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1

Sandwich construction  

NASA Astrophysics Data System (ADS)

A form of composites known as structural sandwich construction is presented in terms of materials used, design details for solving edging and attachment problems, and charts of design material analysis. Sandwich construction is used in nearly all commercial airliners and helicopters, and military air and space vehicles, and it is shown that this method can stiffen a structure without causing a weight increase. The facing material can be made of 2024 or 7075 aluminum alloy, titanium, or stainless steel, and the core material can be wood or foam. The properties of paper honeycomb and various aluminum alloy honeycombs are presented. Factors pertaining to adhesive materials are discussed, including products given off during cure, bonding pressure, and adaptability. Design requirements and manufacturing specifications are resolved using numerous suggestions.

Marshall, A.

2

Sandwich Construction Solar Structural Facets  

SciTech Connect

Silver/glass mirrors have excellent optical properties but need a method of support in order to be used in concentrating solar thermal systems. In collaboration with the Cummins dish/Stirling development program, they started investigating sandwich construction as a way to integrate silver/glass mirrors into solar optical elements. In sandwich construction, membranes such as sheet metal or plastic are bonded to the front and back of a core (like a sandwich). For solar optical elements, a glass mirror is bonded to one of the membranes. This type of construction has the advantages of a high strength-to-weight ratio, and reasonable material and manufacturing cost. The inherent stiffness of sandwich construction mirror panels also facilitates large panels. This can have cost advantages for both the amount of hardware required as well as reduced installation and alignment costs. In addition, by incorporating the panels into the support structure reductions in the amount of structural support required are potentially possible.

Diver, R. B.; Grossman, J.W.

1998-12-22

3

Sandwich construction solar structural facets  

SciTech Connect

Silver/glass mirrors have excellent optical properties but need a method of support in order to be used in concentrating solar thermal systems. In collaboration with the Cummins dish/Stirling development program, the authors started investigating sandwich construction as a way to integrate silver/glass mirrors into solar optical elements. In sandwich construction, membranes such as sheet metal or plastic are bonded to the front and back of a core (like a sandwich). For solar optical elements, a glass mirror is bonded to one of the membranes. This type of construction has the advantages of a high strength-to-weight ratio, and reasonable material and manufacturing cost. The inherent stiffness of sandwich construction mirror panels also facilitates large panels. This can have cost advantages for both the amount of hardware required as well as reduced installation and alignment costs. In addition, by incorporating the panels into the support structure reductions in the amount of structural support required are potentially possible. The authors have investigated sandwich construction panels that employ cores of polystyrene, polyvinyl chloride (PVC) and polyurethane foams as well as conventional aluminum and cardboard honeycombs. The authors investigations have involved fabricating 0.5 x 0.6-m (20 x 24-inch) spherical-contour panels and testing their optical properties and environmental durability. The authors have also performed preliminary cost and performance studies. Evaluations included optical testing with the SunLab 2f and VSHOT tools both before and after exposures to environmental chamber testing. The results showed that sandwich mirror panels are potentially very accurate. However, long-term degradation due to creep was evident in all of the foam core facets. The aluminum honeycomb core facets were accurate and durable. In this paper, the design principles that guided the investigations, estimates of cost, and the results of the experimental investigations are presented.

Diver, R.B.; Grossman, J.W.

1999-07-01

4

Adhesively bonded steel corrugated core sandwich construction for marine applications  

Microsoft Academic Search

The aims of this research were to fabricate an adhesively bonded steel corrugated core sandwich construction suitable for marine applications and to investigate the performance characteristics and failure mechanisms in comparison with other methods of fabrication. Construction of steel corrugated core sandwich structures for the marine industry are shown to be viable using modern structural adhesives. These sandwich structures are

E. M. Knox; M. J. Cowling; I. E. Winkle

1998-01-01

5

Environmental Evaluation of Polyurethane Foam Core Sandwich Panel Construction.  

National Technical Information Service (NTIS)

An environmental evaluation of a sandwich panel bearing wall system for use in one of the Operation Breakthrough housing systems is described. Two samples of polyurethane foam core sandwich construction and four full size wall panels were evaluated. The s...

