Abstract

Miroslav Šilhavý was an outstanding scholar of exceptional depth and clarity, a thinker who persistently sought to reconcile the abstract structures of mathematical analysis with the physical principles governing material behavior. He viewed continuum mechanics not merely as a modeling discipline but as a domain requiring the highest standards of mathematical precision.
His research interests were broad. He defined himself as “a researcher in mathematical methods in continuum mechanics and thermodynamics.” Although his work was primarily foundational in nature, it also encompassed significant applications. The principal mathematical tools he used included the calculus of variations, functional analysis, partial differential equations, convex analysis, geometric measure theory, and matrix theory. His specific areas of interest included plasticity, thermodynamics, the theory of masonry-like bodies, stresses represented by measures, phase transitions in solids, and fractional models in elasticity.
He studied physics at Univerzita Karlova (Charles University) in Prague, graduating in 1973. In 1978, he obtained his PhD (CSc.) from the Czechoslovak Academy of Sciences. He was awarded the Doctor of Science degree in 1991. He spent the major part of his professional career at the Institute of Mathematics of the Czechoslovak Academy of Sciences, later the Czech Academy of Sciences, in Prague. His work was deeply influenced, on one hand, by the classical tradition of rational mechanics associated with Clifford Truesdell and Walter Noll and, on the other hand, by the theory of partial differential equations, particularly through his collaboration with Jindřich Nečas. Together with his PhD advisor, Jan Kratochvíl, he played a key role in promoting and developing rational mechanics in Czechoslovakia and, subsequently, in the Czech Republic.
Over the years, Šilhavý established himself as a leading figure in the continuum mechanics community. He visited the main centers of continuum mechanics worldwide; in particular, he spent 3 years as a visiting professor at the Department of Mathematics of the University of Pisa.
A cornerstone of Šilhavý’s legacy is his monograph The Mechanics and Thermodynamics of Continuous Media, published by Springer in 1997 [31]. This work synthesizes a vast body of knowledge into a coherent framework, presenting the subject with a level of precision that has made it a lasting reference for researchers.
The passing of Miroslav Šilhavý marks a profound loss for the physical and mathematical community. We have lost a gentleman of quiet authority and great personal dignity.
We highlight a few topics in mathematical materials science where Šilhavý’s work has made significant contributions.
1. Interfacial semiconvexities
One of the enduring insights of modern elasticity theory is that the intricate patterns observed in materials are not accidental: they reflect underlying principles of energy minimization and stability. Few researchers have contributed as deeply to this perspective as Miroslav Šilhavý, whose work shaped the mathematical understanding of complex materials, in particular those undergoing phase transformations.
A prominent example is provided by shape memory alloys, materials capable of recovering their original shape after deformation through temperature changes. Such alloys, including Ni–Ti and Cu–Al–Ni, have attracted considerable attention both for their technological importance and for the richness of the mathematical structures they exhibit. Their behavior is governed by the coexistence of two principal phases: a highly symmetric high-temperature phase, known as austenite, and a low-temperature phase, martensite, which appears in multiple symmetry-related variants.
It is precisely the interaction between these variants that gives rise to the remarkable and often intricate microstructures observed in experiments. Explaining these patterns requires a delicate balance between physical modeling and mathematical analysis, a balance that Šilhavý’s work helped to establish in an original way. Namely, the stored energy density of a shape memory alloy is typically non-convex, and, in fact, it is not even rank-one convex; therefore, one cannot expect the lower semicontinuity of the energy integral functional in the weak topology of the underlying function space, usually a reflexive Sobolev space. Multiple minima of the energy density force any minimizing sequence of gradients to oscillate between them, and, indeed, no minimizer does exist. The usual approach to overcome this issue is to add a convex term depending on higher-order deformation gradients to the stored energy density which makes the energy functional weakly lower semicontinuous or to resort to measure-valued solutions, using Young measures, for instance. The main disadvantage of the latter approach is that it does not allow us to control the orientation preservation of admissible deformations. The higher-order gradients, on the contrary, are complicated for numerical implementation.
