157 Fixture Design for Vibration and Shock Testing

This course incorporates a me­chanical design fundamentals segment equivalent to  course 310, "Mechanical Design for Product Reliability," which may be taken by itself. Another version of course 157 (course 157-3) is a standalone course, intended for on-site presentation.

For Whom Intended  This seminar is intended for dynamics test and evaluation personnel desiring an understanding of practical approaches to the design and fabrication of test fixtures used in vibration and shock testing. Tooling Engineers responsible for fixture design need this training.

Fixture Design ExampleQuality Assurance and Reliability specialists will find the course useful. So will test and instrumentation specialists. The writers of specifications for environmental tests and for manufacture of fixtures will benefit from knowledge of practical limitations that exist. Product designers who are seeking solutions to vibration and shock problems will also find the course helpful.

A fixture designer must be able to design a test fixture that will transmit the intended input forces directly to the Device Under Test. To accomplish this, a designer must have specific skills as well as an understanding of vibration and shock, structures, dynamic theory, materials and fabrication.

Brief Course Description  The course commences with an intro­duction to vibration and then covers basic dynamics theory in­cluding relationships between displacement, velocity and accel­eration. Dunker­ley's and Ray­leigh's meth­ods are introduced, with exam­ples. Damping, trans­mis­si­bi­lity ratio and resonance stacking are addressed. The course then covers basic structural theory: tension, com­pression, stress, strain, tor­sion and mo­ments of iner­tia. Exam­ples show the torsional shape factors of different struc­tures.

The instructor then ad­dresses fre­quen­cy and stiffness of beams, plates and gus­sets, pro­viding useful graphs, formu­las and examples. Bolted connections are covered next. Use­ful data on struc­tures, bolted connections etc., is inclu­ded in the course work­book which will be an invaluable reference tool back at the work­bench.

Modal analysis is then discussed, with men­tion of multi-degree-of-free­dom systems, modes and com­plex systems. Measurement and fixturing for modal analysis and testing are covered, before moving on to me­chan­ical shock and its design implications. Methods of isolating assemblies from shock and vi­bra­­tion are covered.

Fatigue is covered, including discussion of crack growth rates, fracture mechanics, the S-N curve, and the use and abuse of ac­celerated testing, including Miner's hypothesis.

Material selection is then covered, with information on over­all and design-limiting material properties. Tools are pro­vided for com­paring different materials. The design funda­men­tals seg­ment covers gen­eral design sug­ges­tions, such as methods for in­creas­ing na­tural frequencies.

The course then moves on to a brief dis­cus­sion of ran­dom vibration, inclu­ding power spectral density theory. The concept of RMS acceleration is dis­cussed, followed by a basic introduction to shakers and vibration testing.

General considerations in fixture design are dis­cussed next, along with an in­troduction to instrumentation and sinu­soi­dal vibration testing, as they apply to the fixture de­sign and evaluation process.

The course outlines a variety of strategies for attaching test items to fixtures, from the simplest adaptor plates to massive custom-designed cast and welded fixtures. Prac­tical simplified designs and fabrication techniques, including bonding, bolting and welding, are discussed and class pro­jects are undertaken to de­sign some typical fixtures.

Diploma Programs  Course 157 is required for TTi's Dynamic Test Specials (DTS) Diploma program. It may be used to satisfy the course 310 requirement in the Mechanical Design Specialist (MDS) Diploma or as as an optional course for any other TTi specialist diploma program.

Related Courses  Course 157-3, a standalone version of 157 including portions of course 310, is available for on-site presentation to experienced designers.

Prerequisites  A TTi Fundamentals of Vibration course would be helpful. Participants will need first-year college mathematics (or equivalent experience) and some facility with fundamental engineering computations. Some familiarity with electrical and mechanical measurements and vibration will be helpful, as will an understanding of and familiarity with tooling and manufacturing.

Text  Each student will receive 180 days access to the on-line electronic course workbook. Renewals and printed textbooks are available for an additional fee.

Course Hours, Certificate and CEUs  Class hours/days for on-site courses can vary from 14-35 hours over 2-5 days as requested by our clients. Upon successful course completion, each participant receives a certificate of completion and one Continuing Education Unit (CEU) for every ten class hours.

OnDemand Internet Complete Course 157 features over 24 hours of video as well as more in-depth reading material. All chapters of course 157 are also available as OnDemand Internet Short Topics. See the course outline below for details.


