Performance Assessment of the Post-Tensioned Anchorage Zone Using High-Strength Concrete Considering Confinement Effect

Post-tensioned anchorage zones need enough strength to resist large forces from jacking forces from prestress and need spiral reinforcement to give confinement effect. High-strength concrete (HSC) has high-strength and brings the advantage of reducing material using and simplifying reinforcing. We tested strain stabilization, load–displacement, and strain of lateral reinforcements. Specimens that used one and two lateral reinforcements without spiral reinforcement did not satisfy the strain stabilization. Load capacity also did not satisfy the condition of 1.1 times the nominal tensile strength of PS strands presented in ETAG 013. On the other hand, specimens that used three and four lateral reinforcements without spiral reinforcement satisfied the strain stabilization but did not satisfy 1.1 times the nominal tensile strength of PS strands. However, the secondary confinement effect could be confirmed from strain stabilization. In addition, the affection of HSC characteristics could be confirmed from a reinforcing level comparing other studies. The main confinement effect could be confirmed from the reinforcement strain results; there was a considerable difference between with and without spiral reinforcement at least 393 MPa. Comprehensively, main and secondary confinement effects are essential in post-tensioned anchorage zones. In addition, the performance of the anchorage zone could be increased by using HSC that the combination of high-strength and confinement effect.

A Data Mining Approach to Investigate the Carbon Nanotubes Mechanical Properties via High-Throughput Molecular Simulation

The relationship of geometrical properties and mechanical properties of carbon nanotubes (CNTs) was investigated by using high-throughput molecular simulation. Geometrical properties such as diameter, number of walls, chirality, and crosslink density were considered. As a key factor in determining the mechanical properties of composites reinforced with CNTs, nominal tensile strength is the focus in this study, which can be calculated by fracture force divided by the full cross-sectional area including the hollow core and the wall thickness. The fracture mode, nominal tensile strength, and nominal Young’s modulus under the condition of CNTs outermost tube loading axial tensile test were evaluated. Three types of fracture modes led by different crosslink densities of CNTs were obtained. By data-mining through large amounts of datasets, we showed that CNTs with small diameter, large number of walls, and crosslinks between walls can have high nominal tensile strength. We demonstrated that zigzag-type CNTs with crosslink density of approximately 1.5% - 2.5%, armchair-type CNTs with crosslink density of approximately 3% - 4% can help improve the load transfer from the outer tube to the inner tube the most.

Machine Learning-Assisted High-Throughput Molecular Dynamics Simulation of High-Mechanical Performance Carbon Nanotube Structure

Carbon nanotubes (CNTs) are novel materials with extraordinary mechanical properties. To gain insight on the design of high-mechanical-performance CNT-reinforced composites, the optimal structure of CNTs with high nominal tensile strength was determined in this study, where the nominal values correspond to the cross-sectional area of the entire specimen, including the hollow core. By using machine learning-assisted high-throughput molecular dynamics (HTMD) simulation, the relationship among the following structural parameters/properties was investigated: diameter, number of walls, chirality, and crosslink density. A database, comprising the various tensile test simulation results, was analyzed using a self-organizing map (SOM). It was observed that the influence of crosslink density on the nominal tensile strength tends to gradually decrease from the outside to the inside; generally, the crosslink density between the outermost wall and its adjacent wall is highly significant. In particular, based on our calculation conditions, five-walled, armchair-type CNTs with an outer diameter of 43.39 Å and crosslink densities (between the inner wall and outer wall) of 1.38 ± 1.16%, 1.13 ± 0.69%, 1.54 ± 0.57%, and 1.36 ± 0.35% were believed to be the optimal structure, with the nominal tensile strength and nominal Young’s modulus reaching approximately 58–64 GPa and 677–698 GPa.

