The document analyzes the structural integrity and wear performance of a module ejector assembly through finite element analysis. Key points: 1) An FEA structural analysis found the extractor body has a safety margin of 58 under a 20G shock load, and the handle has a safety margin of 3.1 under a 100lb extraction force. 2) An FEA contact model and Archard's wear law were used to calculate a "figure of merit" indicating the relative wear potential of stainless steel versus aluminum lever materials. 3) The results predict that a stainless steel lever would wear at a 144% slower rate than an aluminum lever due to the steel's higher hardness.

1. MODULE EJECTOR
ASSEMBLY
FEA STRUCTURAL
& WEAR
ANALYSIS
D . B L A N C H E T
3 / 7 / 2 0 1 3
3 B A S S O C I A T E S

2. ASSUMPTIONS:
Material Stainless Steel – 316 alloy yield strength = 42,000 psi
Module weight = 3.6 lbs
Loading cases :
§ 20G half sine shock 11msec applied in the module extraction direction
§ For shock assume no retention force at the connector – worst case
§ Random vibration loads are negligible.
§ Extraction load = 15 lbs per lever.
Margin of safety (M.O.S.) = (yield strength/applied stress) – 1.0
Solidworks Advanced Professional FEA Simulation

3. SIMPLIFIED MODULE ….STRUCTURAL MODEL
Total Module Weight = 3.6 lbs
Assume no connector
Retention at this edge
(Worst case)
Guide rails
Shock pulse
direction
Flat head chassis
retention screw 2 places
Extraction
Levers
Provide no
Structural
support

4. FEA MODEL – MESHED , HANDLE DETAIL
Shock
pulse

5. MAXIMUM BENDING STRESS UNDER 20G SHOCK
PULSE
Max stress = 709 psi M.O.S. = (42000/709) – 1.0 = 58
Module to Chassis
Retention screw
location

6. AMPLIFIED DISTORTION PLOTS – 3000X
20G half sine 11msec shock pulse load case
Stress 709 psi max Displacement << .001 inches
chassis
wall
fixed
chassis
wall
fixed
Extraction
direction

7. LEVER EXTRACTION LOADING MODEL
Determine the stress in the handle during module extraction
Applied
Force
~ 10 lb
Resultant
Extraction
Load
~ 50 lb or
100 lb per module

8. STRESS CONTOUR VIEWS – HANDLE SHOWN
DEFORMED @100X
.0025
Maximum bending stress
= 10,000 psi
M.O.S. = 3.1
F = 10 lbs
Max
deflection

9. A Very Effective design
CONCLUSIONS:
BASELINE EXTRACTOR ASSEMBLY IN STAINLESS STEEL
The extractor body has a margin
of safety of 58 ; a robust
design
The handle when loaded to
provide 50 lbs of extraction
force (100 lb total) has a
margin of safety of 3.1
9

10. APPENDIX A
LEVER JAWS CONTACT
WEAR ANALYSIS
S T A I N L E S S S T E E L V S . A L U M I N U M W E A R
E S T I M A T E S

11. GOALS & LIMITATIONS
Use Archard’s wear Law supported by FEA to estimate the relative wear of an aluminum vs.
stainless steel lever.
Metal wear is a complex phenomena which is still primarily measured by laboratory testing.
Recent advances in FEA are using complex non-linear modeling to estimate material removal
rates due to contact pressure and material/plating harnesses.
This study uses simple linear FEA to calculate one key variable in Archard’s Law.

12. ARCHARD’S WEAR LAW CIRCA 1930
W = K/H * S * P
§ W = metal removal cubic inches
§ K = a constant for metal categories
§ H = hardness ( Rockwell or Brinell scale)
§ S = sliding distance
§ P = contact pressure
Sanity check
§ More pressure > more wear
§ Harder target material > less wear
§ Assumes target material is softer than the contacting material
Use linear FEA to calculate the local contact pressure P , in p.s.i.
Testing has verified this Law for first order calculations.

13. FEA CONTACT MODEL
Infinitely hard
“wall” material
fixed
High density mesh with
sliding contact elements
Applied
Load
20 lbs
Fixed
rotation
Target material

14. FEA RESULTS , STRESS PLOTS
Stress is not significantly different not a primary variable
Steel lever
max contact stress = 55,000 psi
Aluminum lever
max contact stress = 50,000 psi

15. CALCULATE A WEAR “FIGURE OF MERIT” FOR THIS
DESIGN
F.O.M. ---- Figure of Merit , lower value indicates less wear potential
Lever
Material
K H
Rockwell B
S P
p.s.i.
(FEA)
W
F.O.M.
316
Stainless
Steel
1 95 1 55,000 579
Aluminum
6061-T6
1 60 1 50,000 833

16. WEAR PREDICTION CONCLUSION
Using Archard’s Wear Law a steel lever is predicted to have less potential for wear.
Aluminum will wear at a rate (833/579) = 144 % faster.