Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.
Are the test result figures ratioed to a fixed standard? (eg. the plate type has a cross sectional area of .282"squared, whereas the sheet type has a cross section test area of .375" squared. If the specimens can be of different sizes, then they must give different test results (a toothpick breaks faster than a log). Are these different figures multiplied by there relation to a larger fixed standard, like a square inch?
From what I can gather about it via wikipedia, tensile testing is simple pulling on two ends of a test specimen to find it's plastic yield point and its ultimate break strength. What I don't understand is the variation of the test specimens and how it relates to the single figure listed as the material standard.
I'm guessing a .282"sq. bit of A36 won't hold up to 36,000 pounds of weight.
Tensile strength is measured in psi. Pounds per Square Inch. A one inch by one inch square bar of A36 will be able to withstand approximately 36000 pounds hanging from it. There are also measurements of elastic tensile strength, and yield strength which come into play before ultimate tensile strength. Elastic properties are usually more important than ultimate properties for most of what we do. Staying inside the limit of where metals will return to their original positions and shape is more important than their ultimate strength.
When I was in welding school we prepared specimens for a tensile strength test. The specimens were machined down to 1/4" x 1/4" before testing. It's a lot easier to pull apart a small bar than a large one! Onle took ~2250# of pull to break A36!
Oh my, this caused me to drag out my copy of "The Testing and Inspection of Engineering Materials" by Davis Troxell and Wiskocil, McGraw-Hill Books Co. I haven't opened it since the final exam in mumble mumble.
In the chapter on requirements for tension test specimens it describes 7 different specimen for different materials.
The standard for round materials is round .505 +/- .01 with a 2 +/-.005in gage length (denoted by marks so that the elongation can be measured during testing). The .505 dia gives an even .200 sq in cross section.
The standard for plate, sheet etc. for thicknesses between .01 and .5" has a width of .50 +/- .01 and a 2 +/-.005in gage length (denoted by marks)
The standard for plate, sheet etc. for thicknesses over 3/16" has a width of 1.50 +1/8, -1/4" and a 8 +/-.010in gage length (denoted by marks)
The standard for cast iron is round similar to the round material standard except for dimensions.
There is a standard for wood, concrete and insulating materials.
So the direct answer to your question is, yes, there are standards for tensile (and compression) specimen. And there are standards for the speed at which the tensile test machine is to be operated so all the testing is able to be reproduced. And there are standards for the specimen grippers. etc
All these are described in nauseating detail in ASTM E8 if anyone has insomnia.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
redneckalbertan wrote:Tensile strength is measured in psi. Pounds per Square Inch. A one inch by one inch square bar of A36 will be able to withstand approximately 36000 pounds hanging from it.
Thank you very much, just what I needed. I was going to ask a follow up about the speed of the force applied to the ends, but you covered that before I even mentioned it! (let gravity do the work)
