Fractography

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Fractography

Definition of terms

The term fractography refers to the visual, macroscopic and microscopic analysis of the fracture surfaces of broken components and parts as well as test specimens. This examination method for defining the causes of fracture (see: fracture formation) is used in particular in the context of damage analyses to evaluate the existing damage mechanism, the temporal damage kinetics and the point of origin of the failure (see also: component failure) [1]. Since failure is very often initiated by mechanical stress or overstress, there is also a close connection between fractography and the occurrence of cracks and fractures.

Depending on the type of stress, mechanically induced cracks or fractures can manifest themselves in all materials as macroscopically visible brittle fractures or fatigue fractures, whereby the terms shear, cleavage and mixed fracture are primarily associated with metallic or ceramic materials. For fractography, therefore, the location of crack initiation and the direction of crack propagation are of great importance, in addition to any possible arrest lines or fracture lines (see: waves and arrest lines).

Makroscopic and microscopic fracture characteristics

Fracture mirrors, which are a typical feature of the fracture origin in glass, arrest lines (see also: Fracture types) and fracture propagation lines are referred to as macroscopic fracture features that can be detected visually with the naked eye or with the aid of magnifying glasses, but are usually characterised using light microscopy. For highly fractured fracture surfaces with complex geometry, as is often observed in metallic materials and reinforced plastics, the use of digital microscopes with automatic depth of field correction is recommended (Fig. 1).

Fig. 1:

VHX 500D 3D digital microscope from Keyence GmbH

In contrast, vibration or vibration stripes, honeycombing, Wallner lines and corrosion pits are concrete examples of microscopic fracture features that can usually only be visualised using scanning electron microscopy and scanning atomic force and confocal microscopy at high magnifications.

Regardless of whether a brittle or ductile violent fracture or a fatigue fracture (see: fatigue), the macroscopic and microscopic fracture patterns depend largely on the type of stress (static or dynamic stress, tensile, compressive, bending or torsional stress), which is why the type and temporal course of the mechanical stress must always be considered in damage analyses. The fractography carried out as part of a damage analysis therefore requires a clear evaluation and documentation of the macroscopic and microscopic fracture characteristics (see: fracture types), taking into account the stress acting on the material, if possible a 3D image of the fracture surface morphology and the measurement of the fracture surface topography, as well as the determination of the fracture initiation point. The procedure for performing damage analysis on metallic and polymeric materials using fractographic characterisation methods is described in VDI Guideline 3822 for different damage patterns and types of stress.

See also

• Fibre-matrix adhesion
• Fracture surface
• Ramps, clods and steps
• Vibration fracture
• Fracture parables
• Waves and arrest lines
• Scanning electron microscopy (SEM)
• In-situ tensile test in ESEM with AE

References

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• VDI-Richtlinie: VDI 3822 (2023-12): Schadensanalyse – Grundlagen und Durchführung einer Schadensanalyse
• Becker, W. T., Shipley, R. J. (Eds.): ASM Handbook: Volume 11: Failure Analysis and Prevention. Bd. 11. 10. Edition ASM International (2002) (ISBN 0-871-70704-7)
• Broichhausen, J.: Analyse und Vermeidung von Schäden in Konstruktion, Fertigung und Betrieb. 1st Edition, Carl Hanser Munich (1985) (ISBN 3-446-13409-3)
• Ehrenstein, G. W.: Kunststoff-Schadensanalyse: Methoden und Verfahren. Carl Hanser Munich (1992) (ISBN 3-446-17329-3; see AMK-Library under D 2)
• Ehrenstein, G. W., Engel, L., Klingele, H., Schaper, H.: Scanning Electron Microscopy of Plastics Failure: Rasterelektronenmikroskopie von Kunststoffschäden. Carl Hanser Munich Vienna (2010) (ISBN 3-446-42242-0; see AMK-Library under D 5)
• Engel, L., Ehrenstein, G. W., Klingele, H., Schaper, H.: Rasterelektronenmikroskopische Untersuchungen von Kunststoffschäden. Carl Hanser Munich Vienna (1978) (ISBN 3-446-12560-4; see AMK-Library under D 8)
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• Mobley, K.: Root Cause Failure Analysis. Butterworth-Heinemann (1999) (ISBN 978-0-7506-7158-3)
• Mills, K. (Eds.): ASM Handbook. Bd. 12: Metals Handbook: Volume 12: Fractography. 9. Edition. ASM International (1987) (ISBN 0-871-70018-2)
• Naumann, F. K.: Das Buch der Schadensfälle: Untersuchen, Beurteilen, Vermeiden. Dr. Riederer-Verlag GmbH (1976)
• Neidel, A.: Handbuch Metallschäden: REM-Atlas und Fallbeispiele zur Ursachenanalyse und Vermeidung. 2nd Edition, Carl Hanser Munich Vienna (2011) (ISBN 978-3-446-42775-4)
• Quinn, G. D.: NIST Recommended Practice Guide: Fractography of Ceramics and Glasses. NIST (2006) Download http://www.nist.gov
• Schmitt-Thomas, K. G.: Integrierte Schadenanalyse: Technikgestaltung und das System des Versagens. Springer (2005) (ISBN 3-540-20551-9)
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• Michler, G. H.: Atlas of Polymer Structures, Morphology, Deformation and Fracture Surfaces. Carl Hanser, Munich Vienna (2016) (ISBN 978-1-56990-557-9; see AMK-Library under F 14)