 I will show you one more application where we want to use this particular system and that is this tester. Now permeability as you know is one very important requirement. So air permeability now to the best of my knowledge there is no machine available commercially for helium permeability of a fabric because that is a very very specialized niche area. Applications are made by people for common applications where there is a demand. Now air permeability is a very important requirement automobiles they make these airbags they have to be air permeable or non permeable. Similarly there are many fabrics which have to be non air permeable. So there are testing machines available in the market for air permeability this is one such machine which we bought for around Rs. 70,000 okay. What is happening here is you can see these two plates here actually they are not plates they are these are two elements okay. So you put a fabric piece in between these there is a small circular place where you can keep the patch and then you bring the jaws together and then you tighten it on the top like this. So you create a very tight barrier and then you can connect this system here to air compressor and this particular system it uses now another question I will ask you just to see how innovatively you can think. Well the air is leaking from this fabric but the leak rate is very very less. Now I would like to sense at what rate the air is leaking. So what I do is I put the fabric inside the between the jaw I connect it to a compressor and leave it for 8 hours. Now under the pressure of the and you can regulate the pressure by the there is a pressure control facility here this dial that you see here is basically for pressure control. What delta P you want to create? So I create delta P in the real life for an airship the delta P is very small therefore the air will not leak very rapidly. So maybe it will be 3cc in 8 hours very small amount. How do you measure or how would you measure air leakage of 3cc in 1 hour? What kind of a sensor will you attach to this particular system? So on one side there is pressure on this side there is vacuum or ambient air and now under pressure the air has come but the air which has come in only 3cc or 5cc or 10cc in 8 hours. How do I measure? You cannot put any device which like a rotor meter or something that will work for very high flows the flow rate is very very low so this air will not push you know any big object or a needle or any spring to create pressure to show you the reading think about it yes. No the amount of air is so less and see it is not necessarily vacuum basically both sides have air only both sides are full of both sides have air chamber but in one side the air is 3cc more after 8 hours so it is not nearly not actually a vacuum so I am wrong it is not a vacuum think of some way of measuring 3cc or 4cc or 10cc air leakage over 8 hours increasing weight of 3cc air very difficult then the cost of the balance or the weighing machine will be 10 times the cost of the equipment a weighing machine which can weigh a difference of 3cc weight of air very difficult again this is very simple it is very simple when you hear it you will laugh you can do that so what you can do is you can connect but how much water will 3cc of air push water is 1000 times heavier than air so 3cc of air will not come out the pressure which the water will exert back see for water to move the pressure should be more than the weight it will not displace if water comes out it will displace but the force created by 3cc of air on a column of water is very less so with that force you cannot overcome the inertia see if there was water inside and you can say there is a 3cc of water that will push it up and you make a very thin capillary it will you can measure it but now you are trying to push a column of water with air if there are bubbles through how do I measure the rate how do I measure how do I measure how do I measure see if you have you have water so air has come out it has bubbled through and gone on the top how much air has gone that is what I am saying the height of water displaced will be very small by 3cc or 10cc of air if I have a gas there let us say a coloured gas air will mix with it if you say I will put that I will have a I will have a I will have a column of gas with the partition and now 3cc of air has come it will push it up this could be possible think of something else so I will tell you what they do if I zoom it you will probably see it so if you see on top of this there is a capillary tube ok this capillary tube is connected to the outlet of the upper chamber the chamber which is away from the fabric collector chamber and what they do is this capillary tube has a column of a full of water and inside the column of water we insert an air bubble so they are given a very small device by which you can actually create a small air bubble and this air bubble it is not very clear but I can show you if I zoom further there is a air bubble somewhere here you can see there is some mark is it visible to you or not there is some darkish mark here that is the air bubble so this air bubble is created somewhere at the beginning and there is a recording and then over a period of 8 hours when the air comes out now air will push against air so it will move it and then they have calibrated this tube by leak rate of air so within the within the range of expected leak rates of the gas for 8 hours or whatever duration they have made this tube large enough ok so I will encourage all of you to come to the lab and have a look and maybe do a small experiment on how these systems work so now this is for air permeability but we do not work with air inside the balloon except for testing purposes so to characterize the fabric against helium or hydrogen what we need to do is two things simple things on the inside or on the intake side I can connect a cylinder of gas under pressure a typical gas cylinder hydrogen helium is 140 bar pressure inside so if I open it it will come out at a very high speed so much high speed that if you put a small PVC nozzle that nozzle can become ice cold within 15-30 seconds that is the speed at which helium comes out or hydrogen comes out so you connect this to the cylinder and you knock off this permeability equipment this particular sensor and connect the helium leak detector and when the gas comes out that