Microstructure and lengthscale effects on fracture

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Predicting fracture of materials is a long-standing problem affecting manufacturing and transportation industries, and limiting the development of new fracture tolerant materials. The reasons come from difficulties in experimentally observing failure of materials and from the many microstructural parameters involved in the fracture process. The overall goal of this proposal is to understand the relation between microstructure and fracture properties, in order to design materials with improved fracture resistance. The novelty of the present approach lies in the originality of the experimental techniques and in the precise coupling between experiments and modeling. Fracture generally takes place by the nucleation, growth and linkage of voids or cracks in a material. Using commercial materials to study fracture is difficult due to the large amount of parameters affecting it. In order to decouple these parameters, we have developed a simplified material (or model material) where the fracture process is controlled. It consists of metallic sheets in which voids are artificially introduced using a pulsed laser. The artificial voids mimic voids in commercial materials but in a simplified and controlled fashion. Such control over size and location of the voids provided by the laser drilling technique has never been achieved before and offers many opportunities to better understand fracture. Texture, twinning and lengthscale effects will be investigated in Ti, Mg and Cu samples. Growth and linkage of laser drilled hole in these samples will be monitored during in-situ tensile tests in 2D in a scanning electron microscope and in 3D in an x-ray computed tomography set-up. The outcome of this research program will contribute to our fundamental understanding of texture, twinning and lengthscale effects on fracture. On a more practical level, the knowledge expected from this research program would have a direct impact on the design of damage resistant materials in engineering fields where fracture is an issue such as transportation, manufacturing and nuclear industries.