The paper gives an overview of developments of the SPH method Especial attention is given to the main shortcomings of the original form of the method namely consistency, tensile instability and zero energy modes A derivation of an example of a correction necessary to assure first order consistency is given The origin of the tensile instability and a few proposed solutions to this problem are described Similar consideration is given with respect to the zero energy modes typical for the collocational SPH method

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Review of Development of the Smooth Particle Hydrodynamics (SPH) Method

Bird strike is a serious problem that affects both commercial and military aircrafts. Systematic modeling and simulation of bird strikes are severely lacking, especially for cases involving engine, fan blades, and casings. In the present investigation, explicit 3-D finite element analysis using LS-DYNA is carried out to study the nonlinear transient response of a bird striking a fan system. The bird strike is simulated using Lagrangian blade-bird formulations. The bird is modeled as a fluid jet with a homogenized fluidic constitutive relation, using the Brockman hydrodynamic model, which was found to be the most appropriate. The present simulations are validated using a benchmark test of a bird striking a rigid target that is reported in the literature. Following this validation, a reference case of a bird striking a flexible fan blade was set up and used as the reference case in a series of parametric studies. The effect of bird velocity and its size are examined and attention is given to strikes involving larger birds so as to address the lack of data in this area.

Finite Element Modeling of a Bird Striking an Engine Fan Blade

Acrylic is extensively used in transparent laminate systems with glass, polycarbonate, polyurethane and other polymers. Impact response of laminated structures is a subject of critical interest because of the high probability of impacts occurring during the manufacture, service or maintenance of structures. The impact loading induces a complex interaction between structural and material behaviour. Impact tests have proven inherently difficult to characterize because of the large number of parameters that play a key role in structural behaviour. Evaluation of impact in the case of ballistic tests is usually in terms of the minimum energy required to cause complete penetration or the maximum energy before penetration. So, metrics like V100 ballistic limit and V50 ballistic limit are determined from a series of experiments. However, in low-velocity impacts, these statistical estimates are not appropriate. Furthermore, they do not indicate the failure mechanisms involved, the understanding of which is necessary to select materials for improved impact resistance. Different parameters are required to indicate the severity of the event and provide an understanding of the low-velocity impact behaviour. This paper deals with applying a multi-parameter approach to evaluate the low-velocity impact on circular plates of acrylic. The work presented herein focuses on developing a numerical model to simulate the impact deformation and failure behaviour of brittle polymeric materials such as acrylic. The numerical model was developed using the commercial finite element analysis software ls-dyna, and the results of the simulation is compared with the experimental results obtained from drop tower tests. The dynamic force histories and damage patterns obtained from the finite element simulation show good agreement with the experimental data from drop tower impact tests.

Experimental and numerical analysis of low-velocity impact of plastic laminates

Spacecraft encounter various impact phenomena in space, among which orbital debris impacts are of most concern. These impacts occur at a wide range of velocities. Impact velocities from a few hundreds m/s to one km/s are common in geostationary orbit and even occur in low Earth orbit. However, these high velocity impacts are not fully characterised. It’s required to study the shielding performance in order to assess the spacecraft survivability in the event of high velocity impacts. The paper is divided into two parts. Overall it investigates the capability of hydrocodes to simulate high velocity impacts. Particular interest is given to the post-penetration debris cloud characterisation and the material failure mode identification. Three different methods were used to simulate the impact of an aluminium sphere on a thin aluminium plate. The first part, considers analyses performed using a finite element model with element erosion and a discrete element method where the problem is modelled with discrete finite elements with nodes tied with breakable linkages. The second part of the paper considers the same problems with the Smoothed Particle Hydrodynamics (SPH) method using the MCM solver developed at Cranfield University. All three methods showed good agreement in terms of target damage with the available experimental results. However, their performances are different in terms of debris cloud and failure mode characterisation. As a large number of elements are deleted, the element erosion method shows problems in the petaling failure mode representation and doesn’t allow the post-penetration debris cloud to be characterised. In order to be more reliable, the SPH method needs improvements, in particular to avoid tensile instability. The discrete element method allows good representation and identification of the failure modes even if some improvements in the definition of the node linkage failure criterion are required.

