CAD Report 104AAE Group Members: Adam Rush, Steven Kendell, Abhishek Dabas Page 1 of 9

CAD Report for Module 104AAEThe group that this report concerns was:

Adam Rush, Steven Kendell, Abhishek Dabas. (There were two other members who dropped out of the group during the course they were Tanu Chaturbedi and Karolina Kuk.)

IntroductionHoneycomb structures are commonly found in aerospace applications and have exceptional strength

to weight ratio which is necessary for many structural components especially in aircrafts. High strength material such as steel and titanium have significantly larger weight than weaker materials (copper). This results in a compromise to be made; where a material has sufficient strength and is relatively light such as aluminium. This makes aluminium a perfect material to create a honeycomb structure from. When designing such structures it is advantageous to predict the capabilities of the designed structure before it is manufactured. “Finite element analysis (FEA) is a computerized method for predicting how a product reacts to real-world forces, vibration, heat, fluid flow, and other physical effects.” (http://www.autodesk.com 10/12/15) FEA can also give visualisations of deformation, displacement and the Stress distributions within the structure. The objective of this work is to create a honeycomb structure from Aluminium 3003 and use FEA to test its physical properties in the W and L direction.

Honeycomb Core Structure. The Beginning:

Once the group had been established, we all decided to tackle the honeycomb core as our CAD project. This we all felt was the one best suited to our skills and confidence in our CAD capabilities.

From there we all started going through the tutorials or playing around with creating a (honeycomb) cell in Catia. After a while members of the group had made different levels of progress. Steven and Dean (Abhishek) had gone through the tutorials whereas Adam had worked towards creating a honeycomb cell. But there was a problem with one of our founding group members, Tanu had decided to go part time in her learning and therefore dropped the CAD module. However a new member was found in Karolina. From here all members of the group worked on creating the full honeycomb structure as defined in the coursework handout.

The Middle:All members made significant progress with creating the full structure, we all learned various

methods of creating a cell and then we learned various ways of multiplying that cell to give us a full 20 by 22 structure of cells. One of the more challenging parts of the modelling was creating the thickness of the cell walls, one method used was to create a polygon around the initial polygon and set the distance between the inner and outer polygons to the required amount.

The End:

By the time the second submission was approaching we nearly had a full working honeycomb created by Steven, this is how he did it. It was created, first by producing a hexagonal shape in a plane, producing a constraint where the sides are of length 4.1mm. Four more were then created parallel to each other to create 5 columns, each hexagon is separated by 0.1mm. Using the axis tool I placed a vertical line that was parallel to the vertical cell walls of the hexagon, separated by 0.5mm from the hexagon in the last column. I used the mirror tool, which allowed for me to

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select the 5 hexagons and mirror them along the axis, I repeated this selecting the 10 hexagons and mirroring them in a new axis, resulting in 20 columns. We then exited the plane and used the pad tool, ticking the box labelled ‘thick’, then set thickness 1 & 2 to 0.5mm. I then created another image in the same plane beneath the first row, creating 20 columns of hexagons once again. A constraint between the first rows inner cell wall and the second rows cell wall of 0.5mm was created. This ensured that when the pad tool was used on the second part, and the correct thicknesses was set, that the vertical walls would be 0.2mm thick, compared to the others walls thickness of 0.1mm. I mirrored each part separately, mirroring the first row 11 times, then repeating for the second row, thus creating a total of 22 rows. By creating a distance of 2.021mm between the axis line and the bottom of the row of hexagons I was able to mirror the row of hexagons so that they connected with the correct measurements to the rows of hexagons adjacent. A picture of the CATIA model is shown in Figure 1.

The group was organised and kept on track by the use of the WhatsApp app and outlook e-mail’s new group setting, so that files could be shared.

FEA Testing and analysis.Adam Rush’s Tests:

“For the testing and analysis I decided to base my investigations on the Von Mises stress levels that are shown in the Catia FEA component. Having never heard of Von Mises stress I decided to look it up on the internet. I found this:

“According to the von Mises’s theory, a ductile solid will yield when the distortion energy density reaches a critical value for that material … At the instance of yielding in a uniaxial tensile test, the state of stress in terms of principal stress is given by: σ1 = σY (yield stress) and σ2 = σ3 = 0.”

