Anomalous Strain Rate Effect in Ultrafine Grained Titanium

An anomalous effect was found in the strain rate dependence of severe plastic deformed commercially pure titanium with ultrafinegrained structure. A maximum tensile strength was obtained for ϵ˙=10−3s−1. This did not allow a single strain rate sensitivity parameter to be defined in the interval from ϵ˙=10−5to10−1s−1. Distinct deformation mechanisms for lower and higher strain rates might be the reason for this anomaly

Eco-friendly recycled polypropylene matrix composites incorporated with geopolymer concrete waste particles

Civil construction wastes have been incorporated into polymers for recycling as novel engineering composites. In the present work eco-friendly composites with recycled polypropylene (rPP) matrix incorporated with geopolymer concrete waste particles, wither plain (GCW) or surface-modified with oleic acid (AGC) were investigated. The geopolymer concrete waste particles were mixed with polymer powder to provide an effective dispersion between the different materials. Composites were produced by an initial reactive extrusion processing followed by injection molding. These novel composites with amount of 20, 40 and 50 wt% of GCW particles, both plain as-received and surface-modified, were technically evaluated by tensile tests, statistically analyzed by ANOVA, as well as by water absorption as per ASTM standards. Surface dispersion of nanoparticles was revealed by atomic force microscopy. Microstructural analysis was performed by scanning electron microscopy. The results indicated that these sustainable GCW particles incorporated into rPP matrix exhibit superior processability and water absorption less than 0.01%. The rPP/AGC composites present relatively higher elastic modulus, 629 MPa, as compared to the neat rPP, with 529 MPa. These properties suggest potential sustainable applications in building construction using waste materials.Peer reviewe

Recycled polypropylene matrix nanocomposites reinforced with silane functionalized geopolymer concrete waste

The objective of this work is the processing of recycled polypropylene (rPP) matrix and geopolymer concrete waste (GCW) to develop novel sustainable nanocomposites for engineering applications. Specimens of these nanocomposites were produced from GCW added in proportions of 20, 40 and 50 wt% to rPP. The pulverized waste, with nanometric particles, was used as neat, GCW, or as surface functionalized with vinyl trimethoxy silane (GCW/VTS). Separately, both GCW and GCW/VTS were mixed with rPP by means of extrusion reactive extrusion and injection processing before final molding of specimens. The composition microstructure, thermal stability and tensile properties of the specimens were studied by wide angle X-ray diffraction, thermogravimetry, differential scanning calorimetry, water absorption, tensile tests, and field emission gun scanning electron microscopy with energy dispersive spectroscopy. The main findings were an increased thermal stability and enhanced elastic modulus with incorporation of both GCW and GCW/VTS. A high degree of interaction between GCW filler and rPP matrix, including the first time observed mechanism of PP nanofilaments adhesion, is responsible for a negligible water absorption. A decrease in the crystallinity suggests an interference of GCW in the rPP arrangement of macromolecular chains. (C) 2020 Published by Elsevier B.V.Peer reviewe

Weibull analysis of tensile tested piassava fibers with different diameters

Environmental considerations in addition to technical, economical and societal benefits are increasingly promoting the substitution of natural fibers for glass fiber in polymer matrix composites. However, natural fibers are heterogeneous in their dimensions, specially the cross section, which plays an important role in their mechanical strength. It has been found that the equivalent diameter of fibers such as sisal, ramie, pinea-pple and curaua correlates to different levels of tensile resistance. Piassava is a promising stiff natural fiber for composite reinforcement. In this work, a statistical analysis of tensile strength of piassava fibers using the Weibull methodology was performed. An attempt to correlate the fiber strength, obtained in tensile tests, with the diameter, precisely measured by means of a profile projector, was carried out. The results revealed an inverse dependence between the piassava fiber diameter and corresponding tensile strength. Fracture tip observation by SEM suggested a possible mechanism that could justify this inverse correlation.Keywords: piassava fiber, testing traction, strength/diameter correlation

Izod impact energy study of re-forced polisher matrix compounds with curaous fibers aligned and epoxy matrix reinforced with piassava fibers

Polymer matrix composites have been applied in components such as helmets and shielding for which tough-ness is a major requirement. Natural fiber presents interfacial characteristics with polymeric matrices that favor a high impact energy absorption by the composite structure. The objective of this work was then to assess the Izod impact resistance of polymeric composites reinforced with different amounts, up to 30% in volume, of a promising high strength natural fiber from the Amazon region known as curaua. Among these, the piassava fiber extracted from a palm tree native of South America stands as one of the most rigid with a potential to be used as composite reinforcement. Therefore, the present work investigates the notch toughness behavior, by Izod impact tests, of epoxy composites reinforced with up to 40 % in volume of continuous and aligned piassava fibers.The results showed a remarkable increase in the notch toughness with the amount of incorporated curaua fibers. This can be attributed to a preferential debonding of the fiber/matrix interface, which contributes to an elevated absorbed energy. . It was found that the incorporation of piassava fibers results in significant increase in the impact energy of the composite. Scanning electron microscopy analysis showed that the nature of the piassava fiber interface with the epoxy matrix is the major responsible for the superior toughness of the composite.Keywords:Piassava, curauá, polymer matrix, epoxy matriz, Izo

Mechanical properties of boehmeria nivea natural fabric reinforced epoxy matrix composite prepared by vacuum-assisted resin infusion molding

Natural lignocellulosic fibers and corresponding fabrics have been gaining notoriety in recent decades as reinforcement options for polymer matrices associated with industrially applied composites. These natural fibers and fabrics exhibit competitive properties when compared with some synthetics such as glass fiber. In particular, the use of fabrics made from natural fibers might be considered a more ecient alternative, since they provide multidirectional reinforcement and allow the introduction of a larger volume fraction of fibers in the composite. In this context, it is important to understand the mechanical performance of natural fabric composites as a basic condition to ensure ecient engineering applications. Therefore, it is also important to recognize that ramie fiber exhibiting superior strength can be woven into fabric, but is the least investigated as reinforcement in strong, tough polymers to obtain tougher polymeric composites. Accordingly, this paper presents the preparation of epoxy composite containing 30 vol. % Boehmeria nivea fabric by vacuum-assisted resin infusion molding technique and mechanical behavior characterization of the prepared composite. Obtained results are explained based on the fractography studies of tested samples

Experimental Findings and Validation on Torsional Behaviour of Fibre-Reinforced Concrete Beams: A Review

Fibres have long been utilized in the construction sector to improve the mechanical qualities of structural elements such as beams, columns, and slabs. This study aims to review the torsional behaviour of various forms of fibre reinforced concrete to identify possible enhancements and the practicability of concrete structural beams. Concrete reinforced steel fibre, synthetic fibre, and hybrid fibre are examples of fibre reinforced concrete. The review found that the mixing, orientation, and volume of fibres, the size of coarse particles, the aspect ratio of fibres, and the stiffness of fibres all affect the torsional strength of fibre reinforced concrete. Nevertheless, the application of fibres to recycled self-consolidating concrete of various forms needs to be explored and studied to ascertain its feasibility to facilitate greener concrete. Thus, with the results compiled in this review paper, it was possible to delimit advances and gaps on the effect of editing reinforcement fibres in relation to the torsion of structural element