29 research outputs found
Dynamic responses of metal sandwich beams under high velocity impact considering time inhomogeneity of core deformation
The objective of this paper is to establish a yielding criterion for a sandwich beam by considering the time inhomogeneity of foam core deformation, which results in the time-varied neutral surface and cross-sectional area. Taking into account of the bending and axial stretching, a unified dynamic yielding criterion for metallic sandwich beams considering the mass redistribution along with the core compression is established. A membrane factor is proposed and an analytical solution for the large deflection of the beam under high velocity impact is given. Different from the traditional yielding surface, when the core is partially densified, the yielding surface is asymmetric. Comparison of analytical solutions with numerical ones reveals that the present model improves the prediction accuracy of high-velocity impact responses of fully clamped sandwich beams. The present method can also be degenerated to predict the low velocity/energy impact responses of sandwich beams.The financial supports from the Fundamental Research Funds for the Central University (Nos. 2014JBZ014 and 2014YJS109), the National Science Foundation of China (No. 11272046), and 973 Program (No. 2015CB057800) are acknowledged
Deformation Processes of Metallic Open-Cell Foam Supported Sheet Metals
Sandwich panel has been widely applied to enhance the stiffness to weight performance of components in many industries. The manufacturing procedure of curved metal sandwich panels typically consists of forming the sheet and core material into prescribed shapes and applying the adhesive to bond the material in shaped molds. An alternative manufacturing method is to apply the conventional sheet metal forming technique to deform the flat sandwich panel into a curved panel. However, the face sheet will significantly limit the formability of the sandwich panel. To solve the problem, one face sheet was removed in the sandwich panel to increase the formability, then the metal sheet and the metallic open-cell foam were selected as the face sheet and the core material to form the metallic open-cell foam supported sheet metals.
The main objective of this study is to develop a proper forming method to deform the metallic open-cell foam supported sheet metal without failure occurring. Two forming processes, press brake bending and hydroforming, which can reduce the contact stress to avoid the structure damage were investigated. Experiments were designed to understand the possible failure modes and the failure mechanism. Through the parametric study in the experimental results, the effects of material dimensions, material properties, and test parameters were analyzed to establish a failure criterion. In addition, a finite element analysis with a proper foam model was implemented to further inspect the failure mechanism and develop a guideline for the selection of materials and test parameters.
For the press brake bending process, the experiment results have shown that the supported sheet metal can be successfully bent into a curved panel within small thickness reduction. The prediction in both geometric hoop strain failure criterion and shear strain failure in the finite element analysis were matched and agreed with the experimental result. For the hydroforming process, the experimental result indicated that the major failure mode is the adhesive failure. The early adhesive failure at the perimeter of the attached foam disc caused the open-cell foam to separate from the sheet metal. The required adhesive strength to the attainable dome height relationship was given by finite element analysis
Damage resistance and tolerance investigation of carbon/epoxy skinned honeycomb sandwich panels
This thesis documents the findings of a three year experimental investigation into the impact damage resistance and damage tolerance of composite honeycomb sandwich panels. The primary area of work focuses on the performance of sandwich panels under quasi-static and low-velocity impact loading with hemispherical and flat-ended indenters. The damage resistance is characterised in terms of damage mechanisms and energy absorption. The effects of varying the skin and core materials, skin thickness, core density, panel boundary conditions and indenter shape on the transverse strength and energy absorption of a sandwich panel have been examined. Damage mechanisms are found to include delamination of the impacted skin, core crushing, limited skin-core de bonding and top skin fibre fracture at high loads. In terms of panel construction the skin thickness is found to dominate the panel strength and energy absorption with core density having a lesser influence. Of the external factors considered the indenter noseshape has the largest effect on both failure load and associated damage area. An overview of existing analytical prediction methods is also included and the most significant theories applied and compared with the experimental results from this study. The secondary area of work expands the understanding obtained from the damage resistance study and assesses the ability of a sandwich panel to withstand in-plane compressive loading after sustaining low-velocity impact damage. The importance of the core material is investigated by comparing the compression-after-impact strength of both monolithic carbon-fibre laminates and sandwich panels with either an aluminium or nomex honeycomb core. The in-plane compressive strength of an 8 ply skinned honeycomb sandwich panel is found to be double that of a 16 ply monolithic laminate, with the type of honeycomb also influencing the compressive failure mechanisms and residual compressive strength. It is concluded that under in-plane loading the stabilising effect of the core opposes the de-stabilising effect of any impact damage.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Characterization and Modelling of Composites, Volume II
Composites have been increasingly used in various structural components in the aerospace, marine, automotive, and wind energy sectors. Composites’ material characterization is a vital part of the product development and production process. Physical, mechanical, and chemical characterization helps developers to further their understanding of products and materials, thus ensuring quality control. Achieving an in-depth understanding and consequent improvement of the general performance of these materials, however, still requires complex material modeling and simulation tools, which are often multiscale and encompass multiphysics. This Special Issue is aimed at soliciting promising, recent developments in composite modeling, simulation, and characterization, in both design and manufacturing areas, including experimental as well as industrial-scale case studies. All submitted manuscripts will undergo a rigorous review and will only be considered for publication if they meet journal standards
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Thin-walled composite deployable booms with tape-spring hinges
Deployable structures made from ultra-thin composite materials can
be folded elastically and are able to self-deploy by releasing the
stored strain energy. Their lightness, low cost due to smaller
number of components, and friction insensitive behaviour are key
attractions for space applications.
