Kinetics of a frictional granular motor

Within the framework of a Boltzmann-Lorentz equation, we analyze the dynamics of a granular rotor immersed in a bath of thermalized particles in the presence of a frictional torque on the axis. In numerical simulations of the equation, we observe two scaling regimes at low and high bath temperatures. In the large friction limit, we obtain the exact solution of a model corresponding to asymptotic behavior of the Boltzmann-Lorentz equation. In the limit of large rotor mass and small friction, we derive a Fokker-Planck equation for which the exact solution is also obtained.Comment: 4 pages, 4 Figures, To be published in Phys. Rev. Let

Design optimization for an additively manufactured automotive component

The aim of this paper is to investigate the design optimization and additive manufacture of automotive components. A Titanium brake pedal processed through Selective Laser Melting (SLM) is considered as a test case. Different design optimisation techniques have been employed including topology optimization and lattice structure design. Rather than using a conventional topology optimization method, a recently developed topology optimization method called Iso-XFEM is used in this work. This method is capable of generating high resolution topology optimised solutions using isolines/isosurfaces of a structural performance criterion and eXtended Finite Element Method (XFEM). Lattice structure design is the other technique used in this work for the design of the brake pedal. The idea is to increase the stability of the brake pedal to random loads applied to the foot pad area of the pedal. The use of lattice structures can also significantly reduce the high residual stress induced during the SLM process. The results suggest that the integration of the design optimization techniques with a metal additive manufacturing process enables development of a promising tool for producing lightweight energy efficient automotive components

The thermo-mechanical degradation of ethylene vinyl acetate used as a solar panel adhesive and encapsulant

The thermal ageing of an Ethylene-vinyl Acetate (EVA) polymer used as an adhesive and encapsulant in a photovoltaic module has been investigated. The EVA is used to bond the silicon solar cells to the front glass and backing sheet and to protect the photovoltaic materials from the environment and mechanical damage. Using a range of experimental techniques, including Dynamic Mechanical Analysis, Differential Scanning Calorimetry and Thermo-Gravimetric analysis, it was possible to show a link between changes in mechanical properties with both the transient temperature and the degree of long-time thermal ageing. Importantly, it was possible to show that the ageing related property changes were likely due to long term structural changes rather than any modification of the chemistry of the material

An inverse method for determining the spatially resolved properties of viscoelastic–viscoplastic three-dimensional printed materials

A method using experimental nanoindentation and inverse finite-element analysis (FEA) has been developed that enables the spatial variation of material constitutive properties to be accurately determined. The method was used to measure property variation in a three-dimensional printed (3DP) polymeric material. The accuracy of the method is dependent on the applicability of the constitutive model used in the inverse FEA, hence four potential material models: viscoelastic, viscoelastic–viscoplastic, nonlinear viscoelastic and nonlinear viscoelastic–viscoplastic were evaluated, with the latter enabling the best fit to experimental data. Significant changes in material properties were seen in the depth direction of the 3DP sample, which could be linked to the degree of cross-linking within the material, a feature inherent in a UV-cured layer-by-layer construction method. It is proposed that the method is a powerful tool in the analysis of manufacturing processes with potential spatial property variation that will also enable the accurate prediction of final manufactured part performance

Granular dynamics of a vibrated bed of dumbbells

A two-dimensional vibrated bed of dumbbells was investigated using experiment and numerical simulation. Experimentally, high speed photography in combination with image analysis and tracking software was used to determine the location of the centre of mass and the locations and direction of motion of the component particles of the dumbbells. Numerically, a geometry analogous to that used experimentally was employed and the equations of motion for each of the particles were solved using the distinct element method. It was found that, despite some differences, the numerical simulations agreed reasonably well with the experimental results. Subsequently, the simulation method was used to explore the behaviour of the bed over a range of densities. The moments of the velocity distributions were determined as a function of height for a range of numbers of particles, and it was found that a normal distribution of velocities is a good approximation, except close to the vibrating base where there were suggestions that the distribution of the vertical component of the velocities is a composite of two sets of particles, one pre-collision with the base, and the other post-collision

