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Finite Element Analysis of GPS Based Vehicle Tracking System with Enclosure for Dynamic

Assessment 1Shreenivas Jog, 2Prateek Gupta, 3Mukul Sutaone, 4V.V.Badawe, 5Avinash Kumar, 6Sneha Gade, 7Kshitij Deshpande

1,3Dept. of E and TC, College of Engineering, Pune, India. 4BEPL, Pune, India.

2,5,6,7Dept. of E and TC, Pad.Dr.D.Y.Patil Institute of Engineering and Technology, Pune, India. e-mail: [email protected], [email protected], [email protected], [email protected],

[email protected], [email protected], [email protected]

Abstract— This paper introduces vibration effects on the GPS based Vehicle Tracking System (VTS) to be used in stringent environment like ground based wheeled vehicles in Military applications. This paper also gives a brief idea of failures due to vibration and benefits of the vibration test method. The geometrical model for HE-30 Enclosure with GPS VTS board has been prepared using CATIA software and simulated for stress level analysis using ANSYS Software. ANSYS uses the Finite Element Analysis tool to simulate the natural frequencies and the stress level. The results were obtained through simulation of HE-30 Enclosure with and without shock mounts. These stress levels were compared with the Ultimate Tensile Strength to find out, whether this Enclosure would sustain the applied vibrations. The simulation results have indicated that the maximum stress level of 30.8 MPa for Enclosure without shock mounts has been reduced to 50 KPa for Enclosure with shock mounts. Also, the maximum stress level observed for HE-30 Enclosure, with and without shock mounts is much below the Ultimate Tensile Strength of 310 MPa. HE-30 Enclosure meets the compatibility requirements with JSS-55555 / MIL 810 E standards. The actual vibration test was conducted on GPS VTS board with HE-30 Enclosure. Functional test results were found to be satisfactory and no mechanical damage was observed in the system.

Keywords- Vibration test; ANSYS simulation; FEA; GPS; VTS; Enclosure.

I. INTRODUCTION Ground based vehicle experience vibration because of the

road conditions and vehicle conditions. Equipment mounted in any commercial or military wheeled vehicles are subjected to various vibration levels and shocks. [1], [2] Electronic assemblies experience various thermal and mechanical shocks during manufacturing process or during its tenure of service. Vibrations affect everything from solder joints to connecting cables and circuit boards. This can lead to catastrophic failures that could affect human safety and subsystem performance. Extensive testing on various PCBs can determine the fatigue life of different components, leads and solders joints, based on the dynamic displacement of the PCB. Reliable performance in a dynamic environment requires an understanding of the

natural frequencies at which a component or assembly will vibrate and the impact of any stress or deflection that may occur. This vibration level or resonance frequencies can be simulated in the test laboratories and compared with defense standards JSS-55555 [1] and MIL 810 E. [2] Similarly the performance of the equipment/product can be simulated using ANSYS software based on Finite Element Method (FEM) analysis techniques as a part of virtual product development. This software analysis will give natural frequency values generated at different parts of assembly, accordingly, the design can be modified.

II. VIBRATION TEST

A. Objectives of Vibration Testing [3] • Reduce product design and development time.

• Ensure product’s fitness for moving platforms.

• Reduce in-plant rework due to quality rejection.

• Reduce damage in transit.

• Reduce marginal or non-operational performance and rejection under warranty period.

• Reduce costs and damage claims due to incorrect operation of the product.

• Makes the equipment robust.

B. Basic Types of Vibration Testing 1) Sinusoidal vibration testing: It uses slow change in the

frequency and it is used to reveal a product or package's resonant (sensitive) frequencies. It is one of the oldest types of vibration testing.

