Charles Munafo

Composite Shop Materials and Processes

BMS 5-137 Honeycomb Peel Testing

Adhesive Orientation Effects?

We’ve recently experienced failing climbing drum honeycomb peel results. After analysis a few results from recent previous testing and a discussion of the matter with Ron Ebright at Cytec I was able to piece together what I hope is an understanding of how the orientation of FM377S .08 PSF Film Adhesive effects honeycomb peel values.

Though this report and probably subsequent testing there is the possibility that we’ll be able to show the failures experienced are related purely to adhesive orientation and not a result of processing problems unrelated to the testing itself.

Introduction

Date: 5/20/05

The following materials were used in the manufacture of the test panels:

· 350 Cure Film Adhesives Certified to BMS 5-137, Grade 10

· (Cytec) FM377S .080 PSF | Batch 931.

· Honeycomb test panel manufacture per BSS7207, Type I

Materials

The adhesive film as rolled from the manufacture is backed on one side by polyethylene and the other side has a paper backing. Figures 1 and 2 below show that the scrim is not vertically symmetrical (i.e. the filaments running transverse to the roll direction seem to be positioned on the poly side of the film).

 

Also, the loop highlighted in orange on Figure 1 is what I think Ron Ebright described as a “horseshoe”. If I understood Ron correctly, describing its orientation relative to peel direction seems to also effect peel values.

Adhesive Scrim

Observation and Discussion:

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Figure 1: View From PAPER Side of Scrim

Figure 2: View From POLY Side of Scrim

Pictured below are photographs of peeled test coupon skins with inserted blowups that try to show adhesive orientation. Also listed are peel strength values for the pictured coupons along with a brief discussion for each. Test coupons shown below were selected because they appear to demonstrate the relationship between adhesive orientation and torque values.

Peel Strength = 28.6 in*lbs/3

Failing Result!

 

Observations on Adhesive Orientation:

· Adhesive roll direction aligned with the peel direction of the test coupon.

· Paper backed side of adhesive is directed towards the core.

· Peel Direction is towards the CLOSED end of the “horseshoe”.

 

Comments:

· The –3 coupon from the same test panel was peeled in the same direction as –1 shown here. A nearly identical result of 28.2 was achieved.

 

Peel Strength = 33.4 in*lbs/3”

Observations on Adhesive Orientation:

· Adhesive roll direction aligned with the peel direction of the test coupon.

· Paper backed side of adhesive is directed towards the core.

· Peel Direction is towards the OPEN end of the “horseshoe”.

Comments:

· Important?.... The coupon and the one pictured in Figure 3 above were cut from the same panel. Notice the higher result here. I believe that this is what Ron Ebright described as peeling relative to the open end of the “horseshoe” having an effect on the torque value.

 

Figure 3

Figure 4

Peel Strength = 39.7 in*lbs/3”

Observations on Adhesive Orientation:

· Adhesive roll direction perpendicular to the peel direction of the test coupon.

· PAPER backed side of adhesive is directed towards the core.

Comments:

Result is lower when compared to that of the coupon shown in Figure 6. This seems to demonstrate that the paper vs. poly side toward the core has an effect on peel values.

Figure 5

Peel Strength = 51.0 in*lbs/3”

Observations on Adhesive Orientation:

· Adhesive roll direction perpendicular to the peel direction of the test coupon.

· POLY backed side of adhesive is directed towards the core.

Comments:

Result is higher when compared to that of the coupon shown in Figure 5. This seems to demonstrate that the paper vs. poly side toward the core has an effect on peel values.

Also, notice that the scrim here seems pretty torn up. One would think that this type of failure mode will lead higher peel values due to the elastic nature of scrim filament. It is quite possible that the transverse filaments on the poly side of the scrim (see figures 1 & 2) are linking better to the honeycomb cell walls that is causing this phenomenon.

Figure 6

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· Are these observations in line with what Cytec has experienced? Please let us know if the thinking described above is correct.

· Does Cytec believe that the fluctuations in results can be purely attributed to adhesive orientation? To be honest, I’ve looked at the cure cycle profiles for the above panels and due to problems we’re had recently with our autoclave controls the ramp rates are a little bit off in their consistency. I’m wondering if that may have contributed as well. And to answer that question myself from past experience…. Everything has an effect! Arrrggg! :)

 

Here’s where I think we may go with this next:

 

· If Cytec agrees with the observations above, DAL can devise a test matrix in an attempt to definitively show cause and effect. If we show results of this further testing are in agreement with observations here we will discuss further (in-house) whether or not the parts processed with the failing witness coupons can be deemed serviceable.

 

 

Thanks once again to Ron Ebright from Cytec, who in 10 minutes on the phone brought me a whole lot closer to understanding what’s going on with this.

 

Please contact me at chuck.munafo@delta.com if you have any questions, comments or would like to help in any way.

 

Thanks for taking the time to look this over.

 

Chuck Munafo | Ph: (404) 714-2291 | Fax: (404) 714-0426 | Email: chuck.munafo@delta.com

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UPDATE: Click here for PART 2 of this topic.

It is a follow-up to this page (Posted 5/27/05)