Agricultural machinery manufacturer uses LMS Virtual.Lab to increase endurance simulations
John Deere (Tractor Durability)
John Deere uses Siemens PLM Software solutions to help enhance the reliability of its tractors
Providing valuable insight
Since high risk and tight margins rule international agriculture, farmers opt for equipment that offers versatile features in combination with the endurance required to make it through peak harvesting periods. To further increase the quality and reliability of new tractor models, engineers at John Deere Werke Mannheim (Germany) frontload virtual simulation into the development process of the John Deere 5000 and 6000 Series utility tractors.
The application of complementary simulation strategies in the form of LMS Virtual.Lab™ Motion software and LMS Virtual.Lab™ Durability software from Siemens PLM Software provides valuable insight into how design variations influence tractor quality and reliability. Virtual simulation helps John Deere compress tractor development cycles while delivering better performance, flexibility, comfort and economy at comparable cost.
The farmer’s tractor is like a referee’s whistle or a hunter’s rifle. If there is one thing that a farmer needs to be able to count on, it is the reliability of his tractor, the money-making machine in which he spends a good part of his life. John Deere tractors must withstand the rigors of agriculture, providing sufficient hydraulic power to lift and drive various implements connected to the tractor and working through different soil and weather conditions while pushing and pulling implements. During hectic harvesting periods, the farmer counts on his John Deere to run long days for many weeks. Needless to say, a major tractor breakdown in this period would potentially put the farmer’s revenue at risk.
Quality and reliability are among the critical aspects that set a John Deere tractor apart from other tractors. For the most part, John Deere’s mid-size and large-size utility tractors are designed, developed and manufactured at John Deere Werke Mannheim, Germany. Every year, about 40,000 tractors, all with the company’s trademark green color and yellow rims, are shipped to customers around the world. This number consists of all John Deere 6000 and most 5000 Series tractors, each offering a unique combination of option list items and implement assembly choices. These utility tractors typically offer a high degree of versatility in combination with time-saving features that would be expected of larger tractors.
“Over the last 10 years, John Deere engineers succeeded in substantially reducing the required development time for these tractors while steadily enhancing product performance characteristics and keeping sales prices relatively constant,” says Christian von Holst, senior engineer at John Deere Werke Mannheim.
Depending on virtual simulation
At John Deere, the development process typically starts with an idea phase, during which concerns, ideas, requests, suggestions and remarks are translated into more tangible product requirements. In the subsequent concept phase, ideas are filtered, concepts are proofed and the technical feasibility of suggested approaches are evaluated, all to shape the technical strategy.
After further elaborating on the most promising concepts, the pre-design phase starts and the first designs go into successive stages of prototyping. In the design phase, engineers consistently use insights and results acquired during physical testing to gradually enhance the performance of the new tractor design. Further iterations are executed until the new design fulfills the original product demands; in the case of tractors, those demands usually relate to durability issues.
Over the last decade, John Deere has accelerated the use of virtual simulation in development processes that used to be entirely driven by physical testing.
“By frontloading durability simulations into our tractor design processes, we are better positioned to evaluate the technical feasibility of design modifications and to anticipate the consequences of making more radical design changes,” says von Holst. “Acquiring concrete information in the initial design stages enables us to steer elaborate design efforts into directions that will more likely and efficiently deliver the targeted product requirements. The selection and application of suitable combinations of virtual simulation and physical testing are essential in simulating the impact of potential design changes, such as a modified suspended cab design or a more powerful tractor engine.”
Using multiple simulation methods
Instead of a one-size-fits-all solution, John Deere engineers created a toolbox with multiple durability simulation approaches, each offering specific predictive capabilities and setting different constraints in terms of timing and effort. The so-called classical approach is a component fatigue-life prediction method that runs on LMS Virtual.Lab™ software and starts off on the basis of measured load data. In addition to this approach, they introduced mixed and hybrid simulation approaches, two methods that enable John Deere to integrate the combined use of LMS Virtual.Lab Motion and LMS Virtual.Lab Motion Durability.
Compared to the classical approach, the mixed approach facilitates the simulation of the impact of more profound design changes, as it generates input loads through dynamic motion simulations performed on the tractor design under development. The hybrid approach focuses on the structural flexibility of tractor parts and its effect on dynamic motion and tractor durability.
The classical approach can be illustrated by durability investigations performed on a tractor cabin frame, which faces the loading of a ride on a bumpy circular test track. While driving at constant velocity, the forces acting on the cabin’s coupling points with the tractor frame are measured in addition to specific cabin point displacements and accelerations.
