A mesoscopic materials approach to adhesion (GTF.4901)

Adhesion is the key to modern engineering materials like sandwich and multilayered materials, for composites, but also for coated materials. For useful applications proper adhesion between the materials through their interfaces is crucial. The challenge is to improve the performance and reliability under more and more extreme conditions. The key to tackle this challenge is a micromechanical approach. A series of length scale transitions will provide a quantitative link between the physical mechanics of adhesion and the microscopic bonding properties. Two general classes of interfaces will be considered.

Metal-Inorganic interfaces, especially between metals and ionic-oxide materials. All processes controlled by interface phenomena, such as de-cohesion, seggregation, cavitation and diffusion, occur in the very narrow region where the materials join, and where e.g. properties like elastic moduli, thermal expansion or electric resistivity, differ orders of magnitude from that of the bulk regions. Experimental techniques capable of structural observation at sufficient resolution and preferably during deformation, are required to understand the physical mechanisms in the boundary phenomena. Experimentally the interface energy (free energy per unit area/work of adhesion) has to be determined. How does the core energy and core structure depend on misfit dislocations and bond strength. How does the microstructure evolve as function of mechanical loading and of temperature.

Adhesion in Polymer-Metal components depends macroscopically on geometry and loading conditions (time, temperature), mesoscopically on stress, strain and the associated plastic deformation or microcracking and microscopically on the chemical bonding between the metal (oxide) surface and the functional groups of the polymer. The objective of this project is to develop a procedure to provide a coherent picture of polymer-metal adhesion by means of a micromechanical model spanning all length scales.

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