(http://web.mae.ufl.edu)

Essentially this is saying that, if σ 1, σ2 andσ 3 are the stress levels in the planesx , y andz, then when the stress level in the x plane is equal to the yield stress of the material then the stresses in the other two planes are zero. From this we can say that the Von Mises stresses are a measure of the level of stress in a 3D plane in relation to the yield stress of the material.

Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.Figure 1: Honeycomb Model.

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To test the honeycomb structure I set the mesh size to 5mm. From here I started with compression in the L plane. I set clamps on the bottom row of the structure at the lowest point available, there were 20 clamps used to ensure that the whole structure was covered. Then the load was applied to the top row on the highest points available, there were also 20 load points. However due to the staggered nature of the honeycomb the loads were not directly above the clamps so there would be an offset in the motion in compressing the honeycomb. One possible way round this would be to add a plate to the top and bottom of the honeycomb and place loads and clamps on that instead, but then this structure would also have to be accounted for.

Once the loads and clamps were in place I started with a load of 100N and recorded the Von Mises stress, here I chose to go for an average stress levels when looking at the model, I also decided to find the cell with the maximum stress and record that value. The max stress turned out to be in the lower left corner, this was expected due to the offset in position of the clamps and loads.

Table of loads in the L direction.

Load Weight Average Von Mises Stress Highest stressed cell100N 1.37 e6Nm2 2.54 e6 Nm2

200N 2.74 e6 Nm2 5.08 e6Nm2

300N 4.11 e6 Nm2 7.62 e6 Nm2

400N 5.48e6Nm2 1.02e7Nm2

500N 6.85 e6Nm2 1.27e7Nm2

600N 8.22 e6Nm2 1.52e7Nm2

700N 9.59 e6Nm2 1.78 e7Nm2

800N 1.10 e7Nm2 2.03 e7Nm2

900N 1.23 e7Nm2 2.29 e7Nm2

1000N 1.37 e7Nm2 2.54 e7 Nm2

1100N 1.51e7 Nm2 2.79 e7Nm2

1200N 1.64 e7Nm2 3.05 e7Nm2

1300N 1.78 e7Nm2 3.30e7Nm2

1400N 1.92e7 Nm2 3.56e7Nm2

1500N 2.06 e7Nm2 3.81 e7 Nm2

1600N 2.19 e7Nm2 4.07 e7 Nm2

1700N 2.33e7Nm2 4.32e7Nm2

1800N 2.47 e7Nm2 4.57 e7 Nm2

1900N 2.60 e7Nm2 4.83 e7 Nm2

2000N 2.74 e7 Nm2 5.08 e7Nm2

The structure had not failed at 2000N, but it was severely compressed at this point. The compression would have led to the part being unusable at this load.

For testing the W direction I decided to have the left side of the honeycomb as my load point and the right side as the clamp point, I used the same method as with the loading in the L direction.

CAD Report 104AAE Group Members: Adam Rush, Steven Kendell, Abhishek Dabas Page 4 of 9

Average Von Mises Stress table for loads in the W direction.

Load Weight Average Von Mises Stress Highest stressed cell100N 1.68e6Nm2 3.34 e6 Nm2

200N 3.36e6Nm2 6.68 e6Nm2

300N 5.04 e6Nm2 1.00 e7Nm2

400N 6.72 e6Nm2 1.34 e7Nm2

500N 8.40e6Nm2 1.67 e7Nm2

600N 1.01e7 Nm2 2.00 e7Nm2

700N 1.18 e7Nm2 2.34 e7 Nm2

800N 1.34 e7Nm2 2.67e7Nm2

900N 1.51e7 Nm2 3.01 e7 Nm2

1000N 1.68 e7Nm2 3.34 e7Nm2

1100N 1.85e7Nm2 3.67 e7Nm2

1200N 2.02 e7 Nm2 4.01 e7Nm2

1300N 2.18e7Nm2 4.34 e7 Nm2

1400N 2.35e7Nm2 4.68 e7 Nm2

1500N 2.52 e7 Nm2 5.01e7 Nm2

1600N (*) 2.69 e7Nm2 5.34 e7Nm2

1700N 2.86e7Nm2 5.68 e7Nm2

1800N 3.02 e7 Nm2 6.08 e7Nm2

1900N 3.19e7Nm2 6.35 e7Nm2

2000N 3.36e7Nm2 6.68 e7Nm2

(*) At this point the structure collapsed, for comparison however I continued to increase the loads so that I could compare the stress levels in both directions.

