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1

Damage Tolerance of Resin Transfer Molded Composite Sandwich Constructions.  

National Technical Information Service (NTIS)

The objectives of this program were to investigate several innovative sandwich constructions developed by affordable manufacturing process for their impact damage resistance/tolerance. The sandwich composite concepts considered in this study possessed the...

H. Mahfuz S. Jeelani U. K. Vaidya

1999-01-01

2

Impulsive Loading of Cellular Media in Sandwich Construction  

Microsoft Academic Search

Motivated by recent efforts to mitigate blast loading using energy-absorbing materials, this paper investigates the uniaxial crushing of cellular media in sandwich construction under impulsive pressure loading. The cellular core is modeled using a rigid, perfectly-plastic, locking idealization, as in previous studies, and the front and back faces are modeled as rigid, with pressure loading applied to the front face

Joseph A. Main; George A. Gazonas

2006-01-01

3

Impulsive loading of cellular media in sandwich construction  

Microsoft Academic Search

Motivated by recent efforts to mitigate blast loading using energy absorbing materials, this paper investigates the uniaxial crushing of cellular media in sandwich construction under impulsive pressure loading. The cellular core material is modeled using a rigid, perfectly-plastic, locking idealization, as in previous studies, and the front and back faces are modeled as perfectly rigid. Pressure loading is applied to

Joseph Main; George Gazonas

2005-01-01

4

Composite sandwich constructions for absorbing the electromagnetic waves  

Microsoft Academic Search

RAS (radar absorbing structures) is a key component for weapon systems such as aircrafts, warships, and missiles to achieve both the stealth performance by absorbing EM (Electromagnetic) waves incident on and load bearing capability. In this work, the RAS was fabricated as sandwich constructions composed of nanocomposite, carbon fabric\\/epoxy composite, and PVC foam. The nanocomposite composed of E-glass fabric, epoxy

Po Chul Kim; Dai Gil Lee

2009-01-01

5

Impulsive Loading of Cellular Media in Sandwich Construction  

NASA Astrophysics Data System (ADS)

Motivated by recent efforts to mitigate blast loading using energy-absorbing materials, this paper investigates the uniaxial crushing of cellular media in sandwich construction under impulsive pressure loading. The cellular core is modeled using a rigid, perfectly-plastic, locking idealization, as in previous studies, and the front and back faces are modeled as rigid, with pressure loading applied to the front face and the back face unrestrained. Predictions of this analytical model show excellent agreement with explicit finite element computations, and the model is used to investigate the influence of the mass distribution between the core and the faces. Increasing the mass fraction in the front face is found to increase the impulse required for complete crushing of the cellular core but also to produce undesirable increases in back-face accelerations. Optimal mass distributions are investigated by maximizing the impulse capacity while limiting the back-face accelerations to a specified level.

Main, Joseph A.; Gazonas, George A.

2006-07-01

6

Impulsive loading of cellular media in sandwich construction  

NASA Astrophysics Data System (ADS)

Motivated by recent efforts to mitigate blast loading using energy absorbing materials, this paper investigates the uniaxial crushing of cellular media in sandwich construction under impulsive pressure loading. The cellular core material is modeled using a rigid, perfectly-plastic, locking idealization, as in previous studies, and the front and back faces are modeled as perfectly rigid. Pressure loading is applied to the front face with the back face unrestrained, and two forms of pressure input are considered: a triangular pulse and an idealized impulse of zero duration. The equation of motion for this system, which generalizes previous results for a fixed back face, is derived in nondimensional form in terms of a single coordinate representing the remaining mass fraction of uncompressed core material. Predictions of this analytical model show excellent agreement with computational simulations using the explicit finite element code LS-DYNA. This analytical model is used to investigate the influence of the relative distribution of mass among the core and the front and back faces, with the total mass held constant. An optimal mass distribution is obtained by maximizing the total impulse that can be absorbed, while limiting the back-face accelerations to a specified level.

Main, Joseph; Gazonas, George

2005-07-01

7

BRAZING TITANIUM SANDWICH CONSTRUCTION. Period covered: July 1, 1957 to July 30, 1958  

Microsoft Academic Search

The purpose of this project was to study the feasibillty of fabricating ; titanium alloy face sheet honeycomb sandwiches by brazing techniques. The ; program was conveniently divided into several phases: selection of face sheet ; alloy and brazing alloys, fabrication of sandwiches by various experimental ; methods, and mechanical evaluation of the resulting panels. The emphasis was ; placed

J. F. Rudy; R. M. Necheles; H. Schwartzbart

1958-01-01

8

Highly efficient construction of oriented sandwich structures for surface-enhanced Raman scattering.  

PubMed

The purpose of this study is to solve the problem of low achievement in fabricating sandwich surface-enhanced Raman scattering (SERS) substrates. We demonstrated a highly efficient sandwich structure by the oriented assembly of metal nanoparticles (NPs) on a periodic hexagonal array of metal nanoprisms with 1,4-benzenedithiol (1,4-BDT) as linkers. The metal nanoprism array was prepared by vacuum deposition of metal on a close-packed polystyrene nanosphere pre-patterned substrate. The metal nanoprism array presents different surface properties from the pits left from the removal of polystyrene nanospheres, which causes linkers to selectively adsorb on the metal nanoprism array and sequentially leads to the oriented immobilization of the second-layer metal NPs, avoiding mismatched orientation. These sandwich SERS substrates were characterized by extinction spectroscopy and atomic force microscopy and their enhancement activity was evaluated under different excitation wavelengths. The sandwich structure greatly increases the achievement of 'hot spots' to almost 100% of all the metal nanoprisms and enables a large amplification of SERS signals by a factor of ten. This method has the advantages of simplicity, high efficiency, high throughput, controllability and high reproducibility. It has significance in both the study of SERS substrates and the development of plasmonic devices. PMID:23299563

Guo, Hongyun; Xu, Weiqing; Zhou, Ji; Xu, Shuping; Lombardi, John R

2013-02-01

9

Highly efficient construction of oriented sandwich structures for surface-enhanced Raman scattering  

NASA Astrophysics Data System (ADS)

The purpose of this study is to solve the problem of low achievement in fabricating sandwich surface-enhanced Raman scattering (SERS) substrates. We demonstrated a highly efficient sandwich structure by the oriented assembly of metal nanoparticles (NPs) on a periodic hexagonal array of metal nanoprisms with 1,4-benzenedithiol (1,4-BDT) as linkers. The metal nanoprism array was prepared by vacuum deposition of metal on a close-packed polystyrene nanosphere pre-patterned substrate. The metal nanoprism array presents different surface properties from the pits left from the removal of polystyrene nanospheres, which causes linkers to selectively adsorb on the metal nanoprism array and sequentially leads to the oriented immobilization of the second-layer metal NPs, avoiding mismatched orientation. These sandwich SERS substrates were characterized by extinction spectroscopy and atomic force microscopy and their enhancement activity was evaluated under different excitation wavelengths. The sandwich structure greatly increases the achievement of ‘hot spots’ to almost 100% of all the metal nanoprisms and enables a large amplification of SERS signals by a factor of ten. This method has the advantages of simplicity, high efficiency, high throughput, controllability and high reproducibility. It has significance in both the study of SERS substrates and the development of plasmonic devices.

Guo, Hongyun; Xu, Weiqing; Zhou, Ji; Xu, Shuping; Lombardi, John R.

2013-02-01

10

Construction of DNA sandwich electrochemical biosensor with nanoPbS and nanoAu tags on magnetic microbeads.  

PubMed

A novel and sensitive sandwich electrochemical biosensor based on the amplification of magnetic microbeads and Au nanoparticles (NPs) modified with bio bar code and PbS nanoparticles was constructed in the present work. In this method, the magnetic microspheres were coated with 4 layers polyelectrolytes in order to increase carboxyl groups on the surface of the magnetic microbeads, which enhanced the amount of the capture DNA. The amino-functionalized capture DNA on the surface of magnetic microbeads hybridized with one end of target DNA, the other end of which was hybridized with signal DNA probe labelled with Au NPs on the terminus. The Au NPs were modified with bio bar code and the PbS NPs were used as a marker for identifying the target oligoncleotide. The modification of magnetic microbeads could immobilize more amino-group terminal capture DNA, and the bio bar code could increase the amount of Au NPs that combined with the target DNA. The detection of lead ions performed by anodic stripping voltammetry (ASV) technology further improved the sensitivity of the biosensor. As a result, the present DNA biosensor showed good selectivity and sensitivity by the combined amplification. Under the optimum conditions, the linear relationship with the concentration of the target DNA was ranging from 2.0 x 10(-14) M to 1.0 x 10(-12)M and a detection limit as low as 5.0 x 10(-15)M was obtained. PMID:19447027

Du, Ping; Li, Hongxia; Cao, Wei

2009-07-15

11

Multifunctional sandwich composites  

NASA Astrophysics Data System (ADS)

Sandwich composites find increasing use as flexural load bearing lightweight sub-elements in air/space vehicles, rail/ground transportation, marine and sporting goods. The core in these applications is usually balsa wood, foam or honeycomb with laminated carbon or glass facesheets. A limitation of traditional sandwich onfigurations is that the space in the core becomes inaccessible once the facesheets are bonded in place. Significant multi-functional benefits can be obtained by making either the facesheets or the core, space accessible. Multi-functionality is generally referred to as value added to the structure that enhances functions beyond traditional load bearing. Such functions may include sound/vibration damping, ability to route wires or embed sensors. The present work reviews recent work done in enhancing the functionality of the core by use of the space in the core. The damage created by impact to sandwich constructions is always a limiting issue in design. In the present work, low velocity impact (LVI) response of newer/multi-functional sandwich constructions has been studied. Concepts of increasing sandwich core functionality have been reported.

Vaidya, Uday K.

2003-10-01

12

Composite sandwich construction with syntactic foam core - A practical assessment of post-impact damage and residual strength  

NASA Technical Reports Server (NTRS)

An account is given of an inspection method that has been successfully used to assess the postimpact damage and residual strength of syntactic (glass microspheres in epoxy matrix) foam-core sandwich panels with hybrid (carbon and glass fiber-reinforced) composite skins, which inherently possess high damage tolerance. SEM establishes that the crushing of the microspheres is responsible for the absorption of most of the impact energy. Damage tolerance is a function of the localization of damage by that high impact energy absorption.

Hiel, C.; Dittman, D.; Ishai, O.

1993-01-01

13

Cross Cell Sandwich Core  

NASA Technical Reports Server (NTRS)

A sandwich core comprises two faceplates separated by a plurality of cells. The cells are comprised of walls positioned at oblique angles relative to a perpendicular axis extending through the faceplates. The walls preferably form open cells and are constructed from open cells and are constructed from rows of ribbons. The walls may be obliquely angled relative to more than one plane extending through the perpendicular axis.

Ford, Donald B. (Inventor)

2004-01-01

14

Characteristics of joining inserts for composite sandwich panels  

Microsoft Academic Search

Composite sandwich constructions are widely employed in various light weight structures, because composite sandwich panels have high specific stiffness and high specific bending strength compared to solid panels. Since sandwich panels are basically unsuited to carry localized loads, the sandwich structure should provide joining inserts to transfer the localized loads to other structures.In this work, the load transfer characteristics of

Byoung Jung Kim; Dai Gil Lee

2008-01-01

15

Construction of a specific and sensitive sandwich enzyme immunoassay for 20 kDa human growth hormone  

Microsoft Academic Search

Twenty kilodalton human growth hormone (20K-hGH) is a naturally occurring isoform lacking amino acid residues 32–46 of 22K-hGH. Due to this structural similarity to 22K-hGH, no one has constructed a specific and sensitive assay system for 20K-hGH, which can be used for measuring physiological concentration of this isoform in the circulation. To construct such a specific assay system, we have

Yoshihide Hashimoto; Ichiro Ikeda; Miwa Ikeda; Yuka Takahashi; Masaharu Hosaka; Hiroshi Uchida; Naoko Kono; Hideo Fukui; Tadashi Makino; Masaru Honjo

1998-01-01

16

FAILURE MECHANISMS OF COMPOSITE SANDWICH STRUCTURES  

Microsoft Academic Search

Sandwich construction is of particular interest and widely used, because the concept is very suitable and amenable to the development of lightweight structures with high in-plane and flexural stiffness. Sandwich panels consist typically of two thin face sheets (or facings, or skins) and a lightweight thicker core. They display various failure modes under general bending, shear and in-plane loading. The

E. E Gdoutos

17

Advances in the Structural Modeling of Elastic Sandwich Panels  

Microsoft Academic Search

The area of sandwich construction has been an active field of research for more than five decades. During this period, a large number of mathematical models for structural sandwich panels has been provided, ranging from the early sandwich membrane models to more sophisticated recent approaches. Especially during the past decade, the increasing demand for high-performance, lightweight structures has stimulated a

JÖRG HOHE; LIVIU LIBRESCU

2004-01-01

18

Collapse Mechanism of Foam Cored Sandwich Structures Under Compressive Load  

Microsoft Academic Search

In this work the moisture absorption capability, compressive properties, collapse modes of various types of composite sandwich structures are reported. The tested sandwich structures were constructed with varieties of hybridized skin materials and different compositions of the core materials. The moisture absorption, Flatwise compression and Edgewise compression tests are conducted for core as well as sandwich structures. Comparisons of results

S. Manjunath Yadav; K. V. Arun; S. Basavarajappa; Narendranath S; Santosh Kumar

2011-01-01

19

Sandwich composite approach for EMI shielding structures  

Microsoft Academic Search

A sandwich composite approach has been employed to develop epoxy based polymer matrix composite materials to realize a class of lightweight structures capable of shielding electromagnetic interference (EMI). Hollow glass microspheres embedded syntactic foams (thickness ap 2 mm; density ap 0.6 g\\/cc) of two different varieties have been used as core materials in these sandwich constructions (total thickness ap 2.6

S. Dasgupta; K. Ravi Sekhart; B. N. Ravishankar; M. Kumar; S. Sankaran

2008-01-01

20

Adhesion in sandwiches with aluminum foam core  

Microsoft Academic Search

Fast-moving machine tool assemblies should be light and rigid. Because of the lightweight construction and the dynamic loads\\u000a these assemblies are very often susceptible to vibrations. Aluminum foam sandwiches are laminates with an aluminum foam core\\u000a and compact cover sheets. The foam cores possess a high-energy absorption capacity. Machine tool assemblies made of aluminum\\u000a foam sandwiches offer very high flexural

Reimund Neugebauer; Carsten Lies; Jörg Hohlfeld; Thomas Hipke

2007-01-01

21

Construction, expression, purification and biotin labeling of a single recombinant multi-epitope antigen for double-antigen sandwich ELISA to detect hepatitis C virus antibody.  

PubMed

Based on B cell epitope predictions, a recombinant antigen with multiple epitopes from four Hepatitis C Virus fragments (C, NS3, NS4 and NS5) were engineered. The recombinant gene was then highly expressed in E. coli. The non-modified and C-terminal-modified recombinant proteins were used for coating and biotin labeling, respectively, to establish the double-antigen sandwich ELISA. Ten positive reference samples confirmed by the CHIRON RIBA HCV 3.0 SIA kit were detected positive, Forty one plasma samples were positive among samples from 441 volunteers, which indicated that the recombinant antigen could readily react well with plasma HCV antibody. As critical reagents of double-antigen sandwich ELISA, the recombinant multi-epitope antigen and the C-terminal-modified and biotin-conjugated antigen show good antigenicity. In this study, we provide a simple approach to produce multiple epitopes within one recombinant protein in order to avoid the costly expression of less-effective pools of multiple proteins, which is the conventional strategy of diagnostic antigen production for HCV antibody detection. PMID:21443503

He, Jing; Xiu, Bingshui; Wang, Guohua; Chen, Kun; Feng, Xiaoyan; Song, Xiaoguo; Zhu, Cuixia; Yang, Xiqin; Bai, Guanzhong; Ling, Shigan; Zhang, Heqiu

2011-08-01

22

ACOUSTICS OF SANDWICH STRUCTURES  

Microsoft Academic Search

USC's work on sandwich structure acoustics began in 1998 and has evolved in close collaboration with the M.C. Gill Corporation, a leading manufacturer of sandwich panels for aircraft interiors. The work has had both an applied mission and an academic focus, and presents an example of university-industry collaboration can produce mutual benefit while advancing scientific understanding. Here, we describe our

Steven Nutt; Portia Peters; Christina Naify; Changzheng Huang

23

The Sandwich Generation  

Microsoft Academic Search

This article reviews the literature on the sandwich generation and includes related theories and research. Psychological perspectives on the developmental issues associated with middle adulthood in general, and the sandwich generation in particular, are examined. Clinical vignettes highlight the magnitude of elder care in the United States and the impact on caregivers.

June F. Chisholm

1999-01-01

24

Modeling of sandwich structures  

NASA Astrophysics Data System (ADS)

Much of the work done on active and passive constrained layer beams is done with models using kinematic assumptions proposed by Kerwin, Mead and Markus, and others. Typically these analyses use low-order Euler-Bernoulli beams and assume the base and constraining layers undergo identical transverse displacements. These assumptions are reasonable for cases where the middle layer (normally a relatively soft viscoelastic material) is thin and the constraining layer is relatively weak in bending, but many practical cases arise where these assumptions are violated. A few authors over the years have done studies with less restrictive kinematic assumptions, but none have specifically studied the effects of doing so in the context of passive or active damping design. The field of composite structures is rich with techniques for analyzing sandwich structures with and without simplifying assumptions, and it is on this body of work that this paper is based. The percentage of modal strain energy in the viscoelastic core is used as the primary measure of the accuracy of different sets of assumptions. Elasticity solutions are available for selected sets of assumptions and boundary conditions, and these solutions provide a basis for some of the preliminary studies. A zig-zag method is used to construct a piecewise continuous displacement field (C1 continuity) that satisfies the appropriate stress continuity between layers in a consistent manner. Finite element analysis provides a versatile way to simulate complicated combinations of boundary conditions, degree of coverage, and kinematic assumptions.

Austin, Eric M.; Inman, Daniel J.

1998-06-01

25

Graphene veils and sandwiches.  

PubMed

We report a new and highly versatile approach to artificial layered materials synthesis which borrows concepts of molecular beam epitaxy, self-assembly, and graphite intercalation compounds. It readily yields stacks of graphene (or other two-dimensional sheets) separated by virtually any kind of "guest" species. The new material can be "sandwich like", for which the guest species are relatively closely spaced and form a near-continuous inner layer of the sandwich, or "veil like", where the guest species are widely separated, with each guest individually draped within a close-fitting, protective yet atomically thin graphene net or veil. The veils and sandwiches can be intermixed and used as a two-dimensional platform to control the movements and chemical interactions of guest species. PMID:21770385

Yuk, Jong Min; Kim, Kwanpyo; Alemán, Benjamín; Regan, William; Ryu, Ji Hoon; Park, Jungwon; Ercius, Peter; Lee, Hyuck Mo; Alivisatos, A Paul; Crommie, Michael F; Lee, Jeong Yong; Zettl, Alex

2011-08-10

26

Sandwich Courses: An Integrated Education?  

ERIC Educational Resources Information Center

The idea of organizing courses on the "sandwich principle" of alternate periods of academic study and industrial training is described. Results of a longitudinal study conducted at the University of Bradford are provided throughout the report. Following background information on the sandwich principle, students' reaction to sandwich courses are…

Smithers, Alan G.

27

Fracture of sandwiched composites  

Microsoft Academic Search

Fracture of a pair of collinear cracks in various materials, such as an isotropic strip, an orthotropic strip, a bonded isotropic adhesive layer, and sandwiched orthotropic layers, is investigated. The crack surfaces are subjected to an arbitrary opening pressure p(x). The problems are formulated in terms of Fredholm integral equation of the second kind by making use the techniques of

Lin; Weh-Huei

1989-01-01

28

The LANL Sandwich Test  

Microsoft Academic Search

The Sandwich Test is a recently developed slab-variant of the copper cylinder test which, like its predecessor, is used for obtaining high explosive (HE) product equation-of-state information. A primary motivation of slab geometry is that the liner bends without stretching, making it less prone to breaking at large expansions than for cylindrical geometry. This allows a wider choice of liner

L. G. Hill

2001-01-01

29

The LANL Sandwich Test  

NASA Astrophysics Data System (ADS)

The Sandwich Test is a recently developed slab-variant of the copper cylinder test which, like its predecessor, is used for obtaining high explosive (HE) product equation-of-state information. A primary motivation of slab geometry is that the liner bends without stretching, making it less prone to breaking at large expansions than for cylindrical geometry. This allows a wider choice of liner materials---which need not be as ductile as copper---and also allows the liner to be made thinner. Specifically, the Sandwich Test uses a half-millimeter-thick Tantalum liner, the higher impedance of which gives a detonation state closer to c-j and a better approximation to an ideal smooth trajectory. The thin liner and the fact that pressure decays slower with axial distance in slab geometry also gives better high-pressure resolution than the cylinder test. An additional motivation is that the Sandwich Test accommodates initial temperature extremes (currently -55C to 75C) with a single test design, whereas the cylinder test would be adversely affected by differential expansion/contraction between the HE and liner. The essential design features are outlined, and the general advantages and disadvantages of the two geometries (which depend on several factors) are discussed.

Hill, L. G.

2001-06-01

30

ENGINEERED SANDWICH CORES FOR LARGE WIND TURBINE BLADES  

Microsoft Academic Search

Sandwich construction is employed extensively in th e aerodynamic skins and the shear webs of large wind turbine blades. This paper contains an experimental assessment of innovative fiber- reinforced core (FRC) designs with respect to the b lade application. Two specific FRC designs are compared to low-density PVC foam and medium-density end-grain balsa, which are commonly used as sandwich cores

Frederick Stoll; Rob Banerjee; Rod Brecht; G. Scott Campbell

31

Impact Damage Characterization and Damage Tolerance of Composite Sandwich Airframe Structures.  

National Technical Information Service (NTIS)

The use of composite sandwich construction is rapidly increasing in current and future airframe designs. Typically, these sandwich constructions use thin gage composite facesheets (0.020 inch to 0.045 inch) which are co-cured to honeycomb and foam cores. ...

J. S. Tomblin K. S. Raju J. Liew B. L. Smith

2001-01-01

32

Structural Analysis of Sandwich Foam Panels  

SciTech Connect

The Sandwich Panel Technologies including Structural Insulated Panels (SIPs) can be used to replace the conventional wooden-frame construction method. The main purpose of this Cooperative Research and Development Agreement (CRADA) between UT-Battelle, LLC and SGI Venture, Inc. was to design a novel high R-value type of metal sandwich panelized technology. This CRADA project report presents design concept discussion and numerical analysis results from thermal performance study of this new building envelope system. The main objective of this work was to develop a basic concept of a new generation of wall panel technologies which will have R-value over R-20 will use thermal mass to improve energy performance in cooling dominated climates and will be 100% termite resistant. The main advantages of using sandwich panels are as follows: (1) better energy saving structural panels with high and uniform overall wall R-value across the elevation that could not be achieved in traditional walls; and (2) reducing the use of raw materials or need for virgin lumber. For better utilization of these Sandwich panels, engineers need to have a thorough understanding of the actual performance of the panels and system. Detailed analysis and study on the capacities and deformation of individual panels and its assembly have to be performed to achieve that goal. The major project activity was to conduct structural analysis of the stresses, strains, load capacities, and deformations of individual sandwich components under various load cases. The analysis simulated the actual loading conditions of the regular residential building and used actual material properties of the steel facings and foam.

Kosny, Jan [ORNL; Huo, X. Sharon [Tennessee Technological University

2010-04-01

33

Noise transmission through nonlinear sandwich panels  

NASA Astrophysics Data System (ADS)

An analytical study is presented to predict the noise transmission through nonlinear double wall sandwich panel systems subject to random loading. Viscoelastic and nonlinear spring dash-pot models are chosen to characterize the behavior of the core. The noise transmission through this panel system is determined into an acoustic enclosure of which the interiors are covered with porous absorption materials. The absorbent boundary conditions of the enclosure are accounted for by a two-step transformation of the boundary effect into a wave equation which governs the acoustic pressure field. The nonlinear panel response and interior acoustic pressure are obtained by utilizing modal analyses and Monte Carlo simulation techniques. Numerical results include the nonlinear response time histories and noise reduction. It is found that by proper selection of the dynamic parameters and damping characteristics, the noise transmission can be significantly reduced by the double wall sandwich construction.

Vaicaitis, R.; Hong, H.-K.

1983-04-01

34

Flexural properties of sandwich beams consisting of air plasma sprayed alloy 625 and nickel alloy foam  

Microsoft Academic Search

Sandwich structures are considered as viable engineering constructions due to their unique structural, physical, and mechanical\\u000a properties. An investigation of the mechanical characteristics of sandwich structures suitable for high temperature application\\u000a is presented. A process has developed to produce high temperature sandwich structures by depositing alloy 625 skins on Ni\\u000a alloy foam cores using air plasma spraying (APS). The experimental

F. Azarmi; T. W. Coyle; J. Mostaghimi

2009-01-01

35

Construction  

Cancer.gov

The Biomedical Research Extension Act of 1977 (P.L. 95-83) No statutory changes or report language affecting construction. The Health Program Extension Act of 1980 (P.L. 96-538) No statutory changes or report language affecting construction. The Health Omnibus Program Extension of 1988 (P.L. 100-607) There were no statutory changes to the construction provisions.

36

Impact and post-impact vibration response of protective metal foam composite sandwich plates  

Microsoft Academic Search

Composite sandwich structures composed of a metal foam core possess the ability to provide significant energy absorption under impact from flying debris, routine operation, tool drop, flying projectiles, or crash conditions. Sandwich constructions of aluminum foam core and a variety of facesheets are being increasingly used in a number of applications ranging from turbine shrouds, heat exchangers, pneumatic tool mufflers,

Uday K. Vaidya; Selvum Pillay; Shane Bartus; Chad A. Ulven; Dana T. Grow; Biju Mathew

2006-01-01

37

Sandwich structures for high temperature applications: Microstructural development and mechanical performance  

Microsoft Academic Search

There has been a great deal of interest in the development of sandwich structures as viable engineering constructions. It is due to their unique structural, physical, and mechanical characteristics such as light weight, high strength to weight ratio, high bending stiffness, excellent thermal and acoustical insulation. Although the service temperature for most applications of sandwich structures is low, the outstanding

Fardad Azarmi

2008-01-01

38

MECHANICAL CHARACTERIZATION OF SANDWICH STRUCTURE COMPRISED OF GLASS FIBER REINFORCED CORE: PART 1  

Microsoft Academic Search

This paper aims at demonstrating the feasibility of Glass Fiber Reinforced Polymer (GFRP) systems for low-profile bypass roadways, in particular, sandwich panels comprised of GFRP facings and a Fiber Reinforced Foam (FRF) core. With the purpose of investigating the performance of the sandwich construction, an experimental program, including static and dynamic fatigue tests, was performed. The same type of specimens

S. V. Rocca; A. Nanni

39

Impact failure characteristics in sandwich structures  

Microsoft Academic Search

In the present work we present a systematic experimental investigation of the generation and subsequent evolution of dynamic failure modes in sandwich structures subjected to low-speed impact. Model sandwich specimens involving a compliant polymer core sandwiched between two metal layers were designed and subjected to impact loading to simulate failure evolution mechanisms in real sandwich structures. High-speed photography and dynamic

L. Roy Xu; Ares J. Rosakis

2002-01-01

40

Characterization of sandwich panels for indentation and impact  

NASA Astrophysics Data System (ADS)

The integrity of sandwich structures which are susceptible to impact may deteriorate significantly due to collapse of the core material and delamination of the face sheets. The integration of a thin polyurethane interlayer between the composite face sheet and foam core is known to protect the core material and substantially improve the resistance to impact. The objective of the present work is to characterize the response of sandwich panels, as well as that of the constituents to impact. In particular, the response of polyurethane and foam samples under a range of quasi-static and dynamic loading rates is determined experimentally. Furthermore, the response of sandwich panels to quasi-static indentation and low velocity impact is examined to quantify the extent of damage and how it is affected by the integration of polyurethane interlayers in their construction. This information is useful in the modelling of high velocity impact of sandwich panels; an effort which is currently underway. The results illustrate the benefit of using polyurethane interlayers within the construction of sandwich panels in enhancing their performance under quasi-static indentation and impact loads.

Shazly, M.; Bahei-El-Din, Y.; Salem, S.

2013-07-01

41

Ultralight asymmetric photovoltaic sandwich structures  

Microsoft Academic Search

This work evaluated the possibility of using silicon solar cells as load-carrying elements in composite sandwich structures. Such an ultra-light multifunctional structure is a new concept enabling weight, and thus energy, to be saved in high-tech applications such as solar cars, solar planes or satellites. Composite sandwich structures with a weight of ?800g\\/m2 were developed, based on one 140?m thick

Julien Rion; Yves Leterrier; Jan-Anders E. Månson; Jean-Marie Blairon

2009-01-01

42

ESTIMATION OF HONEYCOMB SANDWICH PROPERTIES THROUGH NUMERICAL HOMOGENIZATION  

Microsoft Academic Search

Honeycomb sandwich panels are widely used in aeronautic industry, and more particularly in the construction of airplane and helicopter trim panels. The current study is motivated by aircraft cabin noise reduction applications, where Active Structural Acoustic Control of the trim panels through piezoelectric patches is considered. As an initial step to such control, predictive models of the panel dynamics are

Corine Florens; Franck Cléro

43

Component sizing approach for the sandwich plate system  

Microsoft Academic Search

The sandwich plate system (SPS) is a bridge deck system consisting of steel face plates bonded to a rigid polyurethane core. SPS bridges are typically constructed as a series of pre-fabricated SPS deck panels compositely connected with traditional steel girders. The decks are thin, lightweight and modular, and can be tailored to numerous applications including both new bridge and rehabilitated

Devin K. Harris

2010-01-01

44

Component sizing approach for the sandwich plate system  

Microsoft Academic Search

The sandwich plate system (SPS) is a bridge deck system consisting of steel face plates bonded to a rigid polyurethane core. SPS bridges are typically constructed as a series of pre-fabricated SPS deck panels compositely connected with traditional steel girders. The decks are thin, lightweight and modular, and can be tailored to numerous applications including both new bridge and rehabilitated

Devin K. Harris

2012-01-01

45

Fatigue performance of sandwich beams with a pyramidal core  

Microsoft Academic Search

Sandwich beams have been manufactured from AISI type 304 stainless steel faces and AL6XN pyramidal core, and subjected to both monotonic and cyclic three-point bending in order to assess their monotonic and cyclic strengths. Collapse mechanisms maps for monotonic loading, and fatigue maps for cyclic loading are constructed with the aid of simple analytical models for the competing failure modes.

F. Côté; N. A. Fleck; V. S. Deshpande

2007-01-01

46

A study of skin-core adhesion in glass fibre reinforced sandwich materials  

NASA Astrophysics Data System (ADS)

A test technique for measuring skin-core adhesion in fibre reinforced sandwich structures has been developed and applied. The test enables the interfacial fracture energy to be measured for most standard sandwich constructions. The technique has been subsequently employed to investigate skin-core adhesion in a number of sandwich structures similar to those currently used in the marine industry. It has been shown that the interfacial fracture toughness of a GFRP-crosslinked PVC sandwich structure can be as high as 2700 J/m2; however, sandwich constructions based on balsa cores offered considerably lower values of interfacial fracture energy. Here it was found that pre-treating the balsa core prior to bonding of the composite skins has a deleterious effect on the measured fracture toughness. Finally, the results of these tests have been correlated with data obtained from conventional climbing drum and short beam shear tests.

Cantwell, W. J.; Davies, P.

1996-11-01

47

Damage and Compressive Failure of Unbalanced Sandwich Composite Panels Subject to a Low-Velocity Impact.  

National Technical Information Service (NTIS)

An unbalanced sandwich composite structure consisting of titanium and glass reinforced plastic (GRP) facesheets with a phenolic honeycomb core will be used for construction of a surface ship mast. Principle areas of concern in using these composites in pr...

L. B. Fuller

1994-01-01

48

Finite Element Modeling of Sandwich Composite Structures Subject to Low Velocity Impact and Delamination.  

National Technical Information Service (NTIS)

Two common concerns in the use of sandwich composite construction are the effects of low velocity impact and delamination upon structural failure. Finite element analysis of these events can provide a comprehensive time history of the resulting stress str...

G. W. Wojcik

1995-01-01

49

Repair of Damage to Marine Sandwich Structures: Part II - Fatigue Testing.  

National Technical Information Service (NTIS)

Sandwich construction panels, comprising glass reinforced polymer (GRP) composite skins and PVC foam core, are in use in the current generation of naval vessels of the mine hunting class. Such structures will inevitably be subjected to damage and any repa...

M. Z. Shah Khan I. Grabovac

2000-01-01

50

Evaluation of the Flexural Rigidity of Sandwich Structures Using Experimentally Obtained Mechanical Properties of the Constituents  

NASA Astrophysics Data System (ADS)

Prediction of mechanical performance of sandwich constructions is a difficult task due to the complex nonlinear and inelastic behavior of the constituent materials. This study tries to utilize an analytical model to estimate the mechanical performance of sandwich structure based on the mechanical properties of the constituents. To this end, the mechanical properties of the core and skin materials were examined separately. The mechanical behavior and deformation mechanism of Ni alloy foam structures have been studied using uniaxial compression testing. The mechanical properties of alloy 625 coating were determined using tensile testing. The flexural rigidity of sandwich structures were calculated using experimentally obtained elastic moduli of the alloy 625 coating and Ni alloy foam. The model was also used to calculate the flexural rigidity of sandwich samples with different skin thicknesses. This study also investigates the effect of post fabrication heat treatment on the mechanical performance of the sandwich structures.

Azarmi, F.; Coyle, T. W.; Mostaghimi, J.

2010-01-01

51

Wire and Packing Tape Sandwiches  

ERIC Educational Resources Information Center

In this article, the author describes how students can combine craft wire with clear packing tape to create a two-dimensional design that can be bent and twisted to create a three-dimensional form. Students sandwich wire designs between two layers of tape. (Contains 1 online resource.)

Rabinowitz, Sandy

2009-01-01

52

Multicriterion optimization of sandwich shell  

NASA Astrophysics Data System (ADS)

In the paper, a solution of the problem of multiobjective optimization of a sandwich rectangular plate is presented. A non-linear problem is formulated by adopting two conflicting objectives, the minimal deformation and the minimal weight, including a set of constraints.

Ostwald, Marian

53

High temperature structural sandwich panels  

NASA Astrophysics Data System (ADS)

High strength composites are being used for making lightweight structural panels that are being employed in aerospace, naval and automotive structures. Recently, there is renewed interest in use of these panels. The major problem of most commercial available sandwich panels is the fire resistance. A recently developed inorganic matrix is investigated for use in cases where fire and high temperature resistance are necessary. The focus of this dissertation is the development of a fireproof composite structural system. Sandwich panels made with polysialate matrices have an excellent potential for use in applications where exposure to high temperatures or fire is a concern. Commercial available sandwich panels will soften and lose nearly all of their compressive strength temperatures lower than 400°C. This dissertation consists of the state of the art, the experimental investigation and the analytical modeling. The state of the art covers the performance of existing high temperature composites, sandwich panels and reinforced concrete beams strengthened with Fiber Reinforced Polymers (FRP). The experimental part consists of four major components: (i) Development of a fireproof syntactic foam with maximum specific strength, (ii) Development of a lightweight syntactic foam based on polystyrene spheres, (iii) Development of the composite system for the skins. The variables are the skin thickness, modulus of elasticity of skin and high temperature resistance, and (iv) Experimental evaluation of the flexural behavior of sandwich panels. Analytical modeling consists of a model for the flexural behavior of lightweight sandwich panels, and a model for deflection calculations of reinforced concrete beams strengthened with FRP subjected to fatigue loading. The experimental and analytical results show that sandwich panels made with polysialate matrices and ceramic spheres do not lose their load bearing capability during severe fire exposure, where temperatures reach several hundred degrees Centigrade. Hence the material has excellent potential for various types of applications. The analytical predictions from both models provide reasonably accurate results. Glass, AR-glass, carbon and Nicalon tows and carbon fabrics could be successfully used as skin reinforcements increasing the flexural stiffness and strength of the core. No occurrence of fiber delamination was observed.

Papakonstantinou, Christos G.

54

Quasicircular orbits of conformal thin-sandwich puncture binary black holes  

SciTech Connect

I construct initial data for equal-mass irrotational binary black holes using the conformal thin-sandwich puncture approach. I locate quasicircular orbits using the effective-potential method, and estimate the location of the innermost stable circular orbit (ISCO). The ISCO prediction is consistent with results for conformal thin-sandwich data produced using excision techniques. These results also show that the ISCOs predicted by the effective-potential and ADM-Komar mass-comparison methods agree for conformal thin-sandwich data, just as they did for Bowen-York data.

Hannam, Mark D. [Center for Gravitational Wave Astronomy, University of Texas at Brownsville, 80 Fort Brown, Brownsville, Texas 78520 (United States)

2005-08-15

55

Development of biobased sandwich structures for mass transit application  

NASA Astrophysics Data System (ADS)

Efforts to increase the biobased content in sandwich composites are being investigated to reduce the dependence on synthetically produced or mined, energy-intensive materials for numerous composite applications. Vegetable oil-based polyurethane foams are gaining recognition as good substitutes for synthetic counter parts while utilizing bast fiber to replace fiberglass is also gaining credence. In this study, soy oil-based polyurethane foam was evaluated as a core in a sandwich construction with facesheets of hybridized kenaf and E-glass fibers in a vinyl ester resin matrix to replace traditionally used plywood sheeting on steel frame for mass transit bus flooring systems. As a first step towards implementation, the static performance of the biobased foam was compared to 100% synthetic foam. Secondly, biobased sandwich structures were processed and their static performance was compared to plywood. The biobased sandwich composites designed and processed were shown to hold promise towards replacing plywood for bus flooring applications by displaying an increase of 130% for flexural strength and 135% for flexural modulus plus better indentation values.

Munusamy, Sethu Raaj

56

Radially sandwiched cylindrical piezoelectric transducer  

NASA Astrophysics Data System (ADS)

A new type of radially sandwiched piezoelectric short cylindrical transducer is developed and its radial vibration is studied. The transducer is composed of a solid metal disk, a radially polarized piezoelectric ceramic short tube and a metal tube. The radial vibrations of the solid metal disk, the radially polarized piezoelectric tube and the metal tube are analyzed and their electromechanical equivalent circuits are introduced. Based on the mechanical boundary conditions among the metal disk, the piezoelectric tube and the metal tube, a three-port electromechanical equivalent circuit for the radially sandwiched transducer is obtained and the frequency equation is given. The theoretical relationship of the resonance and anti-resonance frequencies and the effective electromechanical coupling coefficient with the geometrical dimensions is analyzed. The radial vibration of the sandwiched transducer is simulated by using two different numerical methods. It is shown that the analytical resonance and anti-resonance frequencies are in good agreement with the numerically simulated results. The transducer is expected to be used in piezoelectric resonators, actuators and ultrasonic radiators in ultrasonic and underwater sound applications.

Lin, Shuyu; Fu, Zhiqiang; Zhang, Xiaoli; Wang, Yong; Hu, Jing

2013-01-01

57

Impact response of integrated hollow core sandwich composite panels  

Microsoft Academic Search

This paper deals with an innovative integrated hollow (space) E-glass\\/epoxy core sandwich composite construction that possesses several multi-functional benefits in addition to the providing lightweight and bending stiffness advantages. In comparison with traditional foam and honeycomb cores, the integrated space core provides a means to route wires\\/rods, embed electronic assemblies, and store fuel and fire-retardant foam, among other conceivable benefits.

U. K Vaidya; M. V Hosur; D Earl; S Jeelani

2000-01-01

58

Experimental Analysis of Foam Sandwich Panels with Projection Moiré  

Microsoft Academic Search

\\u000a The use of polymeric and metallic foam sandwich panels in naval, aerospace, railway and automotive constructions is rapidly\\u000a growing in the recent years because of technological improvements in manufacturing processes. However, it is still difficult\\u000a to establish a direct relationship between the mechanical properties possessed by the panel and the specific manufacturing\\u000a process. Mechanisms behind panel deformation, crack growth, fracture

A. Boccaccio; C. Casavola; L. Lamberti; C. Pappalettere

59

Experimental study of acoustical characteristics of honeycomb sandwich structures  

Microsoft Academic Search

Loss factor measurements were performed on sandwich panels to determine the effects of different skin and core materials on the acoustical properties. Results revealed inserting a viscoelastic material in the core's mid-plane resulted in the highest loss factor. Panels constructed with carbon-fiber skins exhibited larger loss factors than glass-fiber skins. Panels designed to achieve subsonic wave speed did not show

Portia Renee Peters

2009-01-01

60

Evaluation of the Flexural Rigidity of Sandwich Structures Using Experimentally Obtained Mechanical Properties of the Constituents  

Microsoft Academic Search

Prediction of mechanical performance of sandwich constructions is a difficult task due to the complex nonlinear and inelastic\\u000a behavior of the constituent materials. This study tries to utilize an analytical model to estimate the mechanical performance\\u000a of sandwich structure based on the mechanical properties of the constituents. To this end, the mechanical properties of the\\u000a core and skin materials were

F. Azarmi; T. W. Coyle; J. Mostaghimi

2010-01-01

61

Buckling of Sandwich Composites; Effects of Core–Skin Debonding and Core Density  

Microsoft Academic Search

Foam–core sandwich composites have been fabricated using innovative co-injection resin infusion technique and tested under in-plane compression. The sandwich construction consisted of Klegcell foam as core materials and S2-glass\\/vinyl ester composites as face sheets. Tests were conducted with various foam densities and also with implanted delamination between the core and the face sheet. The intent was to investigate the effect

Hassan Mahfuz; Syful Islam; Mrinal Saha; Leif Carlsson; Shaik Jeelani

2005-01-01

62

Performance of metallic honeycomb-core sandwich beams under shock loading  

Microsoft Academic Search

Stainless steel square honeycomb core sandwich and solid monolithic beams have been subjected to high-pressure, short-duration impulses using a shock simulation technique involving high-speed impact of Al foam projectiles. The experiments have been designed to achieve two objectives: (i) to demonstrate the benefits of sandwich construction, and (ii) to assess the fidelity of dynamic finite element calculations in simulating the

H. J. Rathbun; D. D. Radford; Z. Xue; M. Y. He; J. Yang; V. Deshpande; N. A. Fleck; J. W. Hutchinson; F. W. Zok; A. G. Evans

2006-01-01

63

Microvibration response of a stochastically excited sandwich beam with a magnetorheological elastomer core and mass  

Microsoft Academic Search

Magnetorheological (MR) elastomers are used to construct a smart sandwich beam for micro-vibration control. The micro-vibration response of a clamped–free sandwich beam with an MR elastomer core and a supplemental mass under stochastic support micro-motion excitation is studied. The dynamic behavior of MR elastomer as a smart viscoelastic material is described by a complex modulus which is controllable by external

Z G Ying; Y Q Ni

2009-01-01

64

Microvibration response of a stochastically excited sandwich beam with a magnetorheological elastomer core and mass  

Microsoft Academic Search

Magnetorheological (MR) elastomers are used to construct a smart sandwich beam for micro-vibration control. The micro-vibration response of a clamped-free sandwich beam with an MR elastomer core and a supplemental mass under stochastic support micro-motion excitation is studied. The dynamic behavior of MR elastomer as a smart viscoelastic material is described by a complex modulus which is controllable by external

Z. G. Ying; Y. Q. Ni

2009-01-01

65

Mechanical behavior of the sandwich structures with carbon fiber-reinforced pyramidal lattice truss core  

Microsoft Academic Search

Sandwich panel construction with carbon fiber-reinforced pyramidal lattice truss is attracting more and more attention due to its superior mechanical properties and multi-functional applications. Pyramidal lattice truss sandwich panels made from carbon fiber reinforced composites materials are manufactured by hot-pressing. The facesheets are interconnected with truss cores, the facesheets and truss cores are manufactured in one manufacturing process without bonding.

Bing Wang; Linzhi Wu; Li Ma; Yuguo Sun; Shanyi Du

2010-01-01

66

Piezoactuation of sandwich plates with viscoelastic cores  

Microsoft Academic Search

Experimental and analytical validations of a Galerkin analysis of sandwich plates is presented in this paper. The 3-layered sandwich plate specimen consists of isotropic face-plates with surface bonded piezo-electric patch actuators, and a viscoelastic core. The experimental validation is conducted by testing sandwiched plates that are 67.31 cm (26.5') long, 52.07 cm (20.5') wide and nominally 0.16 cm (1\\/16') thick.

Gang Wang; Norman M. Wereley

1999-01-01

67

Compressive strength after blast of sandwich composite materials.  

PubMed

Composite sandwich materials have yet to be widely adopted in the construction of naval vessels despite their excellent strength-to-weight ratio and low radar return. One barrier to their wider use is our limited understanding of their performance when subjected to air blast. This paper focuses on this problem and specifically the strength remaining after damage caused during an explosion. Carbon-fibre-reinforced polymer (CFRP) composite skins on a styrene-acrylonitrile (SAN) polymer closed-cell foam core are the primary composite system evaluated. Glass-fibre-reinforced polymer (GFRP) composite skins were also included for comparison in a comparable sandwich configuration. Full-scale blast experiments were conducted, where 1.6×1.3?m sized panels were subjected to blast of a Hopkinson-Cranz scaled distance of 3.02?m?kg(-1/3), 100?kg TNT equivalent at a stand-off distance of 14?m. This explosive blast represents a surface blast threat, where the shockwave propagates in air towards the naval vessel. Hopkinson was the first to investigate the characteristics of this explosive air-blast pulse (Hopkinson 1948 Proc. R. Soc. Lond. A 89, 411-413 (doi:10.1098/rspa.1914.0008)). Further analysis is provided on the performance of the CFRP sandwich panel relative to the GFRP sandwich panel when subjected to blast loading through use of high-speed speckle strain mapping. After the blast events, the residual compressive load-bearing capacity is investigated experimentally, using appropriate loading conditions that an in-service vessel may have to sustain. Residual strength testing is well established for post-impact ballistic assessment, but there has been less research performed on the residual strength of sandwich composites after blast. PMID:24711494

Arora, H; Kelly, M; Worley, A; Del Linz, P; Fergusson, A; Hooper, P A; Dear, J P

2014-01-01

68

Compressive strength after blast of sandwich composite materials  

PubMed Central

Composite sandwich materials have yet to be widely adopted in the construction of naval vessels despite their excellent strength-to-weight ratio and low radar return. One barrier to their wider use is our limited understanding of their performance when subjected to air blast. This paper focuses on this problem and specifically the strength remaining after damage caused during an explosion. Carbon-fibre-reinforced polymer (CFRP) composite skins on a styrene–acrylonitrile (SAN) polymer closed-cell foam core are the primary composite system evaluated. Glass-fibre-reinforced polymer (GFRP) composite skins were also included for comparison in a comparable sandwich configuration. Full-scale blast experiments were conducted, where 1.6×1.3?m sized panels were subjected to blast of a Hopkinson–Cranz scaled distance of 3.02?m?kg?1/3, 100?kg TNT equivalent at a stand-off distance of 14?m. This explosive blast represents a surface blast threat, where the shockwave propagates in air towards the naval vessel. Hopkinson was the first to investigate the characteristics of this explosive air-blast pulse (Hopkinson 1948 Proc. R. Soc. Lond. A 89, 411–413 (doi:10.1098/rspa.1914.0008)). Further analysis is provided on the performance of the CFRP sandwich panel relative to the GFRP sandwich panel when subjected to blast loading through use of high-speed speckle strain mapping. After the blast events, the residual compressive load-bearing capacity is investigated experimentally, using appropriate loading conditions that an in-service vessel may have to sustain. Residual strength testing is well established for post-impact ballistic assessment, but there has been less research performed on the residual strength of sandwich composites after blast.

