Design of Test Apparatus

The testing procedure for the small scale durability test (as specified in ASTM E2190-10 [7]) required a compact and portable displacement mechanism to impart movements on the two lites of glass that would replicate the edge-seal

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FIG. 6—Dial gauge used to measure relative displacement between glass panes in full – scale test assembly 2.

strains in the full-scale test unit. The final design consisted of a four-sided frame made from a bent and welded steel 1/4-in. (6.4-mm) plate. The 14 x 20 in.2 (350 x 500 mm2) IGU was placed into the frame and the lower lite was secured to the frame on all four sides using epoxy resin. The frame was designed to sur­round the four edges of the IGU to adequately apply load to displace the pane of glass; however, there was a nominal clearance of 3/8 in. (9.5 mm) between the steel and IGU edge seal. This allowed for adequate clearance around the edge seal as specified in ASTM E2188-10 [6]. Fasteners and bearing plates were used to displace the upper pane of glass in-plane relative to the lower. In-plane dis­placements are defined as X and Y directions. Another set of fasteners attached to plates adhered by epoxy to the surface of the glass was used to pull the upper pane of glass away from the lower. This out-of-plane displacement is defined as the Z direction. See Fig. 9 for a photograph of the small test frame. In this pho­tograph, there are steel plates and fasteners bonded to the glass at the mid-span of the long 20-in. (500-mm) dimension. The screws shown at these locations were used to lift the outer lite away from the inner lite in the Z direction.

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FIG. 7—Full-scale test assembly 2 gauge location schematic.

To apply the desired displacement between the two panes of glass, two #6- 40 socket-head machine screws were used in each in-plane direction. The data in Table 1 was used to estimate the forces required to strain the outboard lite of the small test units and to determine the size of the screws used to produce the strains. Steel shims and silicone bearing plates were used to distribute load and protect the glass edge (Fig. 10) when moving the plates in the X and Y direc­tions. The applied displacement was measured between the steel frame and dis­placed glass pane using a dial caliper. The out-of-plane displacement was applied using two #6-40 flat-head machine screws that were adhered to the upper unfixed pane of glass with an epoxy resin. This displacement was meas­ured between the steel frame and glass pane using an outside micrometer. Addi­tionally, measurements were taken between the lower fixed pane of glass and

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the steel frame to ensure that the entire IGU did not move relative to the steel frame. All of these measurements were recorded at the time of application and subsequently measured throughout testing. See Table 2 for recorded measure­ments and Fig. 11 for the locations of displacements.

A slight modification was made to the original test frame design because of the high loads required to displace the glass out of plane in the Z direction for the 150 % design test specimens. The outer pane of glass broke in two glass specimens during the application of displacements and these were discarded. Also, two of the tension mechanisms that were secured to the glass with epoxy

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FIG. 9—14 x 20 in.2 (350 x 500 mm2) small test frame with IGU installed.

TABLE 2—Edge-seal measurements.

Frame

number

Design

value

Front lite x2a Д

x3a

Д

y3a

Д

y4a

Д

Z_ta

Д

Z_ba

Д

Date

completed

25

50%

0.014

0.015

0.018

0.019

0.010

0.010

1/24/2011

16

50 %

0.014

0.015

0.022

0.015

0.009

0.011

1/24/2011

18

50 %

0.014

0.015

0.017

0.018

0.010

0.011

1/25/2011

26

50 %

0.013

0.015

0.018

0.016

0.014

0.009

1/25/2011

12

50 %

0.015

0.016

0.021

0.020

0.011

0.009

1/27/2011

24

50 %

0.013

0.014

0.017

0.019

0.011

0.010

1/24/2011

29

100%

0.022

0.022

0.033

0.034

0.018

0.013

1/25/2011

28

100%

0.023

0.022

0.031

0.034

0.013

0.015

1/25/2011

33

100%

0.023

0.020

0.033

0.031

0.016

0.016

1/25/2011

36

100%

0.021

0.021

0.031

0.033

0.014

0.015

1/25/2011

27

100%

0.021

0.020

0.031

0.033

0.016

0.014

1/25/2011

3

100%

0.021

0.022

0.032

0.033

0.016

0.015

1/27/2011

13

150%

0.045

0.039

0.058

0.057

0.035

0.035

3/8/2011

15

150%

0.043

0.041

0.057

0.058

0.033

0.036

3/8/2011

37

150%

0.042

0.043

0.059

0.058

0.036

0.037

3/8/2011

38

150%

0.041

0.043

0.059

0.1

0.036

0.038

3/8/2011

40

150%

0.036

0.042

0.063

0.058

0.037

0.033

3/8/2011

42

150%

0.042

0.044

0.061

0.061

0.035

3/8/2011

aSee Fig. 11 for displacement locations.

FIG. 11—Edge-seal displacement table locations.

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broke free and had to be reinstalled. To avoid stress concentrations for the 150 % tests, a revised tensioning mechanism was designed and installed for these specimens. This mechanism consisted of a longer steel plate adhered to the glass to more effectively distribute load and thereby reduce stress. The new tension mechanism allowed the glass to be deflected in tension to the required degree without additional glass breakage.