I never would have imagined that breaking stuff could be a full time job, let alone such an important one. That’s right, the Test Lab personnel at Norfolk Iron & Metal get to break stuff for a living – and not just for fun, there’s so much more to it.
You see, the specifications that are listed on the certifications are created by standards organizations, in conjunction with both producers and users, and have specific chemical and physical requirements for the material. Standards also exist for regulating the measurement and testing practices, as well as agreed upon tolerances for the material. The goal is to give both producers and users a “common language” when dealing with products and a mutual understanding on what expectations exist for the material. This also helps when it comes to engineering design, fabrication, safety, and even in the marketplace for comparison of available materials.
Did you know that when railroads were first established, each railroad company had their own rail design and they weren’t able to ride on each other’s rails? I know it seems crazy, but this is actually what led to the creation of ASTM (American Society for Testing and Materials), and eventually ASTM International, as it is known as today.
Norfolk Iron & Metal actively participates in ASTM certifications, as well as other standards organizations like ASME, AISI, SAE, and CSA – not only to help develop and maintain the standards that we use today, but also to make sure we are accurately testing and certifying the materials we sell to our customers every day. When the Test Lab personnel are breaking things, they are actually performing a wide variety of ASTM regulated tests to verify that our products comply with the specifications listed on the certifications.
Tensile Testing
They perform tensile testing to determine the strength (yield and tensile) and ductility (elongation) of the material.
This test starts with cutting out samples that look a lot like dog bones (but are specially designed to break in a certain area) on one of our water jets – so there is no heat involved that might affect the material properties and the dimensions are accurate. Each end of the “dog bone” is clamped in a machine designed to pull it apart with an extensometer attached to the middle of it. Once the pulling starts, the extensometer will sense when the material has met its yield point – the point at which the material will not go back to its original shape. The extensometer is then removed and the sample is ripped in half when it meets its breaking point – or ultimate tensile strength.
The differences between the dimensions of the samples before and after pulling apart are used to calculate the elongation percentage – or just how flexible the material is. Yield, tensile, and elongation are common metrics that are called out in standards – typically as minimums, but can also have a max limit.
Charpy Testing
The Test Lab can also perform Charpy testing, or Charpy V-Notch (CVN) Impact testing. This is a unique test, again with specially designed specimens, but the samples are usually cooled to below freezing temperatures before having a weighted pendulum swing down and break them in half.
Steel becomes more brittle at colder temperatures – remember the Titanic? The icy waters made the ship’s hull more brittle so when it hit the infamous iceberg, it split wide open, and the rest is history (poor Jack). The point of this test is to determine how much energy the material can absorb before breaking at a specified temperature, and this is a common requirement for materials used in buildings and bridges, oil rigs to be operated in the arctic or out in the oceans, and even in the roll over protection halos that are found on farm equipment nowadays. From this test we can also determine lateral expansion and percent shear on the broken halves, which is helpful in engineering design.
Chemical Composition Verification
They are also able to verify the steel’s chemical composition by the use of an optical emission spectrometer.
Did you know that each element within steel will give off its own light wavelength when ignited? Our spectrometer acts like a mini spot welder to burn the surface of the material in an ultra-high purity argon chamber and then record the different light wavelengths that are produced. It then will convert that back into the elements like carbon, manganese, silicon, nickel, copper, vanadium, etc., and will report the amount of each that exists within the steel. This information is compared to the producing mill’s certification to make sure that everything is in line with the specification.
Brinell Hardness Testing
Brinell hardness testing is also performed in our lab. This is a much simpler (and quicker) test where a tiny sphere is pressed into the material at a specified force and rate.
A smaller indention means a harder (and stronger) material, and a bigger indention means a softer (and weaker) material. There are well known correlations between hardness and ultimate tensile strength, and this is more routine on samples that might be too small to cut a tensile dog bone out of.
We perform tensile testing, hardness testing, and a chemical analysis on all of our strength graded material from coil – like A36, A572grade 50, A656 grade 80, and A656 grade 100. This is all well above and beyond the normal ASTM certifications requirements, but material variability does exist and we want to make sure that everything we provide to our customers meets the specifications that are listed on our certifications.
All of this testing has given us with lots and lots of data, and has enabled us to become better partners with our vendors as well as our customers. We are able to identify trends, collaborate in product development, and can offer unique testing and certification packages as needed. Our standards work has helped lead to more stringent flatness standards for higher strength materials and also to better identify materials in the marketplace. Our experience and knowledge in these areas is something that we are happy to share with our business partners – and if you’re ever in Norfolk, please be sure to swing on by and help us break some stuff!
Written by: Justin Robinson, Director of Product Quality
