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Engineering Materials - Physical Material Properties

 

Engineering Materials


Physical Properties

 

General Physical Properties

Density

Density is one of the most fundamental physical properties of any material. It is defined as the ratio of an objects mass to its volume. Because most designs are limited by either size and or weight density is an important consideration in many calculations.

Density is a function of the mass of the atoms making up the materials and the distance between them. Massive, closely packed atoms characterize high density materials such as Tungsten or Neptunium. In contrast light, relatively distant atoms compose low density materials such as Beryllium or Aluminum. Density on a macroscopic level is also a function of the microscopic structure of a material. A relatively dense material may be capable of forming a cellular structure such as a foam which can be nearly as strong and much less dense than the bulk material. Composites including natural constituents such as wood and bone, for example, generally rely on microscopic structure to achieve densities far lower than common monolithic materials.

 

Availability/Manufacturability

Availability and manufacturability requirements are often unseen limiting factors in materials selection. The importance of a material being available is obvious. Materials which are not available cannot be used. The importance of processibility is not always so obvious.

Any other desirable qualities are useless if a material cannot be processed into the shape required to perform its function. Most engineering materials in use today have well known substitutes which would perform better and often at lower cost but processes for forming, cutting, machining, joining, etc. are not available or commercially viable. There is often a period of time after a new material is introduced during which its application is severely limited while processing techniques are developed which facilitate its use.

 

Cost

A materials cost is also generally a limiting factor. While cost is universally recognized and perhaps the easiest of all properties to understand there are specific cost considerations for materials selection. Just as materials and their processing go hand in hand so do material costs and processing costs. Understanding the entire processing sequence is critical to accurately evaluating the true cost of a material.

 

Appearance

Because the appearance of many mechanical components seems fairly trivial it is also easy to overlook its importance in the marketing and commercial success of a product.

 

 




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