J. R. Shaver, L. W. Masters, T. W. Reichard, J. H. Pielert

1972-01-01

6

Structural sandwich construction is used in many air and space vehicles, cargo containers, boats and ships. Connection of the sandwich construction component to a framework or substructure  

E-print Network

; tapered joint; tapered sandwich beam; honeycomb core. INTRODUCTION Sandwich construction is one-to-weight ratio and high bending strength. A typical sandwich beam or panel usually consists of honeycomb, foamABSTRACT Structural sandwich construction is used in many air and space vehicles, cargo containers

Vel, Senthil

7

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

8

Transverse Shear Stiffness of a Chevron Folded Core Used in Sandwich Construction  

E-print Network

and that in some cases chevron folded cores are 40% stiffer than honeycomb-like cores. Key words: Sandwich panelsTransverse Shear Stiffness of a Chevron Folded Core Used in Sandwich Construction A. Leb´ee, K. Sab trans- verse shear moduli of a chevron folded core used in sandwich construction are analytically

Boyer, Edmond

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

A study on composite honeycomb sandwich panel structure  

Microsoft Academic Search

Honeycomb sandwich structure combines high flexural rigidity and bending strength with low weight. Sandwich construction plays an increasing role in industry, and sandwich structural designing is an available method for sandwich structures. However, the absence of the design variable is the principal problem of composite sandwich construction. In this paper, the structure and mechanical properties of honeycomb sandwich panels are

Meifeng He; Wenbin Hu

2008-01-01

11

Honeycomb core material for sandwich construction - with common hexagonal walls bonded by thermoplastic resin and free walls carrying layer of resin and masking agent  

Microsoft Academic Search

Abstract:of NL 8902116 (A) \\u000aIn a honeycomb core material for a sandwich construction, the common hexagonal walls are bonded together by a thermoplastic resin, and the free hexagonal walls carry a layer of the same resin and also a masking agent. - A number of plates of raw material are given strips of glue, are laid on one another, and

1991-01-01

12

sandwich structure  

NASA Astrophysics Data System (ADS)

This study investigates the extent to which the TiO2/graphene/TiO2 sandwich structure improves the performance of dye-sensitized solar cells (DSSCs) over that of DSSCs with the traditional structure. Studies have demonstrated that the TiO2/graphene/TiO2 sandwich structure effectively enhances the open circuit voltage ( V oc), short-circuit current density ( J sc), and photoelectrical conversion efficiency ( ?) of DSSCs. The enhanced performance of DSSCs with the sandwich structure can be attributed to an increase in electron transport efficiency and in the absorption of light in the visible range. The DSSC with the sandwich structure in this study exhibited a V oc of 0.6 V, a high J sc of 11.22 mA cm-2, a fill factor (FF) of 0.58, and a calculated ? of 3.93%, which is 60% higher than that of a DSSC with the traditional structure.

Chen, Lung-Chien; Hsu, Chih-Hung; Chan, Po-Shun; Zhang, Xiuyu; Huang, Cing-Jhih

2014-08-01

13

DEVELOPMENT OF BRAZED SANDWICH CONSTRUCTION MATERIALS FOR HIGH TEMPERATURE APPLICATIONS. Period covered: February 15, 1956 to August 15, 1957  

Microsoft Academic Search

An investigation was undertaken to study various base metal-braze alloy ; combinations for honeycomb sandwich structures that would have utllity up to a ; maximum temperature of 1200 F. The base alloys, 17-7PH, 422, A286, 19-9DL,,and ; 17-14 Cu Mo were evaluated silver and nickel base brazing alloys to determine ; their compatability and strength characteristics to develop am optimum

C. F. Burrows; F. J. Jr. Ragland

1957-01-01

14

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

15

Elastic Coupling Effects in Tapered Sandwich Panels with Laminated  

E-print Network

studies. KEY WORDS: sandwich construction, honeycomb core, tapered composite, finite element analysis or panel usually consists of honeycomb, foam, or low-density wood cores sandwiched between isotropicElastic Coupling Effects in Tapered Sandwich Panels with Laminated Anisotropic Composite Facings