Design framework for multifunctional additive manufacturing: placement and routing of three-dimensional printed circuit volumes

A framework for the design of additively manufactured (AM) multimaterial parts with embedded functional systems is presented (e.g., structure with electronic/electrical components and associated conductive paths). Two of the key strands of this proposed framework are placement and routing strategies, which consist of techniques to exploit the true-3D design freedoms of multifunctional AM (MFAM) to create 3D printed circuit volumes (PCVs). Example test cases are presented, which demonstrate the appropriateness and effectiveness of the proposed techniques. The aim of the proposed design framework is to enable exploitation of the rapidly developing capabilities of multimaterial AM

Design framework for multifunctional additive manufacturing: coupled optimization strategy for structures with embedded functional systems

The driver for this research is the development of multi-material additive manufacturing processes that provide the potential for multi-functional parts to be manufactured in a single operation. In order to exploit the potential benefits of this emergent technology, new design, analysis and optimization methods are needed. This paper presents a method that enables in the optimization of a multifunctional part by coupling both the system and structural design aspects. This is achieved by incorporating the effects of a system, comprised of a number of connected functional components, on the structural response of a part within a structural topology optimization procedure. The potential of the proposed method is demonstrated by performing a coupled optimization on a cantilever plate with integrated components and circuitry. The results demonstrate that the method is capable of designing an optimized multifunctional part in which both the structural and system requirements are considered

A novel approach to design lesion-specific stents for minimum recoil

Stent geometries are obtained by topology optimization for minimized compliance under different stenosis levels and plaque material types. Three levels of stenosis by cross-sectional area, i.e., 30%, 40%, and 50% and three different plaque material properties, i.e., calcified, cellular, and hypocellular, were studied. The raw optimization results were converted to clear design concepts and their performance was evaluated by implanting them in their respective stenosed artery types using finite element analysis. The results were compared with a generic stent in similar arteries, which showed that the new designs showed less recoil. This work provides a concept that stents could be tailored to specific lesions in order to minimize recoil and maintain a patent lumen in stenotic arteries

Shape complexity and process energy consumption in electron beam melting: a case of something for nothing in additive manufacturing?

Additive manufacturing (AM) technology is capable of building up component geometry in a layer-by-layer process, entirely without tools, molds, or dies. One advantage of the approach is that it is capable of efficiently creating complex product geometry. Using experimental data collected during the manufacture of a titanium test part on a variant of AM technology, electron beam melting (EBM), this research studies the effect of a variation in product shape complexity on process energy consumption. This is done by applying a computationally quantifiable convexity-based characteristic associated with shape complexity to the test part and correlating this quantity with per-layer process energy consumption on the EBM system. Only a weak correlation is found between the complexity metric and energy consumption (ρ = .35), suggesting that process energy consumption is indeed not driven by shape complexity. This result is discussed in the context of the energy consumption of computer-controlled machining technology, which forms an important substitute to EBM. This article further discusses the impact of available additional shape complexity at the manufacturing process level on the incentives toward minimization of energy inputs, additional benefits arising later within the product’s life cycle, and its implications for value creation possibilities

An investigation of the behavior of solvent based polycaprolactone ink for material jetting

An initial study of processing bioresorbable polycaprolactone (PCL) through material jetting was conducted using a Fujifilm Dimatix DMP-2830 material printer. The aim of this work was to investigate a potential solvent based method of jetting polycaprolactone. Several solvents were attempt to prepared PCL solvent based ink and 1, 4-dioxane was chosen with the consideration of both solubility and safety. The morphology of PCL formed under different substrate temperatures, droplet spacings were investigated. Multi-layer PCL structures were printed and characterized. This work shows that biodegradable polycaporlactone can be processed through material jetting by dissolving it