Arora, H.; Kelly, M.; Worley, A.; Del Linz, P.; Fergusson, A.; Hooper, P. A.; Dear, J. P.

2014-01-01

69

Composite Sandwich Technologies Lighten Components  

NASA Technical Reports Server (NTRS)

Leveraging its private resources with several Small Business Innovation Research (SBIR) contracts with both NASA and the U.S. Department of Defense, WebCore Technologies LLC, of Miamisburg, Ohio, developed a fiber-reinforced foam sandwich panel it calls TYCOR that can be used for a wide variety of industrial and consumer applications. Testing at Glenn Research Center?s Ballistic Impact Facility demonstrated that the technology was able to exhibit excellent damage localization and stiffness during impact. The patented and trademarked material has found use in many demanding applications, including marine, ground transportation, mobile shelters, bridges, and most notably, wind turbines.

2010-01-01

70

A numerical study of periodic sandwich propellants with oxygenated binders  

NASA Astrophysics Data System (ADS)

We examine sandwich propellants constructed from sheets of pure ammonium perchlorate (AP) interleaved with an AP/binder blend, and construct solutions numerically using a code that fully couples gas-phase and solid-phase processes via an unsteady moving interface. This code has been used elsewhere to simulate the burning of random packs of spherical AP particles embedded in binder. We show that for a stoichiometric configuration, variations of the burning rate with ? (a measure of the oxygenation of the AP/binder blend) are not monotonic, but display a weak maximum; and variations of the burning rate with sandwich thickness are monotonic for small ?, but display a minimum for large ? (e.g. ? = 0.5). When the equivalence ratio is varied, the burning rate displays a maximum on the fuel-lean side when ? is small, on the fuel-rich side when ? is large. These results, and the manner in which the sandwich topography varies with the different parameters, suggest that the configuration could be invaluable for validating the model ingredients and parameter values of heterogeneous propellant combustion codes.

Zhou, Xu; Jackson, T. L.; Buckmaster, J.

2003-06-01

71

Development and Evaluation of Stitched Sandwich Panels  

NASA Technical Reports Server (NTRS)

This study explored the feasibility and potential benefits provided by the addition of through-the-thickness reinforcement to sandwich structures. Through-the-thickness stitching is proposed to increase the interlaminar strength and damage tolerance of composite sandwich structures. A low-cost, out-of-autoclave processing method was developed to produce composite sandwich panels with carbon fiber face sheets, a closed-cell foam core, and through-the-thickness Kevlar stitching. The sandwich panels were stitched in a dry preform state, vacuum bagged, and infiltrated using Vacuum Assisted Resin Transfer Molding (VARTM) processing. For comparison purposes, unstitched sandwich panels were produced using the same materials and manufacturing methodology. Test panels were produced initially at the University of Utah and later at NASA Langley Research Center. Four types of mechanical tests were performed: flexural testing, flatwise tensile testing, core shear testing, and edgewise compression testing. Drop-weight impact testing followed by specimen sectioning was performed to characterize the damage resistance of stitched sandwich panels. Compression after impact (CAI) testing was performed to evaluate the damage tolerance of the sandwich panels. Results show significant increases in the flexural stiffness and strength, out-of-plane tensile strength, core shear strength, edgewise compression strength, and compression-after-impact strength of stitched sandwich structures.

Stanley, Larry E.; Adams, Daniel O.; Reeder, James R. (Technical Monitor)

2001-01-01

72

Reliability of inserts in sandwich composite panels  

Microsoft Academic Search

Inserts are commonly used to transfer loads to sandwich composite structures. Local stress concentrations due to inserts are known to cause structural failure, and experimental pull-out tests show that the failure load can vary by 20% between batches of sandwich panels. Clearly, uncertainty in the mechanical properties of the constituent materials needs to be addressed in the design and optimization

Bryan Smith; Biswajit Banerjee

73

Impact and Blast Resistance of Sandwich Plates  

Microsoft Academic Search

Response of conventional and modified sandwich plate designs is examined under static load, impact by a rigid cylindrical or flat indenter, and during and after an exponential pressure impulse lasting for 0.05 ms, at peak pressure of 100 MPa, simulating a nearby explosion. The conventional sandwich design consists of thin outer (loaded side) and inner facesheets made of carbon\\/epoxy fibrous

George J. Dvorak; Yehia A. Bahei-El-Din; Alexander P. Suvorov

2009-01-01

74

SANDWICH STRUCTURE DELAMINATION OF RESIN TRANSFER MOLDING  

Microsoft Academic Search

One of the apparent advantages of sandwich structures is that after the core is made, the sandwich is produced in one process by resin transfer molding (RTM) and no adhesive is used between the core and skins. The bond between the core and skins is therefore likely to depend upon the core material, the type of matrix and the core

Mohammed T. Hayajneh

2001-01-01

75

Graphene-antenna sandwich photodetector.  

PubMed

Nanoscale antennas sandwiched between two graphene monolayers yield a photodetector that efficiently converts visible and near-infrared photons into electrons with an 800% enhancement of the photocurrent relative to the antennaless graphene device. The antenna contributes to the photocurrent in two ways: by the transfer of hot electrons generated in the antenna structure upon plasmon decay, as well as by direct plasmon-enhanced excitation of intrinsic graphene electrons due to the antenna near field. This results in a graphene-based photodetector achieving up to 20% internal quantum efficiency in the visible and near-infrared regions of the spectrum. This device can serve as a model for merging the light-harvesting characteristics of optical frequency antennas with the highly attractive transport properties of graphene in new optoelectronic devices. PMID:22703522

Fang, Zheyu; Liu, Zheng; Wang, Yumin; Ajayan, Pulickel M; Nordlander, Peter; Halas, Naomi J

2012-07-11

76

Sandwich structures for high temperature applications: Microstructural development and mechanical performance  

NASA Astrophysics Data System (ADS)

There has been a great deal of interest in the development of sandwich structures as viable engineering constructions. It is due to their unique structural, physical, and mechanical characteristics such as light weight, high strength to weight ratio, high bending stiffness, excellent thermal and acoustical insulation. Although the service temperature for most applications of sandwich structures is low, the outstanding properties make sandwich constructions attractive for use in high temperature service conditions as well. The overall performance of sandwich constructions depends on the material properties of skin and core, and their geometrical characteristics. An investigation of the characteristics of sandwich structures suitable for high temperature application is presented. The objective of the investigation was to develop a process for producing sandwich structures by depositing alloy 625 skins on Ni foam cores using air plasma spraying (APS), and to characterize the structure and mechanical behavior of the constituents and the sandwich structure. The experimental investigation consisted of optimization of deposition process parameters, microstructural and mechanical characterization of sandwich constituents and testing of mechanical performance of sandwich structures under flexural loading conditions. The responses of the as-received foam, as-sprayed coating, and as-fabricated sandwich structure to heat treatment were investigated. Available analytical models and numerical simulations linking the mechanical properties of the Ni alloy foam, the alloy 625 coating, and the sandwich structure to their physical properties and microstructures were compared with the results of mechanical testing to understand the behavior of the sandwich structure in terms of the properties of the constituents. An empirical model was developed to predict deposition parameters which simultaneously minimize the oxide content and the porosity in the alloy 625 coating. The optimum spraying conditions produced a coating with less than 4% oxide and less than 3% porosity. The elastic modulus of the as-sprayed coating increased from ˜10% of the value of conventionally processed alloy 625 material to ˜25% of that value after a 5 hour heat treatment at 1100°C. The ductility of the as-sprayed samples was as low as 1% compared to 15--20% for conventionally processed materials. The elastic modulus and yield stress of the as-received Ni alloy foam samples was also improved significantly by heat treatment. The mechanical behavior of sandwich structures with skin thickness of 0.5 and 0.1 mm were examined under four point bending test. The flexural rigidity of the sandwich structures increased after heat treatment for both skin thicknesses, however the rigidity was found to be lower in all cases than the rigidity predicted by analytical models based on the measured properties of the constituents. The dominant failure mode observed for the sandwich samples with skin thicknesses of 0.1 mm and 0.5 mm were core yielding and skin indentation, respectively.

Azarmi, Fardad

77

Piezoelectric Active Vibration Control of Damped Sandwich Beams  

NASA Astrophysics Data System (ADS)

This work presents the design and analysis of the piezoelectric active control of damped sandwich beams. This is done using a specific finite element, able to handle sandwich beams with piezoelectric laminated surface layers and viscoelastic core. The piezoelectric direct and converse effects are accounted for through additional electrical degrees of freedom, condensed at the element level. The frequency dependence of the viscoelastic material properties is modelled using additional dissipative variables resulting from an anelastic displacement fields model. A complex-based modal reduction is then proposed and an equivalent real representation of the reduced-order system is constructed. The control design and performance are then evaluated using three control algorithms applied to the reduced-order model, namely, linear quadratic regulator (LQR), linear quadratic gaussian (LQG) and derivative feedback. To guarantee control feasibility and prevent piezoelectric material depoling, these algorithms are used in an iterative form to account for maximum control voltage. Parametric analyses of an actively controlled damped sandwich beam indicate that LQR controllers improve some selected modal dampings, while retaining the passive damping of uncontrolled modes. Derivative feedback controllers are less effective than an LQR one, but their well-known spillover destabilizing effects are attenuated by the increase of stability margins provided by the viscoelastic damping. It is also shown that LQG controllers may perform as well as LQR ones. Moreover, the delay effect induced by the state estimation of LQG associated with the passive attenuation lead to a damping performance similar to that of LQR with less control voltage. The parametric analyses and the comparative study of control strategies for the active control of damped sandwich beams, accounting for frequency dependence of viscoelastic material properties, are some of the originalities of this work. The others are the analysis of the LQG algorithm and the state space real representation of complex modal reduced models for hybrid piezoelectric-active viscoelastic-passive vibration control which are presented for the first time.

TRINDADE, M. A.; BENJEDDOU, A.; OHAYON, R.

2001-09-01

78

Precast concrete sandwich panels subjected to impact loading  

NASA Astrophysics Data System (ADS)

Precast concrete sandwich panels are a relatively new product in the construction industry. The design of these panels incorporates properties that allow for great resilience against temperature fluctuation as well as the very rapid and precise construction of facilities. The concrete sandwich panels investigated in this study represent the second generation of an ongoing research and development project. This second generation of panels have been engineered to construct midsized commercial buildings up to three stories in height as well as residential dwellings. The panels consist of a double-tee structural wythe, a foam core and a fascia wythe, joined by shear connectors. Structures constructed from these panels may be subjected to extreme loading including the effects of seismic and blast loading in addition to wind. The aim of this work was to investigate the behaviour of this particular sandwich panel when subjected to structural impact events. The experimental program consisted of fourteen concrete sandwich panels, five of which were considered full-sized specimens (2700 mm X 1200mm X 270 mm) and nine half-sized specimens (2700mm X 600mm X 270 mm) The panels were subjected to impact loads from a pendulum impact hammer where the total energy applied to the panels was varied by changing the mass of the hammer. The applied loads, displacements, accelerations, and strains at the mid-span of the panel as well as the reaction point forces were monitored during the impact. The behaviour of the panels was determined primarily from the experimental results. The applied loads at low energy levels that caused little to no residual deflection as well as the applied loads at high energy levels that represent catastrophic events and thus caused immediate failure were determined from an impact on the structural and the fascia wythes. Applied loads at intermediate energy levels representing extreme events were also used to determine whether or not the panels could withstand multiple impacts. It was shown that panels impacted on the fascia wythe are capable of withstanding multiple impacts of energy levels in excess of 16 000 J while panels that were impacted on the structural wythe are capable of resisting a single impact delivering an energy level of 10 000 J or multiple impacts from an energy level of 5 000 J. A Single Degree of Freedom (SDOF) model was developed to predict the maximum deflection of the panels and it provided a good approximation of the deflection observed during the experimental program. A high degree of composite action between the two wythes was determined to exist from the results of high speed video imaging and through SDOF modelling.

Runge, Matthew W.

79

Research of Adaptive Sandwiches and Learning Automata.  

National Technical Information Service (NTIS)

The adaptive sandwich consists of layered elements representing an electroluminescent source, a photoconductive receptor, and intervening electrochemical storage (analog) layer with variable transmissivity, and control electronics. The concept has been in...

R. E. J. Moddes L. O. Gilstrap

1965-01-01

80

Local slamming impact of sandwich composite hulls  

Microsoft Academic Search

We develop a hydroelastic model based on a {3,2}-order sandwich composite panel theory and Wagner’s water impact theory for investigating the fluid–structure interaction during the slamming process. The sandwich panel theory incorporates the transverse shear and the transverse normal deformations of the core, while the face sheets are modeled with the Kirchhoff plate theory. The structural model has been validated

Z. Qin; R. C. Batra

2009-01-01

81

Sandwich technique in nasal dorsal augmentation  

Microsoft Academic Search

Tutoplast fascia lata (TFL) has been used as an onlay graft for nasal dorsal augmentation in open approach rhinoplasty; however,\\u000a insertion of layers of moist TFL in the closed approach is technically challenging. We have presented a “sandwich” technique\\u000a which facilitates graft insertion in a closed approach rhinoplasty. The available autologous graft (cartilage or perpendicular\\u000a plate of ethmoid) is sandwiched

Wolfgang Issing; Shahram Anari

2011-01-01

82

Conditional Logistic Regression with Sandwich Estimators  

Cancer.gov

This IBM PC program performs conditional logistic regression on clustered data and calculates a sandwich ("robust") estimator of the covariance of the regression coefficients. Use of the sandwich estimator allows appropriate inferences for either fixed or random effects across clusters. The program uses two modifications to the usual Wald test to adjust for cases where some parameters are estimated from a small number of clusters.

83

Failure Modes of Composite Sandwich Beams  

Microsoft Academic Search

\\u000a The overall performance of sandwich structures depends in general on the properties of the facesheets, the core, the adhesive\\u000a bonding the core to the skins, as well as geometrical dimensions. Sandwich beams under general bending, shear and in-plane\\u000a loading display various failure modes. Their initiation, propagation and interaction depend on the constituent material properties,\\u000a geometry, and type of loading. Failure

Isaac M. Daniel; Emmanuel E. Gdoutos

2009-01-01

84

Impact and Blast Resistance of Sandwich Plates  

Microsoft Academic Search

\\u000a Response of conventional and modified sandwich plate designs is examined under static load, impact by a rigid cylindrical\\u000a or flat indenter, and during and after an exponential pressure impulse lasting for 0.05 ms, at peak pressure of 100 MPa, simulating\\u000a a nearby explosion. The conventional sandwich design consists of thin outer (loaded side) and inner facesheets made of carbon\\/epoxy\\u000a fibrous

George J. Dvorak; Yehia A. Bahei-El-Din; Alexander P. Suvorov

85

Fabrication and mechanical testing of glass fiber entangled sandwich beams: A comparison with honeycomb and foam sandwich beams  

Microsoft Academic Search

The aim of this paper is the fabrication and mechanical testing of entangled sandwich beam specimens and the comparison of their results with standard sandwich specimens with honeycomb and foam as core materials. The entangled sandwich specimens have glass fiber cores and glass woven fabric as skin materials. The tested glass fiber entangled sandwich beams possess low compressive and shear

Amir Shahdin; Laurent Mezeix; Christophe Bouvet; Joseph Morlier; Yves Gourinat

2009-01-01

86

Thermal performance evaluation of precast concrete three-wythe sandwich wall panels  

Microsoft Academic Search

Precast concrete sandwich wall panels are commonly constructed of two wythes of concrete separated by a layer of thermal insulation. In these two-wythe panels, solid concrete regions are often provided for embedded hardware for lifting, handling, and connections, or to provide composite action. These solid concrete regions can have a significant adverse impact on the thermal performance of the panels.

Byoung-Jun Lee; Stephen Pessiki

2006-01-01

87

Classical and Nonclassical Dynamic Problems of Sandwich Shells with a Transversely Soft Core  

Microsoft Academic Search

Based on the hypothesis of similarity of transverse displacements in thin-walled sandwich shells with a transversely soft core under dynamic and static loads, refined geometrically nonlinear dynamic equations of motion are constructed in the case of large variations in the parameters of the stress-strain state (SSS) in the tangential directions. For shells structurally symmetric across the thickness and loaded with

V. N. Paimushin

2001-01-01

88

Automated Handling, Assembly and Packaging of Highly Variable Compliant Food Products - Making a Sandwich  

Microsoft Academic Search

This paper describes the design, construction and testing of an automated system for the assembly and packaging of triangular sandwiches. This process is currently highly labour intensive with little automated machinery available. This paper analyses the current manual production techniques and develops a number of modular workstations which can be incorporated into an existing line in place of human operators.

Steve Davis; M. G. King; J. W. Casson; J. O. Gray; Darwin G. Caldwell

2007-01-01

89

Experimental study of acoustical characteristics of honeycomb sandwich structures  

NASA Astrophysics Data System (ADS)

Loss factor measurements were performed on sandwich panels to determine the effects of different skin and core materials on the acoustical properties. Results revealed inserting a viscoelastic material in the core's mid-plane resulted in the highest loss factor. Panels constructed with carbon-fiber skins exhibited larger loss factors than glass-fiber skins. Panels designed to achieve subsonic wave speed did not show a significant increase in loss factor above the coincidence frequency. The para-aramid core had a larger loss factor value than the meta-aramid core. Acoustic absorption coefficients were measured for honeycomb sandwiches designed to incorporate multiple sound-absorbing devices, including Helmholtz resonators and porous absorbers. The structures consisted of conventional honeycomb cores filled with closed-cell polyurethane foams of various densities and covered with perforated composite facesheets. Honeycomb cores filled with higher density foam resulted in higher absorption coefficients over the frequency range of 50 -- 1250 Hz. However, this trend was not observed at frequencies greater than 1250 Hz, where the honeycomb filled with the highest density foam yielded the lowest absorption coefficient among samples with foam-filled cores. The energy-recycling semi-active vibration suppression method (ERSA) was employed to determine the relationship between vibration suppression and acoustic damping for a honeycomb sandwich panel. Results indicated the ERSA method simultaneously reduced the sound transmitted through the panel and the panel vibration. The largest reduction in sound transmitted through the panel was 14.3% when the vibrations of the panel were reduced by 7.3%. The influence of different design parameters, such as core density, core material, and cell size on wave speeds of honeycomb sandwich structures was experimentally analyzed. Bending and shear wave speeds were measured and related to the transmission loss performance for various material configurations. The shear modulus of the core showed maximum influence on the wave speeds of the samples, while cell size did not have a significant influence on wave speeds or on transmission loss. Skin material affected wave speeds only in the pure bending regime. Honeycomb sandwich structures with a subsonic core and thus reduced wave speed showed increased transmission loss compared to samples without a subsonic core.

Peters, Portia Renee

90

Piezoelectrically-induced guided wave propagation for health monitoring of honeycomb sandwich structures  

NASA Astrophysics Data System (ADS)

Honeycomb sandwich structures have been widely used in marine and aerospace applications due to their high strength/stiffness-to-weight ratio. However, an excessive load or repeated loading in the core tends to induce debonding along the skin-core interface, threatening the integrity and safety of the whole structure. This dissertation focuses on development of guided wave strategies for health monitoring of honeycomb sandwich structures, based on a piezoelectric actuator/sensor network. The honeycomb sandwich panels, which are composed of aluminum alloy (T6061) skins and hexagonal-celled Nomex core, are specifically considered in the study. First, elastic wave propagation mechanism in honeycomb sandwich structures is numerically and experimentally investigated, based on a piezoelectric actuator/sensor system. Influences of cell geometry parameters upon wave propagation are also discussed. Some wave propagation characteristics, such as wave group velocity dispersion relation and mode tuning capabilities, in the honeycomb composite panels are experimentally characterized. Secondly, effects of skin-core debonding upon the leaky guided wave propagation in honeycomb sandwich structures are studied by the finite element simulation. An appropriate signal difference coefficient is defined to represent the differential features caused by debonding. By means of probability analysis of differential features of transmitted guided waves and the image fusion, the final image of the structure is constructed with improved detection precision. A multilevel sensor network strategy is proposed to detect multiple debondings in the honeycomb sandwich structure. Thirdly, an analytical model considering coupled piezo-elastodynamics is developed to quantitatively describe dynamic load transfer between a surface-bonded piezoelectric wafer actuator and a prestressed plate. The finite element method is used to evaluate the accuracy of the analytical prediction. Effects of prestresses on the characteristics of guided wave generation and propagation, such as time-of-flight, amplitude and wave tuning properties of guided wave modes, are analyzed, based on the developed model. Finally, to overcome the limitations of conventional guided wave methods, a baseline-free detection technique by using nonlinear acoustics is developed for debonding identification in honeycomb sandwich structures. The finite element analysis is performed to understand effects of the interaction of two debonded interfaces upon dynamic behavior of the sandwich structure. Specific experimental study is also conducted on the honeycomb sandwich panel to validate the concept. This dissertation study aims to broaden the scope of existing guided wave methods for debonding detection in honeycomb sandwich structures, and provide some insights for health monitoring of in-service structures.

Song, Fei

91

Sandwich Panels Evaluated With Ultrasonic Spectroscopy  

NASA Technical Reports Server (NTRS)

Enhanced, lightweight material systems, such as 17-4PH stainless steel sandwich panels are being developed for use as fan blades and fan containment systems for next-generation engines. The bond strength between the core and face sheets is critical in maintaining the structural integrity of the sandwich structure. To improve the inspection and production of these systems, researchers at the NASA Glenn Research Center are using nondestructive evaluation (NDE) techniques, such as ultrasonic spectroscopy, to evaluate the brazing quality between the face plates and the metallic foam core. The capabilities and limitations of a swept-frequency approach to ultrasonic spectroscopy were evaluated with respect to these sandwich structures. This report discusses results from three regions of a sandwich panel representing different levels of brazing quality between the outer face plates and a metallic foam core. Each region was investigated with ultrasonic spectroscopy. Then, on the basis of the NDE results, three shear specimens sectioned from the sandwich panel to contain each of these regions were mechanically tested.

Cosgriff, Laura M.

2004-01-01

92

Radiant heating tests of several liquid metal heat-pipe sandwich panels  

SciTech Connect

Integral heat pipe sandwich panels, which synergistically combine the thermal efficiency of heat pipes and the structural efficiency of honeycomb sandwich construction, were conceived as a means of alleviating thermal stress problems in the Langley Scramjet Engine. Test panels which utilized two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and a liquid metal working fluid (either sodium or potassium) were tested by radiant heating at various heat load levels. The heat pipe panels reduced maximum temperature differences by 31 percent with sodium working fluid and 45 percent with potassium working fluid. Results indicate that a heat pipe sandwich panel is a potential, simple solution to the engine thermal stress problem. Other interesting applications of the concept include: cold plates for electronic component and circuit card cooling, radiators for large space platforms, low distortion large area structures (e.g., space antennas) and laser mirrors.

Camarda, C.J.; Basiulis, A.

1983-08-01

93

Radiant heating tests of several liquid metal heat-pipe sandwich panels  

NASA Technical Reports Server (NTRS)

Integral heat pipe sandwich panels, which synergistically combine the thermal efficiency of heat pipes and the structural efficiency of honeycomb sandwich construction, were conceived as a means of alleviating thermal stress problems in the Langley Scramjet Engine. Test panels which utilized two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and a liquid metal working fluid (either sodium or potassium) were tested by radiant heating at various heat load levels. The heat pipe panels reduced maximum temperature differences by 31 percent with sodium working fluid and 45 percent with potassium working fluid. Results indicate that a heat pipe sandwich panel is a potential, simple solution to the engine thermal stress problem. Other interesting applications of the concept include: cold plates for electronic component and circuit card cooling, radiators for large space platforms, low distortion large area structures (e.g., space antennas) and laser mirrors.

Camarda, C. J.; Basiulis, A.

1983-01-01

94

Analysis of Stainless Steel Sandwich Panels with a Metal Foam Core for Lightweight Fan Blade Design  

NASA Technical Reports Server (NTRS)

The quest for cheap, low density and high performance materials in the design of aircraft and rotorcraft engine fan and propeller blades poses immense challenges to the materials and structural design engineers. The present study investigates the use of a sandwich foam fan blade mae up of solid face sheets and a metal foam core. The face sheets and the metal foam core material were an aerospace grade precipitation hardened 17-4 PH stainless steel with high strength and high toughness. The resulting structures possesses a high stiffness while being lighter than a similar solid construction. The material properties of 17-4 PH metal foam are reviewed briefly to describe the characteristics of sandwich structure for a fan blade application. A vibration analysis for natural frequencies and a detailed stress analysis on the 17-4 PH sandwich foam blade design for different combinations of kin thickness and core volume are presented with a comparison to a solid titanium blade.

Min, James B.; Ghosn, Louis J.; Lerch, Bradley A.; Raj, Sai V.; Holland, Frederic A., Jr.; Hebsur, Mohan G.

2004-01-01

95

Mechanical and thermal buckling analysis of rectangular sandwich panels under different edge conditions  

NASA Technical Reports Server (NTRS)

The combined load (mechanical or thermal load) buckling equations were established for orthotropic rectangular sandwich panels under four different edge conditions by using the Rayleigh-Ritz method of minimizing the total potential energy of a structural system. Two-dimensional buckling interaction curves and three-dimensional buckling interaction surfaces were constructed for high-temperature honeycomb-core sandwich panels supported under four different edge conditions. The interaction surfaces provide overall comparison of the panel buckling strengths and the domains of symmetrical and antisymmetrical buckling associated with the different edge conditions. In addition, thermal buckling curves of these sandwich panels are presented. The thermal buckling conditions for the cases with and without thermal moments were found to be identical for the small deformation theory.

Ko, William L.

1994-01-01

96

Analysis of Stainless Steel Sandwich Panels with a Metal Foam Care for Lightweight Fan Blade Design  

NASA Technical Reports Server (NTRS)

The quest for cheap, low density and high performance materials in the design of aircraft and rotorcraft engine fan and propeller blades poses immense challenges to the materials and structural design engineers. Traditionally, these components have been fabricated using expensive materials such as light weight titanium alloys, polymeric composite materials and carbon-carbon composites. The present study investigates the use of P sandwich foam fan blade made up of solid face sheets and a metal foam core. The face sheets and the metal foam core material were an aerospace grade precipitation hardened 17-4 PH stainless steel with high strength and high toughness. The stiffness of the sandwich structure is increased by separating the two face sheets by a foam core. The resulting structure possesses a high stiffness while being lighter than a similar solid construction. Since the face sheets carry the applied bending loads, the sandwich architecture is a viable engineering concept. The material properties of 17-4 PH metal foam are reviewed briefly to describe the characteristics of the sandwich structure for a fan blade application. A vibration analysis for natural frequencies and P detailed stress analysis on the 17-4 PH sandwich foam blade design for different combinations of skin thickness and core volume %re presented with a comparison to a solid titanium blade.

Min, James B.; Ghosn, Louis J.; Lerch, Bradley A.; Raj, Sai V.; Holland, Frederic A., Jr.; Hebsur, Mohan G.

2004-01-01

97

Realization of a broadband low-frequency plate silencer using sandwich plates  

NASA Astrophysics Data System (ADS)

A broadband low-frequency plate silencer is realized experimentally using sandwich plates. The silencer consists of an expansion chamber with two side-branch cavities, each covered by a light but extremely stiff plate. The requirement for high bending stiffness and low density of the plate is satisfied with a sandwich construction by adhering two high-rigidity thin sheets with a relatively thick and light foam core. A test rig is built with a square duct of 100 mm in dimension, and each cavity is 100 mm deep and 500 mm long. Three types of sandwich plates with different mechanical properties are tested. The plate having the highest bending stiffness and lowest density results in a measured stopband from 133 to 274 Hz in which the transmission loss is higher than 10 dB over the whole frequency band. Comparisons between the three sandwich plates partly confirm the theoretical findings on the effect of plate properties on the silencer performance. It is also shown that the mathematical model based on homogeneous plates can provide satisfactory prediction on the performance of a sandwich plate silencer in the low-frequency range of interest. Experimental and theoretical results are found to be in fair agreement.

Wang, Chunqi; Cheng, Li; Huang, Lixi

2008-12-01

98

Long-term hygrothermal effects on damage tolerance of hybrid composite sandwich panels  

NASA Technical Reports Server (NTRS)

A sandwich construction, composed of hybrid carbon-glass fiber-reinforced plastic skins and a syntactic foam core, was selected as the design concept for a wind tunnel compressor blade application, where high damage tolerance and durability are of major importance. Beam specimens were prepared from open-edge and encapsulated sandwich panels which had previously been immersed in water at different temperatures for periods of up to about two years in the extreme case. Moisture absorption and strength characteristics, as related to time of exposure to hygrothermal conditions, were evaluated for the sandwich specimens and their constituents (skins and foam). After different exposure periods, low-velocity impact damage was inflicted on most sandwich specimens and damage characteristics were related to impact energy. Eventually, the residual compressive strengths of the damaged (and undamaged) beams were determined flexurally. Test results show that exposure to hygrothermal conditions leads to significant strength reductions for foam specimens and open-edge sandwich panels, compared with reference specimens stored at room temperature. In the case of skin specimens and for beams prepared from encapsulated sanwich panels that had previously been exposed to hygrothermal conditions, moisture absorption was found to improve strength as related to the reference case. The beneficial effect of moisture on skin performance was, however, limited to moisture contents below 1% (at 50 C and lower temperatures). Above this moisture level and at higher temperatures, strength degradation of the skin seems to prevail.

Ishai, Ori; Hiel, Clement; Luft, Michael

1995-01-01

99

Impact resistance of composite laminated sandwich plates  

NASA Astrophysics Data System (ADS)

Investigated are the effects of face layup sequence and core density of a sandwich plate on the impact delamination area of the laminated facesheet. The sandwich plate is made of graphite/epoxy faces and Nomex honeycomb core. The size and shape of delamination due to impact at each interply location have been measured by the room temperature deply technique. The shape of the interply delamination under impact is, in general, found to be two-lobed. The shape exhibits very peculiar regularity under various experimental conditions. The quantitative measurement of delamination size has shown that the face layup with small relative orientation between adjacent plies and high density core are desirable in sandwich plates to reduce the impact delamination.

Kim, Chun-Gon; Jun, Eui-Jin

100

Sandwiched Rényi divergence satisfies data processing inequality  

NASA Astrophysics Data System (ADS)

Sandwiched (quantum) ?-Rényi divergence has been recently defined in the independent works of Wilde et al. ["Strong converse for the classical capacity of entanglement-breaking channels," preprint arXiv:1306.1586 (2013)] and Müller-Lennert et al. ["On quantum Rényi entropies: a new definition, some properties and several conjectures," preprint arXiv:1306.3142v1 (2013)]. This new quantum divergence has already found applications in quantum information theory. Here we further investigate properties of this new quantum divergence. In particular, we show that sandwiched ?-Rényi divergence satisfies the data processing inequality for all values of ? > 1. Moreover we prove that ?-Holevo information, a variant of Holevo information defined in terms of sandwiched ?-Rényi divergence, is super-additive. Our results are based on Hölder's inequality, the Riesz-Thorin theorem and ideas from the theory of complex interpolation. We also employ Sion's minimax theorem.

Beigi, Salman

2013-12-01

101

Galactosylated electrospun membranes for hepatocyte sandwich culture.  

PubMed

In this work, we developed a galactocylated electrospun polyurethane membrane for sandwich culture of hepatocyte sandwich culture. The electrospun fibrous membranes were bio-functionalized with galactose molecules by a UV-crosslinked layer-by-layer polyelectrolyte multilayer deposition technique. The galactosylated electrospun membranes were employed as a top support membrane for the sandwich culture of HepG2/C3A cells on a collagen substrate. Our results demonstrate that HepG2/C3A cells covered by the galactosylated PU membranes form multi-cellular aggregates and lead to improved albumin secretion ability compared to the control membranes (unmodified PU or poly(ethylene imine)-modified PU). Our study reveals the potential of galactosylated electrospun membranes in the application of liver tissue engineering and the regeneration of liver-tissue substitutes. PMID:24583260

Chien, Hsiu-Wen; Lai, Juin-Yih; Tsai, Wei-Bor

2014-04-01

102

Ballistic Impacts on Composite and Sandwich Structures  

NASA Astrophysics Data System (ADS)

Composite and sandwich structures are sometimes subjected to impacts that result in complete perforation. Tests are conducted to determine the velocity required to achieve complete penetration for a given projectile and a model is required for data reduction purposes, to understand the effect of various parameters and to extrapolate for other test conditions. In addition, models capable of predicting the ballistic limit and the extent of damage in composite and sandwich structures are also needed. This chapter presents a comprehensive and critical assessment of the existing literature on this topic.

Abrate, Serge

103

Rayleigh-Ritz Analysis of Sandwich Beams  

NASA Astrophysics Data System (ADS)

The paper discusses the possibility of predicting the dynamic behaviour, in terms of modal frequencies and loss factors, of sandwich beams with a constrained viscoelastic layer configuration. The problem is approached by the Rayleigh-Ritz method so that virtually any boundary condition can be dealt with by applying a single procedure. Simple polynomials are used as admissible functions and evidence of their good performance is given. The method is also suitable for the analysis of those arrangements where not only the viscoelastic material but also the external layers of the sandwich are damped.

FASANA, A.; MARCHESIELLO, S.

2001-04-01

104

Growth Modes of Epitaxial Au/Co/Au Sandwiches.  

National Technical Information Service (NTIS)

This study investigated the optimum growth conditions of epitaxial Gold/Cobalt/Gold (Au/Co/Au) sandwiches with a strong perpendicular magnetic anisotropy. The thermally induced evolution of sandwich morphology, which determines its magnetic properties, wa...

A. Wawro L. T. Baczewski P. Pankowski M. Kisielewski I. Sveklo

2002-01-01

105

Modified Mode-I Cracked Sandwich Beam (CSB) Fracture Test.  

National Technical Information Service (NTIS)

Five composite sandwich panels were fabricated using vacuum assisted resin transfer molding (VARTM). Four of these panels had E-glass/vinylester facesheets and one had carbon/epoxy facesheets. The sandwich panels had different density PVC foam cores. The ...

S. A. Smith K. N. Shivakumar

2001-01-01

106

Critical velocity of sandwich cylindrical shell under moving internal pressure  

Microsoft Academic Search

Critical velocity of an infinite long sandwich shell under moving internal pressure is studied using the sandwich shell theory\\u000a and elastodynamics theory. Propagation of axisymmetric free harmonic waves in the sandwich shell is studied using the sandwich\\u000a shell theory by considering compressibility and transverse shear deformation of the core, and transverse shear deformation\\u000a of face sheets. Based on the elastodynamics

Jia-xi Zhou; Zi-chen Deng; Xiu-hui Hou

2008-01-01

107

Analyse d'inserts pour les structures sandwich composites  

Microsoft Academic Search

Analysis of insert in sandwich composite structures. While designing sandwich structures, a major issue is how to introduce loads. This is usually done by several kinds of inserts (resin, metallic, etc.). Five kinds of inserts for sandwich structure panels are dealt with in this study. An experimental study is performed in order to describe the breaking points of inserts while

F. Noirot; J.-F. Ferrero; J.-J. Barrau; B. Castanie; M. Sudre

2000-01-01

108

Impact Study of Sandwich Composite Structures with Delamination  

Microsoft Academic Search

Finite element analyses were conducted to analyze the dynamic response of an unbalanced sandwich beam, a balanced sandwich beam, and a balanced sandwich plate subject to a low energy impact. In particular, strain versus time history, failure location and mode, and the influence of an existing delamination crack on the failure were investigated. It was found that, in the presence

Y. W. Kwon; G. W. Wojcik

1998-01-01

109

Damage tolerance of a composite sandwich with interleaved foam core  

Microsoft Academic Search

A composite sandwich panel consisting of carbon fiber-reinforced plastic (CFRP) skins and a syntactic foam core was selected as an appropriate structural concept for the design of wind tunnel compressor blades. Interleaving of the core with tough interlayers was done to prevent core cracking and to improve damage tolerance of the sandwich. Simply supported sandwich beam specimens were subjected to

Ori Ishai; Clement Hiel; T Kevin O'Brien

1992-01-01

110

Embedded piezoelectric ceramic transducers in sandwiched beams  

Microsoft Academic Search

Surface bonded piezoelectric ceramic (PZT) transducers are currently the most prominent area of research in structural health monitoring using electromechanical impedance methods. This paper presents a new embedded PZT patch and its interaction with the host sandwiched beam. Durability and protection from surface finish, vandalism and the environment are important features of the embedment. The paper also demonstrates the use

Venu Gopal Madhav Annamdas; Chee Kiong Soh

2006-01-01

111

Sandwich Panels Evaluated With Ultrasonic Spectroscopy.  

National Technical Information Service (NTIS)

Enhanced, lightweight material systems, such as 17-4PH stainless steel sandwich panels are being developed for use as fan blades and fan containment systems for next-generation engines. The bond strength between the core and face sheets is critical in mai...

L. M. Cosgriff

2004-01-01

112

Perforation of honeycomb sandwich plates by projectiles  

Microsoft Academic Search

An analytical solution for the ballistic limit of a honeycomb plate subjected to normal impact by blunt and spherical projectiles is presented. The solution involves a three-stage, perforation process that results in complete perforation of the sandwich. Stages 1–3 describe perforation of the top facesheet, honeycomb core, and bottom facesheet, respectively. Residual velocities in Stages 1 and 2 are found

M. S. Hoo Fatt; K. S. Park

2000-01-01

113

Sandwich technique in nasal dorsal augmentation.  

PubMed

Tutoplast fascia lata (TFL) has been used as an onlay graft for nasal dorsal augmentation in open approach rhinoplasty; however, insertion of layers of moist TFL in the closed approach is technically challenging. We have presented a "sandwich" technique which facilitates graft insertion in a closed approach rhinoplasty. The available autologous graft (cartilage or perpendicular plate of ethmoid) is sandwiched and secured between layers of TFL (sandwich technique) prior to insertion of the graft for nasal dorsal augmentation in a closed rhinoplasty approach. All our cases of nasal dorsal augmentation were reviewed in a 2 year period. Eight cases of nasal dorsal augmentation in secondary rhinoplasty through a closed approach were reviewed. The ease of insertion and the subsequent manipulation of the graft were noted in all the cases. Good aesthetic results have been noticed in all the cases after an average of 14 months follow-up. The sandwich technique ensures ease of the graft insertion and the subsequent manipulation in a closed approach secondary rhinoplasty for dorsal augmentation. PMID:20490814

Issing, Wolfgang; Anari, Shahram

2011-01-01

114

Simulation of impact on sandwich structures  

Microsoft Academic Search

An explicit finite element based simulation tool has been developed to predict the damage within sandwich structures subjected to low velocity impact. The tool, Sandmesh, is capable of automatically generating three-dimensional shell models of both honeycomb and folded structure cores, as well as applying the necessary controls for solution generation. Sandmesh was validated via an experimental test program in which

M. Q. Nguyen; S. S. Jacombs; R. S. Thomson; D. Hachenberg; M. L. Scott

2005-01-01

115

Blast resistance of prismatic sandwich structures  

Microsoft Academic Search

Metallic sandwich panels have emerged as candidate blast resistant structures that can be tailored to contain damage from impulsive loads of the type typically generated by explosives. When such panels are impulsively loaded, the stresses imposed by the core on the front face, as well as those transmitted through the core, govern the response metrics: especially the center displacement, the

Enrico Ferri

2009-01-01

116

Sandwich sheet for lighter body panels  

SciTech Connect

This article describes a new, lightweight sandwich, consisting of a thermoplastic core between two aluminum sheets, developed for horizontal automotive body parts applications. A 65% weight savings may be possible. For environmental reasons, reduction of fuel consumption in passenger cars is of increased concern. One of the most promising solutions is the application of lightweight materials. It is increasingly clear that material substitution will lead to cars in which several materials will be used, depending upon their functions. In the case of horizontal body panels, flexural rigidity is often regarded as the design criterion. Therefore, sheet materials with the least weight per unit area for a given flexural rigidity are likely to be used. Hoogovens Croep has been developing an aluminum/plastic/aluminum sandwich material, called Hylite. It differs from existing panels in two ways. First, the sandwich contains aluminum skins instead of steel, leading to a lower mass per unit area and to the availability of a broader range of sheet sizes. Second, to maintain a high level of flexural rigidity in the service temperature range ([minus]30[degree] to +85[degree] C), the plastic core has been selected so that the shear modulus exceeds a certain minimum over the entire range. Consequently, sound-deadening properties are comparable to solid sheet material as opposed to sandwich panels which contain plastic in a viscoelastic state. Due to contradictory physical requirements, optimization of both light weight and sound deadening properties cannot be achieved in one type of sheet material. Some of Hylite's properties are discussed.

Not Available

1993-05-01

117

Sandwich panels with functionally graded core  

NASA Astrophysics Data System (ADS)

Although sandwich structure offer advantages over other types of structures, it is important to develop new types of materials in order to obtain the absolute minimum weight for given conditions (e.g., structural geometry and loadings). One alternative is represented by functionally graded materials (defined as materials with properties that vary with location within the material in order to optimize a prescribed function). This study presents different analytical and finite element models for sandwich structures with functionally graded core. The trade-off between weight and stiffness as well as a comparison between these structures and sandwich structures with homogenous core is also presented. The problem of low-velocity impact between a sandwich structure with functionally graded core and a rigid spherical indentor is solved. A few advantages and disadvantages of these types of structure are presented. With the new developments in manufacturing methods these materials can be used for a large number of applications ranging from implant teeth to rocket frames.

Apetre, Nicoleta Alina

118

Vibration characteristics of electrorheological elastomer sandwich beams  

NASA Astrophysics Data System (ADS)

The vibration characteristics and control capabilities of a cantilever sandwich beam with electrorheological (ER) elastomers subjected to different electric fields are investigated in this study. Considering ER elastomers as viscoelastic damping materials with electrically controllable properties, a finite element model of a sandwich beam with an ER elastomer core is developed to predict the vibration responses of the proposed beam. An experimental analysis was also conducted to illustrate and evaluate the effects of an electric field on the frequency responses and natural frequencies of the sandwich beam. The results show that natural frequencies of the ER elastomer sandwich beam increase and vibration amplitudes at natural frequencies of the ER elastomer beam decrease, as the strength of the applied electric field increases. It is demonstrated that the vibration characteristics of ER elastomer beams are similar to those of ER fluid beams, which could be controlled by changing the strength of the applied electric field. This controllable characteristic of ER elastomer beams is useful for applications in engineering structures where variable performance is desired.

Wei, Kexiang; Bai, Quan; Meng, Guang; Ye, Lin

2011-05-01

119

Noise transmission by viscoelastic sandwich panels  

NASA Technical Reports Server (NTRS)

An analytical study on low frequency noise transmission into rectangular enclosures by viscoelastic sandwich panels is presented. Soft compressible cores with dilatational modes and hard incompressible cores with dilatational modes neglected are considered as limiting cases of core stiffness. It is reported that these panels can effect significant noise reduction.

Vaicaitis, R.

1977-01-01

120

Enhancement of blast resistance of sandwich plates  

Microsoft Academic Search

This paper examines the effect of design modifications on response of sandwich plates to impulse pressure loads. The objective is to limit damage by delamination of the laminated facesheets and by crushing of the structural foam core. This has been achieved by introducing structural elements for energy storage, and by reducing the damage-related core crushing that dominates response of conventionally

Yehia A. Bahei-El-Din; George J. Dvorak

2008-01-01

121

Wave propagation in a sandwich structure  

Microsoft Academic Search

The propagation of elastic waves in a sandwich structure with two thin stiff face-plates and a thick compliant core is considered in this paper. A complete description of the dispersion relation with no restrictions on frequency and wavelength is provided. This is accomplished by transforming the wave equation to a Hamiltonian system and then using a transfer matrix approach for

Liping Liu; Kaushik Bhattacharya

2009-01-01

122

Piezoactuation of sandwich plates with viscoelastic cores  

NASA Astrophysics Data System (ADS)

Experimental and analytical validations of a Galerkin analysis of sandwich plates is presented in this paper. The 3-layered sandwich plate specimen consists of isotropic face-plates with surface bonded piezo-electric patch actuators, and a viscoelastic core. The experimental validation is conducted by testing sandwiched plates that are 67.31 cm (26.5') long, 52.07 cm (20.5') wide and nominally 0.16 cm (1/16') thick. The analysis includes the membrane and transverse energies in the face plates, and shear energies in the core. The shear modulus of the dissipative core is assumed to be complex and variant with frequency and temperature. The Golla-Hughes-McTavish (GHM) method is used to account for the frequency dependent properties of the viscoelastic core. Experiments have been conducted on sandwich plates with aluminum face-plates under clamped boundary conditions to validate the model for isotropic face-plates. Symmetric and asymmetric sandwiches have been tested. The maximum error in damped natural frequency predictions obtained via the assumed modes solutions is less than 11%. Analytical studies on the influence of the number of assumed modes in the Galerkin approximation, and the temperature variation, have been conducted. Error in the first plate bending mode is 112% when only a single in-plane mode is used; error reduces to 3.95% as the number of in-plane modes is increased to 25 in each of the in-plane directions. The study on the temperature influence shows that every plate mode has a corresponding temperature, wherein the loss factor is maximized.

Wang, Gang; Wereley, Norman M.

