A Primer on Fatigue Damage Spectrum for Accelerated and Reliability Testing

Transcription

1 A Primer on Fatigue Damage Spectrum for Accelerated and Reliability Testing John VanBaren Vibration Research Corporation ASTR 2016, Sep 28-30, Pensacola Beach, FL 1

2 Introduction Use FDS to compare End-Use Environment to Test Environments Apply damage to the same frequency ranges Create a Random PSD that is the Damage Equivalent to imported & weighted time history file(s) Combine Multiple & Complex End-Use Environments Accelerate testing using FDS and Kurtosion ASTR 2016, Sep 28-30, Pensacola Beach, FL 2

3 Alternative Approaches Random Import Create a Test Profile from Time History Data Method 1: Peak Hold PSD Method 2: Average PSD Method 3: Field Data Replication ASTR 2016, Sep 28-30, Pensacola Beach, FL 3

4 Random Import Summary Review Summary information of imported file Acceleration, Velocity, Displacement, Kurtosis ASTR 2016, Sep 28-30, Pensacola Beach, FL 4

5 Random Import Averaging Method FFT of each block of data is averaged together Creates a uniform average power of the test Demand: 5.96 G rms, G pk, K=3 ASTR 2016, Sep 28-30, Pensacola Beach, FL 5

6 Random Import Peak Hold Method Peak Hold FFT based on peaks, not average Extracts the peaks from the blocks of data Peaks are used to create the PSD Demand: 33.35G rms, 150.1G pk,k=3 ASTR 2016, Sep 28-30, Pensacola Beach, FL 6

7 Field Data Replication Method Exact replication of Time History Maintains ordering of Stress Cycles Cannot be accelerated ASTR 2016, Sep 28-30, Pensacola Beach, FL 7

8 Three Key Questions Is it possible to design a test (profile and length of time) that accurately simulates the End-Use Environment of a product throughout its lifetime? Is it possible to confidently combine multiple, complex End-Use environments into a single test profile? Is it possible to reliably accelerate a test and maintain an accurate simulation of imported field data? ASTR 2016, Sep 28-30, Pensacola Beach, FL 8

9 New Method: Fatigue Damage Spectrum Same recording duration and lowest frequency Accounts for time history, duration, and damage ASTR 2016, Sep 28-30, Pensacola Beach, FL 9

10 Applications Create a Random Test Profile that: Is statistically representative of the EUE Is the damage equivalent to multiple imported waveforms Reduces test time by accelerating damage Compare Specs and EUE Validate the random testing being conducted Validate warranty/lifetime expectations Re-create failures in the lab ASTR 2016, Sep 28-30, Pensacola Beach, FL 10

11 Background What is Fatigue Damage? How does the UUT experience damage? Instantaneous Stress Limit Long Term Fatigue Damage Is it statistically possible to shorten test times? Equivalent amount of Fatigue Damage Cannot exceed Instantaneous Stress Limit A specific amount of damage leads to failure ASTR 2016, Sep 28-30, Pensacola Beach, FL 11

12 Background Fatigue Damage n i = number of cycles applied with peak stress, S i N i = number of cycles with peak stress, S i needed to cause failure D = total damage ASTR 2016, Sep 28-30, Pensacola Beach, FL 12

13 Background Computing FDS Acceleration Waveform #1 k Q b c Kurtosion Acceleration Waveform #2 Integrator Velocity Multiply Stress Narrow BandPass Filters Rainflow Counting Algorithm Rainflow Cycles Damage Calculation Fatigue Damage Spectrum Power Spectral Density Acceleration Waveform #3 Single (or narrow range) frequency stress waveforms ASTR 2016, Sep 28-30, Pensacola Beach, FL 13

14 Import Time History File(s) Text SDoF via Smallwood RIRDF ASTR 2016, Sep 28-30, Pensacola Beach, FL 14

15 Plotting the FDS ASTR 2016, Sep 28-30, Pensacola Beach, FL 15

16 Water Bucket Analogy ASTR 2016, Sep 28-30, Pensacola Beach, FL 16

17 FDS The Solution Evaluate Test Tool Appropriateness RS table is not always the best tool to conduct test Effective at high frequencies Not good tool when damage occurs at low freq ASTR 2016, Sep 28-30, Pensacola Beach, FL 17

