Characterization of the Deformation Field Near the Crack-Tip after Bending by Small Angle X-ray Scattering

The inhomogeneous deformation field ahead the crack tip of pre-cracked and bended Charpy-V specimens was monitored by scanning with a highly focussed X-ray beam at the Synchrotron Radiation Facility (ESRF). The measured scattering pattern shows two characteristic features:

• streak-like anisotropic scattering with different symmetry
• isotropic scattering.

The streaks are produced by scattering at the grain boundaries. The slope of the Guinier plot of the scattering intensity in the streaks yields an effective scattering thickness of the grain boundary of 1.4 nm. The isotropic scattering intensity can be explained as scattering at the dislocation structure. Its dependence on the scattering vector follows a Porod law with exponents between -3.3 and -2.8. The local distribution of both the integral scattering intensity and the Porod exponent reflect the shape of the plastic zone ahead of the crack tip.
The results demonstrate that small angle X-ray scattering with a scanning microfocussed beam provides a new method to characterize inhomogeneous deformation states with a resolution of few micrometers.