Acoustic Emission for Evaluating the Reinforcement Effectiveness in Steel Fiber Reinforced Concrete

Steel fiber reinforcement in concrete strongly enhances its ductility and toughness. This is basically due to the additional fracture mechanisms and energy used to overcome the interlocking and adhesion between the fibers and the cementitious matrix. The enhancement of the final properties is measured by mechanical tests and can be assessed only at the end of loading. These processes can be targeted and monitored by acoustic emission (AE) indices offering real-time characterization of the material’s performance much earlier than the final failure or the termination of loading. In this study, steel fiber reinforced concrete (SFRC) beams were tested in bending with simultaneous AE monitoring. Tests conducted independently in different laboratories confirm that the AE behavior at low load levels is very indicative of the amount of reinforcement and consequently, of the final mechanical properties. The reason is that the reinforcement phase is activated through shear stresses in its interphase, a mechanism that is more profound in the presence of higher fiber content, and correspondingly is absent in plain unreinforced material. This finding opens the way to characterize the effectiveness of reinforcement with just a proof loading at less than 30% of the final load bearing capacity.

Long-fibre reinforced polymer composites by 3D printing: influence of nature of reinforcement and processing parameters on mechanical performance

The aim of this study was to identify the effect of material type (matrix and reinforcement) and process parameters, on the mechanical properties of 3D Printed long-fibre reinforced polymer composites manufactured using a commercial 3D Printer (Mark Two). The effect of matrix material (Onyx or polyamide), reinforcement type (Carbon, Kevlar®, and HSHT glass), volume of reinforcement, and reinforcement lay-up orientation on both Ultimate Tensile Strength (UTS) and Flexural Modulus were investigated. For Onyx, carbon fibre reinforcement offered the largest increase in both UTS and Flexural Modulus over unreinforced material (1228 ± 19% and 1114 ± 6% respectively). Kevlar® and HSHT also provided improvements but these were less significant. Similarly, for Nylon, the UTS and Flexural Modulus were increased by 1431 ± 56% and 1924 ± 5% by the addition of carbon fibre reinforcement. Statistical analysis indicated that changing the number of layers of reinforcement had the largest impact on both UTS and Flexural Strength, and all parameters were statistically significant.

Long-fibre Reinforced Polymer Composites by 3D Printing: Influence of Nature of Reinforcement and Processing Parameters on Mechanical Performance

The aim of this study was to identify the effect of material type (matrix and reinforcement) and process parameters, on the mechanical properties of 3D Printed long-fibre reinforced polymer composites manufactured using a commercial 3D Printer (Mark Two). The effect of matrix material (Onyx or polyamide), reinforcement type (Carbon, Kevlar®, and HSHT glass), volume of reinforcement, and reinforcement lay-up orientation on both Ultimate Tensile Strength (UTS) and Flexural Modulus were investigated. For Onyx, carbon fibre reinforcement offered the largest increase in both UTS and Flexural Modulus over unreinforced material (1,228±19 % and 1,114±6 % respectively). Kevlar® and HSHT also provided improvements but these were less significant. Similarly, for Nylon, the UTS and Flexural Modulus were increased by 1,431±56 % and 1,924±5 % by the addition of carbon fibre reinforcement. Statistical analysis indicated that changing the number of layers of reinforcement had the largest impact on both UTS and Flexural Strength, and all parameters were statistically significant.

A Novel Technique for Production of Metal Matrix Composites Reinforced With Carbon Nanotubes

The metal matrix composites (MMCs) have been widely used where high specific properties and temperature resistance are required, particularly in aerospace applications. In this work, an ASTM-1100 aluminum alloy in the form of sheets was reinforced with multiwalled carbon nanotubes (MWCNTs) by a novel technique which we have called sandwich technique. Carbon nanotubes (CNTs) are dispersed in a polyvinyl alcohol (PVA) solution; this solution is poured into a container and dried to obtain a reinforced polymer, which is then stretched to obtain a sheet with CNTs aligned in the stretching direction. These composite sheets were stacked with aluminum sheets, and then these stacks were hot compacted in a die using an argon atmosphere to prevent the damage of the CNTs. During this process, most of the polymer evaporates and aluminum diffusion allows obtaining a consolidated matrix with a banded structure of CNTs. The mechanical properties of the composite were measured by tensile and nano-indentation tests, showing increases of up to 100% in the elastic modulus and significant increases in yield and ultimate strength with respect to unreinforced material. Field emission scanning electron microscopy (FESEM) analyses showed a good dispersion of the CNTs within the bands with no evidence of CNTs' damage. No harmful phases were found in the composite after micro X-ray diffraction (XRD) tests. The results showed that the proposed technique is promissory to solve some of the problems in the nano-MMCs manufacturing such as dispersion and alignment of the reinforcing phase.

