High-performance sealants using rubber composites containing multiwalled carbon nanotubes (MWNTs) were developed in order to probe and excavate oil in deeper wells. However, the stress-strain behavior and the reinforcing mechanism of highly concentrated MWNT/rubber composites subjected to large deformation remain largely unexplored. Here we report on the complete stress-strain relationships of MWNT/rubber composites under uniaxial tension before rupture, with a suggestion of a novel reinforcement effect of high concentration of MWNTs. A theoretical model is developed to understand the reinforcing mechanism and estimate the mechanical properties of MWNT/rubber composites under large deformation. We have demonstrated that persistence length and reorientation of MWNTs during stretch have a significant impact on mechanical properties, such as the modulus of the rubber composite. These results provide guidelines for developing MWNT-reinforced composites to achieve desired nonlinear and extreme mechanical performance for a wide range of applications.
An ASTM standard scratch test is utilized to study the scratch behavior of polymeric coatings on soft and hard substrates. Depending on the different combination of polymeric coatings and substrates utilized, various damage modes can take place, which include coating delamination, transverse cracking, and buckling failure. A soft coating on a hard substrate will give rise to an entirely different scratch damage pattern from those of a hard coating on a soft substrate. The stress and strain responses of scratch on polymeric coating are analyzed using three-dimensional finite element (FE) simulation. The analysis provides mechanistic insights for the observed polymer coating deformation mechanisms and failure modes. Usefulness of the ASTM scratch method and FE modeling to evaluate polymer coating scratch behavior is discussed.
Interfacial shear strengths or static frictions between carbon nanotubes (CNT) in contact at different cross angles are studied by using atomic mechanics. It is shown that the axial interfacial shear strengths between parallel CNTs in commensurate are two orders of magnitude greater than those in incommensurate. This strong chiral dependence is not surprising and is similar to that of the friction between two graphite basal planes. In contrast, we find that the interfacial shear strengths of crossly contacted CNT pairs are much less dependent upon chirality. The estimated values of interfacial shear strengths, ranging from 0.05 to 0.35 GPa, agree very well with experimentally measured results available in the literature. These results may thus be used as a basis for explaining the observed tension strengths of CNT bundles and films that are mainly bonded by van der Waals interactions and the mechanical behaviors of composite materials with highly concentrated CNTs.
Hydrocarbons such as oil and gas are critical resources for the functioning of human societies. Today, with the dearth of easy-to-reach reservoirs, the oil and gas industry is conducting more of its exploration and exploitation activities in difficult-to-reach and harsh environments. Key challenges in exploiting these new reservoirs include extremely high temperatures and pressures. The rubber composites obtained from the carbon nanotubes cellulation technology increases operational ratings from 175 and 140 MPa to 260 and 240 MPa for deeper, hotter conditions, and it is especially appropriate for deepwater reservoirs. We believe that our development of the sealing material to enhance oil recovery from deep, hot reservoirs may help double the R/P ratio. The cellulation technologies can be applied to various matrix composites such as metals, ceramics, and other polymers.
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