New Cushion Curve Method

Transcription

1 New Cushion Curve Method Matt Daum, Ph.D. March Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice

2 Change

3 Change

4 Change

5 Change for the Beloved Cushion Curve?

6 Current Method: Cushion Curve Drop Height 1.25 pcf 1 st Impact Width Weight Length Thickness Deceleration, G's Static Stress, psi

7 X X X XX Limitations of Current Method Deceleration, G's XX X X XX X X X XX X X XX X X 1.5 X X XXX XX X Drop Height, 1.25 pcf, 1 st Impact Static Stress, psi 1. Resource-intensive: ASTM D1596 requires lots of samples and time

8 Limitations of Cushion Curves Drop Height 1.25 pcf 1 st Impact Deceleration, G's Limited Data What if I want to know G level in these areas? Static Stress, psi

9 Limitations of Current Method Lots of samples: ~10,500 for one curve set Lots of time: ~175 hours test time, plus sample making and data analysis Very specific: if you didn t test it, you don t have the curve

10 Something New

11 Something New What if you could Generate a cushion curve for ANY combination of variables? Have all the data for these curves represented in ONE easy equation? Have all this quickly, at a fraction of the effort of the current method?

12 New Method: Stress vs. Energy Called Stress-Energy method Technically, Dynamic stress vs. dynamic energy density Pioneered by Dr. MSU 1990 Stress-Energy is about material properties Relationship b/w variables SL, h, t, and G From ONE equation, can construct ANY cushion curve infinite data from one test! Can be generated with as few as 10 drops

13 New Method: Stress vs. Energy Simply, the relationship between how much energy the material absorbs and how the material reacts to shock Dynamic Energy: Static Loading drop height cushion thickness or, sh t Dynamic Stress: Peak G static loading or, Gs

14 New Method: Stress vs. Energy Deceleration, G's Drop Height 1.25 pcf 1 st Impact Static Stress, psi Relationship between existing variables s = 1.0 h = 36 t = 2.0 Energy = sh/t = 18 Stress = G*s = 50

15 New Method: Stress vs. Energy Drop Height 1.25 pcf 1 st Impact Does it work? Test: predict G s Deceleration, G's h Energy = 18: s t G*s G Static Stress, psi

16 New Method: Stress vs. Energy One equation describing cushion behavior: y = a e bx ANY cushion curve can be calculated Closed cell foam, and corrugated See literature from Burgess, Wenger, etc.

17 New Method: Stress vs. Energy y = a bx e x y x and y from testing = stress = Gs = energy = sh t a and b calculated from curve fitting for each specific material and density

18 New Method: Stress vs. Energy Drop Height 1.25 pcf 1 st Impact 1.0 Limited Data Deceleration, G's Static Stress, psi Don t think of cushion curves as lines on a grid Unlimited Data Think of cushion curves as lines from an equation

19 New Method: Stress vs. Energy 1. Plot Stress vs Energy 2. LSM, or Power Trendline in Excel This equation can now be used to draw any cushion curve Ethafoam Select polyethylene, 1.9pcf 1st Drop A Dynamic Stress, Gs y = e x R 2 = Dynamic Energy, sh/t B

20 Compare Methods Test Apparatus Current: ASTM D1596 Cushion drop test New: Stress vs. Energy Same Collect data height, area, thickness, G, wt Same data, less drops Plot results Calculate Plot G vs static stress n/a Plot Gs vs sh/t Curve fit

21 Compare Methods h w a t G Gs sh/t Data Collection is same Calculate and plot new relationships

22 From Equation to Cushion Curve

23 Case Study

24 Case Study: Background LaserJet User of Arcel 730 Where are the cushion curves? Arcel 730 Generate Cushion Curves? Michigan State Stress Energy Method Develop Test Procedure Clemson Performed Test Collect Data

25 Case Study: Test Objectives Find Stress vs. Energy equation for Arcel pcf 1.7 pcf 2.2 pcf 3.0 pcf

26 Case Study: Test Procedure

27 Case Study: Results Sample Drop # Area Weight h t G sqinches lbs inches inches 30C A C A B A C D E C E D B A E B C A D

28 Case Study: Results ARCEL 1.2M 1st drop Stress (Gs) y = ae R 2 = bx Energy (sh/t) 1.0

29 Case Study: Results Stress vs. Energy equation for Arcel pcf 1.7 pcf 2.2 pcf 3.0 pcf Stress/Energy Equation generated Cushion properties fully characterized ANY cushion curve can now be drawn

30 Conclusion

31 Conclusion Recommendation #1 Convert existing cushion curves into Stress/Energy equations Generate new data?

32 Calculated Values from Existing Cushion Curves Name Material Density (pcf) Impact A B ARCEL 512 Arcel ARCEL 512 Arcel DYLITE D195B EPS DYLITE D195B EPS Eperan EPP EPP Eperan EPP EPP Eperan EPP EPP Eperan EPP EPP Arpro EPP 3413 EPP Arpro EPP 3413 EPP Arpro EPP 3419 EPP Arpro EPP 3419 EPP Ethafoam Nova EPE Ethafoam Nova EPE Ethafoam HS 45 EPE Ethafoam HS 45 EPE Ethafoam 220 EPE Ethafoam 220 EPE Ethafoam Select EPE Ethafoam Select EPE

33 Conclusion Recommendation #2 Re-visit ASTM 1596?

34 Thank You Questions?