1999-06-01

123

Micro-vibration response of a stochastically excited sandwich beam with a magnetorheological elastomer core and mass  

NASA Astrophysics Data System (ADS)

Magnetorheological (MR) elastomers are used to construct a smart sandwich beam for micro-vibration control. The micro-vibration response of a clamped-free sandwich beam with an MR elastomer core and a supplemental mass under stochastic support micro-motion excitation is studied. The dynamic behavior of MR elastomer as a smart viscoelastic material is described by a complex modulus which is controllable by external magnetic field. The sixth-order partial differential equation of motion of the sandwich beam is derived from the dynamic equilibrium, constitutive and geometric relations. A frequency-domain solution method for the stochastic micro-vibration response of the sandwich beam is developed by using the frequency-response function, power spectral density function and spatial eigensolution. The root-mean-square velocity response in terms of the one-third octave frequency band is calculated, and then the response reduction capacity through optimizing the complex modulus of the core is analyzed. Numerical results illustrate the influences of the MR elastomer core parameters on the root-mean-square velocity response and the high response reduction capacity of the sandwich beam. The developed analysis method is applicable to sandwich beams with arbitrary cores described by complex shear moduli under arbitrary stochastic excitations described by power spectral density functions.

Ying, Z. G.; Ni, Y. Q.

2009-09-01

124

Comparison of structural behavior of superplastically formed/diffusion-bonded sandwich structures and honeycomb core sandwich structures  

NASA Technical Reports Server (NTRS)

A superplasticity formed/diffusion-bonded (SPF/DB) orthogonally corrugated core sandwich structure is discussed and its structural behavior is compared to that of a conventional honeycomb core sandwich structure. The stiffness and buckling characteristics of the two types of sandwich structures are compared under conditions of equal structural density. It is shown that under certain conditions, the SPF/DB orthogonally corrugated core sandwich structure is slightly more efficient than the optimum honeycomb core (square-cell core) sandwich structure. However, under different conditions, this effect can be reversed.

Ko, W. L.

1980-01-01

125

Embedded piezoelectric ceramic transducers in sandwiched beams  

NASA Astrophysics Data System (ADS)

Surface bonded piezoelectric ceramic (PZT) transducers are currently the most prominent area of research in structural health monitoring using electromechanical impedance methods. This paper presents a new embedded PZT patch and its interaction with the host sandwiched beam. Durability and protection from surface finish, vandalism and the environment are important features of the embedment. The paper also demonstrates the use of thickness vibration of the PZT patch in electromechanical admittance formulations. This embedded PZT-structure interaction model is based on the new concept of 'average sum impedance'. The formulations used for this model can be conveniently employed to extract the mechanical impedance of any 'unknown' PZT patch embeddable plane structure. The mechanical impedance of the structure is obtained from the admittance signatures of the embedded PZT patch. The proposed model is experimentally verified on sandwiched beams.

Gopal Madhav Annamdas, Venu; Kiong Soh, Chee

2006-04-01

126

Ultrasonic Spectroscopy of Stainless Steel Sandwich Panels  

NASA Technical Reports Server (NTRS)

Enhanced, lightweight material systems, such as 17-4PH stainless steel sandwich panels are being developed for use as fan blades and fan containment material systems for next generation engines. In order to improve the production for these systems, nondestructive evaluation (NDE) techniques, such as ultrasonic spectroscopy, are being utilized to evaluate the brazing quality between the 17-4PH stainless steel face plates and the 17-4PH stainless steel foam core. Based on NDE data, shear tests are performed on sections representing various levels of brazing quality from an initial batch of these sandwich structures. Metallographic characterization of brazing is done to corroborate NDE findings and the observed shear failure mechanisms.

Cosgriff, Laura M.; Lerch, Bradley A.; Hebsur, Mohan G.; Baaklini, George Y.; Ghosn, Louis J.

2003-01-01

127

Testing Falling Peanut Butter Sandwich Myth  

NSDL National Science Digital Library

In this activity related to rotational inertia (page 1 of the PDF), learners will use a bit of scientific experimenting to test if open-faced peanut butter sandwiches really do always land peanut butter side down. Learners will also test other variables, such as drop height, size of bread slice, and whatever else learners can think of, to arrive at some sound conclusions. Relates to the linked video, DragonflyTV: Microgravity.

Twin Cities Public Television, Inc.

2006-01-01

128

Learning About Ratios: A Sandwich Study  

NSDL National Science Digital Library

This lesson introduces students to the concept of ratio through a hands-on, delicious experiment. After an introductory activity where students identify the ratio of girls to boys in a group of 10 selected students, they create six different peanut butter and jelly sandwiches with different ingredient ratios to find which is the tastiest. Students then plan their own similar experiment using other concoctions which can be expressed in ratios.

Weinberg, Sheryl

1999-01-16

129

Mechanical and thermal buckling analysis of sandwich panels under different edge conditions  

NASA Technical Reports Server (NTRS)

By using the Rayleigh-Ritz method of minimizing the total potential energy of a structural system, combined load (mechanical or thermal load) buckling equations are established for orthotropic rectangular sandwich panels supported under four different edge conditions. Two-dimensional buckling interaction curves and three dimensional buckling interaction surfaces are constructed for high-temperature honeycomb-core sandwich panels supported under four different edge conditions. The interaction surfaces provide easy comparison of the panel buckling strengths and the domains of symmetrical and antisymmetrical buckling associated with the different edge conditions. Thermal buckling curves of the sandwich panels also are presented. The thermal buckling conditions for the cases with and without thermal moments were found to be identical for the small deformation theory. In sandwich panels, the effect of transverse shear is quite large, and by neglecting the transverse shear effect, the buckling loads could be overpredicted considerably. Clamping of the edges could greatly increase buckling strength more in compression than in shear.

Ko, William L.

1993-01-01

130

BMI Sandwich Wing Box Analysis and Test  

NASA Technical Reports Server (NTRS)

A composite sandwich single bay wing box test article was developed by Northrop Grumman and tested recently at NASA Langley Research Center. The objectives for the wing box development effort were to provide a demonstration article for manufacturing scale up of structural concepts related to a high speed transport wing, and to validate the structural performance of the design. The box concept consisted of highly loaded composite sandwich wing skins, with moderately loaded composite sandwich spars. The dimensions of the box were chosen to represent a single bay of the main wing box, with a spar spacing of 30 inches, height of 20 inches constant depth, and length of 64 inches. The bismaleimide facesheet laminates and titanium honeycomb core chosen for this task are high temperature materials able to sustain a 300F service temperature. The completed test article is shown in Figure 1. The tests at NASA Langley demonstrated the structures ability to sustain axial tension and compression loads in excess of 20,000 lb/in, and to maintain integrity in the thermal environment. Test procedures, analysis failure predictions, and test results are presented.

Palm, Tod; Mahler, Mary; Shah, Chandu; Rouse, Marshall; Bush, Harold; Wu, Chauncey; Small, William J.

2000-01-01

131

Glass fiber-reinforced polymer\\/steel hybrid honeycomb sandwich concept for bridge deck applications  

Microsoft Academic Search

Glass fiber-reinforced polymer (GFRP) materials possess inherently high strength-to-weight ratios, but their elastic moduli are low relative to civil engineering (CE) construction materials. As a result, serviceability issues are what govern GFRP material design in the CE bridge industry. Therefore, the study objective was to increase the stiffness of a commercial GFRP honeycomb sandwich panel through the inclusion of steel

Nicolas J Lombardi

2008-01-01

132

Optimization of composite sandwich cover panels subjected to compressive loadings  

NASA Technical Reports Server (NTRS)

An analysis and design method is presented for the design of composite sandwich cover panels that includes transverse shear effects and damage tolerance considerations. This method is incorporated into an optimization program called SANDOP (SANDwich OPtimization). SANDOP is used in the present study to design optimized composite sandwich cover panels for transport aircraft wing applications as a demonstration of its capabilities. The results of this design study indicate that optimized composite sandwich cover panels have approximately the same structural efficiency as stiffened composite cover panels designed to identical constraints. Results indicate that inplane stiffness requirements have a large effect on the weight of these composite sandwich cover panels at higher load levels. Increasing the maximum allowable strain and the upper percentage limit of the 0 degree and plus or minus 45 degree plies can yield significant weight savings. The results show that the structural efficiency of these optimized composite sandwich cover panels is relatively insensitive to changes in core density.

Cruz, Juan R.

1991-01-01

133

COMPRESSIVE STRENGTH OF STAINLESS-STEEL SANDWICHES AT ELEVATED TEMPERATURES  

Microsoft Academic Search

Experimental results are presented from crippling tests of specimens in ; the temperature range from 80 to 1,200 deg F. The specimens included resistance-; welded 177 PH stainless-steel sandwiches with single-corrugated cores, type 301 ; stainless-steel sandwiches with doublecorrugated cores, and brazed 17-7 PH ; stainless-steel sandwiches with honeycomb cores. The experimental strengths are ; compared with predicted buckling and

E. E. Mathauser; R. A. Pride

1959-01-01

134

Sandwich panels with Kagome lattice cores reinforced by carbon fibers  

Microsoft Academic Search

Stretching dominated Kagome lattices reinforced by carbon fibers were designed and manufactured. The sandwich panels were assembled with bonded laminate skins. The mechanical behaviors of the sandwich panels were tested by out-of-plane compression, in-plane compression and three-point bending. Different failure modes of the sandwich structures were revealed. The experimental results showed that the carbon fiber reinforced lattice grids are much

H. L. Fan; F. H. Meng; W. Yang

2007-01-01

135

Buckling Analysis of Debonded Sandwich Panel Under Compression  

NASA Technical Reports Server (NTRS)

A sandwich panel with initial through-the-width debonds is analyzed to study the buckling of its faceskin when subject to an in-plane compressive load. The debonded faceskin is modeled as a beam on a Winkler elastic foundation in which the springs of the elastic foundation represent the sandwich foam. The Rayleigh-Ritz and finite-difference methods are used to predict the critical buckling load for various debond lengths and stiffnesses of the sandwich foam. The accuracy of the methods is assessed with a plane-strain finite-element analysis. Results indicate that the elastic foundation approach underpredicts buckling loads for sandwich panels with isotropic foam cores.

Sleight, David W.; Wang, John T.

1995-01-01

136

Elastic constants for superplastically formed/diffusion-bonded sandwich structures  

NASA Technical Reports Server (NTRS)

Formulae and the associated graphs are presented for contrasting the effective elastic constants for a superplastically formed/diffusion-bonded (SPF/DB) corrugated sandwich core and a honeycomb sandwich core. The results used in the comparison of the structural properties of the two types of sandwich cores are under conditions of equal sandwich density. It was found that the stiffness in the thickness direction of the optimum SPF/DB corrugated core (i.e., triangular truss core) was lower than that of the honeycomb core, and that the former had higher transverse shear stiffness than the latter.

Ko, W. L.

1979-01-01

137

Impact and Blast Resistance of Sandwich Plates  

NASA Astrophysics Data System (ADS)

Response of conventional and modified sandwich plate designs is examined under static load, impact by a rigid cylindrical or flat indenter, and during and after an exponential pressure impulse lasting for 0.05 ms, at peak pressure of 100 MPa, simulating a nearby explosion. The conventional sandwich design consists of thin outer (loaded side) and inner facesheets made of carbon/epoxy fibrous laminates, separated by a thick layer of structural foam core. In the three modified designs, one or two thin ductile interlayers are inserted between the outer facesheet and the foam core. Materials selected for the interlayers are a hyperelas-tic rate-independent polyurethane;a compression strain and strain rate dependent, elastic-plastic polyurea;and an elastomeric foam. ABAQUS and LS-Dyna software were used in various response simulations. Performance comparisons between the enhanced and conventional designs show that the modified designs provide much better protection against different damage modes under both load regimes. After impact, local facesheet deflection, core compression, and energy release rate of delamination cracks, which may extend on hidden interfaces between facesheet and core, are all reduced. Under blast or impulse loads, reductions have been observed in the extent of core crushing, facesheet delaminations and vibration amplitudes, and in overall deflections. Similar reductions were found in the kinetic energy and in the stored and dissipated strain energy. Although strain rates as high as 10-4/s1 are produced by the blast pressure, peak strains in the interlayers were too low to raise the flow stress in the polyurea to that in the polyurethane, where a possible rate-dependent response was neglected. Therefore, stiff polyurethane or hard rubber interlayers materials should be used for protection of sandwich plate foam cores against both impact and blast-induced damage.

Dvorak, George J.; Bahei-El-Din, Yehia A.; Suvorov, Alexander P.

138

Development of the LANL sandwich test.  

SciTech Connect

The Sandwich test is slab-variant of the ubiquitous copper cylinder test, and is used to obtain high explosive product equation-of-state information in the same manner as its predecessor. The motivation for slab geometry is (1) better high-pressure resolution, and (2) the ability to accommodate initial temperature extremes for solid explosive samples. The present design allows initial temperatures from -55 C to 75 C. The pros and cons of the two geometries we discussed, followed by a description of the mechanical design and instrumentation. gample data for several ambient PBX 9501 tests demonstrates excellent data quality and repeatability.

Hill, L. G. (Larry G.)

2001-01-01

139

Deflections of anisotropic sandwich beams with variable face sheets and core thicknesses  

NASA Technical Reports Server (NTRS)

A sandwich construction consists of a low-density core material with high strength face sheets bounded to the top and bottom surfaces. The construction has been widely used in the aerospace and marine industries due to its outstanding characteristics such as noise absorption, weight minimization, heat insulation, and better bending stiffness. In sandwich structures used in high-performance aircraft, the face sheets are often made of fiber-reinforced composite materials and the core is made of honeycomb. The structures may also have variable thickness so as to satisfy aerodynamic requirements. In the stress analysis, the constant-thickness face sheets are usually considered as membrane and the core is assumed to be inextensible but deformable in the thickness direction. The static behavior of variable-thickness, isotropic and homogeneous sandwich beams was successfully studied by employing a constant-thickness theory but allowing stiffnesses to vary in accordance with local thickness variations. It has been recently found in a refined theory that the analyses based on the constant thickness theory locally can lead to significant errors in structural responses if the sandwich beam is thickness-tapered and the cores are deformable in transverse shear. The errors arise mainly from two factors: (1) the transverse shear components of the membrane forces in the face sheets alter the transverse shears carried by the core; and (2) the face-sheet membrane strains arise from transverse shear deformation of the core. In practice the variable thickness may not only exist in core but also in face sheets. The thickness-variations may even be a type of step function. In this case the transverse shear stress in the face sheets and bending stress in the core should be taken into account in the refined theory mentioned. In the present study, energy principles are employed in deriving governing equations for general bending of anisotropic sandwich beams with variable thickness in both face sheets and cores. Solutions to these equations are based on a finite difference scheme. As an example in application, a simply supported thickness-tapered sandwich beam subject to a concentrated load at its center is considered. Let W' be the maximum deflection of the beam in which face sheets are considered as membrane, while W'' is that based on using the modified refined theory. It is found that W' is always larger than W'', however, the magnitude of (W'- W'') appears to be insensitive to the change of the taper of the beam.

Lu, Chu-Ho

1994-01-01

140

Deflections of anisotropic sandwich beams with variable face sheets and core thicknesses  

NASA Astrophysics Data System (ADS)

A sandwich construction consists of a low-density core material with high strength face sheets bounded to the top and bottom surfaces. The construction has been widely used in the aerospace and marine industries due to its outstanding characteristics such as noise absorption, weight minimization, heat insulation, and better bending stiffness. In sandwich structures used in high-performance aircraft, the face sheets are often made of fiber-reinforced composite materials and the core is made of honeycomb. The structures may also have variable thickness so as to satisfy aerodynamic requirements. In the stress analysis, the constant-thickness face sheets are usually considered as membrane and the core is assumed to be inextensible but deformable in the thickness direction. The static behavior of variable-thickness, isotropic and homogeneous sandwich beams was successfully studied by employing a constant-thickness theory but allowing stiffnesses to vary in accordance with local thickness variations. It has been recently found in a refined theory that the analyses based on the constant thickness theory locally can lead to significant errors in structural responses if the sandwich beam is thickness-tapered and the cores are deformable in transverse shear. The errors arise mainly from two factors: (1) the transverse shear components of the membrane forces in the face sheets alter the transverse shears carried by the core; and (2) the face-sheet membrane strains arise from transverse shear deformation of the core. In practice the variable thickness may not only exist in core but also in face sheets. The thickness-variations may even be a type of step function. In this case the transverse shear stress in the face sheets and bending stress in the core should be taken into account in the refined theory mentioned. In the present study, energy principles are employed in deriving governing equations for general bending of anisotropic sandwich beams with variable thickness in both face sheets and cores. Solutions to these equations are based on a finite difference scheme. As an example in application, a simply supported thickness-tapered sandwich beam subject to a concentrated load at its center is considered. Let W' be the maximum deflection of the beam in which face sheets are considered as membrane, while W'' is that based on using the modified refined theory. It is found that W' is always larger than W'', however, the magnitude of (W'- W'') appears to be insensitive to the change of the taper of the beam.

Lu, Chu-Ho

1994-12-01

141

Testing of the scintillation sandwich prototype  

SciTech Connect

The 3 m{sup 2} prototype of the surface detector using optical fiber readout was completely prepared for testing measurements in February 1995 at Fermilab. Two 25 mm thick, 3 m{sup 2} acrylic scintillation plates (1.2 {times} 2.5 m{sup 2}) are used for light collection in the upper (above the 25 mm steel plate) and lower (below the steel) counters of the sandwich. The light is collected with the help of 1 mm diameter wavelength shifter fiber loops 3 m long inserted in the grooves on the top surface of the scintillator, 3 fibers per groove. We used Kurary Y11, 200 ppm of shifter dye, and double clad fibers. 1.5 m of clear fibers spliced to each end of the shifter fiber transport the light to the phototube. Spacing between the grooves is 5 cm. The counter`s edges were painted with BICRON (BC620) white reflective paint. The scintillation plates were wrapped with Dupont Tyvek. The glued bundle of fibers is connected to an EMI-9902KB 38 mm phototube through the simple light mixer bar. Used PM has a ``green extended`` rubidium bialkali photocathode. The report contains information on the testing of the scintillation sandwich.

Vashkevich, V. [Moscow State Univ. (Russian Federation). Inst. of Nuclear Physics

1995-06-01

142

Aluminium foam sandwich structures for space applications  

NASA Astrophysics Data System (ADS)

Within a French/German research project the suitability of a new class of materials, so-called aluminium foam sandwiches (AFS), was tested for space applications. While classical sandwich materials require particular, cost and time intensive processing techniques, AFS are suitable for mass production technologies as they are known from car industry and the like. Thus, it is expected that such materials could essentially contribute to cost reduction in space. In order to test the principal applicability and to gain some first experience in how the manufacture of AFS space components could work, a cone 3936 as used in Ariane 5 was chosen as demonstrator. In the forefront, the material had been intensively tested considering mechanical and thermal properties. By means of FEM the results of these experiments were used to simulate the behaviour under load and to optimise the design accordingly. Using AFS suitable production methods, the cone was built and tested simulating the loads during launch. The test results were compared to the predictions made by FEM and showed good agreement.

Schwingel, Dirk; Seeliger, Hans-Wolfgang; Vecchionacci, Claude; Alwes, Detlef; Dittrich, Jürgen

2007-06-01

143

An integrated assembly method of sandwich structured ceramic matrix composites  

Microsoft Academic Search

Sandwich structured composites have been widely studied and applied at ambient temperature in aeronautical, automobile and naval applications. For high temperature applications, an integrated ceramic sandwich structure could take advantage of multiple functions such as skin stiffness and core insulation. For thermo-structural applications, skins must be made of ceramic matrix composites (CMC) because of their strength, their resistance to high

Alberto Ortona; Simone Pusterla; Sandro Gianella

2011-01-01

144

Bending and springback theory of metal-polymer sandwich laminates  

Microsoft Academic Search

In this report an analysis is made of the behavior of sandwich beams in which the core polymer is laminated on both sides with surface metal sheets, each of which has a different thickness and mechanical properties when they are loaded with a uniform bending moment which is then released resulting in springback of the bent sandwich beam. It is

Katsuhiko Ito; Masayuki Kasajima; Susumu Furuya

1981-01-01

145

High Velocity Impact Response of Composite Lattice Core Sandwich Structures  

NASA Astrophysics Data System (ADS)

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.

Wang, Bing; Zhang, Guoqi; Wang, Shixun; Ma, Li; Wu, Linzhi

2014-04-01

146

A Cost Basis for Resource Allocation for Sandwich Courses.  

ERIC Educational Resources Information Center

The use of a computer-based resource allocation procedure for cooperative education ("sandwich" coursework) at the University of Bath in Great Britain is discussed. Costs of undergraduate sandwich courses are compared with those of the more traditional 3-year, full-time undergraduate courses in British universities. Distinction is made between…

Taylor, Bryan J. R.

1984-01-01

147

Practical Instruction in Tissue Culture and Cytogenetics for Sandwich Students.  

ERIC Educational Resources Information Center

Describes the training and practical techniques taught to students involved in a sandwich course at the Tissue Culture and Cytogenetics Unit of the Marie Curie Memorial Foundation, Surrey, England. Students spend a minimum of six months involved in the sandwich course before returning to university for a final academic year. (JR)

Williams, D. C.; Bishun, N. P.

1973-01-01

148

Axisymmetric parametric resonance of polar orthotropic sandwich annular plates  

Microsoft Academic Search

Parametric resonance of polar orthotropic sandwich annular plates with a viscoelastic core layer subjected to a periodic uniform radial stress is studied by the finite element method. The axisymmetric discrete layer annular element and Hamilton's principle are employed to derive the finite element equations of motion for a sandwich plate including the transverse shear effect. The viscoelastic material in the

Yu-Ren Chen; Lien-Wen Chen

2004-01-01

149

Experimental Investigation of Sandwich Flat Panels Under Low Velocity Impact.  

National Technical Information Service (NTIS)

This study evaluated the failure modes and mechanisms associated with increasing face sheet thickness of flat sandwich panels under low velocity impact. The sandwich panels were fabricated using 1.27 cm thick, 145 kg/cu m (9 lb/cu ft), 3.175 mm (1/8 in.) ...

T. M. Harrington

1994-01-01

150

Development of the hybrid insert for composite sandwich satellite structures  

Microsoft Academic Search

Composite sandwich structures which are widely employed in satellite structures require many inserts for assembly. In this study, a new lightweight insert for sandwich structures was developed by reinforcing the web of insert with high strength carbon composite to increase the loading capability with reduced mass. Finite element analysis was performed to numerically predict the load capability of the new

Jun Woo Lim; Dai Gil Lee

2011-01-01

151

Dynamic Stability of a Sandwich Beam with Magnetorheological Core  

Microsoft Academic Search

This study investigated the dynamic stability of a simply supported sandwich beam with a magnetorheological core under an axial harmonic and parametric load. The complex modulus of the magnetorheological material is a function of the applied magnetic field. The governing equation of motion is theoretically derived using the Mead and Markus sandwich beam model, and also by applying Galerkin's method

Zi-Fong Yeh; Yan-Shin Shih

2006-01-01

152

High Velocity Impact Response of Composite Lattice Core Sandwich Structures  

NASA Astrophysics Data System (ADS)

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.

Wang, Bing; Zhang, Guoqi; Wang, Shixun; Ma, Li; Wu, Linzhi

2013-10-01

153

Flexural Properties of Nanoclay Syntactic Foam Sandwich Structures  

Microsoft Academic Search

ABSTRACT Sandwich composites are commonly used for marine, aerospace, and other structural applications due to their exceptional properties, such as low weight, high specific strength and,bending,stiffness [1]. These sandwich structures are produced by attaching two thin but stiff skins to a lightweight thick core. The skins can be madeof fiber reinforced composites, such as glass or carbon fiber reinforced laminates.

Narendra Sankella

2008-01-01

154

PIEZOELECTRIC ACTIVE VIBRATION CONTROL OF DAMPED SANDWICH BEAMS  

Microsoft Academic Search

This work presents the design and analysis of the piezoelectric active control of damped sandwich beams. This is done using a specific finite element, able to handle sandwich beams with piezoelectric laminated surface layers and viscoelastic core. The piezoelectric direct and converse effects are accounted for through additional electrical degrees of freedom, condensed at the element level. The frequency dependence

M. A. TRINDADE; A. Benjeddou; R. Ohayon

2001-01-01

155

Characterization of Wood-Polypropylene Composite Sandwich System  

Microsoft Academic Search

A new wood-polypropylene composite sandwich was made by bonding unidirectional continuous glass fiber reinforced polypropylene (UCGPP) composite to oak wood using a thermoplastic tie layer. In order to evaluate the practical utility of wood-composite sandwich systems, the effects of moisture changes in both continuous and cyclic manner were investigated by monitoring the modulus change. Dynamic mechanical analysis (DMA) of neat

Ganesan Kumar; Karthik Ramani

2000-01-01

156

Damage detection of sandwich structure using time domain reflectometry  

Microsoft Academic Search

Sandwich structure shows high vulnerability at low speed impact, such as hail impact. Several non-destructive health monitoring methods exist, but not many practical methods can detect damage in real time. In this experiment, time domain reflectometry, TDR, is used to detect impact damages on sandwich structure. Time domain reflectometer sends a pulse of signal that travels through electrical pathway and

Seung-il Kim

2009-01-01

157

Tensile properties of stainless steel sandwich sheets with fibrous cores  

Microsoft Academic Search

The unnotched and notched tensile properties of flocked and brazed stainless steel sandwiches with fibrous cores were examined. The tensile stress-strain responses show that the fibres do not carry any load in the flocked sheets and that the load transfer is better facilitated in the brazed sandwich sheets. Notched strength results show that the flocked sheets are notch-insensitive whereas the

M. A. Azeem; C. Shortall; U. Ramamurty

2007-01-01

158

Finite Element Modeling of the Buckling Response of Sandwich Panels  

NASA Technical Reports Server (NTRS)

A comparative study of different modeling approaches for predicting sandwich panel buckling response is described. The study considers sandwich panels with anisotropic face sheets and a very thick core. Results from conventional analytical solutions for sandwich panel overall buckling and face-sheet-wrinkling type modes are compared with solutions obtained using different finite element modeling approaches. Finite element solutions are obtained using layered shell element models, with and without transverse shear flexibility, layered shell/solid element models, with shell elements for the face sheets and solid elements for the core, and sandwich models using a recently developed specialty sandwich element. Convergence characteristics of the shell/solid and sandwich element modeling approaches with respect to in-plane and through-the-thickness discretization, are demonstrated. Results of the study indicate that the specialty sandwich element provides an accurate and effective modeling approach for predicting both overall and localized sandwich panel buckling response. Furthermore, results indicate that anisotropy of the face sheets, along with the ratio of principle elastic moduli, affect the buckling response and these effects may not be represented accurately by analytical solutions. Modeling recommendations are also provided.

Rose, Cheryl A.; Moore, David F.; Knight, Norman F., Jr.; Rankin, Charles C.

2002-01-01

159

Damage tolerance assessment of composite sandwich panels with localised damage  

Microsoft Academic Search

The work described herein is part of a larger context in which the effect of damage in sandwich composite structures for marine applications has been investigated. The overall aim of this effort has been twofold: to develop and verify existing damage assessment models to be used to assess the effect of damage on marine sandwich structures, and to develop a

Dan Zenkert; Andrey Shipsha; Peter Bull; Brian Hayman

2005-01-01

160

Influence of reinforcement type on the mechanical behavior and fire response of hybrid composites and sandwich structures  

NASA Astrophysics Data System (ADS)

Lightweight composites and structural sandwich panels are commonly used in marine and aerospace applications. Using carbon, glass, and a host of other high strength fiber types, a broad range of laminate composites and sandwich panels can be developed. Hybrid composites can be constructed by laminating multiple layers of varying fiber types while sandwich panels are manufactured by laminating rigid fiber facings onto a lightweight core. However, the lack of fire resistance of the polymers used for the fabrication remains a very important problem. The research presented in this dissertation deals with an inorganic matrix (Geopolymer) that can be used to manufacture laminate composites and sandwich panels that are resistant up to 1000°C. This dissertation deals with the influence of fiber type on the mechanical behavior and the fire response of hybrid composites and sandwich structures manufactured using this resin. The results are categorized into the following distinct studies. (i) High strength carbon fibers were combined with low cost E-glass fibers to obtain hybrid laminate composites that are both economical and strong. The E-glass fabrics were used as a core while the carbon fibers were placed on the tension face and on both tension and compression faces. (ii) Structural sandwich beams were developed by laminating various types of reinforcement onto the tension and compression faces of balsa wood cores. The flexural behavior of the beams was then analyzed and compared to beams reinforced with organic composite. The effect of core density was evaluated using oak beams reinforced with inorganic composite. (iii) To measure the fire response, balsa wood sandwich panels were manufactured using a thin layer of a fire-resistant paste to serve for fire protection. Seventeen sandwich panels were fabricated and tested to measure the heat release rates and smoke-generating characteristics. The results indicate that Geopolymer can be effectively used to fabricate both high strength composite plates and sandwich panels. A 2 mm thick coating of fireproofing on balsa wood is sufficient to satisfy FAA fire requirements.

Giancaspro, James William

161

Vibration and formability characteristics of aluminum-polymer sandwich materials  

NASA Astrophysics Data System (ADS)

Metal/polymer/metal sandwich materials are finding increasing use in the automotive industry primarily as lightweight alternatives to steel and aluminum alloys. In addition to low density they also offer other functional benefits e.g. improved vibration damping. In order to exploit such beneficial characteristics it is necessary to examine the manufacturability of these materials. In this work the vibration characteristics and formability were examined in selected materials, chosen from a group of aluminum/polypropylene/aluminum sandwich materials. First, a systematic study was carried out on vibration characteristics of square sandwich plates using 3D finite element models and usefulness of such a 3D displacement field in understanding the damping mechanisms as well as their contributions toward the modal damping were discussed. Second, a study of stretch formability of several sandwich materials was conducted. Since the knowledge of tensile properties is essential for understanding the formability, those properties were determined by performing uniaxial tensile tests on several aluminum/polypropylene/aluminum (HyliteRTM) sandwich materials and their constituent materials. The phenomena of diffused necking and deformation of material up to and beyond the point of necking were systematically investigated. Furthermore, the formability of sandwich materials was assessed by comparing the experimentally determined forming limit diagrams (FLDs) of monolithic 5182 aluminum and several sandwich materials. In addition to the experimental research, theoretical modeling was carried out to predict formability based on the concept of growth of pre-existing defects. One such model, known as M-K analysis, was utilized on the basis of defects existing in (i) the aluminum skins and (ii) the overall thickness of the sandwich. The experimental and theoretical results suggest that the levels of forming limit in sandwich materials are far less than those for monolithic materials of equivalent stiffness. This result may be related to smaller defect factor in the skin of the sandwich materials.

Somayajulu, Thamma S. V.

162

Impact damage in aircraft composite sandwich panels  

NASA Astrophysics Data System (ADS)

An experimental study was conducted to develop an improved understanding of the damage caused by runway debris and environmental threats on aircraft structures. The velocities of impacts for stationary aircraft and aircraft under landing and takeoff speeds was investigated. The impact damage by concrete, asphalt, aluminum, hail and rubber sphere projectiles was explored in detail. Additionally, a kinetic energy and momentum experimental study was performed to look at the nature of the impacts in more detail. A method for recording the contact force history of the impact by an instrumented projectile was developed and tested. The sandwich composite investigated was an IM7-8552 unidirectional prepreg adhered to a NOMEXRTM core with an FM300K film adhesive. Impact experiments were conducted with a gas gun built in-house specifically for delivering projectiles to a sandwich composite target in this specic velocity regime (10--140 m/s). The effect on the impact damage by the projectile was investigated by ultrasonic C-scan, high speed camera and scanning electron and optical microscopy. Ultrasonic C-scans revealed the full extent of damage caused by each projectile, while the high speed camera enabled precise projectile velocity measurements that were used for striking velocity, kinetic energy and momentum analyses. Scanning electron and optical images revealed specific features of the panel failure and manufacturing artifacts within the lamina and honeycomb core. The damage of the panels by different projectiles was found to have a similar damage area for equivalent energy levels, except for rubber which had a damage area that increased greatly with striking velocity. Further investigation was taken by kinetic energy and momentum based comparisons of 19 mm diameter stainless steel sphere projectiles in order to examine the dominating damage mechanisms. The sandwich targets were struck by acrylic, aluminum, alumina, stainless steel and tungsten carbide spheres of the same geometry (19mm diameter) and surface finish. A peak absorbed energy for perforation of 34.5J was identied regardless of the projectile density. The effect of composite panel manufacturing methods on the impact damage and energy absorption of the panel was also investigated. Specifically, damage related to pre-cured facesheets is compared to the co-cured facesheets used throughout the study.

Mordasky, Matthew D.

163

Blast resistance of prismatic sandwich structures  

NASA Astrophysics Data System (ADS)

Metallic sandwich panels have emerged as candidate blast resistant structures that can be tailored to contain damage from impulsive loads of the type typically generated by explosives. When such panels are impulsively loaded, the stresses imposed by the core on the front face, as well as those transmitted through the core, govern the response metrics: especially the center displacement, the resistance to tearing and the loads transmitted to the supports. Prismatic cores such as I-, X-, Y- and Z- cores differ from other cores, such as foams and trusses, in that they do not exhibit constant dynamic crush strength, enabling collapse to occur in a controlled manner. Establishing relationships between core topology crushing response and panel performance is one of the major goals of this research. For this purpose a gas gun instrumented with high speed photography and direct impact Hopkinson pressure bar was built and used to perform laboratory scale high-speed impact tests. Samples of representative prismatic core unit cells were manufactured and tested in compression at axial velocities ranging from quasi-static to 200m/s. The dynamic strength and deformation (buckling) were measured and used to calibrate the imperfections in a finite element model. The model was then used to validate a constitutive model that can be used to predict the blast resistance of prismatic sandwich structures. This research identifies a simple dual level dynamic strength as a common response in metallic prismatic cores. This is due to the dominant effect of plastic shock generated by dynamic loading. Furthermore, it justifies the use of a simple dynamic axial compression test for calibration of the dynamic strength of the core. An analytical model that accounts for the shock effects in a homogenized core and embodies the dual-level dynamic strength is presented. It is shown to capture the experimental observations and simulated results with acceptable fidelity. This model provides the basis for a constitutive model that can be used to understand the response of sandwich plates subject to impulsive loads.

Ferri, Enrico

164

Nanoparticle organization in sandwiched polymer brushes.  

PubMed

The organization of nanoparticles inside grafted polymer layers is governed by the interplay of polymer-induced entropic interactions and the action of externally applied fields. Earlier work had shown that strong external forces can drive the formation of colloidal structures in polymer brushes. Here we show that external fields are not essential to obtain such colloidal patterns: we report Monte Carlo and molecular dynamics simulations that demonstrate that ordered structures can be achieved by compressing a "sandwich" of two grafted polymer layers, or by squeezing a coated nanotube, with nanoparticles in between. We show that the pattern formation can be efficiently controlled by the applied pressure, while the characteristic length-scale, that is, the typical width of the patterns, is sensitive to the length of the polymers. Based on the results of the simulations, we derive an approximate equation of state for nanosandwiches. PMID:24707901

Curk, Tine; Martinez-Veracoechea, Francisco J; Frenkel, Daan; Dobnikar, Jure

2014-05-14

165

Peanut Butter Cracker Sandwich Manufacturing Module  

NSDL National Science Digital Library

For many engineers, their first position after obtaining a B.S. degree is in manufacturing. Job titles like process engineer, product engineer, and quality engineer are common and are directly involved in manufacturing. Most engineering curricula do not cover manufacturing concepts. A student may not even have an opportunity through electives to study manufacturing since smaller engineering colleges rarely have a department of Manufacturing Engineering.A module on peanut butter cracker manufacturing was developed for the Introduction to Engineering course taken by most engineering students in their freshman year. The objective for the students is to design, build and then run a process to manufacture peanut butter cracker sandwiches. The culminating activity is a pilot production run where the students are assigned human operators for their process. The goal for the students is to make a profit during the pilot production run. Material costs, labor costs, quality specifications and selling price all determine whether or not the process was successful. The module includes activities where the students perform calculations and use Excel graphs to determine the process time required to make a profit, the impact of the number of operators on production, the interplay between fixed and variable costs, and the effect of yield on their profit. Students are required to write operating procedures and order supplies based on predictions of the quantity of sandwiches they will produce. Students also learn about quality control and process control, the cost of automation, development costs, and challenges in training operators. After more than two weeks of preparation, the students have 10 minutes to train their operators, and then the operators run the process for 10 minutes. After production day, the students write a report that includes an analysis of their production performance and suggested process modifications. Overall, the module provides a fun and informative introduction to some fundamental manufacturing concepts.The module learning objectives, section descriptions and handouts are included.

2009-08-05

166

Seismic load tests on reinforced concrete beam-column sandwich joints with strengthening measures  

NASA Astrophysics Data System (ADS)

Reinforced concrete high-rise buildings with high strength concrete (HSC) column and normal strength concrete (NSC) floor are popular nowadays. For these structures, it is ineffective to construct beam-column joint with high strength concrete. So beam-column joints with normal strength concrete attract abundant attention and are strongly recommended in china recent years. In this paper, we refer to this type of joints as sandwich joints. In order to improve seismic behavior of sandwich joints with high stress, strengthening measures including addition of vertical dowels, addition of diagonal bars, and enhancement of joint constraint were proposed to apply to engineering practice recent years. In this paper, 6 full scale sandwich joint specimens were test under cyclic load to investigate the validity of strengthening measures. Tested specimens were consist of 1 specimen with additional vertical dowels, 2 specimens with additional diagonal bars, and 1 specimen with additional lateral beams, compared with 2 specimens without strengthening measures. Integrated seismic performances of these specimens were studied, such as load resistance behavior, deflection performance, ductility, energy dissipation behavior, beam bars anchorage capacity and so on. Based on the experimental results, the effect and mechanical behavior of strengthening measures were analyzed.

Yang, Zhi-Hong; Li, Ying-Min; Liu, Jian-Wei

2009-12-01

167

Development and Mechanical Behavior of FML/Aluminium Foam Sandwiches  

NASA Astrophysics Data System (ADS)

In this study, the Fiber-Metal Laminates (FMLs) containing glass fiber reinforced polypropylene (GFPP) and aluminum (Al) sheet were consolidated with Al foam cores for preparing the sandwich panels. The aim of this article is the comparison of the flexural properties of FML/Al foam sandwich panels bonded with various surface modification approaches (silane treatment and combination of silane treatment with polypropylene (PP) based film addition). The FML/foam sandwich systems were fabricated by laminating the components in a mould at 200 °C under 1.5 MPa pressure. The energy absorbtion capacities and flexural mechanical properties of the prepared sandwich systems were evaluated by mechanical tests. Experiments were performed on samples of varying foam thicknesses (8, 20 and 30 mm). The bonding among the sandwich components were achieved by various surface modification techniques. The Al sheet/Al foam sandwiches were also consolidated by bonding the components with an epoxy adhesive to reveal the effect of GFPP on the flexural performance of the sandwich structures.

Ba?türk, S. B.; Tano?lu, M.

2013-10-01

168

Fibrin glue sandwich prevents pancreatic fistula following distal pancreatectomy.  

PubMed

Pancreatic fistula is a major form of morbidity following pancreatic resection. We conducted a nonrandomized clinical trial comparing the sealing and sandwich techniques of spraying fibrin glue to prevent pancreatic fistula following distal pancreatectomy. The pancreas was transected with a scalpel to identify and suture the main pancreatic duct and its small branches. In the sealing group, fibrin glue was sprayed over the closed pancreatic stump and sutures. Alternatively, in the sandwich group fibrin glue was sprayed so as to cover and join the cut surface of the pancreatic remnant, which was then held closed with sutures. Altogether 111 patients were included in the study (90 with gastric cancer, 10 with esophageal cancer, and 11 with pancreatic cancer). Patients were nonrandomly assigned to the sandwich or the sealing group. Morbidity was 21.8% for the patients in the sandwich group versus 33.9% in the sealing group. Pancreatic fistulas occurred in 9.0% of the sandwich group versus 26.8% of the sealing group. The incidence of fistula was thus significantly lower in the sandwich group. The incidence of fistula was also significantly lower in the sandwich group for gastric malignancy patients undergoing extended radical lymphadenectomy down to the paraaortic lymph nodes combined with left adrenalectomy. Of the patients with gastric malignancy, pancreatic fistulas occurred in 9.3% of the sandwich group versus 25.5% of the sealing group. The fibrin glue sandwich technique is simple and reliable and should be valuable for complementing other prophylactic methods of preventing pancreatic fistula. PMID:9564295

Ohwada, S; Ogawa, T; Tanahashi, Y; Nakamura, S; Takeyoshi, I; Ohya, T; Ikeya, T; Kawashima, K; Kawashima, Y; Morishita, Y

1998-05-01

169

Conjoined Cochlear Models:. the Twamp and the Sandwich  

NASA Astrophysics Data System (ADS)

A new model of the cochlea is created by joining parts of the traveling-wave amplifier (TWAMP) and the Sandwich models. The lossy, untuned traveling-wave line of the TWAMP is retained, but the TWAMP's tuned traveling-wave line is replaced by the Sandwich's traveling-wave line that represents the reticular lamina (RL) and scala tympani. The model combines stereocilliary forces, which act between the tectorial membrane (TM) and RL, with somatic outer hair cell forces that power the Sandwich.

Hubbard, Allyn

2009-02-01

170

Low-Velocity Impact on Composite Sandwich Plates.  

National Technical Information Service (NTIS)

The objective of the research is to analytically model the response of composite sandwich plates to low velocity impact. A displacement based, plane stress, finite element code is modified for this purpose. Major new algorithms include 5th order Hermitian...

E. J. Herup

1996-01-01

171

Damage Resistance Characterization of Sandwich Composites Using Response Surfaces.  

National Technical Information Service (NTIS)

The influence of material configuration and impact parameters on the damage-resistance characteristics of sandwich composites comprised of carbon-epoxy woven fabric face sheets and Nomex honeycomb cores were investigated using empirically based response s...

T. E. Lacy I. K. Samarah J. S. Tomblin

2002-01-01

172

External Patch Repair of CFRP/Honeycomb Sandwich.  

National Technical Information Service (NTIS)

This paper addresses the repair of impact-damaged honeycomb sandwich structures with thin skins made of carbon fiber reinforced plastic (CFRP). An experimental study concerned with evaluating several types of bonded external patch repairs is presented. Th...

K. Wolf R. Schindler

1995-01-01

173

Magneto-impedance in sandwich film for magnetic sensor heads  

Microsoft Academic Search

This paper presents results on magneto-impedance (MI) in a NiFe\\/Co\\/NiFe sandwich film of 0.2 ?m thickness, which exhibits the impedance change up to 8% for a field of 4 Oe at a frequency of 400 MHz. The effect of voltage change with the field can be especially large (~200% for 5 Oe) if the sandwich film is incorporated in a

K. Hika; L. V. Panina; K. Mohri

1996-01-01

174

Investigation of Sandwich Panel Parameters Influence on its Natural Frequencies  

NASA Astrophysics Data System (ADS)

In the paper the parametric study of free vibration analysis of sandwich panel is presented. Effects of the face sheet material, as well as those related to the ply-thickness, core thickness and length of the panel are investigated. There are used approaches based on the first order shear deformation theory. Natural frequencies of sandwich panel are calculated by using analytical solution, which is compared with A NSYS results.

Piovár, Stanislav; Kormaníková, Eva

2012-11-01

175

Multi-objective optimization design of radar absorbing sandwich structure  

Microsoft Academic Search

By introducing a dimensionless parameter to couple the two objectives, weight and radar absorbing performance, into a single\\u000a objective function, a multi-objective optimization procedure for the radar absorbing sandwich structure (RASS) with a cellular\\u000a core is proposed. The optimization models considered are one-side clamped sandwich panels with four kinds of cores subject\\u000a to uniformly distributed loads. The average specular reflectivity

Ming-ji Chen; Yong-mao Pei; Dai-ning Fang

2010-01-01

176

Dimensional Changes in CFRP/PMI Foam Core Sandwich Structures  

NASA Astrophysics Data System (ADS)

A sandwich structure was observed from the beginning of life—starting at the vacuum assisted manufacturing process up to several environmental in service conditions. Strain variations due to curing process at the manufacturing, well as thermal fluctuations and humidity environments in service were detected and reviewed by their influence on the overall dimensional stability. The CFRP/PMI foam core sandwich structure was checked for an application as a primary structure in commercial aviation with its specific environmental requirements.

John, M.; Skala, T.; Wagner, T.; Schlimper, R.; Rinker, M.; Schäuble, R.

2013-08-01

177

Impact response of sandwich plates with a pyramidal lattice core  

Microsoft Academic Search

The ballistic performance edge clamped 304 stainless-steel sandwich panels has been measured by impacting the plates at mid-span with a spherical steel projectile whose impact velocity ranged from 250 to 1300ms?1. The sandwich plates comprised two identical face sheets and a pyramidal truss core: the diameter of the impacting spherical projectile was approximately half the 25mm truss core cell size.

Christian J. Yungwirth; Haydn N. G. Wadley; John H. O’Connor; Alan J. Zakraysek; Vikram S. Deshpande

2008-01-01

178

Damage tolerance of low-velocity-impacted composite sandwich structures  

NASA Astrophysics Data System (ADS)

This study is focused on the damage tolerance of composite sandwich structures at the low velocity impact damage level. The ultimate purpose of this research is to fill the current technical gap that there is lack of feasible methodology in the damage tolerant design of the composite sandwich structures and the safety evaluation of impact damaged composite sandwich structures. Based upon Sandwich Compression After Impact (SCAI) tests, a nonlinear finite element model and a modified analytical model were developed and implemented in this study to investigate the damage propagation behavior of an impact damaged composite sandwich panel under in-plane uniaxial compression. In the nonlinear finite element model, due to the symmetry, one quarter of the whole sandwich panel was modeled in ANSYS with corresponding major impact damage modes. A program was coded to control the solving process with the incorporation of the consequential core crushing mechanism by using element deactivation technique. In the analytical model, the impacted facesheet was modeled as an angle-ply composite laminate, which has an initial deflection in shape and is partially supported by an elastic foundation, residing in a compressive stress field. Two coupled Partial Differential Equations (PDEs) were derived and solved numerically. A consequential core crushing mechanism was included in the solving process. Both numerical models successfully captured the damage propagation behavior similar to that in SCAI tests; especially, for the first time, successfully captured the initiation of damage propagation at the points near the damage zone with a good correlation to the experimental results. An even driven failure criterion called Damage Propagation Criterion was proposed by using the critical far field stress corresponding to the initiation of damage propagation near the damage zone as the only characteristic value. With the implementation of this criterion, a feasible methodology was proposed for the engineering applications in the damage tolerant design of composite sandwich structures and the safety evaluation of low velocity impacted composite sandwich structures.

