A thorough understanding of the decomposition of perfluoropolyether (PFPE) lubricants is crucial to achieve heat-assisted magnetic recording (HAMR). In contrast to previous studies, which focused on thermal and catalytic decompositions, we gain insights into the mechano-chemical decomposition of PFPE films confined between the head and disk by performing reactive molecular dynamics simulations with our new ReaxFF force field. By quantifying the decomposition time constants under the operation conditions of HAMR, we infer that, within a heating time of ∼1 ns, pure thermal decomposition hardly occurs, whereas mechano-chemical decomposition is highly likely to occur. The decomposition rate constant of the PFPE films subjected to confined shear increases with normal pressure. The increase is well-fitted by a linear stress-activated Arrhenius curve at high normal pressures, whereas this is not the case at low normal pressures. We caution against extrapolating the linear stress-activated Arrhenius curve, which could cause significant overestimation of decomposition rate constants at low normal pressures. We find that the mechano-chemical decomposition of PFPEs is mainly attributed to the dissociation of C–OH and ether C–O bonds in the polar end groups, and in the main chain, the C–O bond is more likely to dissociate than the C–C bond.

No abstract

Braided carbon fiber reinforced plastics (CFRPs) can be employed in the construction of pressurized vessels to increase performance and reduce overall weight. However, owing to the complex braiding structures resulting from the braiding process, an analysis of the elastic modulus is important as it affects the hoop stress on the pressure vessel. In this study, braided preformed CFRP constructed on a steel cylinder subjected to internal pressure was experimentally investigated using a simple approach that involved estimating the elastic modulus and hoop stress. Five types of braided preformed CFRP with different braiding angles and number of applied layers were analyzed. The elastic modulus and hoop stress can be estimated from these measurements of the internal pressure. The differences in the braided structures result in different strain values and affect the elastic modulus. High braiding angles tend to be more stable against high internal pressure, and exhibit small strain differences and high elastic modulus in the hoop direction. Similar results were observed when additional layers were applied. Increasing the braiding angle and the number of layers can increase the average elastic modulus.

No abstract

No abstract