2) Random vibration testing: Here, the specimen is exposed to random vibration level. Random testing can be used to duplicate transportation vibration, seismic vibration and operating vibration. Random vibration is specified for

2012 International Conference on Communication, Information & Computing Technology (ICCICT), Oct. 19-20, Mumbai, India

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acceptance tests, screening tests and qualification tests as it more closely represents the true environment in which electronic equipment must operate. The test item must be fixed to the vibration table. This is done using a fixture (jig). The fixture must transfer the vibration from the table to the test unit without adversely influencing the test. The vibration that is transferred to the test unit must be measured and controlled. [3]

C. Working of Vibration Test system

Figure 1: Vibration Test System

The essential components of a vibration test system are:

• Vibrator (sometimes referred to as the Shaker)

• Amplifier

• Controller

• Accelerometer

The Device Under Test (DUT) is installed on the vibrator. The sine wave sweep input signal is applied to the Amplifier for resonance search. Output of Amplifier is applied to the Vibrator. The endurance vibration test is conducted for prescribed duration on DUT at resonance frequencies observed. Accelerometer measures the forces being generated at the shaker table and at various points on the DUT. Multi-axis testing is becoming increasingly common because it enables the DUT to be tested in all three axes, giving a more thorough test rather than just shaking in the vertical axis. Normally vibration test is a series of single-axis test with the DUT repositioned for each new axis. [3]

Effects of vibration and shock on electronic circuits are broken component lead wires, crack solder joints, cracking of the component body, broken circuit traces, electrical short circuit and mechanical damages for enclosure. [4] Electronic circuits consist of chassis and PCB assembly. Both have their natural frequency (resonant frequency) which must be considered during design. Fatigue life of PCB gives resonant frequency in sinusoidal vibration and random vibration. Fatigue life of various components and leads depend upon the resonance frequency of the assembly, duration of test and material used. The various steps in determining the accuracy

of the design consist of first calculating the required resonant frequency of the PCB assembly, then computing the required resonant frequency with assembly mounted on the chassis.

D. Design guidelines to reduce the risk of vibration or shock inducing damage to electronic systems [4]

Use of robust Enclosure.

Relative motion between components and PCB should be controlled. Leads should be kept short and larger components should have addition mechanical fixings, such as tie wraps, or it can be glued to PCB. In severe cases complete potting may be necessary.

Vibration problems with connection leads and sockets are common. Leads should be fixed to prevent flexing between the lead and connector. Plugs and sockets may need firm support other than the PCB.

Use Silicone based RTV Rubber compound on the PCB.

Relatively heavy components, such as transformers or chokes should be fixed on PCBs close to supporting pillars.

Avoid use of electromagnetic relays and care should be taken to avoid formation of high stress points (e.g. sharp bends).

Lock tight glue should be used on stainless steel screws for fixing the cover on bottom plate of Enclosure.

Use of Shock mounts for Enclosure.

Use of Rubber mounts along with studs for PCB.

III. IMPLEMENTATION OF GPS VTS SYSTEM WITH ENCLOSURE

GPS Based Vehicle Tracking System used for positioning and localization has been selected as model for research work. HE-30 Enclosure (Aluminum alloy) along with shock mounts has been implemented. HE-30 aluminum alloy has maximum Ultimate Tensile Strength and better mechanical properties as compared to Copper and pure Aluminum.[5] The GPS based Vehicle Tracking System board has been mounted in this Enclosure. The selected HE-30 material can withstand high vibration levels. The shock mounts made of Silicone Rubber [6] further reduces the stress level to a minimum value resulting in the improvement of the mechanical strength for the Enclosure. The HE-30 Enclosure with GPS VTS Board has been designed to work in stringent environment. It had been tested for EMI/EMC test conditions and results were found to be compatible with EMI/EMC Standard MIL-461E. [7] The Enclosure also had been validated for Environmental and Dynamic tests as per JSS-55555 / MIL-810E Standard.


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TABLE I: HE-30 Enclosure Parameters and shock mount details [5-7]

Material details

HE-30 Enclosure

Dimensions details Parameters HE-30

Enclosure Silicone

Shock Mount Young’s modulus

68.9 GPa 7.8MPa Length 188 mm

Poisson’s ratio 0.33 0.4 Breadth 120 mm

Density 2.7 g/cm3 1.25 g/cm3 Height 40 mm Ultimate Tensile Strength (UTS)

310 MPa -- Thickness 3 mm

Table I indicates the mechanical properties and dimension for HE-30 Enclosure.