Xie, Zonghong

179

The Thomsen model of inserts in sandwich composites: An evaluation  

Microsoft Academic Search

An one-dimensional finite element model of a sandwich panel with insert is derived using the approach used in the Thomsen model. The one-dimensional model produces results that are close to those of a two-dimensional axisysmmetric model. Both models assume that the core is homogeneous. Our results indicate that the one-dimensional model may be well suited for small deformations of sandwich

Biswajit Banerjee; Bryan Smith

2010-01-01

180

Bending response of inhomogeneous fiber-reinforced viscoelastic sandwich plates  

Microsoft Academic Search

The static response of an inhomogeneous fiber-reinforced viscoelastic sandwich plate is investigated by using the first-order\\u000a shear deformation theory. Several types of sandwich plates are considered taking into account the symmetry of the plate and\\u000a the thickness of each layer. In addition, two cases are considered depending on the viscoelastic material which are included\\u000a in the core or the faces

M. N. M. Allam; A. M. Zenkour; H. F. El-Mekawy

2010-01-01

181

Fabrication and electromagnetic characteristics of electromagnetic wave absorbing sandwich structures  

Microsoft Academic Search

The radar absorbing structures (RAS) having sandwich structures in the X-band (8.2–12.4GHz) frequencies were designed and fabricated. We added conductive fillers such as carbon black and multi-walled carbon nanotube (MWNT) to composite prepregs and polyurethane foams so as to efficiently increase the absorbing capacity of RAS. In order to improve the mechanical stiffness of RAS, we adopted the sandwich structures

Ki-Yeon Park; Sang-Eui Lee; Chun-Gon Kim; Jae-Hung Han

2006-01-01

182

Enhanced Antibacterial Activity of Silver Nanoparticles/Halloysite Nanotubes/Graphene Nanocomposites with Sandwich-Like Structure  

PubMed Central

A sandwich-like antibacterial reagent (Ag/HNTs/rGO) was constructed through the direct growth of silver nanoparticles on the surface graphene-based HNTs nanosheets. Herein, various nanomaterials were combined by adhesion effect of DOPA after self-polymerization. Ag/HNTs/rGO posses enhanced antibacterial ability against E. coli and S. aureus compared with individual silver nanoparticles, rGO nanosheets or their nanocomposites.

Yu, Liang; Zhang, Yatao; Zhang, Bing; Liu, Jindun

2014-01-01

183

Enhanced Antibacterial Activity of Silver Nanoparticles/Halloysite Nanotubes/Graphene Nanocomposites with Sandwich-Like Structure  

NASA Astrophysics Data System (ADS)

A sandwich-like antibacterial reagent (Ag/HNTs/rGO) was constructed through the direct growth of silver nanoparticles on the surface graphene-based HNTs nanosheets. Herein, various nanomaterials were combined by adhesion effect of DOPA after self-polymerization. Ag/HNTs/rGO posses enhanced antibacterial ability against E. coli and S. aureus compared with individual silver nanoparticles, rGO nanosheets or their nanocomposites.

Yu, Liang; Zhang, Yatao; Zhang, Bing; Liu, Jindun

2014-04-01

184

Enhanced antibacterial activity of silver nanoparticles/halloysite nanotubes/graphene nanocomposites with sandwich-like structure.  

PubMed

A sandwich-like antibacterial reagent (Ag/HNTs/rGO) was constructed through the direct growth of silver nanoparticles on the surface graphene-based HNTs nanosheets. Herein, various nanomaterials were combined by adhesion effect of DOPA after self-polymerization. Ag/HNTs/rGO posses enhanced antibacterial ability against E. coli and S. aureus compared with individual silver nanoparticles, rGO nanosheets or their nanocomposites. PMID:24722502

Yu, Liang; Zhang, Yatao; Zhang, Bing; Liu, Jindun

2014-01-01

185

Foam core materials for structural sandwich panels  

SciTech Connect

The author first investigates the creep of polymer foam cores. Models for the creep of linear and nonlinear viscoelastic polymer foams are proposed. Experimental results for the creep of a rigid polyurethane foam are compared to the mode; agreement is good. The results indicate that creep can limit the design of building panels with polymer foam cores. Next, he studies the potential of using ceramic foams as a core material in building panels. Ceramic foams have a high stiffness, high creep resistance, low cost, and are incombustible. Ceramic foams, however, have a low fracture toughness and tensile strength. Assuming that the variability of cell wall modulus of rupture follows a Weibull distribution, there is a cell size effect on both the fracture toughness and tensile strength. Both the tensile strength and fracture toughness of ceramic foams can be improved by controlling the cell size. Since cell wall deformation of cellular materials is primarily by bending, the mechanical properties of cellular materials may be improved by making cell walls into sandwich structures. Hollow-sphere composites are made by introducing thin-walled hollow spheres into a matrix.

Huang Jongshin.

1991-01-01

186

?-Cyclodextrin cuprate sandwich-type complexes.  

PubMed

Three structures, based on ?-cyclodextrin (?-CD) and metal ions (Cu(2+), Li(+), Na(+), and Rb(+)), have been prepared in aqueous and alkaline media and characterized structurally by single-crystal X-ray diffraction. Their dimeric assemblies adopt cylindrical channels along the c axes in the crystals. Coordinative and hydrogen bonding between the cylinders and the solvent molecules lead to the formation of two-dimensional sheets, with the identity of the alkali-metal ion strongly influencing the precise nature of the solid-state structures. In the case of the Rb(+) complex, coordinative bonding involving the Rb(+) ions leads to the formation of an extended two-dimensional structure. Nonbound solvent molecules can be removed, and gas isotherm analyses confirm the permanent porosity of these new complexes. Carbon dioxide (CO2) adsorption studies show that the extended structure, obtained upon crystallization of the Rb(+)-based sandwich-type dimers, has the highest CO2 sequestration ability of the three ?-CD complexes reported. PMID:23432138

Bagabas, Abdulaziz A; Frasconi, Marco; Iehl, Julien; Hauser, Brad; Farha, Omar K; Hupp, Joseph T; Hartlieb, Karel J; Botros, Youssry Y; Stoddart, J Fraser

2013-03-18

187

Electronically asymmetric bis(porphyrin) sandwich complexes  

SciTech Connect

Bis(porphyrin)metal(IV) complexes (M(porph){sub 2}) have been extensively studies in recent years due to their structural, chemical, and spectroscopic similarity to the {open_quotes}special pair{close_quotes} found in the reaction center of photosynthetic bacteria. Strong interactions arise in the bis(porphyrin) complexes due to the short inter-porphyrin separation (< 3 {angstrom}), which results in properties not seen in mono(porphyrin) analogs. For example, the bis(porphyrin) complexes are considerably easier to oxidize than analogous mono(porphyrin) species, and the M(porph){sub 2{sup n+}} cations (n = 1,2) exhibit near-IR absorptions not found in simple mono(porphyrin)cations. As part of the authors continuing effort to understand the factors that govern the electronic structures of bis(porphyrin) supermolecules, the authors now describe the synthesis of a series of zirconium sandwich complexes. Introduction of electron-withdrawing or -donating groups on the {beta}-pyrrole position considerably affects the electronic properties of these molecules without altering their steric parameters. Thus, peripheral substitution allows modification of the inter-porphyrin {pi} interactions while keeping the inter-porphyrin separation constant. Previous studies have changed the identity of the central metal, but the electronic structure and the interplanar distance could not be varied independently.

Girolami, G.S.; Gorlin, P.A.; Suslick, K.S. [Univ. of Illinois, Urbana, IL (United States)

1994-02-16

188

Organometallic half-sandwich iridium anticancer complexes.  

PubMed

The low-spin 5d(6) Ir(III) organometallic half-sandwich complexes [(?(5)-Cp(x))Ir(XY)Cl](0/+), Cp(x) = Cp*, tetramethyl(phenyl)cyclopentadienyl (Cp(xph)), or tetramethyl(biphenyl)cyclopentadienyl (Cp(xbiph)), XY = 1,10-phenanthroline (4-6), 2,2'-bipyridine (7-9), ethylenediamine (10 and 11), or picolinate (12-14), hydrolyze rapidly. Complexes with N,N-chelating ligands readily form adducts with 9-ethylguanine but not 9-ethyladenine; picolinate complexes bind to both purines. Cytotoxic potency toward A2780 human ovarian cancer cells increases with phenyl substitution on Cp*: Cp(xbiph) > Cp(xph) > Cp*; Cp(xbiph) complexes 6 and 9 have submicromolar activity. Guanine residues are preferential binding sites for 4-6 on plasmid DNA. Hydrophobicity (log P), cell and nucleus accumulation of Ir correlate with cytotoxicity, 6 > 5 > 4; they distribute similarly within cells. The ability to displace DNA intercalator ethidium bromide from DNA correlates with cytotoxicity and viscosity of Ir-DNA adducts. The hydrophobicity and intercalative ability of Cp(xph) and Cp(xbiph) make a major contribution to the anticancer potency of their Ir(III) complexes. PMID:21443199

Liu, Zhe; Habtemariam, Abraha; Pizarro, Ana M; Fletcher, Sally A; Kisova, Anna; Vrana, Oldrich; Salassa, Luca; Bruijnincx, Pieter C A; Clarkson, Guy J; Brabec, Viktor; Sadler, Peter J

2011-04-28

189

Optimization of composite sandwich cover panels subjected to compressive loadings  

NASA Technical Reports Server (NTRS)

An analysis and design method is presented for the design of composite sandwich cover panels that include the transverse shear effects and damage tolerance considerations. This method is incorporated into a sandwich optimization computer program entitled SANDOP. As a demonstration of its capabilities, SANDOP is used in the present study to design optimized composite sandwich cover panels for for transport aircraft wing applications. The results of this design study indicate that optimized composite sandwich cover panels have approximately the same structural efficiency as stiffened composite cover panels designed to satisfy individual constraints. The results also indicate that inplane stiffness requirements have a large effect on the weight of these composite sandwich cover panels at higher load levels. Increasing the maximum allowable strain and the upper percentage limit of the 0 degree and +/- 45 degree plies can yield significant weight savings. The results show that the structural efficiency of these optimized composite sandwich cover panels is relatively insensitive to changes in core density. Thus, core density should be chosen by criteria other than minimum weight (e.g., damage tolerance, ease of manufacture, etc.).

Cruz, Juan R.

1991-01-01

190

The sandwich model: the 'music and dance' of therapeutic action.  

PubMed

My premise is that a 'layered' approach is necessary to understand the process of exchanges that result in therapeutic change. I imagine these processes occurring in three layers - although the number of domains in which change is taking place is actually infinite - such as in a sandwich. The top layer, or top slice of bread of the sandwich, represents a broad view of the change process; it is non-linear and includes the feature of uncertainty, a general principle of dynamic systems theory. The middle layer, or the meat of the sandwich, is explained by theories that are immediately and clinically useful to a therapist, such as psychoanalytic theories. These are primarily linear theories and use language and symbols to 'tell a story of what happened'. The bottom layer, or bottom slice of bread of the sandwich, is the micro-process; this layer includes the moment-to-moment patterns of coordinated rhythms that both communicate meaning and provide the essential scaffold for all higher-level change processes. The micro-process also requires a non-linear theory to make sense of its variability and emergent properties. Taking a bite out of the sandwich will include a 'polysemic bundle of communicative behaviors' (Harrison and Tronick, 2011). I will illustrate the 'sandwich model' with the clinical case of the analytic treatment of a 5 year-old boy. PMID:24354856

Harrison, Alexandra M

2014-04-01

191

Modified Mode-I Cracked Sandwich Beam (CSB) Fracture Test  

NASA Technical Reports Server (NTRS)

Five composite sandwich panels were fabricated using vacuum assisted resin transfer molding (VARTM). Four of these panels had E-glass/vinylester facesheets and one had carbon/epoxy facesheets. The sandwich panels had different density PVC foam cores. The four E-glass panels had core densities of 80, 100, 130, 200 kg/cu m. The sandwich with carbon/epoxy 3 facesheets had a core with density of 100 kg/cu m. Fracture tests were conducted using a modified Cracked Sandwich Beam (CSB) test configuration. Load displacement curves were obtained for loading and unloading of the specimens during crack growth. Various increments of crack growth were monitored. Critical Strain Energy Release Rates (SERR) were determined from the tests using the area method. The critical values of SERR can be considered the fracture toughness of the sandwich material. The fracture toughness ranged 367 J/sq m to 1350 J/sq m over the range of core densities. These results are compared to the Mode-I fracture toughness of the PVC foam core materials and values obtained for foam-cored sandwiches using the TSD specimen. Finite-element analyses (FEA) were performed for the test configuration and Strain Energy Release Rates were calculated using the Virtual Crack Closure Technique (VCCT). The SERR values determined from the FEA were scaled to the fracture loads, or critical loads, obtained from the modified CSB tests. These critical loads were in close agreement with the test values.

Smith, S. A.; Shivakumar, K. N.

2001-01-01

192

Numerical analysis of impact-damaged sandwich composites  

NASA Astrophysics Data System (ADS)

Sandwich structures are used in a wide variety of structural applications due to their relative advantages over other conventional structural materials in terms of improved stability, weight savings, and ease of manufacture and repair. Foreign object impact damage in sandwich composites can result in localized damage to the facings, core, and core-facing interface. Such damage may result in drastic reductions in composite strength, elastic moduli, and durability and damage tolerance characteristics. In this study, physically-motivated numerical models have been developed for predicting the residual strength of impact-damaged sandwich composites comprised of woven-fabric graphite-epoxy facesheets and Nomex honeycomb cores subjected to compression-after-impact loading. Results from non-destructive inspection and destructive sectioning of damaged sandwich panels were used to establish initial conditions for damage (residual facesheet indentation, core crush dimension, etc.) in the numerical analysis. Honeycomb core crush test results were used to establish the nonlinear constitutive behavior for the Nomex core. The influence of initial facesheet property degradation and progressive loss of facesheet structural integrity on the residual strength of impact-damaged sandwich panels was examined. The influence of damage of various types and sizes, specimen geometry, support boundary conditions, and variable material properties on the estimated residual strength is discussed. Facesheet strains from material and geometric nonlinear finite element analyses correlated relatively well with experimentally determined values. Moreover, numerical predictions of residual strength are consistent with experimental observations. Using a methodology similar to that presented in this work, it may be possible to develop robust residual strength estimates for complex sandwich composite structural components with varying levels of in-service damage. Such studies may facilitate sandwich panel design by providing insight into relationships between material configuration and damage progression that lead to improved damage tolerance characteristics.

Hwang, Youngkeun

193

[Establishment and evaluation of a double antibody sandwich ELISA to detect Csa2 protein of Candida albicans].  

PubMed

Objective To establish a double antibody sandwich ELISA for detecting Csa2 protein in Candida albicans infection and evaluate its specificity and sensitivity. Methods A recombinant expression vector pPIC9K-Csa2 was constructed and transformed into Pichia pastoris GS115. A large-scale expression of recombinant Csa2 protein (rCsa2) was optimized using methanol, and the protein was purified in P. pastoris expression system. New Zealand Rabbits and guinea pigs were respectively immunized with the purified rCsa2 to prepare polyclonal antisera. The double antibody sandwich ELISA was established by choosing the optimal dilution of coating antisera and detecting antisera. Different concentrations of rCsa2 and culture supernatants of C. albicans collected at different time points were used to evaluate the sensitivity of detection. The specificity of the sandwich ELISA was evaluated by detecting culture supernatants of other three Candida spp, five Aspergillus spp, Cryptococcus neoformans and Penicillium marneffei. Results The rCsa2 protein was successfully expressed and purified. SDS-PAGE showed that its Mr was 13 300. Western blotting demonstrated that the protein bound to specific antibody. The sensitivity of the sandwich ELISA we established using the high-titer antisera was about 240 pg/mL of rCsa2, and could detect Csa2 protein in the culture supernatant of C. albicans when cultured for as early as 18 hours. There was no cross-reactivity between the culture supernatants of other 10 clinically important fungi and C. albicans. Conclusion The double antibody sandwich ELISA for detecting Csa2 protein has been established with good sensitivity and specificity. Csa2 protein could be used as a new diagnostic marker of C. albicans infection. PMID:25001939

Liu, Lingli; Cai, Jianpiao; Liu, Caiyi; Guo, Yonghui; Pan, Yuxian; Wang, Yanfang; Che, Xiaoyan

2014-07-01

194

The construction of the RFX vacuum vessel  

Microsoft Academic Search

The technologies adopted for constructing the reversed-field pinch experiment (RFX) vacuum vessel are described. The vessel is of all-welded Inconel 625 construction, with very tight dimensional tolerances: 1 mm on the 4-m major diameter, and 0.5 mm on the 1-m minor diameter. Welding the thin Inconel sheets to create the sandwich structure of the wall has been one of the

W. R. Baker; G. Bevilacqua; F. Elio; F. Gnesotto; A. Parma; D. Rigadello; P. Sonato

1989-01-01

195

Composite panels based on woven sandwich-fabric preforms  

NASA Astrophysics Data System (ADS)

A new type of sandwich material was investigated, based on woven sandwich-fabric preforms. Because of the integrally woven nature of the sandwich-fabric the skin-core debonding resistance of panels and structures based on the preform is very high. As the sandwich-fabrics are produced by a large scale textile weaving process (velvet weaving or distance weaving) and already a preform of a sandwich is available, the cost of the final panel or structure can potentially stay limited. Most attention in this work is focussed on the mechanical performance of sandwich-fabric panels. The high skin-core debonding resistance was verified and also indications were found of a good damage tolerance. Both unfoamed and foamed panels were evaluated and compared with existing sandwich panels. Microstructural parameters investigated for unfoamed cores are pile length, pile density, woven pile angles, degree of pile stretching, tilt angles of the piles induced during panel production and resin content and distribution. For foamed panels it is especially the foam density which has an important influence. There appears to be a synergistic effect between piles and foam in the sandwich core, leading to very acceptable mechanical properties. For panels for (semi) structural applications, foaming is almost indispensable once the panel thickness is higher than about 15 mm. To understand the behaviour of foamed panels, attention was paid to the modelling of the mechanics of pure foam. The foam microstructure was modelled with the model of an anisotropic tetrakaidecahedron. The mechanical properties of unfoamed panels were modelled with the help of finite elements. A detailed geometrical description of the core layout was made which was incorporated into a preprocessing program for a finite element code. Attention is paid to the production of panels based on the woven preforms. A newly developed Adhesive Foil Stretching process was investigated. Also the foaming of panels was studied. A lot of attention was paid to a special application in the field of structural damping, where sandwich-fabric panels could be used as spacer in a constrained layer application. The vibrations and damping were modelled with the help of finite elements.

van Vuure, Aart Willem

196

Impact damage analysis of balsawood sandwich composite materials  

NASA Astrophysics Data System (ADS)

In this study, a new composite sandwich structure with a balsa wood core (end grain and regular balsa) in conjunction with E-glass/epoxy face sheets was proposed, fabricated, impact tested, and modeled. The behavior of the sandwich structure under low velocity impact and compression after impact was investigated. Low velocity impact tests were carried out by drop-weight impact tower at different energy levels (8J-35J) to evaluate the impact response of the sandwich structure. Visual inspection, destructive and non destructive evaluation methods have been conducted. For the sandwich plate with end grain core, the damage was very clear and can be visually detected. However, the damage in regular balsa core was not clearly visible and destructive evaluation method was used. Compression testing was done after subjecting the specimens to impact testing. Impact test results; load-time, load-deflection history and energy absorption for sandwich composites with two different cores, end grain and regular balsa were compared and they were investigated at three different impact energies. The results show that the sandwich structures with end grain core are able to withstand impact loading better than the regular balsa core because the higher stiffness of end grain core informs of sustaining higher load and higher overall energy. The results obtained from compression after impact testing show that the strengths of sandwich composites with end grain and regular balsa cores were reduced about 40% and 52%, respectively, after impact. These results were presented in terms of stress-strain curves for both damaged and undamaged specimens. Finite element analysis was conducted on the sandwich composite structure using LS-DYNA code to simulate impact test. A 3- D finite element model was developed and appropriate material properties were given to each component. The computational model was developed to predict the response of sandwich composite under dynamic loading. The experimental and finite element results were matched better for maximum load. However progressive damage accumulation could not predicted well due to lack of sophisticated material damage models in FEA codes.

Abdalslam, Suof Omran

197

In situ processing methods for composite fuselage sandwich structures  

NASA Technical Reports Server (NTRS)

Conventional sandwich structure fabrication methods are labor intensive and high in cost. A low cost method is needed to produce lightweight sandwich structures. Sundstrand has developed a series of in situ composite fabrication methods in which the raw materials (skin and core materials) are placed in a closed mold, and the component is produced in one heating cycle. Internal pressure is generated by chemical agents during the thermal cycles, which consolidates the skins and produces the foam core. The finished part is a net-shape composite sandwich structure with skins and a foamed core. The in situ process reduces cost by eliminating several secondary operations that are used in conventional fabrication methods. Further, a strong molecular bond is produced between the core and skin, which eliminates adhesive bonding and prevents a weak bond section in the sandwich structure. In this investigation, we evaluated the feasibility of the in situ process using thermoset materials currently under consideration for commercial airplane fuselage applications, such as keel sections. The materials used were Hercules 855340 toughened epoxy resin in both liquid and powder forms, and 3M Scotchply PR500 resin, manufactured by 3M Corporation, in powder form. We successfully foamed these resins and produced experimental panels with AS-4/855340 Hercules prepreg skins. Chopped fibers were added to the core to increase performance of the foam. Mechanical property testing on these panels showed properties competitive with other foams. Additional experiments are required to optimize the in situ foam core sandwiches for specific properties and applications.

Saatchi, Hossein; Durako, Bill; Reynolds, Dick; Dost, Ernest; Willden, Kurtis

1993-01-01

198

Sound Transmission through Two Concentric Cylindrical Sandwich Shells  

NASA Technical Reports Server (NTRS)

This paper solves the problem of sound transmission through a system of two infinite concentric cylindrical sandwich shells. The shells are surrounded by external and internal fluid media and there is fluid (air) in the annular space between them. An oblique plane sound wave is incident upon the surface of the outer shell. A uniform flow is moving with a constant velocity in the external fluid medium. Classical thin shell theory is applied to the inner shell and first-order shear deformation theory is applied to the outer shell. A closed form for transmission loss is derived based on modal analysis. Investigations have been made for the impedance of both shells and the transmission loss through the shells from the exterior into the interior. Results are compared for double sandwich shells and single sandwich shells. This study shows that: (1) the impedance of the inner shell is much smaller than that of the outer shell so that the transmission loss is almost the same in both the annular space and the interior cavity of the shells; (2) the two concentric sandwich shells can produce an appreciable increase of transmission loss over single sandwich shells especially in the high frequency range; and (3) design guidelines may be derived with respect to the noise reduction requirement and the pressure in the annular space at a mid-frequency range.

Tang, Yvette Y.; Silcox, Richard J.; Robinson, Jay H.

1996-01-01

199

Feasibility study of a SiC sandwich neutron spectrometer  

NASA Astrophysics Data System (ADS)

Semiconductor sandwich neutron spectrometers are suitable for in-pile measurements of fast reactor spectra thanks to their compact and relatively simple design. We have assembled and tested a sandwich neutron spectrometer based on 4H-silicon carbide (4H-SiC) Schottky diodes. The SiC diodes detect neutrons via neutron-induced charged particles (tritons and alpha particles) produced by 6Li(n,?)3H reaction. 6LiF neutron converter layers are deposited on the front surface of Schottky diodes by magnetron sputtering. The responses of SiC diodes to charged particles were investigated with an 241Am alpha source. A sandwich neutron spectrometer was assembled with two SiC Schottky diodes selected based on the charged-particle-response experimental results. The low-energy neutron response of the sandwich spectrometer was measured in the neutron field of the Chinese Fast Burst Reactor-II (CFBR-II). Spectra of alpha particles and tritons from 6Li(n,?)3H reaction were obtained with two well-resolved peaks. The energy resolution of the sum spectrum was 8.8%. The primary experimental results confirmed the 4H-SiC sandwich neutron spectrometer's feasibility.

Wu, Jian; Lei, Jiarong; Jiang, Yong; Chen, Yu; Rong, Ru; Zou, Dehui; Fan, Xiaoqiang; Chen, Gang; Li, Li; Bai, Song

2013-04-01

200

Wave propagation in sandwich panels with a poroelastic core.  

PubMed

Wave propagation in sandwich panels with a poroelastic core, which is modeled by Biot's theory, is investigated using the waveguide finite element method. A waveguide poroelastic element is developed based on a displacement-pressure weak form. The dispersion curves of the sandwich panel are first identified as propagating or evanescent waves by varying the damping in the panel, and wave characteristics are analyzed by examining their motions. The energy distributions are calculated to identify the dominant motions. Simplified analytical models are also devised to show the main physics of the corresponding waves. This wave propagation analysis provides insight into the vibro-acoustic behavior of sandwich panels lined with elastic porous materials. PMID:24815252

Liu, Hao; Finnveden, Svante; Barbagallo, Mathias; Arteaga, Ines Lopez

2014-05-01

201

Sandwich complex-containing macromolecules: property tunability through versatile synthesis.  

PubMed

Sandwich complexes feature unique properties as the physical and electronic properties of a hydrocarbon ligand or its derivative are integrated into the physical, electronic, magnetic, and optical properties of a metal. Incorporation of these complexes into macromolecules results in intriguing physical, electrical, and optical properties that were hitherto unknown in organic-based macromolecules. These properties are tunable through well-designed synthetic strategies. This review surveys many of the synthetic approaches that have resulted in tuning the properties of sandwich complex-containing macromolecules. While the past two decades have seen an ever-growing number of research publications in this field, gaps remain to be filled. Thus, we expect this review to stimulate research interest towards bridging these gaps, which include the insolubility of some of these macromolecules as well as expanding the scope of the sandwich complexes. PMID:24474608

Abd-El-Aziz, Alaa S; Agatemor, Christian; Etkin, Nola

2014-03-01

202

Actively cooled plate fin sandwich structural panels for hypersonic aircraft  

NASA Technical Reports Server (NTRS)

An unshielded actively cooled structural panel was designed for application to a hypersonic aircraft. The design was an all aluminum stringer-stiffened platefin sandwich structure which used a 60/40 mixture of ethylene glycol/water as the coolant. Eight small test specimens of the basic platefin sandwich concept and three fatigue specimens from critical areas of the panel design was fabricated and tested (at room temperature). A test panel representative of all features of the panel design was fabricated and tested to determine the combined thermal/mechanical performance and structural integrity of the system. The overall findings are that; (1) the stringer-stiffened platefin sandwich actively cooling concept results in a low mass design that is an excellent contender for application to a hypersonic vehicle, and (2) the fabrication processes are state of the art but new or modified facilities are required to support full scale panel fabrication.

Smith, L. M.; Beuyukian, C. S.

1979-01-01

203

Photovoltaic response of symmetric sandwich polymer cells with identical electrodes  

NASA Astrophysics Data System (ADS)

The photovoltaic response of symmetric sandwich polymer cells based on poly[5-(2'-ethylhexyloxy)-2-methoxy-1,4-phenylene vinylene] (MEH-PPV) and MEH-PPV:fullerene blends has been investigated. Identical, semitransparent gold, silver, aluminum, and calcium are used as top and bottom electrodes. Most of the nominally symmetric sandwich cells exhibit pronounced photovoltaic (PV) response. The PV parameters are strongly dependent on the direction of illumination, the active layer thickness, and the evaporation rate of top electrode. Open-circuit voltage as high as 0.7 V has been measured in silver/MEH-PPV/silver cells. The addition of fullerene leads to reduced open-circuit voltage and higher short-circuit current. The photovoltaic response observed in these nominally symmetric sandwich cells is attributed to their different top and bottom electrode interfaces.

Alem, Salima; Gao, Jun; Wantz, Guillaume

2009-08-01

204

Structural Performance of Eco-Core Sandwich Panels  

NASA Astrophysics Data System (ADS)

Eco-Core, a fire resistant core material for sandwich composite structures developed under the US Navy (ONR) program, was used to study its performance as a sandwich beam with glass/vinyl ester face sheet. Performance of Eco-Core was compared with balsa and PVC core sandwich panels. Test specimens were designed to simulate shear, flexural, and edgewise compression loadings. These tests were conducted on Eco-Core as well as balsa and PVC sandwich composite specimens. Failure loads and modes were compared with each other and the analytical prediction. Both Eco-Core and balsa cored sandwich beams had similar failure modes in all three test conditions. In the case of transversely loaded (four-point) beams Eco-Core specimens failed by core shear for span/depth (S/d) ratio less than 4 and the failure mode changed to core tension for S/d >4. This is attributed to weak tensile strength of the core material. An expression for core tension failure load based on beam theory was derived. On the other hand, ductile materials like PVC failed by core indentation. Under edgewise compression, face sheet microbuckling and general buckling are the two potential failure modes for Eco-Core and balsa core sandwich composites. For specimen length/depth ratio L/d <7 the failure is by face sheet microbuckling, for 7 ?L/d ?13 the failure is a combination of face sheet microbuckling, debonding and buckling, and for L/d >13 the failure is by general buckling. Predictions from the existing equations agreed well with the experiment for both core materials. For PVC core, wrinkling/shear buckling and general buckling are the potential failure modes. For L/d ?8.5 the failure is wrinkling and for L/d >8.5 the failure is general buckling.

Shivakumar, Kunigal; Chen, Huanchun

205

Approaches to Design and Evaluation of Sandwich Composites  

NASA Technical Reports Server (NTRS)

This report describes research during the period June 15, 1997 to October 31, 2000. This grant yielded a low cast manufacturing of composite sandwich structures technology and characterization interfacial and subinterfacial cracks in foam core sandwich panels. The manufacturing technology is called the vacuum assisted resin transfer (VARTM). The VARTM is suitable for processing composite materials both at ambient and elevated temperatures and of unlimited component size. This technology has been successfully transferred to a small business fiber preform manufacturing company 3TEX located in Cary, North Carolina. The grant also supported one Ph.D, one M.S and a number of under graduate students, and nine publications and Presentations.

Shivakumar, Kunigal; Raju, I. S. (Technical Monitor); Ambur, D. (Technical Monitor)

2001-01-01

206

The extended high-order sandwich panel theory  

NASA Astrophysics Data System (ADS)

The contribution of this thesis is an extended high-order sandwich panel theory (EHSAPT) for sandwich beams/wide panels, in which the axial stresses are taken into account as well as the shear and transverse normal stresses in the core, and its validation. The general nonlinear formulation of EHSAPT is given in Chapter 2. Validation of the present theory is made by comparison with elasticity solutions and experimental data. The accuracy of EHSAPT is assessed for the standard class of structural analysis problems which include: static loading, static instability (global buckling and wrinkling), free vibrations, and dynamic loading. In Chapter 3 the static response to a half-sine distributed load applied to the top face sheet of a simply supported sandwich beam/wide panel is solved. Validation is made with elasticity, and Euler-Bernoulli beam, first order shear deformation theory, and HSAPT were also included for comparison. In Chapter 4 the static global buckling critical load is determined for a simply supported sandwich beam/wide panel under edgewise loading. Validation is made with elasticity, and Allen's formula and HSAPT are included for comparison. In Chapter 5 the static wrinkling critical load of a simply supported sandwich beam/wide panel is investigated. Validation includes comparison with elasticity, experimental results reported in literature, and recently acquired experimental results. Results using Hoff-Mautner's wrinkling formula and HSAPT are also shown. In Chapter 6 the free vibrations of a simply supported sandwich beam/wide panel are explored, and the predicted antisymmetric and symmetric natural frequencies are compared to experimental results found in the literature and with elasticity. The last validation of EHSAPT is made for the dynamic response to a half-sine distributed load with an exponential time decay applied to the top face sheet of a simply supported sandwich beam. Results are compared with elasticity. The response from using HSAPT is also shown. Chapter 8 presents results from an impact experiment upon a sandwich panel and comparison with EHSAPT. Finally, Chapter 9 gives overall comments on the future work that can be done with EHSAPT.

Phan, Catherine N.

207

Long-range coupling interactions in ferroelectric sandwich structures  

Microsoft Academic Search

We study the ferroelectric system consisting of the sandwich structure (PbTiO3\\/BaTiO3\\/PbTiO3) by using the Ginzburg-Landau phenomenological theory, and emphasize the importance of the long-range coupling interaction to the ferroelectric behavior of the system. We find that after introducing the long-range coupling interaction to the ferroelectric behavior of the sandwich system, the average spontaneous polarization of the interlayer (BaTiO3) increases and

Jian Shen; Yu-Qiang Ma

2001-01-01

208

GRP SANDWICH STRUCTURES FOR 'LIQUID DESIGN' ARCHITECTURE  

Microsoft Academic Search

Technical design of roof and façade structures for architecture has accelerated in the last 3 decades with successive emphasis on free form stretched membrane structures, systemized metal space structures, sophisticated tensegrity structures, glass envelope constructions and load bearing glass structures. This type of architecture is computer-based rather than culture-based. Hence it cannot be regarded as a new style of architecture,

M. Eekhout; R. Visser

209

Performance and Characterization of Shear Ties for Use in Insulated Precast Concrete Sandwich Wall Panels.  

National Technical Information Service (NTIS)

Insulated precast concrete sandwich wall panels are commonly used for exterior cladding on building structures. The insulation is sandwiched between exterior and interior concrete layers to reduce the heating and cooling costs for the structure. The panel...

B. T. Bewick C. Naito J. M. Hoemann M. Beacraft

2010-01-01

210

Dynamic properties of sandwich beams with MWNT\\/polymer nanocomposites as core materials  

Microsoft Academic Search

The dynamic properties of sandwich beams with MWNT\\/polymer nanocomposites as core materials were investigated. The faces of sandwich beams are graphite\\/epoxy laminates. Epoxy and phenolic resins served as a matrix material, and multi-walled carbon nanotubes (MWNTs) provided reinforcement of the fabricated MWNT\\/polymer nanocomposites as core materials for sandwich beams. The frequency responses of sandwich beams under excitation were measured experimentally

Meng-Kao Yeh; Tsung-Han Hsieh

2008-01-01

211

Response and Damage Tolerance of Composite Sandwich Structures under Low Velocity Impact  

Microsoft Academic Search

The deformation and failure response of composite sandwich beams and panels under low velocity impact was reviewed and discussed.\\u000a Sandwich facesheet materials discussed are unidirectional and woven carbon\\/epoxy, and woven glass\\/vinylester composite laminates;\\u000a sandwich core materials investigated include four types of closed cell PVC foams of various densities, and balsa wood. Sandwich\\u000a beams were tested in an instrumented drop tower

I. M. Daniel; J. L. Abot; P. M. Schubel; J.-J. Luo

212

Compression Response of a Sandwich Fuselage Keel Panel With and Without Damage  

NASA Technical Reports Server (NTRS)

Results are presented from an experimental and analytical study of a sandwich fuselage keel panel with and without damage. The fuselage keel panel is constructed of graphite-epoxy skins bonded to a honeycomb core, and is representative of a highly loaded fuselage keel structure. The face sheets of the panel contain several terminated or dropped plies along the length of the panel. The results presented provide a better understanding of the load distribution in damaged and undamaged thick-face-sheet composite sandwich structure with dropped plies and of the failure mechanisms of such structure in the presence of low-speed impact damage and discrete-source damage. The impact-damage condition studied corresponds to barely visible impact damage (BVID), and the discrete-source damage condition studied is a notch machined through both face sheets. Results are presented from an impact-damage screening study conducted on another panel of the same design to determine the impact energy necessary to inflict BVID on the panel. Results are presented from compression tests of the panel in three conditions: undamaged; BVID in two locations; and BVID in two locations and a notch through both face sheets. Surface strains in the face sheets of the undamaged panel and the notched panel obtained experimentally are compared with finite element analysis results. The experimental and analytical results suggest that for the damage conditions studied, discrete-source damage influences the structural performance more than BVID.

McGowan, David M.; Ambur, Damodar R.

1997-01-01

213

Dynamic fracture behavior of model sandwich structures with functionally graded core: a feasibility study  

Microsoft Academic Search

Feasibility of introducing compositional gradients to the core of a sandwich structure and the resulting fracture behavior under impact loading conditions is the primary focus of the study. Model sandwich structures comprising of graded core with bilinear variation of volume fraction of hollow microballoons are considered for experimental and numerical simulations. Conventional sandwiches with homogeneous core are also developed for

M. S Kirugulige; R. Kitey; H. V. Tippur

2005-01-01

214

An analytical model for composite sandwich panels with honeycomb core subjected to high-velocity impact  

Microsoft Academic Search

In this paper, an analytical model for perforation of composite sandwich panels with honeycomb core subjected to high-velocity impact has been developed. The sandwich panel consists of a aluminum honeycomb core sandwiched between two thin composite skins. The solution involves a three-stage, perforation process including perforation of the front composite skin, honeycomb core, and bottom composite skin. The strain and

S. Feli; M. H. Namdari Pour

215

A study on material damping of 0° laminated composite sandwich cantilever beams with a viscoelastic layer  

Microsoft Academic Search

The damping behavior of a 0° laminated sandwich composite beam inserted with a viscoelastic layer is investigated. A quantitative analysis of damping in the sandwich laminated composite beam has been conducted through the theoretical method. Results showed that the viscoelastic core thickness in the sandwich beam and the length of the beam have a great effect on the damping loss

Jong Hee Yim; Shee Yong Cho; Yun Jong Seo; Bor Z. Jang

2003-01-01

216

Effects of thickness and delamination on the damping in honeycomb–foam sandwich beams  

Microsoft Academic Search

In engineering applications where the use of lightweight structures is important, the introduction of a viscoelastic core layer, which has high inherent damping, between two face sheets, can produce a sandwich structure with high damping. Sandwich structures have the additional advantage that their strength to weight ratios are generally superior to those of solid metals. So, sandwich structures are being

Zhuang Li; Malcolm J. Crocker

2006-01-01

217

Finite element formulation of viscoelastic sandwich beams using fractional derivative operators  

Microsoft Academic Search

This paper presents a finite element formulation for transient dynamic analysis of sandwich beams with embedded viscoelastic material using fractional derivative constitutive equations. The sandwich configuration is composed of a viscoelastic core (based on Timoshenko theory) sandwiched between elastic faces (based on Euler–Bernoulli assumptions). The viscoelastic model used to describe the behavior of the core is a four-parameter fractional derivative

A. C. Galucio; J.-F. Deü; R. Ohayon

2004-01-01

218

Finite element formulation of viscoelastic sandwich beams using fractional derivative operators  

Microsoft Academic Search

This paper presents a finite element formulation for transient dynamic analysis of sandwich beams with embedded viscoelastic material using fractional derivative constitutive equations. The sandwich configuration is composed of a viscoelastic core (based on Timoshenko theory) sandwiched between elastic faces (based on Euler-Bernoulli assumptions). The viscoelastic model used to describe the behavior of the core is a four-parameter fractional derivative

A. C. Galucio; J.-F. Deü; R. Ohayon

2004-01-01

219

Experimental characterization and numerical simulations of a syntacticfoam\\/glass-fibre composite sandwich  

Microsoft Academic Search

This note presents the main results of an experimental and numerical investigation on the mechanical behaviour of a composite sandwich primarily designed for naval engineering applications. The skins of the sandwich are made of glass-fibre\\/polymer-matrix composites; their interior layers are connected with interwoven threads called piles which cross the sandwich core. Such core consists of a syntactic foam made by

Alberto Corigliano; Egidio Rizzi; Enrico Papa

2000-01-01

220

The response of honeycomb sandwich panels under low-velocity impact loading  

Microsoft Academic Search

This paper describes the results of an experimental investigation and a numerical simulation on the impact damage on a range of sandwich panels. The test panels are representative of the composite sandwich structure of the engine nacelle Fan Cowl Doors of a large commercial aircraft. The low-velocity impact response of the composites sandwich panels is studied at five energy levels,

M. Meo; R. Vignjevic; G. Marengo

2005-01-01

221

Switching characteristics of submicron dimension Permalloy sandwich films  

Microsoft Academic Search

Submicron magnetoresistive sandwich cells of various sizes are fabricated and their magnetic properties are studied. A novel coupling mechanism of magnetostatic origin has been found to be mainly responsible for unique switching characteristics in cells with small length to width ratio

T. Zhu; J. Shi; K. Nordquist; S. Tehrani; M. Durlam; E. Chen; H. Goronkin

1997-01-01

222

Undergraduate Sandwich Placements: a fresh look at skills  

Microsoft Academic Search

This paper chronicles the design and delivery of a course preparing Business Studies Sandwich undergraduates to find and undertake a one year supervised placement period. The paper describes both the development of specific job?getting skills and the process of preparing students for the placement experience itself.

Ian Winfield; Nick Ellis

1993-01-01

223

Debris Impact on CFRP-AL Honeycomb Sandwich Structure  

NASA Astrophysics Data System (ADS)

In order to do risk assessments of debris impacts on unmanned spacecraft, it is necessary to investigate damage of honeycomb sandwich structures caused by debris impacts. However, the study of the honeycomb sandwich panel with CFRP face sheets has not been sufficiently performed. The purpose of this study is to investigate hypervelocity impact phenomena of CFRP-AL honeycomb sandwich structure. Hypervelocity impact tests were performed with a two-stage light gas gun at University of Padova. Three kinds of CFRP-AL honeycomb sandwich panels which are frequently used as a material of a spacecraft structure were tested. The cell size and the core thickness were varied. Aluminum spheres, 0.8 mm in diameter, were used as projectiles. The tests were performed at a velocity range between 2 and 5 km/sec. After the tests, the projectiles perforated all targets. The perforation holes on the panels were measured, and ultrasonic inspection was performed. The area of the perforation holes of the panel were increased with the impact velocity. The core size of the honeycomb core did not influence the relationship between the hole and the impact velocity. Impacts of the projectile on the foil of honeycomb cell caused heavy damage to a face sheet of the opposite side of the impact surface.

Higashide, Masumi; Nagao, Yosuke; Kibe, Seishiro; Francesconi, Alessandro; Paverin, Daniele

224

Compressive behavior of sandwich panels and laminates with damage  

Microsoft Academic Search

A wrinkling model for sandwich panels in compression is developed with the assumption of an isotropic elastic core. Stresses for the three wrinkling cases coupled with global buckling are expressed by a unified expression. It is shown that the stresses in all three cases are identical for short wavelength wrinkling and can be expressed by a single simplified analytical expression,

Kangmin Niu

1998-01-01

225

Scattering analysis of high performance large sandwich radomes  

Microsoft Academic Search

Large radomes are assembled from many panels connected together forming joints or seams. When the panels are type A sandwiches that are optimized for minimum transmission loss over moderately narrow bandwidths, the seams and joints introduce scattering effects that can degrade the overall electromagnetic performance. Tuning the dielectric seams with conductive wires and optimizing their geometry is, therefore, crucial to

Reuven Shavit; Adam P. Smolski; Eric Michielssen; Raj Mittra

1992-01-01

226

Comparative Impact Tests on Metal Honeycomb Sandwich Structures.  

National Technical Information Service (NTIS)

Impact test results were carried out on metal honeycomb sandwich structures to compare the present structure (i.e. aileron trailing edges of 0.3 mm, 5.322/9 faces and honeycomb 5.453/2, bonded with FM 123-5) to structures with heavier faces and honeycomb....

J. Koetsier

1975-01-01

227

SOUND TRANSMISSION THROUGH A CYLINDRICAL SANDWICH SHELL WITH HONEYCOMB CORE  

Microsoft Academic Search

Sound transmission through an infinite cylindrical sandwich shell is studied in the context of the transmission of airborne sound into aircraft interiors. The cylindrical shell is immersed in fluid media and excited by an oblique incident plane sound wave. The internal and external fluids are different and there is uniform airflow in the external fluid medium. An explicit expression of

Yvette Y. Tang; Jay H. Robinson; Richard J. Silcox

1996-01-01

228

Damping analysis of an advanced sandwich composite structure  

Microsoft Academic Search

The aim of the paper is to determine the most important features of damping in the case of an advanced sandwich composite structure starting from the dampings, dynamic Young moduli and Poisson ratio for every lamina. The structure features two carbon\\/epoxy skins reinforced with a twill weave fabric and an expanded polystyrene (EPS) core. At the damping analysis of fiber

SORIN VLASE; DIANA COTOROS

2006-01-01

229

Characterization of Adhesive Layers in Sandwich Composites by Nondestructive Technique  

Microsoft Academic Search

New nondestructive technique, namely an inverse technique based on vibration tests, to characterize nonlinear mechanical properties of adhesive layers in sandwich composites is developed. An adhesive layer is described as a viscoelastic isotropic material with storage and loss moduli which are both frequency dependent values in wide frequency range. An optimization based on the planning of experiments and response surface

E. Barkanov; M. Wesolowski; A. Chate

2009-01-01

230

Deformation in viscoelastic sandwich composites subject to moisture diffusion  

Microsoft Academic Search

This study analyzes the effect of moisture diffusion on the deformation of viscoelastic sandwich composites, which are composed of orthotropic fiber-reinforced laminated skins and viscoelastic polymeric foam core. It is assumed that the elastic and time-dependent (transient) moduli at any particular location in the foam core depend on the moisture concentration at that location. Sequentially coupled analyses of moisture diffusion

Nikhil Joshi; Anastasia Muliana

2010-01-01

231

Damping optimisation of hybrid active–passive sandwich composite structures  

Microsoft Academic Search

Optimisation of active and passive damping is presented in this paper, using a new mixed layerwise finite element model developed for the analysis and optimisation of hybrid active–passive laminated sandwich plates. Optimisation is conducted through maximisation of modal loss factors, using as design variables the viscoelastic core thickness, the constraining elastic layers ply thicknesses and orientation angles, as well as

A. L. Araújo; P. Martins; C. M. Mota Soares; C. A. Mota Soares; J. Herskovits

232

A sandwich assay for procalcitonin detection for POCT applications  

Microsoft Academic Search

A plastic biochip was developed for the detection of procalcitonin (PCT) and consists of a polymethylmethacrylate (PMMA) chip shaped in order to achieve several flow microchannels. A sandwich assay using a new antibody pairs is implemented with the capture antibody immobilized on the PMMA surface and the target antibody labelled with a fluorophore. A laser diode excites the fluorescent sensing

Francesco Baldini; Luca Bolzoni; Ambra Giannetti; Melanie Kess; Petra M. Kraemer; Elisabeth Kremmer; Giampiero Porro; Folco Senesi; Cosimo Trono

2009-01-01

233

A layerwise model for thin soft core sandwich plates  

Microsoft Academic Search

The application of high damping materials, like high loss factor viscoelastic materials, in the core of sandwich plates can improve their dynamic response and reduce fatigue failure. However, the numerical simulation of the effects of this kind of damping treatment demands a cumbersome computational work, specially during the spatial modelling task of the layered structure. In this work, a layerwise

R. A. S. Moreira; J. Dias Rodrigues

2006-01-01

234

Characterisation and modelling of viscoelastically damped sandwich structures  

Microsoft Academic Search

A passive damping technique with viscoelastic materials is analysed in the present work. Concretely, the constrained layer damping (CLD) configuration, also known as viscoelastically damped sandwich structure, is considered. For an efficient dynamical analysis of viscoelastically damped structures, an accurate material characterisation and suitable mathematical models are necessary for reproducing the real material behaviour. With this aim, a CLD structure

Manex Martinez-Agirre; María Jesus Elejabarrieta

2010-01-01

235

Prediction of loss factors of curved sandwich beams  

Microsoft Academic Search

In this paper an analytical model for the coupled flexural and longitudinal vibration of a curved sandwich beam system is described. The system consists of a primary beam and a constraining beam with a viscoelastic damping material forming the core. The governing equations of motion for the forced vibration of the system are derived using the energy method and Hamilton's

S. He; M. D. Rao

1992-01-01

236

Modular container assembled from fiber reinforced thermoplastic sandwich panels  

DOEpatents

An improved, load bearing, modular design container structure assembled from thermoformed FRTP sandwich panels in which is utilized the unique core-skin edge configuration of the present invention in consideration of improved load bearing performance, improved useful load volume, reduced manufacturing costs, structural weight savings, impact and damage tolerance and repair and replace issues.

