Evaluation of crushing and energy absorption characteristics of bio-inspired nested structures

Mimicking anatomical structures like bone can aid in the development of energy absorbing structures that can achieve desirable properties. Accordingly, this study presents the analysis of tubular nested designs inspired by Haversian bone architecture. Based on this design philosophy, a total of 18 nested tube designs with various geometrical configurations were developed. Within each design, the effect of reinforcement walls on the crashworthiness performance is also analysed. A finite element model, validated using quasi-static experimental tests, was used to study the crashworthiness performance and progressive deformation of the nested system. Based on the results, a multi-criteria decision-making method known as Technique of Order Preference by Similarity to Ideal Solution (TOPSIS) was employed to determine the most suitable cross-section that features high energy absorption and low impact force. Consequently, the study identified a nested tube configuration that exhibits superior crashworthiness and high energy absorbing characteristics. The bio-inspired design methodology presented in this study allows the exploitation of variable nested geometries for the development of high-efficiency energy absorbing structures.Accepted versio

Comparison of different quasi-static loading conditions of additively manufactured composite hexagonal and auxetic cellular structures

Auxetic cellular structures have the potential to revolutionise sandwich panel cores due to their potential superior energy absorption capability. Because of their negative Poisson's ratio, auxetics behave counterintuitively and contract orthogonally under an applied compressive force, resulting in a densification of material in the vicinity of the applied load. This study investigates three cellular structures and compares their compressive energy absorbing characteristics under in-plane and axial loading conditions. Three unit cell topologies are considered; a conventional hexagonal, re-entrant and double arrowhead auxetic structures. The samples were additively manufactured using two different materials, a conventional Nylon and a carbon fibre reinforced composite alternative (Onyx). Finite element simulations are experimentally validated under out of and in-plane loading conditions and the double arrowhead (auxetic) structure is shown to exhibit comparatively superior energy absorption. For the carbon fibre reinforced material, Onyx, the specific energy absorbed by the double arrowhead geometry was 125% and 244% greater than the hexagonal (non-auxetic) and re-entrant (auxetic) structures respectively

Comparison of damage characteristics of adhesively bonded and rivet-connected evtol wing under bird-strike

The advent of electric aircraft, including urban mobility vehicles, has brought renewed attention to the structural integrity of associated lightweight composite airframes. The evolution of composite passenger aircraft demonstrates the advantages of the use of these lightweight materials yet there are still certain structural components which are more susceptible to off-design loading than their metallic counterparts. For example, wing and empennage leading edges, are particularly susceptible to bird strike and are usually still made out of aluminium. Nonetheless, there are certain advantages in pursuing a composite leading edge, such as further weight reduction and enhanced laminar flow. In doing so, it becomes imperative to ensure that its energy absorption characteristics are well understood and can be predicted using computational modelling to reduce the extent of physical testing. For the case of fixed leading edges, energy absorption is likely to be dependent on the way that this leading edge is assembled and attached to the front spar, since the joint itself is a potential energy-absorbing mechanism. In this computational study two approaches are investigated; (i) the leading edge is adhesively-bonded, and (ii) riveted (Fig 1). Soft body impact, to simulate a bird strike, is achieved using Smooth Particle Hydrodynamics (SPH) which is preferred over the Arbitrary Lagrangian Eulerean (ALE) method. The analyses in this study are performed using an explicit finite element solver LS-DYNA. In this article, a composite sandwich wing model, made of unidirectional carbon-fibre polymer composite and a phenolic-based honeycomb core material, is impacted with a soft body mass in accordance with international standards and special conditions given by EASA. These standards are CS-25.631 and the special conditions for eVTOLs. The lay-up of the wing model includes unidirectional prepreg materials pertain to the face and back skin as well as the aforementioned attachment region which connects the spar and the leading edge. The substitute bird model (soft body mass) is configured using a well-defined equation of state model and the properties of homogenous gelatin.<br/

EXPERIMENTAL AND NUMERICAL ANALYSIS OF A LAMINATED BASALT COMPOSITE PLATE SUBJECTED TO BLAST LOAD

The use of the advanced laminated composites is become more important in the structures of many engineering applications such as space stations, aerospace vehicles, automotives and marine structures. Also, with the increasing use of recent composite material structures in the military applications, non-linear dynamic analysis of these materials subjected to blast loads resulting from fuel and nuclear explosions, and the rush of sonic boom are becoming increasingly more significant. The nonlinear dynamic response of a blast loaded laminated basalt composite plate has been investigated experimentally and numerically. The laminated basalt composite plate is fully-clamped at all edges. For numerical analyses, the equations of motion for the plate are derived by the use of the virtual work principle. Approximate solutions are assumed for the space domain and substituted into the equations of motion. Then the Galerkin Method is used to obtain the nonlinear differential equations in the time domain. The Newmark Method is applied to solve the system of coupled nonlinear equations by writing a computer code in MATLAB. On the experimental side of the study, tests have been carried out on the laminated basalt composite plates, in sixteen layers of stacking sequences and obtained by infusion, with fully-clamped edges for blast loads. The approximate-numerical and ANSYS results are compared with the experimental ones. We have obtained a good agreement for the specific points

Outcomes of a cohort of children with hemoglobinopathy receiving oral iron chelators for treatment of transfusional iron overload in Turkey: Results of 3-year follow-up study

Bu çalışma, 11-14, Haziran 2015 tarihlerinde Vienna[Avusturya]’da düzenlenen 20. Congress of European-Hematology-Association Kongresi‘nde bildiri olarak sunulmuştur