Science and Technology of Materials最新文献

In this study, a novel space holder is used for the fabrication of Si foams. The space holder is a graphite composite (GC) with regular spheroidal cells. Conventional space holder materials are not suitable for casting Si foams. The main issue in this context is the differences between the melting point of the foam's base material and the one of common space holders. GC offers many advantages as e.g. low cost, good dissolution by oxidation, high melting point and non-toxicity. This type of space holder is chemically stable when being in contact with liquid and solid Si, and it is, hence, suitable for a melt metallurgical processing route. Si foams are manufactured by applying replication casting. The resulting foam geometry and its surface are analyzed using LM and SEM. XRD measurements are performed to investigate the quality of the Si foam in terms of contamination by graphite or oxygen.

Auxetics are characterized by a negative Poisson's ratio, expanding/contracting in tension/compression. Given this behavior, they are expected to possess high shear, fracture and indentation resistance, and superior damping. The lack of natural isotropic auxetics promoted an effort to design structures that mimic this behavior, e.g. reentrant model. This last is based on honeycombs with inverted protruding ribs. Commonly, this model is employed in lattices and has been thoroughly studied in terms of mechanical properties and deformation behavior. Given that the amount of cells has an influence in the overall internal structural behavior, there seems to be an absence of data that determines the minimum number of cells for such structure to present internal static bulk properties. Recurring to FEA, this study determines the minimum number of cells to obtain an overall face constrained auxetic lattice with internal bulk elastic behavior, namely in terms of normalized Young's modulus and Poisson's ratio. It is shown that adding reentrant cells increases the Poisson's ratio on an exponential rise to maximum function, reducing the normalized Young's modulus on an exponential decay function. Fundamentally, a minimum number of 13 cells per row to obtain an internal bulk behavior in lattices with constrained faces.

The analysis of the structural behaviour of heterogeneous materials is a topic of research in the engineering field. Some heterogeneous materials have a macro-scale behaviour that cannot be predicted without considering the complex processes that occur in lower dimensional scales. Therefore, multi-scale approaches are often proposed in the literature to better predict the homogeneous mechanical properties of these materials. This work uses a multi-scale numerical transition technique, suitable for simulating heterogeneous materials, and combines it with a meshless method – the Radial Point Interpolation Method (RPIM) [1]. Meshless methods only require an unstructured nodal distribution to discretize the problem domain. In the case of the RPIM, the numerical integration of the integro-differential equation from the Galerkin weak form is performed using a background integration mesh. The nodal connectivity is enforced by the overlap of influence-domains defined in each integration point. In this work, using a plane-strain formulation, representative volume elements (RVE) are modelled and periodic boundary conditions are imposed on them. A computational homogenization is implemented and effective elastic properties of a composite material are determined. In the end, the solutions obtained using the RPIM and also a lower-order Finite Element Method are compared with the ones provided in literature.

It is well known that the global climate change is the largest challenge for the society of the 21st century. For managing the resulting consequences, innovative materials become more and more important. Open cell metal foam contributes promising solutions to light-weight design, battery applications and renewable energy harvesting. Still, challenges are present concerning the cutting into a defined shape. Remote laser cutting offers a solution for decreasing the production costs as well as the needed component accuracy. Our investigations reveal that this technique has a high potential concerning cutting speed of open cell aluminum foam, which was increased by more than 500% compared to state-of-the-art laser separation. Furthermore, different material thicknesses up to 20 mm were investigated. Additionally, the limit of the possible contour wall width was decreased to less than the size of one pore. This paper offers insight into the viability of remote laser cutting in overcoming the challenges dealing with mechanical milling or grinding. Investigating the process concerning thermal stress input as well as particle attachments will be the next steps in the future.

Metallic cellular materials are characterized by a low specific weight and a high energy absorption capability, which make them promising for application in devices of the transportation industry in order to meet the requirements of a reduced fuel consumption and carbon dioxide output. This intention necessitates the evaluation of material performance under several load conditions. Investigations have shown that the out-of-plane properties with regard to specific energy absorption (SEA) capability of high-density steel honeycomb structures with square-celled profile are outstanding while the potential under in-plane conditions is distinctly lower. Therefore, FEM-based numerical analyses are conducted by the use of ABAQUS-software to investigate the influence of cell geometry. The results reveal an enhancement of absorbable energy in in-plane direction by applying an ordered sequence of hexagons and triangles, the so-called Kagome geometry. Comparative quasi-static compression tests serve to verify the FE-analysis. The obtained results are discussed with respect to strength level and achieved SEA capability in dependence of the cell geometry and load condition.

The auxetic cellular structures build from inverted tetrapods were fabricated and experimentally tested using uniaxial compression tests in two orthogonal directions. Based on experimental results, the computational models using homogenised material model were developed and validated in LS-DYNA. Furthermore, the computational models based on Smooth Particle Hydrodynamic (SPH) method for simulation of blast loading conditions were developed, verified and validated according to the data available in literature. This computational model was then used to simulate the crush behaviour of composite sandwich panel with auxetic core under blast loading. The results show that the use of the composite sandwich panel with auxetic core reduces the maximum displacement by 33% in comparison to the monolithic plate of the similar mass, while simultaneously a 6% mass reduction can be observed.