Since a table with a list of numbers can sometimes be hard to analyse I have decided to plot the information into a graph.

100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

0

10

20

30

40

50

60

70

Von Mises Stress in both L and W planes

Avg. Stress L Plane

Max Stress L Plane

Avg. Stress W Plane

Max Stress W Plane

Load (N)

Von

Mise

s Str

ess (

×e6N

m2)

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As we can see from the chart, the stress levels are higher in the W plane than in the L plane, also the maximum stresses are also respectively higher. As stated in the table for the W plane the structure failed at 1600N but I continued with the analysis to compare the two plans accurately. It can be seen that the stress levels are proportional to the loads. “

Steven Kendell’s Tests:

“Finite Element Analysis

To analyse the Honeycomb model, I used CATIA generative structural analysis feature. Before submitting my model into FEA, I defined the material properties following the specification that was given. To test the honeycomb structure I set the mesh size to 5mm. First of all I tested the model in the L plane, placing loads on each of the 20 vertices on the top row of the honeycomb, I then set clamps on the bottom row. There was a slight offset due to the staggered nature of the Model. I found the average and maximum displacement of the honeycomb at different loads. The loaded and restrained model is shown in Figure 2.

Another material was also tested, “Aluminium honeycomb is available in four different alloys, aerospace grades 5052 and 5056, and commercial grades 3104 and 3003.” (http://www.hexcel.com 10/12/15)

The material I chose to compare with Aluminium 3003 was Aluminium 5056. The Physical properties of this alloy was found using the MatWeb: Online Materials Information Resource. Figure 3 highlights the physical properties that were necessary to compute the analysis.

Figure 2: Loaded and Restrained Model.

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The difference in Yield strength will allow for an analysis of the Honeycombs where there is a difference in the plasticity.

(http://www.matweb.com 10/12/15)

The results of the finite element analysis of Aluminium 3003 showed that the average and maximum Von mises stress was constant for a given load, and was not dependant on the aluminium alloy. We found a linear

relationship between Von mises stress and the force applied to the structure, the steepness of the curve

shows the amount of stress experienced by the model per Load applied. Figure 4 shows that the curve with the steepest gradient was for the max stress experienced by the model when the load was applied in the W direction. Therefore, the model will experience plastic deformation under a smaller load than if the load was applied in the L plane.

The results that occurred for Aluminium 5052 were identical to that of Aluminium 3003, however the yield strength of Aluminium 5052 is 90MPa. Therefore a much greater load can be applied to the honeycomb before plastic deformation takes place.

Youngs Modulus Yield StrengthAluminium 3003 69GPa 40MPaAluminium 5056 71.0GPa 150MPa

Figure 3: Physical Properties of Aluminium Alloys used in Analysis.

FIGURE 4

FIGURE 5

Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.Figure 3: Physical Properties of Aluminium Alloys used in Analysis.

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Abhishek Dabas’s Results:

Here are the results that Dean has gathered.

