Abstract
In this review article we consider the crack growth resistance of micrometer and sub-micrometer sized samples from the fracture mechanics point of view. Standard fracture mechanics test procedures were developed for macro-scale samples, and reduction of the specimen dimensions by three to five orders of magnitude has severe consequences. This concerns the interpretation of results obtained by micro- and nano-mechanics, as well as the life time and failure prediction of micro- and nano-devices. We discuss the relevant fracture mechanics length scales and their relation to the material-specific structural lengths in order to conduct rigorous fracture mechanics experiments. To ensure general validity and applicability of evaluation concepts, these scaling considerations are detailed for ideally brittle, semi-brittle and micro ductile crack propagation, subject to both monotonic and cyclic loading. Special attention is devoted to the requirements for determining specimen size for various loading types to measure material characteristic crack propagation resistance at small scales. Finally, we discuss novel possibilities of micron and sub-micron fracture mechanics tests to improve the basic understanding of specific crack propagation processes.
Highlights
Fracture mechanics was first proposed about 100 years ago
Irwin [2] introduced the terms energy release rate and stress intensity factor. These quantities are used as crack driving forces under small scale yielding conditions, and the regime where the use of these parameters is valid is denoted as linear elastic fracture mechanics (LEFM)
In typical standard fracture mechanics samples, the first dislocations emitted from the crack tip or generated from internal sources near the tip are embedded in the K-dominated zone
Summary
Fracture mechanics was first proposed about 100 years ago. Griffith [1] used an energy analysis to determine the conditions for the propagation of pre-existing cracks in ideally brittle materials. Irwin [2] introduced the terms energy release rate and stress intensity factor These quantities are used as crack driving forces under small scale yielding conditions, and the regime where the use of these parameters is valid is denoted as linear elastic fracture mechanics (LEFM). Wells [5] and Rice [6] developed the parameters crack tip opening displacement (CTOD) and J-integral, respectively, which permit the description of crack propagation for materials or structures that are too ductile for LEFM consideration These serve as loading parameters for elasto-plastic fracture mechanics (EPFM). How can micro-samples contribute to improve the understanding of crack growth processes in general?
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