Giorgio Simeoli

Monitoring impact damaging of thermoplastic composites

Thermoplastic composites are becoming ever more attractive also to the aeronautical sector. The main advantage lies in the possibility to modify the interface strength of polypropylene based laminates by adjusting the composition of the matrix. Understanding these aspects is of great importance to establish a possible link between the material toughness and the matrix ingredients. The aim of the present work is to ascertain the ability of an infrared imaging device to visualize any change, in the material behaviour to low energy impact, induced by changes in the matrix composition. Attention is given to image processing algorithms; in particular, an original procedure to measure the extension of the impact-affected area is proposed.

Evaluation of impact-affected areas of glass fibre thermoplastic composites from thermographic images

The usefulness of an infrared imaging device, in terms of both acting as a mechanism for surface thermal monitoring when a specimen is being impacted and as a non-destructive evaluation technique, has already been proved. Nevertheless, past investigation has focused on mainly thermoset-matrix composites with little attention towards thermoplastic ones. Conversely, these thermoplastic composites are becoming ever more attractive to the aeronautical sector. Their main advantage lies in the possibility of modifying their interface strength by adjusting the composition of the matrix. However, for a proper exploitation of new materials it is necessary to detail their characterization. The purpose of the present paper is to focus on the use of infrared thermography (IRT) to gain information on the behaviour of thermoplastic composites under impact. In addition, attention is given to image processing algorithms with the aim of more effectively measuring the extension of the impact-affected area.4

Low velocity impact behaviour of polypropylene and epoxy composite laminates reinforced with a basalt woven fabric

Woven basalt fiber composite laminates based on epoxy and polypropylene (PP) resins were dynamically loaded by a falling weight machine, by using a cylindrical impactor with a hemispherical nose. Laminates with the same thickness were investigated to compare their dynamic response. Impact tests were carried out at penetration to obtain the complete load-displacement curve and to measure the penetration energy, and at different energy levels to study the influence of the matrix on the damage start and propagation. A general better behavior of epoxy basalt fibre reinforced plates (BFRP) was noted while, surprisingly, the polypropylene based laminates didn’t show any penetration even at high impact energy highlighting the importance of this study.Woven basalt fiber composite laminates based on epoxy and polypropylene (PP) resins were dynamically loaded by a falling weight machine, by using a cylindrical impactor with a hemispherical nose. Laminates with the same thickness were investigated to compare their dynamic response. Impact tests were carried out at penetration to obtain the complete load-displacement curve and to measure the penetration energy, and at different energy levels to study the influence of the matrix on the damage start and propagation. A general better behavior of epoxy basalt fibre reinforced plates (BFRP) was noted while, surprisingly, the polypropylene based laminates didn’t show any penetration even at high impact energy highlighting the importance of this study.

Environmental Friendly Thermoplastic Composite Laminates Reinforced with Jute Fabric

A commercial jute fabric was used as the reinforcement of two thermoplastic matrices: polypropylene (PP) and poly(lactic acid) (PLA) having glass transition temperatures equal to 8 and 60 °C respectively. The latter were evaluated by previous dynamic-mechanical tests. Plates prepared by conventional film stacking and compression molding procedures have been systematically subjected to low-velocity impact tests at room temperature. The comparison between the two kind of samples, reported not only in terms of load-displacement and energy-time curves but also in light of morphological observations, is discussed taking into account, among others, the rubbery behavior of PP based samples and the glassy nature shown by the fully-biodegradable system PLA/jute at the considered test temperature.

Application of optical interferometric techniques for non-destructive evaluation of novel "green" composite materials

Nowadays the use of advanced composite materials in aeronautics, both civil and military, in automotive and in sport applications, citing some, is well established. The characteristics of composite materials in terms of weight, fatigue resistance and corrosion resistance make them competitive with respect to conventional ones. On the other side, the fabrication process of the most employed composites reinforced by carbon fibers or glass fibers, needs of complex steps that not always are environmental complaisant. Moreover, such fibers are not themselves “green”. For these reasons, in the last decades, the use of natural reinforcing fibers has gained an increasing attention allowing the development of new materials with the same advantages of composite systems but respecting the environment. Furthermore, such materials for their structural complexity are not always compatible with the use of standard non-destructive evaluation as the ultrasounds methods. In this work the efficiency of the employment of optical interferometric techniques as nondestructive evaluation methods in full field modality is proved on novel “green” composite materials. In particular, Electronic Speckle Pattern Interferometry has been tested on different kinds of specimens after flexural tests.

Monitoring thermoplastic composites under cyclic bending tests

This work is concerned with the use of infrared thermography to visualize temperature variations linked to thermo-elastic effects developing over the surface of a specimen undergoing deflection under bending tests. Several specimens are herein considered, which involve change of matrix and/or reinforcement. More specifically, the matrix is either a pure polypropylene, or a polypropylene added with a certain percentage of compatibilizing agent; the reinforcement is made of glass, or jute. Cyclic bending tests are carried out by the aid of an electromechanical actuator. Each specimen is viewed, during deflection, from one surface by an infrared imaging device. As main finding the different specimens display surface temperature variations which depend on the type of material in terms of both matrix and reinforcement.

Low-velocity impact behavior of woven jute/poly(lactic acid) composites

Biocomposite laminates based on poly(lactic acid) (PLA) and woven jute fabric were obtained by film stacking and compression molding techniques. Sample laminates were systematically characterized by impact tests with a falling dart at impact energies equal to 5, 10 and 20 J. Tests showed that, investigated PLA/jute fabric plates suffer only barely visible damages at the first two levels of impact energy while they result to be perforated at 20 J as highlighted by photographic images taken on low and back side of impacted surfaces.

Lock-in thermography for investigation of impact damage in hybrid polypropylene/glass composites

In this contribution, the impact damage modes of a new class of hybrid systems, obtained by the coupling of polypropylene (PP)-based laminates with different interlaminar interface strength and coded as interlaminar-graded interphase strength (IGIS) laminated structures, have been investigated. Several specimens were fabricated by suitably alternating the reinforcement layers with films of the matrix having different intrinsic natures; some specimens were impacted at two energies. All the specimens (impacted or not) have been nondestructively evaluated with lock-in thermography (LT) that is a noncontact, noninvasive technique [10]. The obtained results have been analysed to obtain information on the role played by both the matrix and fibre-stacking sequence on the damage modes, as well as on the overall damage relevance.

Woven glass fabric reinforced laminates based on polyolefin wastes: Thermal, mechanical and dynamic-mechanical properties

Potentialities of polyolefin wastes in place of virgin polypropylene to produce composite laminates have been investigated. Plaques reinforced with a woven glass fabric were prepared by film-stacking technique and systematically analyzed in terms of thermal, mechanical and dynamic-mechanical properties. In case of PP matrices, the use of a typical compatibilizer to improve the adhesion at the interface has been considered. Thermal properties emphasized the chemical nature of plastic wastes. About mechanical properties, static tests showed an increase of flexural parameters for compatibilized systems due to the coupling effect between grafted maleic anhydride and silane groups on the surface of the glass fabric. These effects, maximized for composites based on car bumper wastes, is perfectly reflected in terms of storage modulus and damping ability of products as determined by single-cantilever bending dynamic tests.