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#11
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Why 2024?
In article . com,
Lou wrote: For all or you that are interested. I've made the brackets out of 2024 and the 2024 bends harder, but doesn't seem to snap as easy. Lou Of course, 2024-T3 doesn't snap as easily as 6061-T6! It is the "T number" that determines brittleness (and stiffness). |
#12
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Why 2024?
On Tue, 12 Jun 2007 03:05:30 GMT, Orval Fairbairn
wrote: In article . com, Lou wrote: For all or you that are interested. I've made the brackets out of 2024 and the 2024 bends harder, but doesn't seem to snap as easy. Lou Of course, 2024-T3 doesn't snap as easily as 6061-T6! It is the "T number" that determines brittleness (and stiffness). Orval, stiffness is the same for the same alloy, and substantially the same for all aluminum alloys, independent of heat treatment conditions. "T-number" has nothing to do with stiffness. Yield strengths (and tensile, but yield is the one we USUALLY care about) vary amont alloys and heat treatments. 2024 is about 5% "stiffer" than 6061. 2024-T4 yields about 40% more in tension than 6061-T6 before breaking. |
#13
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Why 2024?
In article ,
GeorgeB wrote: On Tue, 12 Jun 2007 03:05:30 GMT, Orval Fairbairn wrote: In article . com, Lou wrote: For all or you that are interested. I've made the brackets out of 2024 and the 2024 bends harder, but doesn't seem to snap as easy. Lou Of course, 2024-T3 doesn't snap as easily as 6061-T6! It is the "T number" that determines brittleness (and stiffness). Orval, stiffness is the same for the same alloy, and substantially the same for all aluminum alloys, independent of heat treatment conditions. "T-number" has nothing to do with stiffness. No, it isn't! Try to bend some .025 6061-T3 and then some 6061-T6. You will find the T2 bends more easily. Yield strengths (and tensile, but yield is the one we USUALLY care about) vary amont alloys and heat treatments. That is why "T-number" controls stiffness, since bending is the result of inelastic deformation. It takes more torque to bend a piece of T6 vs T3 of the same alloy and thickness. 2024 is about 5% "stiffer" than 6061. 2024-T4 yields about 40% more in tension than 6061-T6 before breaking. Yes. |
#14
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Why 2024?
On Jun 13, 7:30 pm, Orval Fairbairn wrote:
In article , GeorgeB wrote: On Tue, 12 Jun 2007 03:05:30 GMT, Orval Fairbairn wrote: In article . com, Lou wrote: For all or you that are interested. I've made the brackets out of 2024 and the 2024 bends harder, but doesn't seem to snap as easy. Lou Of course, 2024-T3 doesn't snap as easily as 6061-T6! It is the "T number" that determines brittleness (and stiffness). Orval, stiffness is the same for the same alloy, and substantially the same for all aluminum alloys, independent of heat treatment conditions. "T-number" has nothing to do with stiffness. No, it isn't! Try to bend some .025 6061-T3 and then some 6061-T6. You will find the T2 bends more easily. Wrong. GeorgeB was correct. You are confusing yield strength with stiffness. Stiffness refers only to elastic deformation. Strength refers only to plastic deformation. Elastic deformation is when it bends and then springs back to exactly the same shape it was before. Plastic deformation is when it stays bent. The stiffness of a material is the ratio of stress to strain. The formal name for that material property is the spring constant or Young's modulus. Ignoring allotropes for the sake of simplicity, the stiffness of a material depends only on gross composition and is independent of temper. Thus all low-alloy steels have the same stiffness which is just about the same as plain old iron. Yield strength is the minimum stress that will result in plastic deformation (e.g. a permanent bend.) Heat treatment affects yield (and ultimate strength. So if you make a spring out of annealed 4130 and another out of hardened 4130 they will both stretch the same amount for the same applied force, so long as you do not apply so much force that either is permanently stretched. (e.g. the applied stress is in the elastic range) They are equally stiff. However the force that leaves the annealed spring permanently deformed (yielded) is much less than that which leaves the hardened spring deformed. The hardened material is stronger, and so it remains 'springy' over a range of stress that would leave the other spring 'sprung'. The difference between 'spring' steel and ordinary steel is the strength, not the stiffness. The same is true for all alloys, not just steel. Yield strengths (and tensile, but yield is the one we USUALLY care about) vary amont alloys and heat treatments. That is why "T-number" controls stiffness, since bending is the result of inelastic deformation. It takes more torque to bend a piece of T6 vs T3 of the same alloy and thickness. Wrong. It takes equal torque to bend each _in the elastic rage_. It takes more torque to _yield_ the stronger piece. 'Bend' is ambiguous. You can bend the piece and have it spring back all the way (elastic deformation) or you can bend it and have it stay bent (plastic deformation). Stiffness refers only to the elastic deformation. Strength refers only to the plastic deformation. 2024 is about 5% "stiffer" than 6061. 2024-T4 yields about 40% more in tension than 6061-T6 before breaking. Yes. Yes. -- FF |
#15
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Why 2024?
