Fracture Evaluation - Fractography

All metallic components can crack or fracture due to stresses imposed during manufacture or use.  People usually treat those failures phenomenologically, by examining records of manufacture, transport, installation and use.  

However, records do not necessarily capture or illuminate the actual experience of the device.  The fracture surfaces themselves contain the most direct and most specific information available about the causes and conditions of fracture.  An examination of fracture surfaces can reveal the crack initiation site, the direction of crack propagation, the nature of the offending stresses (overload, fatigue, etc.) the direction of loading, and the presence of stress concentrators, material defects, or manufacturing defects that contributed to fracture.  This information can then be used to interpret the cause of fracture as part of a larger failure analysis. Identifying the type and characteristics of a crack is fundamental to identifying the cause. 

Description of fractographic analysis

Fractography consists of optical and SEM examination of the fracture surface. The analyst must be trained to correlate the features of the fracture with specific modes and causes. Lower magnification examination reveals features of deformation, mechanical damage, and large features of the fracture, such as chevrons and beach marks, that indicate the direction of crack propagation.  These observations provide clues about the nature and orientation of stresses that caused the fracture. Higher magnification examination identifies or verifies the cracking mode as overload, fatigue, stress corrosion cracking, or other mode. It also reveals the crack initiation site(s) and material defects or pre-existing features that contributed to fracture.  

Deliverables

Elmet documents fractographic evaluations with overview photographs of the device and the cracked component, and with high magnification photographs of the crack surface.  We interpret the observations for the customer and provide statements of what those observations mean.  We interpret direct observations such as the crack morphology to determine the mode of cracking, the initiation site, and propagation directions, and we infer the stresses and conditions of manufacture or use that caused cracking whenever this is possible. All photographs, SEM images, EDS analyses, and an interpretation of the examination are presented in a written report.  

What to do next

Please email or call us.  We always seek information about the conditions of use to provide context for our evaluation.  If you email us, a photograph of the item is always helpful.