Donnelly, Mathew William (Edgewood, NM); Kasoff, William Andrew (Albuquerque, NM); Mcculloch, Patrick Carl (Irvine, CA); Williams, Frederick Truman (Albuquerque, NM)

2007-12-25

237

Strong Exchange Coupling in Lanthanide Bis(Phthalocyaninato) Sandwich Compounds.  

National Technical Information Service (NTIS)

Bis (phthalocyaninato) lanthanide sandwich compounds, which have the formula Pc2-LnPc1-, have been synthesized for Ln = terbium, homium and lutecium. Low temperature magnetic susceptibility data for Ho (Pc)2 and Tb (Pc)2 show a reduction in moment from th...

K. L. Trojan W. E. Hatfield K. D. Kepler M. L. Kirk

1991-01-01

238

Pulsed terahertz inspection of non-conducting sandwich composites  

NASA Astrophysics Data System (ADS)

Pulsed terahertz inspection enables accurate, contactless and safe for operating personnel evaluation of non-conducting structures. In this paper we present results of pulsed terahertz testing of various sandwich composite structures incorporating glass and basalt fibers based skin materials and spherecore and balsa wood based core materials. Various Time-Frequency Distributions (TFD) are utilized in order to obtain most valuable defects response.

Lopato, P.; Chady, T.

2013-01-01

239

Luftstoetvagsbelastade Sandwichvaeggelement (Blast Loading of Sandwich-Wall Panels).  

National Technical Information Service (NTIS)

Tests have been performed with two types of sandwich-wall panels. The panels have been laterally loaded with hydraulic jacks to obtain the static resistance function. They have also been exposed to blast loading from detonating spheres of Comp B and TNT. ...

R. Forsen

1984-01-01

240

Detection of entrapped moisture in honeycomb sandwich structures  

NASA Technical Reports Server (NTRS)

Thermal neutron moisture detection system detects entrapped moisture in intercellular areas of bonded honeycomb sandwich structures. A radium/beryllium fast neutron source bombards a specimen. The emitted thermal neutrons from the target nucleus are detected and counted by a boron trifluoride thermal neutron detector.

Hallmark, W. B.

1967-01-01

241

6Li foil scintillation sandwich thermal neutron detector  

Microsoft Academic Search

Increasing needs for neutron detection and limited supply of 3He have led to the need for replacement neutron detection technology. This paper presents the design and initial results for a neutron detector (6Li foil scintillator sandwich) that uses lithium metal foil to detect thermal neutrons. The reaction products, primarily triton, deposit most of their energy in thin scintillator films and

K. D. Ianakiev; M. T. Swinhoe; A. Favalli; K. Chung; D. W. MacArthur

2011-01-01

242

Pyramidal lattice sandwich structures with hollow composite trusses  

Microsoft Academic Search

Pyramidal lattice sandwich structures with hollow composite trusses were fabricated using a thermal expansion molding approach. Composite lattice structures with three relative densities were fabricated with two fiber architectures and the out-of-plane compression properties were measured and compared. Lattice cores with a fraction of carbon fibers circumferentially wound around the hollow trusses (Variant 2) exhibited superior mechanical properties compared with

Sha Yin; Linzhi Wu; Li Ma; Steven Nutt

2011-01-01

243

Random vibration of sandwich circular plates  

NASA Astrophysics Data System (ADS)

This paper presents an analytical approach for the general response of double wall circular plates subjected to random excitations. The excitations are either uniform random pressures or stationary random point loads. The double wall construction is separated by a soft linear viscoelastic core. The equations of motion are developed for thin circular plates using Love's theory which has been modified to account for the coupling provided by the viscoelastic core. The analytical solution of forced response is obtained via modal decomposition and a Galerkin type approach. Numerical results investigate the effect of coupling and structural parameters for response minimization.

Bofilios, Dimitri A.; Lyrintzis, Constantinos S.

244

Lightweight composites for modular panelized construction  

NASA Astrophysics Data System (ADS)

Rapid advances in construction materials technology have enabled civil engineers to achieve impressive gains in the safety, economy, and functionality of structures built to serve the common needs of society. Modular building systems is a fast-growing modern, form of construction gaining recognition for its increased efficiency and ability to apply modern technology to the needs of the market place. In the modular construction technique, a single structural panel can perform a number of functions such as providing thermal insulation, vibration damping, and structural strength. These multifunctional panels can be prefabricated in a manufacturing facility and then transferred to the construction site. A system that uses prefabricated panels for construction is called a "panelized construction system". This study focuses on the development of pre-cast, lightweight, multifunctional sandwich composite panels to be used for panelized construction. Two thermoplastic composite panels are proposed in this study, namely Composite Structural Insulated Panels (CSIPs) for exterior walls, floors and roofs, and Open Core Sandwich composite for multifunctional interior walls of a structure. Special manufacturing techniques are developed for manufacturing these panels. The structural behavior of these panels is analyzed based on various building design codes. Detailed descriptions of the design, cost analysis, manufacturing, finite element modeling and structural testing of these proposed panels are included in this study in the of form five peer-reviewed journal articles. The structural testing of the proposed panels involved in this study included flexural testing, axial compression testing, and low and high velocity impact testing. Based on the current study, the proposed CSIP wall and floor panels were found satisfactory, based on building design codes ASCE-7-05 and ACI-318-05. Joining techniques are proposed in this study for connecting the precast panels on the construction site. Keywords: Modular panelized construction, sandwich composites, composite structural insulated panels (CSIPs).

Vaidya, Amol S.

245

Electronic and optical properties of metal-nanoparticle filled graphene sandwiches  

NASA Astrophysics Data System (ADS)

We sandwich gold nanoparticles between graphene sheets and contrast the electronic and optical properties of these hybrid structures to those of single layer graphene with and without gold nanoparticle overlayers, and laminated unfilled double layers. Undecorated graphene has the highest sheet resistance while filled sandwiches have the lowest. The optical extinction spectrum for sandwiches is redshifted and broadened compared to decorated single layer graphene. We also find that the presence of gold nanoparticles in sandwiches shifts the work function relative to unfilled double-layer graphene. The low sheet resistance and favorable optical properties of metal-filled sandwiches make them attractive candidates for optoelectronic applications.

Zaniewski, Anna M.; Schriver, Maria; Gloria Lee, J.; Crommie, M. F.; Zettl, A.

2013-01-01

246

A three-node C deg element for analysis of laminated composite sandwich shells  

NASA Technical Reports Server (NTRS)

A three-node flat shell element with C deg rotation fields has been developed for analysis of arbitrary composite shells. The element may consist of any number of orthotropic layers, each layer having different material properties and angular orientation. The formulation includes coupling between bending and extension, which is essential for analysis of unsymmetric laminates. Shearing deflections are included, since laminated and sandwich construction frequently results in shear stiffness much smaller than bending stiffness. Formulation of the element is straightforward, and calculation of its stiffness matrix is simple and fast. Convergence of solutions with mesh refinement is uniform for both thin and thick shells and is insensitive to element shape, although not as rapid as some other elements that lack one or more capabilities of the newly developed element. An experimental verification of the shall element is reported in the appendix.

Martin, C. Wayne; Lung, S. F.; Gupta, K. K.

1989-01-01

247

Compressive and shear buckling analysis of metal matrix composite sandwich panels under different thermal environments  

NASA Technical Reports Server (NTRS)

Combined inplane compressive and shear buckling analysis was conducted on flat rectangular sandwich panels using the Raleigh-Ritz minimum energy method with a consideration of transverse shear effect of the sandwich core. The sandwich panels were fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that slightly slender (along unidirectional compressive loading axis) rectangular sandwich panels have the most desirable stiffness-to-weight ratios for aerospace structural applications; the degradation of buckling strength of sandwich panels with rising temperature is faster in shear than in compression; and the fiber orientation of the face sheets for optimum combined-load buckling strength of sandwich panels is a strong function of both loading condition and panel aspect ratio. Under the same specific weight and panel aspect ratio, a sandwich panel with metal matrix composite face sheets has much higher buckling strength than one having monolithic face sheets.

Ko, William L.; Jackson, Raymond H.

1993-01-01

248

Compressive and shear buckling analysis of metal matrix composite sandwich panels under different thermal environments  

NASA Astrophysics Data System (ADS)

Combined inplane compressive and shear buckling analysis was conducted on flat rectangular sandwich panels using the Raleigh-Ritz minimum energy method with a consideration of transverse shear effect of the sandwich core. The sandwich panels were fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that slightly slender (along unidirectional compressive loading axis) rectangular sandwich panels have the most desirable stiffness-to-weight ratios for aerospace structural applications; the degradation of buckling strength of sandwich panels with rising temperature is faster in shear than in compression; and the fiber orientation of the face sheets for optimum combined-load buckling strength of sandwich panels is a strong function of both loading condition and panel aspect ratio. Under the same specific weight and panel aspect ratio, a sandwich panel with metal matrix composite face sheets has much higher buckling strength than one having monolithic face sheets.

Ko, William L.; Jackson, Raymond H.

1993-06-01

249

Compressive and shear buckling analysis of metal matrix composite sandwich panels under different thermal environments  

NASA Astrophysics Data System (ADS)

Combined inplane compressive and shear buckling analysis was conducted on flat rectangular sandwich panels using the Raleigh-Ritz minimum energy method with a consideration of transverse shear effect of the sandwich core. The sandwich panels were fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that slightly slender (along unidirectional compressive loading axis) rectangular sandwich panels have the most desirable stiffness-to-weight ratios for aerospace structural applications; the degradation of buckling strength of sandwich panels with rising temperature is faster in shear than in compression; and the fiber orientation of the face sheets for optimum combined-load buckling strength of sandwich panels is a strong function of both loading condition and panel aspect ratio. Under the same specific weight and panel aspect ratio, a sandwich panel with metal matrix composite face sheets has much higher buckling strength than one having monolithic face sheets.

Ko, William L.; Jackson, Raymond H.

250

Analyses of sandwich beams and plates with viscoelastic cores  

NASA Astrophysics Data System (ADS)

A hybrid damping scheme using passive constrained damping layers (PCLD), and surface bonded piezoceramic actuators was proposed for interior cabin noise and vibration control in helicopters. In order to evaluate the performance of these treatments, we need to understand the dynamic behavior of sandwich structures. The analyses of sandwich structures are complicated by the frequency dependent stiffness and damping properties of viscoelastic materials. The methods developed in this thesis specifically deal with finite element methods and assumed modes methods to this problem. A spectral finite element method (SFEM) was developed in the frequency domain for sandwich beam analysis. The results of natural frequencies and frequency responses for two cantilevered beams with different span of PCLD treatments were presented and validated by experimental results and other analyses; including the assumed modes method (AM), and conventional finite element method (CFEM). The SFEM method implicitly accounts for frequency dependent stiffness and damping of viscoelastic materials. However, CFEM and AM method have to use additional internal dissipation coordinates to account for these properties. The Golla-Hughes-McTavish (GHM) damping method was used in both analyses. Also SFEM improves accuracy of frequency predictions compared to the results of CFEM and AM method because of its higher order interpolation functions. We expected to extend SFEM method to two-dimensional sandwich plate structures. But it is extremely difficult to solve the governing equations for a sandwich plate. An alternative method was developed to update the traditional AM method by using plate mode shapes. The plate mode shape functions were solved directly based on the Kantorovich variational method for both transverse bending and in-plane vibration of isotropic rectangular plates. These plate mode shapes were employed to calculate sandwich plates in AM method. The results of natural frequencies; loss factors and frequency response functions were calculated and validated by experimental data and the results by using beam and rod mode shapes. The comparable results were achieved for both analyses with less modes in the case of using plate mode shapes.

Wang, Gang

251

Development of aircraft lavatory compartments with improved fire resistance characteristics. Phase 2: Sandwich panel resin system development  

NASA Technical Reports Server (NTRS)

A NASA-funded program is described which aims to develop a resin system for use in the construction of lavatory wall panels, sidewall panels, and ceiling panels possessing flammability, smoke and gas emission, and toxicity (FS&T) characteristics superior to the existing epoxy resin. Candidate resins studied were phenolic, polyimide, and bismaleimide. Based on the results of a series of FS&T as well as mechanical and aesthetic property tests, a phenolic resin was chosen as the superior material. Material and process specifications covering the phenolic resin based materials were prepared and a method of rating sandwich panel performance was developed.

Anderson, R. A.; Arnold, D. B.; Johnson, G. A.

1979-01-01

252

Bismaleimide resins for flame resistant honeycomb sandwich panels  

NASA Technical Reports Server (NTRS)

Bismaleimide resins are prime candidates for nonflammable aircraft interior panels. Three resin types with different structures and processing characteristics were formulated. Resin M 751 was used to fabricate 100 kg of glass fabric prepregs which were used for the preparation of face sheets for honeycomb sandwich panels. Prepreg characteristics and curing cycles for laminate fabrication are provided. In order to advance beyond the current solvent resin technology for fibre and fabric impregnation, a hot melt solvent-less resin system was prepared and characterized. Preliminary tests were performed to develop a wet bonding process for the fabrication of advanced sandwich honeycomb panels by use of polybismaleimide glass fabric face sheets and polybismaleimide Nomex honeycomb core. B-stage material was used for both the core and the face sheet, providing flatwise tensile properties equivalent to those obtained by the state-of-the-art 3-step process which includes an epoxy adhesive resin.

Stenzenberger, H. D.

1978-01-01

253

Buckling and postbuckling of delaminated composite sandwich beams  

NASA Astrophysics Data System (ADS)

The paper presents elastic buckling and postbuckling analysis of an axially loaded plate with an across-the-width delamination symmetrically located at the interface of the upper face and core. Since the plate undergoes cylindrical bending deformations on the postbuckling states for the cases considered, only one-dimensional formulations are employed. The transverse deflection and bending moment of the postbuckling solutions are obtained by applying the one-dimensional formulations. The explicit closed-form expressions of the critical buckling load and energy release rate are derived based on this postbuckling solution. Because there is no such general solution presented in the literature, verification is done by some special cases such as delaminated composites (without core), perfect sandwiches (without delamination), and thin-film delaminations. The effects of core, face, and delamination length on the buckling load, the delamination growth, and the ultimate axial load capacity of the delaminated composite sandwiches are also discussed.

Hwu, Chyanbin; Hu, Jian S.

1992-07-01

254

Optimal design of active, passive, and hybrid sandwich structures  

NASA Astrophysics Data System (ADS)

This paper presents optimization of active, passive, and hybrid damping treatments in sandwich plates. A new mixed layerwise finite element model has been developed for the analysis of sandwich laminated plates with a viscoelastic core, laminated anisotropic face layers and piezoelectric sensor and actuator layers. Proportional displacement and velocity feedback control laws are implemented to account for co-located active control. Optimization of passive damping is conducted by maximizing modal loss factors, using as design variables the viscoelastic core thickness and the constraining elastic layers ply thicknesses and orientation angles. Optimization of the location of co-located sensor-actuator pairs is also conducted in order to maximize modal loss factors. The optimization problem is solved using gradient-based techniques for passive damping and an implementation of a Genetic Algorithm for the optimal location of sensor-actuator pairs.

Araújo, A. L.; Mota Soares, C. M.; Mota Soares, C. A.

2008-04-01

255

Structural behaviour of sandwich panel shear walls: An experimental analysis  

Microsoft Academic Search

Within a comprehensive research project devoted to analyse the contributing effect of cladding panels on the structural behaviour\\u000a of steel frames under horizontal loads, a suitable experimental procedure has been set up in order to characterise the main\\u000a behavioural parameters of specific shear walls. In particular, with regard to light-weight sandwich panels, which are currently\\u000a used in building as enclosure

G. De Matteis; R. Landolfo

1999-01-01

256

Impact Damage in Sandwich Composite Structures From Gas Gun Tests  

Microsoft Academic Search

The paper studies the High Velocity Impact (HVI) response of aircraft structures by means of gas gun impact tests and post-test\\u000a NDE evaluation. The scope of the activity comprises structural components such as stringer stiffened composite panels and\\u000a a range of composite sandwich structures, with projectiles such as ice, synthetic birds, runway debris and tyre\\/rim debris.\\u000a The tests and simulations

Nathalie Toso-Pentecote; Alastair Johnson

257

Left ventricle remodelling by double-patch sandwich technique  

Microsoft Academic Search

BACKGROUND: The sandwich double-patch technique was adopted as an alternative method for reconstruction of the left ventricle after excision of postinfarction dysfunctional myocardium to solve technical problems due to the thick edges of the ventricular wall. METHODS: Over a 5-year period, 12 of 21 patients with postinfarction antero-apical left ventricular aneurysm had thick wall edges after wall excision. It was

Ernesto Tappainer; Vinicio Fiorani; Nicola Pederzolli; Jacopo Manfredi; Andrea Nocchi; Mario Zogno

2007-01-01

258

Damping optimization of viscoelastic laminated sandwich composite structures  

Microsoft Academic Search

Recent developments on the optimization of passive damping for vibration reduction in sandwich structures are presented in\\u000a this paper, showing the importance of appropriate finite element models associated with gradient based optimizers for computationally\\u000a efficient damping maximization programs. A new finite element model for anisotropic laminated plate structures with viscoelastic\\u000a core and laminated anisotropic face layers has been formulated, using

A. L. Araújo; P. Martins; C. M. Mota Soares; C. A. Mota Soares; J. Herskovits

2009-01-01

259

Sandwich beam theory and the analysis of constrained layer damping  

Microsoft Academic Search

This paper deals with the analysis of sandwich beams and constrained layer damping in beams. A three-layered beam theory has been given in which the continuity of displacements and the transverse shear stresses has been satisfied at the interfaces. Axial displacement field in each layer has been assumed to be non-linear with respect to the thickness co-ordinate. This resulted in

A. Bhimaraddi

1995-01-01

260

Hole delocalization in oxidized cerium(IV) porphyrin sandwich complexes  

Microsoft Academic Search

Optical absorption, electron paramagnetic resonance, and resonance Raman spectra are reported for the one-electron oxidation products of the Ce(IV) sandwich porphyrins, Ce(OEP)â and Ce(TPP)â (OEP = octaethylporphyrin; TPP = tetraphenylporphyrin). These data, in conjunction with electrochemical measurements, indicate that the holes of both oxidized species are delocalized on the vibrational and probably the electronic time scales. In Ce(OEP)â\\/sup +\\/, the

Robert J. Donohoe; John K. Duchowski; David F. Bocian

1988-01-01

261

Fibrin Glue Sandwich Prevents Pancreatic Fistula following Distal Pancreatectomy  

Microsoft Academic Search

. Pancreatic fistula is a major form of morbidity following pancreatic resection. We conducted a nonrandomized clinical\\u000a trial comparing the sealing and sandwich techniques of spraying fibrin glue to prevent pancreatic fistula following distal\\u000a pancreatectomy. The pancreas was transected with a scalpel to identify and suture the main pancreatic duct and its small branches.\\u000a In the sealing group, fibrin glue

Susumu Ohwada; Tetsushi Ogawa; Yoshifumi Tanahashi; Seiji Nakamura; Izumi Takeyoshi; Toshihiro Ohya; Toshiroh Ikeya; Kenji Kawashima; Yoshiyuki Kawashima; Yasuo Morishita

1998-01-01

262

Hypervelocity Impact Evaluation of Metal Foam Core Sandwich Structures  

NASA Technical Reports Server (NTRS)

A series of hypervelocity impact (HVI) tests were conducted by the NASA Johnson Space Center (JSC) Hypervelocity Impact Technology Facility (HITF) [1], building 267 (Houston, Texas) between January 2003 and December 2005 to test the HVI performance of metal foams, as compared to the metal honeycomb panels currently in service. The HITF testing was conducted at the NASA JSC White Sands Testing Facility (WSTF) at Las Cruces, New Mexico. Eric L. Christiansen, Ph.D., and NASA Lead for Micro-Meteoroid Orbital Debris (MMOD) Protection requested these hypervelocity impact tests as part of shielding research conducted for the JSC Center Director Discretionary Fund (CDDF) project. The structure tested is a metal foam sandwich structure; a metal foam core between two metal facesheets. Aluminum and Titanium metals were tested for foam sandwich and honeycomb sandwich structures. Aluminum honeycomb core material is currently used in Orbiter Vehicle (OV) radiator panels and in other places in space structures. It has many desirable characteristics and performs well by many measures, especially when normalized by density. Aluminum honeycomb does not perform well in Hypervelocity Impact (HVI) Testing. This is a concern, as honeycomb panels are often exposed to space environments, and take on the role of Micrometeoroid / Orbital Debris (MMOD) shielding. Therefore, information on possible replacement core materials which perform adequately in all necessary functions of the material would be useful. In this report, HVI data is gathered for these two core materials in certain configurations and compared to gain understanding of the metal foam HVI performance.

Yasensky, John; Christiansen, Eric L.

2007-01-01

263

Sandwich enzyme-linked immunosorbent assay for Taiwan cobra venom.  

PubMed

Poisonous snake bite victims usually have difficulty identifying the species, and clinical manifestations alone are not reliable because of overlapping symptoms. Thus, it is important to develop a quick and reliable mean of identifying the snake responsible. We describe the development of a sandwich-ELISA method for detection of venom in biological samples and apply it to a case of snakebite to confirm the clinical diagnosis. The sandwich-ELISA takes 6 h to complete. Cobra venom antigen gave positive absorbance at about 500 pg/ml. Good linearity with R2 values over 0.99 were observed in dilution series of 1:100 ng/mL of cobra venom in calf serum and human urine. A snakebite initially thought to be Trimeresurus mucrosquamatus was proven cobra with a serum venom level up to 288 ngmL 3 h after envenoming. Sandwich-ELISA provides a rapid and accurate method for clinical identification and evaluation of toxic antigens circulating in individuals bitten by the Taiwan cobra snake. PMID:12136964

Huang, Yu-Ping; Yu, Yi-Jung; Hung, Dong-Zong

2002-08-01

264

Analysis of the sandwich piezoelectric ultrasonic transducer in coupled vibration  

NASA Astrophysics Data System (ADS)

The coupled vibration of the sandwich piezoelectric transducer with a large cross-section is analyzed using an approximate analytic method. The resonance frequency equations of the transducer are derived and the effect of the geometrical dimensions on the resonance frequency is studied. It is illustrated that when the radial vibration in the transducer is considered, the vibration of the sandwich transducer becomes more complex. Apart from the longitudinal resonance frequency, the radial resonance frequency can also be obtained. For comparison, numerical methods are also used to simulate the coupled vibration; the resonance frequency and the vibrational displacement distribution are computed. Compared with one-dimensional longitudinal theory, the radial dimensions of the transducer are no longer limited because the coupled vibration is considered. Compared with numerical methods, the physical meaning of the analytic method is concise. It is illustrated that the resonance frequencies obtained from the coupled resonance frequency equations are in good agreement with those from numerical methods, and they are in better agreement with the measured results than those from one-dimensional theory. Since the radial and the coupled vibration are considered in the analysis, more resonance frequencies can be obtained. Therefore, using the coupled resonance frequency equations, the sandwich transducer with multifrequency or wide frequency bandwidth can be designed and used in ultrasonic cleaning, ultrasonic sonochemistry and other applications. .

Shuyu, Lin

2005-02-01

265

Prediction of impact damage on stitched sandwich composite panels  

NASA Astrophysics Data System (ADS)

Based on the analysis of experiments, the damage of composite stitched foam-core sandwich structure under low-velocity impact has been studied in this paper. A numerical simulation is performed to predict the effects of stitching on the low-velocity impact response of stitched sandwich composite panels. The results of numerical simulation show that the damage areas of upper face sheet are greater than the lower one for both unstitched and stitched sandwich, however, the main patterns of damage are different. For the unstitched structure, the upper face sheet's damage is the main pattern of damage, whereas the crushing damage is the stitched one's main damage. The finite element results have corresponded well with the experimental results, which prove the correctness of the finite element model. The results indicate that stitching does not increase the load at which delamination begins to propagate, but greatly reduces the extent of delamination growth at the end of the impact event. Then, the damage areas' change has been taken into consideration as some factors change, those various factors include the impact energy, the thickness of upper panel, the thickness of foam core and the stitched density (stitched row spacing×needle spacing, suture thickness). And also it presents some related theoretical analysis.

Zheng, Xitao; Gou, Linhu; Zheng, Xiaoxia; Zhang, Jianfeng

2009-07-01

266

Sandwich beam theory and the analysis of constrained layer damping  

NASA Astrophysics Data System (ADS)

This paper deals with the analysis of sandwich beams and constrained layer damping in beams. A three-layered beam theory has been given in which the continuity of displacements and the transverse shear stresses has been satisfied at the interfaces. Axial displacement field in each layer has been assumed to be non-linear with respect to the thickness co-ordinate. This resulted in a non-uniform shear stress variation across the thickness of each layer. Continuity conditions at the interfaces have been used in order to reduce the number of displacement parameters considerably. The final displacement parameters of the problem are only those corresponding to the base layer. The proposed sandwich beam theory has been used to predict the loss factors of a viscoelastically damped simply supported beam. Numerical results have shown that the existing models on constrained layer damping analysis are not suitable when the core is very thick (as is the case in sandwich beams) or when the core modulus is lower.

Bhimaraddi, A.

1995-01-01

267

Size Effects in Impact Damage of Composite Sandwich Panels  

NASA Technical Reports Server (NTRS)

Panel size has a large effect on the impact response and resultant damage level of honeycomb sandwich panels. It has been observed during impact testing that panels of the same design but different panel sizes will show large differences in damage when impacted with the same impact energy. To study this effect, a test program was conducted with instrumented impact testing of three different sizes of sandwich panels to obtain data on panel response and residual damage. In concert with the test program. a closed form analysis method was developed that incorporates the effects of damage on the impact response. This analysis method will predict both the impact response and the residual damage of a simply-supported sandwich panel impacted at any position on the panel. The damage is incorporated by the use of an experimental load-indentation curve obtained for the face-sheet/honeycomb and indentor combination under study. This curve inherently includes the damage response and can be obtained quasi-statically from a rigidly-backed specimen or a specimen with any support conditions. Good correlation has been obtained between the test data and the analysis results for the maximum force and residual indentation. The predictions can be improved by using a dynamic indentation curve. Analyses have also been done using the MSC/DYTRAN finite element code.

Dobyns, Alan; Jackson, Wade

2003-01-01

268

Vibration Characteristics Determined for Stainless Steel Sandwich Panels With a Metal Foam Core for Lightweight Fan Blade Design  

NASA Technical Reports Server (NTRS)

The goal of this project at the NASA Glenn Research Center is to provide fan materials that are safer, weigh less, and cost less than the currently used titanium alloy or polymer matrix composite fans. The proposed material system is a sandwich fan construction made up of thin solid face sheets and a lightweight metal foam core. The stiffness of the sandwich structure is increased by separating the two face sheets by the foam layer. The resulting structure has a high stiffness and lighter weight in comparison to the solid facesheet material alone. The face sheets carry the applied in-plane and bending loads (ref. 1). The metal foam core must resist the transverse shear and transverse normal loads, as well as keep the facings supported and working as a single unit. Metal foams have ranges of mechanical properties, such as light weight, impact resistance, and vibration suppression (ref. 2), which makes them more suitable for use in lightweight fan structures. Metal foams have been available for decades (refs. 3 and 4), but the difficulties in the original processes and high costs have prevented their widespread use. However, advances in production techniques and cost reduction have created a new interest in this class of materials (ref. 5). The material chosen for the face sheet and the metal foam for this study was the aerospace-grade stainless steel 17-4PH. This steel was chosen because of its attractive mechanical properties and the ease with which it can be made through the powder metallurgy process (ref. 6). The advantages of a metal foam core, in comparison to a typical honeycomb core, are material isotropy and the ease of forming complex geometries, such as fan blades. A section of a 17-4PH sandwich structure is shown in the following photograph. Part of process of designing any blade is to determine the natural frequencies of the particular blade shape. A designer needs to predict the resonance frequencies of a new blade design to properly identify a useful operating range. Operating a blade at or near the resonance frequencies leads to high-cycle fatigue, which ultimately limits the blade's durability and life. So the aim of this study is to determine the variation of the resonance frequencies for an idealized sandwich blade as a function of its face-sheet thickness, core thickness, and foam density. The finite element method is used to determine the natural frequencies for an idealized rectangular sandwich blade. The proven Lanczos method (ref. 7) is used in the study to extract the natural frequency.

Ghosn, Louis J.; Min, James B.; Raj, Sai V.; Lerch, Bradley A.; Holland, Frederic A., Jr.

2004-01-01

269

Effects of thickness and delamination on the damping in honeycomb foam sandwich beams  

NASA Astrophysics Data System (ADS)

In engineering applications where the use of lightweight structures is important, the introduction of a viscoelastic core layer, which has high inherent damping, between two face sheets, can produce a sandwich structure with high damping. Sandwich structures have the additional advantage that their strength to weight ratios are generally superior to those of solid metals. So, sandwich structures are being used increasingly in transportation vehicles. Knowledge of the passive damping of sandwich structures and attempts to improve their damping at the design stage thus are important. Some theoretical models for passive damping in composite sandwich structures are reviewed in this paper. The effects of the thickness of the core and face sheets, and delamination on damping are analyzed. Measurements on honeycomb-foam sandwich beams with different configurations and thicknesses have been performed and the results compared with the theoretical predictions.

Li, Zhuang; Crocker, Malcolm J.

2006-06-01

270

Classical and First-Order Shear Deformation Analysis of Sandwich Plates  

Microsoft Academic Search

\\u000a This chapter will present classical laminated plate theory (CLPT) analysis of composite face sheets and sandwich plates. It\\u000a is recognized that the transverse shear deformation is not incorporated in CLPT. Shear deformation of sandwich plates is important\\u000a and first-order shear deformation analysis will be outlined. Applications of CLPT and first-order shear deformation analysis\\u000a to sandwich panels will be presented. Two

L. A. Carlsson; G. A. Kardomateas

271

Modeling and experimental validation of a sandwich plate with isotropic face plates and viscoelestic core  

Microsoft Academic Search

We analyze and experimentally validate an analysis of a sandwich plate structure, where anisotropic face plates sandwich a viscoelastic core. Existing analytical models have been modified to incorporate piezo-actuation in anisotropic and 3-layered thin plates, using the variational energy method. The 3-layered sandwich consists of anisotropic face- plates with surface bonded piezo-electric actuators, and a viscoelastic core. The analysis includes

Sudha Veermani; Norman M. Wereley

1997-01-01

272

An adaptive dead-zone inverse controller for systems with sandwiched dead-zones  

Microsoft Academic Search

This paper addresses adaptive control of sandwich nonlinear systems having an unknown sandwiched deadzone between the linear dynamic blocks, as illustrated by a hydraulic valve system. An adaptive hybrid control scheme for control of such sandwiched dead-zone systems is developed. The proposed control scheme employs an inner-loop discrete-time feedback design and an outer-loop continuous-time feedback design, combined with an adaptive

Avinash Taware; Gang Tao; C. Teolis

2001-01-01

273

Smart Composite Sandwich Structures for Future Aerospace Application -Damage Detection and Suppression-: a Review  

NASA Astrophysics Data System (ADS)

Sandwich structures with advanced composite facesheets are attracting much attention as a solution to maximize the potential of composite materials. However, the composite sandwich structures are prone to damage, such as impact damage and debonding. Although these damages are difficult to detect using conventional nondestructive inspection method, they cause significant reduction in the mechanical properties. Hence, several researchers have attempted to detect and suppress the damages using smart sensors and actuators. In this paper recent developments on smart technologies to improve reliability of the composite sandwich structures are reviewed. First, the state-of-the-art sandwich technology in aerospace application is presented. Next, typical damages in composite sandwich structures are described, which is essential to effectively apply the smart technologies to sandwich structures. Then, smart technologies which have been applied to sandwich structures are briefly shown with focusing specific properties of sandwich structures. It includes damage detection using dynamic response, wave propagation and optical fiber sensors. Finally, a smart honeycomb sandwich concept is also presented.

Takeda, Nobuo; Minakuchi, Shu; Okabe, Yoji

274

Experimental evaluation of two 36 inch by 47 inch graphite/epoxy sandwich shear webs  

NASA Technical Reports Server (NTRS)

The design is described and test of two large (36 in. x 47 in.) graphite/epoxy sandwich shear webs. One sandwich web was designed to exhibit strength failure of the facings at a shear load of 7638 lbs/in., which is a characteristic loading for the space shuttle orbiter main engine thrust beam structure. The second sandwich web was designed to exhibit general instability failure at a shear load of 5000 lbs/in., to identify problem areas of stability critical sandwich webs and to assess the adequacy of contemporary analysis techniques.

Bush, H. G.

1975-01-01

275

Fiber-Reinforced-Foam (FRF) Core Composite Sandwich Panel Concept for Advanced Composites Technologi  

NASA Technical Reports Server (NTRS)

Fiber-Reinforced-Foam (FRF) Core Composite Sandwich Panel Concept for Advanced Composites Technologies Project - Preliminary Manufacturing Demonstration Articles for Ares V Payload Shroud Barrel Acreage Structure

2010-01-01

276

Energy absorption capabilities of composite sandwich panels under blast loads  

NASA Astrophysics Data System (ADS)

As blast threats on military and civilian structures continue to be a significant concern, there remains a need for improved design strategies to increase blast resistance capabilities. The approach to blast resistance proposed here is focused on dissipating the high levels of pressure induced during a blast through maximizing the potential for energy absorption of composite sandwich panels, which are a competitive structural member type due to the inherent energy absorption capabilities of fiber reinforced polymer (FRP) composites. Furthermore, the middle core in the sandwich panels can be designed as a sacrificial layer allowing for a significant amount of deformation or progressive failure to maximize the potential for energy absorption. The research here is aimed at the optimization of composite sandwich panels for blast mitigation via energy absorption mechanisms. The energy absorption mechanisms considered include absorbed strain energy due to inelastic deformation as well as energy dissipation through progressive failure of the core of the sandwich panels. The methods employed in the research consist of a combination of experimentally-validated finite element analysis (FEA) and the derivation and use of a simplified analytical model. The key components of the scope of work then includes: establishment of quantified energy absorption criteria, validation of the selected FE modeling techniques, development of the simplified analytical model, investigation of influential core architectures and geometric parameters, and investigation of influential material properties. For the parameters that are identified as being most-influential, recommended values for these parameters are suggested in conceptual terms that are conducive to designing composite sandwich panels for various blast threats. Based on reviewing the energy response characteristic of the panel under blast loading, a non-dimensional parameter AET/ ET (absorbed energy, AET, normalized by total energy, ET) was suggested to compare energy absorption capabilities of the structures under blast loading. In addition, AEweb/ET (where AEweb is the energy absorbed by the middle core) was also employed to evaluate the energy absorption contribution from the web. Taking advantage of FEA and the simplified analytical model, the influences of material properties as well as core architectures and geometries on energy absorption capabilities (quantified by AET/ ET and AEweb/E T) were investigated through parametric studies. Results from the material property investigation indicated that density of the front face sheet and strength were most influential on the energy absorption capability of the composite sandwich panels under blast loading. The study to investigate the potential effectiveness of energy absorbed via inelastic deformation compared to energy absorbed via progressive failure indicated that for practical applications (where the position of bomb is usually unknown and the panel is designed to be the same anywhere), the energy absorption via inelastic deformation is the more efficient approach. Regarding the geometric optimization, it was found that a core architecture consisting of vertically-oriented webs was ideal. The optimum values for these parameters can be generally described as those which cause the most inelasticity, but not failure, of the face sheets and webs.

Sankar Ray, Tirtha

277

Analysis and Fabrication of Paraboloidal CFRP Sandwich Mirrors  

NASA Astrophysics Data System (ADS)

The low areal weight requirements of telescopes in aerospace applications has driven the study on composite mirrors for several years. For example, the primary parabolic mirror in a balloon-borne, Cassegrain telescope required an optical quality better than 30 microns in figure RMS error. A parametric study on composite sandwich mirrors was conducted by using finite element analysis as well as optical analysis. The factors covered the cell sizes, core materials, core thicknesses, face layups, and support configurations. Based on theoretical calculations, many high quality spherical composite sandwich mirrors were generated by using a non-heat curing process. The CFRP faces and Nomex core were chosen as the baseline materials for mirror fabrication due to their high strength and low weight. The proposed replication method applied an interface layer between face and surface coat to eliminate print -through problems. Many important goals have been realized in those mirror samples with optical laser interferometer testing. These include the figure RMS error less than 2 microns and the surface RMS error less than 0.05 micron. The areal weights of the mirror samples are less than 7 kg/m ^2. The thermal stability of these mirrors was observed from the optical results with thermal cycling tests. The proposed 2-meter parabolic composite sandwich mirror, with an areal weight of less than 10 kg/m ^2, would consist of either (0/90/45/ -45) _{rm S} layup faces with an optimal 3^{' '} core or (QC) layup faces with a total core thickness of 5 inches. Both a ring support around the equator and the 18-point Hindle-type support would lead to the best optical quality under both self weight and thermal loading.

Hong, Tayo Steve

278

Water intrusion in thin-skinned composite honeycomb sandwich structures  

NASA Technical Reports Server (NTRS)

Thin-skinned composite honeycomb sandwich structures from the trailing edge of the U.S. Army's Apache and Chinook helicopters have been tested to ascertain their susceptibility to water intrusion as well as such intrusions' effects on impact damage and cyclic loading. Minimum-impact and fatigue conditions were determined which would create microcracks sufficiently large to allow the passage of water through the skins; damage sufficient for this to occur was for some skins undetectable under a 40X-magnification optical microscope. Flow rate was a function of moisture content, damage, applied strain, and pressure differences.

Jackson, Wade C.; O'Brien, T. Kevin

1988-01-01

279

A sandwich assay for procalcitonin detection for POCT applications  

NASA Astrophysics Data System (ADS)

A plastic biochip was developed for the detection of procalcitonin (PCT) and consists of a polymethylmethacrylate (PMMA) chip shaped in order to achieve several flow microchannels. A sandwich assay using a new antibody pairs is implemented with the capture antibody immobilized on the PMMA surface and the target antibody labelled with a fluorophore. A laser diode excites the fluorescent sensing layer. Thanks to the anisotropy of the fluorescence the emitted light travels along the thickness of the plastic material. The fluorescence coming out from the chip is collected by 1 mm plastic optical fibre and detected with a spectrum analyser.

Baldini, Francesco; Bolzoni, Luca; Giannetti, Ambra; Kess, Melanie; Kraemer, Petra M.; Kremmer, Elisabeth; Porro, Giampiero; Senesi, Folco; Trono, Cosimo

2009-02-01

280

Deformation and fracture of impulsively loaded sandwich panels  

NASA Astrophysics Data System (ADS)

Light metal sandwich panel structures with cellular cores have attracted interest for multifunctional applications which exploit their high bend strength and impact energy absorption. This concept has been explored here using a model 6061-T6 aluminum alloy system fabricated by friction stir weld joining extruded sandwich panels with a triangular corrugated core. Micro-hardness and miniature tensile coupon testing revealed that friction stir welding reduced the strength and ductility in the welds and a narrow heat affected zone on either side of the weld by approximately 30%. Square, edge clamped sandwich panels and solid plates of equal mass per unit area were subjected to localized impulsive loading by the impact of explosively accelerated, water saturated, sand shells. The hydrodynamic load and impulse applied by the sand were gradually increased by reducing the stand-off distance between the test charge and panel surfaces. The sandwich panels suffered global bending and stretching, and localized core crushing. As the pressure applied by the sand increased, face sheet fracture by a combination of tensile stretching and shear-off occurred first at the two clamped edges of the panels that were parallel with the corrugation and weld direction. The plane of these fractures always lay within the heat affected zone of the longitudinal welds. For the most intensively loaded panels additional cracks occurred at the other clamped boundaries and in the center of the panel. To investigate the dynamic deformation and fracture processes, a particle-based method has been used to simulate the impulsive loading of the panels. This has been combined with a finite element analysis utilizing a modified Johnson-Cook constitutive relation and a Cockcroft-Latham fracture criterion that accounted for local variation in material properties. The fully coupled simulation approach enabled the relationships between the soil-explosive test charge design, panel geometry, spatially varying material properties and the panel's deformation and dynamic failure responses to be explored. This comprehensive study reveals the existence of a strong instability in the loading that results from changes in sand particle reflection during dynamic evolution of the panel's surface topology. Significant fluid-structure interaction effects are also discovered at the sample sides and corners due to changes of the sand reflection angle by the edge clamping system.

Wadley, H. N. G.; Børvik, T.; Olovsson, L.; Wetzel, J. J.; Dharmasena, K. P.; Hopperstad, O. S.; Deshpande, V. S.; Hutchinson, J. W.

2013-02-01

281

Residual Strength of Sandwich Structure Subjected to Low Velocity Impact  

NASA Astrophysics Data System (ADS)

The goals are to identify the strength reduction behavior and its statistical properties of sandwich structure subjected to low velocity impact. For these, the impact tests were performed using the impact tester and the damages are inspected by SAM. And then, subsequent static tests are conducted under flexural loading for the impacted structures. The strength reduction behavior is evaluated via the residual strength prediction model. Also, a statistical model is developed to identify the fluctuation of residual strength. The model well describes the distribution of residual strength.

Kang, Ki-Weon; Kim, Jung-Kyu; Cheong, Seong-Kyun; Kim, Heung-Seob

282

Low-velocity impact tests on fibrous composite sandwich structures  

NASA Technical Reports Server (NTRS)

The effect of low-velocity projectile impact on the load-carrying ability of the composite sandwich structural components is investigated experimentally, the impact simulating the damage caused by runway debris and the accidental dropping of hand tools during servicing on secondary aircraft structures made with composites. The sandwich-type beam specimens were fabricated with graphite/epoxy face sheets, aluminum honeycomb core, and a steel (back) plate. A four-point beam-loading apparatus was used, and the ultimate strength, ultimate strain, and residual strength of the composites were determined. A faired curve is presented indicating the lower bound of the failure threshold for each of the laminate configurations tested in compression and tension as a function of the projectile impact energy. It is shown that strength degradation due to impact is dependent on the laminate configuration and the fiber/matrix combination. The laminates having more angle plies near the impact surface and unidirectional plies elsewhere seem to show extensive interply and intraply fiber delaminations at failure relative to the laminates with a cross-ply on the impact surface.

Sharma, A. V.

1981-01-01

283

Experimental and Numerical Analysis of Inserts in Sandwich Structures  

NASA Astrophysics Data System (ADS)

In aeronautics, sandwich structures are widely used for secondary structures like flaps or landing gear doors. In the case of landing gear doors, the junction is made by a local reinforcement called an insert. This insert is made by a resin molded in the Nomex™ sandwich core. Such structures are still designed mainly using test results and the lack of an efficient numerical model remains a problem. The purpose of this study is on the one hand to perform experiments in order to be able to identify the failure modes and on the other hand to propose an efficient numerical model. Pull-out tests with cycling were conducted and 3D displacement measured by optical methods. The potential failure modes are numerous (delamination, local fiber breaking, skin/core debonding, core crushing, core shear buckling, potting failure, etc.). Experiments demonstrated that, for the lower loads, the non-linearity and the hysteresis are mainly due to core shear buckling. From this observation, the nonlinear behavior of the core is identified by a 3 point-bending test. The shear-modulus damage law is then implemented on a non-linear finite element model and an acceptable correlation of the tests is achieved. As a consequence, some improvements of the technology will be proposed, manufactured and tested.

Bunyawanichakul, P.; Castanie, B.; Barrau, J.-J.

2005-05-01

284

Manufacturing aluminum sandwich structures by means of superplastic forming  

SciTech Connect

The continued need for lightweight, yet inexpensive, manufacturing techniques in the transportation industry has lead to an increased interest in the use of sandwich structures. This paper examines the possibilities of manufacturing large-scale aluminum sandwich structures using superplastic forming. The materials tested were Mg-alloyed production quality aluminum (Al 5083-O, Al 5083-H321) and Aluminum 1561. Tensile tests at elevated temperatures were performed in order to establish the suitability of the test materials for superplastic forming. The microstructural changes in the test material specimens were examined. Thereafter numerical simulation of the Al 5083-O forming process was conducted based on the tensile test results. The numerical simulation results were subsequently used to estimate forming parameters and the feasibility of manufacturing large-scale structures by superplastic forming. The results indicate that higher strain can be reached at higher temperatures for the test materials. Aluminum alloy 1561 exhibited the largest elongation to fracture and Al 5083-H321 the smallest. Strain appeared to be temperature dependent but not much affected by the strain rate. Metallographic examination clarified that Al-5083-O and Al-5083-H321 showed susceptibility for cavity forming whereas Aluminum 1561 formed relatively few voids. The numerical simulation indicated that Al 5083-O can be superplastically formed using relatively low forming pressure (0.9--1.4 bar).

Impioe, P.; Pimenoff, J.; Haenninen, H.; Heinaekari, M.

2000-07-01

285

Perforation of aluminium foam core sandwich panels under impact loading  

NASA Astrophysics Data System (ADS)

This paper reports an original inverse perforation tests on foam core sandwich panels under impact loading. The key point is the use of an instrumented Hopkinson pressure bar as a perforator and at the same time a measuring device. It aims at a high quality piercing force record during the whole perforation process, which is a lack of common free-flying projectile - target testing schemes. This new testing arrangement allows for the measurement of piercing force-displacement curves under quasi-static and impact loadings of sandwich samples, which is made of 40?mm AlSi7Mg0.5 Cymat foam cores and 0.8?mm thick 2024 T3 aluminium sheet as top and bottom skins. Compared with quasi-static top skin peak loads (the maximal load before the perforation of top skins) obtained under same geometric and clamping conditions and even in the case that the used foam core (Cymat) and aluminium skin sheet are known and have been confirmed rate insensitive, a significant enhancement under impact loading (25%) of the top skin peak load is found.

