Transverse Cracking Induced Acoustic Emission in Carbon Fiber-Epoxy Matrix Composite Laminates

Transverse cracking induced acoustic emission in carbon fiber/epoxy matrix composite laminates is studied both experimentally and numerically. The influence of the type of sensor, specimen thickness and ply stacking sequence is investigated. The frequency content corresponding to the same damage mechanism differs significantly depending on the sensor and the stacking sequence. However, the frequency centroid does not wholly depend on the ply thickness except for the inner ply crack and a sensor located close enough to the crack. Outer ply cracking exhibits signals with a low-frequency content, not depending much on the ply thickness, contrary to inner ply cracking, for which the frequency content is higher and more dependent on the ply thickness. Frequency peaks and frequency centroids obtained experimentally are well captured by numerical simulations of the transverse cracking induced acoustic emission for different ply thicknesses.

Influence of Rigid Brazilian Natural Fiber Arrangements in Polymer Composites: Energy Absorption and Ballistic Efficiency

Since the mid-2000s, several studies were carried out regarding the development of ballistic resistant materials based on polymeric matrix composites reinforced with natural lignocellulosic fibers (NLFs). The results reported so far are promising and are often comparable to commonly used materials such as KevlarTM, especially when used as an intermediate layer in a multilayer armor system (MAS). However, the most suitable configuration for these polymer composites reinforced with NLFs when subjected to high strain rates still lacks investigation. This work aimed to evaluate four possible arrangements for epoxy matrix composite reinforced with a stiff Brazilian NLF, piassava fiber, regarding energy absorption, and ballistic efficiency. Performance was evaluated against the ballistic impact of high-energy 7.62 mm ammunition. Obtained results were statistically validated by means of analysis of variance (ANOVA) and Tukey’s honest test. Furthermore, the micromechanics associated with the failure of these composites were determined. Energy absorption of the same magnitude as KevlarTM and indentation depth below the limit predicted by NIJ standard were obtained for all conditions.

Design of a bonnet of a sport vehicle realized with an innovative recyclable Polymeric Matrix Composite and virtual characterization of the related sandwich structure

This article presents the design activities of an automotive component to be produced using a recyclable cleavable-epoxy Matrix Composite and Basalt-Derived Mineral Fibres. The material innovations are being studied within project C2CC (www.c2cc-project.eu), aimed at satisfying latest EU directives regarding end-of-life reuse and C-footprint reduction. The main targets are the weight reduction, obtained employing materials with lower footprint, namely a biomass derived epoxy and a cradle-to-cradle recyclable mineral fiber, that is a fibre that (differently from carbon fibre) can be remelted to long fibre with no decrease in mechanical specifications [1]. For recycling both the resin and the fibre, a the cleavable hardener was adopted [2] developed by Connnora Inc (US), which avoids the need of pyrolysis to recover and recycle the fibers from prepreg scraps and end-of-life components. The main project demonstrator is the front bonnet of segment A vehicle FIAT 500 Abarth. One approach to reach the component expected performances is using the semifinished composite materials (prepregs) produced by the project to manufacture a final structural sandwich. From the modelling point of view, this work carries out a multiscale approach starting from the basic constituents of skin and core and ending with the model at the mesoscale of the specimens of the sandwich. The simulation activity was conducted considering the possible recyclable sandwich cores, and the comparison aims at selecting the optimal ones for this specific automotive component.

Ballistic Performance of Ramie Fabric Reinforcing Graphene Oxide-Incorporated Epoxy Matrix Composite

Graphene oxide (GO) incorporation in natural fiber composites has recently defined a novel class of materials with enhanced properties for applications, including ballistic armors. In the present work, the performance of a 0.5 vol % GO-incorporated epoxy matrix composite reinforced with 30 vol % fabric made of ramie fibers was investigated by stand-alone ballistic tests against the threat of a 0.22 lead projectile. Composite characterization was also performed by Fourier-transform infrared spectroscopy, thermal analysis and X-ray diffraction. Ballistic tests disclosed an absorbed energy of 130 J, which is higher than those reported for other natural fabrics epoxy composite, 74–97 J, as well as plain Kevlar (synthetic aramid fabric), 100 J, with the same thickness. This is attributed to the improved adhesion between the ramie fabric and the composite matrix due to the GO—incorporated epoxy. The onset of thermal degradation above 300 °C indicates a relatively higher working temperature as compared to common natural fiber polymer composites. DSC peaks show a low amount of heat absorbed or release due to glass transition endothermic (113–121 °C) and volatile release exothermic (~132 °C) events. The 1030 cm−1 prominent FTIR band, associated with GO bands between epoxy chains and graphene oxide groups, suggested an effective distribution of GO throughout the composite matrix. As expected, XRD of the 30 vol % ramie fabric-reinforced GO-incorporated epoxy matrix composite confirmed the displacement of the (0 0 1) peak of GO by 8° due to intercalation of epoxy chains into the spacing between GO layers. By improving the adhesion to the ramie fabric and enhancing the thermal stability of the epoxy matrix, as well as by superior absorption energy from projectile penetration, the GO may contribute to the composite effective ballistic performance.