Prediction of Design Margin for Diesel Exhaust Fluid Tank Bracket by FEA Approach

Diesel exhaust fluid is used to minimize the air pollution created by diesel engine. It is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. It is used to lower nitrogen oxides concentration. Diesel exhaust fluid tank is supported on bracket. The main objective of this project is to predict the robust FEA approach for diesel exhaust fluid tank bracket using Ansys Workbench tool. The current FEA analysis results are not close to test results. In this project, robust FEA modelling approach is developed which have frequency, acceleration and strain responses of simulation close to test results


I. INTRODUCTION:
In mechanical engineering, a bracket is intermediate component for fixing one part to another. Bracket is the intermediate between the two components and fixes the one to the other. It is used to support or hold the components together.

II. ANALYSIS:
Analysis of bracket is carried out in Ansys workbench tool. The assembly consist of fixture, bracket and tank. The fixture and bracket are made of aluminum and structural steel respectively. Diesel exhaust fluid tank is made of highdensity polyethylene rubber. Properties of materials are shown in table 1.

Modal analysis and random vibration analysis:
Modal analysis is used to determine the mode shapes and modal frequencies of bracket. Mode shape represents a specific pattern of vibration executed by a mechanical system at a specific frequency. The governing equation for modal analysis is given as, The acceleration versus frequency graph for testing and simulation is plotted to find frequency at different peaks and compare it.

(a) Axial (X) direction:
The axial direction frequencies of bracket at different peaks is considered for comparison between testing and simulation results. The gap between testing and simulation for cceleration Grms and strain rms is determined in terms of percentage difference. (ii) Acceleration and strain response: The percentage difference of acceleration Grms and strain rms are 41.80% and 4.64% respectively. The acceleration Grms of simulation is not close to test result.

(b) Lateral (Z) direction:
The lateral direction frequencies of bracket at different peaks is considered for comparison between testing and simulation results. The gap between testing and simulation for cceleration Grms and strain rms is determined in terms of percentage difference.        (ii) Acceleration and strain response: The percentage difference of acceleration Grms and strain rms are 37.25% and 27.05% respectively. The results are not within acceptance limit for beam contact between fixture and bracket.  (ii) Acceleration and strain response: The percentage difference of acceleration Grms and strain rms are 23.15% and 66.27% respectively.

No separation contact:
To restrict sliding motion and separation between parts in normal direction and allow sliding motion in tangential direction of fixture no separation contact is given between vertical and horizontal plate of fixture.  (ii) Acceleration and strain response: The percentage difference of acceleration Grms and strain rms are 44.44% and 5.32% respectively. The acceleration Grms of simulation is not matching with testing result.  (ii) Acceleration and strain response: The gap between testing and simulation results for acceleration Grms and strain rms are 21.92% and 78.10% respectively.

Considering slip plate of shaker table:
To consider the actual contacts between slip plate and fixture in testing condition, slip plate of shaker table is considered. The input is applied to slip plate instead of base plate of fixture. This can affect the input profile transmitted to bracket.  (ii) Acceleration and strain response: The gap between testing and simulation results for acceleration Grms and srain rms are 45.38% and 40.25% respectively.

With slip plate considering material damping:
Material damping factor of structural steel, EPDM rubber and magnesium is considered. Damping factor considered for structural steel, EPDM rubber and magnesium material are 2%, 5% and 1% respectively. There is no change in frequency response but the amplitude of acceleration and strain is reduced.

Acceleration and strain response:
The gap between testing and simulation results for acceleration Grms and strain rms are given in table. ACKNOWLEDGEMENT: The author wish to thank Amar A. Mali, Kishor Deshmukh and Giridharan Balakumar Applied Mechanics Engineer, CES, Cummins Technical Center India, Pune for providing the technical support for this work.
Note: The values of frequency, acceleration (g 2 / Hz), acceleration Grms and strain rms are not displayed as the data is confindential of Cummins India ltd.