Aluminium Model of Transparent SUV
https://me.jhu.edu/thwang/notes/Scaling-II.pdf
The above is a second version. Alternating the tabs from internal to external and using tapes to fix the shape.
Density of Aluminium is 2.7 g/c.c.
This modelling took less than 1 hour using the same tools as the paper model. Thinking and printing took much longer.
Yesterday, I went looking for printers of A0 plans. Not many in Kota Kinabalu. One shop, Kinabalu Printing Shop or Page 8 at Kingfisher, Likas, keep on cropping up. It charges RM 9 for printing, but when asked, also RM 9 for copying. Bormas charges RM 6 for printing, RM 3 when I asked them.
I went to Bormas at Jalan Gaya but it iturned out it cannot print, only photocopy. They recommend 21 Printing but it quotes RM 25 for printing and photocopying. So I went to Page 8 to print. It took less than 15 minutes but I took a coffee break. Went back to Bormas to photocopy.
The printed plans are not exactly 1/10 scale. 44.2 cm for 4.5 m actual. I used the polystyrene sheet as a base to bend the aluminium sheets. That polystyrene was more than 5 years in my office because I wanted to model aeroplanes. I also have a one foot aluminium sheet for years, little used but not enough now for this car. I bought a 3 feet wide sheets at a length of 2 feet, at the rate of RM 8.80 per foot. It turned out too short. So need to buy a 4 feet wide sheet for 2 feet at RM 10.80 per foot. It is dirty but I do not use this aluminium for the finished model. It is only a mold.
The weakness of paper models is the lack of structure. It assumes we the sheets are flat and bent only at designated places which are straight lines. Good for rigid sheets.
That is why I need to provide cross sections to fix its shape more accurately. This aluminium model is not glues yet so that I can insert cross sections or other ideas. Initially, I just use polystyrene sheets as its base. This model is completed but I need to build better versions. We shall keep on improving non-stop.
Using double sided tapes do not work. Easily becoming apart. Using the alternating tabs allow a strong frame such that a cross section may not be necessary. Because this model is to be used as a heated mold for acrylic, I shall try to use aliminium tapes around this model.
The 1/10 th aluminium model with 0.5 mm sheet weighs 270 g, equivalent to 270 kg full scale.
A plastic model, 0.55 mm thick weighs 122 g without its base.
This video shows you how strong the model is against deformation. It was able to withstand more than 2,000 g of force exerted on its rooftop. Even 500 g, 200 g of extra weight moves the skin only a little bit. The sheet should be able to withstand the weight of a person easily.
Not surprising because, in full scale, it is like having an exoskeleton of aluminium, 5 mm thick.
Compared to acrylic, its yield strength is only 40 MPa, while Acrylic is 70 MPa. Density wise Aluminium is half as heavy as Acrylic, so at the same thickness, they should have the same yield strength.
However, Aluminium has an ultimate Yield Strength 120 MPa, making it 3 times stronger as Acrylic in a collision. Acrylic ultimate strength is the same as its yield strength because it is brittle.
Density of Acrylic is 1.2 g / c.c.
That is a 100 g weight. At 50g, its shape is still intact. At 1/38 th scale, rounded to 40 th, assuming cubic scaling effect for weights, this is equivalent to 6,400 kg. This is 6 cars weight. The paper is 0.1 mm thick, so equivalent to 40 mm thick of paper. Paper appears stronger than plastic or even aluminium. Stronger than even plywood.
Does it really make sense, or could it be due to wrong scaling factors? But paper is denser than plywood so it could be possible for paper to be stronger than aluminium.
What it means is that, the scaling factor for deformation is to the square, not cubed. For a 1/40 scale, we multiply the bending force by 1,600. So 100 g, is equivalent to 160 kg, which is a more reasonable figure.
For the 0.5 mm thick aluminiun model, 2 kg force is equivalent to 200 kg, which is higher than a full size car made of 4 mm thick paper. The plastic model can withstand 3 kg without permanent damage, so should withstand a weight of 300 kg on its roof.
It is not under the same acceleration, but scaled force or scaled acceleration. Force is cubed, while acceleration is just the scale factor. The scale factor is usually the length dimension, L.
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