SHOCK ANALYSIS USING THE PSEUDO VELOCITY SHOCK SPECTRUM PART 2

1
SHOCK ANALYSIS USING THE PSEUDO VELOCITY SHOCK
SPECTRUMPART 2

• Howard A. Gaberson, Ph.D., P.E.
• Consultant
• 234 Corsicana Drive
• Oxnard, CA 93036-1300
• [phone]
• hagaberson_at_att.net

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SHOCK ANALYSIS USING THE PSEUDO VELOCITY SHOCK
SPECTRUMPART 2

• Pseudo velocity is compared to relative velocity
  shock spectra on 4CP and we find problems with
  relative velocity.
• Relative velocity has low frequency problem, and
  doesn't show the maximum acceleration.
• Review tests to determine which transient motion
  analyses method is the best indicator of damage
  potential.
• The best damage potential analysis is the damped
  PVSS on 4CP.
• Shaker Shock and Miscellaneous Issues

3
All kinds of shocks package drops, collisions,
transportation bumps, but face it explosions are
where its at

• Wait and see Ive got one.
• Late 60s Prairie Flat

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PRARIE FLAT ALBERTA
5
TNT PILE PHOTO
6
Explosion I
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Explosion II
8
This first set of slides tests relative velocity
vs. PV as a spectrum ordinate

• Now we look at four shocks, and their integrals
  to velocity and displacement.
• Then I calculated their relative and pseudo
  velocity shock spectra and overlaid them.
• Relative velocity is about equal to pseudo
  velocity in the severe zone, but has no useful
  asymptotes or other meaning on 4CP.
• Peak relative velocity doesn't seem helpful.

9
Reeds time history
Peak accel 130
Velocity change and peak velocity are 120 ips
Max displacement 2.4 in
10
Very Low Frequency SDOF Relative Velocity

• Relative velocity sees peak shock (bogey)
  velocity.
• Pseudo Velocity sees peak shock (bogey)
  deflection.

11
Rel Vel SS and PVSS for Reed
Vel change 120
2.4 inches
130 g's
12
Reed SSs, 5 Damping
Blue rel vel does not hit asymptotes Agrees in
center severe section
2.4 inches
130 gs
13
HS54 Time History
14
Rel Vel SS and PVSS for HS54
270 ips
I should have drawn 54 inch line.
130 g's
15
HS54 SSs, 5 Damping
Blue is rel vel, doesnt hit accel
asymptote. Magenta is PV
16
HW4 Time History
900 g's
300 ips Vel change
8 inches
17
Rel Vel SS and PVSS for HW4
300 ips
Blue is rel vel Magenta is PV At low frequencies,
rel vel is max velocity, PV is max z
8 inches
18
HW4 SSs, 5 Damping
Low frequency SDOF see peak rel vel
PV shows peak spring deflection
900 g's
19
HW4 SSs, 10 Damping
Meaningless
20
El Centro EQ Time History
Peak g 0.35
Peak vel is 15, vel change is about 20 ips
Max z about 70 in.
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Rel Vel SS and PVSS for El Centro
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Rel Vel SS and PVSS for El Centro EQ
Peak velocity 15 ips
Velocity change 20 ips
70"
0.35 g
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Consider Testing Analysis Methods on Equally
Severe Shocks

• Develop several equally severe shocks all able
  to just fail same equipment.
• Find analysis methods that show them all somewhat
  equally severe.
• Such an analysis is needed to describe shock
  severity.
• Needed to describe equipment hardness or
  fragility.

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Equipment Fragility-Hardness

• The most severe shock equipment survives
• Shock severity concept needed
• Pseudo-velocity shock spectrum on four coordinate
  paper Recommended by Eubanks and Juskie, 1963
  SVB
• Somewhat adopted by the seismic and nuclear
  defense community
• Chalmers and I advocated PVSS

25
Equipment Lowest Modal Frequency

• Postulate equipment can only accept energy and be
  damaged at its modal frequencies
• To damage equipment shock must have high PV at
  equipment modal frequencies.
• Shock isolation reduces the higher frequency,
  high PV severe range
• An item may be damaged by dropping on a concrete
  floor but survive a fall on a carpet because the
  carpet cushion reduced the severe high PV range
  to frequencies below the equipment's lowest
  frequency.

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Equipment to test

• 50. Squirrel cage blower selected
• Failure blower cant blow (pressure drop through
  orifice)
• Failure Equipment becomes hazardous
• Purchased about 15

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Develop equally severe shocks

• Test same equipment on progressively increasing
  different shock tests
• Drop tests terminal peak, half sine, hard
  phenolic block
• Mil-s-901 Light weight, medium weight, heavy
  weight
• TP60, HS54, PB24, LW72, MW36, HW4

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Abbreviations

• TP60, 60 inch drop to a terminal peak saw tooth
• HS54, 54 inch drop on rubber pad to get half sine
• PB24, 24 inch drop on hard phenolic block
• LW72, 72 inch hammer drop to shelf bracket on
  light weight shock machine
• MW36, 36 in hammer drop on the medium weight
  shock machine
• HW4, 4th shot on the floating shock platform at
  Hunters Point

