Many applied materials like metals and solid – state polymers consist of multiple phases. Their properties depend crucially on the internal phase – structure, i.e. the fraction and local distribution of the phases, their composition and their molecular configuration. Chemical aspects influence the mechanical properties as well as mechanical load couples back to chemistry. This strong interrelation is expressed in the thermodynamic functional of the material which is composed of a thermo – chemical or thermo-solutal part on the one hand and a temperature – dependent mechanical part on the other hand. The mutual interaction between chemistry and mechanics in applied materials is the central goal of the proposed priority program.
Human hair, as a common example for a shape memory polymer, changes its shape by the intake of water, or it keeps its curly state after drying. Also metals, commonly viewed as dead bodies, show strong mechanical response on changes of their constitution. They expand or contract by the formation of new crystallographic phases, or show a macroscopic response by the sheering of crystal lattices. In return, external load or external fields can prevent or enhance phase separation both in metals and polymers. Most applied materials are stabilized far out of equilibrium by an internal balance of chemical and mechanical forces.
The separate focus on either the chemical aspect or the mechanical aspect respectively in different scientific communities, of course, results originally from good scientific practice: theoretical models are developed for cases in which individual phenomena can well be separated. In these cases a clear identification of cause and effect is possible which can be unambiguously formulated in constitutive equations including a consistent parameterization. Dependent on the tradition in the different scientific communities (here we address the communities of ‘computational thermodynamics’, ‘continuum mechanics’ and ‘theory of materials’, as well as ‘polymer sciences’ and ‘metallurgy’, in a broader sense the community of ‘computational materials science’) the individual focus on individual phenomena led to the development of different classes of theoretical descriptions specialized on individual features that are dominating in the applications under consideration. In this priority program we a im to combine these approaches for materials with strong thermo-chemo-mechanical coupling.
Examples of such materials are high – strength steels, where the supersaturated crystal lattice locks plastic relaxation, Ni – base superalloys in which a two phase structure is stabilized by mechanical interaction. Immiscible polymer blends show enhanced stiffness and toughness due to a phase – separation between the components. In filled elastomers and fibre – reinforced polymers the mechanical properties depend on the chemical state of an interfacial layer which changes under external mechanical load. All these materials cannot be understood neglecting the interplay between phase structure and mechanics.
Combining methods of computational thermodynamics and mechanics, developed for metals, with methods for history dependent phase – structures and their mechanical behavior, developed for polymers, on a general theoretical basis will evolve the full power of predictive materials modeling. It will enable scientists to describe structure and property of materials dependent on the process history and external chemo-mechanical load in a comprehensive way. In order to support the development and the validation of new comprehensive models and methods, also experimental investigations and the support from atomistic simulations are needed. This is the starting situation of the priority program:
- It is aimed to demonstrate the superiority and technological potential of coupled thermo-chemical and thermo-mechanical modeling for key metal and polymer materials.
- It is aimed to develop physically based material models with full coupling between chemistry and mechanics, taking into account the process history.
- It is aimed to develop comprehensive computational tools by joining the competence of different communities: materials, thermodynamics, mechanics, metals and polymers.
- It is aimed to integrate experimentalists and developers of simulation software to combine best data with best models and best numerical techniques.
- It is aimed at bringing together the scientific communities from computational thermodynamics, continuum mechanics and materials sciences.
The collaborative research within the new SPP shall establish a new paradigm of physically bases material modeling integrating the influence of process history and external chemo-mechanical load to be applicable to optimize production, properties and life time of applied materials for a sustainable economy.