engineering&research

The treated reseach topics belong to various fields, which differ greatly from one another.
The scientific research is principally (but not exclusively) related to the numerical aspects of the Solid
Mechanics, and it is finalized to practical engineering applications.

#### Constitutive modeling of geomaterials

Geomaterials are a wide class of materials, usually identified as brittle, or quasi brittle. For example, rocks, soils, concrete and masonries are geomaterials. Also advanced materials, such as ceramics, belong to this class.

The objective of this research is the development of constitutive models for this class of materials, under the classical Theory of Plasticity.

Such constitutive models may be applied in nonlinear Finite Element analysis of advanced engineering problems, as geotechnical applications or simulations of the mechanical behavior of old masonries.

From a numerical point of view, the constitutive modeling of these materials is particularly critical, due to the difficulties to achieve convergence in Finite Element analyses of boundary value problems. For this reason, differently from the typical literature approaches, the numerical efficiency and the stability of the integration algorithm is a key point in order to assure the applicability of the developed models to a wide class of practical engineering problems.

#### Gradient plasticity of metals

The main goal of this research project is the development of constitutive models that allows one to take into account the nonlocal effects (gradient effects) of the mechanical response of polycrystalline metallic materials subjected to plastic deformation.

The plastic response of metals, at the micron scale, is influenced by the grain boundaries, that constraint the dislocations flow.

At this scale, the mechanical properties of a metallic specimen, subject for example to bending or torsion, strongly depend on the specimen size, and they are quite different with respect to those observed at the macroscopic scale.

In particular, diminishing the specimen size, one observes an improvement of the mechanical properties (strengthening and variation of strain hardening) The classical Plasticity Theory cannot take into account such phenomena, since it is not explicitly referred on any intrinsic material scale.

Other models have been proposed in the literature, called ?Gradient Plasticity models?. They are based on nonlinear partial differential equations in which the spatial gradient of the plastic strains explicitly appears.

The numerical integration of such differential equations using the Finite Element Method is particularly complex, due to their strong nonlinearity.

The research topic is then based both on the development of this class of constitutive models, and on the numerical techniques allowing their integration for the simulation of engineering boundary value problems.

#### Constitutive modeling of composite materials

The main objective of this research is the development of constitutive models for composite materials, in particular for syntactic foams. They are particulate composites in which a thermoset polymer matrix, usually made of vinyl ester or epoxy resin is filled with of hollow spheres, also called balloons. They are usually made by glass, ceramic, or metal. These composites find applications in aerospace and marine systems for their closed-cell microstructure.

The mechanical behavior of the syntactic foams is reproduced by means of numerical homogenization techniques, based on Finite Element micromechanical simulations of a representative volume (RVE) of composite material.

To perform these analyses, it is fundamental the modeling of the mechanical behavior both of polymeric materials constituting the matrix, and of the failure of the fillers, typically of brittle type.

#### Constitutive modeling of metals subject to large deformations

The goal of this scientific research is the development of constitutive models for metals subject to large deformations, which allow the simulation of metal forming processes using the Finite Element method. The objective of these simulations in engineering practice is twice. Firstly, using parametric analyses, one will design a productive process that minimizes the costs.

Secondly, especially for cold processes, one can simulate (and the optimize) the mechanical properties of the produced pieces. Especially for this scope, it is fundamental both the correct reproduction of the residual stress profiles in the work pieces, and the accurate modeling of the material mechanical behavior, usually subject during the process to severe loading? unloading cycles with very large plastic strains, difficult to be correctly reproduced numerically.

Finally, these constitutive models should allow the simulation of defects (such as chevron cracks or surface defects) in the work pieces, due for example to wrong combinations of design parameters.

#### Development of analytical solutions for drawing processes

This research project is focused on the development of analytical tools for the estimation of the force to cold draw wires or rectangular plates. These analytical models must take into account the different combination of die geometries, area reduction, and the friction conditions.

Such models are very important to the design of drawing metal forming processes. In fact, even if the numerical analyses are probably the most powerful tool today available to optimize metal forming processes, the design of a real industrial process involves parametric analyses, which require a single numerical simulation for each combination of the process parameters. For this reason, analytical models, allowing (at least) an initial design of the process, are very important.

Moreover, it should be noted that the most adopted design procedures of metal forming processes in the engineering practice are still based on the limit analysis technique.

The developed analytical solutions are based on the limit analysis techniques.

#### Coupled fluid-structure numerical simulations for acoustic problems

This research project involves the numerical simulation of coupled (acoustic) fluid-structure problems using the Finite Element method.

In particular, in this scientific research it is employed the Finite Element method to design the acoustic response of devices for the correction of rooms for the listening of the music, especially at mid and low frequencies.

