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FRACTOGRAHY – A FORENSIC TOOL

Polymers and ceramics are enjoying an increasingly prominent position in engineered products. However, metals are still the most common group of materials used in industrial machinery, consumer goods, and automobiles. It is therefore not surprising that the majority of serious failures of these products involve metal components.

A metal component is said to have failed when: it has undergone excessive deformation, has fractured, or has excessively corroded or worn. In a large percentage of metal failures a component has fractured.

Vital Role

The discipline of fractography plays a vital role in analyzing fractured metal components. Simply put, fractography is the determination of a fracture process based on the topography of a fracture surface.

Fractography can reveal valuable information concerning fracture initiation sites, the mechanism of fracture initiation, mechanisms of crack growth, metallurgical defects, environmental effects, and elapsed time from crack initiation to final failure. Of course, fractography is only one of many steps required for a thorough analysis of a fractured component. Often chemical analysis, hardness testing, tensile testing, metallographic sectioning and examination, and design calculations are also required to allow the failure analyst to draw conclusions concerning the cause of a fracture.

The tools of the fractographer are: the unaided eye, the optical microscope, and the electron microscope. At Walters Consulting Corporation, we carry out macroscopic examinations (magnifications ranging from 1X to 100X) of fracture surfaces with the unaided eye and with our stereo optical microscope with quartz illumination. We carry out microscopic (magnifications ranging from 100X to 10,000 X and higher) examinations on a scanning electron microscope (SEM) with an energy dispersive X-Ray spectrometer (EDX) detector.

Some fracture surface features may only be detectable over limited magnification ranges. Therefore, we analyze fractures at progressive magnifications: first the unaided eye, then the optical microscope, then the scanning electron microscope. Important information can be missed if the full range of magnifications is not used.

Indispensable Tool

Fractographic clues can be used in conjunction with information derived by chemical analysis, hardness testing, tensile testing, metallographic sectioning and examination, and design calculations to allow the failure analyst to determine the cause of the fracture. Fractography is an indispensable tool used by the failure analysts at Walters Consulting Corporation when analyzing fractured metal components to determine the causes of failures and assist in the assessment of liability.

 
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