Kuniharu Ushijima

An investigation into the compressive properties of stainless steel micro-lattice structures

This article presents a theoretical analysis for predicting the initial stiffness E*, and plastic collapse strength σ* pl of BCC micro-lattice blocks under compressive loading. This theoretical analysis is based on the observed deformation mechanisms, and can, in principle, be developed to predict the elastic properties of other micro-lattice structures. The analytical solutions are verified by comparing the predictions with FEM data using 1D beam and 3D solid elements and uniaxial compression tests on samples fabricated by selective laser melting. The FEM predictions using the 3D solid elements agree well with the experimental data for a wide range of strut aspect ratios, d/L. In addition, the range of applicability of the analytical model and the FEM predictions using beam elements are clarified.

The Properties of Lattice Structures Manufactured Using Selective Laser Melting

This paper outlines the findings of an on-going research study investigating the properties of a range of steel and titanium-based micro-lattice structures manufactured using the selective laser melting (SLM) technique. Initially, tension tests have been conducted on strands manufactured at different build angles. Micro-lattice block structures, with struts oriented at +/-45o were then tested in compression at quasi-static rates of loading. The failure mechanisms have been investigated using both optical and scanning electron microscopy. These tests have highlighted the attractive properties offered by these complex architectures.

Robotic Stretcher for SMA Patient: Preliminary Tests on Controllability and Safety

Abstract Diseases such as ALS and SMA often cause motor disabilities by progressive loss of muscle power. However, some patients must lie horizontally and thus cannot operate a wheelchair. The aim of this study was to develop a robotic stretcher for an SMA patient with severe motor disabilities to enable her to maneuver independently inside a building. In the concept of the stretcher, the user can drive the stretcher using an applicable operating device while watching a display feed from cameras mounted on the stretcher. We have developed some new devices with operating algorithm, mechanical frame and control system suitable to the users limited abilities (motion in only one finger), and verified their functions by tests with prototype machine. In addition, we show some results of a risk assessment of the prototype machine.

Shear Response of Three-Dimensional Micro-Lattice Structures

In this paper, the shear response of three-dimensional micro-lattice structures was investigated based on numerical stress analysis, FEM. The mechanical properties strongly depend on the number of unit cell in three directions x,y,z, and for a flat structure (number of cells in y-direction Ny=1), the deformation pattern observed in the structure can be classified into two types. The shear modulus G*for a flat structure obtained by FEM can be estimated by the elementary beam theory with a good accuracy. Also, for a flat structure with slender struts, the collapse is occurred by elastic buckling, and that with relatively thicker struts, the collapse strength agrees well with the theoretical result. Moreover, for the case of the cubic structure, if the structure has the same number of unit cell in x- and z- directions (numbers of cells in two directions Nx=Nz=M), the shear modulus G* shows a unit curve regardless of the number M, so that the modulus can be estimated by using the curve for various cubic structures.

The shear response of lightweight corrugated core structures

A combination of experimental, analytical and numerical techniques is used to characterise the shear response of lightweight corrugations based on glass fibre and carbon fibre reinforced epoxy resins. The corrugations were manufactured via a compression moulding procedure in which composite prepregs are cured between two serrated mould halves. The properties of the composite corrugations are compared with those offered by a similar aluminium system. Subsequent mechanical testing was undertaken using an Arcan rig capable of generating a range of loading conditions between pure shear and pure compression. As a result of difficulties in accurately measuring the displacement of the cores under mixed-loading conditions, an analytical model was used to predict the stiffness characteristics of the cores as a function of loading angle. The accuracy of the model was assessed using a finite element analysis. The final part of this investigation focused on fitting the measured values of maximum strength to an appropriate failure criterion. An examination of the corrugated structures during combined compression–shear loading indicated that the composite samples failed as a result of buckling in the strands and in certain cases, delamination between the composite plies. Both the analytical model and the finite element analysis indicated that the stiffness of composite and aluminium cores did not vary significantly with loading angle. An analysis of the strength characteristics of the corrugated cores showed that the aluminium corrugations could be accurately represented using a two-dimensional quadratic failure criterion. In contrast, due to the initiation of delamination within the composite struts, an additional component in the failure criterion was required to accurately capture the response of the composite corrugations.

