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Simulation analysis of the influence of changing mechanical characteristics of polyurethane foams
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The article analyzes the processes of attenuation of impulse loads in foam materials with closed-cell. In the framework of the couple stress elasticity, the analysis of the distribution of dynamic radial stresses in foam media with tunnel cavities of constant cross-section under the action of an impulse load of different duration applied to the cavity boundary in the radial direction is performed. An analytical-numerical approach is used for calculating of the dynamic stresses, which is based on the application of the Fourier transform over time and the modified boundary integral equation method. Numerical calculations of the dynamic stresses were performed using the method of mechanical quadrature and collocation method. The modified algorithm for discrete inverse Fourier transform was used for the calculation of the originals of the dynamic radial stresses. Based on the analysis of numerical calculations, the influence of the impulse duration on the attenuation rate of the pulse load in foam media is established.
The article is devoted to developing a method for assessing the optimality of the mechanical characteristics of foam materials based on using the Cobb-Douglas model within the framework of Cosserat mechanics. The results of experimental studies for foamed polymer materials with closed cells were used for modeling. The Cobb-Douglas model used for modeling allows accounting for the nonlinear dependence of the Shear modulus on the density and cell sizes of the material. The developed approach allows the evaluation of the influence of material density and pore sizes on changes in shear-rotational waves in the medium. Based on the approaches proposed in the work, the analytical-numerical modeling method is convenient and practical for foam, porous, and other structurally heterogeneous materials. The advantage of this approach is the ability to evaluate the mechanical characteristics of foam-structure materials widely used in production without special laboratory tests. This approach significantly expands the scope of the application of foamed polymers.KeywordsPolyurethane FoamCosserat ElasticityShear-Rotation WaveCobb–Douglas ModelR&D Investment
This paper shows the experimental results of impact hammer tests conducted on sand and composite sand-polyurethane samples at different confining pressures. It was found that polyurethane can mitigate the propagation of waves generated by an impact, thereby influencing seismic isolation. Also, accelerations in the composite samples were reduced in relation to the percentage of polyurethane present. A theoretical lumped-mass model (calibrated based on the experimental results) interpreted the experimental results and enabled an in-depth parametric analysis. This analysis shows that the proposed isolation method is efficient, as the damping coefficient of the polyurethane and the soil/polyurethane impedance ratio increased.
It exists an unchanging requirement in modern society to achieve an ideal fuel economy using light acoustic packaging with good sound absorption performance. The Polyurethane (PU) foam with excellent damping properties usually has the characteristics of low mass and low density. Therefore, it is often considered as an ideal sound‐absorbing packaging material. With the further research on the PU foam, we have learned that the inherent microstructure of the PU foam has a special effect on its sound absorption performance. In this paper, the authors theoretically demonstrate the effect of cell size, connectivity and relative pore diameter on sound absorption performance by numerical simulation analysis. From the numerical simulation analysis, the results show that the three cellular structure factors have different effects on the parameters of the Johnson‐Champoux‐Allard (JCA) acoustic model, and all of them can improve the sound absorption coefficient of PU foam. Additionally, the further analysis indicates that the relative pore diameter is the most vital factor to improve the sound absorption performance in the entire frequency domain. This research could be applied to industrial production to reduce the amount of acoustic packaging material used in vehicles while improving the acoustic quality of vehicles. Soybean oil‐based polyol replaces part of petroleum polyol to prepare polyurethane foam. The foam microstructure is replicated to create periodic unit cell models. The theoretical sound absorption coefficients of different models are obtained by using Johnson‐Champoux‐Allard acoustic model. The effects of cell size, relative pore diameter, and connectivity on sound absorption performance are studied through experiments and simulations.
This work examines elastic wave propagation phenomena in open-cell foams with the use of the Bloch wave method and finite element analysis. Random foam topologies are generated with the Surface Evolver and subsequently meshed with Timoshenko beam elements, creating open-cell foam models. Convergence studies on band diagrams of different domain sizes indicate that a representative volume element (RVE) consists of at least 83 cells. Wave directionality and energy flow features are investigated by extracting phase and group velocity plots. Explicit dynamic simulations are performed on finite size domains of the considered foam structure to validate the RVE results. The effect of topological disorder is studied in detail, and excellent agreement is found between the wave behavior of the random foam and that of both the regular and perturbed Kelvin foams in the low-frequency regime. In higher modes and frequencies, however, as the wavelengths become smaller, disorder has a significant effect and the deviation between regular and random foam increases significantly.
This paper investigates the ability of a syntactic epoxy foam and an expanded polyurethane foam to mitigate intense (several GPa) and short duration (T < 1 µs) stress waves. Plate impact and electron beam irradiation experiments have been conducted to study their dynamic mechanical responses. Interferometer Doppler Laser method is used to record the target rear surface velocity. A two-wave structure associated with the propagation of an elastic precursor and the compaction of the pores has been observed. The compaction stress level deduced from the velocity measurement is a good indicator of mitigation capability of the foams. Quasi-static tests and dynamic soft recovery experiments have also been performed to determine the compaction mechanisms of these polymeric foams. In the polyurethane foam, the pores were closed by elastic buckling of the matrix and damage of the cellular structure. In the epoxy foam, the compaction is due to the crushing of glass microspheres. A strain rate dependent compaction model successfully represents the macroscopic response of these polymeric foams.
Experiments and simulations are performed to study the interaction of solitary waves in a granular crystal with a plastically compressible and rate-sensitive test medium in the form of rigid polyurethane (PU) foam. We study the effects of the foam's compressive strength and elastic modulus on the nonlinear wave dynamics near the interface and on the formation of reflected solitary waves. Experiments are conducted using a granular crystal composed of a vertical array of spherical steel particles, directly contacting the foamed polyurethane samples. Single solitary waves are generated in the chain through striker particle impact, and the temporal profiles of the incident and reflected solitary waves are recorded by placing an instrumented sensor particle in the chain. The measurements show that travel time and wave amplitude of the reflected solitary waves are highly sensitive to the elasto-plastic properties of the inspection medium, particularly when the intensity of the incident solitary waves is increased. The measurements were compared to the predictions obtained with a coupled discrete/finite element model and good agreement was reported. The predictions show that when the amplitude of the incident solitary wave increases, the response transitions from an elastic regime to a regime dominated by plastic compression.
This article describes the experimental investigation of Cosserat (or micropolar) elasticity and surface damage effects in closed-cell polymethacrylimide foams of different densities. The method of size effects was used to find the degree of Cosserat behaviour for both cylindrical and square cross-section specimens in bending and torsion. The foams were found to behave as Cosserat materials in which slender specimens appear less stiff than thick ones, provided sufficient care is taken when machining the specimens. Surface damage caused by the machining process may cause the apparent stiffness to decrease with decreasing specimen size, giving an opposite softening size effect.
Wave propagation characteristics in nanoporous metal foam nanobeams
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