Šilhavý, in analogy with the bulk polyconvexity of stored energies introduced by J.M. Ball, defined the notion of interfacial polyconvexity [66,67]. The state of the material with the reference configuration
Here, the bulk energy
The phase distribution is encoded by a function
reflecting that exactly one phase is present at almost every point. Here,
1.1. Bulk and interfacial polyconvexity
Within each phase, the material is modeled as hyperelastic. The bulk energy takes the form
A key structural assumption is that each stored energy density is polyconvex, i.e.,
with
While the bulk energy governs behavior within phases, it is the interfacial energy that determines how different phases arrange themselves. Interfaces carry energy due to the incompatibility of neighboring variants, and their structure is strongly influenced by the deformation. Šilhavý introduced a remarkably elegant formulation of interfacial polyconvex energies, in which the density between phases i and j depends on the unit normal vector to the interface and on the interface deformation gradient
with
where
The arguments of
One of the conceptual strengths of this theory is its ability to handle highly irregular interfaces. Clearly, in typical situations, where
Note that
A central theme in Šilhavý’s work on interfacial polyconvexity is the extension of classical variational concepts to the interfacial setting. In particular, the notion of interface quasiconvexity defined for
see [69]. Here,
2. Thermodynamics
Miroslav Šilhavý has been very active in the foundations of thermodynamics. His view on this discipline has been profoundly influenced by the work of J. W. Gibbs. We report here the second paragraph in the preface of his celebrated 1997 text The Mechanics and Thermodynamics of Continuous Media [31]:
At present, the major challenge to the nonlinear thermoelasticity is posed by phase transformations with changes in symmetry. J. W. Gibbs’ immensely influential treatise On the Equilibrium of Heterogeneous Substances has provided a highly successful theory of phase transitions in fluids. Gibbs brought the view that the thermodynamics is not only the theory of heat but also a theory of equilibrium, with the main tool being the minimum principles. A large portion of the book is an extension of Gibbs’ ideas to bodies of general symmetry by the methods of the calculus of variations. The interplay between the convexity properties of the stored energy functions, the resulting equations, and the physics of the phenomena is a leading theme.
2.1. From efficiency to entropy
Šilhavý, together with W. A. Day, demonstrated [1,3] that it is possible to reverse the assertion that the efficiency of a cycle for a thermoelastic body is a result of the postulation of the existence of entropy, i.e., the expression of the efficiency implies the existence of entropy. The set of the states of a thermomechanical system is an open and arc-wise connected subset U of a real Banach space
for every state
Day and Šilhavý [1] showed that the two propositions below imply each other.
where
The perspective offered by the theorem of Day and Šilhavý is appealing not only from the point of view of mathematical rigor, which was emphasized by the authors, but also for the foundations of physics and engineering.
2.2. Mathematical formalization of thermodynamics
In a series of papers [8,9,12], Šilhavý introduced the heat distribution measure associated with a thermodynamical process. Let
Then, he defined the net gain of heat of the body
where m is the mass measure (normally defined as the standard volume measure, rescaled by the mass density ϱ), […] convert the vague verbal statements of the second law of Carnot, Clausius, Kelvin, and Planck into meaningful mathematical conditions.
In a double-paper [10,11], Šilhavý then developed a general axiomatic treatment of the Second Law of Thermodynamics for general, non-equilibrium processes that need not obey the First Law. First, he proved an abstract theorem providing the inequalities for systems of this type. Then, he showed that these inequalities reduce to generalizations of the Clausius inequality for systems that do obey the First Law.
3. No-tension materials
The no-tension model characterizes a material that responds linearly elastically under compression while being unable to carry tensile stresses. More precisely, the stress tensor
where ℂ denotes the elasticity tensor, and
Šilhavý’s work, often in collaboration with Massimiliano Lucchesi, Cristina Padovani, and Nicola Zani, has provided major contributions to the mathematical analysis of equilibrium problems in masonry structures. A key innovation has been the introduction of tensor-valued measures whose distributional divergence is a vector-valued measure, allowing for the description of stress concentrations on lower-dimensional sets (such as surfaces and curves).
More precisely, in Lucchesi et al. [52], a tensor-valued measure
for all smooth functions
A tensor-valued measure
for all smooth functions
Within this framework, in Lucchesi et al. [52], several examples of two-dimensional panels under different loads have been analyzed, with explicit determination of the singular stress lines.
In Lucchesi et al. [58], a formulation encoding the no-tension constraint of masonry is proposed, and the notions of weak compatibility (loads equilibrated by measure-valued stresses) and strong compatibility (loads equilibrated by square-integrable stresses) are introduced.
The no-tension constraint is expressed by requiring that a tensor-valued measure
Given a region
for every smooth function
A more restrictive notion arises when one considers absolutely continuous measures. Specifically, let the loads and stress be of the form
where
for every smooth test function
The distinction between weak and strong compatibility reflects the regularity of the stress field: in the weak case, stresses may concentrate on lower-dimensional sets (e.g., along cracks or interfaces), while in the strong case, they are genuinely distributed over the bulk, see [63].
The importance of strong compatibility is clarified by the associated variational formulation. Defining the total energy functional
one finds that the loads
Weak compatibility is generally easier to establish, since admissible stresses may be measure-valued and concentrate on lower-dimensional sets. A key contribution of Šilhavý and collaborators is to provide conditions under which weak compatibility implies strong compatibility, see [58]. These conditions typically involve geometric properties of the domain and integrability assumptions on the loads, ensuring that measure-valued equilibrating stresses do not exhibit singular concentrations.
Footnotes
Acknowledgements
We thank M. Lucchesi for providing us with the CV and the list of publications of M. Šilhavý.