Numerical simulation of high velocity impacts on thin metallic targets I and II

A case for holding portable electronic devices of variable sizes. The case extends around five sides of the device. The case comprising a back panel (1) and four side panels (2) extending away from the back panel. At least one of the side panels comprises a plurality of flexible protrusions (6) extending inwardly at an angle other than 90° from the at least one side panel, the protrusions (6) being capable of deforming inwardly by at least 0.5 mm. The side panels (2) comprise an inwardly facing flexible lip (8) formed at the end of the side panels (2) away from the back panel, the lip being angled towards the back panel (5) of the case.

Case for a portable electronic device

Lagrangian finite element methods have been used extensively in the past to study the non-linear transient behaviour of materials, ranging from crash tests of cars to simulating bird strikes on planes. However, as this type of space discretisation does not allow for motion of the material through the mesh when modelling extremely large deformations, the mesh becomes highly distorted. This paper describes some limitations and applicability of this type of analysis for high velocity impacts. A method for dealing with this problem by the erosion of elements is proposed, where the main driver is the definition of element failure strains. Results were compared with empirical perforation results and were found to be in good agreement. The results were then used to simulate high velocity impacts upon a multi-layered aluminium target in order to predict a ballistic limit curve. LS-DYNA3D was used as the FE solver for all simulations. Meshes were generated using Truegrid.

Finite Element Modelling of Failure of a Multi-Material Target due to High Velocity Space Debris Impacts

Some embodiments include a protective cover for a mobile display device. The protective cover includes a housing, a backplane, a liner, and a lip. The housing includes an outer portion and an inner portion, wherein the outer portion of the housing has a rectangular frame structure to provide a protective shell along an outer edge of the mobile display device, and wherein the inner portion receives and secures the mobile display device. The backplane is comprised of a rigid material and is coupled to a backside of the housing and provides a protective shell along a back side of the mobile display device. The liner has a corrugated soft rubber or polymer construction including a successive pattern of protrusions separated by a distance and is coupled to the inner portion of the housing. The lip is coupled to a front side of the housing to retain the mobile display device within the housing.

Protective Cover For Mobile Display Device

Einige Ausfuhrungsbeispiele umfassen eine Schutzabdeckung fur eine mobile Anzeigevorrichtung mit einem Gehause, einer Ruckwand, einer Auskleidung und einer Lippe. Das Gehause umfasst einen auseren Abschnitt und einen inneren Abschnitt, wobei der ausere Abschnitt des Gehauses eine rechteckige Rahmenstruktur aufweist, um eine Schutzhulle entlang einer Ausenkante der mobilen Anzeigevorrichtung bereitzustellen, und wobei der innere Abschnitt die mobile Anzeigevorrichtung aufnimmt und befestigt. Die Ruckwand besteht aus einem starren Material und ist mit einer Ruckseite des Gehauses gekoppelt und stellt eine Schutzhulle entlang einer Ruckseite der mobilen Anzeigevorrichtung bereit. Die Auskleidung weist eine gerippte weiche Gummi- oder Polymerkonstruktion mit einem aufeinander folgenden Muster von Vorsprungen, die um einen Abstand getrennt sind, auf und ist mit dem inneren Abschnitt des Gehauses gekoppelt. Die Lippe ist mit einer Vorderseite des Gehauses gekoppelt, um die mobile Anzeigevorrichtung innerhalb des Gehauses festzuhalten.

Kevin Hughes

Papers

Finite Element Modelling of Failure of a Multi-Material Target due to High Velocity Space Debris Impacts

Protective Cover For Mobile Display Device

Schutzabdeckung für eine mobile anzeigevorrichtung