Vel, Senthil

16

The strength characteristics of aluminum honeycomb sandwich panels  

Microsoft Academic Search

Aluminum sandwich construction has been recognized as a promising concept for structural design of lightweight transportation systems such as aircraft, high-speed trains and fast ships. The aim of the present study is to investigate the strength characteristics of aluminum sandwich panels with aluminum honeycomb core theoretically and experimentally. A series of strength tests are carried out on aluminum honeycomb-cored sandwich

Jeom Kee Paik; Anil K Thayamballi; Gyu Sung Kim

1999-01-01

17

INNOVATIVE 3-D FRP SANDWICH PANELS FOR BRIDGE DECKS TAREK K. HASSAN (1)  

E-print Network

construction technology made of composite materials. Currently, foam and honeycomb core sandwich composites. The cores used in sandwich construction can be divided into four main groups; corrugated, honeycomb, balsa wood and foams. Balsa wood was the first core material to be used in sandwich construction. Honeycomb

18

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

19

Impact analysis of fiber reinforced polymer honeycomb composite sandwich beams  

Microsoft Academic Search

Large scale fiber reinforced polymer (FRP) composite structures have been used in highway bridge and building construction. Recent applications have demonstrated that FRP honeycomb sandwich panels can be effectively and economically applied for both new construction and rehabilitation and replacement of existing structures. This paper is concerned with impact analysis of an as-manufactured FRP honeycomb sandwich system with sinusoidal core

Pizhong Qiao; Mijia Yang

2007-01-01

20

Failure behaviour of honeycomb sandwich corner joints and inserts  

Microsoft Academic Search

In nearly all sandwich constructions certain types of joints have to be used for assembly, but little is known about their failure behaviour. This paper deals with the investigation of the mechanical behaviour of three different corner joints as a right-angled connection of two sandwich panels and of two different potted inserts as a localised load introduction in Nomex® honeycomb

Sebastian Heimbs; Marc Pein

2009-01-01

21

Underwater blast loading of sandwich beams: Regimes of behaviour  

Microsoft Academic Search

Finite element (FE) calculations are used to develop a comprehensive understanding of the dynamic response of sandwich beams subjected to underwater blast loading, including the effects of fluid–structure interaction. Design maps are constructed to show the regimes of behaviour over a broad range of loading intensity, sandwich panel geometry and material strength. Over the entire range of parameters investigated, the

M. T. Tilbrook; V. S. Deshpande; N. A. Fleck

2009-01-01

22

Design of Sandwich Structures  

E-print Network

Failure modes for sandwich beams of GFRP laminate skins and Nomex honeycomb core are investigated. Theoretical models using honeycomb mechanics and classical beam theory are described. A failure mode map for loading under 3-point bending...

Petras, Achilles

23

Failure mode maps for honeycomb sandwich panels  

Microsoft Academic Search

Failure modes for sandwich beams of GFRP laminate skins and Nomex honeycomb core are investigated. Theoretical models using honeycomb mechanics and classical beam theory are described. A failure mode map for loading under 3-point bending is constructed, showing the dependence of failure mode and load on the ratio of skin thickness to span length and honeycomb relative density. Beam specimens

A. Petras; M. P. F. Sutcliffe

1999-01-01

24

Designing structural sandwich composites  

SciTech Connect

Composite sandwich structures have been used in aircraft for many years. Most are based on honeycomb cores with relatively high modulus composite skin materials. Today, with increasing use of composites in many other markets, designing structural sandwich composites has become very important. Most of these applications use relatively low modulus composite skins and a low density core other than honeycomb. The mechanics and the failure mode of these sandwich structures differ significantly from honeycomb core structures. Designers of structural sandwich composites must take into account not only the safety of a structural part, defined as strength design, but the functionality of the part as well. Doing so requires rigidity design, in which both strength and deflection requirements must be met. The process of optimizing dimensions is initially based on rigidity requirements. Once these are met, strength verification can be carried out. In addition to design strength and rigidity, the designer must also select structural core material which meets the temperature, pressure, and processing conditions of molding composite sandwich skins, a core material which results in good skin-to-core bonding, and one which provides good economics. ISORCA has been conducting research and development on a new concept of structural syntactic phenolic foam, called Alba-Core{trademark}. It excels in shear modulus, compression strength, temperature stability, skin resin absorption, skin bonding, smoke, flame, toxicity, and moisture absorption. It is moldable to any shape, can be made with domestic raw materials, and has very attractive economics.