An investigation of the effect of methyl cellulose and sodium polyacrylate on the hydrosorption properties of a vulcanisate based on chloroprene rubber*

The effect of hydrophilic additives – MC-2000 methyl cellulose and sodium polyacrylate – on the properties of a vulcanisate based on Neoprene W was studied. The rubber mixes were prepared in two stages: at the first stage, hydrophilic additives were introduced into the rubber; at the second stage, the remaining ingredients were introduced. Vulcanisation was carried out at a temperature of 150°C for 30 min. The viscosity of the rubber mixes, M, was measured at 120°C on an MVR 3000 Basic viscometer (MonTech), and the vulcanisation characteristics and vulcanisation rate, v, were measured on an MDR 3000 Basic rheometer (MonTech) at 170°C in accordance with ASTM D2084-79. From the results of these measurements it follows that, with the combined use of methyl cellulose and sodium polyacrylate, there is a synergistic reduction in M and in the vulcanisation rate of the rubber mixes. A vulcanisate containing both hydrophilic additives possesses the best hydrosorption properties and has satisfactory physicomechanical properties (nominal tensile strength, elongation at break, hardness, and tear strength). The values of these properties and their changes on exposure of the vulcanisate to distilled water (70°C, 24 h) meet the requirements laid down for water-swelling rubber sealing elements.

Rate-Dependent Scaling of Dynamic Tensile Strength of Quasibrittle Structures

This paper investigates the effect of strain rate on the scaling behavior of dynamic tensile strength of quasibrittle structures. The theoretical framework is anchored by a rate-dependent finite weakest link model. The model involves a rate-dependent length scale, which captures the transition from localized damage to diffused damage with an increasing strain rate. As a result, the model predicts a rate- and size-dependent probability distribution function of the nominal tensile strength. The transitional behavior of the strength distribution directly leads to the rate and size effects on the mean and standard deviation of the tensile strength. The model is verified by a series of stochastic discrete element simulations of dynamic fracture of aluminum nitride specimens. The simulations involve a set of geometrically similar specimens of various sizes subjected to a number of different strain rates. Both random microstructure geometry and fracture properties are considered in these simulations. The simulated damage pattern indicates that an increase in the strain rate results in a more diffusive cracking pattern, which supports the theoretical formulation. The simulated rate and size effects on the mean and standard deviation of the nominal tensile strength agree well with the predictions by the rate-dependent finite weakest link model.

Mechanical, thermal, and morphological properties of nanoporous reinforced polysulfone membranes

The effect of three different diphenols including 1,1′-thiobis(2-naphthol) (TBN), 2,2′-thiobis(4-methyl phenol) (TBMP) and curcumin (CUR) used in the preparation of sulfonated poly(ether sulfide sulfone) (SPESS) on the mechanical, thermal, and morphological properties of polysulfone (PSf) membranes was studied. In this regard, the morphological characteristics of the nanoporous membranes were explored by developed image analyzer program. Based on the obtained results, PSf membrane modified by SPESS-TBN copolymer showed the best nominal tensile strength in comparison to the other samples with the value of 206 MPa. The optimum real tensile strength with the value of 322 MPa was observed for SPESS-TBMP membrane. It was found that the addition of SPESS, improved the mechanical and thermal properties as well as the performance of membranes. Inspections of scanning electron microscopic images for evaluation of the void properties of membranes revealed that there were 42.3, 8.76, 41.45 and 15.92% of void contents within the structures of neat PSf membrane, SPESS-CUR, SPESS-TBMP and SPESS-TBN, respectively. Moreover, some conceptual relations between morphological and mechanical properties were presented. Finally, the effect of the membrane chemical structure on the mechanical, thermal, and morphological properties was discussed in this study.

High Strength and High Ductility in Electrodeposited Nanocrystalline Ni–W Alloy

The tensile specimen of nanocrystalline Ni–W alloys with 50 μm × 20 μm in area and 4 mm in gauge length was made by using an electrodeposit together with ultraviolet light lithographic technique. The composition and grain size were Ni-16.9 at.% W and about 6 nm, respectively. Tensile testing of the alloy was carried out. The nominal tensile strength and Young’s modulus were about 2.7 GPa and 123 GPa, respectively. The elastic strain and plastic strain were about 2 % and 1 %, respectively. The stress-strain curve showed work hardening. The macroscopic fracture part yielded necking and the microscopic fracture surface showed dimple pattern. As mentioned above, this electrodeposited nanocrystalline Ni-W alloy showed high strength, low elastic modulus and high ductility.