Bending stiffness of circular multilayer van der Waals material sheets

We study the bending stiffness of symmetrically bent circular multilayer van der Waals (vdW) material sheets, which corresponds to the non-isometric configuration in bulge tests. Frenkel sinusoidal function is employed to describe the periodic interlayer tractions due to the lattice structure nature and the bending stiffness of sheets is theoretically extracted via an energetic consideration. Our quantitative prediction shows good agreement with recent experimental results, where the bending stiffness of different types of sheets with the comparable thickness could follow a trend opposite to their Young's moduli. Based on our model, we propose that this trend may experience a transition as the thickness decreases. Apart from the apparent effects of Young's modulus and interlayer shear strength, the interlayer distance is also found to have an important impact on the bending stiffness. In addition, according to our analysis on the size effect, the bending stiffness of such symmetrically bent circular sheets can steadily own a relatively large value, in contrast to the cases of isometric deformations.

Effect of sizing agent on interfacial properties of carbon fiber-reinforced PMMA composite

The surface treatment of carbon fibers (CFs) was carried out using a self-synthesized sizing agent. The effects of sizing agent on the surface of CFs and the interface properties of CF/polymethyl methacrylate (PMMA) composites were mainly studied. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and static contact angle were used to compare and study the CFs before and after the surface treatment, including surface morphology, surface chemical element composition, and wettability of the surface. The influence of sizing agent on the mechanical properties of CF/PMMA resin composite interface was investigated. The results show that after sizing treatment, the CF surface O/C value increased by 35.1% and the contact angles of CF and resin decreased by 16.2%. The interfacial shear strength and interlayer shear strength increased by 12.6%.

Influence of Polymer Matrix Chemical Nature and Molding Technology on the Quality of Carbon Fiber Reinforced Polymer Parts

The experimental research results of porosity, interlayer shear strength and flexural modulus of carbon fiber reinforced plastics (CFRP) depending on the chemical composition of the binder and molding technology are presented. The standard vacuum infusion technology and its two modifications differing in vacuum bag assembling order and initial material are applied. The best characteristics of CFRP are achieved with the improved technology №2 using two vacuum bags. The differences between two compounds with various hardener chemical nature are compared. Optimal characteristics are obtained by using compound with diaminodiphenylsulfone hardener.

Factors Affecting the Interlayer Shear Strength of Laboratory and Field Samples

Asphalt emulsion is the most widely used tack coat material in the U.S. The objective of this study is to investigate factors that may affect the interlayer bond shear strength of asphalt emulsion tack coats of both laboratory and field compacted samples. The laboratory study included six types of tack coat materials applied on two surfaces with two residual application rates. The field study phase involved validation of the interlayer shear performance findings using field cores extracted from paving projects. The field study included taking cores of the existing layer, emulsions used for interlayer bonding, and loose mixes of new asphalt layers. Materials were collected to produce the laboratory prepared specimens for comparison with the field cores. Results of the laboratory study demonstrate that there is a direct relationship between the roughness (texture) of the existing surface and the interlayer shear strength (ISS) between two surfaces. Statistical analysis provided a strong correlation and indicated that 79% of the data variance can be explained with surface texture, emulsion type, application rate, and replicate effects. Comparing field cores with laboratory produced samples showed no clear relationship between the shear strength of laboratory and field specimens. It is speculated that the difference in compaction of the upper layers in the laboratory and field, and effect of shearing during coring of the samples from the field, resulted in higher laboratory shear values relative to field core values. The study highlights major challenges in using laboratory prepared samples to predict field behavior of tack coats.

Effect of Emulsion Type on Bond Behavior of Asphalt Concrete Layers in Cold Regions

Tack coat materials, which are typically emulsified bituminous products, are used to provide a sufficient bond between asphalt concrete (AC) layers/lifts. Owing to construction limitations and severe temperature variations in cold regions, agencies are investigating the use of fast curing and non-tracking emulsions as tack coat materials. The objective of this study is to evaluate the performance of various tack coat products in cold climates. Several tack coat products were installed during a field study in Saskatchewan, Canada. The tack coat products included slow setting, medium setting, and three proprietary fast curing/non-tracking emulsions. Core samples were collected three weeks after construction to evaluate the initial interlayer shear strength (ISS) for typical construction conditions in cold regions. Although the ISS values for all of the products, except one SS-1 section, varied in a narrow range, this does not indicate that all products will have a similar long-term performance. The modes of failure for the bond strength samples were classified into two types according to the shape and location of the failure surface: type A and type B. Failure type B indicates that the tack coat material can successfully provide sufficient bond strength to make the two AC lifts behave as one thick homogenous layer. The results showed that the failure mode should be included as an evaluation criterion in addition to ISS. The results showed that the energy required to reach peak shear stress is a comprehensive parameter that should also be considered when evaluating tack coat materials.