Meteer, C.L. [ISORCA, Inc., Granville, OH (United States)

1996-11-01

25

Development of carbon-carbon sandwich panels  

NASA Astrophysics Data System (ADS)

The Electrostatic Gravity Gradiometer (EGG) is the main payload of the Gravity field and steady state Ocean Circulation Explorer (GOCE) mission, which has the objectives of producing models of the Earth's gravity field and geoid with high resolution and accuracy. The EGG allows measuring the components of the gravity gradient tensor by means of a set of accelerometers. To meet the outstanding measurement requirements, the EGG structure must provide high dimensional stability under the expected environmental conditions. Carbon-Carbon technology has been selected for the construction of the sandwich panels, which support the accelerometers and their electronics, as well as the thermal control unit. This technology in fact offers good thermo-elastic characteristics, low sensitivity to moisture (only for organic assembly), high panel stiffness-to-mass ratio. Due to the lack of heritage for large-size sandwich structures, a dedicated evaluation and qualification program has been established for the demonstration of the suitability of the sandwich and associated manufacturing processes to the GOCE applications. Following the evaluation of candidate materials and associated bonding techniques, a preferred baseline has been selected that is undergoing qualification testing. A safe two-steps manufacturing process of the sandwich panels has been adopted: C/C face-sheets and honeycomb cores are procured from Hitco Carbon Composites Inc, USA, and their assembly is performed by Alcatel Space through organic bonding, to obtain the final sandwich structure. The results of the evaluation and of the first qualification tests are presented in the paper.

Panin, Fabio; Lutz-Nivet, Martine; Lemaire, Hugues

2003-09-01

26

Buckling of cylindrical sandwich shells with metal foam cores J.W. Hutchinson a,*, M.Y. He b  

E-print Network

producing sandwiches without the usual environmental and delamination susceptibilities of honeycomb and Sobel (1977) established the weight competitiveness of a honeycomb sandwich construction for cylindrical of these sandwiches is much greater than that for honeycomb construction. Indeed, Budiansky (1999) has found that ¯at

Hutchinson, John W.

27

Homogenization of sandwich structures  

Microsoft Academic Search

SUMMARY A homogenization method is proposed for sandwich structures consisting of two plates interlaced with beams and shells in a periodic, lattice structure. The proposed method is a quasi-continuum approach where the constitutive response is obtained from the generalized forces of the interlacing elements. Buckling is studied as part of this model. Comparison of the homogenized model with fully discrete

T. Rabczuk; J. Y. Kim; E. Samaniego; T. Belytschko

2004-01-01

28

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.

29

Composite Sandwich Panels  

NSDL National Science Digital Library

This module, created by Brian D. Finn of the University of Washington, "investigates the fundamental aspects of designing composite sandwich panels." These boards are commonly used to create surfboards, wake boards, and corrugated cardboard. They are also heavily implemented in the aerospace industry; this includes items such as wing flaps, aircraft floors and overhead storage bins. The module features an abstract, objective, curriculum overview, procedures, mathematical calculations and references. In the end, students will learn to build, test and analyze the strength of these composite materials.

Finn, Brian

2009-09-30

30

Fatigue performance of sandwich beams with a pyramidal core F. Co^te, N.A. Fleck, V.S. Deshpande *  

E-print Network

Abstract Sandwich beams have been manufactured from AISI type 304 stainless steel faces and AL6XN pyramidal as useful design guides, and take the sandwich beam geometry as axes. The construction of the maps takes

Fleck, Norman A.

