A Novel Design Approach for Electronic Equipment - FEA Based Methodology

A Novel Design Approach for Electronic Equipment

FEA Based ethodology

© 2015, HCL Technologies. Reproduction Prohibited. This document is protected under Copyright by the Author, all rights reserved.

Abstract

Abbreviations

Introduction

Problem Definition

Solution and Implementation

FEA-to-Actual Test Correlation

Business Relevance / Practical Implementation on Live ProjectsBusiness Relevance / Practical Implementation on Live Projects

Best Practices

Conclusion and Recommendations

References

Author Info

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Table of Contents


This paper describes the design approach established to study and simulate the vibration behavior of elec-tronic products and provide good correlation between test data and FE simulation through a well calibrated analytical model. This established and validated approach/methodology has been practically implemented in various real time projects for various HCL clients, thereby eliminating/minimizing the actual hardware testing and prototyping efforts resulting in a significant reduction in turnaround time, increased product cost savings and improved productivity. An added advantage that this approach provides is an opportunity to study and validate several other design configurations resulting in a robust and reliable product.validate several other design configurations resulting in a robust and reliable product.

Sl.No

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FEA

PSD

PCB

MPC

CAE

Finite Element Analysis

Power Spectral Density

Printed Circuit Board

Multi Point Constraints

Computer Aided Engineering

Full FormAcronyms

Abstract

In order to meet stringent product and functional requirements, all electronic products have to comply with various thermal, structural and vibration standards and cater to other challenges like unique product design with enhanced functionalities, space constraints, aesthetics, and more.

One of the most important requirements of an electronic product is to withstand significantly high shock and vibration levels caused due to various user handling and environmental situations viz. product shipping and handling, transportation, end user handling and abuse, earth quake/seismic loading, etc.

Introduction

A traditional design approach deals with designing and analyzing the product and validating it thereafter using the typical hardware testing which involves a considerable amount of effort and cost. This cost can be ever-increasing in case various design iterations are to be tried out.

Problem Definition

Abbreviations

FEA Based Methodology | 3


This latest design approach developed here, results in providing a simulation based design which helps in virtually simulating the structural and vibration behavior for different design iterations and load conditions. This, in turn, eliminates/minimizes the need for actual testing and thus saves cost and overall turnaround time.

Extensive FE Based Approach/Methodology

To effectively use the latest FE based approach, the steps below have been adopted which results in building a simulation based design that compares well with testing:

Understanding the product geometry in terms of distribution and placement of different components/ sub-assemblies in order to account for right mass and stiffness. Simulating the right loading and boundary conditions keeping in mind the test setup configuration and actual usage scenarios. Analyzing and interpreting the simulation results, mapping and correlating test data with analytical model results, and perform calibration. Evaluating the design strength and vibration levels using empirical equations e.g. Steinberg's equations for the maximum allowable out of plane PCB deflections, margin of safety calculations for actual compo nent stress levels, etc.

Figure 1. Product Design Cycle

Solution and Implementation


FEA Simulation for "SHOCK and Random Vibration" Loading

Shock simulation (also known as time-history simulation) is a technique used to determine the dynamic response of a structure under the action of any general time-dependent loads such as impact load due to shipping and handling, end-user abuse, etc.

This type of analysis is used to determine the time-varying displacements, strains, stresses, and forces in a structure as it responds to any combination of static, transient, and harmonic loads.

The maximum faired acceleration value that is used as an input for shock FEA has been calculated using the empirical equation below:

∆V = 0.24 A*T (Environmental Tests Procedure - Product Shock Tests - Document Section 760) where, ∆V = Velocity change (in/s) A = Max. Faired Acceleration (g) T = Pulse duration (ms) T = Pulse duration (ms)

Figure 2. FEA Simulation

Figure 3. Faired Acceleration Value



In order to calculate the load curve for half sine pulse loading, the empirical equation below can be used: Acceleration (g) = 386.4*A*Sin (∏*n/R)

Where,g : Acceleration in g'sA : Total Shock pulse 'g' value obtained using ∆V equation shown previouslyn : Data points 1,2,3.....RR : Number of Acceleration resolution data points

