Failure Analysis and Prevention
SUPRIYA B
Department of Mechanical Engineering
Failure Analysis and Prevention
Categories of Failure
There are many ways to categorize failures and material damage in terms of forms, mechanisms, or
cause. No one system
is necessarily complete and consistent with the multitude of possibilities. However, categories can
help prioritize or
identify avenues of investigation, as long as the categories do not limit critical inquiry.
Categories of Material Stressors
To determine the cause of material failure, one must consider the active stressors. A stressor is an
external influence that
can be a direct or indirect cause of failure. Understanding these influences is important for effective
failure analysis and
determining root cause. Likewise, mitigation of the stressors is often the most logical solution to
reducing susceptibility to
failure. The influence of stressors is heavily dependent on the susceptibility of the component,
performance criteria, the
magnitude of the stressor, exposure, and the material susceptibility.
Failure Analysis and Prevention
The six stressors are:
· Mechanical: Applied static, dynamic or cyclic loads, pressure, impact,
fabrication-induced residual stresses,
applied end movements
· Chemical: Inadvertent acute or chronic exposure to an aggressive chemical
environment, material compatibility
issues
· Electrochemical: A susceptible metal in a corrosive aqueous environment
· Thermal: Exposure to elevated temperatures resulting in materials degradation
· Radiation: Ultraviolet lighting, sunlight, ionizing radiation from nuclear power
plants, and so forth
· Electrical: Applied electrical stress due to the presence of an electric field
Failure Analysis and Prevention
Four Categories of Failures
The physical failure of materials can be placed in one of many categories
depending on the classification system.
The following four categories are a convenient way to descriptively categorize
and discuss failures, with the ultimate goal of understanding causes and
preventing failures
· Distortion or undesired deformation
· Fracture
· Corrosion
· Wear
Failure Analysis and Prevention
Failure Analysis and Prevention
Failure Analysis and Prevention
For any of these failure types, materials performance plays a critical role. Just as the
performance of a component or system is dependent on the behavior of the materials of
construction under the service conditions, the manner in which a component or system
sustains a physical failure is strongly affected by materials performance. For example,
corrosion failures of dissimilar metals in physical contact in an aggressive environment are
associated with the differences in the electrochemical behavior as a result of the chemical
compositions of the two metals. This illustrates that one of the most basic tenets in materials
science and engineering applies to failures: the interaction of the composition, processing,
structure, and properties defines materials performance (Fig. 37), whether satisfactory or
unsatisfactory (Ref 40).
Failure Analysis and Prevention
Failure Analysis and Prevention
Example of distortion in an overloaded valve stem
Failure Analysis and Prevention
Example of a brittle fracture of A36 structural steel,
after sustaining fatigue
cracking initially (at arrows).
Failure Analysis and Prevention
Typical stress-strain diagrams
Failure Analysis and Prevention
Failure Analysis and Prevention
Example of distortion in an overloaded valve stem
Failure Analysis and Prevention
Example of a brittle fracture of A36 structural steel,
after sustaining fatigue
cracking initially (at arrows).
Failure Analysis and Prevention
Typical stress-strain diagrams
Failure Analysis and Prevention
Failure Analysis and Prevention
Example of distortion in an overloaded valve stem
Failure Analysis and Prevention
Example of a brittle fracture of A36 structural steel,
after sustaining fatigue
cracking initially (at arrows).
Failure Analysis and Prevention
Typical stress-strain diagrams
Thank you
SUPRIYA B
Department of Mechanical Engineering
