Finite Element Analysis on the Unloading Elastic Modulus of Aluminum Foams by Unit-cell Model
This paper presents finite element analyses (FEA) on the unloading elastic moduli of aluminum foams under uniaxial loading and bending conditions. The unit-cell model of Gibson and Ashby was utilized in the FEA with elasto-perfectly plastic material. Compression, tension, and bending tests simulations were carried out using Abaqus software. The non-linearity effect caused by structural imperfection/buckling of unit-cell was incorporated. From the compressive test simulation, it was confirmed that the results showed good agreement with the referred experimental data. This means that the developed FE model can be regarded as an RVE model of aluminum foams. Then, the deformation characteristic and elastic modulus obtained from all simulations were compared and examined. As the results, the elastic modulus obtained from bending test demonstrated higher value than that of under uniaxial loads. This discrepancy increases gradually as the relative density decreases. The mechanism responsible for generating the discrepancy in stiffness was discussed. Furthermore, this work points out the necessity of measuring both Young’s and flexural moduli for designing an engineering structure using foam materials especially when accuracy and precision are demanded.
Investigation of Compressive Behavior of Pre-folded Thin-walled Column Fabricated by 3D Printing
This paper reveals the mechanical behavior of thin-walled columns with pre-folded patterns subjected to compressive loading. The column specimens (Polylactic Acid) are fabricated using Fused Deposition Modeling 3D printer and subjected to quasi-static compressive loading to investigate their mechanical behavior (by modifying the specimens' cross-section patterns and folding angles). The column specimens are simulated by finite element analysis to understand how the stress distribution and local deformation affecting the stiffness, strength, and overall deformation. The experiments showed that introducing the pre-folded pattern in a thin-walled column with different cross-sections can dramatically lower its structural stiffness (85%) and compressive strength (69%), but increase its deformability (115%), which is good agreement with numerical simulation. The variation of cross-section patterns and pre-folding angle could effectively modify the compressive mechanical behavior. Moreover, the results demonstrate how the FDM 3D Printing method can be used in fabricating a thin-walled column with irregular shapes and then to modify its deformability. This finding can be useful for designing any complex structures requiring specific stiffness and deformation such as suspension devices, prosthetic devices in biomechanics, and robotic structures.
Acetylation analysis of saccharides. 2. Microanalysis of neutral glycosphingolipids by means of acetylation with radioactive acetic anhydride.
Abstract The quantitative analysis of mixtures of glycosphingolipids by acetylation with radioactive acetic anhydride and separation by thin-layer chromatography is described. The method was primarily developed for screening of glycosphingolipid composition of tissues, cultured cells, and virus preparations. The sensitivity and linearity of the method is demonstrated. Although theoretically a much higher sensitivity is achievable, in practive about 10 −9 g of glycosphingolipid can be detected and tentatively identified. As an example, the acetylation pattern of lipids from a preparation of herpes simplex virus is demonstrated.