31

Thermomechanical response of metal foam sandwich panels for structural thermal protection systems in hypersonic vehicles  

Microsoft Academic Search

Sandwich panels with metal foam cores are proposed for load-bearing structural components in actively cooled thermal protection systems for aerospace vehicles. Prototype acreage metal foam sandwich panels (MFSP's) are constructed and analyzed with the central goal of characterizing the thermomechanical response of the system. MFSP's are subjected to uniform temperature fields and equibiaxial loading in a novel experimental load frame.

Joseph F. Rakow

2005-01-01

32

Impact Damage of Partially Foam-filled Co-injected Honeycomb Core Sandwich Composites  

Microsoft Academic Search

The present study considers filling of honeycomb type cores with foam to produce sandwich constructions. The potential benefits of this approach are enhancement of damage resistance, and ability to process honeycomb type sandwich structures through cost-effective vacuum assisted resin transfer molding (VARTM). As weight penalty is incurred in complete filling of honeycomb cells with foam, an alternative approach to reduce

Uday K Vaidya; C. Ulven; S. Pillay; H. Ricks

2003-01-01

33

On the dynamic response of sandwich composites and their core materials  

Microsoft Academic Search

Sandwich composites are being aggressively pursued as structural materials by various defense and commercial industries. These include navy, air force, army, automotive and sporting industries to name a few. In the context of structural load bearing members and absorbing dynamic loads, foam core sandwich composites offer unique advantages over traditional composites. The cellular construction of the foam materials not only

Hassan Mahfuz; Tonnia Thomas; Vijay Rangari; Shaik Jeelani

2006-01-01

34

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

35

Facesheet Delamination of Composite Sandwich Materials at Cryogenic Temperatures  

NASA Technical Reports Server (NTRS)

The next generation of space transportation vehicles will require advances in lightweight structural materials and related design concepts to meet the increased demands on performance. One potential source for significant structural weight reduction is the replacement of traditional metallic cryogenic fuel tanks with new designs for polymeric matrix composite tanks. These new tank designs may take the form of thin-walled sandwich constructed with lightweight core and composite facesheets. Life-time durability requirements imply the materials must safely carry pressure loads, external structural loads, resist leakage and operate over an extremely wide temperature range. Aside from catastrophic events like tank wall penetration, one of the most likely scenarios for failure of a tank wall of sandwich construction is the permeation of cryogenic fluid into the sandwich core and the subsequent delamination of the sandwich facesheet due to the build-up of excessive internal pressure. The research presented in this paper was undertaken to help understand this specific problem of core to facesheet delamination in cryogenic environments and relate this data to basic mechanical properties. The experimental results presented herein provide data on the strain energy release rate (toughness) of the interface between the facesheet and the core of a composite sandwich subjected to simulated internal pressure. A unique test apparatus and associated test methods are described and the results are presented to highlight the effects of cryogenic temperature on the measured material properties.

Gates, Thomas S.; Odegard, Gregory M.; Herring, Helen M.

2003-01-01

36

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

37

Hybrid inorganic-organic polyrotaxane, pseudorotaxane, and sandwich.  

PubMed

Inorganic copper(I)/silver(I) halide/pseudohalide components are used to thread classical organic tetracationic macrocycles, cyclobis(paraquat-p-phenylene) and cyclobis(paraquat-4,4'-biphenylene), to construct crystalline inorganic-organic adducts, featuring an unprecedented hybrid polyrotaxane and several unusual hybrid pseudorotaxanes and sandwiches. PMID:24003939

Yu, Li; Li, Mian; Zhou, Xiao-Ping; Li, Dan

2013-09-16

38

A small-deflection theory for curved sandwich plates  

NASA Technical Reports Server (NTRS)

A small-deflection theory that takes into account deformations due to transverse shear is presented for the elastic-behavior analysis of orthotropic plates of constant cylindrical curvature, with consideration of buckling included. The theory is applicable primarily to sandwich construction. (author)

Stein, Manuel; Mayers, J

1951-01-01

39

Web buckling behavior under in-plane compression and shear loads for web reinforced composite sandwich core  

Microsoft Academic Search

Sandwich construction is one of the most functional forms of composite structures developed by the composite industry. Due to the increasing demand of web-reinforced core for composite sandwich construction, a research study is needed to investigate the web plate instability under shear, compression, and combined loading. If the web, which is an integral part of the three dimensional web core

