Physics of Failure
This chapter considers materials integrity in technical applications and analyzes loads and environmental influences leading eventually to materials deterioration and may cause defects, faults, and failures of structures, systems, and components.
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Physics of Failure Horst Czichos
This chapter considers materials integrity in technical applications and analyses loads and environmental influences leading eventually to materials deterioration and may cause defects, faults and failures of structures, systems and components.
3.1
Overview
The discussion on the objects of technical diagnostics in the previous chapter has shown that engineered materials in technical applications are subject to loads and environmental influences (see Fig. 2.3), which can be broadly classified into basic physical categories as – – – – –
mechanical thermal electromagnetic environmental tribological
occurring as all physical processes in space (point, line, surface/interface, volume effects in materials) and time (static, dynamic, stochastic phenomena). Whereas Fig. 3.1 gives a simplified overall compilation of potential failure mechanisms, the occurrence of actual failures depends on the function and structure of the technical system under consideration and must be individually determined and assessed by the methods and techniques for diagnostics and monitoring (see Part B of the handbook). In the following, a brief overview of physics of failure is given organized in terms of the general physical categories of Fig. 3.1 and based on the characterization of materials properties and performance in the Springer Handbook of Metrology and Testing [1].
action of potentials, fields, forces attack of radiation, chemicals, organisms, fluids, particles, solids
Figure 3.1 illustrates that—initiated by the interacting loads and environmental influences—various failure mechanisms are possible,
3.2
Mechanical Loads and Related Failure Mechanisms
The response of a material to an external mechanical loading characterizes its mechanical properties. The single mechanical loading modes (which often interact in practice) are categorized as tension, compression, bending, shear, and torsion, see Fig. 3.2.
H. Czichos (&) Beuth Hochschule für Technik, Luxemburger Straße 20a, 13353 Berlin, Germany e-mail: [email protected] H. Czichos (ed.), Handbook of Technical Diagnostics, DOI: 10.1007/978-3-642-25850-3_3, Springer-Verlag Berlin Heidelberg 2013
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H. Czichos
Fig. 3.1 Overview of physics of failure
3.2.1
Deformation, Elasticity, Strength
As illustrated schematically in the upper right part of Fig. 3.2 for quasi-static tensile loading, stress r = F/A0 gives the intensity of a mechanical force F that passes through the materials crosssectional area A0. Strain e = Dl/l0 gives the relative displacement of points within the material. Stress–strain curves depend basically on materials composition and microstructure and are influenced by the loading manner, strain rate, temperature, and chemical environment. They show typically three different regimes: • First, when the applied load is small, deformation is reversible, that is, elastic deformation occurs. Stresses are proportional to elastic strains (Hooke’s law: r = E 9 e). The slope between tensile stress and tensile elastic strain
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