Tom Cotton Stress Test: Why We Might Get a Headache From New Glasses.
If i put those on it stretches it, and it puts a lot of stress on my temples and over a period of time, i get a big headache and if the glasses manufacturers measure the stress right here, they could tell how much force was being applied to The side of my head and make it small enough in order for it not to give me a headache or bother me today, we’re going to bond an 060 sl strain gauge a c4a series of gauge we’re, going to bond it to the highest stressed area right Here in the temple and we’re going to measure the stress or strain as i put these glasses on with my larger than usual head, okay, the first step in this surface, preparation and bonding is to take our gc6 it’s, an isopropyl alcohol, material and we’re, going to Degrease, the glass, i would normally use a csm3 degreaser, but this is a plastic material and it might degrade the surface. So the first thing i’m going to do is take a gauze sponge saturate it thoroughly with the gc6 isopropyl alcohol and i’m going to degrease the temple portion of this glass next step i’m, going to go straight to a weta braid with a silicon carbide, abrasive paper And the conditioner a because this surface is relatively smooth.
I don’t really have to approach it from a multi, um grit, consistency so i’m, going to take the conditioner, a the mild phosphoric acid solution, i’m going to wet the surface of the glasses and then i’m going to lightly wet a braid.
Now, if i didn’t do this one, the organic materials that are on the surface might contaminate the gauge bond line and two you need to have a rough enough surface for it to have something to adhere to the glass. The plastic here would be very, very slick and not possibly give a good bond. If you look at that now, it has kind of a burnished look to it. The next step in thoroughly cleaning the surface before bonding we’re, going to again use the conditioner, a the mild phosphoric acid solution and i’m going to saturate a gauze, a cotton tip, applicator and then i’m going to scrub the area. This removes any loose organic materials and helps to completely clean and flush the area with the conditioner, a the mild phosphoric acid solution, and i need to now absorb that excess material that’s contaminated and with a single wiping motion, i will absorb that material off of the Glasses, the last step in surface preparation if we use the conditioner a as the last step and we use this m bond 200 adhesive, which i plan to use, we would not be successful because it is very ph sensitive i’m going to take the neutralizer 5a it’s.
An ammonia solution with a little detergent and it’s going to bring the ph up to neutral and or slightly basic right now, it’s down in the neighborhood of a two or three ph and we’re, going to get it up to a neutral or slightly basic i’m.
Now going to use a dry, gauze sponge fold, it into quarters and absorb the excess neutralizer 5a now i’m, going to lay the gauge out on this glass plate and the glass plate must be chemically clean. Also so i’m going to take a couple of drops of neutralizer 5a a clean, gauze, sponge and i’m going to scrub the surface of the glass plate. We don’t want to contaminate the gauge during the process of bonding it now here we have that c4a series of gauge and i’m going to take the lead wire this little twist tie and take it off. So i’ll have less stress on the gauge. I want to have just the individual strand holding it at this point now. There’S two sides to this gauge one is shiny. The other is dull. We want to have the dull side down that’s what we’re going to bond into position so i’m going to slide the acetate folder off. This is going to be a little tricky because it’s got a little spring to it. I’M, going to use the pct 3m tape. I’M, going to pull off a piece about 0, 2, 3 inches long and i’m gon na throw that away because it might have been contaminated while it was sitting here, work uh on the bench.
In fact, i’ve got a folded piece there. So now, i’m gon na take a piece out. Oh two, three inches long it’s, not ultra critical. I like to stretch it in between my fingers now i’m going to lay the gauge down dull side down across the glass plate, now notice i’m going across the gauge, and typically you would go along the long axis of the gauge.