Elnasri, I.; Zhao, H.; Girard, Y.

2006-08-01

286

Sandwich Composite, Syntactic Foam Core Based, Application for Space Structures  

NASA Technical Reports Server (NTRS)

The current Solid Rocket Booster (SRB) launch vehicle has several metal based components that require a Thermal Protective System (TPS) be applied to the exterior surface to ensure its structural integrity and to protect the interior hardware from aerodynamic heating. TPS materials have distinct disadvantages associated with their use. One disadvantage to the application of TPS is that it can act as a debris source to the Space Shuttle Orbiter during flight and it also adds weight to the system without directly contributing any structural strength. One of the specific areas examined under this program was to replace a metal/TPS system with polymer based composites. A polymer matrix based sandwich composite was developed which had both structural and insulative properties to meet the high aerodynamic structural and heating load survival requirements. The SRB Nose Cap was selected as a candidate for this application. The sandwich system being qualified for this application is a carbon/epoxy outer and inner skin with a high strength-low thermal conductivity syntactic foam core.

Hodge, Andrew J.; Kaul, Raj K.; McMahon, William M.; Reinarts, Thomas

2000-01-01

287

Impact Delamination and Fracture in Aluminum/Acrylic Sandwich Plates  

NASA Technical Reports Server (NTRS)

Impact-induced delamination and fracture in 6061-T6 aluminum/cast acrylic sandwich plates adhered by epoxy were generated in an instrumented drop-weight impact machine. Although only a small dent was produced on the aluminum side when a hemispherical penetrator tup was dropped onto it from a couple of inches, a large ring of delamination at the interface was observed. The delamination damage was often accompanied by severe shattering in the acrylic substratum. Damage patterns in the acrylic layer include radial and ring cracks and, together with delamination at the interface, may cause peeling-off of acrylic material from the sandwich plate. Theory of stress-wave propagation can be used to explain these damage patterns. The impact tests were conducted at various temperatures. The results also show clearly that temperature effect is very important in impact damage. For pure cast acrylic nil-ductile transition (NDT) occurs between 185-195 F. Excessive impact energy was dissipated into fracture energy when tested at temperature below this range or through plastic deformation when tested at temperature above the NDT temperature. Results from this study will be used as baseline data for studying fiber-metal laminates, such as GLARE and ARALL for advanced aeronautical and astronautical applications.

Liaw, Benjamin; Zeichner, Glenn; Liu, Yanxiong; Bowles, Kenneth J. (Technical Monitor)

2000-01-01

288

Sandwich antibody arrays using recombinant antibody-binding protein L.  

PubMed

Antibody arrays are a useful for detecting antigens and other antibodies. This technique typically requires a uniform and well-defined orientation of antibodies attached to a surface for optimal performance. A uniform orientation can be achieved by modification of antibodies to include a single site for attachment. Thus, uniformly oriented antibody arrays require a bioengineered modification for the antibodies directly immobilization on the solid surface. In this study, we describe a "sandwich-type" antibody array where unmodified antibodies are oriented through binding with regioselectively immobilized recombinant antibody-binding protein L. Recombinant proL-CVIA bearing C-terminal CVIA motif is post-translationally modified with an alkyne group by protein farnesyltransferase (PFTase) at the cysteine residue in the CVIA sequence to give proL-CVIApf, which is covalently attached to an azido-modified glass slide by a Huisgen [3 + 2] cycloaddition reaction. Slides bearing antibodies bound to slides coated with regioselectively immobilized proL-CVIApf gave stronger fluorescence outputs and those where the antibody-binding protein was immobilized in random orientations on an epoxy-modified slide. Properly selected capture and detection antibodies did not cross-react with immobilized proL-CVIApf in sandwich arrays, and the proL-CVIApf slides can be used for multiple cycles of detected over a period of several months. PMID:24841983

Seo, Jin-Soo; Poulter, C Dale

2014-06-10

289

Vibration analysis and design optimization of viscoelastic sandwich cylindrical shell  

NASA Astrophysics Data System (ADS)

Damping properties of viscoelastic sandwich structure can be improved by changing some parameters such as thickness of the layers, distribution of partial treatments, slippage between layers at the interfaces, cutting and its distribution at the top and core layers. Since the optimization problem may result in a thick core layer, for achieving more accuracy a new higher-order Taylor's expansion of transverse and in-plane displacement fields is developed for the core layer of sandwich cylindrical shell in which the displacement fields at the core layer are compatibly described in terms of the displacement fields at the elastic faces. The presented model includes fewer parameters than the previously developed models and therefore decreases the number of degree of freedom in the finite element modeling. The transverse normal stress in the core layer is also considered. The formulations are developed to consider the slippage between layers at the interfaces. Finally, by combining the finite element method and the optimization algorithms based on the genetic algorithm and sequential quadratic programming technique, a design optimization methodology has been formulated to maximize the damping characteristics using the optimal number and location of cuts and partial treatments with optimal thicknesses of top and core layers.

Mohammadi, Farough; Sedaghati, Ramin

2012-06-01

290

Foam-injected sandwich panels with continuous-reinforced facings  

NASA Astrophysics Data System (ADS)

Thermoplastic foam injection molding (FIM) in combination with insert molding (IM) offers a possibility to generate sandwich panels in a one-step process. The prepared face sheets are first positioned inside the mold. A preheating process is carried out using quartz infrared emitters, which are mounted on a linear robot, before the mold is closed. The injection of the gas/melt mixture is combined with an embossing of the mold to further improve the face-core-adhesion. Finally, to initiate the foaming process, adjust the extent of foaming of the core and achieve the desired component dimensions, a mold opening stroke is carried out. The process described was performed with different facing materials, layer dimensions and overall wall thicknesses. Drawn PP fabrics (Curv®) as well as PP/GF70 tapes and consolidated sheets (unidirectional) were used to generate sandwich panels in a range of 5 to 6.4 mm thickness. PP was also chosen to form the foamed core which, in combination with the Curv® face sheets, produces a fully recyclable self-reinforced polymer (SRP) composite. Detailed process descriptions and the results of bending tests demonstrate the high potential. Other focuses are the preheating process and the foam structure.

Menrath, A.; Henning, F.; Huber, T.; Roch, A.; Riess, C.

2014-05-01

291

Fatigue and fracture of foam cores used in sandwich composites  

NASA Astrophysics Data System (ADS)

This study focused on the fracture and fatigue crack growth behavior in polyvinylchloride (PVC) and polyethersulfone (PES) foams. A new sandwich double cantilever beam (DCB) test specimen was implemented. Elastic foundation and finite element analysis and experimental testing confirmed that the DCB specimen is appropriate for static and cyclic crack propagation testing of soft polymer foams. A comprehensive experimental mechanical analysis was conducted on PVC foams of densities ranging from 45 to 100 kg/m3 and PES foams of densities ranging from 60 to 130 kg/m3. An in-situ scanning electron microscope study on miniature foam fracture specimens showed that crack propagation in the PVC foam was inter-cellular and in the PES foam, failure occurred predominately by extensional failure of vertical cell edges. Sandwich DCB specimens were loaded cyclically as well. For the PVC foams, the crack growth rates were substantially influence by the density. For the PES foams, there was no clear indication about the influence of foam density on the crack growth rate.

Saenz, Elio

292

Construction documents.  

PubMed

Contractors base their bids on construction documents and use them as their daily "nuts and bolts" guide in constructing the building. They are the owner's legal instrument to insure that the building they want is constructed as they intended. This article defines and examines the vital significance of construction documents. Of particular interest is the discussion of owner and architect responsibilities during the construction documents (CD) phase, contractual agreements on these responsibilities, and how to minimize potential problems. PMID:10291622

Diaz, J R

1988-01-01

293

Construction aggregates  

USGS Publications Warehouse

Part of the 1994 Industrial Minerals Review. The production, consumption, and applications of construction aggregates are reviewed. In 1994, the production of construction aggregates, which includes crushed stone and construction sand and gravel combined, increased 7.7 percent to 2.14 Gt compared with the previous year. These record production levels are mostly a result of funding for highway construction work provided by the Intermodal Surface Transportation Efficiency Act of 1991. Demand is expected to increase for construction aggregates in 1995.

Tepordei, V. V.

1995-01-01

294

Smart Composite Sandwich Structures for Future Aerospace Application Damage Detection and Suppression: a Review  

Microsoft Academic Search

Sandwich structures with advanced composite facesheets are attracting much attention as a solution to maximize the potential of composite materials. However, the composite sandwich structures are prone to damage, such as impact damage and debonding. Although these damages are difficult to detect using conventional nondestructive inspection method, they cause significant reduction in the mechanical properties. Hence, several researchers have attempted

Nobuo Takeda; Shu Minakuchi; Yoji Okabe

2007-01-01

295

Free vibration analysis of sandwich beam with FG core using the element free Galerkin method  

Microsoft Academic Search

In this paper, free vibration analysis of sandwich beams with functionally graded material as core material is investigated. For the analysis, the element free Galerkin method and Galerkin formulation for two dimensional elasticity problems are considered. Penalty method is used for modeling of interface between the face sheets and the core in the sandwich beam. Using the similarity of materials

M. Chehel Amirani; S. M. R. Khalili; N. Nemati

2009-01-01

296

THE RESISTANCE OF METALLIC SANDWICH BEAMS WITH LATTICE CORES TO UNDERWATER SHOCK LOADING  

Microsoft Academic Search

Analytical models for the dynamic response of sandwich beams to an under-water shock are developed. The relative performance of the clamped beams is sensitive to the choice of the core topology of the beams. It is found that lattice cores with high through-thickness and longitudinal strength outperform metallic foam cores. It is concluded that sandwich panels have high potential as

Norman A. Fleck

297

Vibration and stability of rotating polar orthotropic sandwich annular plates with a viscoelastic core layer  

Microsoft Academic Search

A sandwich annular plate is built with two face layers of polar orthotropic material and a viscoelastic core layer. The non-axisymmetric vibration and stability problem of the rotating sandwich plate are analyzed by using the finite element method. By employing the discrete layer annular element and Hamilton’s principle, the finite element equations of motion that consider the effects of transverse

Yu-Ren Chen; Lien-Wen Chen

2007-01-01

298

Multimodal passive vibration control of sandwich beams with shunted shear piezoelectric materials  

Microsoft Academic Search

This work presents a performance analysis of multimodal passive vibration control of a sandwich beam using shear piezoelectric materials, embedded in a sandwich beam core, connected to independent resistive shunt circuits. Shear piezoelectric actuators were recently shown to be more interesting for higher frequencies and stiffer structures. In particular, for shunted damping, it was shown that equivalent material loss factors

M A Trindade; C E B Maio

2008-01-01

299

THE TRANSVERSE RESPONSE OF SANDWICH PANELS TO AN UNDERWATER SHOCK WAVE  

Microsoft Academic Search

The response of submerged structures to an underwater shock wave involves both structural and fluid behaviour. For sandwich structures the response to an initial shock wave in the transverse direction is significantly different from that of a homogeneous structure. This is due to the elastic properties of the core in the sandwich. For a homogeneous structure one cavitation zone is

K. Mäkinen

1999-01-01

300

Vibration and thermal buckling of composite sandwich beams with viscoelastic core  

Microsoft Academic Search

The paper deals with the vibration and thermal buckling behavior of sandwich beams with composite facings and viscoelastic core. Sandwich plate and beam elements are compared in this context. Each composite laminate is modeled as an equivalent single layer. Steady state temperature field is assumed. The formulation is a decoupled thermo mechanical formulation where in the temperatures in the domain

V. Pradeep; N. Ganesan; K. Bhaskar

2007-01-01

301

Parameter Estimation in Hybrid Active-Passive Laminated Sandwich Composite Structures  

Microsoft Academic Search

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative models, with unknown parameters that are to be estimated

A. L. Araújo; C. M. Mota Soares; C. A. Mota Soares; J. Herskovits

2010-01-01

302

Axisymmetric dynamic instability of rotating polar orthotropic sandwich annular plates with a constrained damping layer  

Microsoft Academic Search

A sandwich annular plate built with two constrained layers of polar orthotropic material and a viscoelastic core layer is subjected to a periodic uniform radial stress while rotating. The axisymmetric dynamic instability of such a rotating sandwich plate is analyzed using finite elements. By employing a discrete layer axisymmetric annular element and Hamilton’s principle, the finite element equations of motion

Yu-Ren Chen; Lien-Wen Chen; Ching-Cheng Wang

2006-01-01

303

Critical comparison of viscoelastic damping and electrorheological fluid core damping in composite sandwich skew plates  

Microsoft Academic Search

Composite sandwich structures have extensive applications due to their high strength and structural efficiency. Skew fibre-reinforced composite laminates are used as important structural elements in modern structural design, particularly in the aerospace industry. Natural frequency of these skew laminates is of primary significance to structural designers. The present article studies the free vibration and damping characteristics of sandwich skew plates

G. Vishnu Narayana; N. Ganesan

2007-01-01

304

Characterisation by Inverse Techniques of Elastic, Viscoelastic and Piezoelectric Properties of Anisotropic Sandwich Adaptive Structures  

Microsoft Academic Search

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative models, with unknown parameters that are to be estimated

Aurelio L. Araújo; Cristovao M. Mota Soares; Carlos A. Mota Soares; Jose Herskovits

2010-01-01

305

Thermoelastic buckling and vibration behavior of a functionally graded sandwich beam with constrained viscoelastic core  

Microsoft Academic Search

In this article, buckling and vibration behavior of a functionally graded material (FGM) sandwich beam having constrained viscoelastic layer (VEL) is studied in thermal environment by using finite element formulation. The FGM sandwich beam is assumed to be clamped on both edges. The material properties of FGM are functionally graded in thickness direction according to volume fraction power law distribution.

Rajesh K. Bhangale; N. Ganesan

2006-01-01

306

Dynamic analysis of composite sandwich plates with damping modelled using high-order shear deformation theory  

Microsoft Academic Search

The dynamic behaviour of fibre reinforced plastic sandwich plates with PVC foam core is investigated in this paper. Recently, the authors have developed an analytical method based on Reddy's refined high-order shear deformation theory to study the dynamic behaviour of undamped fibre reinforced plastic (FRP) sandwich plates. The present paper explains how the dynamic constitutive material properties (obtained by carrying

M. Meunier; R. A. Shenoi

2001-01-01

307

Dynamic analysis of magnetorheological elastomer-based sandwich beam with conductive skins under various boundary conditions  

Microsoft Academic Search

The dynamic analysis of a three-layered symmetric sandwich beam with magnetorheological elastomer (MRE) embedded viscoelastic core and conductive skins subjected to a periodic axial load have been carried out under various boundary conditions. As the skins of the sandwich beam are conductive, magnetic loads are applied to the skins during vibration. Due to the field-dependent shear modulus of MRE material,

B. Nayak; S. K. Dwivedy; K. S. R. K. Murthy

2011-01-01

308

Properties and mechanical behaviour of novel sandwich composites made of syntactic foam and paper skin  

Microsoft Academic Search

Novel sandwich composites made of syntactic foam core, paper skin, and starch adhesive for interface between syntactic foam core and paper skin, were manufactured by varying starch content in adhesive for interface. Two different microsphere size groups (SL75 and SL300) were employed for syntactic foam core manufacture with pre-mould processing method. Mechanical behaviour of manufactured sandwich composites in relation with

Ho Sung Kim

309

Integration of Mechanics and Acoustics in a Sandwich Fuselage. Part IV  

Microsoft Academic Search

Until now only the stiffened skin structural concept has been discussed. A different structural concept is the sandwich concept. Sandwiches consist out of layers. The outer layers are called facings and are generally thin and of high density. These facings are supposed to resist most of the edgewise loads and flat-wise bending moments. The inner layer is called the core

M. J. L. van Tooren; L. A. Krakers; A. Beukers

2005-01-01

310

Experimental investigation of strain rate effects on the crushing characteristics of composite sandwich panels  

Microsoft Academic Search

In the present work, the influence of strain rate on the collapse modes, the crushing mechanisms and the energy absorption characteristics of four types of composite sandwich panels was investigated in a series of impact and static in-plane tests. The tested sandwich specimens were formed combining two types of glass fibre reinforced plastic (FRP) faceplate laminates with three types of

A. G. Mamalis; D. P. Papapostolou

2010-01-01

311

The high velocity impact response of composite and FML-reinforced sandwich structures  

Microsoft Academic Search

The high velocity impact response of a range of novel aluminium foam sandwich structures has been investigated using a nitrogen gas gun. Tests were undertaken on sandwich structures based on plain composite and fibre-metal laminate (FML) skins. Impact testing was conducted using a 10 mm diameter projectile at energies up to that required to achieve complete perforation of the target.

G. Reyes Villanueva; W. J. Cantwell

2004-01-01

312

Ply drop-off effects in CFRP\\/honeycomb sandwich panels—experimental results  

Microsoft Academic Search

The results of a combined experimental and theoretical investigation of local bending effects induced by ply drop-off in CFRP\\/honeycomb sandwich panels are presented. The objective of the investigation was to validate a simple model for engineering analysis of sandwich panels with tapered face laminates presented in a previous paper. The experimental investigation was conducted by using electronic speckle pattern interferometry

O. T. Thomson; W. Rits; D. C. G. Eaton; O. Dupont; P. Queekers

1996-01-01

313

High renewable content sandwich structures based on flax-basalt hybrids and biobased epoxy polymers  

NASA Astrophysics Data System (ADS)

In the last years, a growing interest in the development of high environmental efficiency materials has been detected and this situation is more accentuated in the field of polymers and polymer composites. In this work, green composite sandwich structures with high renewable content have been developed with core cork materials. The base resin for composites was a biobased epoxy resin derived from epoxidized vegetable oils. Hybrid basalt-flax fabrics have been used as reinforcements for composites and the influence of the stacking sequence has been evaluated in order to optimize the appropriate laminate structure for the sandwich bases. Core cork materials with different thickness have been used to evaluate performance of sandwich structures thus leading to high renewable content composite sandwich structures. Results show that position of basalt fabrics plays a key role in flexural fracture of sandwich structures due to differences in stiffness between flax and basalt fibers.

Colomina, S.; Boronat, T.; Fenollar, O.; Sánchez-Nacher, L.; Balart, R.

2014-05-01

314

Natural cork agglomerate employed as an environmentally friendly solution for quiet sandwich composites.  

PubMed

Carbon fiber-synthetic foam core sandwich composites are widely used for many structural applications due to their superior mechanical performance and low weight. Unfortunately these structures typically have very poor acoustic performance. There is increasingly growing demand in mitigating this noise issue in sandwich composite structures. This study shows that marrying carbon fiber composites with natural cork in a sandwich structure provides a synergistic effect yielding a noise-free sandwich composite structure without the sacrifice of mechanical performance or weight. Moreover the cork-core sandwich composites boast a 250% improvement in damping performance, providing increased durability and lifetime operation. Additionally as the world seeks environmentally friendly materials, the harvesting of cork is a natural, renewable process which reduces subsequent carbon footprints. Such a transition from synthetic foam cores to natural cork cores could provide unprecedented improvements in acoustic and vibrational performance in applications such as aircraft cabins or wind turbine blades. PMID:22574250

Sargianis, James; Kim, Hyung-ick; Suhr, Jonghwan

2012-01-01

315

Buckling and Vibration Behavior of a Viscoelastic Sandwich Cylinder under Thermal Environment  

NASA Astrophysics Data System (ADS)

This paper presents the buckling and vibration behavior of a viscoelastic sandwich cylinder in a thermal environment analyzed using the semi analytical finite element method. The analysis is carried out using a decoupled thermo mechanical formulation. The temperature field in the shell domain is evaluated using an eight-noded axisymmetric ring element. Buckling and vibration analyses are carried out using a two-noded sandwich shell element in the semi-analytical finite element method. Buckling temperatures are calculated for sandwich shells with two different core materials. The effect of temperature-dependent core shear modulus on buckling temperature and vibration behavior has been investigated for sandwich shells with different mechanical boundary conditions. Variations of natural frequencies and loss factors with temperature have also been examined for sandwich shells with two different core materials.

Pradeep, V.; Ganesan, N.; Padmanabhan, C.

2006-10-01

316

Vibration analysis of sandwich rectangular plates with magnetorheological elastomer damping treatment  

NASA Astrophysics Data System (ADS)

In this study, the vibration analysis of sandwich rectangular plates with magnetorheological (MR) elastomer damping treatment is presented. The rectangular plate is combined with a magnetorheological elastomer core layer and a constraining layer to improve the vibration behaviors of the sandwich system. The MR material shows variations in the rheological properties when subjected to varying magnetic fields. Additionally, the MR material exhibits a rapid time response and is applicable to structures or devices when a tunable system is required. The magnetorheological elastomer is found to have a significant effect on the vibration characteristics of the sandwich rectangular plate. The modal damper and the natural frequencies for the sandwich plate system are calculated for various magnetic fields and some designed parameters by utilizing the finite element method. The damping effects of the sandwich plate system can be controlled and changed when different magnetic field strengths are applied.

Yeh, Jia-Yi

2013-03-01

317

Construction 2004.  

National Technical Information Service (NTIS)

Partial Contents: Portland Cement Concrete Pavements (Stringline Effects on Concrete Pavement Construction, Assessment of Profiler Performance for Construction, Quality Control with Simulated Profilograph index, Active Crack Control for Continuously Reinf...

2004-01-01

318

Construction, 2006.  

National Technical Information Service (NTIS)

Contents: Part 1-Construction Management: Quantification of Risk Cost Associated with Short-Term Warranty-Based Specifications for Pavements; Visually Improving Construction Contract Administration; and Quantity-Based Approach to Preliminary Cost Estimate...

2006-01-01

319

Electrochemical construction  

DOEpatents

An electrochemical cell construction features a novel co-extruded plastic electrode in an interleaved construction with a novel integral separator-spacer. Also featured is a leak and impact resistant construction for preventing the spill of corrosive materials in the event of rupture.

Einstein, Harry (Springfield, NJ); Grimes, Patrick G. (Westfield, NJ)

1983-08-23

320

Hole delocalization in oxidized cerium(IV) porphyrin sandwich complexes  

SciTech Connect

Optical absorption, electron paramagnetic resonance, and resonance Raman spectra are reported for the one-electron oxidation products of the Ce(IV) sandwich porphyrins, Ce(OEP)/sub 2/ and Ce(TPP)/sub 2/ (OEP = octaethylporphyrin; TPP = tetraphenylporphyrin). These data, in conjunction with electrochemical measurements, indicate that the holes of both oxidized species are delocalized on the vibrational and probably the electronic time scales. In Ce(OEP)/sub 2//sup +/, the hole is delocalized through purely porphyrin-porphyrin interactions. In Ce(TPP)/sub 2//sup +/, delocalization is further facilitated by participation of the f orbitals of the Ce(IV) ion. The different characteristics of the redox orbitals of Ce(OEP)/sub 2//sup +/ and Ce(TPP)/sub 2//sup +/ are accounted for by the fact that oxidation occurs from an a/sub lu/-like orbital in the former complex and from an a/sub 2u/-like orbital in the latter.

Donohoe, R.J.; Duchowski, J.K.; Bocian, D.F.

1988-08-31

321

Predicting The Compression Strength Of Impact-Damaged Sandwich Panels  

NASA Technical Reports Server (NTRS)

The objective of this work was to develop a technique for predicting the residual compression strength of sandwich panels containing impact damage in one facesheet. The technique was tailored to predict the strength of specimens that exhibit a failure mode involving the formation of kink bands at locations of peak strain in the region of impact damage. Under continued compression loading, the kink bands propagate in a stable manner perpendicular to the applied load. When a critical kink-band length is reached, growth becomes unstable corresponding to panel failure. The analysis follows in two sections. The first section calculates the far-field stress required for stable kink-band growth and the second calculates that required for unstable growth. The residual strength prediction is made when the stress for stable growth becomes equal to that for unstable kink-band growth. Initial comparisons between analysis and experiment show good agreement.

Ratcliffe, James; Jackson, Wade; Schaff, Jeffery

1990-01-01

322

Effects of Impact Damage in Midplane Asymmetric Sandwich Composites  

NASA Technical Reports Server (NTRS)

Several structural sandwich composites arc in service on military and commercial aerospace vehicles, however, these components have been limited to secondary structures partly because the impact damage and damage tolerance of these composites have not been extensively characterized. To improve durability, safety, and life cycle performance of PMCs while reducing maintenance costs, combined analysis, and test methods that provide a means of predicting critical engineering properties after impact damage of the structure, must be developed. A key enabling technology here is the establishment of the correlation between the impact test results conducted in the laboratory and the mechanics-based phenomenological solutions. This research was undertaken to investigate the compression and flexural properties following low velocity impact of a nomex/phenolic honeycomb core, fiberglass/epoxy facesheet, midplane asymmetric sandwich composite. One facesheet (thin side) was composed of two plies of the fiberglass/epoxy (0/90), while the other facesheet (thick side) was composed of four plies (0/90/0/90) of fiberglass/epoxy. Due to the differences in facesheet thickness, impact damage was separately induced on the thick side as well as the thin side. The compression and flexural strength properties for each damage arrangement were compared using different levels of impact energy ranging from 0 to 452 Joules. In all cases, higher impact energy resulted in decreased compression and flexural strength. Impact on the thin side showed slightly more retention of compression strength at low impact levels, whereas higher residual compressive strength was observed from impact on the thick side at higher impact levels. Different facesheet thicknesses or midplane asymmetry, played an important role in the flexural strength, however, low velocity impact on the both the thick and thin fiberglass/epoxy facesheet side showed an almost linear loss of flexural strength to saturation.

Meador, Michael (Technical Monitor); Webb, M. Mensah; Veezie, David R.

2003-01-01

323

Modified Opsite(R) Sandwich for Temporary Abdominal Closure: A Non-Traumatic Experience  

PubMed Central

INTRODUCTION Laparostomy techniques have advanced since the advent of damage control surgery for the critically injured patient. Numerous methods of temporary abdominal closure (TAC) are described in the literature with most reports focusing on trauma. We describe a modified technique for TAC and report its use in a series of critically ill non-trauma patients. PATIENTS AND METHODS Eleven patients under the care of one consultant underwent TAC over a 36-month period. A standardised technique was used in all cases and this is described. Severity of illness at the time of the first laparotomy was assessed using the Portsmouth variant of the Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (P-POSSUM). RESULTS Nineteen TACs were performed in 11 patients with a variety of serious surgical conditions. In-hospital mortality was zero despite seven of the patients having an individual P-POSSUM predicted mortality in excess of 50%. The laparostomy dressing proved simple in construction, facilitated nursing care and was well-tolerated in the critical care environment. All patients underwent definitive fascial closure during the index admission. CONCLUSIONS Laparostomy is a useful technique outwith the context of trauma. We have demonstrated the utility of the modified Opsite® sandwich vacuum pack for TAC in a series of critically ill patients with a universally favourable outcome. This small study suggests that selective use of TAC may reduce surgical mortality.

Wilde, JM; Loudon, MA

2007-01-01

324

Open-sandwich immunoassay for sensitive and broad-range detection of a shellfish toxin gonyautoxin.  

PubMed

At present, the analytical method for paralytic shellfish poisoning (PSP) toxins in shellfish is the mouse bioassay (MBA), which is an official method of the Association of Analytical Communities (AOAC [8]). However, the low sensitivity and concerns over the number of live animals required for testing have been cited as the major reason for seeking its replacement. In this report, we employed an open-sandwich immunoassay (OS-IA) to detect gonyautoxin (GTX2/3), a kind of PSP toxins. OS-IA, which utilizes the antigen-induced enhancement of antibody VH/VL interaction, can measure a small molecule antigen in a noncompetitive format. Hence it has a wider working range and shorter measurement time. We isolated anti-GTX2/3 antibody gene from a hybridoma GT-13A by screening a Fab-displaying phage library. Then the vectors for OS-IA were constructed, and examined for antigen concentration-dependency of the VH/VL interaction by OS-ELISA. As a result, in each case, signal intensity increases notably in a wide concentration range (0.1 to >1000 ng mL(-1)) of free GTX2/3, which was enough to cover its regulation value (80 ?g 100 g(-1)) in many countries. So OS-IA will be widely applicable to detect PSP toxins in shellfish meats and in drinking water. PMID:23953213

Hara, Yuko; Dong, Jinhua; Ueda, Hiroshi

2013-09-01

325

A comparative study of the impact properties of sandwich materials with different cores  

NASA Astrophysics Data System (ADS)

Sandwich panels are made of two high strength skins bonded to either side of a light weight core and are used in applications where high stiffness combined with low structural weight is required. The purpose of this paper is to compare the mechanical response of several sandwich panels whose core materials are different. Sandwich panels with glass fibre-reinforced polymer face sheets were used, combined with five different cores; polystyrene foam, polypropylene honeycomb, two different density Balsa wood and Cork. All specimens were subjected to low velocity impact and their structural response (Force-displacement curves) were compared to quasistatic response of the panel tested using an hemispherical indenter.

Ramakrishnan, K. R.; Shankar, K.; Viot, P.; Guerard, S.

2012-08-01

326

Theoretical design of novel trinuclear sandwich complexes with central M3 triangles (M = Ni, Pd, Pt).  

PubMed

On the basis of the 18-electron rule, we theoretically designed a series of sandwich complexes [M(3)L(2)(CO)(3)](q) (M = Ni, Pd, Pt; L = C(7)H(7), P(5), P(6), As(5), As(6); q = 2+, 0, or 2-) by means of density functional theory computations. These sandwich structures are of high stability, revealed by their strong donating and back-donating metal-ligand interactions, considerable aromatic characters as well as sizable energy gaps. All these proposed sandwich structures might serve as promising building blocks for new nanomaterials. PMID:21361283

Jin, Peng; Li, Fengyu; Chen, Zhongfang

2011-03-24

327

Steps toward 8m honeycomb mirror blanks. III - 1.8m honeycomb sandwich blanks cast from borosilicate glass  

NASA Technical Reports Server (NTRS)

The design, fabrication techniques, and equipment used for producing two 1.8-m honeycomb sandwich blanks, eventually leading to production of 8-m blanks, are reported. The procedure employed 85 cast hexagonal tiles at the bottom section, affixed against flotation by SiC bolts. The two plano concave mirrors are 1.83 m thick, weight 500 kg, and are each designed for 19 supports of astatic-lever type. Both blanks are of high quality and with an adequately low bubble content; one is to be figured to high-precision 0.25-arcsecond images, and is to be tested on the Multiple Mirror Telescope. Construction of a spin-casting facility based on the same principle is being planned for test-fabricating spin-cast mirrors on a smaller scale.

Angel, J. R. P.; Hill, J. M.

1984-01-01

328

Construction aggregates  

USGS Publications Warehouse

Part of a special section on industrial minerals in 1993. The 1993 production of construction aggregates increased 6.3 percent over the 1992 figure, to reach 2.01 Gt. This represents the highest estimated annual production of combined crushed stone and construction sand and gravel ever recorded in the U.S. The outlook for construction aggregates and the issues facing the industry are discussed.

Tepordei, V. V.

1994-01-01

329

Construction aggregates  

USGS Publications Warehouse

Construction aggregates consist primarily of crushed stone and construction sand and gravel. Total estimated production of construction aggregates increased in 1999 by about 2% to 2.39 Gt (2.64 billion st) compared with 1998. This record production level continued an expansion that began in 1992. By commodities, crushed stone production increased 3.3%, while sand and gravel production increased by about 0.5%.

Langer, W. H.; Tepordei, V. V.; Bolen, W. P.

2000-01-01

330

Construction aggregates  

USGS Publications Warehouse

Part of the Annual Commodities Review 1995. Production of construction aggregates such as crushed stone and construction sand and gravel showed a marginal increase in 1995. Most of the 1995 increases were due to funding for highway construction work. The major areas of concern to the industry included issues relating to wetlands classification and the classification of crystalline silica as a probable human carcinogen. Despite this, an increase in demand is anticipated for 1996.

Tepordei, V. V.

1996-01-01

331

Construction and commissioning of the CALICE analog hadron calorimeter prototype  

Microsoft Academic Search

An analog hadron calorimeter (AHCAL) prototype of 5.3 nuclear interaction lengths thickness has been constructed by members of the CALICE Collaboration. The AHCAL prototype consists of a 38-layer sandwich structure of steel plates and highly-segmented scintillator tiles that are read out by wavelength-shifting fibers coupled to SiPMs. The signal is amplified and shaped with a custom-designed ASIC. A calibration\\/monitoring system

C. Adloff; Y. Karyotakis; J. Repond; A. Brandt; H. Brown; K. De; C. Medina; J. Smith; J. Li; M. Sosebee; A. White; J. Yu; T. Buanes; G. Eigen; Y. Mikami; O. Miller; N. K. Watson; J. A. Wilson; T. Goto; G. Mavromanolakis; M. A. Thomson; D. R. Ward; W. Yan; D. Benchekroun; A. Hoummada; Y. Khoulaki; M. Oreglia; M. Benyamna; C. Cârloganu; P. Gay; J. Ha; G. C. Blazey; D. Chakraborty; A. Dyshkant; K. Francis; D. Hedin; G. Lima; V. Zutshi; V. A. Babkin; S. N. Bazylev; Yu I. Fedotov; V. M. Slepnev; I. A. Tiapkin; S. V. Volgin; J.-Y. Hostachy; L. Morin; N. D'Ascenzo; U. Cornett; D. David; R. Fabbri; G. Falley; N. Feege; K. Gadow; E. Garutti; P. Göttlicher; T. Jung; S. Karstensen; V. Korbel; A.-I. Lucaci-Timoce; B. Lutz; N. Meyer; V. Morgunov; M. Reinecke; S. Schätzel; S. Schmidt; F. Sefkow; P. Smirnov; A. Vargas-Trevino; N. Wattimena; O. Wendt; M. Groll; R.-D. Heuer; S. Richter; J. Samson; A. Kaplan; H.-Ch Schultz-Coulon; W. Shen; A. Tadday; B. Bilki; E. Norbeck; Y. Onel; E. J. Kim; G. Kim; D.-W. Kim; K. Lee; S. C. Lee; K. Kawagoe; Y. Tamura; J. A. Ballin; P. D. Dauncey; A.-M. Magnan; H. Yilmaz; O. Zorba; V. Bartsch; M. Postranecky; M. Warren; M. Wing; M. Faucci Giannelli; M. G. Green; F. Salvatore; R. Kieffer; I. Laktineh; M. C. Fouz; D. S. Bailey; R. J. Barlow; R. J. Thompson; M. Batouritski; O. Dvornikov; Yu Shulhevich; N. Shumeiko; A. Solin; P. Starovoitov; V. Tchekhovski; A. Terletski; B. Bobchenko; M. Chadeeva; M. Danilov; O. Markin; R. Mizuk; E. Novikov; V. Rusinov; E. Tarkovsky; V. Andreev; N. Kirikova; A. Komar; V. Kozlov; Y. Soloviev; A. Terkulov; P. Buzhan; B. Dolgoshein; A. Ilyin; V. Kantserov; V. Kaplin; A. Karakash; E. Popova; S. Smirnov; N. Baranova; E. Boos; L. Gladilin; D. Karmanov; M. Korolev; M. Merkin; A. Savin; A. Voronin; A. Topkar; A. Frey; C. Kiesling; S. Lu; K. Prothmann; K. Seidel; F. Simon; C. Soldner; L. Weuste; B. Bouquet; S. Callier; P. Cornebise; F. Dulucq; J. Fleury; H. Li; G. Martin-Chassard; F. Richard; Ch de la Taille; R. Poeschl; L. Raux; M. Ruan; N. Seguin-Moreau; F. Wicek; M. Anduze; V. Boudry; J.-C. Brient; G. Gaycken; R. Cornat; D. Jeans; P. Mora de Freitas; G. Musat; M. Reinhard; A. Rougé; J.-Ch Vanel; H. Videau; K.-H. Park; J. Zacek; J. Cvach; P. Gallus; M. Havranek; M. Janata; J. Kvasnicka; M. Marcisovsky; I. Polak; J. Popule; L. Tomasek; M. Tomasek; P. Ruzicka; P. Sicho; J. Smolik; V. Vrba; J. Zalesak; Yu Arestov; V. Ammosov; B. Chuiko; V. Gapienko; Y. Gilitski; V. Koreshev; A. Semak; Yu Sviridov; V. Zaets; B. Belhorma; M. Belmir; A. Baird; R. N. Halsall; S. W. Nam; I. H. Park; J. Yang; J.-S. Chai; J.-T. Kim; Y. Kim; J. Kang; Y.-J. Kwon; I. Kim; T. Lee; J. Sung; S. Itoh; K. Kotera; M. Nishiyama; T. Takeshita; S. Weber; C. Zeitnitz

2010-01-01

332

Compressive behavior of sandwich panels and laminates with damage  

NASA Astrophysics Data System (ADS)

A wrinkling model for sandwich panels in compression is developed with the assumption of an isotropic elastic core. Stresses for the three wrinkling cases coupled with global buckling are expressed by a unified expression. It is shown that the stresses in all three cases are identical for short wavelength wrinkling and can be expressed by a single simplified analytical expression, but may differ significantly in moderate and long wavelength wrinkling and for these cases are given by simplified analytical expressions. Based on the conducted analysis limitations of the commonly used Winkler, Pasternak and two-parameter models are discussed. Exact closed form solutions of the buckling load and mode shape are obtained for a face layer debonded locally from the core of a sandwich panel. The effects of length and location of debonds and the end constraints of the face layer on the load carrying capacity are discussed. Interactive effects due to two debonds are also studied. A master curve based on a classical solution is developed by employing the characteristic length normalization and the modification to the usual Winkler foundation constant, and it agrees very well with published results of a finite element analysis. A beam-plate element method for composite sheets is developed for both multiple aligned delaminations and multi-ply parallel delaminations. Our result shows that the buckling load of the beam-plate with multiple aligned delamination is mainly decided by a major delamination. A simple reduced model is suggested to remove overlapping of the secondary delaminated portion. The buckling load is dramatically reduced by multi-ply parallel delaminations due to antisymmetric modes. The classical results of compressive strength in fiber reinforced composites are rederived by using a new generalized Timoshenko beam model. Introducing a "shear hinge" to simulate a kink band and using the method of split rigidities it is shown that not only an initial fiber misalignment but also any misalignment in the loading system can affect the critical stress for kinking. A new mechanism based on shear instability of matrix is proposed for kink band formation and a simple formula is then derived to predict the kink band angle.

Niu, Kangmin

333

Worldwide construction  

Microsoft Academic Search

The paper lists major construction projects in worldwide processing and pipelining, showing capacities, contractors, estimated costs, and time of construction. The lists are divided into refineries, petrochemical plants, sulfur recovery units, gas processing plants, pipelines, and related fuel facilities. This last classification includes cogeneration plants, coal liquefaction and gasification plants, biomass power plants, geothermal power plants, integrated coal gasification combined-cycle

1994-01-01

334

Constructing quarks  

SciTech Connect

The book Constructing Quarks, by Andrew Pickering is reviewed. Constructing Quarks consists of two parts. The introductory and final chapters concern sociological and philosophical aspects of high energy physics and the intervening chapters present a history of its development. The reviewer takes exception with some ideas presented by Pickering.

Pickering, A.

1984-01-01

335

Characteristics of Load-Bearing Sandwich Panels for Housing (State of the-Art Report).  

National Technical Information Service (NTIS)

The report is concerned with the proper design and application of sandwich panels for housing. It is a 'state-of-the-art' report including information available on structural design, fire safety, acoustic environment, dimensional stability, thermal enviro...

1973-01-01

336

Mechanical Characterizations of the Dispersion U3Si2-Al Fuel Plate with Sandwich Structure  

NASA Astrophysics Data System (ADS)

This paper is to assess effect of the dispersion U3Si2-Al fuel plate with sandwich structure on its mechanical properties and to assess the quality of this fuel plate by the suitable processing because the optimum performance of fuel plate affects directly the safety and reliability of a power reactor. For this purpose, the mechanical properties of the fuel plate with sandwich structure were described that the relationship between the strength and the sandwich microstructure of dispersion U3Si2-Al fuel plate based on the experimental investigations and the fracture analysis of SEM images. These results shown that it can be improved that the mechanical properties of dispersion U3Si2-Al fuel plate with sandwich structure by the optimizing clad material, U3Si2-Al powder composite contents and process of rolling as well as the optimizing the heat treatment methods.

Wang, Xi-Shu; Xu, Yong

2003-05-01

337

Damage Characteristics and Residual Strength of Composite Sandwich Panels Impacted with and Without Compression Loading.  

National Technical Information Service (NTIS)

The results of an experimental study of the impact damage characteristics and residual strength of composite sandwich panels impacted with and without a compression loading are presented. Results of impact damage screening tests conducted to identify the ...

D. M. McGowan D. R. Ambur

1998-01-01

338

Effect of Temperature on Composite Sandwich Structures Subjected to Low Velocity Impact.  

National Technical Information Service (NTIS)

The effect of low velocity projectile impact on sandwich-type structural components was investigated. The materials used in the fabrication of the impact surface were graphite-, Kevlar-, and boron-fibers with appropriate epoxy matrices. The testing of the...

A. V. Sharma

1980-01-01

339

An investigation on low velocity impact response of multilayer sandwich composite structures.  

PubMed

The effects of adding an extra layer within a sandwich panel and two different core types in top and bottom cores on low velocity impact loadings are studied experimentally in this paper. The panel includes polymer composite laminated sheets for faces and the internal laminated sheet called extra layer sheet, and two types of crushable foams are selected as the core material. Low velocity impact tests were carried out by drop hammer testing machine to the clamped multilayer sandwich panels with expanded polypropylene (EPP) and polyurethane rigid (PUR) in the top and bottom cores. Local displacement of the top core, contact force and deflection of the sandwich panel were obtained for different locations of the internal sheet; meanwhile the EPP and PUR were used in the top and bottom cores alternatively. It was found that the core material type has made significant role in improving the sandwich panel's behavior compared with the effect of extra layer location. PMID:24453804

Jedari Salami, S; Sadighi, M; Shakeri, M; Moeinfar, M

2013-01-01

340

Research in the Field of Fiberglassreinforced Sandwich Structure for Airframe Use.  

National Technical Information Service (NTIS)

The research covered in this report involves investigation of the effects of raw materials usage and fabrication process variables on the final strength properties of fiberglass-reinforced plastic (FRP) sandwich structure suitable for use as a primary air...

G. Nordby J. Noyes W. C. Crisman

1964-01-01

341

High Strength and Impact Damage Tolerant Syntactic Foam for High Performance Sandwich Structures.  

National Technical Information Service (NTIS)

This study explored a novel higher strength and higher impact tolerant syntactic foam for composite sandwich structures. A unique microstructure was designed and realized through a unique manufacturing technology. The foam was fabricated by dispersing rub...

G. Li

2006-01-01

342

In-Plane Transient Response of a Sandwich Ring to Radial Impact.  

National Technical Information Service (NTIS)

The transient response of sandwich rings to concentrated radial impulsive loads is studied on the basis of a Timoshenko-type theory. Solutions are obtained by integral transform techniques and also by representation in series of normal modes. Numerical re...

G. Herrmann L. M. Keer M. J. Sagartz

1970-01-01

343

Simulation of Prestressed Concrete Sandwich Panels Subjected to Blast Loads (Preprint).  

National Technical Information Service (NTIS)

This paper discusses simulation methodology used to analyze static and dynamic behavior of foam insulated concrete sandwich wall panels through ultimate capacity. The experimental program used for model development and validation involved component-level ...

B. T. Bewick C. M. Newberry J. M. Hoemann J. S. Davidson

2010-01-01

344

Preparation and characterization of sandwich-structure polyethersulfone membrane with pH sensitivity  

Microsoft Academic Search

In this paper, a novel sandwich-structure polyethersulfone (PES) membrane with pH-sensitivity was developed. The membrane was composed of three layers. The top and bottom layers were made of PES; while the middle layer was prepared by a mixture of cross-linked poly(acrylic acid) (PAA) microgels and PES. The sandwich-structure PES membrane showed evident pH sensitivity and pH reversibility as the pH

Jialiang Xie; Qiang Wei; Baihai Su; Bosi Qian; Qiyao Ling; Changsheng Zhao

2009-01-01

345

Self-healing sandwich panels: Restoration of compressive strength after impact  

Microsoft Academic Search

Impact damage can significantly reduce the strength of composite sandwich panels, giving rise to large factors of safety in design. A self-healing sandwich panel was designed and manufactured. Specimens were tested in edgewise compression-after-impact to prove the concept. The self-healing system consists of vascular networks carrying the two liquid components of an epoxy resin system. After damage and autonomous self-healing,

H. R. Williams; R. S. Trask; I. P. Bond

2008-01-01

346

All-optical pulse switching and shaping by a nonlinear sandwich  

SciTech Connect

We demonstrate a simple model system comprised of a thin nonlinear layer sandwiched between two glass plates. This double Nonlinear Interface allows the investigation of both the transmitted and reflected beams for all-optical switching. Various potential applications of this Nonlinear Sandwich based on its intensity-dependent reflectivity and transmissivity are discussed. Focus is given to energy limiting, prepulse suppression, pulse shortening, and shaping. Experimental results show feasibility of these applications. 7 refs., 6 figs.

Strobl, K.; Golub, I.

