Numerical Simulation of Mechanical Properties of Cellular Materials Using Computed Tomography Analysis

Numerical simulation on thermal properties of closed-cell metal foams with different cell size distributions and cell shapes

The dynamic responses of layered polyvinyl chloride (PVC) foam sandwich panels under air blast loads were investigated by employing 3D numerical simulation method. PVC foam of different densities and Kevlar composite were selected, respectively, as core and face sheets of sandwich panels. The quasi-static mechanical behavior of PVC foam was tested by a quasi-static compression experiment. Two types of density-graded panels (three-layer foam core and six-layer foam core) were analyzed under different explosive charge to explore the effect of gradient arrangement and the layer number of foam core. The validation of the simulation approach was studied by a comparison of simulation results with the existing experimental results from the literature. The deformation characteristics, support reactions and energy absorption of sandwich panels were analyzed to explore the blast resistance of the graded foam sandwich structures. It can be found that the gradient strategy of foam core has a significant influence on the PVC foam sandwich panel under air blast loads, and increasing the thickness of the back sheet is an effective measurement to improve the blast resistance of PVC foam sandwich panel with Kevlar face sheet.

Epoxy-modified bismaleimide (BMI) foams were prepared through prepolymerization and foaming. Density-adjustable BMI foams with closed-cell structures were produced. The influence of prepolymerization time on bubble growth and morphology, as well as the compressive and heat resistant properties of the foams, were thoroughly investigated. BMI prepolymerization was an effective method for controlling the bubble growth rate, the bubble size and its distribution, and the foam density. As the prepolymerization time increased, the matrix viscosity, the number of cells per unit volume and the foam density increased, whereas, the bubble growth rate and cell size decreased, and the cell size distribution became narrower. The compressive strength and modulus increased with increasing prepolymerization time. The dimensional stability temperatures of the BMI foams were all above 200°C, as determined by their base materials, and were unaffected by prepolymerization time.

Numerical simulations of mechanical properties of alumina foams based on computed tomography

Numerical simulation of the actual bridge deck overlay of asphalt mixture performance, interface unit is thin, leading to the final simulated pavement displacement value is too large, do not meet the actual mechanics for this problem is proposed based on virtual reality overlay of asphalt mixture performance numerical simulation deck. The bridge deck pavement is described by the method based on continuum mechanics, the mechanical values are generated, the ductile damage rule is used to judge the output mechanical values, the mechanical performance model is constructed, and the virtual reality technology is used to realize the numerical simulation and complete the research and analysis. The asphalt mixture with certain parameters is selected to make the bridge deck pavement components, and the experimental environment is set up. Two traditional numerical simulation methods and the researched numerical simulation methods are used to carry out the experiments. The results show that: the bridge deck paving obtained by the researched numerical simulation method displacement value closest to the actual value of displacement, numerical simulation results more accurate.

The diffusion influence of seawater on the static and interlayer cracking properties of a polyvinyl chloride foam sandwich structure is investigated in this study. After soaking specimens in seawater for various durations, various comparison tests are performed to investigate the effects of seawater. Compression tests for H60 and H200 polyvinyl chloride foam specimens are conducted to study strength and modulus degradation, and the results show that immerging time and temperature have significant effects on polyvinyl chloride foam properties. Tensile tests for glass-fibre-reinforced plastic panels, four-point bending tests and double cantilever bending tests for polyvinyl chloride foam sandwich specimens are also performed. The results show that seawater immerging treatment has a noticeable influence on glass-fibre-reinforced plastic tensile properties and interlayer critical energy release rate values, but has almost no effect on bending properties of foam sandwich specimen. Furthermore, a rate-dependent phenomenon is observed in double cantilever bending tests, in which higher loading rate will lead to larger critical energy release values. Numerical simulation is also performed to illustrate the cracking process of double cantilever bending tests and shows a certain accuracy. The simulation also demonstrates that the viscoelasticity of foam material after immerging treatment results in the rate-dependent characterization of double cantilever bending tests.

