PRODUCT & PACKAGE VIBRATION TESTING PRODUCT & PACKAGE TESTING VIBRATION & SHOCK

Transcription

1 PRODUCT & PACKAGE VIBRATION TESTING PRODUCT & PACKAGE TESTING VIBRATION & SHOCK Herb Schueneman Chairman, WESTPAK, Inc. Founder, Chairman WESTPAK, INC. March 2016 Dec 2015

2 What s This All About? Why, how, and when do we mechanically test products and package systems? What do we learn from this? What do we do with the information? 2

3 Agenda Background, terminology, etc. Vibration Dynamics Spring/Mass Models; Forces vs. Free Response Types of Excitation; Sine, Random, Acoustic, Sources of input Resonance, Transmissibility, Damping, Fatigue Package Cushioning (springs), A/A plots Design for Vibration 3

4 Dynamics The study of mass that is moving in a flexible environment Flexibility implies springs so the study of dynamics starts with a thorough understanding of Spring/Mass Systems 4

5 SDOF Spring/Mass System MASS 5

6 SDOF Spring/Mass System AN INPUT APPLIED HERE RESULTS IN FREE VIBRATION OF THE MASS MASS AN INPUT APPLIED HERE RESULTS IN FORCED VIBRATION OF THE MASS 6

7 SDOF Spring/Mass System Maximum strain energy MASS Maximum velocity 7

8 Spring Mode Doesn t Matter Tension Compression 8

9 Natural Frequency f n 1 2 K M 3.13 K M M K 9

10 Natural or Resonant Frequency As earlier noted, excitation of the mass results in motion we call free vibration or Natural Frequency, fn. Excitation of the base results in forced vibration of the mass. When the forcing frequency = fn, the mass response is max and is said to be in resonance. 10

11 SDOF vs. MDOF Normal products are pretty complex. A multiple degree of freedom (MDOF) model is more appropriate however much more complex and difficult to analyze. 11

12 Spring Types Almost all products or product/package systems can be analyzed and modeled as complex spring/mass systems. But maybe not Linear Springs.. 12

13 Spring Types Linear Spring D F k=f/d =W/k A p= F n X V 13

14 Spring Types Non-Linear / Hardening Spring d k d SPRING FORCE = 2kd tan (def) 2d 14

15 Spring Types Non-Linear / Softening Spring k F 1 SPRING FORCE =kd tanh def d DEFLECTION 15

16 Spring Types SDOF models assume linear springs Most flexibility in systems is non-linear (Printed Circuit Boards) However, most systems can be analyzed in a near linear portion of their deflection range so that s why we use the linear model 16

17 Coupling M Coupled vs. Uncoupled Motion A F 1 B F 2 F 3 The mass is a homogenous rigid block with center of gravity (cg) at point A. The response of the block to F1 is pure vertical motion. The response of the block to F2 is pure rotational motion. The response of the block to F3 is pure horizontal motion. 17

18 Coupling Coupled vs. Uncoupled Motion M A B F 2 F 3 If (cg) is at point B, F1 produces both vertical and rotational motion of the block. In this case, the motion is said to be coupled. F 1 With (cg) at point B, F3 produces uncoupled horizontal motion. 18

19 Time for Questions! 19

20 Resonance Resonance occurs when a component or system is forced at its fn. Spring/Mass response is amplified at resonance. This is where damage, fatigue, etc. is most likely to happen. 20

21 Resonance Transmissibility Plot Ar Ai f 21

22 How the Test is Conducted Example Vibration Machine Types of Equipment Electrodynamic shaker Hydraulic shaker Single or multi-axis Acoustic (reverberant) chamber 22

23 Types of Mechanical Excitation All Spring/Mass systems respond at their natural frequencies because they can t do anything else. Excitation can be: Sinusoidal Random or pseudo-random Acoustic Other 23

24 Excitation: the Good & the Bad Type Positive Not-So-Positive Sinusoidal Easy to understand Good visual feedback Grandfathered tried & true Random Quicker Less fatigue potential Realistic Matches real life Acoustic Usable for heavy systems Good high frequency Gives false amplification values Over-test for fatigue potential Doesn t account for constructive and destructive interferences between systems More complex Requires a specific controller Very expensive Requires large chamber & analytical capability 24

25 Damping Damping (Rc) is expressed as a ratio of observed damping to Critical Damping in a system. 25

26 Damping Critical Damping is where the mass returns to its initial position in the minimum time without overshoot. 26

27 Mechanical Fatigue Fatigue is the weakening of a material caused by repeatedly applied loads. It is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. Resonance is the prime contributor. Non-critical damping is a factor. 27