1991-01-01

347

Optimal design of box-section sandwich beams subject to moving load  

Microsoft Academic Search

Minimum weight designs of sandwich beams subject to moving load are performed as a function of prescribed load index, where\\u000a the stiffness and strength constraints are both considered. The dynamic properties of sandwich beams are detected and validated\\u000a through finite element simulation. Five different topologies are optimized and compared. Numerical results show that the topology\\u000a of a hollow tube with

Xiuhui Hou; Zichen Deng; Jiaxi Zhou

2010-01-01

348

Phage display selection of EGFR-specific antibodies by capture-sandwich panning  

Microsoft Academic Search

Sandwich ELISA experiment requires two mutually compatible affinity reagents, typically antibodies, that are highly sensitive\\u000a and specific to the target analyte in its native conformation, and whose epitopes do not overlap each other’s. Finding or\\u000a developing a pair of antibodies that meet these requirements can be a challenge and many otherwise useful antibodies fail\\u000a in sandwich ELISA-format analysis. In order

Min Kyung Ki; Kyung Jae Kang; Hyunbo Shim

2010-01-01

349

Processing of nanoclay filled sandwich composites and their response to low-velocity impact loading  

Microsoft Academic Search

In this study, sandwich panels were fabricated with neat and nanophased foam cores and 3-layered plain weave carbon fabric\\/SC-15 epoxy-nanoclay composite face sheets. Neat and nanophased foam cores with Nanocor® I-28E nanoclay at a loading of 0.5% and 1% by weight were prepared. Sandwich panels were then fabricated using co-injection resin transfer molding process. The facesheets were made by infusing

M. V. Hosur; A. A. Mohammed; S. Zainuddin; S. Jeelani

2008-01-01

350

Characterisation by Inverse Techniques of Elastic, Viscoelastic and Piezoelectric Properties of Anisotropic Sandwich Adaptive Structures  

Microsoft Academic Search

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency\\u000a dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces\\u000a of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative\\u000a models, with unknown parameters that are to be estimated

Aurelio L. Araújo; Cristovao M. Mota Soares; Carlos A. Mota Soares; Jose Herskovits

2010-01-01

351

A Quasi-Exact Dynamic Finite Element for Free Vibration Analysis of Sandwich Beams  

Microsoft Academic Search

A Dynamic Finite Element (DFE) model for the vibration analysis of three-layered sandwich beams is presented. The governing\\u000a differential equations of motion of the sandwich beam for the general case, when the properties of each layer are dissimilar,\\u000a are exploited. Displacement fields are imposed such that the face layers follow the Rayleigh beam assumptions, while the core\\u000a is governed by

Seyed M. Hashemi; Ernest J. Adique

2010-01-01

352

Sandwich ELISA Microarrays: Generating Reliable and Reproducible Assays for High-Throughput Screens  

SciTech Connect

The sandwich ELISA microarray is a powerful screening tool in biomarker discovery and validation due to its ability to simultaneously probe for multiple proteins in a miniaturized assay. The technical challenges of generating and processing the arrays are numerous. However, careful attention to possible pitfalls in the development of your antibody microarray assay can overcome these challenges. In this chapter, we describe in detail the steps that are involved in generating a reliable and reproducible sandwich ELISA microarray assay.

Gonzalez, Rachel M.; Varnum, Susan M.; Zangar, Richard C.

2009-05-11

353

Sandwich microgravimetric immunoassay: sensitive and specific detection of low molecular weight analytes using piezoelectric quartz crystal  

Microsoft Academic Search

A multi-channel sandwich microgravimetric immunoassay (sMIA), using the quartz crystal microbalance (QCM) principle, has been developed to quantify low molecular weight substances in standard solutions. An antigen is sandwiched between two antigen-specific antibodies: the first antibody is coated on the quartz crystal surface and the second antibody is used for the detection of analyte. The concentration of low molecular weight

Satish Saha; Manoj Raje; C. Raman Suri

2002-01-01

354

Temperature Effects on the Impact Behavior of Fiberglass and Fiberglass\\/Kevlar Sandwich Composites  

Microsoft Academic Search

Impact tests were performed on sandwich composites with Fiberglass and Fiberglass\\/Kevlar face sheets subjected to varied temperatures. A number of specimens were tested at ?50 to 120 °C temperature range and at 20, 30, and 45 J low velocity energy levels. Impact properties of the sandwich composites that were evaluated include maximum normal and shear stresses, maximum energy absorption, non-dimensional parameters

Aaron Halvorsen; Amin Salehi-Khojn; Mohammad Mahinfalah; Reza Nakhaei-Jazar

2006-01-01

355

Modification of the electron-gas model for complexes of the sandwich type  

SciTech Connect

The quantum-mechanical two-dimensional electron-gas model for unsubstituted sandwiches with transition metals has been developed further. The use of a relation of the virial-theorem type between the kinetic and potential energies has made it possible to dispense with the energy parameters and to relate the electronic structure of the sandwiches to a single variable geometric parameter, viz., the metal-carbon distance.

Chistyakov, A.L.

1986-05-01

356

Tentacle probe sandwich assay in porous polymer monolith improves specificity, sensitivity and kinetics  

Microsoft Academic Search

Nucleic acid sandwich assays improve low-density array analysis through the addition of a capture probe and a specific label, increasing specificity and sensitivity. Here, we employ photo-initiated porous polymer monolith (PPM) as a high-surface area substrate for sandwich assay analysis. PPMs are shown to enhance extraction efficiency by 20-fold from 2kl of sample. We further compare the performance of labeled

Brent C. Satterfield; Michael R. Caplan; Jay A. A. West

2008-01-01

357

A Monte Carlo Algorithm Simulation of Antiferroelectricity in Sandwich Structural Film  

Microsoft Academic Search

We prepared BaTiO3\\/BiFeO3\\/BaTiO3 sandwich structural film by sol-gel process. Antiferroelectric hysteresis loop was observed in the sandwich structural film. A Monte Carlo simulation based on Ising model using a 100× 100 polarization grid is carried out. Simulating result matches to the experimental result very well and it shows that the antiferroelectricity is originated from the antiferroelectric couple between the different

Yuxia Sun; Hongri Liu

2011-01-01

358

Mechanism of conductive losses in a sandwich-structured planar inductor  

SciTech Connect

In this paper conductive losses in a sandwich-structured planar inductor are discussed. Analysis by FDM (finite difference method) of the current distributions in a rectangular conductor sandwiched between magnetic material revealed that the current is concentrated near the conductor edges. It is also shown that filling gaps with magnetic material is effective for reducing ac resistances, especially when the width of the conductor is much larger than the skin depth.

Yamaguchi, T.; Sasada, I.; Harada, K. (Kyushu Univ., Fukuoka (Japan))

1993-03-01

359

Theoretical analysis of the deformation of SMP sandwich beam in flexure  

Microsoft Academic Search

Shape memory polymers (SMPs) can have a large frozen strain but with a very small recovery stiffness in comparison with shape\\u000a memory metals or ceramics. To provide more deployable stresses for the application of actuators, sandwich beams consisting\\u000a of a SMP core and two thin metallic skins were considered. The packaging behaviors of two types of SMP sandwich beams, aluminum\\/SMP\\/aluminum

Z. D. Wang; Z. F. Li

360

Experimental and Numerical Investigation of Free Vibrations of Composite Sandwich Beams with Curvature and Debonds  

Microsoft Academic Search

In this paper experimental and numerical results concerning the dynamic response of composite sandwich beams with curvature\\u000a and debonds are reported. Sandwich beams made of carbon\\/epoxy face sheets and polyurethane foam core material were manufactured\\u000a with four different radii of curvature and debonds between the top and bottom interface of face sheet and foam core. Dynamic\\u000a response was obtained using

B. O. Baba; S. Thoppul; R. F. Gibson

2011-01-01

361

Windsurf-Board Sandwich Panels Under Static Indentation  

NASA Astrophysics Data System (ADS)

In recent years composite materials have found application in several fields as sport and sea transportation, where the incidence of the cost of materials is not significant compared with the required high mechanical performances. As a matter of fact, in some sports the whole equipment is nowadays realized in composite materials (i.e. windsurf boards, snowboards). The aim of the present work is to evaluate the mechanical performance of some sandwich structures produced by vacuum bagging technology for the windsurf boards production. The behaviour of the structures is tested under static indentation conditions; different fibres materials, for the skins, and different polystyrene foams, for the core, have been taken into account. In particular both the effect of the kind of fibre (glass, carbon and kevlar fibres) and the effect of the polystyrene cells size (and its density) have been investigated. The purpose was to obtain a stiff structure able to bear localized loads. Additionally, the effects induced on the indentation resistance by both the speed and the diameter of pin have been analysed.

Borsellino, C.; Calabrese, L.; di Bella, G.

2008-03-01

362

Refined Zigzag Theory for Laminated Composite and Sandwich Plates  

NASA Technical Reports Server (NTRS)

A refined zigzag theory is presented for laminated-composite and sandwich plates that includes the kinematics of first-order shear deformation theory as its baseline. The theory is variationally consistent and is derived from the virtual work principle. Novel piecewise-linear zigzag functions that provide a more realistic representation of the deformation states of transverse-shear-flexible plates than other similar theories are used. The formulation does not enforce full continuity of the transverse shear stresses across the plate s thickness, yet is robust. Transverse-shear correction factors are not required to yield accurate results. The theory is devoid of the shortcomings inherent in the previous zigzag theories including shear-force inconsistency and difficulties in simulating clamped boundary conditions, which have greatly limited the accuracy of these theories. This new theory requires only C(sup 0)-continuous kinematic approximations and is perfectly suited for developing computationally efficient finite elements. The theory should be useful for obtaining relatively efficient, accurate estimates of structural response needed to design high-performance load-bearing aerospace structures.

Tessler, Alexander; DiSciuva, Marco; Gherlone, Marco

2009-01-01

363

An extraterrestrial sandwich: The perils of food in space.  

PubMed

Food was and is an essential component in human space exploration. If it had not proved possible to eat and digest in space, none of the long-term space missions of the last four decades would have been achievable. Every country that has sent an astronaut on a mission has used its national foods as a means of stating both their presence and their identity to their colleagues in the programme and their citizens at home: in space, as on earth, food has provided a means of asserting national culture. From the earliest missions, the US and USSR's differing attitudes to the programme have been reflected in the food provided and the respective administrations' approaches to feeding in space. The contrast between the US focus on space travel and the USSR's focus on space living is highlighted through their attitudes to the often vexed question of what astronauts and cosmonauts should be permitted to eat, illustrated by the corned-beef sandwich incident of 1965. PMID:20138668

Levi, Jane

2010-03-01

364

Sandwiched structural panel having a bi-directional core structure  

NASA Technical Reports Server (NTRS)

A structural panel assembly has a bi-directional core structure sandwiched between and secured to a pair of outer side wall members. The core structure is formed from first and second perpendicular series of elongated strip members having crenelated configurations. The strip members in the first series thereof are transversely interwoven with the strip members in the second series thereof in a manner such that crest portions of the strip members in the first series overlie and oppose trough portions of the strip members in the second series, and trough portions of the strip members in the first series underlie and oppose crest portions of the strip members in the second series. The crest portions of all of the strip members lie generally in a first plane and are secured to the inner side of one of the panel assembly outer side walls, and the trough portions of all of the strip members lie generally in a second plane and are secured to the inner side of the other panel assembly outer side wall.

Weddendorf, Bruce (Inventor)

1995-01-01

365

Sandwich module prototype progress for space solar power  

NASA Astrophysics Data System (ADS)

Space solar power (SSP) has been broadly defined as the collection of solar energy in space and its wireless transmission for use on earth. This approach potentially gives the benefit of provision of baseload power while avoiding the losses due to the day/night cycle and tropospheric effects that are associated with terrestrial solar power. Proponents have contended that the implementation of such systems could offer energy security, environmental, and technological advantages to those who would undertake their development. Among recent implementations commonly proposed for SSP, the modular symmetrical concentrator (MSC) and other modular concepts have received considerable attention. Each employs an array of modules for performing conversion of concentrated sunlight into microwaves or laser beams for transmission to earth. While prototypes of such modules have been designed and developed previously by several groups, none have been subjected to the challenging conditions inherent to the space environment and the possible solar concentration levels in which an array of modules might be required to operate. The research described herein details our team's efforts in the development of photovoltaic arrays, power electronics, microwave conversion electronics, and antennas for microwave-based "sandwich" module prototypes. The implementation status and testing results of the prototypes are reviewed.

Jaffe, Paul; Hodkin, Jason; Harrington, Forest; Person, Clark; Nurnberger, Michael; Nguyen, Bang; LaCava, Susie; Scheiman, Dave; Stewart, Grant; Han, Andrew; Hettwer, Ethan; Rhoades, Daniel

2014-02-01

366

Parametric results for heat transfer across honeycomb sandwich panels  

NASA Technical Reports Server (NTRS)

The problem of heat transfer across honeycomb sandwich panels is theoretically investigated. The basic objective is to predict the rear surface temperature as a function of time when the front surface is exposed to a prescribed heat flux; the faces are bounded by planar sheets so that the air circulation in the honeycomb cells is bounded and contained. The influence of the air circulation on convective heat transfer is explicitly included. Drawing upon previous investigators' results that indicated various relations for the Nusselt numbers vs Rayleigh numbers in different regimes of the aspect ratio (defined as the ratio of the cell height to cell width), parametric calculations are performed to predict the rear surface temperatures. Chemical degradation of the material, especially the glue holding the face material on the end, is important but has not yet been included. The results indicate that decreasing the cell width, increasing the cell wall thickness and increasing the cell height all have beneficial effects upon the heat transfer; i.e., all of these variations reduce rear surface temperature for a given time for a prescribed heat flux on the front surface.

Ramohalli, K.; Sahakian, J.

1981-01-01

367

Aptamer carbon nanodot sandwich used for fluorescent detection of protein.  

PubMed

Carbon nanodots (C-Dots) have attracted growing interest in recent years due to their low cost, ready scalability, excellent chemical stability, biocompatibility, colloidal stability, and resilience of photoluminescence. They have been employed as novel, ideal fluorescent probes for bio-imaging and smart sensing. In addition, taking advantage of their low-cytotoxicity, C-Dots have potential applications in biochemical and cell biological fields. Herein, we present the first assay with aptamer-functionalized C-Dots as a sensory platform for protein detection. The presence of thrombin can induce the aptamer-modified fluorescent C-Dots to form a sandwich structure with aptamer-functionalized silica nanoparticles through specific protein/aptamer interaction. The assay shows high specificity toward thrombin. A detection limit of 1 nM is obtained, which is significantly improved as compared to that of many previously reported fluorescence-based thrombin detection assays. Using other modified aptamers and antibodies instead of thrombin binding aptamers, this strategy may offer a suitable approach for detection of other proteins in biological, pharmaceutical and nano-mechanical applications. PMID:23050264

Xu, Bailu; Zhao, Chuanqi; Wei, Weili; Ren, Jinsong; Miyoshi, Daisuke; Sugimoto, Naoki; Qu, Xiaogang

2012-12-01

368

Mechanical properties characterization of composite sandwich materials intended for space antenna applications  

NASA Technical Reports Server (NTRS)

The composite materials proposed for use in the Advanced Communications Technology Satellite (ACTS) Program contains a new, high modulus graphite fiber as the reinforcement. A study was conducted to measure certain mechanical properties of the new fiber-reinforced material as well as of a composite-faced aluminum honeycomb sandwich structure. Properties were measured at -157, 22, and 121 C. Complete characterization of this material was not intended. Longitudinal tensile, picture-frame shear, short-beam shear, and flexural tests were performed on specimens of the composite face-sheet materials. Unidirectional, cross-plied, and quasi-isotropic fiber composite ply layup designs were fabricated and tested. These designs had been studied by using NASA's Integrated Composite Analyzer (ICAN) computer program. Flexural tests were conducted on (+/- 60/0 deg) sub s composite-faced sandwich structure material. Resistance strain gages were used to measure strains in the tensile, picture-frame, and sandwich flexural tests. The sandwich flexural strength was limited by the core strength at -157 and 22 C. The adhesive bond strength was the limiting factor at 121 C. Adhesive mechanical properties are reflected in sandwich structure flexural properties when the span-to-depth ratio is great enough to allow a significant shear effect on the load-deflection behavior of the sandwich beam. Most measured properties agreed satisfactorily with the properties predicted by ICAN.

Bowles, Kenneth J.; Vannucci, Raymond D.

1986-01-01

369

Mechanical properties characterization of composite sandwich materials intended for space antenna applications  

NASA Technical Reports Server (NTRS)

The composite materials proposed for use in the Advanced Communications Technology Satellite (ACTS) program contains a new, high modulus graphite fiber as the reinforcement. A study was conducted to measure certain mechanical properties of the new fiber-reinforced material as well as of a composite-faced aluminum honeycomb sandwich structure. Properties were measured at -157, 22, and 121 C. Complete characterization of this material was not intended. Longitudinal tensile, picture-frame shear, short-beam shear, and flexural tests were performed on specimens of the composite face-sheet materials. Unidirectional, cross-plied, and quasi-isotropic fiber composite ply layup designs were fabricated and tested. These designs had been studied by using NASA's Integrated Composite Analyzer (ICAN) computer program. Flexural tests were conducted on (+/- 60/0 deg) sub s composite-faced sandwich structure material. Resistance strain gages were used to measure strains in the tensile, picture-frame, and sandwich flexural tests. The sandwich flexural strength was limited by the core strength at 157 and 22 c. The adhesive bond strength was the limiting factor at 121 C. Adhesive mechanical properties are reflected in sandwich structure flexural properties when the span-to-depth ratio is great enough to allow a significant shear effect on the load-deflection behavior of the sandwich beam. Most measured properties agreed satisfactorily with the properties predicted by ICAN.

Bowles, Kenneth J.; Vannucci, Raymond D.

1989-01-01

370

The Transverse Response of Sandwich Panels to AN Underwater Shock Wave  

NASA Astrophysics Data System (ADS)

The response of submerged structures to an underwater shock wave involves both structural and fluid behaviour. For sandwich structures the response to an initial shock wave in the transverse direction is significantly different from that of a homogeneous structure. This is due to the elastic properties of the core in the sandwich. For a homogeneous structure one cavitation zone is initially developed and the position of this zone is dependent on the assumed cavitation pressure. At a sandwich structure two cavitation zones initially appear, one adjacent to the structure and another away from the structure, depending again on the assumed cavitation pressure. The response of a sandwich panel in the transverse direction is also investigated, using a combination of a numerical method and finite elements, developed for the fluid-structure interaction problem. The method includes the appearance of cavitation in the fluid, it is found that, as the sandwich section is moving, the faces in the sandwich oscillate about the core. The nonlinear properties of the faces give rise to considerable transverse strain which may very well be high enough to cause delamination in the faces, debonding between the faces and the core, or core failure.

Mäkinen, K.

1999-07-01

371

Modeling and experimental validation of a sandwich plate with isotropic face plates and viscoelestic core  

NASA Astrophysics Data System (ADS)

We analyze and experimentally validate an analysis of a sandwich plate structure, where anisotropic face plates sandwich a viscoelastic core. Existing analytical models have been modified to incorporate piezo-actuation in anisotropic and 3-layered thin plates, using the variational energy method. The 3-layered sandwich consists of anisotropic face- plates with surface bonded piezo-electric actuators, and a viscoelastic core. The analysis includes the membrane and transverse energies in the face plates, and shear in the viscoelastic core. A constant, complex shear modulus was used for the dissipative core, thus frequency and temperature dependence of viscoelastic properties is neglected in this model. Simplified forms of the equations are stated based on neglecting shear in face-plates. Experiments were conducted on sandwich plates with aluminum face-plates under clamped boundary conditions to validate the simplified model. Symmetric and asymmetric sandwiches were tested. The maximum error in the first eight natural frequency predictions obtained via the assumed modes solution is less than 10%. Analytical studies on the influence of the number of assumed modes in the Galerkin approximation, and the core storage modulus variation, were conducted. The importance of the in- plane extension modes in sandwich plate analysis was demonstrated. Error in the first natural frequency is nearly 100% when in-plane modes are ignored; error reduces and converges to 6.7% as number of modes is increased to 16 in each of the in-plane directions for each face plate.

Veermani, Sudha; Wereley, Norman M.

1997-05-01

372

Sandwich concept: enhancement for direct absorption measurements by laser-induced deflection (LID) technique  

NASA Astrophysics Data System (ADS)

The new sandwich concept for absolute photo-thermal absorption measurements using the laser induced deflection (LID) technique is introduced and tested in comparison to the standard LID concept. The sandwich concept's idea is the decoupling of the optical materials for the pump and probe beams by placing a sample of investigation in between two optical (sandwich) plates. The pump beam is guided through the sample whereas the probe beams are deflected within the sandwich plates by the thermal lens that is generated by heat transfer from the irradiated sample. Electrical simulation and laser experiments reveal that using appropriate optical materials for the sandwich plates, the absorption detection limit for photo-thermally insensitive materials can be lowered by up to two orders of magnitude. Another advantage of the sandwich concept, the shrinking of the currently required minimum sample size, was used to investigate the laser induced absorption change in a Nd:YVO4 crystal at 1030nm. It was found that the absorption in Nd:YVO4 lowers due to the laser irradiation but partially recovers during irradiation breaks. Furthermore, absorption spectroscopy has been performed at two LBO crystals in the wavelength range 410...600nm to study the absorption structure around the SHG wavelengths of common high power lasers based on Neodymium doped laser crystals.

Mühlig, Ch.; Bublitz, S.; Paa, W.

2012-11-01

373

Construction aggregates  

USGS Publications Warehouse

The estimated production during 2000 of construction aggregates, crushed stone, and construction sand and gravel increased by about 2.6% to 2.7 Gt (3 billion st), compared with 1999. The expansion that started in 1992 continued with record production levels for the ninth consecutive year. By commodity, construction sand and gravel production increased by 4.5% to 1.16 Gt (1.28 billion st), while crushed stone production increased by 1.3% to 1.56 Gt (1.72 billion st).

Bolen, W. P.; Tepordei, V. V.

2001-01-01

374

Construction 2003  

National Technical Information Service (NTIS)

Partial Contents: Portland Cement Concrete Pavements (Use of a Ride Quality Index for Construction Quality Control and Acceptance Specifications); Bituminous Pavements (Application of Infrared Imaging and Ground-Penetrating Radar to Detect Segregation in ...

2003-01-01

375

Construction crane  

NSDL National Science Digital Library

People who operate construction cranes carrying heavy loads must be coordinated. The load on the crane must not injure any workers or anyone else near the site. They must be careful to maneuver heavy loads around buildings without hitting them.

N/A N/A (None;)

2007-07-25

376

Worldwide construction  

SciTech Connect

The paper lists major construction projects in worldwide processing and pipelining, showing capacities, contractors, estimated costs, and time of construction. The lists are divided into refineries, petrochemical plants, sulfur recovery units, gas processing plants, pipelines, and related fuel facilities. This last classification includes cogeneration plants, coal liquefaction and gasification plants, biomass power plants, geothermal power plants, integrated coal gasification combined-cycle power plants, and a coal briquetting plant.

Williamson, M.

1994-10-17

377

Construction aggregates  

USGS Publications Warehouse

Construction aggregates, primarily stone, sand and gravel, are recovered from widespread naturally occurring mineral deposits and processed for use primarily in the construction industry. They are mined, crushed, sorted by size and sold loose or combined with portland cement or asphaltic cement to make concrete products to build roads, houses, buildings, and other structures. Much smaller quantities are used in agriculture, cement manufacture, chemical and metallurgical processes, glass production and many other products.

Nelson, T. I.; Bolen, W. P.

2007-01-01

378

Construction aggregates  

USGS Publications Warehouse

Part of a special section on the market performance of industrial minerals in 1992. Production of construction aggregates increased by 4.6 percent in 1992. This increase was due, in part, to the increased funding for transportation and infrastructure projects. The U.S. produced about 1.05 Gt of crushed stone and an estimated 734 Mt of construction sand and gravel in 1992. Demand is expected to increase by about 5 percent in 1993.

Tepordei, V. V.

1993-01-01

379

A Refined Zigzag Beam Theory for Composite and Sandwich Beams  

NASA Technical Reports Server (NTRS)

A new refined theory for laminated composite and sandwich beams that contains the kinematics of the Timoshenko Beam Theory as a proper baseline subset is presented. This variationally consistent theory is derived from the virtual work principle and employs a novel piecewise linear zigzag function that provides a more realistic representation of the deformation states of transverse-shear flexible beams than other similar theories. This new zigzag function is unique in that it vanishes at the top and bottom bounding surfaces of a beam. The formulation does not enforce continuity of the transverse shear stress across the beam s cross-section, yet is robust. Two major shortcomings that are inherent in the previous zigzag theories, shear-force inconsistency and difficulties in simulating clamped boundary conditions, and that have greatly limited the utility of these previous theories are discussed in detail. An approach that has successfully resolved these shortcomings is presented herein. Exact solutions for simply supported and cantilevered beams subjected to static loads are derived and the improved modelling capability of the new zigzag beam theory is demonstrated. In particular, extensive results for thick beams with highly heterogeneous material lay-ups are discussed and compared with corresponding results obtained from elasticity solutions, two other zigzag theories, and high-fidelity finite element analyses. Comparisons with the baseline Timoshenko Beam Theory are also presented. The comparisons clearly show the improved accuracy of the new, refined zigzag theory presented herein over similar existing theories. This new theory can be readily extended to plate and shell structures, and should be useful for obtaining relatively low-cost, accurate estimates of structural response needed to design an important class of high-performance aerospace structures.

Tessler, Alexander; Sciuva, Marco Di; Gherlone, Marco

2009-01-01

380

Characterization of digoxin uptake in sandwich-cultured human hepatocytes.  

PubMed

Digoxin is a drug that is commonly used to treat congestive heart failure. Because of digoxin's narrow therapeutic index, patients are susceptible to drug-drug interaction-mediated cardiotoxicity. Digoxin is primarily cleared renally; however, a significant component of clearance is due to multidrug resistance 1-mediated transport into bile. Digoxin is reported to be actively transported into human hepatocytes by the organic anion-transporting polypeptide 1B3 (OATP1B3); however, further characterization has not been fully described. The purpose of this study was to investigate the hepatic uptake mechanisms of [(3)H]digoxin using sandwich-cultured human hepatocytes (SCHH) and transporter-expressing cells. Digoxin uptake in SCHH involves both a saturable (carrier-mediated) process and a passive (nonsaturable) process. At low concentrations, the saturable component exhibited an apparent K(m) of 2.39 ?M and a V(max) of 4.49 pmol/(min · mg protein). The calculated passive diffusion clearance was 1.25 ?l/(min · mg protein). Uptake of [(3)H]digoxin in SCHH was not inhibited by a variety of substrates or inhibitors for OATP1B1, OATP1B3, OATP2B1, organic anion transporter 2, organic cation transporter 1, and monocarboxylate transporter 8. Cytochalasin B, which inhibits glucose transporters, did not significantly inhibit digoxin uptake, whereas the flavonoids quercetin and rutin inhibited uptake by ?50%. Nonlabeled digoxin inhibited [(3)H]digoxin uptake by ?50%. Studies with OATP-transfected human embryonic kidney cells or oocytes showed that digoxin is not a substrate of OATP1B1, OATP2B1, or OATP1B3. In conclusion, the data suggest that digoxin uptake in SCHH involves both saturable and passive processes. The saturable process is mediated by an as yet undetermined digoxin transporter(s). PMID:20926619

Kimoto, Emi; Chupka, Jonathan; Xiao, Yongling; Bi, Yi-An; Duignan, David B

2011-01-01

381

A novel manifold–manifold distance index applied to looseness state assessment of viscoelastic sandwich structures  

NASA Astrophysics Data System (ADS)

Viscoelastic sandwich structures (VSS) are widely used in mechanical equipment; their state assessment is necessary to detect structural states and to keep equipment running with high reliability. This paper proposes a novel manifold–manifold distance-based assessment (M2DBA) method for assessing the looseness state in VSSs. In the M2DBA method, a manifold–manifold distance is viewed as a health index. To design the index, response signals from the structure are firstly acquired by condition monitoring technology and a Hankel matrix is constructed by using the response signals to describe state patterns of the VSS. Thereafter, a subspace analysis method, that is, principal component analysis (PCA), is performed to extract the condition subspace hidden in the Hankel matrix. From the subspace, pattern changes in dynamic structural properties are characterized. Further, a Grassmann manifold (GM) is formed by organizing a set of subspaces. The manifold is mapped to a reproducing kernel Hilbert space (RKHS), where support vector data description (SVDD) is used to model the manifold as a hypersphere. Finally, a health index is defined as the cosine of the angle between the hypersphere centers corresponding to the structural baseline state and the looseness state. The defined health index contains similarity information existing in the two structural states, so structural looseness states can be effectively identified. Moreover, the health index is derived by analysis of the global properties of subspace sets, which is different from traditional subspace analysis methods. The effectiveness of the health index for state assessment is validated by test data collected from a VSS subjected to different degrees of looseness. The results show that the health index is a very effective metric for detecting the occurrence and extension of structural looseness. Comparison results indicate that the defined index outperforms some existing state-of-the-art ones.

Sun, Chuang; Zhang, Zhousuo; Guo, Ting; Luo, Xue; Qu, Jinxiu; Zhang, Chenxuan; Cheng, Wei; Li, Bing

2014-06-01

382

Trail Construction  

NSDL National Science Digital Library

In this highly physical outdoor activity, learners construct and compare experimental trail sections to select the best trail-construction technique for their site. As they measure, evaluate and build, they must consider factors including erosion, slope, materials, labor, cost, human effort, and various environmental impacts. The slope measuring component not only involves mathematical problem-solving, but can incorporate measurement of human health performance, since one way of measuring slope in this activity can be having learners check their pulse as they climb a hill. This activity can be well combined with the "Hold a Hill" and "Cardiac Hill" activities from the same resource.

Science, Lawrence H.

1982-01-01

383

Use of a Sandwich Plate System in a Virginia Bridge.  

National Technical Information Service (NTIS)

The deterioration of the nation's civil infrastructure has prompted the investigation of numerous solutions to the problem. Some of these solutions have come in the form of innovative materials for new construction, whereas others have considered rehabili...

D. K. Harris T. E. Cousins T. M. Murray

2009-01-01

384

Hypervelocity Impact Performance of Open Cell Foam Core Sandwich Panel Structures  

NASA Technical Reports Server (NTRS)

Metallic foams are a relatively new class of materials with low density and novel physical, mechanical, thermal, electrical and acoustic properties. Although incompletely characterized, they offer comparable mechanical performance to traditional spacecraft structural materials (i.e. honeycomb sandwich panels) without detrimental through-thickness channeling cells. There are two competing types of metallic foams: open cell and closed cell. Open cell foams are considered the more promising technology due to their lower weight and higher degree of homogeneity. Leading micrometeoroid and orbital debris shields (MMOD) incorporate thin plates separated by a void space (i.e. Whipple shield). Inclusion of intermediate fabric layers, or multiple bumper plates have led to significant performance enhancements, yet these shields require additional non-ballistic mass for installation (fasteners, supports, etc.) that can consume up to 35% of the total shield weight [1]. Structural panels, such as open cell foam core sandwich panels, that are also capable of providing sufficient MMOD protection, represent a significant potential for increased efficiency in hypervelocity impact shielding from a systems perspective through a reduction in required non-ballistic mass. In this paper, the results of an extensive impact test program on aluminum foam core sandwich panels are reported. The effect of pore density, and core thickness on shielding performance have been evaluated over impact velocities ranging from 2.2 - 9.3 km/s at various angles. A number of additional tests on alternate sandwich panel configurations of comparable-weight have also been performed, including aluminum honeycomb sandwich panels (see Figure 1), Nomex honeycomb core sandwich panels, and 3D aluminum honeycomb sandwich panels. A total of 70 hypervelocity impact tests are reported, from which an empirical ballistic limit equation (BLE) has been derived. The BLE is in the standard form suitable for implementation in risk analysis software, and includes the effect of panel thickness, core density, and facesheet material properties. A comparison between the shielding performance of foam core sandwich panel structures and common MMOD shielding configurations is made for both conservative (additional 35% non-ballistic mass) and optimistic (additional mass equal to 30% of bumper mass) considerations. Suggestions to improve the shielding performance of foam core sandwich panels are made, including the use of outer mesh layers, intermediate fabric/composite layers, and varying pore density.

Ryan, Shannon; Christiansen, Eric; Lear, Dana

2009-01-01

385

Abstract Constructions.  

ERIC Educational Resources Information Center

Describes a lesson designed to culminate a year of eighth-grade art classes in which students explore elements of design and space by creating 3-D abstract constructions. Outlines the process of using foam board and markers to create various shapes and optical effects. (DSK)

Pietropola, Anne

1998-01-01

386

Constructive Criticism.  

ERIC Educational Resources Information Center

Many crucial questions need to be answered before a college embarks on a construction project and makes a substantial financial commitment. Computer modeling techniques can be used to make even complex project feasibility analyses. Available from Peat, Marwick, Mitchell & Co., 345 Park Avenue, New York, NY 10154. (MSE)

Lieberfeld, Lawrence

1982-01-01

387

A ballistic limit equation for hypervelocity impacts on composite honeycomb sandwich panel satellite structures  

NASA Astrophysics Data System (ADS)

During a recent experimental test campaign performed in the framework of ESA Contract 16721, the ballistic performance of multiple satellite-representative Carbon Fibre Reinforced Plastic (CFRP)/Aluminium honeycomb sandwich panel structural configurations (GOCE, Radarsat-2, Herschel/Planck, BeppoSax) was investigated using the two-stage light-gas guns at EMI. The experimental results were used to develop and validate a new empirical Ballistic Limit Equation (BLE), which was derived from an existing Whipple-shield BLE. This new BLE provided a good level of accuracy in predicting the ballistic performance of stand-alone sandwich panel structures. Additionally, the equation is capable of predicting the ballistic limit of a thin Al plate located at a standoff behind the sandwich panel structure. This thin plate is the representative of internal satellite systems, e.g. an Al electronic box cover, a wall of a metallic vessel, etc. Good agreement was achieved with both the experimental test campaign results and additional test data from the literature for the vast majority of set-ups investigated. For some experiments, the ballistic limit was conservatively predicted, a result attributed to shortcomings in correctly accounting for the presence of high surface density multi-layer insulation on the outer facesheet. Four existing BLEs commonly applied for application with stand-alone sandwich panels were reviewed using the new impact test data. It was found that a number of these common approaches provided non-conservative predictions for sandwich panels with CFRP facesheets.

Ryan, S.; Schaefer, F.; Destefanis, R.; Lambert, M.

388

Fabrication research on the sandwich layered cathode electrode for a triode field emission display prototype  

NASA Astrophysics Data System (ADS)

Based on an effective screen-printing process, a novel sandwich layered cathode electrode was developed on a cathode faceplate. The ZnO electrode was sandwiched between an indium tin oxide (ITO) electrode layer and a silver electrode layer, and the carbon nanotube was prepared directly on the exposed ITO electrode layer surface. The cathode potential could be conducted to the carbon nanotube with the sandwich layered cathode electrode. Using the carbon nanotube as a field emitter, a triode field emission display prototype with a sandwich layered cathode electrode was fabricated, which possessed a better field emission characteristic, higher luminous brightness and better emission image luminance uniformity. The turn-on electric field was 1.88 V/?m and the measured maximum field emission current was 2273.6 ?A at 3.19 V/?m. By the method of adjusting the field emission current, the electron-emitting uniform capacity of the carbon nanotube cold cathode could be modified, and the emission image luminance uniformity and the emission current stability of triode field emission display prototype was also be improved significantly. The emission current fluctuation of the sandwich layered cathode electrode type field emission display was less than 1.1%. Furthermore, the total manufacture cost of the triode field emission display prototype was low.

Yukui, Li; Xiaoquan, Li; Xinghui, Liu; Wenke, Lu; Fanguang, Zeng

2013-07-01

389

Evaluation of modal-based damage detection techniques for composite aircraft sandwich structures  

NASA Astrophysics Data System (ADS)

Composite sandwich structures are important as structural components in modern lightweight aircraft, but are susceptible to catastrophic failure without obvious forewarning. Internal damage, such as disbonding between skin and core, is detrimental to the structures' strength and integrity and thus must be detected before reaching critical levels. However, highly directional low density cores, such as Nomex honeycomb, make the task of damage detection and health monitoring difficult. One possible method for detecting damage in composite sandwich structures, which seems to have received very little research attention, is analysis of global modal parameters. This study will investigate the viability of modal analysis techniques for detecting skin-core disbonds in carbon fiber-Nomex honeycomb sandwich panels through laboratory testing. A series of carbon fiber prepreg and Nomex honeycomb sandwich panels-representative of structural components used in lightweight composite airframes-were fabricated by means of autoclave co-cure. All panels were of equal dimensions and two were made with predetermined sizes of disbonded areas, created by substituting areas of Teflon release film in place of epoxy film adhesive during the cure. A laser vibrometer was used to capture frequency response functions (FRF) of all panels, and then real and imaginary FRFs at different locations on each plate and operating shapes for each plate were compared. Preliminary results suggest that vibration-based techniques hold promise for damage detection of composite sandwich structures.

Oliver, J. A.; Kosmatka, J. B.

2005-05-01

390

Study on the sandwich piezoelectric ceramic ultrasonic transducer in thickness vibration  

NASA Astrophysics Data System (ADS)

A sandwich piezoelectric ceramic ultrasonic transducer in thickness vibration is studied. The transducer consists of front and back metal masses, and coaxially segmented, thickness polarized piezoelectric ceramic thin rings. For this kind of sandwich piezoelectric transducers in thickness vibration, it is required that the lateral dimension of the transducer is sufficiently large compared with its longitudinal dimension so that no lateral displacements in the transducer can occur (laterally clamped). In this paper, the thickness vibration of the piezoelectric ceramic stack consisting of a number of identical piezoelectric ceramic thin rings is analysed and its electro-mechanical equivalent circuit is obtained. The resonance frequency equation for the sandwich piezoelectric ceramic ultrasonic transducer in thickness vibration is derived. Based on the frequency equation, two sandwich piezoelectric ceramic ultrasonic transducers are designed and manufactured, and their resonance frequencies are measured. It is shown that the measured resonance frequencies are in good agreement with the theoretical results. This kind of sandwich piezoelectric ultrasonic transducer is expected to be used in megasonic ultrasonic cleaning and sonochemistry where high power and high frequency ultrasound is needed.

Lin, Shuyu; Tian, Hua

2008-02-01

391

Compression After Impact Testing of Sandwich Structures Using the Four Point Bend Test  

NASA Technical Reports Server (NTRS)

For many composite laminated structures, the design is driven by data obtained from Compression after Impact (CAI) testing. There currently is no standard for CAI testing of sandwich structures although there is one for solid laminates of a certain thickness and lay-up configuration. Most sandwich CAI testing has followed the basic technique of this standard where the loaded ends are precision machined and placed between two platens and compressed until failure. If little or no damage is present during the compression tests, the loaded ends may need to be potted to prevent end brooming. By putting a sandwich beam in a four point bend configuration, the region between the inner supports is put under a compressive load and a sandwich laminate with damage can be tested in this manner without the need for precision machining. Also, specimens with no damage can be taken to failure so direct comparisons between damaged and undamaged strength can be made. Data is presented that demonstrates the four point bend CAI test and is compared with end loaded compression tests of the same sandwich structure.

Nettles, Alan T.; Gregory, Elizabeth; Jackson, Justin; Kenworthy, Devon

2008-01-01

392

A Study on Flexural Properties of Sandwich Structures with Fiber/Metal Laminate Face Sheets  

NASA Astrophysics Data System (ADS)

In this work, a new family of sandwich structures with fiber metal laminate (FML) faces is investigated. FMLs have benefits over both metal and fiber reinforced composites. To investigate the bending properties of sandwich beams with FML faces and compare with similar sandwich beams with fibrous composite faces, 6 groups of specimen with different layer arrangements were made and tested. Results show that FML faces have good resistance against transverse local loads and minimize stress concentration and local deformations of skin and core under the loading tip. In addition, FML faces have a good integrity even after plateau region of foam cores and prevent from catastrophic failures, which cannot be seen in fibrous composite faces. Also, FML faces are lighter than metal faces and have better connection with foam cores. Sandwich beams with FML faces have a larger elastic region because of simultaneous deformation of top and bottom faces and larger failure strain thanks to good durability of FMLs. A geometrical nonlinear classical theory is used to predict force-deflection behavior. In this model an explicit formula between symmetrical sandwich beams deflections and applied force which can be useful for designers, is derived. Good agreement is obtained between the analytical predictions and experimental results. Also, analytical results are compared with small deformation solution in a parametric study, and the effects of geometric parameters on difference between linear and nonlinear results are discussed.

Dariushi, S.; Sadighi, M.

2013-10-01

393

Thermal buckling and vibration behavior of multi-layer rectangular viscoelastic sandwich plates  

NASA Astrophysics Data System (ADS)

The present work deals with the thermal buckling and vibration behavior of multi-layer rectangular viscoelastic sandwich plates. A decoupled thermo-mechanical analysis is made by using finite element method. An all side clamped ( C- C- C- C) plate under thermal loads is analyzed for thermal buckling, frequency and damping behavior. The temperature-dependent characteristics of complex shear modulus of viscoelastic core are accounted. The formulation proposed by Kathua and Cheung [Bending and vibration of multi-layer sandwich beams and plates, International Journal for Numerical Methods in Engineering 6 (1973) 11-24] has been extended to study the thermal buckling and for predicting the critical buckling temperature of the multi-layer viscoelastic sandwich plates. The variation of natural frequency and loss factor with temperature has been studied. A parametric study is conducted to estimate the effect of core thickness and progressive sandwiching. Several interesting phenomenon like shifting of modes with temperature, decrease of membrane stiffness with the increase in core thickness and increase in level of sandwiching has been observed.

Pradeep, V.; Ganesan, N.

2008-02-01

394

Thermostructural Behavior of a Hypersonic Aircraft Sandwich Panel Subjected to Heating on One Side  

NASA Technical Reports Server (NTRS)

Thermostructural analysis was performed on a heated titanium honeycomb-core sandwich panel. The sandwich panel was supported at its four edges with spar-like substructures that acted as heat sinks, which are generally not considered in the classical analysis. One side of the panel was heated to high temperature to simulate aerodynamic heating during hypersonic flight. Two types of surface heating were considered: (1) flat-temperature profile, which ignores the effect of edge heat sinks, and (2) dome-shaped-temperature profile, which approximates the actual surface temperature distribution associated with the existence of edge heat sinks. The finite-element method was used to calculate the deformation field and thermal stress distributions in the face sheets and core of the sandwich panel. The detailed thermal stress distributions in the sandwich panel are presented, and critical stress regions are identified. The study shows how the magnitudes of those critical stresses and their locations change with different heating and edge conditions. This technical report presents comprehensive, three-dimensional graphical displays of thermal stress distributions in every part of a titanium honeycomb-core sandwich panel subjected to hypersonic heating on one side. The plots offer quick visualization of the structural response of the panel and are very useful for hot structures designers to identify the critical stress regions.

Ko, William L.

1997-01-01

395

Dynamic analysis of magnetorheological elastomer-based sandwich beam with conductive skins under various boundary conditions  

NASA Astrophysics Data System (ADS)

The dynamic analysis of a three-layered symmetric sandwich beam with magnetorheological elastomer (MRE) embedded viscoelastic core and conductive skins subjected to a periodic axial load have been carried out under various boundary conditions. As the skins of the sandwich beam are conductive, magnetic loads are applied to the skins during vibration. Due to the field-dependent shear modulus of MRE material, the stiffness of the MRE embedded sandwich beam can be changed by the application of magnetic fields. Using extended Hamilton's principle along with generalized Galarkin's method the governing equation of motion has been derived. The free vibration analysis of the system has been carried out and the results are compared with the published experimental and analytical results which are found to be in good agreement. The parametric instability regions of the sandwich beam have been determined for various boundary conditions. Here, recently developed magnetorheological elastomer based on natural rubber containing iron particles and carbon blacks have been used. The effects of magnetic field, length of MRE patch, core thickness, percentage of iron particles and carbon blacks on the regions of parametric instability for first three modes of vibration have been studied. These results have been compared with the parametric instability regions of the sandwich beam with fully viscoelastic core to show the passive and active vibration reduction of these structures using MRE and magnetic field. Also, the results are compared with those obtained using higher order theory.

Nayak, B.; Dwivedy, S. K.; Murthy, K. S. R. K.

2011-04-01

396

Feasibility of active sandwich detectors for single-shot dual-energy imaging  

NASA Astrophysics Data System (ADS)

We revisit the doubly-layered sandwich detector configuration for single-shot dual-energy x-ray imaging. In order to understand its proper operation, we investigated the contrast-to-noise performance in terms of the x-ray beam setup using the Monte Carlo methods. Using a pair of active photodiode arrays coupled to phosphor screens, we have built a sandwich detector. For better spectral separation between the projection images obtained from the front and rear detectors during a single x-ray exposure, we inserted a copper sheet between two detectors. We have successfully obtained soft tissue- and bone-enhanced images for a postmortem mouse with the developed sandwich detector using weighted logarithmic subtraction, and the image quality was comparable to those achieved by the conventional kVp-switching technique. Although some problems to be mitigated for the optimal and practical use, for example, the scatter effect and image registration, are still left, the performance of the sandwich detector for single-shot dual-energy x-ray imaging is promising. We expect that the active sandwich detector will provide motion-artifact-free dual-energy images with a reasonable image quality.

Yun, Seungman; Han, Jong Chul; Kim, Dong Woon; Youn, Hanbean; Kim, Ho Kyung; Tanguay, Jesse; Cunningham, Ian A.

2014-03-01

397

Lherzolite-saturated melt compositions of peridotite MM3: results of near-solidus micro- sandwich experiments  

NASA Astrophysics Data System (ADS)

Results of the 1 GPa diamond-aggregate melting experiments of Baker and Stolper (1) and Baker et al. (2) on the peridotite composition MM3 continue to be controversial (3,4), especially regarding the observation (1,2) of high SiO2 and low TiO2 contents of partial melts produced near the solidus. Here we present the results of four 1 GPa micro-sandwich experiments on MM3 at near-solidus temperatures of 1245-1250°C. As in our earlier experiments (1,2), the MM3 mix consists of natural olivine, orthopyroxene, clinopyroxene, and spinel grains that are less than 15 microns in size. Four different synthetic glass compositions were used and all lie off the compositional trends defined by the MM3 partial melts in oxide vs. MgO space (1,2,5). Experimental charges were constructed by placing a small chip of synthetic glass (0.4-0.8 mg) within a much larger mass (13-14 mg) of powdered MM3; each combined glass-MM3 sample was run in a graphite crucible within a sealed Pt capsule for 122 to 144 hr in a piston cylinder apparatus. At P and T, the initial glass chip within a charge generates a small pool of liquid whose composition shifts as it equilibrates with the MM3 solid phase assemblage. If the near- solidus MM3 partial melting trend of (1,2,5) is correct, then experiments with different initial glass compositions will produce final liquids that are consistent with this compositional trend. Except for TiO2 vs. MgO in one experiment, the final glasses all lie within 1-2 sigma of the oxide vs. MgO trends defined by the partial melts of MM3 (1,2,5). Note, that by minimizing the amount of basaltic glass added to MM3 in each experiment (mass fractions varied from 0.03-0.06), the glasses do not substantially perturb the bulk composition of the starting peridotite, which minimizes the need for iterative sandwich experiments (e.g., 6). We also compared the liquid compositions from both the peridotite melting experiments and traditional sandwich experiments of (4; done using a synthetic oxide mix of MM3) with our data (1,2,5). The two data sets overlap at the 1-2 sigma level when liquid compositions are plotted as a function of liquid MgO content and thus, contrary to the claims of (4), the two data sets are consistent with each other. The divergence of the two data sets when liquid compositions are plotted as a function of temperature reflects the increasing concentration of K2O, P2O5, H2O, and Cl in the partial melts of (1,2) compared to the liquids of (4), whose synthetic bulk compositions were K2O, P2O5, and Cl-free. Results of our micro-sandwich experiments lend support to the partial melting trend of (1,2,5) on MM3, especially with regard to the high SiO2 and low TiO2 contents in liquids at low degrees of partial melting.(1) Baker and Stolper (1994) GCA 58, 2811-2827; (2) Baker et al. (1995) Nature 375, 308-311; (3) Falloon et al. (1997) EPSL 152, 149-162; (4) Falloon et al. (1999) JPet 40, 1343-1375; (5) Hirschmann et al. GCA 62, 883-902; (6) Robinson et al. (1998) EPSL 155, 97-111

Baker, M. B.; Stolper, E. M.

