Abstract
Shear localisation in thin bands is an important process involved in the plastic deformation of materials subject to stress. This process is often sensitive to the sample microstructure (amorphous/crystalline). Here we show using the scanning µ-SAXS technique, how these different microstructures influence the plastic deformations in a drying colloidal film. In crystalline samples, the presence of an ordering transition at the compaction front was directly identified through the development of a six-fold symmetry in the scattering pattern in 20 wt% samples. It is shown that plastic deformations in individual groups of particles during the compaction process can be tracked and measured in real time. Higher concentration suspensions were found to result in amorphous structures. The transition between crystalline and amorphous microstructures with initial particle concentration was also found to correlate with the appearance of shear bands. Through 2D spatial mapping of the local film structure, the presence of shear bands in the films was directly related to the microscale spatial variations in strain magnitude and compression direction. Our measurements also showed that shear bands lead to a reduction in the local particle volume fraction ~1–2%, indicating significant dilatancy.
Highlights
Relating the plastic response of materials under an applied stress to their microstructure is a problem of fundamental importance in a range of areas of materials science including granular[1], complex fluids[2] and metal alloys/glasses[3,4]
It was shown that a drying colloidal film can exhibit shear bands[5,6,7]
In this study we have shown how the μ-Small Angle X-ray Scattering (SAXS) mode at the European Synchrotron and Radiation Facility (ESRF) beamline can be used to study the spatially varying dynamics of a drying colloidal film
Summary
Received: 5 April 2018 Accepted: 14 August 2018 Published: xx xx xxxx film studied with scanning μ-SAXS. Films of drying colloidal suspension have been widely studied using Small Angle X-ray Scattering (SAXS)[7,13,14,15,16] Using this technique changes in the mean volume fraction[13] and strain[7] as the drying front moves can be inferred by collecting SAXS patterns from the relatively small region exposed to the incident beam. We were able to measure key quantities such as the local strain, direction of maximum compression and volume fraction simultaneously, and show how these are related to the much larger scale shear banding instability.
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