The deterioration of a material by chemical or electro-chemical interaction with its environment. Corrosion can take on many forms depending on the type of material which is corroded, the stresses the material is subjected to in service while corrosion is occurring, and the environment to which the material is exposed. Examples of the various types [...]
A simple formability test in which a strip of metal is bent over a mandrel of specified radius. The bend is then examined for cracks or tears. If present, these cracks or tears indicate a failure if they are greater than a specified length. Bend testing is performed on plate or sheet metal which is [...]
Adhesive wear occurs at the interface between two sliding surfaces. A shaft rotating in a bushing is a good example of two such surfaces. If there is insufficient lubrication between the shaft and the bushing, the resulting friction will cause a buildup of heat. This can lead to elevated temperatures at relatively small localized areas, [...]
A test procedure that determines the tensile strength and tensile properties of a material. To perform this test, a bar is machined from the material to be tested. The bar can be machined from an actual part or component or it can be made from stock that will be used to manufacture a component. Test [...]
Stress corrosion cracking (SCC) results from a combination of tensile stress and corrosion. Initiation of stress corrosion cracks usually begins at a small surface corrosion pit (see pitting corrosion) that is subjected to tensile stress. The tensile stress “stretches” the opposite sides of the pit apart which exposes new material at the bottom of the pit [...]
A Scanning Electron Microscope (SEM) offers several major advantages over the more common and familial optical microscope. (1) The SEM has higher magnification capabilities than an optical microscope (100,000X compared to 1000X for an optical microscope). (2) The SEM can obtain in-focus images of rough samples which have a large variation in vertical height. In [...]
A hardness testing technique in which an indenter is pressed into a test sample by a weight or load. The indenter contacts the surface of the test sample upon the application of a light pre-load, called the minor load. This “sets” the indenter in the sample and determines the starting point of indenter penetration. A [...]
Residual stresses are internal forces contained within a part after the original source of those stresses has been removed. Typical sources of stress include loads applied in deforming operations such as bending, forging or extruding, and temperature gradients such as those encountered in casting and welding. When a metal part is permanently deformed, as in [...]
The microstructure of a material determines its properties. The understanding and modification of microstructure is, in many respects, the foundation of materials analysis and engineering. Like all matter, metals are composed of atoms. These atoms combine in small clusters which are called crystals. Groups of crystals combine to form grains. The size, shape, orientation and [...]
Hydrogen embrittlement fractures occur when a metal absorbs hydrogen from an external source. There are numerous potential sources of hydrogen in both the manufacturing process and service environment. These include moist corrosion, arc welding with damp electrodes, acid pickling or cleaning solutions, and electroplating baths containing hydrochloric acid. In order for a hydrogen embrittlement fracture [...]
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