This dissertation presents a design methodology for lightweight
composite booms with multiple tape-spring hinges. The whole process
of folding and deployment of the tape-spring hinges under both
quasi-static and dynamic loading has been captured in detail through
finite element simulations, starting from a micro-mechanical model
of the laminate based on the measured geometry and elastic
properties of the woven tows. A stress-resultant based
six-dimensional failure criterion has been developed for checking if
the structure would be damaged.
A detailed study of the quasi-static folding and deployment of a
tape-spring hinge made from a two-ply plain-weave laminate of
carbon-fibre reinforced plastic has been carried out. A particular
version of this hinge was constructed and its moment-rotation
profile during quasi-static deployment was measured. Folding and
deployment simulations of the tape-spring hinge were carried out
with the commercial finite element package Abaqus/Explicit, starting
from the as-built, unstrained structure. The folding simulation
includes the effects of pinching the hinge in the middle to reduce
the peak moment required to fold it. The deployment simulation fully
captures both the steady-state moment part of the deployment and the
final snap back to the deployed configuration. An alternative
simulation without pinching the hinge provides an estimate of the
maximum moment that could be carried by the hinge during operation.
This moment is about double the snap-back moment for the particular
hinge design that was considered.
The dynamic deployment of a tape-spring hinge boom has been studied
both experimentally and by means of detailed finite-element
simulations. It has been shown that the deployment of the boom can
be divided into three phases: deployment; latching, which may
involves buckling of the tape springs and large rotations of the
boom; and vibration of the boom in the latched configuration. The
second phase is the most critical as the boom can fold backwards and
hence interfere with other spacecraft components.
A geometric optimisation study was carried out by parameterising the
slot geometry in terms of slot length, width and end circle
diameter. The stress-resultant based failure criterion was then used
to analyse the safety of the structure. The optimisation study was
focused on finding a hinge design that can be folded 180 degrees
with the shortest possible slot length. Simulations have shown that
the strains can be significantly reduced by allowing the end
cross-sections to deform freely. Based on the simulations a
failure-critical design and a failure-safe design were selected and
experimentally verified. The failure-safe optimised design is six
times stiffer in torsion, twice stiffer axially and stores two and a
half times more strain energy than the previously considered design.
Finally, an example of designing a 1 m long self-deployable boom
that could be folded around a spacecraft has been presented. The
safety of this two-hinge boom has been evaluated during both stowage
and dynamic deployment. A safe design that latches without any
overshoot was selected and validated by a dynamic deployment
experiment
Technical Design Report for the PANDA Micro Vertex Detector
This document illustrates the technical layout and the expected performance of the Micro Vertex Detector (MVD) of the PANDA experiment. The MVD will detect charged particles as close as possible to the interaction zone. Design criteria and the optimisation process as well as the technical solutions chosen are discussed and the results of this process are subjected to extensive Monte Carlo physics studies. The route towards realisation of the detector is
outlined
Advances in Structural Mechanics Modeled with FEM
It is well known that many structural and physical problems cannot be solved by analytical approaches. These problems require the development of numerical methods to get approximate but accurate solutions. The minite element method (FEM) represents one of the most typical methodologies that can be used to achieve this aim, due to its simple implementation, easy adaptability, and very good accuracy. For these reasons, the FEM is a widespread technique which is employed in many engineering fields, such as civil, mechanical, and aerospace engineering. The large-scale deployment of powerful computers and the consequent recent improvement of the computational resources have provided the tools to develop numerical approaches that are able to solve more complex structural systems characterized by peculiar mechanical configurations. Laminated or multi-phase composites, structures made of innovative materials, and nanostructures are just some examples of applications that are commonly and accurately solved by the FEM. Analogously, the same numerical approaches can be employed to validate the results of experimental tests. The main aim of this Special Issue is to collect numerical investigations focused on the use of the finite element metho
Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress
Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018
Proceedings of the 9th fib International PhD Symposium in Civil Engineering : Karlsruhe Institute of Technology (KIT), 22 - 25 July 2012, Karlsruhe, Germany
The fib International PhD Symposium in Civil Engineering is an established event in the academic calendar of doctoral students. It is held under the patronage of the International Federation for Structural Concrete (fib), one of the main international associations that disseminates knowledge about concrete and concrete structures. The 9th fib International PhD Symposium was held at the Karlsruhe Institute of Technology (KIT), Germany, from July 22 to 25, 2012