Natural rubber (NR) foams reinforced by a physical hybrid of nanographene/carbon nanotubes were fabricated using a two-roll mill and compression molding process. The effects of nanographene (GNS) and carbon nanotubes (CNT) were investigated on the curing behavior, foam morphology, and mechanical and thermal properties of the NR nanocomposite foams. Microscope investigations showed that the GNS/CNT hybrid fillers acted as nucleation agents and increased the cell density and decreased the cell size and wall thickness. Simultaneously, the cell size distribution became narrower, containing more uniform multiple closed-cell pores. The rheometric results showed that the GNS/CNT hybrids accelerated the curing process and decreased the scorch time from 6.81 to 5.08 min and the curing time from 14.3 to 11.12 min. Other results showed that the GNS/CNT hybrid improved the foam’s curing behavior. The degradation temperature of the nanocomposites at 5 wt.% and 50 wt.% weight loss increased from 407 °C to 414 °C and from 339 °C to 346 °C, respectively, and the residual ash increased from 5.7 wt.% to 12.23 wt.% with increasing hybrid nanofiller content. As the amount of the GNS/CNT hybrids increased in the rubber matrix, the modulus also increased, and the Tg increased slightly from −45.77 °C to −38.69 °C. The mechanical properties of the NR nanocomposite foams, including the hardness, resilience, and compression, were also improved by incorporating GNS/CNT hybrid fillers. Overall, the incorporation of the nano hybrid fillers elevated the desirable properties of the rubber foam.

SummaryBackgroundFirst tarsometatarsal joint (TMT-1) hypermobility might cause hallux valgus deformity (HV), and recurrence following surgical correction. Anatomic findings, indicating tibialis anterior tendon (TAT) involvement in TMT‑1 stabilization, led to the development of cross-glide test allowing clinical TMT‑1 stability testing. Cross-glide test function was evaluated in anatomical specimens and in the clinical setting, compared to simulated weight-bearing computer tomography (CT) analysis.MethodsCross-glide test was evaluated in 6 healthy lower leg specimens before and after TAT transection. Clinical testing was performed prospectively in 36 feet (6 controls, 21 HV, 9 recurrent HV); consecutive weight-bearing CT analysis was performed. Results from clinical testing were compared to CT analysis.ResultsTMT‑1 instability significantly increased in anatomic specimens following TAT transection (p = 0.009). In the clinical setting, all healthy feet were cross-glide test negative, 62% of HV cases and all recurrent HV feet were positive. In the CT analysis- Compared to controls the HV cases revealed significantly increased MT‑1 internal rotation (p = 0.003) and decreased dorsal angle (p = 0.002), considered as collapsing forefoot signs; HV recurrent cases revealed similar results. Positive cross-glide tested cases revealed increased MT‑1 internal rotation values (p < 0.001) and dorsal angle values (p < 0.001) in CT analysis. Strikingly, cross-glide test positive HV cases revealed significantly increased internal TMT‑1 rotation (p = 0.043) in CT analysis, and HV and IMT (intermetatarsal) angle were significantly higher (p = 0.005, p = 0.006). 15 HV recurrence cases, treated with TMT‑1 arthrodesis, revealed no recurrence during follow-up.ConclusionCross-glide test allows reliable clinical TMT‑1 instability testing, via TAT tension, and is less laborious than CT analysis. We recommend TMT‑1 arthrodesis in cases with instability in clinical testing, to avoid HV recurrence.Video onlineThe online version of this article contains one video. The article and the video are online available (10.1007/s00508-020-01705-x). The video can be found in the article back matter as “Electronic Supplementary Material”.

Representative elementary volumes required to characterize the normal spectral emittance of silicon carbide foams used as volumetric solar absorbers

ABSTRACTIn this paper, the effects of silicone surfactant on the mechanical, thermal, and acoustical properties of flexible polyurethane foams are studied. At first, by introducing the reactions of the foam production and expressing the stoichiometric relationships, a method is provided to select the amounts of the basic compounds for getting the desirable properties. By knowing the OH number of polyol and the NCO content of isocyanate after selecting an amount of a blowing agent for the reaction, the quantity of each compound to produce the desirable foam can be found. Then different foams with various amounts of surfactant are produced. By preparing proper samples, the mechanical, thermal, nonacoustical, and acoustical properties of the foams are measured or calculated by using different instruments. The nonacoustical properties are obtained based on two distinct methods, i.e., a semiphenomenological method and an indirect method. The obtained properties are validated by comparing the calculated theoretical sound absorption coefficients with the measured ones. The results show that with a small increase of surfactant, the acoustical properties of foam samples improve by about 50% without any significant changes in other mechanical and thermal properties of the foams. This improvement results from the variations of reticulation rate and cell size. In addition, the initial desirable porosity and density considered in the stoichiometric relations are fairly achieved in produced samples. These results validate the accuracy of the stoichiometric relations.

