# Presentation: 062453

## NOVA Structural PVC Design   NOvA Collaboration Meeting May 2005     Hans Jostlein                    <number>

-  Time dependence of sample elongation under stress.
- Data are shown in units of “Microstrain” (ppm elongation) versus time in days.
- The rate of creep is consistent with being exponentially dependent on the stress.

**We present about one year’s  worth of  creep data **
- on PVC cut from a commercial car wash  door extrusion made by Extrutech..
- Creep can be well represented so far by a logarithmic time dependence.

## Creep Rate Versus Stress

- :  The creep rates in  Fig. 2 were approximated as simple exponentials (by hand; not shown in the figure) for the data beyond day 3 or so.
- The _rates_ are approximately an exponential function of the stress.

## Published PVC Creep Rates vs. our Data

- Published creep rates are similar, but about 30% higher .
- Log response holds (more or less) for very long times..
- We will measure creep and Modulus for “our” PVC

## NOVA Structural PVC Design   NOvA Collaboration Meeting May 2005     Hans Jostlein                    <number>

**We relate those creep results to allowable design stress and strain in PVC**

- Using this example as an “acceptable deformation”,
- We go back and calculate an “acceptable strain”,
- Yielding acceptable creep rate and hence stress.
- The result is  1466 psi, based on the PVC Extrutech sample we measured.

## NOVA Structural PVC Design   NOvA Collaboration Meeting May 2005     Hans Jostlein                    <number>

**Creep  Effects on block swelling**
- In a nutshell,  the deformation increases over time due to creep.
- At the same time the stresses are reduced , again due to creep.
- Nature, for once helps here:  the highest stressed points in the structure relax their stresses the fastest.
-  A detailed model calculation remains to be done to confirm the details.
- Expectation:  32-plane blocs remain acceptable.

## Note:  Buckling stability safety factor is not affected by Creep.

**32-planes buckling calculation for a distributed G load (top guided****)**

- Note:  Buckling stability safety factor is not affected by Creep.

## So, What is the Design these Days ?

**So, What is the Design these Days ?**

** ********  ****Nothing Has  Changed ******
- The Front wall of the building serves as the first Bookend.
- The detector is built in 8-plane blocks that are raised and attached to the existing detector planes to form 32-plane blocks.
- At that point an air gap is provided using a top and bottom spacer.
- The airgap accommodates the swelling of the block from oil pressure,
- due to elastic and to creep deformation.
- 32-plane blocks are stable against buckling.
- We know its works.
- Detail Design work and dimensioning is yet to be done.

## NOVA Structural PVC Design   NOvA Collaboration Meeting May 2005     Hans Jostlein                    <number>

**We propose a cell profile with rounded corners that reduces the stress in the PVC** **drastically**
- We also  show  a shape for the outermost cell in vertical planes

## Stresses in the Rounded  Cell Shape

- The Maximum Stress is now well below 1000 psi
- We are no longer relying on X-Y  plane gluing to manage stresses.

## Pressure Testing and Creep

- Creep is fastest when stress is first applied.
- The 3-cell sample was exposed to 72 psi for just a couple of minutes,  and bowed visibly.
- We think we need to pressure test all extrusions to perhaps well above the 20psi service pressure, to eliminate defective extrusions.
- Extrusions may deform permanently during this test.
- This is not all bad.
- It imprints on  the material a pre-creep,
- which will reduce subsequent creep deformation.
**Example:**  Plastic strapping is made of Polypropylene, pre-extended by 40 %, to avoid creep during service.

## A  Second Bookend ?

**A  Second Bookend ?**
**Needed for cosmics ?**
- Not Obvious.
- Photons would go the wrong way after entering the back face of the detector
**Can serve double duty as “ultimate protection”**
- We can design air gaps to accept elastic swelling and creep swelling of the blocks (with 2x safety factor)
- If swelling or creep should be much larger, a second bookend will constrain the detector.
- With proper design, this should not be needed.

## Snout  Design

- Snout  Design

- Fiber
- Routing
- Board

- Electronics

- Cover gets glued on last

- Extension
- To get above
- Oil level
- (Hor. Only)

- Cover is a step platform