The Importance of Determining Metal Strength and the Use of Metallographic Microscopes
How important is metal strength? Imagine how your life would depend on the steel and metal bars that hold up your condominium unit or how strong those sheets of metals that make up a plane should be when you’re traveling at high speeds thousands of miles in the sky. Imagine also how strong the metals on the bridge or overpass you have to use everyday should be to hold you up and thousands of other drivers like you as you drive to and from work. Those, and for a million other different reasons, metal strength is important.
In terms of metal manufacturing, metal strength is just one of the qualities of production that is studied and ensured. However, it is by no means less important, considering that a lot of things depend on how strong the metal should be in order to ensure the safety and well being of its end users: us.
How is metal made stronger?
Metal strength is often called tensile strength. This refers to the resistance manifested by a certain object (in this case, metal) to the external forces that try to tear it apart or break it. Tensile strength is also a definition of a metal’s maximum limitations in terms of tensile stress, expressed as force per unit of cross sectional area. This is measured as kgs. per sq. cm. or lbs. per sq. inch. Metal or tensile strength is that limit that the material reaches before it gives or ruptures.
Theoretically, what makes a metal strong is the quality of its crystals. The higher the tensile strength that a single crystal can achieve, the stronger the metal. Although in materials engineering, metal strength as exhibited by the material’s single crystal should be the same as the external force needed to pull the metal’s molecules apart, certain impurities in the actual microstructure of metals make it impossible to achieve that kind of pure strength.
That being said, it is just logical that each metal exhibits different tensile strengths, particularly because they have different atomic makeup and certain microstructure characteristics. The manufacturing process used to produce a metal product or alloy also contributes to its strength. The manufacturing process will always affect a metal’s microstructure. That explains in part why different metals with the same thickness and sample size do not necessarily exhibit the same metal strengths when exposed to the same amount of force.
Design and production processes are also factors that determine metal strength. Steel alloys formed into fine wires, for example, may not exhibit much strength but given the proper heat treatment, they can reach tensile strengths of about 250,000 lbs. per sq. in. Suspension bridge cables are not made up of several solid metal rods but of thousands of small wires with very high metal strength. So high, in fact, that they even surpass those of solid rods.
Certain factors also come into play, affecting metal strength. The shape of the metal, for example, will determine whether it can withstand a force or not. A flat sheet of metal will be less capable of holding up a weight than a folded or corrugated piece.
Corrosion can also affect metal strength. Metals that have been oxygenated or exposed to the elements are likely to be stressed, making them easier to bend or pull apart. Fatigue and regular wear and tear on a particular area will also reduce the material’s strength. Temperature is also a factor – extremely high and extremely low can change a metal’s strength limit.
And finally, there is also such thing as manufacturing flaw, which often renders the metal sub-par and weak. A mistake in the choice and amount of metals used in production, for example, can result to a less than ideal product. Certain errors in the production process can also contribute significantly.
Testing for tensile strength
In materials science, many sophisticated machines are used to test materials. These often require minimal human effort or calculation since these equipment are programmed to function and compute required figures automatically. However, in certain areas where the determination of a material’s metal strength is necessary, there is no replacing the human eye and an expert’s opinion.
To check for minute evidence of metal fatigue, for example, a metallographic microscope may be used. Fatigue will usually show up on the surface of the metal and to the trained eye of the observer, these weakened areas are easy to spot. A visual examination of metal can also supplement metal strength tests since components of a metal sample may be viewed and different metals and alloys used in the production may be identified. Using the metal etching process, certain microstructural characteristics such as inclusions, grain size, grain structure, porosity and even evidence of microshrinkage may be seen.
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