On Wed, 13 Jun 2007 19:30:04 GMT, Orval Fairbairn
wrote: Of course, 2024-T3 doesn't snap as easily as 6061-T6! It is the "T number" that determines brittleness (and stiffness). Orval, stiffness is the same for the same alloy, and substantially the same for all aluminum alloys, independent of heat treatment conditions. "T-number" has nothing to do with stiffness. No, it isn't! Try to bend some .025 6061-T3 and then some 6061-T6. You will find the T2 bends more easily. If you want to use incorrect terminology, that is fine. Stiffness has nothing to do with plastic deformation. If you take the same size piece of 5052, 6061, 2024, or 7075 and load them the same BEFORE plastic deformation, you will see virtually no (less than 10%) difference in deflection vs load. A socket head capscrew, US, is about 220,000 psi yield strength. A cheap hex head bolt is about 30,000p psi yield strength. For the same load, before plastic (inelastic as you use) deformation, both will stretch the same and recover the same. Yield strengths (and tensile, but yield is the one we USUALLY care about) vary among alloys and heat treatments. That is why "T-number" controls stiffness, since bending is the result of inelastic deformation. It takes more torque to bend a piece of T6 vs T3 of the same alloy and thickness. Stiffness and INelastic (usually referred to as "plastic") deformation have less in common than your and my knowledge of material science. 2024 is about 5% "stiffer" than 6061. 2024-T4 yields about 40% more in tension than 6061-T6 before breaking. Yes. 2024-T0 is 5% stiffer than 6061-T6. 6061-T6 is 25% stronger than 2024-T0. |
#16
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Why 2024?
On Jun 15, 7:15 am, GeorgeB wrote:
On Wed, 13 Jun 2007 19:30:04 GMT, Orval Fairbairn wrote: Of course, 2024-T3 doesn't snap as easily as 6061-T6! It is the "T number" that determines brittleness (and stiffness). Orval, stiffness is the same for the same alloy, and substantially the same for all aluminum alloys, independent of heat treatment conditions. "T-number" has nothing to do with stiffness. No, it isn't! Try to bend some .025 6061-T3 and then some 6061-T6. You will find the T2 bends more easily. If you want to use incorrect terminology, that is fine. Stiffness has nothing to do with plastic deformation. If you take the same size piece of 5052, 6061, 2024, or 7075 and load them the same BEFORE plastic deformation, you will see virtually no (less than 10%) difference in deflection vs load. A socket head capscrew, US, is about 220,000 psi yield strength. A cheap hex head bolt is about 30,000p psi yield strength. For the same load, before plastic (inelastic as you use) deformation, both will stretch the same and recover the same. Yield strengths (and tensile, but yield is the one we USUALLY care about) vary among alloys and heat treatments. That is why "T-number" controls stiffness, since bending is the result of inelastic deformation. It takes more torque to bend a piece of T6 vs T3 of the same alloy and thickness. Stiffness and INelastic (usually referred to as "plastic") deformation have less in common than your and my knowledge of material science. 2024 is about 5% "stiffer" than 6061. 2024-T4 yields about 40% more in tension than 6061-T6 before breaking. Yes. 2024-T0 is 5% stiffer than 6061-T6. 6061-T6 is 25% stronger than 2024-T0. You're not confusing 2024T4 with 2024T0, I hope? Dan |
#18
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Why 2024?
10% in my world is hardly "virtually no" Ah, and where does "less than 10%" fall? |
#19
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Why 2024?
On Jun 15, 3:18 pm, Bob Kuykendall wrote:
10% in my world is hardly "virtually no" Ah, and where does "less than 10%" fall? For those with the time and interest, MIL-HDBK-5H has just about everything you might want to know about use of aluminum in aircraft structures (see chapter 3). Other metals are covered too. It's freely available on the web courtesy of our tax dollars. "MILITARY HANDBOOK, METALLIC MATERIALS AND ELEMENTS FOR AEROSPACE VEHICLE STRUCTURES" http://snap.lbl.gov/pub/nj_bscw.cgi/...h%20Metals.pdf Enjoy, Craig |
#20
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Why 2024?
On Jun 15, 9:07 pm, clare at snyder.on.ca wrote:
On Fri, 15 Jun 2007 11:43:05 -0700, wrote: On Jun 15, 7:15 am, GeorgeB wrote: On Wed, 13 Jun 2007 19:30:04 GMT, Orval Fairbairn . If you want to use incorrect terminology, that is fine. Stiffness has nothing to do with plastic deformation. If you take the same size piece of 5052, 6061, 2024, or 7075 and load them the same BEFORE plastic deformation, you will see virtually no (less than 10%) difference in deflection vs load. 10% in my world is hardly "virtually no" Regardless, the reason 2024 than 6061 for shop bent brackets is because it is stronger, not because it is stiffer. -- FF |
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