This research evaluates the rheological and mechanical properties of polymer- and nanomaterials-modified bitumen by incorporating nanosilica (NSA), nanoclay (NCY), and Acrylonitrile Styrene Acrylate (ASA) at 5% by weight of the bitumen. The samples were prepared at 165 °C for one hour to obtain homogeneous blends. All samples were subjected to short- and long-term aging to simulate the effects of different operating conditions. The research conducted a series of tests, including consistency, frequency sweep, and multiple creep stress and recovery (MSCR) using the dynamic shear rheometer (DSR) and bending beam rheometer (BBR). The results showed that all modified bitumen outperformed the neat bitumen. The frequency sweep showed a higher complex modulus (G*) and lower phase angle (δ), indicating enhanced viscoelastic properties and, thus, higher resistance to permanent deformation. The BBR test revealed that the bitumen modified with NCY5% has a creep stiffness of 47.13 MPa, a 51.5% improvement compared to the neat bitumen, while the NSA5% has the highest m-value, a 28.5% enhancement compared with the neat bitumen. The MSCR showed that the modified blends have better recovery properties and, therefore, better resistance to permanent deformation under repeated loadings. The aging index demonstrated that the modified bitumen is less vulnerable to aging and maintains their good flexibility and resistance to permanent deformations. Finally, these results showed that adding 5% polymer and nanomaterials improved the bitumen’s’ performance before and after aging by reducing permanent deformation and enhancing crack resistance at low temperatures, thus extending the pavement service life and making them an effective alternative for improving pavement performance in various climatic conditions and under high traffic loads.

The paper gives an overview of issues relating to the characterisation of the progressive collapse of core cellular materials used in sandwich construction. The specific structural application addressed is foreign object impact, and in this case the core cellular material is subject to multi axial stresses, progressive collapse and possible rupture. Crushable foams have been used for many years as core materials. Possible foam materials are based on polymers (e.g. Divinycell, Rohacell), metals (e.g. Alporas) and graphite. It has been shown that the mechanical properties of cellular materials, e.g. elastic behaviour, uniaxial crush and densification, are dependent on the cell geometry, on the cell size (foam density) and on the parent material.

Influence of Recycled Polyurethane Polyol on the Properties of Flexible Polyurethane Foams

The local series system with typical common plate rubber support/pier in highway reinforced concrete girder bridge is the object of the current research. The finite element numerical simulation method is used to study sensitive parameters – the mechanical properties of the series system under the horizontal load. The simulated results show that the interface bonding strength between the bearing and adjacent structure is reduced; the equivalent shear deformation and the horizontal force of bearing under horizontal load change insignificantly with the increase of horizontal displacement. However, the total shear deformation and equivalent shear deformation increase with the increase of the axial compression ratio. In addition, the top horizontal force and displacement of the pier significantly decrease with reduction of the connection strength at both ends of the bearing. Therefore, adjusting the axial compression ratio of the pier and interfacial connection mode can obviously affect the mechanical properties of the support and adjacent structure, even the failure mode of the local structure. This approach can help estimate the mechanical properties of the existing bridge and determine the reasonable maintenance plan.

In this study, experimental investigation and numerical simulation of the compressive stiffness, effective plastic stress-strain behaviour, the hardness and thermal stability of tin alloy parts subjected to equal channel angular extrusion (ECAE) process were investigated. The numerical simulation was carried out using Automatic Dynamic Incremental Non-linear Analysis (ADINA) and the results were compared with the experiment. The as-received and extruded Sn alloy samples were subjected to metallographic examination using scanning electron and optical microscopy. The external fracture that was observed during ECAE did not show at the interior parts on the optical image. The results of compressive and hardness tests showed that stiffness, modulus, and hardness values increased with the number of extrusions. However, the maximum compressive stress and strain also increased marginally after the second ECAE pass. The thermal properties and transformations of the sample were studied with differential scanning calorimetry (DSC). The effective strain of the samples was simulated and observed to increase with each extrusion pass. The severe plastic deformation brought about by ECAE processing increased dislocation density (work hardening) in the affected parts accounting for an increase in the modulus of the alloy. ECAE processing is, therefore, a potential tool for enhancing the mechanical properties of tin alloy.