Søren Fæster

Analysis of bearing steel exposed to rolling contact fatigue

The objective of this work is to characterize fatigue damage in roller bearings under conditions of high load and slippage. A test rig constructed for rolling contact fatigue tests of rings is described, and test results are presented for rings taken from two spherical roller bearings. The preparation of the rings and the loading situation are explained. Test conditions are chosen with the aim of achieving pitting formation at the contacting surfaces. During testing the contact pressure, torque and the rotational speed are monitored and recorded. After testing the tested rings have been characterized using X-ray tomography and scanning electron microscopy. The observations confirm that rolling contact fatigue testing at high loads leads to pitting failure at the contacting surfaces. The pitting mostly appears on one side of the contact, attributed to a nonuniform contact pressure in the axial direction.

Synchrotron measurements of local microstructure and residual strains in ductile cast iron

The local microstructure and distribution of thermally induced residual strains in ferrite matrix grains around an individual spherical graphite nodule in ductile cast iron (DCI) were measured using a synchrotron X-ray micro-diffraction technique. It is found that the matrix grains are deformed, containing dislocations and dislocation boundaries. Each of the residual strain components in the matrix grains exhibits a complex pattern along the circumferential direction of the nodule. Along the radial direction of the nodule, strain gradients from the interface to the grain interior are seen for some strain components, but only in some matrix grains. The observed residual strain patterns have been analysed by finite element modelling, and a comparison between the simulation and experiments is given. The present study of local residual stress by both experimental characterization and simulation provide much needed information for understanding the mechanical properties of DCI, and represent an important contribution for the microstructural design of new DCI materials.

Characterization of voids in shock-loaded Al single crystal by combining X-ray tomography and electron microscopy

A combination of X-ray tomography and electron backscatter diffraction (EBSD) was applied to investigate both the shape of voids and the plastic deformation around voids in an Al single crystal shock-loaded in the <1 2 3> direction. The combination of these two techniques allows the addition of crystallographic information to X-ray tomography and allows the addition of three-dimensional information to EBSD data. It is found that the voids are octahedral with {1 1 1} faces and that regular patterns of lattice reorientation exist around individual voids. The results provide new insights to the process of void growth during shock loading, which is important for both civil and military applications.

36th Risø International Symposium on Materials Science

The theme of the 37th Riso International Symposium is the scientific basis for understanding the performance of composite materials. Specifically, the Symposium focuses on the underlying mechanisms that control the properties of composites, which will lead to better and more reliable model predictions. This will serve to support and further promote the technological development of composite solutions. The present state of composite development was founded by the first scientific studies on composites in the 1960s, establishing fundamental models for fibre reinforcement in composites. Technological challenges have required continued development of more advanced materials models and experimental techniques to study the underlying mechanisms and phenomena for specific composite properties and performance, both the interactions between fibres and matrix, and the more complex loading modes such as fatigue and fracture behaviour. Further work has addressed the development of new fibre and matrix materials, improved composite manufacturing techniques, and recently, recycling routes for composites. The present Symposium Proceedings cover fundamental studies on the properties and performance of a range of fibre composite systems, such as polymer matrix composites, biocomposites, nanocomposites, and hybrid composites. Examples of matters addressed are stress-strain behaviour of fibres, cure kinetics and residual stresses in matrices, chemistry and mechanical evaluation of fibre/matrix interfaces, microstructure and micromechanics of composites, damage evolution and ductility in composites, effects of composite manufacturing, and recycling opportunities. The Proceedings contain 10 invited papers, and 40 contributed papers. The 37th Riso International Symposium is organised by the Section of Composites and Materials Mechanics, Department of Wind Energy, Technical University of Denmark (DTU), at the Riso Campus. We would like to thank all those at DTU Wind Energy who assisted in the preparation of the Symposium. We appreciate additionally the support from the international advisory committee consisting of: E. Greenhalgh, UK; F. Paris, Spain; T. Peijs, UK; K. Pickering, New Zealand; K. Schulte, Germany; R. Talreja, USA; J. Thomason, UK; J. Varna, Sweden. We gratefully acknowledge financial support from the following foundations: Civilingenior Frederik Leth Christiansens Almennyttige Fond, Knud Hojgaards Fond, Otto Monsteds Fond, Danish Center for Applied Mathematics and Mechanics (DCAMM).