Modelisation of Thermally Induced Jitter in a Slender Structure

The thermomechanical interactions of onboard space vehicles is an interesting field of research and study. Since the pioneering paper by Bruno Boley, published in 1954, many authors have given their relevant contribution to the comprehension of phenomena not otherwise investigable if not with a cross-sectoral approach and a multidisciplinary methodology. The anomaly that occurred to the spacecraft Alouette 1, in 1962, marked the beginning of a long series of unexpected events due to unconceivable coupling between the mechanical and thermal behaviour of the system. This work aims to emphasise, by means of a simple model, the basic mechanism responsible for elastic vibrations induced by a thermal shock. This is a widespread event experienced by a spacecraft during the transitions shadow-sun and vice-versa or when a flexible appendage, previously shadowed by the spacecraft's main body, comes to the light as a consequence of an attitude manoeuvre [Ulysses, 1990]. For the investigation, a very slender structure has been considered in order to make the thermal and mechanical characteristic times comparable and realise the conditions of strong coupling. The accurate thermal analysis provides an equivalent thermal bending moment, depending on time, which appears as a boundary condition in the subsequent modal analysis of the structural element, where it plays the role of a trigger of elastic transverse vibrations.

Investigation of deformation behavior of PETG-FDM-printed metamaterials with pantographic substructures based on different slicing strategies

Based on the progress and advances of additive manufacturing technologies, design and production of complex structures became cheaper and therefore rather possible in the recent past. A promising example of such complex structure is a so-called pantographic structure, which can be described as a metamaterial consisting of repeated substructure. In this substructure, two planes, which consist of two arrays of beams being orthogonally aligned to each other, are interconnected by cylinders/pivots. Different inner geometries were taken into account and additively manufactured by means of fused deposition modeling technique using polyethylene terephthalate glycol (PETG) as filament material. To further understand the effect of different manufacturing parameters on the mechanical deformation behavior, three types of specimens have been investigated by means of displacement-controlled extension tests. Different slicing approaches were implemented to eliminate process-related problems. Small and large deformations are investigated separately. Furthermore, 2D digital image correlation was used to calculate strains on the outer surface of the metamaterial. Two finite-element simulations based on linear elastic isotropic model and linear elastic transverse isotropic model have been carried out for small deformations. Standardized extension tests have been performed on 3D-printed PETG according to ISO 527-2. Results obtained from finite-element method have been validated by experimental results of small deformations. These results are in good agreement with linear elastic transverse isotropic model (up to about [Formula: see text] of axial elongation), though the response of large deformations indicates a nonlinear inelastic material behavior. Nevertheless, all samples are able to withstand outer loading conditions after the first rupture, resulting in resilience against ultimate failure.

Modeling the interaction of a beam of elastic vibrations with the surface of an object under acoustic non-destructive testing

Physical and mathematical models are developed that describe the refraction by a concave cylindrical surface of a field of an elastic transverse wave arbitrarily incident on a surface from a liquid. Immersion control of a small-diameter pipeline is considered. Keywords acoustics, ultrasound, immersion control, physical and mathematical model, bent surface, small-diameter pipeline. [email protected]

Justification of parameters of vehicles with elastic partitions for transporting potatoes

Elastic partitions have been developed to be installed in the body of a vehicle and allowing to reduce damage to tubers when unloading by reducing the speed and, accordingly, the interaction of potatoes with the working surfaces of the machine and neighboring tubers. A mathematical model of a device for transporting and unloading root crops has been developed, taking into account the physical properties of root crops, the physical and geometric characteristics of the container and elastic partitions, as well as the parameters of the unloading process. As a result of comparative field tests of a serial MAZ 5516 truck body and an experimental MAZ 5516 truck body with installed transverse partitions, it was found that the use of the developed elastic transverse partitions reduces damage to potato tubers from 5.3% to 2.9%.

Elastic transverse electron scattering form factors of 11Li exotic nucleus

The elastic transverse electron scattering form factors have been studied for the 11Li nucleus using the Two- Frequency Shell Model (TFSM) approach. The single-particle wave functions of harmonic-oscillator (HO) potential are used with two different oscillator parameters bcore and bhalo. According to this model, the core nucleons of 9Li nucleus are assumed to move in the model space of spsdpf. The outer halo (2-neutron) in 11Li is assumed to move in the pure 1p1/2, 1d5/2, 2s1/2 orbit. The shell model calculations are carried out for core nucleons using the spsdpf-interaction. The elastic magnetic electron scattering of the stable 7Li and exotic 11Li nuclei are also investigated through Plane Wave Born Approximation (PWBA). It is found that the difference between the total form factors of unstable isotope (11Li halo) and stable isotope 7Li is in magnitude. The measured value of the magnetic moment is also reproduced.

Improved quasi-static twin-fiber transverse compression of several high-performance fibers

The method of determining the quasi-static transverse compressive response of several high-performance polymer fibers was improved upon from a previous twin-fiber transverse compression setup in order to detect small initial high compliance signals while maintaining consistent diametral compression. Two fibers were laid parallel between two polished tool steel platens, and the fibers were subsequently compressed using a piezo-electric actuator at quasi-static rates. The new experimental setup ensures that the compression cycle begins when extremely small load signals are detected so that initial elastic transverse moduli may be more accurately measured. Nominal stress–strain curves were obtained for several types of high-performance fibers. The results show good agreement with previously obtained measurements. S-glass fibers exhibited a vastly different mechanical response compared to the polymer fibers.