The uses of carbon nanotubes (CNTs) in nanotechnology and leading industries are of extreme importance and they have many applications. One such application is producing nanotube thin pages called buckypaper. These pages, known as nanotube sheets, have significant physical, chemical, mechanical, thermodynamic and electromagnetic properties, such as being several times stronger than steel. In spite of e orts devoted to the development of procedures for the production of buckypaper, not many attempts have been made to understand their mechanical behavior. Computer simulations can be used as a powerful tool to discover the mechanical properties of these materials. The aim of the present research is to investigate the mechanical behavior of buckypaper using the finite element method. Toward this goal, the molecular network of buckypaper, which consists of a regular arrangement of CNTs, is modeled as a structure with its atoms as nodes, its bonds as 3-D-beam elements and Van der Waals forces by means of nonlinear forces. A computer program is then developed to calculate the mechanical properties of buckypaper especially the modulus of elasticity. In this program, the nanotubes are arranged together to create a simple ordered network with periodic boundary conditions resembling real buckypaper. The obtained results from this procedure are compared with those derived from molecular mechanics.

Background: The purpose of this in vitro study was to evaluate the effect of five different surface treatments on the mechanical property and antimicrobial effect of three desiccated glass ionomer cements. Materials and Methods: In this in vitro experimental study, 300 rectangular blocks of three different restorative materials were fabricated using an aluminum mold, Group I (n = 100) Micron bioactive, Group II (n = 100) GC Fuji IX GP Extra, and Group III (n = 100) bioglass R. These blocks were stored in 100% humidity for 24 h and then placed in air to desiccate for another 24 h. These groups were further divided into two major groups (n = 50) for both mechanical (Flexural) and antimicrobial testing. The blocks of mechanical and antimicrobial groups were further divided into five subgroups (n = 10) based on the medias used for surface treatment (senquelNaF, MI varnish, chlorhex plus, kedodent mouthwash, and 100% humidity [control]). Flexural strength (FS) was measured using the universal testing machine. Fracture strength of groups was compared using the one‑ way analysis of variance and Tukey’ s post hoc test with P ≤ 0. 05 considered statistically significant. Antimicrobial effect was carried out by covering the specimens in a suspension of Streptococcus mutans followed by incubation for 24 h. The blocks were later washed, vortex mixed, serially diluted, and plated. Ccolony‑ forming unit/ml was calculated after 3 days of incubation. Data were then analyzed using the Kruskal– Wallis and Mann– Whitney U nonparametric test, with P ≤ 0. 05 considered statistically significant. Results: Micron bioactive with the surface treatment of MI varnish significantly exhibited highest FS. Surface treatment of desiccated restorative materials with chlorhex plus exhibited no growth of S. mutans. GC Fuji IX GP Extra with surface treatment of MI varnish exhibited highest reduction in S. mutans growth compared to other experimental group. Conclusion: Surface treatment of restorative material with MI varnish improved their mechanical and antimicrobial property while among three restorative materials Micron bioactive showed better mechanical property, whereas GC Fuji IX GP Extra exhibited better antimicrobial property.

The friction stir process (FSP) is a solid state process, which has been used to insert reinforcing particles into the structure of a material to create a composite with improved properties. Magnesium is a light structural metal that is increasingly used in the aerospace and automobile industries. In this research, SiC nanoparticles were added to AZ31 alloy using FSP in two overlaps of 100% and 50% passes. In 100% pass overlapping, nanoparticles were added in 4, 8 and 16 volume percentages and in 50% pass overlapping only nanoparticles in 4 volume percent were added. The FSP process performed as 4 consecutive passes in both overlaps along with rapid cooling. Microstructure, hardness and tensile strength of created composites were examined. The results suggested that adding reinforcing materials causes reduction in the size of the grains, uniformity of structure and increase in the hardness of material. SiC nanoparticles distributed uniformly through the AZ31 alloy. By increasing volume fraction of reinforcing materials, yield stress of the material increased but ultimate stress and formability properties reduced. In 50% overlapping state, the yield stress in directions, either parallel or perpendicular to the pin direction, increased rather than 100% overlapping state, but the ultimate stress and elongation properties reduced. This reduction was greater in the perpendicular direction relative to the pin direction.