Polymers

Synthetic polymers can be found in food additives, composite materials, drug packaging, artificial organs and solar cells. Biopolymers, such as DNA, actin, collagen and fibrin, play important roles in the body. Aside from the widely used, technical polymers have been designed or processed with particular properties in mind, irrespective of their chemical composition. Functional polymers, on the other hand, are usually selected based on specific chemical groups rather than physical properties. These tend to be exploited for novel optical and electronic applications, such as gas sensors.

At the ESRF, polymers have been one of the main subjects of research since its early days. Thanks to the ESRF, researchers can now:

• Carry out time-resolved studies to monitor molecular chains and hydrogen bonds in polymers.
• Use of microfocus X-ray beams to characterise nanostructure of fibre-reinforced composites and high performance fibres.
• On axis scanning microdiffraction for skin-core morphologies.
• Measurements of the strains in metal and ceramic phases separately and simultaneously in metal matrix composites using X-ray diffraction.
• Following the internal failure mechanisms of composites using X-ray tomography.
• Determination of the spatial distribution of defects at polymer interfaces. 
• Study of polymer crystallisation at elevated temperatures using nano-calorimeter and nanobeam diffraction.
• Combination of wide-angle X-ray scattering and fluorescence data to assess the position, size and orientation of particles in carbon nanotube fibres.
• Study of the influence of temperature and deformation on the molecular scale to reveal physical mechanisms behind macroscopic phenomena such as thermal expansion.

CASE STUDY

STUDYING CRACK PROPAGATION IN COMPOSITES AT HIGH PRESSURES

Company

University of Manchester and Rolls-Royce

Challenge

Crack propagation in metallic materials is well understood. But aircraft manufacturers are increasingly turning to more complicated composite materials that are lighter, stronger and can operate at higher temperatures. Lower weight reduces fuel consumption, while higher engine operating temperatures allow aeroengines to be more efficient. The challenge is to understand how cracks propagate in such materials.

Sample

Titanium reinforced with silicon carbide fibres. This composite material can operate at higher temperatures than titanium alone, making it a promising candidate for jet engine parts.

Solution

Electron microscopy reveals the surface features of micro-cracks, but synchrotron X-rays penetrate tens of millimetres into a sample where the behaviour of cracks can be very different. On beamline ID15, scientists can use imaging, to see how cracks grow, and diffraction, which tells them about the local stresses that the cracks grow under.

Benefits

The ability to monitor cracks under load at high temperatures allows researchers to evaluate the potential of these materials under realistic conditions. It also helps to make realistic estimates

of the lifetime of existing components and to design safer, more crack-resistant materials for the future.

Better knowledge of crack propagation transfers directly to other industries in which failure is unacceptable, notably the nuclear industry.

Proc. R. Soc. A 468 2722.

Acta Materialia 60 958.

3D crack-tip microscopy shows a crack (purple) growing in a composite material containing silicon carbide fibres.