Sparse Approximations of the Schur Complement for Parallel Algebraic Hybrid Solvers in 3D

<正>In this paper we study the computational performance of variants of an algebraic additive Schwarz preconditioner for the Schur complement for the solution of large sparse linear systems.In earlier works,the local Schur complements were computed exactly using a sparse direct solver.The robustness of the preconditioner comes at the price of this memory and time intensive computation that is the main bottleneck of the approach for tackling huge problems.In this work we investigate the use of sparse approximation of the dense local Schur complements.These approximations are computed using a partial incomplete LU factorization.Such a numerical calculation is the core of the multi-level incomplete factorization such as the one implemented in pARMS. The numerical and computing performance of the new numerical scheme is illustrated on a set of large 3D convection-diffusion problems;preliminary experiments on linear systems arising from structural mechanics are also reported.     

Physical aging phenomena in silica and glass beads filled elastomers (EPDM)

The physical aging concept is generally used to explain the typical behavior of amorphous glassy materials such as amorphous polymers. It can be easily evidenced by measuring the effect of a static deformation on the dynamic mechanical properties. In this paper, an attempt is made to determine the “glassy” behavior of elastomeric EPDM chains when they are confined in the vicinity of the filler (glass beads, silicas) surface. It is demonstrated that glassy behavior and physical aging phenomena are detected even with a filled elastomer. Furthermore, the influence of the filler volume fraction, the filler nature and of filler surface treatments with silanes were studied. Finally, an original attempt is made to explain filler-rubber reinforcement by a kind of bimodal network created from linkages between a densely packed interfacial region and the outer loose matrix.     

Synthesis and properties of segmented poly(hydroxyether-siloxane)

Segmented or block poly(hydroxyether-siloxane) copolymers were synthesized by both a monomer-oligomer or an oligomer-oligomer synthetic approach. Perfectly alternating sequence distributions were obtained from the monomer or oligomer(s) bearing mutually reactive end groups, and the hydroxyether linkages are formed simultaneously with the growth of the second block. Differential scanning calorimetry (DSC), Dynamic Mechanical Thermal Analyzer (DMTA), and small angle X-ray scattering (SAXS) results indicated that microphase separated morphologies were achieved for each of the copolymers, even those structures synthesized by the monomer-oligomer route. The mechanical properties of the networks ranged from a rubber toughened thermoplastic to a thermoplastic elastomer and depended on which phase was predominantly continuous.