Behavior of Confined Concrete using Prestressing Skew Bars

This paper presents the results of an experimental study on the biaxial compression behavior of concrete prism confined using pre-stressed bars. The pre-stressed bars could provide passive confinement stress, that preventing the lateral strain of the prism from increasing leading to an increase in both the initial modulus of elasticity and prism compressive strength. The confined concrete had a higher compressive strength that was directly proportional to the confinement bar pressing force and lower ductility than the plain prisms. The concrete initial modulus of elasticity is directly proportioned to the confinement lateral pressure of the prestressing bar and inversely proportion with the spacing between prestressing bars. It was simple to find out that the best pre-stressing stress was 10 N/mm2, also the compressive strength of the confined concrete with pre-stressed skew bars was greater than the compressive strength of the unconfined concrete by more 3.3 times.

Strain-Softening Characteristics of Hydrate-Bearing Sediments and Modified Duncan–Chang Model

Marine hydrate exploitation may trigger the seabed geological disaster, such as seafloor collapse and landslide. It is critically important to understand the mechanical properties of hydrate-bearing sediment. Strain-softening observation is a typical behavior of hydrate-bearing sediment (HBS) and exhibits more significant at higher hydrate saturation. This paper performed a series of triaxial compression tests on methane hydrate-bearing sand to analyze the influence rule and mechanism of hydrate saturation on the strain-softening characteristic, stiffness, and strength and introduced the strain-softening index to quantificationally characterize the strain-softening behaviors of HBS with different hydrate saturations. Based on the analyses on the mechanical behavior of HBS, the Duncan–Chang model is extended to address the stress-strain curves of HBS. Two empirical formulas with hydrate saturation embedded are used to characterize the enhanced initial modulus and strength for HBS, respectively. To address the strain-softening behavior of HBS, the modified Duncan–Chang model introduced a damage factor into the strength of HBS. To validate the modified Duncan–Chang model, four different triaxial compression tests are simulated. The good consistence between simulated result and experimental data demonstrates that the modified Duncan–Chang model is capable of reflecting the influence of hydrate saturation not only on the stiffness and strength but also on the strain-softening characteristics of HBS.

Constitutive Model of N15 Propellant considering the Confining Pressure Effect

To describe the effect of confining pressure on the mechanical responses of N15 propellant, a constitutive model considering the confining pressure effect was first established for N15 propellant based on the elastic-viscoelastic correspondence principle. Then, the mechanical properties of N15 solid propellant under different confining pressures were obtained using confining pressure test system, and the obtained results indicate that the initial modulus of propellant did not change with confining pressure, but the maximum tensile strength, rupture strength, the maximum elongation, and elongation at break increased with increasing confining pressure. In conjunction with propellants’ mesoscopic structure and cross-section analysis, the mechanical mechanism of confining pressure effect on propellant was initially disclosed. Due to confining pressure, the particle dewetting inside the propellant was reduced, the hole propagation was delayed, and crack extension inhibited germination, proving that confining pressure has a strengthening impact on the propellant. Finally, assuming that the model parameters were dependent on pressure, the model parameters acquisition and validation were conducted. The results demonstrated that constitutive model can describe confining pressure influence on the mechanical properties of N15 propellant accurately.

Applying Feasibility Investigation of Resin Modifying Agent in Asphalt Pavement Materials

In order to promote the resin modifying agent applied into pavement materials, a type of resin modifying agent was selected as the modifier to prepare modified asphalt. The molecular crystal structure of the modifying material was characterized by using the X-ray diffraction test (XRD). The microstructure and element composition of PA6 was investigated through focused ion beam scanning electron microscopy (FIB-SEM). The thermal property and functional groups of PA6 were studied by thermogravimetric analysis-Fourier infrared spectroscopy (TG-FTIR) test. The physical property and rheological properties of PA modified asphalt were evaluated to confirm the applying feasibility of PA6 in asphalt. The results indicated that PA6 was the semicrystalline polymer and the existence of γ crystal form might improve the toughness of asphalt materials effectively. The thermal decomposition process of PA6 could be divided into three stages roughly: inert weight loss stage, rapid weight loss stage, and stable stage. The amount of PA6 modifier should be appropriately controlled during the application process to ensure the comprehensive effect of PA6 on high-temperature performance and low-temperature performance. The corresponding initial modulus attenuation value of PA modified asphalt was less than 70# asphalt under the same test conditions.

