Stefano Angioni

Impact damage resistance and damage suppression properties of shape memory alloys in hybrid composites—a review

Composite materials are known to have a poor resistance to through-the-thickness impact loading. There are various methods for improving their impact damage tolerance, such as fiber toughening, matrix toughening, interface toughening, through-the-thickness reinforcements, and selective interlayers and hybrids. Hybrid composites with improved impact resistance are particularly useful in military and commercial civil applications. Hybridizing composites using shape memory alloys (SMA) is one solution since SMA materials can absorb the energy of the impact through superelastic deformation or recovery stress, reducing the effects of the impact on the composite structure. The SMA material may be embedded in the hybrid composites (SMAHC) in many different forms and also the characteristics of the fiber reinforcements may vary, such as SMA wires in woven laminates or SMA foils in unidirectional laminates, only to cite two examples. We will review the state of the art of SMAHC for the purpose of damage suppression. Both the active and passive damage suppression mechanisms will be considered.

A critical review of homogenization methods for 2D woven composites

In this article analytical methods for predicting the mechanical properties of 2D woven composites with different weave patterns and materials are reviewed. These approaches are then evaluated by comparing them to experimental and numerical results.

A Comparison Between Optimized Active Thermography and Digital Shearography for Detection of Damage in Aerospace Composite Structures

The main goal of this research is to compare capabilities of two different Non-Destructive Testing (NDT) methods, thermosonics and digital shearography (DISH), to recognize and image back drilled hole defects. Thermosonics was optimized by varying magnitude of the heat flux, the excitation frequency, the number of excitation cycles, acquisition time, frame rate etc. DISH was optimized by investigating the test objects by dynamic loading approach in order to identify per each defect the (0 1) mode shape and the corresponding resonance frequency. In this way, whilst thermosonics provided the initial infrared imaging of the panel for a pass/fail test, DISH has been performed to provide the delamination quantitative assessment.

Modeling of thermal wave propagation in damaged composites with internal source

SMArt Thermography exploits the electrothermal properties of multifunctional smart structures, which are created by embedding shape memory alloy (SMA) wires in traditional carbon fibre reinforced composite laminates (known as SMArt composites), in order to detect the structural flaws using an embedded source. Such a system enables a built-in, fast, cost-effective and in-depth assessment of the structural damage as it overcomes the limitations of standard thermography techniques. However, a theoretical background of the thermal wave propagation behaviour, especially in the presence of internal structural defects, is needed to better interpret the observations/data acquired during the experiments and to optimise those critical parameters such as the mechanical and thermal properties of the composite laminate, the depth of the SMA wires and the intensity of the excitation energy. This information is essential to enhance the sensitivity of the system, thus to evaluate the integrity of the medium with different types of damage. For this purpose, this paper aims at developing an analytical model for SMArt composites, which is able to predict the temperature contrast on the surface of the laminate in the presence of in-plane internal damage (delamination-like) using pulsed thermography. Such a model, based on the Green’s function formalism for one-dimensional heat equation, takes into account the thermal lateral diffusion around the defect and it can be used to compute the defect depth within the laminate. The results showed good agreement between the analytical model and the measured thermal waves using an infrared (IR) camera. Particularly, the contrast temperature curves were found to change significantly depending on the defect opening.