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material testing
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LearningTranscript
00:00Good afternoon friends. Today I am going to explain how to conduct the bending test on timber specimen.
00:10The aim of this experiment is to observe the behavior of the given timber beam specimen subjected to two point loading up to the failure and to determine the moment of inertia that is I, bending moment M, bending stress F and B.
00:30In order to conduct this bending test on the timber specimen there are few apparatus which are required. The first one is the universal testing machine. Usually the bending test is conducted on universal testing machine and second apparatus which is required for this sample this test is bending test assembly and third important apparatus is the vernier caliper as well as the scale and the dial gain.
01:00Which is used to measure the deflection during the bending test and the observations made in this timber bending test are the type of timber.
01:15This is the type of timber that is the acacia and the total length of sample is 554 mm that you have to measure with the help of this steel room.
01:28That is the second important observation that is called as the total length of beam or total length of a sample that is represented by L that is 554 mm here.
01:41And second, third observation, the bearing length of a sample, so in order to find out the bearing length of a sample, so what you have to do from this end leave 25 mm and from this end you leave 25 mm and you mark it and draw the line, draw the line.
02:01And the distance between these two lines and the distance between these two lines is called as the effective length of beam that is represented by the capital L.
02:14The distance between these two lines is called as the effective length that is 504 mm, 504 mm.
02:22So, once again that you have to measure with the help of the steel room that is capital L and in addition to this, in addition to this, the breadth of the sample, the breadth of a beam you have to measure with the help of the steel room that is 50 mm.
02:39That is represented by small beam that is represented by small beam and also the depth of the beam, the depth of the beam or the sample or the specimen you have to measure that is represented by small d that is also once again 50 mm that you have to measure once again using this, the scale.
03:00So, after the measurement of the beam, so after the measurement of the beam, the measurement of the various dimensions of the sample, so the next step is to conduct the experiment by keeping the specimen on the platform of that universal testing machine and afterwards gradually you have to apply the load till the fracture, so that I am going to explain later.
03:25And later, this is the universal testing machine, which we are using to conduct the bending test, apart from this bending test, you can conduct the tensile test, compression test, shear test using the same universal testing machine.
03:42So, the nearly 4 to 5 different experiments which you can conduct by using the same UTM that is the reason it is called as the universal testing machine.
03:52Here, here today, I am going to explain the procedure for conducting the bending test on the sample that is the wood or the timber.
04:02So, this is the timber sample or the specimen and the various dimensions are marked on this one that already have explained and after marking all those various dimensions, you have to keep it on two rollers.
04:18So, these are the two rollers and you have to keep it in such a way that the effective length has to come over these lines.
04:29By keeping this in your mind, you have to keep the sample over these two rollers.
04:36After keeping this, you have to keep the channel.
04:40So, this is the, here, in this, in this, the bending test, you are not applying the load directly.
04:47If you apply the load directly, what happens immediately, the specimen is going to break.
04:52In order to avoid that one, gradually you are applying the load to the sample through the channel and these two rollers.
05:00And these two rollers, which, which are, which are kept over these lines.
05:07So, this line, before the keeping these two rollers over this one, so entire effective length, you have to divide it into, divide into three equal portions.
05:19And here, the each portion is 168 mm.
05:24This is 168 mm, this is 168 mm and this is again 168 mm and from here to here is the effective length that is represented by the L.
05:33And by keeping these two rollers over these lines, this is 168 mm.
05:38And after, over these rollers, you have to keep the channel and on this channel, you have to apply the load, that is called as a W.
05:47And the moment you apply the load W, that is equally divided into the W by 2 over here and W by 2 over here.
05:56And the initial load, what we are taking for this bending test is 2.5 kN.
06:02And gradually, you have to increase the load intensity till the fracture.
06:11This is the dire gauge of this universal testing machine, which we are using to conduct the bending test on the timber sample.
06:18Here, in this dire gauge, the each division, each small division indicates 0.5 kN of low.
06:26Please remember, each the small division, that indicates 0.5 kN of, that is the, the low.
06:36And this bigger division, there are, this, the bigger division, bigger division is divided into 5 equal parts.
06:44So, there are 5 divisions, 0.5 into 5 and total the load these two indicate is 2.5 kN.
06:52So, that is the reason, the initial reading, what we are taking, the initial load, what we are taking for the bending test is 2.5 kN.
07:03Later, the next load is 5 kN, next one is 7.5 kN, next one is 10 kN.
07:10So, you continue the same intensity of load till the fracture of the sample.
07:16And for each and every load, for each and every load, the deflection that occurs on this sample, timber sample,
07:25you have to measure using the dial gauge which is attached to the bed of this universal testing machine.
07:32So, this is the dial gauge, this is the dial gauge which is used to measure the deflection.
07:38For each and every load, you have to measure the deflection that occurs on this timber sample.
07:45Coming to the tabular column, in the tabular column, there is a first column, that is serial number.
07:59Second column is the total load in, total load W in kN.
08:03Then the point load, the total load we are dividing into two point loads.
08:10So, each point load becomes W by 2 and W by 2.
08:14So, these we are applying to the sample through those rollers as well as the channel,
08:20so which already have shown on that machine.
08:22Later, for each and every reading load, point load, the deflection you have to calculate using the dial gauge.
08:30And the corresponding bending stress you have to calculate and how to calculate this bending test,
08:36that I am going to explain later.
08:38So, here, this is the dial gauge.
08:43The first load, what we have selected is 2.5 kN.
08:47The first load, what we have selected is 2.5 kN.
