Certain equipment must be designed and tested to withstand external vibration excitation. This is common in the military, naval, aerospace and other industries. The equipment is typically mounted on a shaker table and subjected to base excitation. The input may be random vibration if the… Read more
The NASA/JPL Environmental Test Laboratory (ETL) developed and built a tunable beam shock test bench based on a design from Sandia National Laboratory many years ago. ETL has been using this test system successfully since October 2008. The excitation is provided by a projectile driven… Read more
There is a need to derive a power spectral density (PSD) envelope for nonstationary acceleration time histories, including launch vehicle data, so that components can be designed and tested accordingly. Three methods are considered in the following paper using an actual flight accelerometer record. The… Read more
Prerequisite Reference Papers David O. Smallwood, An Improved Recursive Formula for Calculating Shock Response Spectra, Shock and Vibration Bulletin, No. 51, May 1981. DS_SRS1.pdf Rainflow Counting Tutorial Fatigue Damage Spectrum, Time Domain Fatigue Damage Spectrum Dirlik Method for PSDs Optimized PSD FDS Nonstationary * *… Read more
Assume that input and response acceleration PSDs have been measured. The corresponding displacement PSDs can be readily calculated. But the relative displacement cannot be calculated accurately because the phase angles are discarded in the PSD calculation. The best method is to perform the relative displacement… Read more
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… Read more
A typical SRS specification has a ramp and plateau. The best way to meet this specification type is with a complex oscillating pulse. In some cases, a classical shock pulse may be used, but this will cause an over-test at certain frequencies. Also, classical pulses… Read more
1. Band-Splitting 2. Time-Level Equivalence 3. PSD Synthesis using Sine Series PowerPoint Slides: webinar_41_psd_topics.pptx Audio/Visual File: NESC Academy PSD Special Topics – Recommend viewing in Firefox with Sliverlight Plugin * * * Matlab script: Vibrationdata Signal Analysis Package * * * Here is a brief guideline… Read more
Shock and vibration environments produce dynamic stresses which can cause material failure in structures. The potential failure modes include fatigue, yielding, and ultimate stress limit. F.V. Hunt wrote a seminal paper on this subject, titled “Stress and Stress Limits on the Attainable Velocity in Mechanical… Read more
Wayne Tustin is a pioneer in the field of shock and vibration training. I have had the opportunity to learn from him at several IEST meetings and other conferences. He taught me the meaning of SRS (G) and PSD (G^2/Hz) units, when I was… Read more