The Finite Element numerical simulations, based on dynamic analyses both in the time and in the frequency domains, constitute the basis to develop simplified analytical models that can be employed in the engineering practice to design such acoustic devices.

Geomaterials are a wide class of materials, usually identified as brittle, or quasi brittle. For example, rocks, soils, concrete and masonries are geomaterials. Also advanced materials, such as ceramics, belong to this class.

The objective of this research is the development of constitutive models for this class of materials, under the classical Theory of Plasticity.

Such constitutive models may be applied in nonlinear Finite Element analysis of advanced engineering problems, as geotechnical applications or simulations of the mechanical behavior of old masonries.

From a numerical point of view, the constitutive modeling of these materials is particularly critical, due to the difficulties to achieve convergence in Finite Element analyses of boundary value problems. For this reason, differently from the typical literature approaches, the numerical efficiency and the stability of the integration algorithm is a key point in order to assure the applicability of the developed models to a wide class of practical engineering problems.

The main goal of this research project is the development of constitutive models that allows one to take into account the nonlocal effects (gradient effects) of the mechanical response of polycrystalline metallic materials subjected to plastic deformation.

The plastic response of metals, at the micron scale, is influenced by the grain boundaries, that constraint the dislocations flow.

At this scale, the mechanical properties of a metallic specimen, subject for example to bending or torsion, strongly depend on the specimen size, and they are quite different with respect to those observed at the macroscopic scale.

In particular, diminishing the specimen size, one observes an improvement of the mechanical properties (strengthening and variation of strain hardening) The classical Plasticity Theory cannot take into account such phenomena, since it is not explicitly referred on any intrinsic material scale.

Other models have been proposed in the literature, called ?Gradient Plasticity models?. They are based on nonlinear partial differential equations in which the spatial gradient of the plastic strains explicitly appears.

The numerical integration of such differential equations using the Finite Element Method is particularly complex, due to their strong nonlinearity.

The research topic is then based both on the development of this class of constitutive models, and on the numerical techniques allowing their integration for the simulation of engineering boundary value problems.

The main objective of this research is the development of constitutive models for composite materials, in particular for syntactic foams. They are particulate composites in which a thermoset polymer matrix, usually made of vinyl ester or epoxy resin is filled with of hollow spheres, also called balloons. They are usually made by glass, ceramic, or metal. These composites find applications in aerospace and marine systems for their closed-cell microstructure.

The mechanical behavior of the syntactic foams is reproduced by means of numerical homogenization techniques, based on Finite Element micromechanical simulations of a representative volume (RVE) of composite material.

To perform these analyses, it is fundamental the modeling of the mechanical behavior both of polymeric materials constituting the matrix, and of the failure of the fillers, typically of brittle type.

The goal of this scientific research is the development of constitutive models for metals subject to large deformations, which allow the simulation of metal forming processes using the Finite Element method. The objective of these simulations in engineering practice is twice. Firstly, using parametric analyses, one will design a productive process that minimizes the costs.

Secondly, especially for cold processes, one can simulate (and the optimize) the mechanical properties of the produced pieces. Especially for this scope, it is fundamental both the correct reproduction of the residual stress profiles in the work pieces, and the accurate modeling of the material mechanical behavior, usually subject during the process to severe loading? unloading cycles with very large plastic strains, difficult to be correctly reproduced numerically.

Finally, these constitutive models should allow the simulation of defects (such as chevron cracks or surface defects) in the work pieces, due for example to wrong combinations of design parameters.

This research project is focused on the development of analytical tools for the estimation of the force to cold draw wires or rectangular plates. These analytical models must take into account the different combination of die geometries, area reduction, and the friction conditions.

Such models are very important to the design of drawing metal forming processes. In fact, even if the numerical analyses are probably the most powerful tool today available to optimize metal forming processes, the design of a real industrial process involves parametric analyses, which require a single numerical simulation for each combination of the process parameters. For this reason, analytical models, allowing (at least) an initial design of the process, are very important.

Moreover, it should be noted that the most adopted design procedures of metal forming processes in the engineering practice are still based on the limit analysis technique.

The developed analytical solutions are based on the limit analysis techniques.

This research project involves the numerical simulation of coupled (acoustic) fluid-structure problems using the Finite Element method.

In particular, in this scientific research it is employed the Finite Element method to design the acoustic response of devices for the correction of rooms for the listening of the music, especially at mid and low frequencies.

The Finite Element numerical simulations, based on dynamic analyses both in the time and in the frequency domains, constitute the basis to develop simplified analytical models that can be employed in the engineering practice to design such acoustic devices.