28 Sources of Vibration Input Sources of input include: Operation Rotating equipment (cooling fans, motors, etc.) Nearby influences Strong air currents Earthquakes Non-Operating Transportation, shipping (the biggest), logistics Normal movement within intended environment 28

29 Typical Test Procedures Sine search & dwell is still used (problems..) Random dwell is more common Margin test (to failure) has gained wide acceptance (HALT) Imposed by third party Attempt to duplicate the in-use environment (military vehicles & weapons) Lots of creativity in test procedures. (be VERY careful here.) 29

30 Common Test Specs ASTM D3580 (doesn t say much) IEC , -47 (similar) Federal Std 101-C (very dated) ISO various standards JIS - Japanese Industrial Standards MIL STD 167, 810 Telcordia GR-63 CORE (Bell System origin; POTS Plain Old Telephone System) 30

31 Establishing the Test Plan Design of Experiment (DoE) Characterize environments EUT will see Define test inputs to cover all environments Consider Combined Environments Remember shipping / distribution (severe!) Determine acceptance criteria / inspections Quantitative when possible Cosmetic, functional, safety 31

32 Establishing the Test Plan Start Small First: Test temperature and basic mechanical vibration Second: Comprehensive testing (single environment) Third: Combined Environment testing (as applicable) 32

33 Combined Environment Test Inputs Every product will see different environments Sample EUT: Ruggedized Laptop Computer Test inputs discussed Temperature + Vibration Impact Testing + Temperature Extremes Freefall Drop Testing + Temperature Extremes Mechanical Cycling + Temperature Extremes Temperature + Pressure Fluid Submersion + Temperature + Pressure Thermal Shock 33

34 Temperature + Vibration Background of AGREE Testing Typical Test Cyclic functional operation Temperature by application X, Y, Z axis in single direction Random frequency domain by application Transport (1Hz 300Hz) Bare Product (5Hz 2,000Hz) Test Standards MIL-STD-883, MIL-HDBK-781 Variations of Testing Common Issues / Results Unsupported / surface mount component failure Permanent failure to operate correctly 34

35 End Result Ruggedized product Free of latent mechanical defects Good to great reliability out of the box A prioritized list of improvements to be made Verification for meeting a spec requirement 35

36 How About the Package Cushion? One of the functions of a cushion system is to dampen vibration input at those frequencies where the product is sensitive. In essence, we need to know the dynamic spring rate of the cushion. Now we know the PRODUCT vibration sensitivity. Now we need to determine the CUSHION vibration characteristics so that an optimum package system can be designed. 36

37 Vibration Cushion Dynamics Vibration Cushion Curves (called Amplification/Attenuation Plots ) are developed by loading a cushion, shaking it, and measuring the response. Guided Test Block Method 37

38 Vibration Cushion Dynamics T-C MODEL C-C MODEL Alternate Method MASS RESPONSE ACCELEROMETER CUSHION MASS CUSHION INPUT ACCELEROMETER CUSHION VIBRATION TABLE VIBRATION TABLE MASS ADHERED TO FOAM MASS ISOLATED BETWEEN SO THAT THE SPRING TWO SPRINGS (CUSHION) WORKS IN BOTH (CUSHIONS) THAT WORK TENSION AND COMPRESSION IN COMPRESSION ONLY 38

39 Vibration Cushion Dynamics CUSHION TEST SAMPLE CUSHION TEST SAMPLE ELECTRODYNAMIC SHAKER 39

40 Vibration Cushion Dynamics For either method, the S/M system is excited (random or sine vibration) and the response/input ratio is plotted as a function of frequency. 40

41 Vibration Cushion Dynamics The important points on this plot are identified here: A B C 41

42 Vibration Cushion Dynamics The mass on the cushion is changed and the process (transmissibility plot) is repeated. After 5 (min) plots, the data might look like this: 42

43 Vibration Cushion Dynamics The data is then transferred to the Amplification/Attenuation plot 43

44 Vibration Cushion Dynamics Here s how the data is used: 44

45 Time for Questions! 45

46 About WESTPAK, INC. Two Locations: San Jose Laboratory San Diego Laboratory 83 Great Oaks Boulevard Roselle Street San Jose, CA San Diego, CA Contact Us 46

47 THANK YOU! Please Contact Us with any questions or testing assistance needs. We are here to help you! Herb Schueneman Founder, Chairman WESTPAK, INC. 47