Marco Gigliotti

A Novel Numerical Delamination Growth Initiation Approach for the Preliminary Design of Damage Tolerant Composite Structures

In this article, a novel numerical approach for the delamination growth simulation in composite panels under compressive load is proposed. This approach, suitable for preliminary design and optimization purposes, is able to simulate the delamination propagation by means of a limited number of linear analyses. It is based on the determination of the delamination buckling and on the evaluation of the energy released during the delamination propagation by means of eigenvalue and linear static analyses. The proposed approach has been implemented into the finite element code ANSYS and applied to composite panels with circular embedded and rectangular through-the-width delaminations under compressive load. A first validation has been carried out by comparing the results in terms of delamination growth load and energy release rate distributions along the delamination front to two-dimensional and three-dimensional nonlinear results taken from literature.

Effect of carbon nanotubes on the thermoelectric properties of CFRP laminate for aircraft applications

The present paper focuses on the thermoelectric behavior of carbon nanotube-charged carbon fiber-reinforced polymer composite materials for aircraft applications. Two types of samples: Type A with carbon nanotube and Type B without carbon nanotube), and with two different stacking sequences (unidirectional—[0]8, cross orthogonal—[0/90]4) were manufactured for the thermoelectric experiments, DC electrical current was injected through the specimens, and the temperature of the specimens was monitored simultaneously in order to deduce the effect of carbon nanotube on the electrical conductivity change of the specimen. During the test, transient and steady temperature fields were measured on the sample surfaces by infrared thermography, and real-time voltage measurements monitor the sample electrical resistance. The results show that the presence of carbon nanotube produces increasing values of longitudinal electric conductivity σ L of about 10%. At 9 A, the maximum temperature value is around 95℃ for unidirectional and 145℃ for cross orthogonal samples. The presence of carbon nanotube tends to decrease the entire range of maximum temperatures, about 7% on average for the unidirectional and about 4% on average for cross orthogonal samples.

On cyclical hygrothermal fields in laminated plates

This article focuses on the calculation of transient and cyclical hygrothermal fields in laminated composite plates. Water diffusion is simulated by employing Fick’s law, while thermal fields are assumed to be uniform: temperature and water concentration are coupled through the coefficient of hygroscopic diffusivity, which follows a classical Arrhenius law. Relative humidity and temperature at the plate boundary vary in a transient/cyclic way, reproducing real complex environmental conditions. Analytical solutions of the cyclical hygrothermal fields in laminated plates can be employed as benchmark for numerical calculations and for evaluating the induced hygrothermal stress, therefore, for structural, design and optimisation purposes.

Residual thermal strains and stresses in organic matrix composite materials

ABSTRACT Residual strain/stress may arise in organic matrix composite materials due to the intrinsic heterogeneity of their elementary constituents (polymer matrix and fibrous reinforcements), for instance, during material processing, thermal cycling, for harsh in-service conditions. This article illustrates some method to “measure” residual/internal strains/stresses of thermal origin—at both the microscopic and the mesoscopic levels—by inverse analysis of the matrix shrinkage profiles between fibers in unidirectional composite (at the microscopic scale) and the measure of the deflection (curvature) of 0/90 unsymmetric plates (mesoscopic scale). The analysis is carried out by using multiphysical phenomenological models.

Decoupling of water and oxygen diffusion phenomena in order to prove the occurrence of thermo-oxidation during hygrothermal aging of thermosetting resins for RTM composite applications

A novel experimental/numerical method is set up in order to decouple water and oxygen diffusion phenomena and to prove the occurrence of thermo-oxidation during hygrothermal aging of thermosetting resins for RTM composite applications. The method consists of creating artificial environmental conditions under pure water, pure oxygen and a water/oxygen mixture and in following the mass uptake of polymer samples during aging. Global and local (ultra-microindentation) mechanical properties of samples are then measured during and after aging, for each environmental conditioning. By analyzing the gravimetric curves with the aid of diffusion–reaction models and the results of mechanical tests, it is shown that water and oxygen diffusion phenomena are coupled in a complex way and that diffusion/reaction phenomena between water and oxygen take place during hygrothermal aging.

Some Examples of “Multi-Physical” Fatigue of Organic Matrix Composites for Aircraft Applications

This paper presents, discusses and review some recent results concerning the interaction between mechanics and the environment during fatigue tests carried out under accelerated environmental conditioning of laminated and woven Organic Matrix Composites (OMC) for high temperature aircraft parts, the synergy between electrical and mechanical fields during electro-mechanical fatigue of composite laminates for fuselage applications the damage behavior of 3D woven OMC under thermal cycling.For all case studies, the capabilities of the PPRIME Institute to perform such tests reproducing “multi-physical” fatigue environment and characterizing the phenomenology associated to multi-physics coupling at several scales will be highlighted. The main issues related to the development of “multi-physics” models for proper interpretation of test results are also reviewed.