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There's been some talk of "voids" and "particles" I would add "coarse grain structure". These in the sense of physical properties can be good or bad or have little effect depending on the nature and end use of the material.
Used to be when a casting cracked it was "stop drilled" the drilled hole had a way of preventing the crack from propogating. For the same reason, inclusions and voids in some materials make them a bit more fatigue resistant, some less.
Any common alloy is a careful balance of dozens of properties not the least of which is cost. Stressed parts in old cars were made form frequently rich and relatively expensive alloys. Makers of traditional hand planes and chisels look for pre '70's automotive leaf springs for re-forge stock. Model "T" Ford driveshafts have been converted to countless uses.
Castings used in aircraft structure looks crystaline when it fails - like a brittle cast iron fracture - but there's considerable yield before it does. If you look closely at a machined portion near the fracture the deformed metal looks porous and the crystaline nature of the material stands out clearly in the surface. First time I saw this in an piece of aircraft wreckage I was shocked. Then I reflected that aircraft are made of the strongest and lightest materials. There must be some reason that particular alloy is used. Later discussion with an old metallurgist confirmed my conclusions.
The Navy builds warship structure from a low carbon steel with superb welding and cold water ductility properties. If the ship is grounded (what ship won't be at some time in its career) they want the plates to deform rather than tear or shear. Plastic deformation keeps the plates intact and the water out. Extra thickness is provided as a corrosion allowance.
The hull could be made of something corrosion resistant but even the lower alloy stainless suffer from chloride stress corrosion, fatigue susceptability.
While most austinetic stainlesses weld very well, there's the problem of securing the same corrosion properties in the weld as the base metal. Cost is enough to scuttle forever the notion of stainless steel hulls; even low alloy stainless contains significant percentages of nickel and chromium making it maybe ten times as expensive as low carbon steel.
Material selection for high stressed part continues. High revving racing engines with characteristic strain reversals and middling heat have been very well met with what could be called conventional materials commonly used in the automotive industry.
My performance car expertise is spotty and now its certainly out of date but here's an example of stuff doesn't have to be expensive to perform well. For a long time, Chevy and Chrysler used closed die forged alloy steel cranks while Ford used cast nodular iron. The manufacturing costs for the forged crank were said to be double the cast crank. I've seen liturature where The Ford cast crank is superior in terms of longevity and catastrophic failure compared to the forged crank. The tensile tests of the cast crank were lower but there were properties inherent in the material that uniquely suited it to requirements of automotive cranks.
The same was previously true of titanium connecting rods Vs alloy steel but superior design and greater knowledge of the inner mysteries of titanium has resulted in titanium as the preferred choice in the spare-no-cost world of competition.
One reason why "billet aluminum" is popular for after market automotive parts is that there was mountains of it available in the form of aircraft production remnents in Southern California in the early boom years of hot-rodding. It was also easy to machine and provide with colorful anodizing. What we have here is an economic incentive become tradtion. Here is the only reference to "billet" in this piece.
Hot-rod magazines are rife with know-it-all writers of shallow experience blathering to an uncritical readership about how adding this pile of (expensive) parts makes 16 (or 162) more HP when no before and after instrumented test data is offered.
The assumption is their readership is ignorant. The tragedy is the assumption is frequently correct; there is a sucker born every minute.
I watched as an acquaintance of mine poured tens of thousands of dollars in a racing engine over a period of three years working from magazine ads claims ignoring cautionary tales from the knowledgable (not me, I didn't know him well enough to trash his dreams).
When he was done the drag racing rules had evolved and most of his work wasted so far as the competitive advantages he'd built into his '69 Pontiac GTO: the racing world went and moved the goal post.
To add insult to injury, he trailered his car to a famous local competition shop for a dyno tune-up. He assumed from the magazines he read he'd get over 500 HP from his 389. In fact he got less than 400 in spite of the tune-up shop's best efforts. It was porting and pistons, they didn't work together.
All that time and money and he didn't even have a worthy street rod. His world was crushed. He not only invested a lot of money but his expectations of glory and all for nought. It seems silly to put it this way but its true: he grieved for more than a year. His wife had a hard four years thanks to this debacle but she persevered and their family came out of this obsession intact.
The fool-and-his-money market seems to be fading from the performance parts scene I'm glad to say, but it's not gone completely.
While it's a great pleasure to me to work on fine mechanisms and assemble well designed and fitted parts I think there should be some benefit attached to the work. After-market kits and modifications have become much more competitive these days and the manufacturers no longer have an eager uncritical customer base. They're forced to provide some support for their assertions (least their competition leap into the breach) thus the assertions have become more moderate and less comprehensive.
I love the expressions: "Show me", "Why", and the expression on the saleman's face when you confound him by offering a simple uncontrovertable refutation.
My point is to love the pretty go-fast stuff (I do) but remain skeptical.