TABLE II: Specifications for Vibration on HE-30 Enclosure [1]

Parameters Specification

Frequency 13 to 500 Hz Acceleration 4g

Damping ratio 0.6 Displacement ± 6 mm

Table II indicates the specifications for vibration conducted on HE-30 enclosure with GPS Board as per JSS-55555. The vibration test has been conducted in all three axes on GPS VTS board with enclosure as per the above specifications at ARAI (Automotive Research Association of India), Pune. The functional operation of the system was found to be satisfactory and no mechanical damage was found in the system.

IV. SIMULATION USING ANSYS SOFTWARE In Virtual product development, performing simulation

analysis on the prototypes for better and cost effective designs can be undertaken. Stages in product development consist of designing, simulating, improving and finally manufacturing. FEA (Finite Element Analysis) is a mathematical analysis based software tool which applies laws of mechanics and determines product information beyond the capability of any test program. ANSYS uses the FEA tool to simulate the natural frequencies of a part or an assembly and use this information to modify the design or materials used. ANSYS software is based on the Finite Element Method and is capable of performing stress analysis, thermal analysis, modal analysis, frequency response analysis, transient simulation and also coupled field analysis. [8]

The Ansys multiphysics can couple various physical domains such as structural, thermal and electromagnetics. Ansys Parametric Design Language (APDL) allows users to execute all the commands required to pre process, solve and post process the problem, from a separate text file known as Macro.

A. Flowchart for Simulation of HE-30 Enclosure for mechanical stress level.

Figure 2: Flowchart for simulation

Choose HE-30 as the material for the Enclosure and Silicone rubber shock

mount

Enter the dimensions: Length: 188mm; Breadth: 120mm Height: 40mm; Thickness: 3mm

Design the Enclosure and Shock mounts using CATIA Software

Import the model in the ANSYS 12 software

Enter the various Mechanical properties of the element HE-30

Young’s Modulus: 68.9 GPa Density: 2.7 g/cm3 Poisson’s Ratio: 0.33

Carry out various Simulation steps for Harmonic Analysis in this software

Carry out Harmonic analysis with and without shock mounts

Enter the test conditions as per MIL Grade Frequency: 13 to 500 Hz; Acceleration: 4g; Displacement: ±6mm; Damping ratio: 0.6

If maximum stress < UTS

Select the material for vibration analysis

Observe stress levels obtained

Modify the design / material

HE-30 material will sustain the vibration test

Yes

No


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Figure 2 shows the Flow-chart for simulation of HE-30 Enclosure for different stress levels through Finite Element Method using Ansys software.

B. Algorithm for Simulation of HE-30 Enclosure for mechanical stress level.

Selection of material and profiling of the selected

material.

Modeling the enclosure using CATIA software for dimensions. Length: 188mm; Breadth: 120mm, Height: 40mm; Thickness: 3mm.

Importing this model in ANSYS software.

Feeding the mechanical properties: Young’s Modulus: 68.9 GPa; Density: 2.7 g/cm3; Poisson’s Ratio: 0.33.

Defining the test specification for vibration analysis Frequency: 13 to 500 Hz; Acceleration: 4g; Displacement: ±6 mm; Damping Ratio: 0.6.

Simulation of Enclosure using Harmonic analysis

Comparing the obtained result with the standards.

If the maximum stress is less than the UTS, HE-30 material will sustain the vibrations, otherwise go to re-selection of material / design modification.

V. RESULTS OF THE SIMULATION Figure 3 indicates HE-30 EMI Enclosure with shock mounts designed for GPS based Vehicle Tracking System. [7]

Figure 3: HE-30 Enclosure with Shock mounts

Figure 4 and Figure 5 shows the stress level of Enclosure without and with shock mounts respectively. The red color at the centre of the Enclosure indicates high Stress level. As we move away from the centre, the stress level decreases. The blue color shows the minimum stress level. The maximum stress level at the centre of the Enclosure without shock mounts is 30.8 MPa, whereas by using shock mounts, the stress level was reduced to 50 KPa.

