Research
The use of instabilities to create materials with tunable properties
When excessive load is applied, a structure may become unstable. Beyond the instability threshold rapid and dramatic changes of the structural geometry occur, sometimes leading to new, beautiful and detailed pattern. Traditionally instabilities have been viewed as an inconvenience, with research focusing on how to avoid them. Instead they can be exploited to create new materials with improved and switchable properties. Many technological applications, including acoustics,optics and electronics, require the development of new materials with improved and possibly even tunable properties. This investigation will pave the road to the use of the pattern switch occurring at instability for creating a new class of materials with switchable functionalities. Possible and exciting applications are phononic/photonic crystals with tunable band gaps and materials with tunable negative Poisson’s ratio.
Materials with regular micro-structure
Both Nature and technological applications make extensive use of materials characterized by a regular micro-structure to achieve different properties and attributes. Examples are given by phononic/photonic crystals, sensors, super-hydrophobic surfaces and the surface structure of beetles and fishes. We explore the nonlinear microscopic behavior and failure of such materials.
Rate Dependent Mechanical Performance of Polymeric Materials: Constitutive modeling
The deformation and failure behavior of polymers at high rates of loading are important functions for numerous applications including ballistic and blast protection as well as sports equipment. Polymeric materials possess highly rate sensitive material response which offers different mechanical deformation and failure behavior in different temperature and frequency regimes. This time-dependent mechanical behavior is evidenced by rate-dependent elastic moduli, yield strength, post-yield behavior and failure mechanisms. We focus on the development of constitutive models that capture and predict the observed behavior up to large strains.Mechanics of hysteretic large strain behavior of natural fibers
X-ray diffraction studies have shown that numerous natural fibers have a multidomain
architecture composed of folded modules which are linked together in series
along a macromolecular chain. This microstructure leads to a strong rate and
temperature dependent mechanical behavior and one which exhibits a stretchinduced
softening of the mechanical response due to evolution in the underlying
morphology with imposed stretch. Synthetic copolymers such as thermoplastic
polyurethanes exhibit similar structure and mechanical behavior.
We focus on the development of a constitutive model for the stress-strain behavior
of natural fibers based on the underlying protein network structure and its evolution
with strain.Structural interfaces
Many biological and optimal materials, at multiple scales, consist of what can be idealized as continuous bodies joined by structural interfaces. To introduce into the analysis the microstructure properties, a new model of structural interfaces is developed: a true structure is introduced in the transition zone, joining continuous bodies, with geometrical and material properties directly obtained from those of the interfacial microstructure.
Discrete-fibers model for bridged cracks
Fibers bridging the surfaces of a crack or an elliptical void represent an example of a structural interface and can therefore be analyzed within this framework. For two-dimensional linear elasticity, it is possible to analytically attack and solve the case of an elliptical void, subject to arbitrary uniform stress at infinity, when a generic geometry of fibers (with linear behavior) are bridging the surfaces of the void.