well as the front side of the control arm, had no spider in existence.
And RBE2 spider was created at the front end of the lower control arm (Highlighted Green area at the front)-
After that the parameters that are changed from Default values-
a. Vehicle CG (Height from the ground)-
Value changed from the default value is- 750 mm
b. Vehicle Weight-
Value changed from the default value is- 18500.00 N
c. Front breaking Ratio-
Value changed from the default value is- 0.650
d. Wheelbase-
Value changed from the default value is- 3000 mm
e. Axle ratio-
Value changed from the default value is- 5.00
Further, the same left control arm was mirrored along the X-Z plane and then attached to the existing system by navigating in the model browser. And all the nodes were aligned with the system using options -
a. Find all
b. Align all
The analysis was run, by changing the simulation type from Transient to Quasi-static analysis and the End time for simulation was 6 seconds and the rest of the settings were kept tot default.
The following results were obtained when the modified parameters -
Results-
1. Displacement in the Lower control arm-
The Displacements on both the lower control arms were obtained as-
Maximum- 1.134E+02 mm (MAG)
Minimum- 9.753E-02 mm (MAG)
2. Stress in the Lower Control arm-
The stresses on both the lower control arms were obtained as-
Maximum- 8.126E+03 (MAG) von Mises
Minimum- 8.124E-12 (MAG) von Mises
3. Strain in Lower Control arm-
The Strains on both the lower control arms were obtained as-
Maximum- 2.165E-02 (MAG) von Mises
Minimum- 3.024E-17 (MAG) von Mises
Furthermore, the same procedure was followed with the original default values and the results were compared with Results which were obtained previously.
The following results were obtained when the modified parameters -
Results and comparisons are attached to the excel sheet and uploaded on the google drive.
Link- https://drive.google.com/open?id=1068TiplzIZL0rJ1rmngx2fWabeg7sbLDsh_loexFO7s
Comparison-
The .zip folder of the project is attached to the google drive.