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Cracking is a Stress Relief Mechanism

Cracking within a component is simply a response to stress.

When a part cracks, regardless of the material, it is an indication that the stress exceeded the strength of the material over a given time period, under specific loading conditions. Cracking is a stress relief mechanism. This is true:

  • Whether the stress is internal or external
  • Whether the stress is static, intermittent, or cyclic
  • Whether the stress is associated with loading in tension, compression, shear, or bending.

Cracking stress relief mechanism

A fractographic examination can help to understand the stress responsible for part failure. Fractography is the examination of the fracture surface and surrounding area on a failed part, typically performed across a range of magnifications using visual and microscopic techniques. The fractographic examination is a key part of a failure analysis. It provides information on the mode of failure, as well as the type, magnitude, form, and directionality of the stresses.

For example, I have worked on a number of failures within cylindrical design features. At the most basic level, fractography can be used to determine if the stress responsible for the failure was axial which results in circumferential or transverse cracking, or hoop which produces longitudinal cracking.

Fractography cylinder cracking directionality

Do not overlook fractography as a powerful step in a failure investigation. With experience, mechanical insight, and materials knowledge, fractography can provide information allowing an understanding of the stress associated with the part failure.

Jeffrey A. Jansen

Jeffrey A. Jansen is the Engineering Manager and a Partner at The Madison Group. He was elected as a Fellow of the Society by the Society of Plastics Engineers. Jeff is a proven plastic professional with more than 30 years of experience solving problems and addressing opportunities related to polymeric materials. He specializes in failure analysis, material identification and selection, as well as compatibility, aging, and lifetime prediction studies for thermoplastic materials. Jeff has performed over 5,000 investigations, both for industrial clients and as a part of litigation. He regularly presents seminars and webinars, covering a wide range of topics related to plastics failure, material performance, testing, and polymer technology. Jeff is a graduate of Carroll College and the Milwaukee School of Engineering.