Charaterizations of 3D printed re-entrant pattern/aramid knit composite prepared by various tilting angles

This study intended to compare and analyze the Poisson's ratio and mechanical properties of aramid knit (ARNT), 3D printed auxetic re-entrant pattern (3DP-RE), and 2 types of composite fabrics manufactured with ARNT and 3DP-RE. Specimens were manufactured by 3D printing the re-entrant pattern with a CFDM (conveyor fused deposition modeling) 3D printer and TPU (thermoplastic polyurethane) filament, combining with aramid knit in 2 ways. Then, Poisson's ratio, bending, compression, and tensile properties were tested. As a result of Poisson's ratio, 3DP-RE and its 2 types of composite fabric showed negative Poisson's ratio at all angles and deformed stable at 0° and 90° than the bias direction. The bending strength confirmed that the composite fabric showed a lower value. But, the strain at max bending strength was greater than a substrate fabric. At the compression properties, it has been confirmed that compression strength and toughness are improved when manufacturing composite fabrics. As a result of tensile properties, 3DP-RE and composite fabrics were significantly more initial modulus, elongation and toughness than ARNT and were shown to be the largest in gradient 90°. Therefore, it is confirmed that the performance is excellent when fabricated as a 3DP-RE/ARNT composite fabric, and based on the results of studies, we intend to use it as the basic data for composite fabrics of auxetic structure suitable for shoe uppers.

Effect of Microstructure on Micro-Mechanical Properties of Composite Solid Propellant

This study was aimed at determining the effect of microstructure on the macro-mechanical behavior of a composite solid propellant. The microstructure model of a composite solid propellant was generated using molecular dynamics algorithm. The correlation of how microstructural mechanical properties and the effect of initial interface defects in propellant act on the macro-mechanics were studied. Results of this study showed that the mechanical properties of propellant rely heavily on its mesoscopic structure. The grain filling volume fraction mainly influences the propellant initial modulus, the higher the volume fraction, the higher initial modulus. Additionally, it was found that the ratio of particles influences the tensile strength and breaking elongation rate of the propellant. The big particles could also improve the initial modulus of a propellant, but decrease its tensile strength and breaking elongation rate. Furthermore, the initial defects lowered the uniaxial tensile modulus, tensile strength, and the relaxation modulus of propellant, but did not affect the relaxation behavior of the propellant.

Influence of Injection Rate on Mechanical Properties of the Molding Composition Based on Polyamide 6 and Carbon Nanotubes

This paper is devoted to obtaining and investigating polymer composites based on polyamide-6 and carbon nanotubes. Polyamide 6, type 210/310, was used as a polymer matrix, and carbon nanotubes manufactured by OcSiAl were used as a modifier. The components were compounded in a co-rotating twin-screw extruder HAAKE Rheomex OS PTW 16 to obtain granulate. The granulate was processed by injection molding on a Babyplast 6/10V machine to obtain test samples as double-sided blades (ISO-527-2, type 5A). Elastic strength tests were carried out on a Gotech UAI-7000M universal tensile-testing machine. It has been shown that introduction of 0.15% CNT promotes an increase in the yield point and the initial modulus of elasticity with a significant decrease in the ultimate strength. The maximum value of the tensile strength (161 MPa) has been obtained for the specified composition at an injection rate of 12.9 ml/s.