Influence of fly ash particles on tensile and impact behaviour of aluminium (Al/3Cu/8.5Si) metal matrix composites

The present work aimed to study the tensile and impact behaviour of fly ash particle reinforced aluminium matrix composites. Fly ash particles reinforced aluminium (Al/3Cu/8.5Si) matrix composites were fabricated by the stir casting technique. Three different size ranges of fly ash particles (50–75, 75–103 and 103–150 μm) were used. The composites were subjected to tensile and impact tests. The tensile and impact fracture surfaces of the aluminium alloy and composites were investigated using a scanning electron microscope to characterise the fracture mechanism of the composites. The tensile strength of composites increased, while the ductility and impact strength of composites decreased with an increase in fly ash particle content. The fracture surface of the unreinforced material was characterised by uneven distribution of a large number of dimples resulting in ductile failure. In the case of composites, the presence of hard and brittle reinforcement particles in the ductile aluminium matrix places constraints on the plastic flow of the matrix leading to brittle failure with an increase in fly ash particles.

Wear Properties of an In-Situ Processed TiC-Reinforced Bronze

In this work, an Al-bronze alloy is reinforced with TiC through reaction of the alloy melt with methane gas. The resultant alloy is then centrifugally cast in cylindrical molds. It is found that the surface at the inner diameter of the cast contained in-situ produced TiC as well as Fe-rich inclusions. Metallographic observations using optical and scanning electron microscopy confirmed the presence of TiC particles (30 % volume), alpha and beta grains including iron precipitates. Cylindrical pins are machined from the inner surface and tested under various conditions in a three pin on disk Falex machine. Pins are tested under a constant load of 2.86 MPa and friction and wear rates are determined from measurements of weight losses versus wear lengths. It is found that under the applied load the reinforced material exhibits high friction and relatively low wear when compared with the unreinforced material. Apparently, under these conditions the TiC particles become abrasive particles thus contributing to wear of the steel counter-face through three body abrasive wear.

Elevated temperature mechanical behavior of CoSi and particulate reinforced CoSi produced by spray atomization and co-deposition

Monolithic CoSi and TiB2 reinforced CoSi materials were produced by spray atomization and co-deposition. The creep behavior of both materials at elevated temperature was investigated. The unreinforced material of grain size ≍25 μm exhibited a stress exponent of three, activation energy for creep of 320 kJ/mole, dislocation substructure of homogeneously distributed dislocations, and inverse creep transients upon stress increases. These results suggest that the creep behavior of CoSi is controlled by a dislocation glide mechanism. In contrast, the reinforced material of a finer grain size (≍10 μm) exhibited a stress exponent of unity, activation energy for creep of 240 kJ/mole, and negligible creep transients upon stress increases, suggesting that the creep behavior of the reinforced material is controlled by a diffusional creep mechanism. The creep resistance of the reinforced material was lower than that for the unreinforced material. This is a result of the finer grain size and higher porosity in the reinforced material.

Effects of reinforcing elements on the behavior of weakly cemented sands

Plane strain test results from weakly cemented sand samples with various types of reinforcement inclusions are reported. Mesh and anchored fibre types of reinforcements are shown to more than double the plane strain shear strength of a 33:1 sand–cement mixture. Other types of inclusions were not as effective, with some actually producing a strength decrease. All inclusions increased the ductility of this weakly cemented sand, allowing the material to absorb strains of 4–6% rather than the 0.5 – 1% of failure strain in the unreinforced material. The application of reinforcements to cemented tailings used for mine backfill is briefly discussed. Key words: reinforced backfill, cemented sand, behavior, mining.