what are and how does different testings on steels performed? tnx?

Answer 1

The number one test for metals is the tensile test; which is a test run until failure.

A super strong machine is attached to a sample with two clamps and it pulls the clamps apart. The strength, in tons, is measured. When the metal approaches the point of failure it is too stressed, because most metal will stretch and deform (called plastic deformation) just before it fails. So a graph of the strength is made, but graphing the pressure of in the machine. The scientists can tell when the machine spikes and the metal starts to deform and finally fails. The idea is to pick a failure point before that spike. Then include a safety factor to pick a point of a lower pressure.

This way a manufacturer can give the strength, rated in pounds per square inch, of the sample. For example in concrete steel is used because steel rebars give good tensile (pulling) strength, while concrete has poor tensile strength but great strength under compression or pressure. Reinforced concrete is the standard for the construction industry because it makes a very cheap, very strong material that can resist forces in almost every direction.

The Empire State Building was built mostly of steel, but its modern rivals use a concrete core that supports a steel frame work. The concrete covered reinforcing steel is more fireproof and so meets safety codes. This is how the New York World Trade Center buildings were made. The fireproofing over the steel in the World Trade Center failed under the extreme heat of the fire; in fact some of it may have been blown off in the collision. For a few thousand dollars more the depth of the insulation could have been increased and the building may not have failed. However, at the time, the building did meet fire codes and people thought that there was enough fire proofing on the steel. Remember a bomber flew into the Empire State Building and exploded. It did not bring down the building though because the fireproofing was thicker.

You can’t blame the people who built the World Trade Center, they were trying to make it as cheaply as possible as safely as possible, and the building did survive the crash and the resulting explosion. It was the fire that killed the buildings. New York and the World has re-written its fire safety codes to increase the amount of fire-proofing foam included over the steel.

If you get a fire hot enough then even the steel inside the concrete will fail, but usually it is the last to fail. In the case of the World Trade Center the original failure was just too high up. The load had to fall on the lower beams, which were also burning. At one point the load got to be too much and the building suffered total failure. However, that point took long enough so that most of the people below the floors where the airplanes crashed got out in time; despite a public address warning telling them to return to their offices.

The concrete reinforced steel core that I mentioned acted as a chimney so that there was too much heat and smoke for the people on the floors above the plane crash couldn’t escape. This was due to a failure in the drywall, and the fire codes have been changed to address that problem as well. The building that replaces the World Trade Center will be able to withstand the same attack and survive with a possibility for all the people, not killed in the original crash, to escape.

By the way concrete is tested with a slump test. A special cone of a specific height, top radius and bottom radius is filled with wet concrete. The cone is then lifted and the concrete falls. The amount of distance of this fall is the slump. Stiffer concrete has a smaller slump distance and so is used for things like road bridges. The number and type of additives that can increase the curing time and the strength of the concrete that can be added are limited by the designer’s limit on the slump test. This is specified in the original contract drawings and technical specifications which are used to prepare the bid for the job.

In other industries, like the automobile industry various metals are added to the steel to make is stronger, but usually the stronger the more brittle. So a compromise must be made between how much of an element like magnesium or titanium is added to the steel. Modern engine blocks are made of aluminum, unlike the old V-8 steel block engine invented by Ford and used up until the 1980s. Japanese companies pioneered the use of aluminum engine blocks to improve performance by decreasing weight. In the case of an engine block it has to hold moving parts, exploding parts, hot temperatures, all while operating very fast and under tough conditions. The tensile strength of the engine block is tested the same way that I described above. The compression strength is tested by simply putting a series of huge concrete blocks on the sample until it bends. Many tensile machines can be reversed to test compression as well. Then the sample has to be tested under heat in an oven, the mix of the steel or aluminum used has to face this test, and it too is tested to the point of destruction. Only then can the engineers calculate a safety factor to make sure that even in an engine fire the engine block won’t melt.

One problem with new cars is that a piston can be blown; it literally explodes out of the engine block blowing the top manifold off. In new engines this can happen when the piston rings are too stiff, the piston holes aren’t worn enough or other resistance is still present. If the engine is blueprinted then the specifications are increased from 0.001” to a tolerance of 0.0001” so the performance is enhanced, but the cost is increased since it has to be machined to exacting specifications.

The United Testing Laboratories (UTL) is a government agency that makes a lot of tests for safety standards in the US they test for every thing from the amount of lead in paint to the strength of a metal chain, to the amount of electricity that a wire can safely conduct. Most industries do their own testing, like Mattel Corporation in the recent lead case. The US government set the standards at the UTL, or other agencies, but they require the industries themselves to meet the standards and perform the tests. So each company that uses steel either tests it themselves, or they have a supplier that does the tests for them and guarantees to provide the material at the required strength. The various industries that use the products are responsible for testing to make sure it meets government standards. In the case of Mattel they are responsible for the requirement to meet standards so they conduct random tests to insure it happens. The Chinese company that made the toy has the same responsibilities, because their contract lists the maximum amount of lead that can be in their paint. So those companies have to do the tests as well. The company that supplies or makes the paint has to test it as well. In China the paint is probably custom mixed in the factory so the testing failure falls into their laps. This is probably why one Chinese CEO of one of these companies committed suicide. He didn’t do the testing himself, but as CEO it was his job to make sure the testing was done by his engineers. A failure like this is hard to make and goes through several steps where it could have been caught. That is why it is so major of a problem.

In the engineering and construction trade the steel is rated and so the manufacturer guarantees the strength. Concrete is mixed in the truck and on site so the testing is done by an engineer on site. A car company that uses steel will either test the material themselves (like their engine blocks) or they will require the manufacturer to do the tests like the suppliers of their windshield wipers.

Answer 2

The minimum properties reported are tensile strength, yield strength and % elongation. Tensile is reported in pounds per square inches required to break a measured sample into 2 pieces. Yield strength is also reported in PSI as the point when the sample begins to distort or stretch. % elongation is how much it stretches before it breaks.
An example of how these values are used would be how much weight would a piece of steel support without bending or breaking.
Mild steel such as grade A-36 which is the specification for structural steel such as beams, angles and channels has a minimum yield strength of 36000 pounds per sqare inch. The tensile strength is reported for informational purposes for the most part because it is the yield strength that is used for the minimum design requirement.
High strength steel such as A-514 has a minimum yield strength of 100,000 PSI and is used for heavy equipment such as back hoes, graders, truck frames, etc.
The actual testing is done by making a sample of the steel that looks like a dumb bell, larger on the ends than the middle. It is then put in a machine that grabs the ends and pulls to failure(tensile) and records the other values during the test.