Investigation of Small- to Large-Strain Moduli Correlations of Rockfill Materials – Application to Romaine-2 Dam

Establishment of a relationship between the shear wave velocity (Vs) and other geotechnical parameters of rockfill soils at large strains (oedometer modulus, Moedo, tangent modulus, Et) is considered a significant step towards more precise modelling of earth-structure deformation behaviour. In this study, four samples of different gradations, reconstituted from the rockfill materials used in the construction of the Romaine-2 dam, were experimented to correlate the small strain to large strain moduli. Development of Moedo and Vs with consolidation was measured in the laboratory using the piezoelectric ring-actuator technique (P-RAT) incorporated in a large oedometer. Therefore, a correlation between Moedo and small strain shear modulus Go was proposed. Moreover, numerical simulations were performed based on the Duncan-Chang hyperbolic model to correlate the Vs to Duncan-Chang initial modulus(Ei). Based on the experimental and numerical data, a relation between Ei and Vs of the tested rockfill has been established. Verification studies were also carried out on in-situ measurements during Romaine-2 dam construction, proofing the ability of the proposed relationships to predict Ei related to the minor principal stress (σ3) from in-situ Vs measurement. The proposed correlations could help the geotechnical designers to estimate accurately the deformation of rockfill materials from in-situ Vs measurement.

Analysis of PLA Composite Filaments Reinforced with Lignin and Polymerised-Lignin-Treated NFC

Polylactic acid (PLA) is one of the most suitable materials for 3D printing. Blending with nanoparticles improves some of its properties, broadening its application possibilities. The article presents a study of composite PLA matrix filaments with added unmodified and lignin/polymerised lignin surface-modified nanofibrillated cellulose (NFC). The influence of untreated and surface-modified NFC on morphological, mechanical, technological, infrared spectroscopic, and dynamic mechanical properties was evaluated for different groups of samples. As determined by the stereo and scanning electron microscopy, the unmodified and surface-modified NFCs with lignin and polymerised lignin were present in the form of plate-shaped agglomerates. The addition of NFC slightly reduced the filaments’ tensile strength, stretchability, and ability to absorb energy, while in contrast, the initial modulus slightly improved. By adding NFC to the PLA matrix, the bending storage modulus (E’) decreased slightly at lower temperatures, especially in the PLA samples with 3 wt% and 5 wt% NFC. When NFC was modified with lignin and polymerised lignin, an increase in E’ was noticed, especially in the glassy state.

Combustion Characteristics of Nanoaluminium-Based Composite Solid Propellants: An Overview

The nanosized powders have gained attention to produce materials exhibiting novel properties and for developing advanced technologies as well. Nanosized materials exhibit substantially favourable qualities such as improved catalytic activity, augmentation in reactivity, and reduction in melting temperature. Several researchers have pointed out the influence of ultrafine aluminium (∼100 nm) and nanoaluminium (<100 nm) on burning rates of the composite solid propellants comprising AP as the oxidizer. The inclusion of ultrafine aluminium augments the burning rate of the composite propellants by means of aluminium particle’s ignition through the leading edge flames (LEFs) anchoring above the interfaces of coarse AP/binder and the binder/fine AP matrix flames as well. The sandwiches containing 15% of nanoaluminium solid loading in the binder lamina exhibit the burning rate increment of about 20–30%. It was noticed that the burning rate increment with nanoaluminium is around 1.6–2 times with respect to the propellant compositions without aluminium for various pressure ranges and also for different micron-sized aluminium particles in the composition. The addition of nano-Al in the composite propellants washes out the plateaus in burning rate trends that are perceived from non-Al and microaluminized propellants; however, the burning rates of nanoaluminized propellants demonstrate low-pressure exponents at the higher pressure level. The contribution of catalysts towards the burning rate in the nanoaluminized propellants is reduced and is apparent only with nanosized catalysts. The near-surface nanoaluminium ignition and diffusion-limited nano-Al particle combustion contribute heat to the propellant-regressing surface that dominates the burning rate. Quench-collected nanoaluminized propellant residues display notable agglomeration, although a minor percentage of the agglomerates are in the 1–3 µm range; however, these are within 5 µm in size. Percentage of elongation and initial modulus of the propellant are decreased when the coarse AP particles are replaced by aluminium in the propellant composition.