Elias Anis Toubia

2008-01-01

40

Cellular Truss Core Sandwich Structures  

Microsoft Academic Search

Sandwich structures with open cell truss cores are a relatively new class of multifunctional material systems that can be made using affordable deformation, assembly and joining processes. A variety of cellular core architectures have recently been made from wrought metal alloys using inexpensive textile and perforated sheet methods. Here, the design, fabrication and properties for these types of structures is

David J. Sypeck

2005-01-01

41

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

42

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.

43

Wrinkling Prevention Methods for Sandwich Panel Structure  

NASA Astrophysics Data System (ADS)

In this paper, we proposed a method for preventing the wrinkling of the facings of a sandwich panel whose outer and inner facings were at different temperatures. By using this method, the wrinkling of the outer facing of a sandwich panel structure, such as a sandwich panel refrigerator box, could be prevented. In order to prevent the facings of the structure from wrinkling, it was necessary to determine the wrinkling strength using a compressive test, and to reduce the thermal stress of the sandwich panel structure to less than the wrinkling strength. It was observed that a sandwich panel structure with slits in the facing reduced the thermal stress. In this study, we used sandwich panel containers to examine whether this proposed method could prevent a sandwich panel from wrinkling.

Dahara, Koichiro; Sanmaru, Kazuya; Yano, Toshihiro; Noguchi, Hiroshi

44

Veterans' informal caregivers in the "sandwich generation": a systematic review toward a resilience model.  

PubMed

Social work theory advanced the formulation of the construct of the sandwich generation to apply to the emerging generational cohort of caregivers, most often middle-aged women, who were caring for maturing children and aging parents simultaneously. This systematic review extends that focus by synthesizing the literature on sandwich generation caregivers for the general aging population with dementia and for veterans with dementia and polytrauma. It develops potential protective mechanisms based on empirical literature to support an intervention resilience model for social work practitioners. This theoretical model addresses adaptive coping of sandwich- generation families facing ongoing challenges related to caregiving demands. PMID:24611766

Smith-Osborne, Alexa; Felderhoff, Brandi

2014-01-01

45

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

46

High Strain Rate Response of Sandwich Composites with Nanophased Cores  

Microsoft Academic Search

Polyurethane foam materials have been used as core materials in a sandwich construction with S2-Glass\\/SC-15 facings. The foam material has been manufactured from liquid polymer precursors of polyurethane. The precursors are made of two components; part-A (diphenylmethane diisocyanate) and part-B (polyol). In one set of experiments, part-A was mixed with part-B to manufacture the foam. In another set, TiO2 nanoparticles

Hassan Mahfuz; Mohammed F. Uddin; Vijaya K. Rangari; Mrinal C. Saha; Shaik Zainuddin; Shaik Jeelani

2005-01-01

47

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

48

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

2014-05-13

49

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

50

Facesheet Wrinkling in Sandwich Structures  

NASA Technical Reports Server (NTRS)

The purpose of this paper is to provide a concise summary of the state-of-the-art for the analysis of the facesheet wrinkling mode of failure in sandwich structures. This document is not an exhaustive review of the published research related to facesheet wrinkling. Instead, a smaller number of key papers are reviewed in order to provide designers and analysts with a working understanding of the state-of-the-art. Designers and analysts should use this survey to guide their judgement when deciding which one of a wide variety of available facesheet wrinkling design formulas is applicable to a specific design problem.

Ley, Robert P.; Lin, Weichuan; Mbanefo, Uy

1999-01-01

51

Cellular Metal Truss Core Sandwich Structures**  

E-print Network

rigidity. Honeycomb core sandwich structures are the current state-of-the-art choice for weight sensitiveCellular Metal Truss Core Sandwich Structures** By David J. Sypeck* and Haydn N. G. Wadley 1. Introduction Cellular metals have attracted interest as alternatives to honeycomb when used as the cores

Wadley, Haydn

52

Sandwich SPS Model at the IAC Exhibition  

Microsoft Academic Search

power generator \\/ transmitter of the sandwich structure and large reflectors. The concept has many benefits: (1) Heavy long power transmission lines on the solar paddles and a rotary joint for the connection between the solar paddles and the microwave transmitter are unnecessary for the sandwich concept, because the solar cells are directly and shortly connected to high power amplifiers.