The dynamic loads are then applied to the finite element (FE) model of the cabin frame, and the subsequent simulation identifies the stresses and strains that are present in the cabin structure. On the basis of these results, engineers run simulations in LMS Virtual.Lab Durability to obtain the fatigue-life performance of the cabin design and assess the impact of suggested cabin modifications. Simulations performed on round-edged and square-edged cabin mounts enabled engineers to extend the fatigue life of the cabin frame’s most damaged location beyond the targeted value, while reducing maximum stress in the base material and the seam weld.
Although the classical approach enables the user to deal with non-linear FE models, its validity is restricted to relatively small changes on the level of the investigated part. As a consequence, this classical durability simulation method cannot be used to predict the effect of more drastic part modifications or changes made to mount properties and locations.
Leveraging LMS Virtual.Lab Motion
John Deere engineers introduced the mixed approach to extend durability simulation capabilities beyond the classical approach. Instead of running physical tests to generate the load data, John Deere engineers used LMS Virtual.Lab Motion to model tractor subassemblies, tie them together and perform full-tractor dynamic motion simulations. By having realistically modeled tractor designs run over dedicated virtual tracks, engineers are able to retrieve the resulting load data as well as the resulting internal forces in the assembly.
The acquired load data serves as input in subsequent FE and durability simulation steps that are identical to the classical durability simulation approach.
“System-level simulations in LMS Virtual.Lab Motion are essential in simulating the durability effect of more profound design changes,” says von Holst. “With the mixed durability simulation approach, we’re able to reliably predict the impact of modified bushing characteristics or adapted mount locations on the fatigue life of a tractor cabin or other component. Unlike other software solutions, LMS Virtual.Lab Motion offers generic modeling capabilities that allow us to flexibly and realistically model full-tractor designs.
“Although the modeling of a new tractor design requires considerable effort as well as in-depth CAE expertise, we’re able to use these models to support multiple simulation purposes, including durability, ride and handling, control mechanism and tractor-implement interaction.”
John Deere refers to the third option in the durability simulation toolbox as the hybrid approach. A key benefit of this method is the ability to consider the structural flexibility of specific tractor components, such as suspension parts, cabin mounts and wheel cover brackets. The FE modeling of flexible parts is performed according to the requirements of a Craig-Bampton analysis, which can be automatically initiated and driven from LMS Virtual.Lab. During full-tractor simulations, LMS Virtual.Lab Motion is used to calculate modal participation factors to characterize the deformations of the flexible bodies and ultimately to retrieve the reaction forces that apply to these parts. The transient stress and strain history results of the motion simulations are used as input for the subsequent durability analysis, which detects the weakest spots of the flexible parts being evaluated.
Reducing physical prototypes
“A typical component that is investigated by means of the hybrid approach is an actuator assembly bracket that is connected to the tractor frame,” says von Holst. “Since these rather thin brackets operate while carrying many times their own weight, it is necessary to model such components as flexible bodies. The deformation of the bracket and the excitation of its natural frequencies lead to altered mechanism motion, unwanted system vibrations and significant changes in internal loads.
“This hybrid approach, which tightly integrates multi-body simulation with flexible-body analysis and fatigue-life prediction, allows us to evaluate the durability of the bracket in context of realistic full-tractor performance before completing the design process. With LMS Virtual.Lab graphic postprocessing features, we’re able to zoom in on specific durability hot spots on the tractor components and gain insight into the underlying root causes.
“The identified hot spots also make it possible to organize more detailed physical tests later on that more specifically focus on the critical areas detected on the virtual prototype. In many situations, the capabilities of the hybrid durability simulation approach overcompensate for the additional processing power that is required and the method’s restriction to linear FE investigations.”
Virtual simulation has evolved into a more accepted and trustworthy source of information that is already applicable from the early conceptual design stages onwards.
“The introduction of LMS Virtual.Lab Durability in the early design stages – when there is still plenty of design freedom – positively impacts tractor reliability and reduces the number of required prototype tests,” says von Holst. “The added value of LMS Virtual.Lab on virtual durability investigations performed at John Deere is significant as it serves as the critical backbone of the hybrid approach and increases the efficiency of the mixed approach.
“In this way, LMS Virtual.Lab helps John Deere strengthen its capability to provide compelling reasons for farmers to buy new tractors by offering better performance, flexibility, comfort, economy and secured reliability.”