Robotic stretcher for spinal muscular atrophy patient: Preliminary tests of user controllability

Diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy (SMA) often cause motor disabilities through the progressive loss of muscle power. However, some patients must lie horizontally and thus cannot operate a wheelchair. The aim of this study was to develop a robotic stretcher for an SMA patient with severe motor disabilities to enable her to maneuver independently inside a building. The concept underlying the stretcher is that the user should be able to drive the stretcher using an applicable operating device while watching a display feed from cameras mounted on the stretcher. We have developed new devices with an operating algorithm, mechanical frame and control system suitable to the users limited abilities (motion in only one finger), and verified their functions through tests of a prototype machine operated by the target user.

Evaluation of heat dissipation and structural response of a cellular panel as a heat exchanger

This paper investigates the heat dissipation performance and structural response of two-dimensional cellular structures (based on triangular, square and honeycomb designs) using the finite element analysis technique. Three parameters are used to describe the heat transfer capacity of the structures, these being the heat dissipation Q, the pressure loss ΔP and the temperature difference between the outer wall and the fluid, T w − T f ¯ . In addition, the relative normal stiffness E∕Es is used to assess structural performance. These values are dependent upon both the geometry of the cellular unit and also the relative density ρ of the cellular structure. In this study, the effect of varying the cell geometry on these parameters is investigated numerically. Based on the findings of this investigation, it is concluded that a honeycomb panel, with a relative density ρ = 0.45, exhibits the optimum design for use in the manufacture of a heat exchanger.

ENERGY ABSORPTION EFFICIENCY IN CELLULAR SOLIDS

In this paper, a new type of honeycomb structure is proposed to enhance the energy absorption capacity for a honeycomb structure, and investigated its energy absorption efficiency (absorbed energy per unit volume) by finite element method (FEM). This model has small arc-shaped parts on the double cell wall, and can be manufactured by a similar way of standard honeycomb structures. Also, the proposed structure has large rigidity of plastic bending without increasing the mass. In this paper, effects of geometrical properties on the energy absorption characteristics are discussed.

Study on Strain Concentration for Cylindrical Tubes Under Axial Compressive Loading

In this paper, elastoplastic post-buckling behavior of cylindrical tubes under axial compression is studied by using finite element method. In our study, the effects of tube geometries and strain hardening characteristics on high strain concentrations in circumferential direction eθ which arise at the vertex of outward wrinkles are investigated. It is found that the maximum value of eθ depends on the thickness-to-radius ratio t/R and the nondimentional hardening coefficient Eh /E, and independent of the length-to-radius ratio L/R. In addition, in order to evaluate the maximum strain eθ,max , the effects of tube geometries and strain hardening characteristics on the deformed shapes of folding wrinkles are also discussed.Copyright

Evaluating Path of Stress Triaxiality to Fracture of Thin Steel Sheet Using Stereovision

A stereovision technique based on digital image correlation is applied to the evaluation of the stress triaxiality and fracture strain of thin steel sheet. A tensile testing specimen with notches made of high strength steel sheet is loaded and the surface displacements are measured from both sides of the specimen surface using two stereovision systems. Not only the in-plane strains but the through-thickness strains are evaluated from the measurement results of the displacements on the both surfaces of the specimen. The variation of the stress triaxiality at an evaluation point is evaluated from the measured strains. The fracture strain is also evaluated from the strain measurement results. Experimental results show that the stress triaxiality and the fracture strain of thin steel sheet can be evaluated by the surface strain measurement. The results can be utilized for simulating deformation and predicting fracture of a component made of thin steel sheet.