Геометричне моделювання плетіння сіткополотна в невагомості за допомогою інерційного розкриття подвійного маятника

We proposed a geometrical model for weaving a wire cloth using the oscillations of a system of two-link pendulums within an abstract plane and under conditions of weightlessness. It is expected to initiate oscillations through the application of pulses to each of the nodal elements of each of the pendulums, induced by two pulse jet engines. The pendulums are arranged in line on the platform, aligned with an abstract plane. The plane moves in the direction of its normal using the jet engines. Attachment points of the dual pendulums are selected so that when unfolded their last loads come into contact. Upon simultaneous initiation of oscillations of all pendulums and setting the platform in motion, we consider traces from the spatial displacements of the last loads of pendulums. It is assumed that wire that accepts the shape of the specified traces comes from the last loads and forms the zigzag-like elements of the mesh. In order to fix elements of the mesh, it is suggested that they should be point welded at the moments of contact between the last loads of the pendulums. A description of the inertial unfolding of dual pendulums is compiled using a Lagrange equation of the second kind, in which potential energy was not taken into consideration because of weightlessness. Reliability of the considered geometrical model for weaving a wire cloth was verified in a series of created animated videos that illustrated the process of formation of the elements of a wire cloth. Results might prove useful for designing large-sized structures in weightlessness, for example, antennas for ultralong waves.Предложен способ изготовления в невесомости металлического сетеполотна при помощи колебаний ряда двухзвенных маятников. Колебания возникают благодаря влиянию на узлы элементов маятника импульсов двух реактивных двигателей, тем самым обеспечивая его инерционное раскрытие. Описание процесса инерционного раскрытия маятника выполнено с помощью уравнения Лагранжа второго рода. Результаты целесообразно использовать при проектировании масштабных сетеполотен, например активных поверхностей антенн длинноволнового диапазона, и их изготовления в условиях невесомостиЗапропоновано спосіб виготовлення у невагомості металевого сіткополотна за допомогою коливань ряду подвійних маятників. Коливання виникають завдяки впливу на вузли елементів маятника імпульсів двох реактивних двигунів, тим самим забезпечуючи його інерційне розкриття. Опис процесу інерційного розкриття маятника виконано за допомогою рівняння Лагранжа другого роду. Результати доцільно використати при проектуванні масштабних сіткополотен, наприклад активних поверхонь антен довгохвильового діапазону, та їх виготовлення в умовах невагомост

Modeling aging and mechanical rejuvenation of amorphous solids

The elasto-viscoplasticity of amorphous solids is modeled, with a focus on the effects of physical aging and mechanical rejuvenation. Using nonequilibrium thermodynamics, the concept of kinetic and configurational subsystems has been employed. The Hamiltonian structure of reversible dynamics is exploited to derive a constitutive relation for the stress tensor. Furthermore, it is demonstrated that accounting for mechanical rejuvenation results in a modification of the driving force for viscoplastic flow

Concurrent two-scale model for the viscoelastic behavior of elastomers filled with hard nanoparticles

\u3cp\u3eA dynamic two-scale model is developed for describing the mechanical behavior of elastomers filled with hard nanoparticles. Using nonequilibrium thermodynamics, a closed system of evolution equations is derived, coupling continuum mechanics with a fine-scale description on the level of filler particles. So doing, a constitutive stress–strain relation emerges that is applicable to transient situations. In addition to the number density of filler particles, the particle arrangement is captured by the distribution of the difference vector between two representative interacting particles, which makes this model efficient in comparison with many-particle models. The two-particle model presented here is analyzed numerically in oscillatory deformation, for two purposes. First, the nonlinearity of the model is studied in detail, in terms of the Payne effect, that compares favorably with the literature. And second, the two-particle model is compared with a corresponding many-particle model in the literature.\u3c/p\u3

Two-scale model for the effect of physical aging in elastomers filled with hard nanoparticles

\u3cp\u3eA two-scale model is developed, and solved numerically, to describe the mechanical behavior of elastomers filled with hard nanoparticles. Of particular interest is the slow recovery of the elastic modulus after large-amplitude oscillatory deformation. To account for this effect, the physical aging of the glassy bridges between the filler particles is captured with two thermal degrees of freedom for the matrix material, namely a kinetic and a configurational one. Formulating the two-scale model enriched with aging in a nonequilibrium thermodynamics context, first results in a constitutive relation for the Cauchy stress tensor. Second, the dynamics of physical aging is described, which eventually results in the slow recovery of the elastic modulus with waiting time. The proposed model is investigated numerically under large amplitude oscillatory shear deformation. Of particular interest in this respect is the coupling of the micro-scale dynamics with the physical aging on the macroscopic scale. This coupling is examined in detail, both in an approximate way using a Gaussian approximation, as well as numerically, under specific conditions. It turns out that the CONNFFESSIT approach (Laso and Öttinger 1993 [46]) can not be employed for the numerical solution of the model under arbitrary loading conditions because of the novel structure of the two-level coupling term. While a procedure for solving the model numerically for the case of strong applied deformation is presented in this paper, other solution methodologies need to be sought for the cases of weak and no applied deformation.\u3c/p\u3

Two-subsystem thermodynamics for the mechanics of aging amorphous solids

The effect of physical aging on the mechanics of amorphous solids as well as mechanical rejuvenation is modeled with nonequilibrium thermodynamics, using the concept of two thermal subsystems, namely a kinetic one and a configurational one. Earlier work (Semkiv and Hütter in J Non-Equilib Thermodyn 41(2):79-88, 2016) is extended to account for a fully general coupling of the two thermal subsystems. This coupling gives rise to hypoelastic-type contributions in the expression for the Cauchy stress tensor, that reduces to the more common hyperelastic case for sufficiently long aging. The general model, particularly the reversible and irreversible couplings between the thermal subsystems, is compared in detail with models in the literature (Boyce et al. in Mech Mater 7:15-33, 1988; Buckley et al. in J Mech Phys Solids 52:2355-2377, 2004; Klompen et al. in Macromolecules 38:6997-7008, 2005; Kamrin and Bouchbinder in J Mech Phys Solids 73:269-288, 2014; Xiao and Nguyen in J Mech Phys Solids 82:62-81, 2015). It is found that only for the case of Kamrin and Bouchbinder (J Mech Phys Solids 73:269-288, 2014) there is a nontrivial coupling between the thermal subsystems in the reversible dynamics, for which the Jacobi identity is automatically satisfied. Moreover, in their work as well as in Boyce et al. (Mech Mater 7:15-33, 1988), viscoplastic deformation is driven by the deviatoric part of the Cauchy stress tensor, while for Buckley et al. (J Mech Phys Solids 52:2355-2377, 2004) and Xiao and Nguyen (J Mech Phys Solids 82:62-81, 2015) this is not the case

First characterization of a novel grain calorimeter: the GRAiNITA prototype

International audienceA novel type of calorimeter based on grains of inorganicscintillating crystal readout by wave length shifting fibers isproposed. The concept and main features as well as the prototypedesign are introduced and the first results obtained using cosmicrays are presented. The number of photo-electrons generated bycosmic rays muons in the prototype detector is estimated to be ofthe order of 10000 photo-electrons per GeV, validating the conceptof this next-generation shashlik calorimeter