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• Critical initiation pressure of particle reinforced composites is obtained by the design of initiation test. • Particle reinforced composites reaches complete initiation state as the load pressure exceeds 11.95 GPa. • The internal correlation models between energy release behavior and impact load pressure are established. The effect of impact pressure on energy release behavior of high-energy insensitive particle reinforced composites is investigated. The results show that as the impact pressure reaches 5.39 GPa, the high-energy insensitive particulate reinforced composites initiation occurs for the first time. With the increase of the impact pressure, the gas pressure inside the high-pressure explosion chamber increases gradually until the impact pressure increases to 11.95 GPa. The quantitative relationship between impact pressure and energy release behavior is established. [ABSTRACT FROM AUTHOR]

Additive manufacturing has rapidly transformed over the years, moving from simply prototyping to producing objects and structures with advanced materials. The process, also known as 3D printing, enables complex shapes to be generated with great freedom of creation and low waste of resources. Although polymers have been widely used for the manufacture of small objects, the poorer mechanical properties and time required for 3D printing make the technique impractical for the production of real size structural components. This paper presents the development of a larger-diameter head nozzle for the manufacturing of a polymer-based material reinforced with continuous yarns. To address this issue, a continuous yarn reinforcing method was developed, utilizing a modified Fused Filament Fabrication (FFF) hotend adapted to the in-nozzle impregnation of vegetable fibers (i.e., a process by which the yarn and matrix are joined in a single nozzle), such as jute, ramie, and sisal, combined with polylactic acid (PLA) to produce bio-based printed filaments with diameters up to 3 mm. The combination of these materials aims to create printed composites with better mechanical properties and, above all, to meet the environmental need for low-energy biodegradable materials from natural sources that ultimately contribute to reduce the sector's ecological footprint. It was observed that the reinforced samples achieved gains of 28.6% in strength and 28.9% in stiffness in comparison to the unreinforced matrix, using fiber contents up to 48.2% that reduce the polymer utilization per printed volume. The feasibility of the production of multilayer components using the developed method was also confirmed for different types of reinforcement and printing paths. [ABSTRACT FROM AUTHOR]

We have prepared a novel 3D porous biomaterial combining poly ( dl -lactic acid) (PDLLA) and graphene and multi-walled carbon nanotubes oxides (MWCNTO-GO) composite. PDLLA as control and a high loading of PDLLA/MWCNTO-GO (50/50 w/w) bioscaffolds were prepared and functionalized. MWCNTs were exfoliated to form MWCNTO-GO by oxygen plasma etching. The later was also applied to enhance the scaffolds wettability, attaching oxygen-containing groups on their surfaces. This approach produced a porous architecture observed by scanning electron microscopy and semi-quantified by electrochemical analysis. The later also indicated a notable increase on the conductivity of PDLLA/MWCNTO-GO scaffold compared to MWCNTO-GO free PDLLA (about 5 orders of magnitudes at low frequencies). Thermogravimetric analysis showed that the MWCNTO-GO acted protecting the PDLLA matrix, enhancing its thermal stability. The PDLLA/MWCNTO-GO scaffolds had significant cellular adhesion, did not present cytotoxicity effect, besides reduced bactericidal proliferation and produced mineralized tissues in SBF media. The metallic MWCNTO-GO powder held together by PDLLA polymer opens a whole new branch of applications, including bioelectroanalyses, drug delivery systems and tissue engineering. [ABSTRACT FROM AUTHOR]

The electromagnetic characteristics of polyimide/carbonyl iron absorbers synthesized by compression molding using the polyimide precursors (poly (amic acid) solution (PAA)) and different shape of carbonyl iron (CI) were studied at 8.2-12.4 GHz. Curing process of polyimide was monitored by Fourier transform infrared spectroscopy (FT-IR). The influences of CI filler loading and morphology on the microstructure, electromagnetic properties and flexural strength were characterized. The distribution of filler is uniform throughout the polyimide matrix. The X-ray diffraction (XRD) results show the polyimide matrix can protect the CI particles from oxidation. Both the complex permittivity and complex permeability increase with increasing the CI volume fraction. The minimum reflection loss containing spherical CI is -11 dB at 12.4 GHz and flaky CI is 9.7 at 10.3GHz for the composites with 60 wt.% CI. The flexural strengths of the composites are up to 73 MPa and 68 MPa for flaky CI and spherical CI composites, respectively. [ABSTRACT FROM AUTHOR]

Abstract: One of the most important difficulties faced by in situ structural health monitoring approaches when establishing a relationship between a specific damage mechanism and its acoustic signature is the lack of an appropriate signal processing method able to deal with the non-stationary acoustic signals. The purpose of this paper is to use the Hilbert–Huang transform for the extraction of new relevant damage descriptor to be adopted for Acoustic Emission (AE) pattern recognition in order to help understanding the damage process. AE signals collected from unidirectional glass-fiber reinforced polymer composites samples were studied. First, the frequency content of the recorded signals in each test is analyzed. Secondly, the performance of the Hilbert–Huang transform damage classification approach is evaluated. [Copyright &y& Elsevier]

Based on a structural model for wave-controlled impact, a modified Hertzian contact law was used to investigate the impact responses of composite laminates. The original nonlinear governing equation was transformed into two linear equations using asymptotic expansion. Closed-form solution can be derived for the first linear homogeneous equation, which is the equation of motion for single degree of freedom system with viscous damping. The second linear nonhomogeneous equation was solved numerically. The overall impact responses for wave-controlled impacts can be obtained semianalytically and agree well with the numerical solutions of nonlinear governing equations. The proposed methodology is useful for providing guidance to numerical simulation of impact on complex composite structures with contact laws fitting from experimental data. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced polymer (CFRP) sheets can be used to strengthen existing reinforced concrete members. However, debonding (separation of the CFRP sheet from the concrete surface) may occur at less than 50% of CFRP sheet’s tensile capacity, implying that half of the CFRP material is ineffective in increasing the strength of a concrete member. The use of carbon fiber anchors can increase the amount of tension carried in the CFRP sheets. Forty specimens were tested to develop initial design parameters of carbon fiber anchors. Tests showed that by providing anchors with a total cross-sectional area at least two times greater than that of the longitudinal sheet, it was possible to fracture the CFRP sheets. The best results were obtained using a greater number of smaller anchors. Further, surface preparation is unimportant when the CFRP sheets were well anchored and a 1:4 transition slope can manage any offsets in surface level. The general anchor design was then implemented on a series of long beams and demonstrated that the full CFRP sheet tensile capacity can be realized without incurring limitations due to debonding. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the role of the copolymers and nanoparticles during elaboration of new stable composite materials. We have shown that the interactions between the mesophases that form the copolymers and nanoscopic particles can lead to highly organized hybrid materials. The morphology of such composites depends on the characteristics of both copolymers and nanoparticles. On one hand, diblock copolymers must form a strong segregation limit and have a higher mass. On the other hand, nanoparticles must show strong affinity for one of the two polymeric species of the copolymer and be as small as possible. In this case, a composite organic–inorganic material can be obtained with a periodic distribution of the particles in the polymeric matrix. This study can be applied to other copolymer-nanoparticle mixtures and used to design advanced composite architectures. [Copyright &y& Elsevier]