N. Kaya; M. Iwashita; Y. Okuda; H. Ashina; Y. Sakaguchi

2002-01-01

53

Properties of polyurethane foam/coconut coir fiber as a core material and as a sandwich composites component  

NASA Astrophysics Data System (ADS)

This research focuses on the fabrication and characterization of sandwich composite panels using glass fiber composite skin and polyurethane foam reinforced coconut coir fiber core. The main objectives are to characterize the physical and mechanical properties and to elucidate the effect of coconut coir fibers in polyurethane foam cores and sandwich composite panels. Coconut coir fibers were used as reinforcement in polyurethane foams in which later were applied as the core in sandwich composites ranged from 5 wt% to 20 wt%. The physical and mechanical properties found to be significant at 5 wt% coconut coir fiber in polyurethane foam cores as well as in sandwich composites. It was found that composites properties serve better in sandwich composites construction.

Azmi, M. A.; Abdullah, H. Z.; Idris, M. I.

2013-12-01

54

Assessment of sandwich models for the prediction of sound transmission loss in unidirectional sandwich panels  

Microsoft Academic Search

The consistent higher-order approach and the two-parameter foundation formulation are used for the derivation of sound transmission loss in symmetric unidirectional (infinitely wide) sandwich panels with isotropic face sheets. In both models, transmission loss is calculated using decoupled equations representing symmetric and anti-symmetric motions of a sandwich panel. The closed-form expressions for impedances and transmission coefficient of a symmetric sandwich

Tongan Wang; Vladimir S. Sokolinsky; Shankar Rajaram; Steven R. Nutt

2005-01-01

55

Shear lag in truss core sandwich beams  

E-print Network

An experimental study was conducted to investigate the possible influence of shear lag in the discrepancy between the theoretical and measured stiffness of truss core sandwich beams. In previous studies, the measured values ...

Roberts, Ryan (Ryan M.)

2005-01-01

56

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.

57

Fracture behavior of some lightweight sandwich structures  

SciTech Connect

The mechanical flexural properties of foams and honeycombs are studied using three-point bending tests. It is suggested that the role of adhesives and their interface properties are considered with various attached skin and core structures for high performance light weight composites. The results of acoustic emission analysis on the foam core sandwich structures are also identified. In compared foam sandwich structure with that of honeycomb, more enhanced role of interface are observed in foam cores.

Lee, J.R.; Park, S.J. [Korea Research Inst. of Chemical Technology, Taejeon (Korea, Republic of). Polymer and Composite Materials Lab.

1995-10-01

58

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

59

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

60

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

61

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

62

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

63

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

64

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

65

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

66

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

67

Sandwiched Rényi divergence satisfies data processing inequality  

SciTech Connect

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 http://arxiv.org/abs/arXiv:1306.1586 (2013)] and Müller-Lennert et al. [“On quantum Rényi entropies: a new definition, some properties and several conjectures,” preprint http://arxiv.org/abs/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 [School of Mathematics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5746, Tehran (Iran, Islamic Republic of)] [School of Mathematics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5746, Tehran (Iran, Islamic Republic of)

2013-12-15

68

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

69

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

70

Eigenmode sensitivity of damped sandwich structures  

NASA Astrophysics Data System (ADS)

The modeling of the linear free vibration of a sandwich structure including viscoelastic layers yields a complex nonlinear eigenvalue problem. In this paper, the sensitivity of eigensolutions is computed using a homotopy-based asymptotic numerical method, then a first-order automatic differentiation. The generality of the proposed method enables us to consider any analytical frequency-dependent viscoelastic law in the modeling and the sensitivity computation. Its application potential is demonstrated by computing the sensitivity of eigenmodes, eigenfrequencies and modal loss factors of sandwich beams and plates to various perturbations. xml:lang="fr"