Figure 4. Input & Output Responses, Simulation Model and Test Unit

Figure 5. FEA Simulation Results



Analysis Results and Modal Correlation/Calibration Techniques

After simulating the product assembly for impact shock loading, the un-calibrated results from the first itera-tion model are mapped onto the test data to get the initial behavior predicted. If the initial match shows a huge disagreement of analytical model results with test data, the following weak points should be targeted/-fine-tuned to calibrate the model:

The boundary conditions (constraints locations) should be rechecked and simulated as close as possible to the test setup. The distribution of mass and stiffness in the simulated model should be checked against the actual test unit for placement of various components /sub-assemblies. If a particular component/sub-assembly contributes enough to the overall stiffness of the structure, it should not be modeled as lumped mass. Instead, an approximate geometry with slightly realistic material property values should be used. Two adjacent components should be tied together using MPCs/Constraints equations only if the distance between them is negligibly small. Distant components tied together using MPC will provide unnecessary


Figure 6. Dave S Steinberg's deflection equations for Shock and Random Vibrations analysis


Acceptance Criteria for 'Shock' Loading

The FE simulation results (PCB board out-of-plane deflections, stresses, strains, etc.) are compared with various acceptance criteria based upon the empirical equations as shown below. The maximum allowable out-of-plane board deflections are calculated using Dave S Steinberg's deflection equations for Shock and Random Vibrations analysis. Margin of Safety calculations are also performed to get the overall board strength against random and shock impact loading.

Using all the above mentioned empirical equations for shock load calculation, response prediction and com-parison with acceptance criteria, FE simulation is performed for initial iteration which then gets calibrated using test data. After incorporating the above mentioned calibration technique, a good analysis-to-test data match has been obtained as shown in Figure 8.

Figure 7. Margin of Safety calculations

Figure 8.Test-to-FEA correlation


FEA-to-Actual Test Correlation


This extensive FEA based design methodology has actually been successfully implemented for a number of HCL business partners / clients over the past two years and has generated numerous successful case studies:

Successful implementation on “Hydro Mechanical Control Unit” for a renowned Aircrafts Brakes System OEM worldwide. Successful implementation on “Electronics Server Data Storage Assembly” for a renowned Tier 1 supplier of Data Servers worldwide. Successful implementation and validation on various other Electronic Enclosure Assemblies for a Tier 1 and 2 supplier of sensors, valves, actuators, etc.


Business Relevance / Practical Implementation on Live Projects

Figure 9. Implementation of FEA Design Methodology on Actual Real time Projects @ HCL

The mathematical calculations above for the maximum allowable deflections and peak accelerations help the FE analyst to cross-check the FEA results and validate the numbers through safety margin calculations. The Steinberg empirical calculations for PCB max out-of-plane deformation can be used to calculate the safety margins and validate the design, and are universally accepted by Enclosure Design Engineers as it has strong theoretical and practical correlations.

Best Practices


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Copyright@ HCCopyright@ HCL TechnologiesAll rights reserved.

Praveen AhujaHCL Engineering and R&D Services

Reference

Conclusion and Recommendations

Author Info

Vibration Analysis of Electronic Equipment, Dave S. Steinberg, Third Edition, McGraw Hills publications

Environmental Tests Procedure -Product Shock Tests - Document Section 760

ANSYS 12.1 Help Documentation

AIAA Paper, #2004-1535, A. Brown and D. McGhee

This extensive FEA based design methodology, substantiated by the usage of various empirical equations, Test-to-FEA correlation and model calibration, has been successfully implemented in various real time design projects leading to the following business benefits:

Iterative design using parametric modeling, leading to an optimized solution within the constrained design space. Faster turnaround time, leading to an overall reduction in product design cycle. Significant reduction in testing and prototyping cost and efforts. Enhanced productivity and efficiency. Ability to identify unforeseen problem areas in the system.

The overall simulation time can be reduced further with the help of automation tools like scripts/macros. Pro-gramming languages can also be used for easier and faster post processing of FE simulation results.


A Novel Design Approach for Electronic Equipment - FEA Based Methodology

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