[This message has been edited by Forrest Addy (edited 02-11-2003).]
Used to be when a casting cracked it was "stop drilled" the drilled hole had a way of preventing the crack from propogating. For the same reason, inclusions and voids in some materials make them a bit more fatigue resistant, some less.
Any common alloy is a careful balance of dozens of properties not the least of which is cost. Stressed parts in old cars were made form frequently rich and relatively expensive alloys. Makers of traditional hand planes and chisels look for pre '70's automotive leaf springs for re-forge stock. Model "T" Ford driveshafts have been converted to countless uses.
Castings used in aircraft structure looks crystaline when it fails - like a brittle cast iron fracture - but there's considerable yield before it does. If you look closely at a machined portion near the fracture the deformed metal looks porous and the crystaline nature of the material stands out clearly in the surface. First time I saw this in an piece of aircraft wreckage I was shocked. Then I reflected that aircraft are made of the strongest and lightest materials. There must be some reason that particular alloy is used. Later discussion with an old metallurgist confirmed my conclusions.
The Navy builds warship structure from a low carbon steel with superb welding and cold water ductility properties. If the ship is grounded (what ship won't be at some time in its career) they want the plates to deform rather than tear or shear. Plastic deformation keeps the plates intact and the water out. Extra thickness is provided as a corrosion allowance.
The hull could be made of something corrosion resistant but even the lower alloy stainless suffer from chloride stress corrosion, fatigue susceptability.
While most austinetic stainlesses weld very well, there's the problem of securing the same corrosion properties in the weld as the base metal. Cost is enough to scuttle forever the notion of stainless steel hulls; even low alloy stainless contains significant percentages of nickel and chromium making it maybe ten times as expensive as low carbon steel.
Material selection for high stressed part continues. High revving racing engines with characteristic strain reversals and middling heat have been very well met with what could be called conventional materials commonly used in the automotive industry.
My performance car expertise is spotty and now its certainly out of date but here's an example of stuff doesn't have to be expensive to perform well. For a long time, Chevy and Chrysler used closed die forged alloy steel cranks while Ford used cast nodular iron. The manufacturing costs for the forged crank were said to be double the cast crank. I've seen liturature where The Ford cast crank is superior in terms of longevity and catastrophic failure compared to the forged crank. The tensile tests of the cast crank were lower but there were properties inherent in the material that uniquely suited it to requirements of automotive cranks.
The same was previously true of titanium connecting rods Vs alloy steel but superior design and greater knowledge of the inner mysteries of titanium has resulted in titanium as the preferred choice in the spare-no-cost world of competition.
One reason why "billet aluminum" is popular for after market automotive parts is that there was mountains of it available in the form of aircraft production remnents in Southern California in the early boom years of hot-rodding. It was also easy to machine and provide with colorful anodizing. What we have here is an economic incentive become tradtion. Here is the only reference to "billet" in this piece.
Hot-rod magazines are rife with know-it-all writers of shallow experience blathering to an uncritical readership about how adding this pile of (expensive) parts makes 16 (or 162) more HP when no before and after instrumented test data is offered.
The assumption is their readership is ignorant. The tragedy is the assumption is frequently correct; there is a sucker born every minute.
I watched as an acquaintance of mine poured tens of thousands of dollars in a racing engine over a period of three years working from magazine ads claims ignoring cautionary tales from the knowledgable (not me, I didn't know him well enough to trash his dreams).
When he was done the drag racing rules had evolved and most of his work wasted so far as the competitive advantages he'd built into his '69 Pontiac GTO: the racing world went and moved the goal post.
To add insult to injury, he trailered his car to a famous local competition shop for a dyno tune-up. He assumed from the magazines he read he'd get over 500 HP from his 389. In fact he got less than 400 in spite of the tune-up shop's best efforts. It was porting and pistons, they didn't work together.
All that time and money and he didn't even have a worthy street rod. His world was crushed. He not only invested a lot of money but his expectations of glory and all for nought. It seems silly to put it this way but its true: he grieved for more than a year. His wife had a hard four years thanks to this debacle but she persevered and their family came out of this obsession intact.
The fool-and-his-money market seems to be fading from the performance parts scene I'm glad to say, but it's not gone completely.
While it's a great pleasure to me to work on fine mechanisms and assemble well designed and fitted parts I think there should be some benefit attached to the work. After-market kits and modifications have become much more competitive these days and the manufacturers no longer have an eager uncritical customer base. They're forced to provide some support for their assertions (least their competition leap into the breach) thus the assertions have become more moderate and less comprehensive.
I love the expressions: "Show me", "Why", and the expression on the saleman's face when you confound him by offering a simple uncontrovertable refutation.
My point is to love the pretty go-fast stuff (I do) but remain skeptical.
[This message has been edited by Forrest Addy (edited 02-11-2003).]
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