Course Outline

310 - Chapter 1 - Introduction to Vibration

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OnDemand Short Topics$100.00

310 - Chapter 2 - Dynamic Force and Motion

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OnDemand Short Topics$350.00
  • Laws of Motion
  • Weight vs. Mass
  • Gravity
  • Density
  • Force, Mass and Acceleration
  • Degrees of Freedom
  • Displacement
  • Velocity
  • Acceleration
  • Natural Frequency
  • Sinusoidal Waveform
  • Modeling Complex (MDoF) Systems
  • Dunkerley's and Rayleigh's Methods
  • Transmissibility
  • Isolation
  • Damping
  • Examples

310 - Chapter 3 - Review of Structural Design Fundamentals

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OnDemand Short Topics$400.00
  • Material Properties
  • Tension and Compression
  • Stress and Strain
  • Shear
  • Torque
  • Moments of inertia
  • Torsional Stiffness
  • Torsional Shape Factors
  • Bending Stiffness
  • Instability of beams and flanges

310 - Chapter 4 - Designing for Stiffness

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OnDemand Short Topics$150.00
  • Natural frequency and stiffness graphs for various structures
  • Beam Formulas
  • Plate frequency parameters, examples
  • Column Resonance
  • Axial Resonance
  • Example: Stresses in a Loaded Beam

310 - Chapter 5 - Bolted Connections

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OnDemand Short Topics$300.00
  • Preload
  • Data on Bolts
  • Design of Bolted Joints
  • Stiffness Data
  • Required flange material area
  • Material thickness, stiffness

310 - Chapter 6 - Modal Analysis and Modal Testing

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OnDemand Short Topics$100.00
  • Applications
  • Modes, Natural Frequencies
  • Fixturing for Impedance and Modal Testing
  • Finite Element Analysis (FEA)
  • Example

310 - Chapter 7 - Random Vibration

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OnDemand Short Topics$50.00
  • Demonstrations-Sinusoidal Vibration, Complex Waveform, Random Vibration
  • Probability Density
  • Power Spectral Density (PSD)
  • Shaker Power Spectral Density Response
  • Equalization
  • Calculating the RMS Acceleration from Spectral Plot

310 - Chapter 8 - Mechanical Shock

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OnDemand Short Topics$100.00
  • Causes of Shock, Effects and Remedies of Shock
  • Transient or Shock Tests
  • Shock Pulse shapes, Shock Isolation Example

310 - Chapter 9 - Fatigue

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OnDemand Short Topics$150.00
  • Fatigue-Crack-Growth Rate
  • How Materials Behave: The S-N Curve
  • Factors Influencing Fatigue Behavior
  • Stress Concentration
  • Photoelasticity
  • Fracture Mechanics
    • Fracture Toughness of Some Common Materials
    • Crack Propagation
    • Crack Growth Rate
    • Example of a Fracture Surface
    • Fracture Surfaces
  • Forensics
  • Failure Models
    • Failure Mechanism
    • Time-Dependent Failures
    • First Passage Model (Time to Failure)
  • The Goodman Diagram
  • The Constant Life Diagram
  • Exceeding a Critical Stress During Random Vibration
  • Inverse Power Law Model - Time to Failure
  • Fatigue Damage Model Based Upon S-N Curve - Number of Cycles to Failure
    • Idealized S-N Curve for Structural Materials
  • Fatigue Damage Model Based on Crack Growth Rate
  • Crack Growth Rate vs. Stress Intensity Factor
    • Stress Intensity Factors
  • Miner's Hypothesis for Fatigue Damage Accumulation
    • Miner's "Rule" Cautions
    • Determination of Effective Excitation
    • Fatigue, Miner’s Rule Example
  • Typical Endurance Limits
  • "S-N" Curve from Fatigue Testing
  • Fatigue Case Study
  • Example: Rating a Printed Circuit Board

310 - Chapter 10 - Material Selection in Engineering Design

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OnDemand Short Topics$50.00
  • Overall & Design-Limiting Material Properties
  • Application-Specific Material Properties
  • Example: Optimization of Shaker Table

310 - Chapter 11 - Chassis Analysis Example

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OnDemand Short Topics$50.00
  • Chassis Dynamics, Section Properties
  • Increasing Resonant Frequency, Torsion
  • Rotational Inertia

310 - Chapter 12 - Design Suggestions

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OnDemand Short Topics$50.00

157 - Chapter 1 - Introduction to Vibration Test Equipment

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OnDemand Short Topics$100.00
  • Electrodynamic Shakers
  • Force ratings, Displacement and Velocity Limits
  • Effective Mass of Exciter Table
  • Electrohydraulic Shakers
  • Reaction Mass Effect
  • Slip Plates
  • Hydrostatic Bearings
  • Overturning Moment

157 - Chapter 2 - Introduction to Fixture Design

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OnDemand Short Topics$100.00
  • Purpose of the Fixture
  • Fixture Performance
  • Considerations in Fixture Design

157 - Chapter 3 - Vibration Test Fixtures - General Remarks

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OnDemand Short Topics$100.00
  • The "black art" of designing fixtures
  • Function of the test fixture
  • Difficulty in achieving identical motion at all attach points
  • Required information about the test item and the test program
  • Required information about shaker
  • Bolting to the shaker table
  • An example of successful redesign
  • Fixture weight relative to test item weight
  • Temperature and altitude affect fixture design for combined environments