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Failures consisted of

• Spider members broken or deformed belt flies off
• Motor knocked out of its supports belt flies off
  or motor cant turn
• Self tapping bolts deformed, loosened, pulled out
• Feet bolt holes deformed

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Blowers as purchased trivial failure.
Test blower as originally configured. Arrows
point to thin spider members supporting bearings,
and to sheet metal screws. Notice sheet metal
legs.
Weak sheet metal motor mount beam.
f1
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Trivial failure
Original configuration, trivial failure.
32
Trivial failure, another view.
Original bent sheet metal motor support. Trivial
failure.
33
Motor Mounted on Base Plate
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Tagamis China Lake MRC Shock Machine
Drop table shock machine.
Rubber pad for half sine test.
f3a
35
Shock Machine with Terminal Peak Programmer
Mylar covered opening with orifice to
simulate realistic delta p.
Manometer to check for adequate delta p
f3b
Terminal peak sawtooth programmer
36
Phenolic Block High Impact Set Up
Phenolic block taped to shock machine anvil
for short duration half sine test, pb24
f3c
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Blower on Navy Lightweight Shock Machine
Mounted to deck fixture on light- weight shock
mach.
f4
38
Perspective View of Lightweight Shock Machine
Blower on lightweight shock machine
Hammer
f4a5
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Blower Mounted on Navy Medium Weight Shock Machine
Mounted on medium wgt shock machine. Extra plates
added to increase weight.
f2
40
Two Blowers Mounted in FSP
Two blowers installed in FSP. One
foundation stiff, and the other less stiff
f5
41
HS54 Failures
Spot weld fail
HS54 failure. Spot weld pulled out allowing
belt to loosen.
f6
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TP60 Failures
TP60 failure. Pulley side bearing support spot
weld failed allowing bearing support to
deflect and loosen belt
f7
43
PB24 Failures
PB24 failure. Spider member pulled out of
housing, loosing belt.
f8
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MW36 Failures
MW 36 failure
Leg pulled away from blower body. Sheet
metal screws gone.
Bearing support bent
Motor mount bent rubbing pulley
Accelerometer
f9
Leg deformed
45
More MW36 Failures
MW36 failure
Loosened self tapping screws
Bent spider members
Deformed legs
f10
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MW36 Failures Detail
MW36 damage. Motor bearing housing popped out of
end bracket
Accels
f11
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HW4 Failures
HW4 failure.
Sheet metal leg pulled away from blower body
Bent spider members
Motor clamp bent and rubbing against pulley. Belt
gone.
Loose self tapping screws
f12
48
More HW4 Failures
Screw gone
Bending
HW4 failure
f13
49
HW4 Motor Damage
Non pulley end of motor support bracket deformed.
Motor bearing support popped out of bracket.
f14
50
HW4 Motor Collar Bent
HW4 Failure. Bent motor clamp. Motor pivoted
about clamp and lost belt.
f15
51
Failures consisted of

• Spider members broken or deformed belt flies off
• Motor knocked out of its supports belt flies off
  or motor cant turn
• Self tapping bolts deformed, loosened, pulled out
• Feet bolt holes deformed

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HS54 Time History
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HW4 Time History
54
LW72 Time History
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MW36 Time History
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PB24 Time History
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TP60 Time History
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Time histories, same scale
Here's all 6 shocks plotted to same scale. Only
one of these did not fail the blower.
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Composite Undamped SRS
5 of these 6 shock spectra failed the blower
which 5?
HS54r,HW4g,LW72b MW36blk,PB24m,TP60c
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Composite 5 Damped SRS
5 of these 6 shock spectra failed the blower
which 5?
HS54r,HW4g,LW72b MW36blk,PB24m,TP60c
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Composite 10 Damped SRS
HS54r,HW4g,LW72b MW36blk,PB24m,TP60c
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Composite 20 Damped SRS
5 of these 6 shock spectra failed the blower
which 5?
HS54r,HW4g,LW72b MW36blk,PB24m,TP60c
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Composite FT Magnitudes
FT magnitude of a shock is its residual PVSS. 5
of these 6 FT magnitudes failed the blower which
5?
HS54r,HW4g,LW72b MW36blk,PB24m,TP60c
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Composite Undamped PVSS on 4CP
5 of these 6 shock spectra failed the blower
which 5?
HS54r,HW4g,LW72b MW36blk, PB24m,TP60c
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Composite 5 Damped PVSS on 4CP
5 of these 6 shock spectra failed the blower
which 5? (Any light?)
HS54r,HW4g,LW72b MW36blk,PB24m,TP60c
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Composite 10 Damped PVSS on 4CP
5 of these 6 shock spectra failed the blower
which 5?
HS54r,HW4g,LW72b MW36blk,PB24m,TP60c
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Composite 20 Damped PVSS on 4CP
5 of these 6 shock spectra failed the blower
which 5?
HS54r,HWg,LW72b MW36blk,PB24m,TP60c
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Conclusions Presented evidence that

• Damped Pseudo-velocity shock spectrum is the best
  severity indicator
• Peak gs and time histories are useless
• Shock spectrum calculation must become widely
  available
• Collect digitized time histories and make
  available so others can test