1. Development of a low material endplate for LP1 and ILD
Dan Peterson, Cornell
At previous meetings,
models of LP1 endplate and FEA calculation of deflection
getting ready to make small beam prototypes to
measure ability of FEA to model mechanical properties
start of an ILD endplate (space-frame) model
convergence problems with FEA calculations
convergence problems with FEA calculations
for a simplified ILD endplate (space frame) model
construction of small beam prototypes,
modeling updates,
addressing FEA calculations for the ILD endplate model
introduced the Equivalent-Plate-Spaceframe
Today support of ILD endplate – add inner field cage
“Equivalent-Plate-Spaceframe” model of LP1 endplate
measurements of deflections of the small beam prototypes

2. Promotional picture – 8 layers, Equivalent-Plate-Spaceframe

3. (inside view)
As a reminder (from ) ,
The “equivalent-plate” model of the ILD endplate
is fully populated with
spaceframe-separator-plates: above-rows and
and in-rows (in the same row, between modules).
This model has a full thickness of 100mm, radius 1.8m, and a mass of 136kg.
the thickness is then 1.34g/cm2, 6%X0.

4. FEA calculations of deflection and stress (ok, stress is not shown)
Complete Model
“space-frame-separator-plates”
ring outside layer 8
ring inside layer 1
all intermediate rings
all radial lines within rows
Endplate Support: outer field cage
deflection=0.056 mm/100N
or 1.23 mm
New
Endplate Support:
outer and inner field cages
deflection= mm/100N
or 0.22 mm
(not simply a factor of 4 because
the support is at non-zero radius)

5. Modeling updates (from 2010-10-28)
All space frame models (small beam, LP1, ILD)
use a common calculation form for the parameters describing the mounting block
that provides the flat for the center screw,
the ability to turn on/off the wings for the side screws,
and reduces errors.
For the LP1 endplate, radial orientation struts have added in “row 4” and “row 0”.

6. (from )
A further simplified model is required for the FEA of the ILD spaceframe endplate.
I observed earlier that simple vertical struts can be analyzed.
In the “equivalent-plate” model, pairs of struts are replaced with a plate.
Optimizing the parameters for equal material in the plate as in the struts,
equal deflection of the beam in the two models,
The plate width is 35% of the span of a pair of struts,
the plate thickness (into the page) is 50% of the strut thickness.
“equivalent plate”
“realistic struts”

7. Completed “equivalent-plate” model of the LP1 endplate
Revised specifications for equivalent plates
(equal material, equal deflection)
width multiplier thickness multiplier
small beam (was 0.35) (was 0.50) LP

8. Simple beam prototypes
(updated from )
So, the prototypes and the different levels of modeling and construction
fit into the design of the ILD endplate.
Models of
“strut”
Space frame
Models of
“equivalent plate”
Space frame
Construction
Simple beam prototypes
Calibrate “equivalent plate” to “strut
Calibrate the model to reality
July 2011
LP1 endplate
Apply LP1 experience to ILD design.
Use the “equivalent plate” for FEA
ILD endplate

9. Progress on the Small Beam Prototypes (from 2010-10-28)
“Strut” space frame
Al-carbon hybrid
Parts have been delivered by the vendor.
“LP1” is ready to measure.
The “Strut” space frame was easier to
assemble than expected.
“LP1”
The aluminum-carbon fiber hybrid requires assembly.
I am using these fiber chips, experimenting with the mixture.
I also have Kevlar fiber in bulk form.

10. An issue with the FEA calculations is that they are based on solid models;
the real devices include several joints:
where the threaded rods meet both the
struts
and mounting blocks,
and where the mounting blocks
connect to the plates.
The parts were constructed to calibrate the
FEA of the models.

11. Measurements of the Strut Spaceframe
The physical device was loaded with 8.5 lbs (38.6 N)
concentrated is a 15cm wide region at the center.
The unloaded profile shows wiggles ~ 150 microns (0.006 inch) peak-to-peak.
This is expected without the iterative machining and stress relief.
For the current LP1, the material remaining was 750 microns, 250 microns.
Or, the wiggle may be due to poorly balanced struts. TBD
(2) The difference of loaded w.r.t. unloaded is my result.
(3) Single measurements were recorded to significance inch (2.5 micron)
and have σ≈ inch (1.25 micron).

12. Measurements of the LP1 Mullion design
The physical device was loaded with 8.5 lbs (38.6 N)
concentrated is a 15cm wide region at the center.
The unloaded profile shows wiggles ~ 50 microns (0.002 inch) peak-to-peak.
This tends to support the speculation that this is from
not employing the iterative machining and stress relief;
less wiggle is expected with the LP1 mullion.
(2) The difference of loaded w.r.t. unloaded is my result.
(3) Maximum deflection is mm vs mm for spaceframe.
Ratio is 8. From , expected 6.
Some parameter have changed and this is isolated loading.

13. Analysis of measurements of the LP1 Mullion design
Here, the FEA calculation
is artificially increase by
a factor of
The measurements are calibrated to a 100N load,
over a 15cm region in the center.
Note that the deflection for the LP1 Mullion beam
is MORE than the FEA calculation, by 16%
but the shape is accurately reproduced.

14. Analysis of measurements of the Strut Spaceframe
This is without any artificial
calibration of the data or FEA.
One might say, based on the result
from the LP1 Mullion, that the
spaceframe measurement is 16% low
w.r.t. the FEA.
The shape is accurately reproduced.
There may be several sources of error in the measurement.
The model struts have diameter: 6mm solid, mm2 area,
the physical device has struts with 7mm OD, 4.8mm ID, mm2 area.
(The physical device has much of the ID filled with threaded rod;
there is some uncertainty in the effective cross sectional area.)
However, changing the area of the strut in the model to 20.2 mm2 area
results in an increase of the maximum deflection from mm to .1181mm, 6%.
Similarly, uncertainty in how to treat the exposed threaded rod
leads to an uncertainty of ~1%.

15. Conclusions
The FEA calculations of the “strut spaceframe”
is consistent with the measurements of the physical device, to ~16%.
The largest uncertainty is due to the discrepancy observed for the LP1 mullion.
The calibration of the “equivalent-plate spaceframe” to the “strut spaceframe”,
for the case of the LP1 endplate, is similar to the small beam.
Can/should we make the “equivalent-plate spaceframe” for LP1 and ILD?
I am considering making LP1 endplates in both “strut” and “equivalent-plate” designs.
The inner plate (supports the modules) and outer plate can be identical.
We should still think about stiffness requirements for the ILD endplate
and how much more space (in Z) can be allowed.
I still must make the advanced LP1 endplate by July.
The drawing are not still ready.
I am still going to complete the aluminum/carbon hybrid small-beams.