2007-12-01

398

Construction block  

US Patent & Trademark Office Database

A construction block is provided that includes at least one base member that includes a plurality of lower side wall receptacles. The construction block further includes a plurality of side wall assemblies. Each of the side wall assemblies includes a plurality of interconnected panels. Each of the panels is hingedly connected to each adjacent one of the panels of the respective one of the side wall assemblies. Each of the side wall assemblies defines a hollow load chamber having an open top and an open bottom. At least some of the panels of each of the side wall assemblies are angled relative to one another. Each of the lower side wall receptacles receives one of the side wall assemblies.

2010-08-03

399

Penetration and perforation of composite sandwich panels by hemispherical and conical projectiles  

SciTech Connect

The results of penetration and perforation tests carried out on composite sandwich panels with GRP skins and PVC foam cores using hemispherical-ended and conical-nosed indenters/projectiles under quasi-static, drop-weight, and ballistic impact conditions, with impact velocities up to 305 m/s, are described. Load-displacement characteristics under quasi-static loading are presented and the ballistic limits as well as perforation energies are determined. A classification of the sandwich panel responses based on the panel thickness-to-projectile diameter ratio is deduced. General empirical formulas that predict the dynamic perforation energies for fiber-reinforced plastic (FRP) laminates and composite sandwich panels loaded by hemispherical-ended projectiles are derived. The empirical equations correlate well with available experimental data. It is shown that, to a first approximation, the formulas obtained for hemispherical-ended projectiles are also applicable to conical-nosed projectiles.

Reddy, T.Y.; Wen, H.M.; Reid, S.R.; Soden, P.D. [Univ. of Manchester Inst. of Science and Technology (United Kingdom). Applied Mechanics Div.

1998-05-01

400

A Higher-Order Bending Theory for Laminated Composite and Sandwich Beams  

NASA Technical Reports Server (NTRS)

A higher-order bending theory is derived for laminated composite and sandwich beams. This is accomplished by assuming a special form for the axial and transverse displacement expansions. An independent expansion is also assumed for the transverse normal stress. Appropriate shear correction factors based on energy considerations are used to adjust the shear stiffness. A set of transverse normal correction factors is introduced, leading to significant improvements in the transverse normal strain and stress for laminated composite and sandwich beams. A closed-form solution to the cylindrical elasticity solutions for a wide range of beam aspect ratios and commonly used material systems. Accurate shear stresses for a wide range of laminates, including the challenging unsymmetric composite and sandwich laminates, are obtained using an original corrected integration scheme. For application of the theory to a wider range of problems, guidelines for finite element approximations are presented.

Cook, Geoffrey M.

1997-01-01

401

A main group metal sandwich: five lithium cations jammed between two corannulene tetraanion decks.  

PubMed

Lithium-coordinated polyaromatic anions such as tetrareduced corannulene, C(20)H(10)(4-) (1(4-)), are useful substrates to model and ultimately improve the graphitic electrodes in lithium-ion (Li(+)) batteries. Previous studies suggested that 1(4-) forms dimers encasing four Li(+) ions in solution. Here, we report a single-crystal x-ray diffraction analysis confirming the formation of a sandwich-type supramolecular aggregate with a high degree of alkali metal intercalation. In contrast to the prior model, our data reveal that five Li(+) ions are sandwiched between the two tetrareduced corannulene decks, and (7)Li nuclear magnetic resonance spectroscopy delineates a conserved structure in tetrahydrofuran solution. Remarkably, the sandwich is robust in both solution and solid states even in the presence of crown ethers that compete for Li(+) coordination. These results should help elucidate Li(+) intercalation motifs between curved carbon surfaces more broadly. PMID:21852497

Zabula, Alexander V; Filatov, Alexander S; Spisak, Sarah N; Rogachev, Andrey Yu; Petrukhina, Marina A

2011-08-19

402

Distortion-free single point imaging of multi-layered composite sandwich panel structures.  

PubMed

The results of a magnetic resonance imaging (MRI) investigation concerning the effects of an aluminum honeycomb sandwich panel on the B1 and B0 fields and on subsequent image quality are presented. Although the sandwich panel structure, representative of an aircraft composite material, distorts B0 and attenuates B1, distortion-free imaging is possible using single point (constant time) imaging techniques. A new expression is derived for the error caused by gradient field distortion due to the heterogeneous magnetic susceptibility within a sample and this error is shown not to cause geometric distortion in the image. The origin of the B0 distortion in the sample under investigation was also examined. The graphite-epoxy 'skin' of the panel is the principal source of the B0 distortion. Successful imaging of these structures sets the stage for the development of methods for detecting moisture ingress and degradation within composite sandwich structures. PMID:15082262

Marble, Andrew E; Mastikhin, Igor V; MacGregor, Rod P; Akl, Mohamad; LaPlante, Gabriel; Colpitts, Bruce G; Lee-Sullivan, Pearl; Balcom, Bruce J

2004-05-01

403

Penetration Depth of Closed-Cell Aluminum Foam Sandwich Structures under Low Velocity Impact  

NASA Astrophysics Data System (ADS)

In this paper, the response of closed-cell aluminum foam sandwich structures under low velocity impact of an ogival-ended mild steel projectile was studied. An analytical model was proposed to predict the penetration depth as well as residual velocity based on the dynamic cavity expansion theory and the Poncelet resistance formula using in the closed-cell aluminum foam sandwich panel. A high-pressure air gun was employed to execute penetration depth tests. Two tests had been done and the results were measured, those are, the residual velocity of the first layer (aluminum plate) and the penetration depth of the sandwich panel. Simultaneously, the finite element analysis software LS-DYNA was utilized for describing the penetrating process of steel projectiles normal impact. It was found that both residual velocity and penetration depth showed nonlinear variation against impact velocity, also the analytical results showed acceptable deviation with those from tests and FEM simulations during specific impact velocities.

Chen, Yu-Liang; Chen, Hong-Chang

404

Preparation and microwave absorption properties of metal magnetic micropowder-coated honeycomb sandwich structures  

NASA Astrophysics Data System (ADS)

Radar absorbing materials with metal magnetic micropowder-coated honeycomb sandwich structures are prepared by a spray process. Metal magnetic micropowder is applied as an absorber which maintains a high absorption, and a honeycomb sandwich structure as a supporter enhancing mechanical strength. The microwave absorption properties are measured by a network analyzer system in the frequency range of 2.6-18 GHz. The concentration of the MMP and the coating thickness of the absorber affect the attenuation properties, a suitable value of them contributing to a broad bandwidth and high loss. A matching layer is introduced to the honeycomb sandwich structure on top, which allows the incident electromagnetic wave to enter and largely get attenuated through the absorbing system, increasing the microwave absorption.

He, Yanfei; Gong, Rongzhou; Cao, Heng; Wang, Xian; Zheng, Yi

2007-10-01

405

Design and analysis of a plate-fin sandwich actively cooled structural panel  

NASA Technical Reports Server (NTRS)

The skin structure of hydrogen fueled hypersonic transport vehicles traveling at Mach 6 and above must be designed to withstand, for relatively long periods of time, the aerodynamic heating effects which are far more severe than those encountered by the supersonic aircraft of today. The use of conventional aircraft materials such as aluminum in combination with forced convection active cooling to accommodate aerodynamic heating is addressed. The basic active cooling concept consists of a stringer stiffened plate-fin sandwich. The sandwich surface is subjected to the aerodynamic heat flux which is transferred, via convection, to a coolant that is forced through the sandwich under pressure. The coolant, in turn, circulates in a closed loop through a hydrogen heat exchanger and back through the skin panel.

Smith, L. M.

1978-01-01

406

Influence of residual stresses on the tensile strength of composite-metal sandwich laminates  

NASA Technical Reports Server (NTRS)

The tensile strength of boron-epoxy/aluminum sandwich laminates is discussed relative to the residual thermal stresses generated by curing and bonding at elevated temperatures. It is shown that the sandwich laminates investigated exhibit three dinstinct modes of failure, depending upon the fiber orientation of the composite. Sandwich laminates with moderate to high percentage of 0-deg fibers exhibit early failures initiated by edge effect; laminates with moderate to high percentage of 90-deg fibers fail according to a first-ply failure criterion; laminates with moderate to high percentages of plus or minus 45 deg plies fail at strains equal to or greater than the failure strain of the corresponding all-composite laminate.

Herakovich, C. T.; Wong, D. M.

1977-01-01

407

A plastic indentation model for sandwich beams with metallic foam cores  

NASA Astrophysics Data System (ADS)

Light weight high performance sandwich composite structures have been used extensively in various load bearing applications. Experiments have shown that the indentation significantly reduces the load bearing capacity of sandwiched beams. In this paper, the indentation behavior of foam core sandwich beams without considering the globally axial and flexural deformation was analyzed using the principle of virtual velocities. A concisely theoretical solution of loading capacity and denting profile was presented. The denting load was found to be proportional to the square root of the denting depth. A finite element model was established to verify the prediction of the model. The load-indentation curves and the profiles of the dented zone predicted by theoretical model and numerical simulation are in good agreement.

Xie, Zhong-You; Yu, Ji-Lin; Zheng, Zhi-Jun

2011-12-01

408

Observation of spin-polarized tunneling in thin proximity-effect sandwiches  

SciTech Connect

Use of a tunneling Hamiltonian model for thin proximity-effect sandwiches in high parallel fields has indicated the possibility of spin splitting the quasiparticle density of states past the point where the up- and down-spin densities of states will cross. This crossing is signified by a large zero-bias peak in the tunneling conductance. In this paper we review the theory leading to this prediction and present the results of spin-polarized tunneling experiments in Al-oxide-Mg-Al junctions. Measurements at 0.4 K on a sandwich with 40 A of Al over 25 A of Mg at fields from zero to 3.4 tesla (where the sandwich went into the normal state) were in qualitative agreement with the theoretical predictions, including the peak at zero bias at the higher field values.

Gallagher, W.J.; Paraskevopoulos, D.E.; Tedrow, P.M.; Frota-Pessoa, S.; Schwartz, B.B.

1980-02-01

409

Spin-valve giant magnetoresistance in scandium-benzene sandwich cluster  

NASA Astrophysics Data System (ADS)

Using density functional theory and non-equilibrium Green's function method, we investigate the magnetic and transport properties of organic Scn(C6H6)n+1 (n=1\\text{-}3 ) sandwich clusters. The results show that the sandwiches possess high stabilities and large magnetic moments, and our prediction is in agreement with the experimental observation. With Ni as two electrodes, significant spin-valve giant magnetoresistance was found in Sc3(C6H6)4 molecular junction. Furthermore, all the sandwiches can be viewed as a new kind of spin filter. Specially, by changing the magnetization orientation of one electrode, Sc2(C6H6)3 molecular junction could effectively control the spin orientation of the electron in the system.

Yang, Z.; Zhang, B. L.; Liu, X. G.; Yang, Y. Z.; Li, X. Y.; Xiong, S. J.; Xu, B. S.

2013-12-01

410

Thermoelastic buckling and vibration behavior of a functionally graded sandwich beam with constrained viscoelastic core  

NASA Astrophysics Data System (ADS)

In this article, buckling and vibration behavior of a functionally graded material (FGM) sandwich beam having constrained viscoelastic layer (VEL) is studied in thermal environment by using finite element formulation. The FGM sandwich beam is assumed to be clamped on both edges. The material properties of FGM are functionally graded in thickness direction according to volume fraction power law distribution. Temperature dependent material properties of FGM stiff layer and shear modulus of viscoelastic layer are considered to carry out buckling and vibration analysis. Numerical studies involving the understanding the effect of power law index, core to stiff layer ratio on the thermal buckling temperature as well as on vibration has been carried out. In addition influence of temperature on natural frequencies and loss factors have been examined for FGM sandwich beam.

Bhangale, Rajesh K.; Ganesan, N.

2006-08-01

411

Three-dimensional solutions for thermomechanical stresses in sandwich panels and shells  

NASA Technical Reports Server (NTRS)

Analytic three-dimensional thermoelasticity solutions are presented for static problems of simply supported sandwich panels and cylindrical shells subjected to mechanical and thermal loads. The panels and shells have laminated composite face sheets of arbitrary thickness separated by a core. Each of the individual layers of the face sheets and the core is modeled as a three-dimensional continuum. Analytic first-order sensitivity coefficients are evaluated to assess the sensitivity of the responses to variations in material parameters of the face sheets and the core, as well as to variations in the curvatures and thicknesses of the sandwich and face sheets. Also, the strain energy associated with various stress components in the face sheets and core are calculated and compared. The information obtained in the present study can aid the development and assessment of two-dimensional models for sandwich structures and illuminate the role of particular material parameters in an equivalent model for the core.

Burton, W. Scott; Noor, Ahmed K.

1995-01-01

412

Construction measurements  

SciTech Connect

This text/reference on construction measurements contains material concerning electronic surveying and remote sensing. New to this edition is coverage of the GPS satellite positioning system, electronic distance measurement (EDM), laser sweep, calculator techniques, radial surveying and tracking, Loran-C, inertial navigation surveying, 3-point resection, computer software, and electronic fieldbooks. It covers the difference of elevation, angle measurements and directions, coordinate surveying and layout, offshore measurements, and random field and office techniques.

Barry, B.A.

1988-01-01

413

Construct It!  

NSDL National Science Digital Library

Students use simple household materials, such as PVC piping and compact mirrors, to construct models of laser-based security systems. The protected object (a "mummified troll" or another treasure of your choosing) is placed "on display" in the center of the modeled room and protected by a laser system that utilizes a laser beam reflected off mirrors to trigger a light trip sensor with alarm.

VU Bioengineering RET Program, School of Engineering,

414

Using Conducting Wire at A-Sandwich Junctions to Improve the Transmission Performance of Radomes  

NASA Astrophysics Data System (ADS)

We present design procedures for using conducting wires in A-sandwich junctions to achieve high transmission performance; benchtest results validate the procedures. The scattering characteristics of the junction are obtained by solving the electric field integral equation of volumetric equivalent currents. The transmission performance is evaluated by subtracting the scattered fields of the same-sized A-sandwich panel in order to offset the effect of edge diffraction. Optimum wire width is determined by examining transmission performance with different arrangements. The designed junction achieves high transmission performance. The measured scattering characteristics of a bench model demonstrate the validity of the presented method.

Inasawa, Yoshio; Nishimura, Toshio; Tsuruta, Jun; Miyashita, Hiroaki; Konishi, Yoshihiko

415

Analyses for Debonding of Stitched Composite Sandwich Structures Using Improved Constitutive Models  

NASA Technical Reports Server (NTRS)

A fracture mechanics analysis based on strain energy release rates is used to study the effect of stitching in bonded sandwich beam configurations. Finite elements are used to model the configurations. The stitches were modeled as discrete nonlinear spring elements with a compliance determined by experiment. The constitutive models were developed using the results of flatwise tension tests from sandwich material rather than monolithic material. The analyses show that increasing stitch stiffness, stitch density and debond length decrease strain energy release rates for a fixed applied load.

Glaessgen, E. H.; Sleight, D. W.; Krishnamurthy, T.; Raju, I. S.

2001-01-01

416

Blast Performance of Sandwich Composites with In-Plane Compressive Loading  

Microsoft Academic Search

An experimental investigation was conducted to evaluate the dynamic performance of E-glass Vinyl Ester composite face sheet\\u000a \\/ foam core sandwich panels when subjected to pre-compression and subsequent blast loading. The sandwich panels were subjected\\u000a to 0 kN, 15 kN and 25 kN of in plane compression respectively, prior to transverse blast wave loading with peak incident pressure\\u000a of 1 MPa and velocity of

E. Wang; A. Shukla

417

The propagation of guided waves in composite, sandwich-like structures and their use for NDT  

NASA Astrophysics Data System (ADS)

Guided modes in a sandwich plate are studied. The numerical model takes into account the anisotropy and viscoelasticity properties of skins and core, and the coupling with air surrounding the plate. Dispersion curves and through-thickness fields are predicted for various modes, showing fundamental differences with classical Lamb modes. A strong effect of viscoelasticity on the dispersion curves is also demonstrated. Phase velocity measurements using air-coupled transducers confirm the original behavior of guided modes in the non-symmetric, sandwich, test plate. .

Castaings, Michel; Hosten, Bernard

2001-04-01

418

Parameter Estimation in Hybrid Active-Passive Laminated Sandwich Composite Structures  

SciTech Connect

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative models, with unknown parameters that are to be estimated by an inverse technique, using experimentally measured natural frequencies and associated modal loss factors. The inverse problem is formulated as a constrained minimization problem, and gradient based optimization techniques are employed. An application case is presented and discussed, focused on identification of viscoelastic frequency dependent core material properties.

Araujo, A. L. [ESTIG-Polytechnic Institute of Braganca, Campus de Sta. Apolonia, Apartado 1134, 5301-857 Braganca (Portugal); Mota Soares, C. M.; Mota Soares, C. A. [IDMEC/IST-Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon (Portugal); Herskovits, J. [COPPE/UFRJ-Federal University of Rio de Janeiro, Caixa Postal 68503, 21945-970 Rio de Janeiro (Brazil)

2010-05-21

419

Modeling and Identification of Nonlinear Cascade and Sandwich Systems with General Backlash  

NASA Astrophysics Data System (ADS)

The paper deals with modeling and identification of nonlinear cascade and sandwich systems including general backlash, where instead of the straight lines determining the upward and downward parts of backlash characteristic, general curves are considered. This enables more precise modeling of mechanical parts and improves the performance of control systems. The analytical description of the general backlash leads to mathematical models of the cascade system with output general backlash and the sandwich system with internal general backlash, where all the model parameters are separated. Hence, the identification is solved as a quasi-linear problem. Iterative algorithms with internal variables estimation are proposed and illustrative examples are included.

Vörös, Jozef

2014-03-01

420

Solvent extraction of lanthanoid picrates with crown ethers: preferential sandwich complexation and unique cation selectivities  

SciTech Connect

Quantitative solvent extractions of aqueous lanthanoid picrates with 15-crown-5 and 18-crown-6 were conducted at low ionic strength in the absence of background salts. An overwhelming preference for the sandwich complexation and unique cation selectivities were observed. The peak extraction constants were found for samarium with 15-crown-5 (1:2 stoichiometry) and for cerium and praseodymium with 18-crown-6 (1:1 and 1:2 stoichiometries, respectively). The facile sandwich complexation and unique cation selectivities are interpreted in terms of the heavy hydration of lanthanoid ions of high charge density.

Nakagawa, K.; Okada, S.; Inoue, Y.; Tai, A.; Hakushi, T.

1988-11-15

421

Characterisation by Inverse Techniques of Elastic, Viscoelastic and Piezoelectric Properties of Anisotropic Sandwich Adaptive Structures  

NASA Astrophysics Data System (ADS)

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative models, with unknown parameters that are to be estimated by an inverse technique, using experimentally measured natural frequencies and associated modal loss factors. The inverse problem is formulated as a constrained minimisation problem, and gradient based optimization techniques are employed. Applications are presented and discussed, focused on the identification of viscoelastic frequency dependent core material properties.

Araújo, Aurelio L.; Mota Soares, Cristovao M.; Mota Soares, Carlos A.; Herskovits, Jose

2010-10-01

422

Conformal thin-sandwich puncture initial data for boosted black holes  

SciTech Connect

We apply the puncture approach to conformal thin-sandwich black-hole initial data. We solve numerically the conformal thin-sandwich puncture (CTSP) equations for a single black hole with nonzero linear momentum. We show that conformally-flat solutions for a boosted black hole have the same maximum gravitational radiation content as the corresponding Bowen-York solution in the conformal transverse-traceless decomposition. We find that the physical properties of these data are independent of the free slicing parameter.

Hannam, Mark D.; Cook, Gregory B. [Center for Gravitational Wave Astronomy, University of Texas at Brownsville, 80 Fort Brown, Brownsville, Texas 78520 (United States); Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109 (United States)

2005-04-15

423

Optical fiber SPR biosensor with sandwich assay for the detection of prostate specific antigen  

NASA Astrophysics Data System (ADS)

We present a new, sensitive, few mode fiber (FMF) surface plasmon resonance (SPR) biosensor with a sandwich assay for the detection of PSA. The side-polished FMF biosensor does not need a polarizer and a thin high-index overlayer. The optical sensitivity of the SPR sensor was determined as 2.5 × 10 -6 RIU. In the SPR PSA sensor, the SPR signals were amplified by a factor of 6 in average over no secondary antibody, using the sandwich assay. The proposed FMF SPR biosensor has great potential for real-time analysis of immune reaction between biomolecules and the advantages of high-sensitivity and label-free detection.

Jang, Hyun Soo; Park, Kwang No; Kang, Chang Duk; Kim, Jun Pyo; Sim, Sang Jun; Lee, Kyung Shik

2009-07-01

424

Spectroscopic characterization of lanthanide octaethylporphyrin sandwich complexes. Effects of strong. pi. pi. interaction  

Microsoft Academic Search

Optical absorption and resonance Raman spectra are reported for the lanthanide sandwich porphyrins, Eu{sup III}(OEP)â, Nd{sup III}(OEP)â, and La{sup III}(OEP)â (OEP = octaethylporphyrin). These complexes contain a single hole in the porphyrin Ï system and are electronically similar to the Ce{sup IV} sandwich porphyrin cation radical Ce{sup IV}(OEP)â{sup +}. Variable-temperature (10-300 K) UV-vis and near-infrared (NIR) spectra are obtained for

John K. Duchowski; David F. Bocian

1990-01-01

425

Compression and impact testing of two-layer composite pyramidal-core sandwich panels  

Microsoft Academic Search

Quasi-static uniform compression tests and low-velocity concentrated impact tests were conducted to reveal the failure mechanisms and energy absorption capacity of two-layer carbon fiber composite sandwich panels with pyramidal truss cores. Three different volume-fraction cores (i.e., with different relative densities) were fabricated: 1.25%, 1.81%, and 2.27%. Two-layer sandwich panels with identical volume-fraction cores (either 1.25% or 2.27%), and also stepwise

Jian Xiong; Ashkan Vaziri; Li Ma; Jim Papadopoulos; Linzhi Wu

426

An efficient and simple refined theory for nonlinear bending analysis of functionally graded sandwich plates  

NASA Astrophysics Data System (ADS)

In this paper, an efficient and simple refined theory is presented for nonlinear bending analysis of functionally graded sandwich plates. The theory presented is variationally consistent, does not require the shear correction factor, and gives rise to transverse shear stress variations such that the transverse shear stresses vary parabolically across the plate thickness, satisfying shear-stress-free surface conditions. The energy concept along with the present theory and the first- and third-order shear deformation theories is used to predict the large deflection and the stress distribution across the thickness of functionally graded sandwich plates.

Kaci, A.; Draiche, K.; Zidi, M.; Houari, M. S. A.; Tounsi, A.

2013-09-01

427

A {3,2}-Order Bending Theory for Laminated Composite and Sandwich Beams  

NASA Technical Reports Server (NTRS)

A higher-order bending theory is derived for laminated composite and sandwich beams thus extending the recent {1,2}-order theory to include third-order axial effect without introducing additional kinematic variables. The present theory is of order {3,2} and includes both transverse shear and transverse normal deformations. A closed-form solution to the cylindrical bending problem is derived and compared with the corresponding exact elasticity solution. The numerical comparisons are focused on the most challenging material systems and beam aspect ratios which include moderate-to-thick unsymmetric composite and sandwich laminates. Advantages and limitations of the theory are discussed.

Cook, Geoffrey M.; Tessler, Alexander

1998-01-01

428

Microstructure of the combustion zone: Thin-binder AP-polymer sandwiches  

NASA Technical Reports Server (NTRS)

Experimental results are summarized for systematic quench-burning tests on ammonium perchlorate-HC binder sandwiches with binder thicknesses in the range 10 - 150 microns. Tests included three binders (polysulfide, polybutadiene-acrylonitrile, and hydroxy terminated polybutadiene), and pressures from 1.4 to 14 MPa. In addition, deflagration limits were determined in terms of binder thickness and pressure. Results are discussed in terms of a qualitative theory of sandwich burning consolidated from various sources. Some aspects of the observed results are explained only speculatively.

Price, E. W.; Panyam, R. R.; Sigman, R. K.

1980-01-01

429

Dynamic Response of In-plane Prestressed Sandwich Panels with a Viscoelastic Flexible Core and Different Boundary Conditions  

Microsoft Academic Search

A new mathematical method and double Fourier series set of functions is developed to find out the local and global transverse and in-plane mode shapes, damped natural frequencies and modal loss factors in composite sandwich panels with multilayered laminated face sheets, viscoelastic flexible core and arbitrary boundary conditions. An improved high order sandwich plate theory (IHSAPT) is applied to investigate

K. Malekzadeh; M. R. Khalili; A. Jafari; R. K. Mittal

2006-01-01

430

FREE VIBRATION ANALYSIS OF SANDWICH BEAM WITH ELASTIC OR VISCOELASTIC CORE BY APPLYING THE DISCRETE GREEN FUNCTION  

Microsoft Academic Search

A method of analysis of the free vibration of a three-layer sandwich beam with an elastic or viscoelastic core and arbitrary boundary conditions is presented. The characteristic equation of the free vibration is derived by applying the Green function which is obtained as a discrete solution of differential equations governing the flexural behaviour of the sandwich beam under the action

T. Sakiyama; H. Matsuda; C. Morita

1996-01-01

431

Boom Construction  

NSDL National Science Digital Library

Student teams design their own booms (bridges) and engage in a friendly competition with other teams to test their designs. Each team strives to design a boom that is light, can hold a certain amount of weight, and is affordable to build. Teams are also assessed on how close their design estimations are to the final weight and cost of their boom "construction." This activity teaches students how to simplify the math behind the risk and estimation process that takes place at every engineering firm prior to the bidding phaseâwhen an engineering firm calculates how much money it will take to build the project and then "bids" against other competitors.

AMPS GK-12 Program,

432

Damage Detection and Impact Testing on Laminated and Sandwich Composite Panels  

NASA Technical Reports Server (NTRS)

This research investigates health monitoring of sandwich shell composites to determine if the Transmittance Functions (TF) are effective in determining the present of damage. The health monitoring test was conducted on the sandwich plates before and after low velocity impacts using the health monitoring technique given in TFs are a NDE (Nondestructive Evaluation) technique that utilizes the ratios of cross-spectrums to auto-spectrums between two response points on the sandwich composites. The test for transmittance was conducted on the same density foam core throughout the experiment. The test specimens were 17.8 cm by 25.4 cm in dimension. The external sheets (face sheets) were created from graphite/epoxy laminate with dimension of 1.58 mm thick. The polymethacrylide (Rohacell) foam core was 12.7 mm thick. These samples experienced a transformation in the TF that was considered the low velocity impact damage. The low velocity damage was observed in the TFs for the sandwich composites.

Hughes, Derke R.; Craft, William J.; Schulz, Mark J.; Naser, Ahmad S.; Martin, William N.

1998-01-01

433

Impact failure characteristics in sandwich structures. Part II: Effects of impact speed and interfacial strength  

Microsoft Academic Search

In this paper, we describe the second part of an experimental investigation concentrating on the study of the effects of impact speed and interfacial bond strength on the dynamic failure of model sandwich structures. Results show that even small variations in impact speed and bond strength substantially influence the initiation behavior of delamination (location and nucleation time) and lead to

L. Roy Xu; Ares J. Rosakis

2002-01-01

434

Laminated Composite Sandwich Plates with a Weak Compressible Core Impacted by Blast Loading.  

National Technical Information Service (NTIS)

The governing theory of asymmetric sandwich plates with a first- order compressible core impacted by a Friedlander-type of blast has been presented and simplified for the case of symmetric cross-ply and single-layered orthotropic facings. In all cases, it...

S. Arepally T. Hause

2011-01-01

435

A sandwich-type triple-decker lanthanide complex with mixed phthalocyanine and Schiff base ligands.  

PubMed

A new triple-decker dinuclear sandwich-type dysprosium complex based on both the phthalocyanine ligand and the tetradentate Schiff base ligand was synthesized, which is of interest for synthetic chemistry and also shows single-molecule magnetic behaviour. PMID:23818021

Gao, Feng; Li, Yu-Yang; Liu, Cai-Ming; Li, Yi-Zhi; Zuo, Jing-Lin

2013-08-21

436

Uniaxial crushing of sandwich plates under air blast: Influence of mass distribution  

Microsoft Academic Search

Motivated by recent efforts to mitigate blast loading using energy-absorbing materials, this paper uses analytical and computational modeling to investigate the influence of mass distribution on the uniaxial crushing of cellular sandwich plates under air blast loading. In the analytical model, the cellular core is represented using a rigid, perfectly-plastic, locking idealization, as in previous studies, and the front and

Joseph A. Main; George A. Gazonas

2008-01-01

437

ON THE BEHAVIOUR OF FLUID-LOADED SANDWICH PANELS WITH MEAN FLOW  

Microsoft Academic Search

This paper considers a fluid-loaded sandwich panel, made up of layers of relatively rigid skin material surrounding a layer of less dense core material, with an unsteady point driver in steady mean flow. For a simple plate Brazier-Smith and Scott, and Crighton and Oswell predicted a number of unusual phenomena, including absolute instability, a neutral mode with its group velocity

N. Peake; S. V. Sorokin

2001-01-01

438

Design and test of lightweight sandwich T-joint for naval ships  

Microsoft Academic Search

Within the EUCLID project, ‘Survivability, Durability and Performance of Naval Composite Structures’, one task is to develop improved fibre composite joints for naval ship super structures. One type of joint in such a super structure is a T-joint between sandwich panels. An existing design consists of panels joined by filler and overlaminates of the same thickness as the skin laminates.

Helmuth Toftegaard; Aage Lystrup

2005-01-01

439

WRINKLING STRESSES IN HONEYCOMB SANDWICH PANELS USING DISCRETE AND CONTINUUM CORE REPRESENTATIONS  

Microsoft Academic Search

This study, examines the implications of modelling wrinkling in sandwich honeycomb cores using a simplified continuum representation of the core. Localised wrinkling in honeycomb panels is traditionally modelled using a continuum core. In a continuum core, the support provided to the facesheet is constant, whilst in reality; it is discrete with cellular core. Classical linear wrinkling expressions, based on this

R. A Staal; D. P. W Horrigan; G. D Mallinson; K Jayaraman

440

Loading, Degradation and Repair of F-111 Bonded Honeycomb Sandwich Panels - Preliminary Study  

Microsoft Academic Search

Many of the fixed and removable panels on the RAAF F-111 aircraft are made up of bonded honeycomb sandwich panels. Experience with the RAAF fleet has shown that a serious problem exists with degradation and damage of these panels. A review of the literature was undertaken to gain an understanding of the extent of this problem. It was found that

S. Whitehead; M. McDonald; R. A. Bartholomeusz

441

Static and dynamic analysis of soft core sandwich panels with through-thickness deformation  

Microsoft Academic Search

Sandwich plates represent an efficient structural element, providing a high stiffness\\/weight ratio characteristic. Moreover, when using this structural element, different design configurations and materials in the core can be adopted in order to obtain desired properties. From high dissipation elastomers to light and stiff honeycombs, several core materials may be applied, looking for high damping ratios or simply to obtain

R. A. S. Moreira; J. Dias Rodrigues

2010-01-01

442

High-fidelity modeling for health monitoring in honeycomb sandwich structures  

Microsoft Academic Search

High-Fidelity Model of the sandwich composite structure with real geometry is reported. The model includes two composite facesheets, honeycomb core, piezoelectric actuator\\/sensors, adhesive layers, and the impactor. The novel feature of the model is that it includes modeling of the impact and wave propagationin the structure before and after the impact. Results of modeling of the wave propagation, impact, and

Dmitry G. Luchinsky; Vasyl Hafiychuk; Vadim Smelyanskiy; Richard W. Tyson; James. L. Walker; Jimmy L. Miller

2011-01-01

443

An analytical and experimental investigation of sandwich composites subjected to low-velocity impact  

NASA Astrophysics Data System (ADS)

This study involves an experimental and analytical investigation of low-velocity impact phenomenon in sandwich composite structures. The analytical solution of a three-dimensional finite-geometry multi-layer specially orthotropic panel subjected to static and transient transverse loading cases is presented. The governing equations of the static and dynamic formulations are derived from Reissner's functional and solved by enforcing the continuity of traction and displacement components between adjacent layers. For the dynamic loading case, the governing equations are solved by applying Fourier or Laplace transformation in time. Additionally, the static solution is extended to solve the contact problem between the sandwich laminate and a rigid sphere. An iterative method is employed to determine the sphere's unknown contact area and pressure distribution. A failure criterion is then applied to the sandwich laminate's stress and strain field to predict impact damage. The analytical accuracy of the present study is verified through comparisons with finite element models, other analyses, and through experimentation. Low-velocity impact tests were conducted to characterize the type and extent of the damage observed in a variety of sandwich configurations with graphite/epoxy face sheets and foam or honeycomb cores. Correlation of the residual indentation and cross-sectional views of the impacted specimens provides a criterion for the extent of damage. Quasi-static indentation tests are also performed and show excellent agreement when compared with the analytical predictions. Finally, piezoelectric polyvinylidene fluoride (PVF2) film sensors are found to be effective in detecting low-velocity impact.

Anderson, Todd Alan

1999-12-01

444

New Method of Impregnating PEI Sheets for the In-situ Foaming of Sandwiches.  

National Technical Information Service (NTIS)

A new method is described to make foamable films for the production of in-situ foamed sandwiches. The method consists of placing a polymer film in a bath with a swelling agent and, when equilibrium swelling has been reached, placing the film in a bath wit...

P. W. C. Provo Kluit

1995-01-01

445

Optimum stacking sequence design of composite sandwich panel using genetic algorithms  

NASA Astrophysics Data System (ADS)

Composite sandwich structures recently gained preference for various structural components over conventional metals and simple composite laminates in the aerospace industries. For most widely used composite sandwich structures, the optimization problems only requires the determination of the best stacking sequence and the number of laminae with different fiber orientations. Genetic algorithm optimization technique based on Darwin's theory of survival of the fittest and evolution is most suitable for solving such optimization problems. The present research work focuses on the stacking sequence optimization of composite sandwich panels with laminated face-sheets for both critical buckling load maximization and thickness minimization problems, subjected to bi-axial compressive loading. In the previous studies, only balanced and even-numbered simple composite laminate panels have been investigated ignoring the effects of bending-twisting coupling terms. The current work broadens the application of genetic algorithms to more complex composite sandwich panels with balanced, unbalanced, even and odd-numbered face-sheet laminates including the effects of bending-twisting coupling terms.

Bir, Amarpreet Singh

446

A wave propagation model for the high velocity impact response of a composite sandwich panel  

Microsoft Academic Search

A solution methodology to predict the residual velocity of a hemispherical-nose cylindrical projectile impacting a composite sandwich panel at high velocity is presented. The term high velocity impact is used to describe impact scenarios where the projectile perforates the panel and exits with a residual velocity. The solution is derived from a wave propagation model involving deformation and failure of

Michelle S. Hoo Fatt; Dushyanth Sirivolu

2010-01-01

447

DIAPHRAGM ACTION OF SANDWICH PANELS IN PIN-JOINTED STEEL STRUCTURES: A SEISMIC STUDY  

Microsoft Academic Search

The paper focuses on the seismic response of steel pin-jointed frames braced by lightweight cladding panels. In particular, with the aim to investigate the performance of such a structural scheme when acting as a dissipative system, a wide numerical study has been developed. It is based upon available shear tests on screwed sandwich panels, whose experimental cyclic responses are properly

GIANFRANCO DE MATTEIS; RAFFAELE LANDOLFO

2000-01-01

448

Deep-water sedimentary environments of the northwestern Weddell Sea and South Sandwich Islands, Antarctica  

Microsoft Academic Search

Two transects have been sampled using short cores (multi and box), seabed photography, video sequences, and sediment profile images across the northwestern Weddell Sea and South Sandwich Forearc, Antarctica. A total of 12 core stations were examined for sediment structure, texture and composition to determine their depositional history. Four of the core stations from the Weddell Continental Slope, Abyssal Plain

John A. Howe; Tracy M. Shimmield; Robert Diaz

2004-01-01

449

Thermomechanical vibration of FGM sandwich beam under variable elastic foundations using differential quadrature method  

Microsoft Academic Search

Thermo-mechanical vibration analysis of functionally graded (FG) beams and functionally graded sandwich (FGSW) beams are presented. The functionally graded material (FGM) beams are considered to be resting on variable (i) Winkler foundation and (ii) two-parameter elastic foundation. The material properties of these beams are assumed to be varying in the thickness direction. The governing differential equations for beam vibration are

S. C. Pradhan; T. Murmu

2009-01-01

450

Postbuckling of sandwich plates with FGM face sheets and temperature-dependent properties  

Microsoft Academic Search

Compressive postbuckling under thermal environments and thermal postbuckling due to heat conduction are presented for a simply supported, sandwich plate with FGM face sheets. The material properties of FGM face sheets are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties

Hui-Shen Shen; Shi-Rong Li

2008-01-01

451

Vapour Phase Growth of Thick Monocrystalline GaN Epitaxial Layers by Sandwich-Method.  

National Technical Information Service (NTIS)

We have modified a setup for growing GaN heteroepitaxial layers of large area and obtained 20 such structures on silicon carbide (SiC) and sapphire (Al2O3) substrates of 8 mm2 in size 50-150 micrometers thickness by Sublimation Sandwich Method (SSM). The ...

E. N. Mokov Y. A. Vodakov A. D. Roenkov P. G. Baranov M. E. Boiko

1996-01-01

452

Elastic wave propagation in hexagonal honeycomb sandwich panels: Physical understanding and numerical modeling  

Microsoft Academic Search

This paper gives theoretical and numerical analyses of elastic wave propagation phenomena in sandwich panels with a honeycomb core, especially when the frequency domain of interest is large and involves high frequencies. In the literature, computational models represent rather these panels as an equivalent homogeneous continuum using shell type finite element mesh than use a detailed ``geometrically exact'' finite element

A. Grédé; B. Tie; D. Aubry

2006-01-01

453

Optimal design and parameter estimation of frequency dependent viscoelastic laminated sandwich composite plates  

Microsoft Academic Search

Recent developments in optimization and parameter estimation of frequency dependent passive damping of sandwich structures with viscoelastic core are presented in this paper. A finite element model for anisotropic laminated plate structures with viscoelastic frequency dependent core and laminated anisotropic face layers has been formulated, using a mixed layerwise approach, by considering a higher order shear deformation theory (HSDT) to

A. L. Araújo; C. M. Mota Soares; C. A. Mota Soares; J. Herskovits

2010-01-01

454

The propagation of guided waves in composite, sandwich-like structures and their use for NDT  

Microsoft Academic Search

Guided modes in a sandwich plate are studied. The numerical model takes into account the anisotropy and viscoelasticity properties of skins and core, and the coupling with air surrounding the plate. Dispersion curves and through-thickness fields are predicted for various modes, showing fundamental differences with classical Lamb modes. A strong effect of viscoelasticity on the dispersion curves is also demonstrated.

Michel Castaings; Bernard Hosten

2001-01-01

455

Axisymmetrical vibrations of a circular sandwich shell with a viscoelastic core layer  

Microsoft Academic Search

Axisymmetrical vibration of a finite-length cylindrical sandwich shell with a viscoelastic core layer is investigated. Expressing the viscoelastic property of the core material in terms of a complex shear modulus, the partial differential equation of motion is derived. The solution of this differential equation subject to satisfying the boundary conditions, which have been discussed in detail, yields the frequency equation

H. H. Pan

1969-01-01

456

Effect of Torsion and Warping on the Free Vibration of Sandwich Beams  

Microsoft Academic Search

The problem on free vibrations of wide sandwich beams is tackled in this paper. Torsional and warping effects in addition to flexure are included in the formulation of the dynamic problem. In order to show the effects of bending-torsion coupling and warping on the natural frequencies and the corresponding vibration modes, three cases are considered. First, the warping and torsion

K. S. Numayr; H. A. Qablan

2005-01-01

457

Modeling thick composite laminate and sandwich structures with linear viscoelastic damping  

Microsoft Academic Search

The paper describes the modeling of thick composite laminate and sandwich plates and beams with linear viscoelastic treatments. A discrete laminate model (DLM) is described, validated and compared to numerical spectral finite elements method (SFEM), finite element method (FEM) and experimental results. The DLM approach assumes each layer as thick laminate with orthotropic orientation, rotational inertia and transversal shearing, membrane

Sebastian Ghinet; Noureddine Atalla

2011-01-01

458

Vibration analysis of composite sandwich beams with viscoelastic core by using differential transform method  

Microsoft Academic Search

This paper deals with the vibration analysis of a three layered composite beam with a viscoelastic core. First, the equations of motion that govern the free vibrations of the sandwich beam are derived by applying Hamilton’s principle. Then, these equations are solved by using differential transform method (DTM) in the frequency domain. The variation of modal loss factor with system

Aytac Arikoglu; Ibrahim Ozkol

2010-01-01

459

Compression-after-Impact Strength of Sandwich Panels with Core Crushing Damage  

NASA Astrophysics Data System (ADS)

Compression-after-impact (CAI) strength of foam-cored sandwich panels with composite face sheets is investigated experimentally. The low-velocity impact by a semi-spherical (blunt) projectile is considered, producing a damage mainly in a form of core crushing accompanied by a permanent indentation (residual dent) in the face sheet. Instrumentation of the panels by strain gauges and digital speckle photography analysis are used to study the effect of damage on failure mechanisms in the panel. Residual dent growth inwards toward the mid-plane of a sandwich panel followed by a complete separation of the face sheet is identified as the failure mode. CAI strength of sandwich panels is shown to decrease with increasing impact damage size. Destructive sectioning of sandwich panels is used to characterise damage parameters and morphology for implementation in a finite element model. The finite element model that accounts for relevant details of impact damage morphology is developed and proposed for failure analysis and CAI strength predictions of damaged panels demonstrating a good correlation with experimental results.

Shipsha, Andrey; Zenkert, Dan

2005-05-01

460

Response of Composite Fuselage Sandwich Side Panels Subjected to Internal Pressure and Axial Tension  

NASA Technical Reports Server (NTRS)

The results from an experimental and analytical study of two composite sandwich fuselage side panels for a transport aircraft are presented. Each panel has two window cutouts and three frames and utilizes a distinctly different structural concept. These panels have been evaluated with internal pressure loads that generate biaxial tension loading conditions. Design limit load and design ultimate load tests have been performed on both panels. One of the sandwich panels was tested with the middle frame removed to demonstrate the suitability of this two-frame design for supporting the prescribed biaxial loading conditions with twice the initial frame spacing of 20 inches. A damage tolerance study was conducted on the two-frame panel by cutting a notch in the panel that originates at the edge of a cutout and extends in the panel hoop direction through the window-belt area. This panel with a notch was tested in a combined-load condition to demonstrate the structural damage tolerance at the design limit load condition. Both the sandwich panel designs successfully satisfied all desired load requirements in the experimental part of the study, and experimental results from the two-frame panel with and without damage are fully explained by the analytical results. The results of this study suggest that there is potential for using sandwich structural concepts with greater than the usual 20-in. wide frame spacing to further reduce aircraft fuselage structural weight.

Rouse, Marshall; Ambur, Damodar R.; Dopker, Bernard; Shah, Bharat

1998-01-01

461

Non-linear finite element analysis of inserts in composite sandwich structures  

Microsoft Academic Search

In aeronautics, sandwich structures are widely used for secondary structures like flaps, landing gear doors or commercial equipment. The technologies used to join these kinds of structures are numerous: direct bonding or joining, tapered areas, T-joints, etc. The most common is certainly the use of local reinforcement called an insert. The insert technologies are numerous and this study focuses on

P. Bunyawanichakul; B. Castanié; J.-J. Barrau

2008-01-01

462

Development and Validation of Sandwich ELISA Microarrays with Minimal Assay Interference  

Microsoft Academic Search

Sandwich enzyme-linked immunosorbent assay (ELISA) microarrays are emerging as a strong candidate platform for multiplex biomarker analysis because of the ELISAs ability to quantitatively measure rare proteins in complex biological fluids. Advantages of this platform are high-throughput potential, assay sensitivity and stringency, and the similarity to the standard ELISA test, which facilitates assay transfer from a research setting to a

Rachel M. Gonzalez; Shannon L. Seurynck-Servoss; Sheila A. Crowley; Marty Brown; Gilbert S. Omenn; Daniel F. Hayes; Richard C. Zangar

2008-01-01

463

A Viscoelastic Sandwich Finite Element Model for the Analysis of Passive, Active and Hybrid Structures  

Microsoft Academic Search

In this paper we present a finite element model for the analysis of active sandwich laminated plates with a viscoelastic core and laminated anisotropic face layers, as well as piezoelectric sensor and actuator layers. The model is formulated using a mixed layerwise approach, by considering a higher order shear deformation theory (HSDT) to represent the displacement field of the viscoelastic

Aurelio L. Araújo; Cristovao M. Mota Soares; Carlos A. Mota Soares

2010-01-01

464

A numerical study of free and forced vibration of composite sandwich beam with viscoelastic core  

Microsoft Academic Search

In this article, higher order theory for sandwich beam with composite faces and viscoelastic core is achieved by considering independent transverse displacements on two faces and linear variations through the depth of the beam core. In addition, the effects of Young modulus, rotational inertia and core kinetic energy are considered to modify the “Mead & Markus” theory that is used

H. Arvin; M. Sadighi; A. R. Ohadi

2010-01-01

465

Sensitivity analysis of frequency response functions of composite sandwich plates containing viscoelastic layers  

Microsoft Academic Search

In the scope of structural dynamics, sensitivity analysis is a very useful tool in a number of numerical procedures such as parameter identification, model updating, optimal design and uncertainty propagation. In this paper the formulation of first-order sensitivity analysis of complex frequency response functions (FRFs) is developed for composite sandwich plates composed by a combination of fiber-reinforced and elastomeric viscoelastic

A. M. G. de Lima; A. W. Faria; D. A. Rade

2010-01-01

466