Federica Daghia

Identification and validation of an enhanced mesomodel for laminated composites within the WWFE-III

The accurate prediction of damage and failure in laminated composites is still a major issue in many structural applications. The paper provides a detailed description of a new damage mesomodel and examines its application to solve material and structural problems for the Test Cases proposed in the Third World-Wide Failure Exercise (WWFE-III). The cases cover various materials (glass/epoxy and carbon/epoxy), lay-ups (unidirectional, cross ply, quasi-isotropic, angle ply and general multi-directional laminates), loadings (uniaxial, biaxial, bending, thermal and loading-unloading) and features (ply sequence, size effects and open hole). The model deals with various damage scenarios and mechanisms of degradation, including diffuse intralaminar damage, diffuse interface damage, localized delamination, fibre breakage and plasticity, and can predict the evolution of a laminate’s response until final failure. Some issues concerning the limited information available in the exercise for the identification of the parameters of the mesomodel are also discussed.

Fabrication and Thermo-Mechanical Characterization of a Shape Memory Alloy Hybrid Composite

Shape memory alloy (SMA) elements embedded in a structure allow to control the structural properties, thanks to their coupled thermo-mechanical behavior. In this study, the manufacturing and the shape control abilities of glass fiber/polyester resin SMA hybrid composites (SMAHCs) were experimentally investigated. Mechanical and calorimetric characterizations of SMA were carried out and correlated to the thermo-mechanical behavior of the SMAHC. The SMAHC was manufactured by the Vacuum Infusion Process that uses dry fibers and liquid matrix for the composite production. A polyester resin having a curing temperature lower than the SMA Austenite transition temperature was chosen as matrix, so a blocking system for the SMA wires was not needed during the cure. The thermo-mechanical behavior of the SMAHC was investigated by monitoring the shape change of the plate during heating of the embedded wires. The results give some indications on the appropriate characterization and choice of materials for SMAHC manufacturing.

A micromechanics-based interface mesomodel for virtual testing of laminated composites

BackgroundThe prediction of the behavior of laminated composite structures up to final fracture continues to be a challenge today. Indeed, failure may occur due to the interaction of small-scale degradations, such as transverse intraply cracks and interface delamination, which are difficult to account for in calculations on the structure’s scale.MethodsHere, in order to model the interaction of intralaminar and interlaminar degradations, we develop a new and relatively simple micromechanics-based interface mesomodel which differs from classical cohesive interface models, since it includes the coupling between transverse intraply cracks and interface delamination.ResultsThe new interface model was implemented in a finite element code and used in the simulation of tensile tests on unnotched and holed specimens. Simulations with a classical cohesive interface model (not including coupling) were also carried out.ConclusionsThe simulations highlight the need for introducing intra-/interlaminar’s behavior coupling in order to accurately predict the damage evolution and failure stress and mode.

Comparison of Mechanical Tests for the Identification of Composite Defects Using Full-Field Measurements and the Modified Constitutive Relation Error

Composite parts manufactured in large batches always present defects. These may not influence the behavior of the structure or might on the contrary be seriously detrimental to the performance of the component. In the first case, their presence is negligible, in the other case it is fundamental to be aware of their presence to foresee countermeasures. In this framework, being able to localize and estimate the intensities of flaws is extremely interesting. In this article, we present an approach based on the Modified Constitutive Relation Error to characterize defects, employing as input the displacements field measured from simple static and dynamic tests. The identification capabilities from tensile, bending, vibration and compression tests are compared using pseudo-experimental results as input data; then the identification is shown on a real case for buckling experiments to show the potential of the method.