Pietenpol-List: Re: Pietenpol-List Digest: 34 Msgs - 02/24/01

[matronics]

Original Posted By: "Robert Haines"
Chris,You touched on the subject that Jack Phillips was refering to when youwere talking about "Those Magnificant Men..." and the wires failingbecause they were brittle. Anything you do to steel (with theexception of melting it and adding additional elements) to change itsstrength is only affecting the crystiline structure of the metal.Anyone who doesn't want a lesson on steel accept my appoligies anddelete this message.Here we go...In materials, the arrangement of atoms has much to do about thematerial's properties. Imagine the atom as a ball and to make astrong, dense material, the trick is to get as many of these ballspacked into a fixed space. If you had four balls, you could make acube. But you look at the cube and you see that there is space in thecenter where the round balls don't fit. So try it with three ballsarrange in a triangle. Then stack another triange top of it butrotated 120 degrees so the two sets fit tighter. What I am trying tosay is that there are many ways that atoms stack together. I'm goingto use carbon as an example. Coal and a diamond are the samematerial, only the atoms are arrange differently. Actually, a diamondis the most efficient and dense way carbon atoms can be arranged. Thesame situation happens with iron.The next idea to understand is that the cubes or trianges formed don'talways fit together. Imagine if you had a bunch of blocks, all cubes.Most times, these blocks are not stacked and packed neatly together(If you have kids, you know that the blocks are all over the damnhouse... oh, sorry). If they were packed neatly together, they wouldactually be one bigger block, but they never are. There is alwayssome misalignment. This is fundamentally a crystaline structure; abunch of blocks packed tightly together but not perfectly aligned.Now to steel. 10xx steel is just a little more complex in thatsometimes you have blocks made from just iron, and sometimes they'remade from iron and carbon (Fe3C). So now your large iron blockssurrounded by small blocks of Fe3C. If you understand how sand andgravel work together to make strong concrete, you understand this.4130 has iron, carbon, manganese, silicon, and chromium all doingdifferent things making several types of blocks.Those three ideas are what you need to know to understand 10xx steel.You have two different flavors of blocks, the blocks can change shapeif the atoms are arranged differently, and the block can be arrangeddifferently.Cold work, fatigue, and annealing - Take a dozen blocks and arrangethem in neat rows and columns on the floor. If you want to push someof the columns but not all, it's not that hard because they are neatlyarranged. Now push on a row. It's not that easy because you justscrewed up your neat arrangement by moving a couple of columns. Itbecomes HARDER TO DO. Because they weren't neat, the edge of someblocks hit the blocks in other rows and they pushed more and so on andso on. This is cold working or fatiguing a metal. When you bend ametal, you move the crystiline structure and create voids andmisalignments. This makes it harder to bend it the next time. Youcan create a harder steel by cold working (which is just beating itand screwing up the arrangement of the blocks). You can also do thisby heating the metal and quickly cooling it by throwing it into water(quinch hardening). You can fix this by moderately heating the metalhot enough (80 - 170 C) so the crystal structures move into positionsof less stress and allowing them the time to do so (anealing).If you heat to a higher temperatures (200 - 900 C) and control thecooling in different ways, you can destroy and regrow the crystilinestructures themselves and change the relationships of the iron and theiron and carbon.Most of us do not have the capabilities to do this type of heattreatment so we are limited to anealing and cold working to modify thestrength. Chris, with this statement, I hope I have answered yourquestion.Robert HainesMurphysboro, Illinois****snip****I have been told that you can't really heat treat the straight carbonsteels (10XX series). There is not much you can do with it. It comeshardand it stays hard or it comes soft and it stays soft or it comessomehwerein between and stays that way. I thought it is only when you addothermetals to the carbon and iron mix that you begin to have the abilitytosoften and harden the metal through the various heat treatedprocesses. Isthis true? Anybody?We need to nail down this aircraft wire thing once and for all.Chris BobkaTechnical Counselor**********________________________________________________________________________________

[matronics]

Original Posted By: "Graham Hansen"
Not necessarily so. Why are there antidrag wires in the wing? Idon't plan on going in reverse.The cross wire bracing is so that you can tension the tension wirewithout warping the structure. One wire only may be required tocounter the design load, the other is to counter that wires tension.Robert Haines*******When you look at a Jenny fuselage with the fabric off, you will seethatthere is a wire X between all the wood sections of the truss. If loadreversal was not a consideration, then we would only see the wiregoingacross one way, the direction of the tensile load. Since the wiresdon'twork in compression, loads are carried by the wires alternately as theloadreverses. That is why we see an X of wires, proof that both tensileandcompressive loads exist just about everywhere in the structure and whyweshould not mess with changing wall thicknesses.chris bobkaTC*******________________________________________________________________________________