History-of-Mechanical-Properties

History-of-Mechanical-Properties - A bit of History:...

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A bit of History: D.Ast dast@ccmr.cornell.edu 255 4140
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First serious interest in Mechanical Properties of Materials
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All these articles were made by exposing Iron Oxide at high T to CO/CO 2 from a charcoal fire. To convert sponge iron into useful iron by hammering was expensive
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1709 Darby manages to reduce iron oxide with coke (from coal) achieving “a more fluid iron” .Pig Iron was born Design: NO overpressure Vacuum => 7.5 PSI FAIL SAFE DESIGN AS MATERIAL PROPERTIES WERE WILDLY VARYING
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Water boils at atmospheric pressure Steam condensed by Water spray Condensed water return to boiler via “Snifing valve” Water needed was pumped up from a stream into this holding tank
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The Newcomb engine was completely safe ! The worst case was im plosion, not ex plosion There was no overpressure of any kind => well matched to quality of iron available. Working pressure 7.5 PSI Piston area 2124 inch squared Total Force on piston 15,930 Lb Stroke 7 feet Work per stroke, force x distance => 111,500 ft-Lb Power at 12 strokes per minute 1,338,000 ft-lb per minute => 40.5 Hp ! Not bad… it certainly beat a horse!
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The Newcomb engine used enormous amounts of coal because much steam was wasted in heating the cylinder back to 212 F (cooled before to about 60 F). Also, the Newcomb engine could not do deliver the rotational power needed for cotton mills. Next James Watt…. 63 Years later, it takes a while to make progress ….
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Watt realized that the steam entering the always hot cylinder would via an escape valve, rush into condensor, a separate container surrounded by water. The Watt engine was still an “atmospheric engine” Watt separated steam working from steam condensing
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Watt’s insight was a flash of genius, because back then, nobody could see why steam should be so attracted by cold water that it voluntarily would go there…. . Of course, we know - and you learned it - that the vapor pressure is seeking equilibrium with the vapor pressure over the water reservoir in the condenser. But to Watt’s contemporaries, this concept was as remote as the moon. NOTE THAT IN AN “ATMOSPHERIC ENGINE” THE LOADING ON THE CYLINDER IS COMPRESSIVE STESS WHICH IS A MUCH SAFER DESIGN FOR A BRITTLE MATERIAL. Revisit FAILURE ENVELOPE discussed in last lecture
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4 years after Watt first engine, first iron in architecture Telford’s famous bridges Coalbrookdale (Home of Darby ) Cast Iron Wrought iron Cast Fe
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Thomas Telford (1755-1834) The design of bridges required characterisation of mechanical properties TENSILE TEST And mathematical tool MATH, FAILURE CRITERIA
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Telford’s 1826 master piece used wrought iron chain bars Experimentally, he found that the UTS was 50 KSI, and yield stress 25 KSI The working stress in the bridge was 12.5 KSI (Telford most likely never calculated it but derived from experiments and models) THE BRIDGE IS STILL IN SERVICE TODAY BUT HAS BEEN REBUILD TO TAKE ACCOMMODATE LOADS NEVER ENVISIONED BY TELFORD. THE NEW LINKS HAVE LOADS OF
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History-of-Mechanical-Properties - A bit of History:...

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