Influence of Force Chains Behaviors on Strength of Al/W/PTFE Granular Composite

Mesoscale simulation is conducted to investigate the effect of force chains between metal particles on the mechanical behavior of aluminum-tungsten-polytetrafluoroethylene (Al/W/PTFE) granular composite under a strain-controlled loading. A two-dimensional model followed the random distribution of particles is developed. Dynamic simulations are performed with variations in the size of Al particles to reveal the strength and fracture mechanisms of the composites. The results indicate that, force chains governed by the number and the size of metal particles significantly affects the global compressive response and macro-cracks propagation. The stability and reconstruction of mesoscale force chains explain the phenomenon that a higher strength is observed in the material with fine Al particles. Combined with the angle between particles, we examine the properties of force chains and the network as they evolve during the course of the deformation. Findings indicate that reactive composites tend to produce shorter chains, and straighter force chains with a smaller force angle result in a macroscopically stronger granular material.

Effects of mechanical and electronic properties for B2 FeAl modified by several kinds of point defects: First-principles study

Elastic, fracture and deformation behavior of B2 FeAl intermetallics modified by ternary additions as well as Al/Fe vacancy defects and anti-sites have been investigated based on density functional theory (DFT). Formation enthalpy indicates that ternary additions Sc, Y, Mo and W have a preference for Al site. While Fe site is more easily replaced by ternary Cu and Zn. Moreover, vacancy and antisite defects can be stable in FeAl. Pugh criteria ([Formula: see text] ratio), Poisson’s ratio [Formula: see text] and Cauchy pressure show that Sc, Y, Mo, W and Al vacancy (Al anti-site by Fe atom) can effectively improve the ductility of FeAl. Dislocation emission and micro-cracks propagation show that the improved ductility is due to the promoted dislocation emission but suppressed micro-cracks propagation. Bonding analyses reveal that the improved ductility is mainly own to the weakened the covalent interactions and strengthened the metallic interactions.

Crack assessment of RC beam-column joints subjected to cyclic lateral loading using Acoustic Emission (AE): The influence of shear links aspect

Existing reinforced concrete (RC) beam-column joints that are designed mainly to resist gravity load, may encounter serious problems in low to moderate seismic regions. The moderate earthquake in Ranau affected numerous old buildings, caused by uncontrolled cracks propagation found in RC member, beam-column joint. Effects of the shear reinforcement between offset links on cracks formation on RC beam-column joints were investigated under cyclic lateral loading with acoustic emission (AE) technique monitoring. The control specimen (BCJ-1) without additional shear reinforcement showed more irregular cracks thus concrete cover spall observed at early DR level compared to other specimens with shear reinforcement between offset links. Sudden drop of AE hits beyond 2.25% DR level with significant increase in crack width showed that BCJ-1 was no longer able to resist higher loads due to de-bonding between reinforcement and concrete. From RA-AF graphs, failure was exhibited according to DR stages with respect to crack characteristics.

Mechanical and morphology properties of titanium oxide-epoxy nanocomposites

In the current work, the influences of titanium oxide (TO) on nanocomposites using epoxy (EP) resin have been investigated. EP resin was added to various contents in terms of volume of TO (6%). Based on the casting method, the TO-EP nanocomposites were prepared. Mechanical properties in terms of tensile, impact and hardness properties exhibited improvements in the mechanical results of the TO-EP nanocomposites. The experimental results exhibited that the enhancement in the tensile strength, impact, and hardness was found to be 14 MPa, 40.1 J/mm2 and 228.9 HV, respectively. Moreover, the effect of the strength has decreased compared with pointing to brittleness that increased the TO-EP nanocomposites. Field emission scanning electron microscopy (FESEM) analysis was used to perform a microstructure analysis which in turn revealed how TO obstruction the cracks propagation in the nanocomposites. The interface between the TO and the EP nanocomposites was observed using the FESEM images. The results highlighted that the TO-EP nanocomposites can be used a wide range of industrial applications such as biomedical application.

Inner stress analysis through methods of X-ray diffractometry in deposited metal and in periweld area by alloy rare-earth elements

Through the methods of X-ray diffractometry there are defined values of residual stresses in a weld metal and a periweld area obtained by hand arc welding deposition with experimental powder wires with the different rare-earth element composition of the Tomtorsky deposit (Yakutia, Russia). It is revealed that in the deposited metal and in the periweld area (PWA) with REM there are formed tensile inner stresses. In weld metal and in the PWA deposited with wire containing 0.7% of REMs there are revealed tensile inner residual stresses which cam serve as an additional mechanism restraining a formation stage and delaying a process of post-welding cracks propagation. An optimum composition of powder wires with the modifying REM admixture is offered.

Measurement of strength and microstructural characteristics of epoxypolimers cured by thermal and microwave methods

In this work, we studied the strength parameters, fractographic patterns, and the microstructure of epoxy polymer samples cured both by thermal and microwave methods at various temperature, power, and time conditions. The dependence of strength on curing conditions is determined using the tensile test method. To achieve maximum strength for both curing methods optimum conditions were found. A comparative fractographic analysis of microwave and thermal cured samples fractures having similar strength characteristics was carried out by electron microscopy. It was found that microwave field curing leads to the globules size increase in the cured epoxy polymer and an increase in the number of nanopores in the material. Plastic samples local deformation is also more pronounced during fracture, which leads to a greater difference of the main and secondary cracks propagation velocities ratio. The relationship between the studied samples optical density in the wavelength range from 360 to 2500 nm and the parameters of both curing methods (microwave and thermal) was established.

Fracture failure analysis of the pump shaft

The failure reasons of the circulating pump shaft in the upper section of the quench tower were analyzed by means of chemical composition analysis, macroscopic observation, metallographic examination and fracture section analysis. The analysis result shows that the calcium-silicate inclusions in the surface of the pump shaft cause the microcracks and the parallel fatigue sources, which leads to the fatigue cracks propagation under alternating load and finally the shaft is fatigue fractured.