HALT/HASS for Product Reliability

test-facility-halt-third

Highly Accelerated Life Testing (HALT) is a process for ruggedization of preproduction products.  It is also referred to as AST (Accelerated Stress Testing).

Highly Accelerated Stress Screening (HASS) is the production screen for products once they have been characterized in HALT.

HALT and HASS each use very high rate of change temperature chambers which are combined with multi-axis pneumatic vibration systems.

Slides: HALT/HASS for Product Reliability: HALT_HASS.pptx

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A function for synthesizing a rough approximation of a HALT/HASS acceleration time history (repetitive shock) is included in:

Matlab script: Vibrationdata Signal Analysis Package

The function can be accessed via:

>> vibrationdata > Miscellaneous > generate > HALT/HASS simulation

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More later…

– Tom Irvine

Beam Supported by End Springs

beam_springs
A function for calculating the natural frequencies and mode shapes for an elastic beam supported by end springs is included in:

Matlab script: Vibrationdata Signal Analysis Package

The function can be accessed via:

>> vibrationdata > Miscellaneous > Structural Dynamics > Beam Bending > Beam with End Springs, FEA

Options for calculating the beam response to an applied force will be added soon.

– Tom Irvine

Normal Tolerance Factors

Maximum predicted environment (MPE) levels can be derived for acoustic, shock, and vibration levels where flight data is available.  The enveloping for multiple sets of data can be performed using tolerance factors as described in the following papers.

Normal Tolerance Factors for Upper Tolerance Limits: normal_tolerance_factors.pdf

Uncertainty Margins in Aerospace Vibroacoustic Levels: uncertainty.pdf

A function for calculating tolerance factors is given in:

Matlab script: Vibrationdata Signal Analysis Package

>> vibrationdata > Miscellaneous > Statistical Distributions & Tolerance Factors > Tolerance Factors

– Tom Irvine

Electronic Circuit Board Design Reliability Lessons Learned

Here are some papers:

Electronic Circuit Board Design Reliability Lessons Learned: electronics_design_reliability.pdf

Effect of Conformal Coating on Circuit Board Vibration Response:  conformal_coat.pdf

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Steinberg’s Vibration Analysis for Electronic Equipment describes the methods for designing electronic equipment that must work with a high degree of reliability in severe shock and vibration environments. This text provides practical methods for analyzing circuit boards and other equipment. Topics include sinusoidal vibration, random vibration, fatigue, classical shock, and shock response spectrum.

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See also:  Vibrationdata Steinberg

– Tom Irvine

SDOF System Response to Initial Velocity & Displacement

Mass_spring

I have added a function for calculating the free vibration response of an SDOF system to initial conditions to the Vibrationdata GUI package.

Matlab script: Vibrationdata Signal Analysis Package

>> vibrationdata  > Miscellaneous > Structural Dynamics > Spring-Mass Systems > SDOF Free Vibration Response to Initial Conditions

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Reference: free.pdf

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– Tom Irvine

IEEE Std 693-2005, Recommended Practice for Seismic Design of Substations

I am currently researching IEEE Std 693…

One of its recommended shaker test methods for power equipment is to use a “sine beat” acceleration time history. The main frequency is selected as the equipment’s natural frequency.

The minimum number of beats is 5 with a minimum of 10 cycles within each beat pulse. There is also a pause between beat pulses.

A problem with this approach is that the corresponding displacement has a stair-step effect for a whole number of cycles. This offset disappears if an extra half-cycle is added. An example would be to use 10.5 cycles.

Here is a slide presentation:  IEEE_693_sine_beat.pptx

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I have added a function for generating IEEE sine beat time histories to the Vibrationdata GUI package.

Matlab script: Vibrationdata Signal Analysis Package

>> vibrationdata > Miscellaneous > Generate Signal > IEEE std 693 Sine Beat

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The package also has a function for generating the Required Shock Spectrum (RSS) levels.

>> vibrationdata > Import Data to Matlab > SRS Library Array > IEEE std 693 RSS, Various

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References

An Implementation of an Earthquake Test, According to the Sine-Beat Method: Sine_beat.pdf

Seismic Considerations of Circuit Breakers: Seismic_Considerations_of_Circuit_Breakers.pdf

IEEE 693 Seismic Qualificaiton of Composites for Substation High-Voltage Equipment: 13_2306.pdf 

– Tom Irvine

Cylindrical Shell Natural Frequencies & Mode Shapes

A function for calculating cylindrical shell natural frequencies via the wave method is now included in the Vibrationdata GUI package.

Matlab script: Vibrationdata Signal Analysis Package

This function may be accessed via:
vibrationdata > Structural Dynamics > Rings & Cylinders > Cylinder, Wave Model

Reference Papers

Study on applicability of modal analysis of thin finite length
cylindrical shells using wave propagation approach:  Link

Natural Frequencies of a Finite, Thin-Walled Cylindrical Shell: cylindrical_shell.pdf

– Tom Irvine

Response of an Undamped Two-degree-of-Freedom System to Base Displacement Excitaiton

twodof_disp

The following is mostly an academic problem.

The Response of an Undamped Two-degree-of-freedom System
Subjected to Base Displacement via Modal Analysis:  twodof_base_disp_modal.pdf

The Response of an Undamped Two-degree-of-freedom System
Subjected to Base Displacement via Laplace Transforms: twodof_base_disp_Laplace.pdf

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See also:  Two-degree-of-freedom Systems

– Tom Irvine

Fluid Slosh in a Basin or Tank

Sloshing can occur in swimming pools, trucks carrying liquids, rocket vehicle propellant tanks and in other situations.

Sloshing of propellants may adversely affect the stability of a space vehicle and the integrity of the tank structure. Sloshing describes the free-surface oscillations of fluid in a partially filled tank. The oscillations result from lateral and longitudinal displacements or angular motions of the vehicle.

I have added a function for calculating slosh natural frequencies to the Vibrationdata GUI package.

Matlab script: Vibrationdata Signal Analysis Package

The slosh function may be accessed via:
vibrationdata > Miscellaneous > Fluid Systems > Slosh

References

An Introduction to Fluid Slosh:  slosh_intro.pdf

NASA SP-106 The Dynamic Behavior of Liquids in Moving Containers
NASA SP-8009 Propellant Slosh Loads
NASA SP-8031 Slosh Suppresion

– Tom Irvine

Fatigue Damage including Mean Stress

Options for including mean stress have been added to the Vibrationdata GUI package’s Fatigue Toolbox, for both stress time histories and PSDs.

Four methods are available:

Gerber
Goodman
Morrow
Soderberg

Matlab script: Vibrationdata Signal Analysis Package

Here are some charts from Iowa State University: Fatigue Mean Stress

– Tom Irvine