But in this case, with the lead wire pre attached like this, it makes it easier to do it this way. I am now going to at a shallow angle, lift this up. Transfer it over to the gauge location, where i believe the highest strain or stress will be, and i will attach the gauge handling tape to the back side of the glasses. I now need to expose the bonding surface, which i’m doing quite nicely there, the catalyst c. Our m bond 200 is a sono acrylic adhesive, instant, setting and i’m going to be using the catalyst c, which is basically a controlling agent and on the inside of the neck of the bottle i’m, going to hit it eight to ten times. Removing. Almost all of that material and then with a single wiping motion, i’m going to wet the backing of the gauge and i’m going to wait a full 60 second minute, we’ve, now waited the full one minute of air dry time for the catalyst c we’re. Now going to apply the m bond 200, then i’m going to hold a clamping pressure of one minute of thumb, pressure and then they’ll be two minutes under the tape.
I need to have a gauze sponge at the ready. This is what i’ll do is to spread the adhesive out, as i go i’m gon na put a single drop of the adhesive right at the cusp of the tape and the gauge i’m going to pull it tautly across toward me and with a wiping motion.
I’M, going to squeegee out the excess and then follow with my thumb. Now i have one minute of thumb, pressure and then two minutes under the tape. The sino acrylic adhesive is probably the easiest and quickest of our adhesive systems to work with it does have its limitations of temperature and elongation, but for general purpose, stress analysis, work, it’s, a great tool. Okay, we’ve completed our one minute of thumb, pressure and two minutes under the tape, and at this point we can remove our gauge handling tape and, if all has gone well and the demo gods are with me, it will i’ll be able to peel the tape up, Which was quite nicely done, there get rid of the pc or the p ct 3m tape. Now i’ve exposed the electrical connections and i’m a little bit vulnerable now. So what i want to do is take some of the paper drafting tape. Pdt 3 saw a strip an inch inch and a half long it’s, not critical and i’m going to stream relief. This wire because it’s most vulnerable at this point, if i snag that wire it’s all over but the crying okay, so i’m gon na strain relief.
That and i’m going to electrically check it out and then hook it up to the instrument and before i do that, with my great confidence in this micro measurement strain gauge i’m going to go ahead and put on the environmental protection now, in this case, this is A piece of eyeglass materials and not going to be exposed to any very bad environment, so i’m, going to use the m code, a it’s, a polyurethane material, single component.
It air dries in about 15 minutes with the volatiles and about 24 hours full cure. So to complete the gauge installation, i just brush the m code, a over the gauge and then train it in the lead wire system and, if all goes well sometime tomorrow, we’ll test the gauge okay, our m code, a is completely cured, i’ve connected it as a Quarter bridge to the p3 strain indicator recorder i put in the proper bridge configuration which is a quarter bridge i put in the gauge factor, which is 2.09 i’ve balanced out the bridge and i’m. Seeing about a three or four count deviation here: that’s, because the plastic material tends to creep a little bit and i’ve just loaded it previously. Now, having done that i’m going to take off my glasses and i’m going to put these on and notice, as i put these on they’re going to stretch, and if i look here, i have a compressive strain of normally 620 micro strain it’s, it’s varying slightly here And that’s putting a fairly significant pressure on my temple now i can’t correlate the pain in my head to the micro strain on the glasses, but i can tell you that this is too much and if the cust, if the vendor wanted to help me with my Glasses, he would reduce the amount of strain or stress that’s, pressing on the side of my temples and that’s, a simple application of a strain gauge that’s available online.
This is a gauge that we is in our online shop, it’s, the o60sl, and if you go to the online shop, this will be the first linear strain gauge that you see. There are many others, just like it and or other configurations and or a series of gauges, including cea series of gauges, c4a series of gauges and the like. If you have any questions about the online shop contact our applications engineering department, we would be happy to show you exactly how it works and how to get the gauges that you need promptly. Okay, to recap, the materials that we use. The initial degrees with that was our gc6 isopropyl alcohol reagent grade of that, then we switched to the conditioner a the mild phosphoric acid solution, the neutralizer 5a, both of which were used in the surface preparation. Along with our silicon carbide abrasive paper, we used the scp 2. Then we applied the gauge handling tape, it’s the pct 3m. Having applied the gauge handling tape, we used the o60 uh sl strain gauge, it’s, a linear strain gauge 350 ohms three conductor, and then we finally buttoned it all up with the m code a and environmental protection which is commensurate with an indoor environment or relatively benign.