FEA Based Durability Evaluation of HD Tipper Chassis and Cab Through Correlated Transient and Fatigue Analysis 2011-26-0013

Durability evaluation and Fatigue Life estimation for commercial vehicle Chassis and Cab is an important milestone during product design and development. Commonly used methods like endurance testing of vehicles on field, accelerated testing on four-posters or test tracks are time consuming and costly. On the other hand, virtual methods for durability evaluation give useful information early in design cycle and save considerable time and cost. They give flexibility to evaluate multiple design options and accommodate design changes early in product development cycle.

Virtual testing methods commonly used in industry for durability evaluation of truck Chassis and Cab are combination of Multi-body Simulation (in software like Adams) and Fatigue Life estimation (in software like FEMFAT). These MBS models for truck are rigid or partly flexible and the simulation run-time increases drastically with increase in number of flexible parts in model. Vehicle suspensions are modelled mostly as rigid mechanisms with appropriate stiffness at the joints. Transient simulations done through MBS methods are mostly short duration with four-poster or six poster inputs. Dynamic correlation between test and simulation for these MBS methods are about 70-80%. Modal stresses and modal coordinates from MBS simulations are given as input to the fatigue solver for life estimation. Low level of dynamic correlation has manifold effect on accuracy of life estimates [1].

A different approach has been developed in VECV for durability evaluation of Truck Chassis and Cab, entirely through Finite Element Analysis route. This FEA approach has the biggest advantage of keeping entire model as flexible.

Full flexibility in the model greatly improves the capture of Chassis, Suspension and Cab modes and helps in achieving improved dynamic correlation. Forces or accelerations as measured from test data acquisition in mines and test tracks are given as inputs to the Finite Element model of vehicle for transient analysis in Nastran. Nowadays, high performance compute servers make it quite convenient to run these FEA based transient analysis for a time period of 100-150 seconds with small time-steps. Smaller time-steps and full flexibility of the model enable high dynamic correlation between test and simulation in range of 85-95%. Stress vs. time output from the transient analysis in Nastran and fatigue material properties are given as input to fatigue solver FEMFAT which gives the life estimates for the Chassis and Cab. Since the stress vs. time history in this FEA based approach is for reasonably long duration, like 100-150 seconds, approximations in fatigue analysis are reduced and better estimates of life are obtained [2].

VE Commercial Vehicles is one of the leading commercial vehicle manufacturer in India with presence in both truck and bus segments. This paper will discuss the above described FEA based methodology for durability evaluation of a Heavy Duty Tipper Chassis and Cab through correlated transient and fatigue analysis. Service load data was acquired on Tipper in Mines, Construction Sites and Test Tracks and is used for transient analysis in Nastran. The FEA model is correlated for displacements and strains in time as well as frequency domain with the measured test data. Nastran stress vs. time results are used for fatigue life estimation in FEMFAT. Correlation is also done for damage calculated from test data and FEA results. High level of dynamic and fatigue correlations between test and simulation were obtained for Tipper Chassis and Cab.

This FEA based durability evaluation methodology will help VECV in design of Chassis and Cab and their life prediction, early in product development cycle for all future projects.