I. Papa

Delamination on GFRP laminates impacted at room and lower temperatures: Comparison between epoxy and vinylester resins

Low velocity impact tests at three different impact energy values and three different temperatures, were performed on glass fibre composite laminates made by infusion technology. Two different resins, epoxy and vinylester, were considered to impregnate the fibres: the first is mainly of aeronautical interest whereas the second one is mainly applied in Naval field. The specimens were first completely destroyed to obtain the complete load-displacement curve. The latter allowed the evaluation of the increasing impact energies, 5, 10 and 20J, used to investigate about the start and propagation of the damage inside the laminates. The delamination was investigated by the very commonly used Ultra Sound technique and the results obtained on the different materials at different temperatures were compared. A general better behaviour of vinylester resin was noted.

Experimental investigation on CFRP milling by low power Q-switched Yb:YAG laser source

In the present study, laser milling of CFRP plate by means of a 30W Q-Switched Yb:YAG fiber laser is investigated through statistical analysis. Milling tests were performed at the nominal power changing the pulse power; the scanning speed, the hatch distance and the released energy. Design of Experiments (DoE) and ANalysis Of VAriance (ANOVA) were applied with the aim to improve the process performances in term of material removal rate and heat affected zone extension. The results show that, the adopted laser is an effective solution for the CFRP milling. Moreover, adopting an accurate approach to the problem, process variability and material damages can be easily reduced.

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.

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.

Acoustic Emission Source Location in Unidirectional Carbon-Fibre-Reinforced Plastic Plates Using Virtually Trained Artificial Neural Networks

Acoustic emission source location in a unidirectional carbon‐fibre‐reinforced plastic plate was attempted employing Artificial Neural Network (ANN) technology. The acoustic emission events were produced by a lead break, and the response wave received by piezoelectric sensors, type VS150‐M resonant at 150 kHz. The waves were detected by a Vallen AMSY4 eight‐channel instrumentation. The time of arrival, determined through the conventional threshold crossing technique, was used to measure the dependence of wave velocity on fibre orientation. A simple empirical formula, relying on classical lamination and suggested by wave propagation theory, was able to accurately model the experimental trend. Based on the formula, virtual training and testing data sets were generated for the case of a plate monitored by three transducers, and adopted to select two potentially effective ANN architectures. For final validation, experimental tests were carried out, positioning the source at predetermined points evenly distribu...