JENNIFER RASBERRY, Business Manager/QC Manager, Metallurgical & Materials Technologies Inc.
Working at an engineering firm that determines why things break (in layman's terms), I hear the term "material specifications" often. Typically, I hear these words when we are requesting background information from a client. In order to determine why a product or system failed, we often need to understand the design of the end-product and the material properties specified. Unfortunately, incomplete material specifications typically cause big product failures.
Material specifications can be valuable and truly mitigate risk and reduce liability.
What is a material specification? Material specifications are a set of documents that identify the properties of a material. Think of material specifications as a recipe for materials. Material specifications often denote the chemical and mechanical properties of the material. As consumers, we are excited to see this document because it portrays quality control and, in turn, mitigated risk (consumer view) and reduced liability (merchant view). However, are these defined characteristics valuable enough to truly mitigate risk and reduce liability?
When determining the material specifications needed for a product, consider four questions about the product that the material will be used for:
What is the purpose of the product? Knowing the product, whether it is a screw for attaching a curtain rod or a rivet for attaching an airplane wing, helps determine the properties of the material needed and the criticality of the material specifications. The use of the product helps to determine the loads applied to the material, the residing environment of the material and the processes that the material will be exposed to in order to produce the product.
Which processes are the material exposed to in order to produce the product? Depending on your product, your material may be exposed to multiple processes such as machining, welding and other manufacturing processes. Each of these will have an effect on the microstructure of the material.
Microstructure plays an important role in materials since it can dictate the physical properties of the material. Something as simple as temperature and the length of time that the material is exposed to the temperature can change the physical properties.
When metals are welded, the rate at which the metals are heated and cooled has a profound impact on their physical properties. For instance, in steels, the heat causes a change in the microstructure of the metal. Rapid cooling will result in the metal becoming hard and brittle. Increasing the time it takes to cool the steel will result in a decrease in strength and higher ductility and toughness.
Will the product have any loads applied? Returning to the curtain-rod screw example, to determine the necessary tensile strength of the screw, you may only need to consider the magnitude of the weight of the rod and curtain. The load is fixed (not changing) so the properties to be notated are rather simple.
However, the material properties to be considered for the airplane-wing rivet are more complex. The load applied to the rivet is variable, meaning that the load applied to the rivet while the airplane is parked is different than the load applied while the plane is in motion. Due to the variable load, the microstructure has to be defined so that fatigue is considered in the material properties.
What environment will the product reside in? Will your product be used in what is considered a normal environment? Or will the product be exposed to chlorides (chlorine) and sulfides (sulfur)? These elements, among others, have a high frequency rate of inciting corrosion, which may weaken/thin metals to the point of product failure.
Materials are complex. By taking into account the product environment, applied loads to the product and processes that the material will endure prior to defining the material properties needed, material specifications can be valuable and truly mitigate risk and reduce liability.
For more information, visit www. mmtinc.com or call (800) 772-0251.
