Virtual test development of tractor rear roll bar ROPS using MFBD

Product: Tractor ROPS (Roll-Over Protective Structure)

Purpose of Analysis: Implementation of the virtual test of ROPS using MFBD

A ROPS (Roll-Over Protective Structure) is a structure to protect the driver from injury when a tractor or heavy equipment rolls over. A ROPS must be able to sufficiently absorb the impact with the ground and provide a safe space for the driver when the vehicle is overturned, The test procedure for evaluating the safety of such ROPS is prescribed in OECD Codes in the Agricultural Mechanization Promotion Act. In this project, a virtual ROPS test was implemented using RecurDyn’s implicit solver-based MFBD toolkit. After that, the convergence and error of the solution were evaluated by comparing the results with static nonlinear analysis.

Process

① Created an MBD model including a model of the driver safety zone, ROPS, and load actuator.

② Created a flexible model of the ROPS. (modeled with shell elements because it is long and thin.)

- Geo Surface Contact was used between the rigid load actuator and ROPS modeled using FFlex to minimize oscillations in contact.

- Modeled welds with FDR (RBE2) elements considering the characteristics of mid-surface type shell elements, which have difficulty in sharing nodes.

③ Implemented a consecutive displacement load test.

④ Evaluated and compared the maximum displacements that satisfied the required energy.

Key Technologies for Analysis

• Multi Flexible Body Dynamics (MFBD) technology that can accurately reproduce the virtual test of an ROPS
  
• FDR (RBE2) that can model welding of mid-surface type FE elements
• Scenario Analysis and Contact On/Off control to implement a consecutive displacement load test

Toolkits

• RecurDyn/Professional
• RecurDyn/FFlex

Customer Challenges

• Loss of time and cost from preparing samples for physical tests
• Need for evaluation of safety in advance for various possible design changes
• Need to implement a consecutive load control methodology that preserves residual stresses
• Simpler contact definition and higher convergence than nonlinear static analysis
• Need for simulation time reduction

Solutions

• Implementation of a simulation model using RecurDyn MFBD technology that can replace the physical test
• Reduction of simulation time by creating a shell element flexible body from the mid-surface geometry from a CAD model
• Use of multi-linear isotropic hardening that allows for large deformation of structures and their plastic material nonlinearities
• Safety zone violation check at each load stage while the plastic deformation was preserved using the consecutive analysis
  • Use of enabling and disabling contact through Scenario analysis for the consecutive analysis

Outcomes

• An ROPS nonlinear simulation model was developed that utilizes RecurDyn’s implicit MFBD solver.
• It was confirmed that the simulated maximum displacement error was similar to physical test results.
• Higher solution convergence was obtained with a relatively simple contact definition than using static nonlinear analysis.
• The same simulation method as the physical test environment was implemented by applying the displacement control method using the Scenario analysis.

Other Applications

• Cosimulation of Tractor mid-mower
  •  Analyzing the dynamic behavior of a tractor with a mid-mower using RecurDyn and particle method