detector is very precise it can measure so this is one project which I want some student to do this could be a good project for any student who wants to work on a practical fabrication just connect the cylinder and device a connector for the HLD so this is to be modified for determining one student actually came and tried attempted doing it but he could not get much ideas so he ended up just testing this for some information ok then one other issue it may not be useful for us that much because we use envelope at low pressure but in our systems can you envisage a situation at which the delta p increases increases increases and becomes unbearable in an LTA system normally the pressure inside is not very large but can there be a situation yeah so suppose there is a balloon which is cut and it starts going up delta p keeps increasing because p outside keeps falling a time will come and the fabric will tear so this particular system is a digital bursting strength tester so what you do in this is you in this particular area below this you just put a small piece of fabric of a particular shape and it increases the pressure till there is a hole created and it tells you what is the reading so you come to know that this fabric can withstand delta p of so much therefore you can work out at what height this balloon will tear so for that purpose we can use this equipment then we have a flex tester a typical LTA envelope will go up deployed for some time come down again go up again come down maybe to take care of the winds you may lower it raise it lower it raise it it will undergo flexure because delta p will keep changing so there is some flex tester available which test the fatigue behavior of fabric so what you do is you basically just attach strips and they just keep moving like this and it tells you after how many such oscillations the envelope starts developing permanent strain okay so this machine can test 6 percent at a time you put all 6 specimens in the jaws hold it and put the machine on it just starts moving like this and it just tells you so you will see when you tested there are cracks developing and this crack slowly propagate and then it breaks and then it just stops and tells you that this particular fabric can withstand so many cycles I will know that if I make an arrow straight with this material I can permit 6 deployments and the 7th deployment there is a chance that there will be some cracks provided the pressure difference is matching with the load coming now another area which is of important is flame propagation you saw in hidden ball that when the flame started in the front very quickly it came to the rear so for that we have purchased one instrument called as a flammability tester so what is done in this system is that you have a standard LPG or a small LPG cylinder and there is a small equipment here a small pin here where a flame can be developed and then there is a inclined scale I will try to make it little bit larger you can see this so you see this particular thing is the flame holder at this point the flame is created it is nothing but a small syringe through which the LPG comes out and you just put a match there and the LPG catches fire so there will be a flame and then there is this inclined system on which you mount the fabric and on top of the fabric what you do is you have this you have this simple thread okay and this thread is connected to the to the fabric at a point near which the flame will be created or actually you put it across this length on the top so what happens is that when you ignite the clock starts and then the flame travels when the flame reaches the thread the thread burns when the thread burns then this particular system drops for this weight it drops and it detects so the time between the flame propagation to the tester dropping is measured so you know that flame will spread at this rate in this fabric some fabrics are very good the flame does not spread or it spread at a very low rate in some cases it spreads very fast so the post ignition behavior of fabric can be tested interestingly none of these equipment were actually designed for LTS systems they were designed for commercial fabrics and other things but we have you know we have tried to we have we have procured them basically for trying to adapt them okay so this is the this is the basic system and then we have also a hot air oven so if we want to make a pizza in the lab we have an oven we can easily use it this can go up to 250 degree centigrade enough to make a nice pizza so students have never tried it I do not know why I would have done it if I was a student in this lab so what we do here is subject the material to high temperatures and then do the testing to find out what is the effect of exposure to temperature on the properties and if you want to create the effect of long-term aging and you want to accelerate that you can do it by subjecting into temperature it is very accurate up to 1 degree accuracy you can create temperature okay these are some of the fabrics which have been tested by our students in the lab I have taken this material from a paper which they presented recently in IIT Madras there was a paper on material science and technology so you can see that we have material available from 35 GSM to 215 GSM in the lab and we have also measured their thicknesses we have a very nice thickness gauge also so there is a nanoclip nanoclip polyester which is used by us to make very very small airships such as the flying fish I should I show you the flying fish I will show it to you sometime then we have red colored pu coated nylon nylon habit with pu coating and then so you can see it is 40 43 GSM slightly more than this one but it has got much better strength then we did the bursting strength and maneuverability characteristics so you can see for PVC and nanoclip also there is no there is no value because it just burns immediately but other fabrics you can see that the flame rates are different and then we did some testing on the breaking load versus elongation so some materials have got a very very strong breaking load but elongation is very less and some they have a very low load at least they elongate a lot so PVC stretches very easily but does not break it breaks only I mean 100 Newton 10 kg is enough to start stretching PVC but it elongates a lot right okay so I think on that note we can stop for today.