157 - Chapter 4 - Interface Items

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OnDemand Short Topics$50.00
  • Introduction
  • Table expanders
  • Horizontal accessory tables: oil-film slip tables
  • Connecting horizontal accessory tables to shakers
  • Horizontal accessory tables: hydrostatic bearings
  • Misuse of horizontal accessory tables
  • Avoid using bolts in shear
  • A note of warning on wide plates

157 - Chapter 5 - Measurement and Readout of Vibration

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OnDemand Short Topics$100.00
  • Accelerometers
  • Amplifiers
  • Frequency response
  • Mounting affects frequency response
  • Cable routing affects frequency response
  • Cross-axis sensitivity
  • Hand-held probe accelerometers
  • Readout of Vibration Intensity and Frequency: Conversion to numbers
  • Oscilloscopes and oscillographs
  • X-Y plotters and pen recorders
  • Decibel scaling
  • Need for tracking filter in evaluating fixtures
  • Calibration checks on the entire measuring system
  • Day-to-day accelerometer calibration in a "working" laboratory

157 - Chapter 6 - Vibration Testing Specifications

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OnDemand Short Topics$50.00
  • What a fixture designer needs to know about specifications
  • A typical specification
  • Mounting the test article
  • Eliminating variables
  • Location of the control accelerometer
  • Intent of Specifications better met by use of multiple accelerometers
  • Fixture should minimize variations in motion intensity
  • Standardization needed

157 - Chapter 7 - Basic Fixture Types

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OnDemand Short Topics$50.00
  • Introduction
  • Adapter plates
  • Cube fixtures
  • Hemispheres
  • Conical fixtures
  • Enclosed box fixtures
  • Drum fixtures
  • L-type fixtures
  • T-type fixtures
  • Open box fixtures

157 - Chapter 8 - Fixture Fabrication Methods

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OnDemand Short Topics$200.00
  • Introduction
  • Materials for fixtures
  • Machining fixtures from solid stock
  • Bolted fixtures
  • Cast fixtures
  • Welded fixtures
  • Bonded fixtures
  • Laminated fixtures
  • Epoxy formed fixtures
  • Potted fixtures
  • Foamed plastics for damping
  • Inserts

157 - Chapter 9 - Fixture Evaluation

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OnDemand Short Topics$50.00
  • Importance of Evaluating Fixtures
  • Transmissibility vs. frequency
  • Plotting Transmissibility vs. Frequency: Setups
  • Example—Determining Resonant Frequency of a Fixture
  • Apparent Resonances
  • Judging a Good Fixture
  • Sweep Rates
  • Evaluation with Load
  • Improving a Faulty Fixture
  • L-Fixture FEA Results
  • Keeping Records of Fixtures
  • Damping Ratio Measurements

157 - Chapter 10 - Orthogonal Motion—Cross Talk

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OnDemand Short Topics$50.00
  • Describing Non-Straight-Line Motion
  • Test Specifications
  • Idealized Shaker Motion
  • Linear and Orthogonal Motion
  • Orthogonal Motion With Load
  • Large Shaker May be Economical
  • Accelerometer May be Faulty

157 - Chapter 11 - Fixture Design for Random Vibration and Shock

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OnDemand Short Topics$50.00
  • Fixtures for Random Vibration Testing
  • Random Vibration for Fixture Evaluation
  • Transmissibility Measurements for Random
  • Shock Testing
  • Fixture Design for Shock Tests

157 - Chapter 12 - Analysis of an L-Fixture

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OnDemand Short Topics$50.00
  • Description of the fixture
  • Basic dimensions
  • Procedure for Analysis
  • Step-by-step analysis

157 - Chapter 13 - Class Project: Designing a Cubical Fixture

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OnDemand Short Topics$50.00
  • Suggested Cubical Fixture (Project 1)
  • Cubic Fixture Design Project: Process
    • Part 1. Axial Mode
    • Part 2. Bending Mode
  • Details
  • Results
  • Material Options
  • Configuration Obtained by Finite Element Analysis

310 - Appendix B - Glossary of Symbols and Units

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OnDemand Short Topics$25.00

310 - Appendix B - Index of Equations in 310

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OnDemand Short Topics$25.00

157 - Appendix B - Index of Equations in 157

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OnDemand Short Topics$25.00

310 - Appendix C - Dynamic Force and Motion (Reference)

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OnDemand Short Topics$25.00

310 - Appendix D - Index of Graphs and Tables

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OnDemand Short Topics$25.00

310 - Appendix E - Understanding Decibels and Octaves

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OnDemand Short Topics$25.00

157 - Appendix C - Lissajous Patterns

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OnDemand Short Topics$25.00
  • Lissajous Pattern Development
  • Use of Lissajous Patterns to Evaluate Vibration Responses

Final Review


Award of Certificates for successful completion

Click for a printable course outline (pdf).

Revised 6/23/18