18 FDS The Solution Incorporate FDS and Kurtosion Combine and weight multiple time histories to reflect service life Validate existing test methods Improve test protocols Create a random test profile that is the damage equivalent of the imported time history files, then accelerate it! ASTR 2016, Sep 28-30, Pensacola Beach, FL 18

19 Enter m and Q Values Import Time History file(s) weight proportional to Service life Set frequency range same lowest frequency for all files Enter Target Life Accelerate the Test Add Kurtosis Create the Table Accelerated Stress Testing and Reliability Creating a Test with FDS ASTR 2016, Sep 28-30, Pensacola Beach, FL 19

20 For Analysis or general testing m = 8 Q = 10 V-Note #0017 For advanced testing Statistical Analysis m Calculator V-Note #0018 Accelerated Stress Testing and Reliability What do you do for m and Q? ASTR 2016, Sep 28-30, Pensacola Beach, FL 20

21 Import a Time History File Set Analysis Frequency Range Set frequency resolution, e.g. 1/24 th octave Select the Acceleration Time History File Scan the File ASTR 2016, Sep 28-30, Pensacola Beach, FL 21

22 Combining FDS Import multiple time history files-weight by time and/or number of events, e.g. transients, potholes Select Combine FDS Add Scan, Select next waveform, Repeat ASTR 2016, Sep 28-30, Pensacola Beach, FL 22

23 FDS Parameters ASTR 2016, Sep 28-30, Pensacola Beach, FL 23

24 Test Compression Weight each waveform by exposure time, and/or number of discrete events Accelerate the test creating a Gaussian PSD profile that is the damage equivalent to the total target life. ASTR 2016, Sep 28-30, Pensacola Beach, FL 24

25 Combined Fatigue Damage vs. Frequency Service Life, Spec Reqts, Warranty, compare with HALT Step Stress ASTR 2016, Sep 28-30, Pensacola Beach, FL 25

26 Add Kurtosis Kurtosis can be added to the waveform More realistic representation of real world peaks Lowers g rms requirement of the test profile Some tests jack the RMS to achieve peaks assuming 3σ Reduced Shaker duty cycle F=ma, but Less heat generation ASTR 2016, Sep 28-30, Pensacola Beach, FL 26

27 FDS Accommodates Kurtosis ASTR 2016, Sep 28-30, Pensacola Beach, FL 27

28 Creating a PSD Convert the combined FDS to PSD- Create Table Creates a test of equivalent damage to all combined waveforms ASTR 2016, Sep 28-30, Pensacola Beach, FL 28

29 Conclusions Use FDS to compare End-Use Environment to Test Environments Apply damage to the same frequency ranges Create a Random PSD that is the Damage Equivalent to imported & weighted time history file(s) Combine Multiple & Complex End-Use Environments Accelerate testing using FDS and Kurtosion ASTR 2016, Sep 28-30, Pensacola Beach, FL 29

30 [1] A. Steinwolf, Shaker simulation of random vibration with a high kurtosis value, in Journal of the IEST, May/June 1997, pp [2] P. VanBaren, The missing knob on your random vibration controller, in Sound and Vibration, October 2005, pp References [3] G. R. Henderson and A. G. Piersol, Fatigue Damage Related Descriptor for Random Vibration Test Environments, in Sound & Vibration, October 1995, p. 21. [4] J. VanBaren and P. VanBaren, The Fatigue Damage Spectrum and Kurtosis Control, in Sound & Vibration, October 2012, p. 10. [5] MIL-STD-810 G; Method 514.6, Annex A. ASTR 2016, Sep 28-30, Pensacola Beach, FL 30

31 Biography John Van Baren is the president of Vibration Research Corporation, Jenison Michigan, which he founded in He is a graduate of Calvin College, and the University of Michigan Engineering School. John is a registered professional engineer in the state of Michigan. His experience includes 35 years in R&D of various capacities in the vibration world. He has designed electro-dynamic shaker systems, switching power amplifiers, and PC based shaker controllers. He was a pioneer in the application of time history replication on electrodynamic shakers, introduction of Kurtosion to random vibration control, introduction of the Fatigue Damage Spectrum to random vibration control, and continues to guide the company forward as a leader in the field of vibration control. He also has an interest in General Aviation. ASTR 2016, Sep 28-30, Pensacola Beach, FL 31

32 THANK-YOU John VanBaren Vibration Research ASTR 2016, Sep 28-30, Pensacola Beach, FL 32