Figure 4: HE-30 Enclosure with GPS VTS Board showing simulated

Stress level without Shock Mounts

Figure 5: HE-30 Enclosure with GPS VTS Board showing simulated Stress level with Shock Mounts

TABLE III: Colour code for different stress level

Colour Code for different stress

levels related to Figure 4

Colour Code for different stress levels related to Figure 5

107 Pa 104 Pa 104 Pa

3.201 2.316 1.879 1.737

1.447 1.158 0.974 0.578 0.289 0.000

30.808

27.818

24.834

21.850

18.866

15.883

12.899

9.914

9.914

6.930

6.325

5.719

5.114

4.508

0.515

0.00037


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Figure 6: Comparison of Stress level for the HE-30 Enclosure (with and without shock mounts) and the Ultimate Tensile Strength

Table III shows the stress levels for the HE-30 Enclosure with and without shock mounts for different colour codes. Figure 6 shows the plot of different stress levels against frequency for the HE-30 Enclosure with and without shock mounts. The graph shows that the stress level in both the cases are much below the Ultimate Tensile Strength for HE-30 material which is 310 MPa (standard value). It can be verified that the stress level is reduced by approximately 600 times after using shock mounts along with HE-30 Enclosure.

VI. CONCLUSION This paper outlines the importance of vibration test, types of vibration test, effects of vibration test on electronics systems, working of the vibration test system and the guidelines to reduce the effects of vibration. Stress level of HE-30 Enclosure is simulated in ANSYS software through FEM Analysis. Solution obtained by this analysis is compared for the HE-30 Enclosure with and without shock mounts. Maximum Stress level without shock mounts was found to be

30.8 MPa which has been reduced to 50 KPa when Silicone rubber shock mounts were fitted to the Enclosure. Also, the maximum Stress level was much below the Ultimate Tensile Strength of 310 MPa for HE-30 Enclosure. The validation of HE-30 enclosure has been done through actual vibration test and the functional performance of the GPS VTS with Enclosure was found to be satisfactory. No mechanical damage of any kind was observed in the system. Hence, HE-30 Enclosure meets the compatibility requirements with JSS-55555 / MIL 810E standards for vibration specifications.

ACKNOWLEDGMENT The authors would like to sincerely thank Pd.Dr. D.Y.Patil

Institute of Engineering and Technology, Automotive Research Association of India (ARAI) and University of Pune for their valuable help for this research proposal.

REFERENCES [1] JSS-55555 Standard, revision 2, Environmental Test Method for

Electronic and Electrical Equpiment, Revised: 2000. [2] MIL Standard 810 E (Environmental), Revised: July 1989. [3] Richard Baker “Introduction to Vibration”, Vibration Test System and

specifications, Available : http://freespace.virgin.net/richard.baker10/ book/ vint_1.htm.

[4] Shreenivas Jog, M.S.Sutaone, and Vishweshwar Badave, “Ruggedisation Methodologies for GPS based Vehicle Tracking System”, in Proceedings, IEEE(IACSIT) International Conference on Electronic Computer Technology (ICECT-2011), Volume 2, pp 214-218, Kanyakumari, India, April-2011.

[5] Datasheet and specifications for HE-30 Aluminum alloy, Available : www.aircraftmaterialsuk.com..

[6] STOP-CHOC make Shock mounts, SCA 15507, Available: www.common.leocom.jp/datasheets/185666_57513.pdf.

[7] Shreenivas Jog, M.S.Sutaone, and Vishweshwar Badave, “HE-30 Aluminum Ruggediesd EMI Enclosure for GPS based Vehicle Tracking System”, in Proceedings, IEEE, International conference on Wireless Communication, Vehicular Technology and Aerospace and Electronic System Technology (Wireless VITAE 2011), pp.1-5, Chennai, India, March 2011.

[8] Ansys operational manual for FEM and Finite Element Analysis.


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