Polyether ether ketone (PEEK) is a high-performance, semi-crystalline thermoplastic that is used in a wide range of engineering applications, including some structural components of aircraft. The design of new PEEK-based composite materials can be greatly facilitated with a precise understanding of the multiscale structure and behavior of semi-crystalline PEEK. Molecular Dynamics (MD) modeling can efficiently predict the response of single-phase polymers at the nanometer length scale, and micromechanics can be used to predict the bulk-level properties of multi-phase materials based on the microstructure. In this study, MD modeling was used to predict the mechanical response of the amorphous and crystalline phases of PEEK. Employing the MD simulation results as input, the hierarchical microstructure of PEEK, which combines these two phases, was modeled using NASA's micromechanics MSGMC (Multi-Scale Generalized Method of Cells) code. The predicted bulk mechanical properties of semi-crystalline PEEK agree well with the scientific literature data, thus validating the multiscale modeling approach. Thus, the proposed multiscale modeling method can be used to accurately and efficiently predict the mechanical response of other micro-structurally complex polymer systems.
Pisani, W., Radue, M., Chinkanjanarot, S., Bednarcyk, B., Pineda, E., Waters, K., Pandey, R., King, J. A., & Odegard, G. M. (2019). Multiscale modeling of PEEK using reactive molecular dynamics modeling and micromechanics. Polymer, 163, 96-105. Retrieved from: -p/2087
Unlike the bulk boron compounds, boron clusters Bn (n < 20) are quasiplanar, or even planar, with a symmetrical bond distribution, aromatic [11-13] and their existence is confirmed by the experiment . From the Aufbau principle postulated by Boustani  it follows that these quasiplanar isomers are more stable than their icosahedral counterparts. Recently Szwacki et al.  have predicted the existence of a planar and aromatic boron compound, named borozene, which has strong similitudes with benzene.
The decrease of the bond length average by increasing the size of the cluster is also seen in the Coronene 19, i.e., a molecule of Coronene surrounded by a series of benzene rings, where, by using the same level of calculation, a 0.021 Å decrease of the same parameter is found with respect to the Coronene. It is also interesting to note that the reduction of the bond length takes place in particular in the inner bonds which tend to have the same value. The cohesive energies, evaluated in the minimal basis set for both clusters, were of 6.437 eV for B6 and 6.449 eV for B24. These values were calculated from
Do you have any conflicting interests *Conflicting interests helpClose Conflicting interests help Please list any fees and grants from, employment by, consultancy for, shared ownership in or any close relationship with, at any time over the preceding 36 months, any organisation whose interests may be affected by the publication of the response. Please also list any non-financial associations or interests (personal, professional, political, institutional, religious or other) that a reasonable reader would want to know about in relation to the submitted work. This pertains to all the authors of the piece, their spouses or partners.
We discuss a systematic methodology that leads to the reconstruction of the material profile of either single, or assemblies of one-dimensional flexural components endowed with Timoshenko-theory assumptions. The probed structures are subjected to user-specified transient excitations: we use the complete waveforms, recorded directly in the time-domain at only a few measurement stations, to drive the profile reconstruction using a partial-differential- equation-constrained optimization approach. We discuss the solution of the ensuing state, adjoint, and control problems, and the alleviation of profile multiplicity by means of either Tikhonov or total variation regularization. We report on numerical experiments using synthetic data that show satisfactory reconstruction of a variety of profiles, including smoothly and sharply varying profiles, as well as profiles exhibiting localized discontinuities. The method is well suited for imaging structures for condition assessment purposes, and can handle either diffusive or localized damage without need for a reference undamaged state. 59ce067264