LAVG LMAX WAVG WMAX100 1.08 2.15 3.21 6.42200 2.15 4.3 6.43 12.9300 3.23 6.45 9.64 19.3400 4.3 8.6 12.9 25.7500 5.38 10.8 16.1 32.1600 6.46 12.9 19.3 38.5700 7.53 15.1 22.5 44.9800 8.61 17.2 25.7 51.4900 9.68 19.4 28.9 57.8

1000 10.8 21.5 32.1 64.21100 11.8 23.7 35.3 70.61200 12.9 25.8 38.5 771300 14 28 41.8 83.51400 15.1 30.1 45 89.91500 16.1 32.3 48.2 96.31600 17.2 34.4 51.4 1031700 18.3 36.6 54.6 1091800 19.4 38.7 57.8 1161900 20.4 40.9 61 1222000 21.5 43 64.2 128

100300

500700

9001100

13001500

17001900

0

20

40

60

80

100

120

140

Von Mises Stress (Dean)

Avg Von Mises L DirectionMax Von Mises L DirectionAvg Von Mises W DirectionMax Von Mises W Direction

Loads (N)

Von

Mise

s (M

Pa)

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As you can see the graph shows that there is a linear relation between load and Von Mises stress levels.

Comparison of the FEA’s

The four different sets of data allow us to make a strong comparison between the load and the Von Mises stress values. Although the tests were carried out by different people in different ways and had the units given in different ways, we can say that there is definitely a linear relation between the Load and the comparative Von Mises stress. Each of the graphs show a roughly straight line increasing from left to right, since each of the graphs show the same linear pattern we can conclude that the data gathered are consistent at least with each other.

Starting with the L plane, we can conclude that for every X newton load amount there will be a corresponding Y value for the Von Mises stress, this value will be in the form of Y=mX+c where both m and c are constants for the equation but when the load is a 0N the stress level will be a 0 as well therefore we can conclude that c has a value of 0. In fact this equation y=mx+c holds true for each set of data gathered, the only difference is in the values of m, since c will always be 0 when the load is at 0N. It can be seen from the graphs that the value for m increases as look at different parts of the data, hence the graph. The bottom line in the graph shows the values for the L plane at an average value for Von Mises stress, the second line shows values for the L plane but this time at the max value for Von Mises stress. The third line shows, however, the values for the W plane at the average value for Von Mises stress and the fourth shows the values for the W plane at the max value for Von Mises stress. Here we must note that there is a difference in the gradient of the line for the W plane compared to the L plane in both the average values and the max values of Von Mises stress. In noting this we can begin to say that there is less structural stability in the W plane than in the L plane, this can be said because it can clearly be seen that there are higher stress values in the W plane compared to the L plane. The reason for the lower structural stability could be in the fact that in the L plane the vertical walls have a thickness of 0.2mm whereas in the W plane the corresponding “vertical” walls only have a thickness of 0.1mm.

There are ways that we could optimise this design both in the testing of the design and in its complete state. Firstly for testing we could affix plates to the top and bottom, or to the left and right hand sides, of the structure and use those to fully distribute the weight across the whole structure, but the downside to this potential method would be that this would cause an increase in the weight of the structure and its stability, the idea behind the honeycomb structure is that it is lightweight and flexible in the L and W planes but rigid in the T plane. In the design of the honeycomb we could make all vertical walls in either direction 0.2mm rather than just in the L plane. I don’t think this would seriously increase the weight of the object and it would give comparable strength in in compression in both the L plane and in the W plane.

In Conclusion:Although each member of the group came at the task with different ideas and skill sets we

have all found that we have learned something new whilst doing this project. We managed to create a working honeycomb structure and we all managed to test it in FEA. Although our methods of creating and testing were different we found that the results that we each obtained were comparable which would suggest that the results were either the same or similar enough. On the downside though we were hoping to have enough time to optimise the design and create a better honeycomb than when we started, but with illnesses and people dropping out we found ourselves

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out of time to do the optimisation, but we can learn from this for the next project that we come to as a group.

References:http://web.mae.ufl.edu: http://web.mae.ufl.edu/nkim/eas4200c/VonMisesCriterion.pdf (04/12/15)

http://www.autodesk.com: http://www.autodesk.com/solutions/finite-element-analysis (10/12/15)

http://www.hexcel.com: http://www.hexcel.com/Resources/DataSheets/Brochure-Data-Sheets/Honeycomb_Attributes_and_Properties.pdf (10/12/15)

http://www.matweb.com:http://www.matweb.com/search/datasheet.aspx?matguid=aaaabe41a20a4ed2b48270f7f2ef1b2d (10/12/15)