Asssociate Professor C. A. Steeves
Associate Director, Graduate Studies
University of Toronto
Institute for Aerospace Studies
4925 Dufferin St., Toronto, Ontario, Canada M3H 5T6
Email: csteeves (at) utias.utoronto.ca
- Ph.D. – Cambridge University
- B.A.Sc. – University of British Columbia
- B.A. – University of Toronto
The UTIAS Advanced Aerospace Structures Group, led by Prof Craig Steeves, performs research aimed at enhancing aircraft and spacecraft performance by combining complex structural and functional elements in an optimal configuration. Fibre composite materials are key components of this research, because it is possible to exploit the geometric complexity inherent in composites to achieve additional functional capabilities. For example, composites can be structured to be strong, stiff and light, and to have desirable vibrational characteristics. This depends both upon accurate models of the mechanical behaviour of arbitrarily configured composites and upon an ability to choose optimal designs within a very large design space. Modeling and optimal design of complex structured systems are the two interconnected foci of the research group.
Current work is concentrated on complex composite structures and on hybrid nanocrystalline microtrusses. Two specific types of composite structure are under investigation. The first is composite plates with locally variable fibre direction. By varying the fibre direction throughout a structure, it is possible to design additional functional properties into the system, such as novel vibration characteristics, while retaining high strength. Another complex composite structure is the truss-core sandwich, which is a light, stiff beam consisting of two composite face sheets separated by a truss-like composite core. These, because of the geometric complexity of the core truss, enable very precise tailoring of certain properties, such as acoustic transmission behaviour.
Hybrid nanocrystalline microtrusses are fabricated by making polymer truss preforms through a rapid-protoyping process, then coating the preforms with high-performance nanocrystalline metal. This produces a very light, strong structure which can be tailored at four length scales, offering a designer wide latitude for optimisation. Typically these have been configured as truss-like sandwich structures. While microtrusses were the initial focus of this research, the concept of using rapid prototyped polymers coated with nanocrystalline metals is relevant to a very braod range of aerospace structures and components. Further fundamental research is ongoing to determine the behaviour of a variety of hybrid metal-polymer structures.
Other work includes research on lattices, which are truss-like structures consisting of repeating unit cells. By using two or more materials and selecting the correct geometry, lattices can be designed to have additional useful properties. For example, by combining two materials with different coefficients of thermal expansion, a lattice with zero effective thermal expansion can be created. These lattices can be used in thermal protection systems or as stable surfaces of mirrors for space-based telescopes. Additional research on lattice materials is to investigate wave propagation through three-dimensional lattices, with such lattices to be used as vibration isolators for attachments between aircraft engines and wings.
The Multifunctional Structures Lab contains essential experimental equipment to carry out this research. Central is a 100 kN servohydraulic load frame with a variety of loading rigs that enable mechanical tests on a wide range of specimens and materials. The load frame is also equipped with an environmental chamber for high-temperature testing. A lab-scale gas gun complements this equipment for high strain rate testing. Data acquisition is usually through non-contact methods, such as digital image correlation and laser extensometry. Fabrication facilities include a high-precision polymer rapid prototyper and a wet lay-up composites bench. Through a close collaboration with the Department of Materials Science and Engineering, we also have access to a nanocrystalline electrodeposition facility, as well as a state-of-the-art electron microscopy suite, which is equipped with an in situ testing rig for extremely small-scale experiments.
We are always looking for talented and enthusiastic graduate students wanting to join our group. Please e-mail Prof Steeves if you would like more information.
Prof Steeves has both a Bachelor of Arts degree in International Relations from Trinity College, University of Toronto and a Bachelor of Applied Science in Civil Engineering from the University of British Columbia. He received his Doctor of Philosophy in 2002 from the Cambridge University Engineering Department, studying composite mechanics and minimum-weight design of composite structures in Prof Norman Fleck’s Micromechanics Group. Subsequently Prof Steeves joined the Princeton University Department of Mechanical and Aerospace Engineering with Prof Richard Miles on a project examining the use of multifunctional sandwich structures in the context of magnetohydrodynamic power generation on reentering space vehicles. Finally, Prof Steeves worked with Prof Tony Evans at the Materials Department of the University of California, Santa Barbara on topics related to materials and structures enabling airbreathing hypersonic flight before moving to UTIAS in 2009.