Composite materials are combinations of two or more constituent materials (or phases) characterized by physical, chemical and/or mechanical properties remarkably different between them. When the constituents are combined, the result is a composite which properties are anyway different from the relevant ones of the single components.
This Research Project (RP) focuses on the structural behavior of composites and is scheduled in four main groups of tasks, Work Packages. WP1 is dedicated to the modeling of composites and attention is paid to methodologies for constitutive behavior modeling and failure mechanism prediction. WP2 concerns the testing of prototypes and samples of composite materials, with specific reference to application of composites in structural fields. Simulation analyses are the task of WP3, where the main findings of the first two work packages are collected and combined to move a step forward in the state of the art. WP4, refers to the dissemination of the results, through both conference proceedings and journal articles. Aiming at guarantee the feasibility of the RP, the four WPs, described in the following sections, are organized with appropriate time overlaps and with a clear partition of the activities and tasks among all the participants.
All work packages will be developed considering both the linear and non-linear structural response, in both static and dynamic contexts. The proposed approaches fall within the scope of mechanical and numerical modeling of non-homogeneous materials, where the relative experimental validation is a decisive task prior to practical applications. During the simulations, particular attention will be paid to the predictive capabilities of the models for the evaluation of the ultimate loadings, whether these are related to the material strength or to phenomena of loss of stability. Textile Reinforced Mortar composite is one of the most significance case study that the research project aims to approach.
The following sub-sections sum up: the themes addressed in the proposed research, the innovation contained in the project and the expected results.
SUMMARY OF THE RESEARCH TOPICS
The focus of the research program is the analysis of the mechanical behavior of structural elements in composite materials and the design of high performance materials for reinforcing and consolidation of existing structures. The main objective is to develop suitable constitutive models, together with novel (more computationally efficient) strategies to connect the different scales exhibit by composites. Both experimental testing and numerical simulations will be used to drive the research and for validation purposes.
INNOVATION OF THE PROJECT
In the technical literature it is recognized that macroscopic material properties, such as stiffness and strength, are governed by processes occurring at one to several scales below the level of observation. In this RP the mechanical behavior of composites, coupled with other concurrent physical phenomena, is investigated, relying on effective constitutive and structural modeling and advanced numerical methods.
Textile Reinforced Mortar is one of the most significance case studies that the research project aims to approach. In the last few years, the growing need to recover, reinforce and strengthen existing masonry and concrete buildings damaged by seismic events or degraded by ageing, led to the development of innovative materials and new repair techniques with low environmental impact and high efficacy. Fiber Reinforced Cementitious Matrix (FRCM), also called Textile Reinforced Mortar (TRM), applied as external reinforcement and acting as an additional tensile-resistant element, proved to be very effective in increasing both mechanical strength and ductility of structures.
In the proposed research, phase-field models are developed by using multiscale and variational techniques, with the aim of describing the complex cracking and delamination phenomena that leads to the failure of the above-mentioned composite systems. Specific dissipative energies, depending on plastic and damage internal variables, are incorporated into the formulations to account for the inelastic sources of the composite, and to reproduce possible failures of the system constituents, and, as often observed in experiments, to capture debonding and slippage at the fiber-to-matrix interface, when large tensile loadings are applied to the system. After implementation in finite element codes, modeling simulations will be performed with the purpose of exploring the ductile response exhibited by FRCM systems, typically characterized by stress-softening processes of progressive damaging.
PROGRESS BEYOND THE STATE OF THE ART
A significant contribution and a deeper insight to the theory of multi-field continua are expected from the RP. The crucial task is to develop more reliable tools for the analysis of coarse scale problems dominated by microstructure, and in particular by scale effects. Indeed, when classical usual (grade 1) model fails in detect the structural response, enhanced homogenization procedures are required in order to account for internal length scales and dispersion of phases. Non-linear computational multiscale and variational approaches will be proposed. To cover some notable gaps of the current knowledge, specific strategies for numerical solutions in the dynamic framework will be also investigated. The impact of structural improvement in failure mechanisms of existing structures will be addressed through the combined use of the information coming from the proposed models and the main results provided in the technical literature and standard codes. Then, the project aims are searched beyond the current state-of-art of in the sector of composites and their implementation as construction materials in new or existing civil structures. In particular, it is expected to take advantage from different expertise of the researchers composing the research group in the field of structural modeling, simulation and identification.
Accordingly to the previous discussion, the following main findings are expected from the research project: 1) novel constitutive models able to retain at the macroscopic level the microscopic features and capable to detect failure mechanisms (evolutionary damages, instabilities, etc.); 2) structural modeling of notable elements and materials of greater interest in civil engineering applications (like TRM composites); 3) computational advanced tools for structural analysis and optimization of new and existing constructions, for both the linear and non-linear response, either in static or in dynamic framework; 4) analysis, design and experimental tests of existing and/or performance improved composite materials.