The proposed characterization method is based on the knowledge of free vibration characteristics of plate specimens. Effective laminate properties are estimated through minimization of the error between known and predicted natural frequencies. Metamodeling is used for approximating the relationship between the material properties and the corresponding natural frequencies. This results in an economical characterization process, applicable to a large number of specimens of various shapes and dimensions. The proposed strategy is first tested on a range of hypothetical composite materials with numerically simulated test results, then applied to reliable published experimental data. It is thus shown to have the potential of a fast and accurate, in-situ characterization tool.

Abstract. Electric vehicles are increasingly popular as an alternative to fossil fuel vehicles. The presence of batteries and electric motors poses different risks in collision accidents. The deformation of the batteries could spark a fire or explosion that in turn could endanger the passengers. The prototype of an Indonesian electric city car is currently being developed, which includes a battery pack located underneath the passenger compartment and electric motors in the front compartment. A crashworthiness design against side pole impact, in accordance with the Euro NCAP standard, was simulated numerically. In order to reduce the risk of battery explosion, an impact energy absorbing structure is proposed for implementation at the sides of the batteries. The structure of the four-passenger hatchback electric city car was modeled using all-shell elements with material properties for common automotive application and analyzed using the finite element method with dynamic plasticity capability. For the preliminary design, the minimum deformation of the batteries that can cause battery explosion was used as the failure criteria. From a number of design alternatives, the use of aluminum foam as impact energy absorber produced sufficient protection for the battery pack against side pole impact, hence effectively reducing the risk to an acceptable limit.

Abstract. Retraction spring is a type of orthodontic apparatus that is used to move a tooth with respect to another by utilizing its spring back effect. It is made of metallic wire formed to individual orthodontic cases. A specific geometry results in a set of force system, consisting of forces and moments, that provides specific movement effect when it is pre-activated to the adjacent teeth. Currently, orthodontists select its geometry depending on their knowledge and experience. It is based on separate and less-than-comprehensive literatures that not all orthodontists have access to. It may result in inaccuracies in treating individual tooth retraction case. Engineering approach to estimating retraction spring structural behavior is proposed through analytical, numerical and empirical methods. Castigliano method is used as the analytical approach, whilst finite element method is used as the numerical approach. The two simulation approaches were compared to the experiments to obtain the best simulation model. The behavior of the simulation models agree well with those of experiments. Hence, the simulation models were used to simulate a large number of geometries to form database of structural behavior of retraction spring that could be used in the geometry selection by orthodontists.

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Cellular structures can be classified into foams, honeycombs, and lattice structures. Each type of structure has its characteristics. Various applications of cellular structures can be found in aviation, bioengineering, automotive, and other fields. In the automotive sector, cellular structures have been used for structural applications and impact- absorbing modules, for example, for protecting the electric vehicle battery pack against impact loading. The challenges that limit the application of cellular structures today include systematically designing pseudo-random cellular structures, assessing which cellular patterns are most suitable for a particular application, and mastery of manufacturing technology for efficient mass production of cellular structures. In this paper, the authors examine the state-of-the-art technology in geometry, applications, and manufacturing of various cellular structures carried out by researchers to obtain an overview of the current conditions for further development of these cellular structures. Limited manufacturing capabilities encourage researchers to design an optimal cellular structure to be applied to a particular function but have high manufacturability. The development of additive manufacturing technology has provided opportunities for researchers to produce an optimal cellular structure commercially soon.