Carbon-Epoxy Composite Base Plates for the PHOBOS Spectrometer Arms J.Michalowski, M.Stodulski The H.Niewodniczanski Institute of Nuclear Physics, Krakow

Carbon-Epoxy Composite Base Plates for the PHOBOS Spectrometer Arms

J.Michalowski, M.Stodulski

The H.Niewodniczanski

Institute of Nuclear Physics, Krakow

March 2000

PHOBOS Report 00-02

March, 2000 e-mail:[email protected]; [email protected] 2

Introduction

Original base plates for the PHOBOS spectrometer arms were designed and fabricated from aluminum sandwich plates reinforced with aluminum rectangles situated, mostly, on their top surfaces along edges. There are also reinforcing rectangles from the bottom in the region where the magnet coils were cut off. Due to design constraints and requirements the base plates cannot be thicker than 5 mm and their sag should not exceed 300 microns. The base plates with silicon modules are placed in stable magnetic field of 2 T. Design assumption was that the magnetic filed would be ramped up and down in a controlled way to avoid eddy current effects.


Aluminum outer base plate (sag measurement)

Aluminum base plate (E = 70 GPa) with cooling frames prepared for sag

measurementsm ALplate= 3.2 kg, m total = 13.5 kg

Comparison of measured and calculated sags for the aluminum base plate

|sagmax| = ~ 300 microns

Lead pieces simulating weight of silicon modules, flex cables and water

-400

-300

-200

-100

0

100

200

300

400

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Fastening point number

Sag

in

mic

rons

Measured

Calculated


Aluminum base plates in magnetic field

It has turned out that uncontrolled drop of the magnetic field can occur while the magnet crashed. Tests were performed to check the behavior of the fabricated base plates in case of the magnet crash. The plates were observed through theodolites allowing the measurement of the plate displacements. The magnet crash at full current (3600 A) caused a motion of the aluminum base plates about 1 mm in the horizontal and about 0.5 mm in the vertical direction. Silicon modules mounted on the base plates could be damaged in case of real magnet crash. Other materials considered as a replacement for aluminum were also tested. Most promising results were obtained for carbon-epoxy composite.


Design and fabrication of the base plates from a carbon-epoxy composite

The results of the magnet crash tests performed triggered the decision to construct new base plates from a carbon-epoxy composite. Two basic guidelines are applied to the new design:• shape and dimensions of both, the old and new base plates,

are the same,• design of details should be modified in order to take

advantage of new technology.

Design and fabrication of the carbon-epoxy composite base plates is described on the following pages (6 -17).


Sandwich plate design (5 mm thick)

1

2

1 Outer skins of sandwich plate:• material - high modulus carbon fiber (E = 395 GPa) tissue St886, epoxy resin• skin thickness 0.5mm

Core of sandwich plate:• material - rohacel foam and G11 inserts• core thickness 4 mm


Sandwich plate core - 1 (4 mm thick)

2

1

1 - G11 frame along plate edges and reinforcing ribs facilitating future machining2 - Carbon-epoxy skin of sandwich plate



7

23

72

45

1

1 - rohacel foam 2 - G11 inserts along top rib 3 - G11 inserts along bottom rib4 - G11 insert in mounting region of frames # 1,2,3,4

6

5- G11 inserts in mounting regions of frames # 5,6,7,86 - G11 insert in mounting region of cable posts7 - G11 inserts in support point regions



2

13

1 - G11 inserts in the bottom rib regions2 - G11 insert in mounting region of the cooling frames # 1,2,3,43 - G11 inserts in mounting region of the cable posts



32

1

1 - twelve G11 inserts to mount cooling frames # 5,6,7,82 - two G11 inserts for survey markers (at current location)3 - two G11 inserts for additional survey markers (near supporting points)


Carbon-epoxy composite sandwich plate

Carbon-epoxy composite sandwich plate - already laminated; there is no reinforcing rib, yet


Lamination of carbon fiber reinforcing ribs

1 - plywood mould prepared for lamination of unidirectional carbon fiber (T300, E = 230 GPa) reinforcing ribs2 - groove for the top rib3 - groove for the bottom rib4 - aluminum pieces to press the ribs during lamination

1

3

2

44


Gluing of the bottom rib and bushings

1

2

3

1 - bottom rib (not visible) already glued

2 - G11 bushings for mounting the cooling frames

and aluminum ones for survey markers already glued

3 - plate edges machined to glue the top rib


Carbon-epoxy composite base plate for the PHOBOS inner spectrometer arm in Krakow

3 1

2

4

1 - carbon-epoxy composite sandwich plate (E = 80 GPa)

2 - bottom rib (E = 115 GPa)

3 - G11 and aluminum bushings

4 - top rib (E = 115 GPa)


General manager of the carbon-epoxy composite base plate project

J.Michalowski with the carbon-epoxy composite base plate


PHOBOS inner base plate at the Chemistry lab

1

1 - three points to support the spectrometer base plate in the magnet


PHOBOS inner base plate at the Chemistry lab

1

1 - mounts for the hall probe


Magnetic and mechanical features of the carbon-epoxy composite base plate

The carbon-epoxy composite base plate for the PHOBOS inner arm was tested in the magnet crash conditions. Aluminum cooling frames and cable holders were mounted on the base plate. Two points on the base plate and one on a cooling frame were observed through theodolites.

No motion observed during magnet crash!

Sag of the new base plate was not measured. However, mechanical rigidity of the carbon-epoxy composite plate is roughly 40% bigger than that of the aluminum plate. Thus, its sag is expected to be smaller than that measured for the aluminum base plate.

Flexural rigidity better than in case of aluminum plate!

Documents

Carbon-Epoxy Composite Base Plates for the PHOBOS Spectrometer Arms J.Michalowski, M.Stodulski The H.Niewodniczanski Institute of Nuclear Physics, Krakow