08:51This is the knob which is helpful to select the particular load for the bending test.
08:56The first serial number 1, the total load is 2.5 kN.
09:02For the applied load of 2.5 kN, the corresponding deflection we have to calculate using this dial gauge.
09:15The corresponding deflection that is measured with the help of this scale, it is something.
09:24For the applied load of 2.5 kN, the corresponding deflection in the sample is 1.85 mm, that is measured with the help of this dial gauge.
09:43In the next step, the load, what we have selected is 5.5 kN.
09:52Using this knob, you have to select a load of 5 kN.
09:56And for that 5 kN load, what we have selected, the corresponding deflection, you have to measure.
10:05The deflection is 2.7 mm.
10:09So, like this, you go on applying the load in a regular interval till the fracture of the sample.
10:21Once the specimen gets fractured, stop applying the load and for each and every load, find out the corresponding deformation, also the corresponding bending stress.
10:32See here, this is the tabular column for the bending test.
10:42As I already told you, the serial number 1, for that one is the initial load applied on the sample is 2.5 kN.
10:51For that, the 1.85 is the deflection which is measured using the dial gauge.
10:58So, the next load is 5 kN and the corresponding deformation is 2.7 mm.
11:06And the next load is 7.5 kN.
11:10For that, the 3.55 mm is the deflection which is observed from the dial gauge.
11:17The next intensity of load is 10 kN.
11:20The corresponding deflection is 4.2 mm.
11:23The next load is 12.5 mm.
11:26The corresponding deflection is 4.7 mm.
11:29Again, the load has been increased to 15 mm.
11:32For that, the deflection is 5.38 mm.
11:35Again, the load has been increased to 17.5 kN.
11:39For that, the deflection is 5.8 mm.
11:42So, go on increasing the intensity of the load till the fracture.
11:48Here, in this bending test, the fracture has occurred for a particular load of 30 kN.
11:54For that 30 kN, the deflection is 10.2 mm.
11:58So, using this tabular data, so what is given in the tabular column, so you have to find out the moment of inertia, distance from the extreme fiber of the neutral axis, bending moment, bending stress, maximum deflection, as well as the angst modulus.
12:14Also, you have to draw the one very important graph that is called as the load versus the deflection.
12:19Coming to the calculation fact, using this various relationship or using this various formula, you have to find out the first important thing that is called as the moment of inertia that is represented by I.
12:34So, for that particular section, the moment of inertia is calculated using B into D raised to Q divided by 12, where B is the breadth of the timber sample, which is 50 mm, D is the depth of the sample, that is 50 mm, divided by 12.
12:55So, this particular formula, so this particular formula, I, that is equal to B into Q divided by 12, which is for particular, the section of the timber.
13:05So, using this, find out the moment of inertia, which is in mm raised to 4.
13:11Later, the distance from the extreme fiber of the neutral axis, that is D by 2.
13:17So, the total depth of a sample is 50 mm, so D is 50 mm divided by 2.
13:24So, it is equal to 25 mm, that is nothing but the distance from the extreme fiber of the neutral.
13:32And the same way, you have to calculate the bending moment, that is capital L, that is W into L divided by 6.
13:41The W is nothing but the applied load for each and every reading.
13:46And the capital L is the effective length of a sample or the beam, that is 504 mm.
13:52And how to calculate this finite, effective length L, that already I have discussed.
13:59Using this formula, you find out the bending moment, that is Newton mm, that is in Newton mm.
14:05So, later, the bending stress for each and every reading, you have to calculate.
14:11The bending stress for each and every reading, for each and every load, you have to calculate using this formula.
14:18And bending stress is represented by small f, that is equal to m, that is the bending moment divided by the moment of inertia into D by 2.
14:28By using this relationship, you find out the f for each and every reading, after finding out of that f, you substitute that bending stress in the tabular column.
14:39Later, the maximum deflection delta max, you have to find out, so here, in order to find out the maximum deflection, no equation, no relationship, no formula, simply, you just search the maximum deflection in the deformation column.
14:58Take the maximum deflection from the deformation column, and you write it here, that is called as the maximum deflection of the beam.
15:07And at the end, you are finding out the Young's modulus of the timber, that is E, that is equal to 23 into L raised to 3 LQ, that L is nothing but the effective length,
15:19divided by 36 I, I is the moment of inertia, into the load, divided by the delta max.
15:27So, using this relationship, you try to find out the Young's modulus of a timber sample.
15:34Also, apart from these calculations, you have to draw the graph, that is load versus the deflection graph.
15:43Along the y-axis, you have to take the load, which is in kilonewton.
15:47From the tabular column, you have to take the load, that is in kilonewton.
15:52Also, from the tabular column, you have to take the deflection, which is in mm, and you have to draw this, the load versus the deflection curve.
16:01You are going to get the nature of curve approximately like this.
16:05So, this last point indicates the fracture of a sample.
16:09So, this is what one of the experiment called as the bending test on a timber specimen using the universal testing machine.
16:17So, this is what one of the models of race is, so it will help you see a column in the middle of the building.
16:22So, what the numbers are going to be, you know, the best of fact is that, about 32 we have to take it.
16:28So, let's go ahead and do that.
16:30So, this is what one of the Inglow that happens.
16:32So, this one of the departments, I have to take the load of, is that this one of the characters,
16:37so that this one of the characters, I read them in the middle of the game,
16:39so that this one of the characters are going to be a bit easier for a bit of a bit of a bit of a bit of an inch of a bit of an inch of её.
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