Lampoh, Komlanvi; Charpentier, Isabelle; El Mostafa, Daya

2014-12-01

71

Damage Tolerance of Naval Sandwich Panels  

NASA Astrophysics Data System (ADS)

This paper is a review of activities concerning various damage tolerance modelling and testing aspects of sandwich panels for typical Naval applications. It starts with a review of testing methods for primarily core materials and how to extract properties and data required for damage tolerance assessment. Next some typical damage types are defined and how they are modelled with the aim of predicting their effect on load bearing capacity. The paper then describes in brief how such models can used in the context of providing a systematic damage assessment scheme for composite sandwich ship structures.

Zenkert, Dan

72

High Strain Rate Response of Sandwich Composites with Nanophased Cores  

NASA Astrophysics Data System (ADS)

Polyurethane foam materials have been used as core materials in a sandwich construction with S2-Glass/SC-15 facings. The foam material has been manufactured from liquid polymer precursors of polyurethane. The precursors are made of two components; part-A (diphenylmethane diisocyanate) and part-B (polyol). In one set of experiments, part-A was mixed with part-B to manufacture the foam. In another set, TiO2 nanoparticles have been dispersed in part-A through ultrasonic cavitation technique. The loading of nanoparticles was 3% by weight of the total polymer precursor. The TiO2 nanoparticles were spherical in shape, and were about 29 nm in diameter. Sonic cavitation was carried out with a vibrasound liquid processor at 20 kHz frequency with a power intensity of about 100 kW/m2. The two categories of foams manufactured in this manner were termed as neat and nanophased. Sandwich composites were then fabricated using these two categories of core materials using a co-injection resin transfer molding (CIRTM) technique. Test samples extracted from the panel were subjected to quasi-static as well as high strain rate loadings. Rate of loading varied from 0.002 s-1 to around 1300 s-1. It has been observed that infusion of nanoparticles had a direct correlation with the cell geometry. The cell dimensions increased by about 46% with particle infusion suggesting that nanoparticles might have worked as catalysts during the foaming process. Correspondingly, enhancement in thermal properties was also noticed especially in the TGA experiments. There was also a significant improvement in mechanical properties due to nanoparticle infusion. Average increase in sandwich strength and energy absorption with nanophased cores was between 40 60% over their neat counterparts. Details of manufacturing and analyses of thermal and mechanical tests are presented in this paper.

Mahfuz, Hassan; Uddin, Mohammed F.; Rangari, Vijaya K.; Saha, Mrinal C.; Zainuddin, Shaik; Jeelani, Shaik

2005-05-01

73

Mechanical behavior of dip-brazed aluminum sandwich panels  

E-print Network

An experimental study was carried out to determine the mechanical behavior of sandwich panels containing cellular cores of varying shape. Compression and four point bend tests were performed on sandwich panels with square ...

Hohmann, Brian P. (Brian Patrick)

2007-01-01

74

Feedback Sandwiches Affect Perceptions but Not Performance  

ERIC Educational Resources Information Center

The feedback sandwich technique-make positive comments; provide critique; end with positive comments-is commonly recommended to feedback givers despite scant evidence of its efficacy. These two studies (N = 20; N = 350) of written peer feedback with third-year medical students on clinical patient note-writing assignments indicate that students…

Parkes, Jay; Abercrombie, Sara; McCarty, Teresita

2013-01-01

75

Career Counseling for the Sandwich Generation.  

ERIC Educational Resources Information Center

The Sandwich Generation refers to individuals who have multiple caregiving responsibilities for children under 18, as well as parents, grandparents or other aging relatives. Employees who are the caregivers cannot help but bring the stress of the situation to the workplace. Existing research suggests that these responsibilities take a toll on…

Byrd, Virginia

76

Self-healing composite sandwich structures  

Microsoft Academic Search

Impact damage can degrade the flexural strength of composite sandwich structures by over 50% due to a loss of skin support inducing localized skin buckling. Various self-healing methodologies have been applied to laminated composites but the concept of delivering a healing agent from a remote reservoir to a region of damage via a vascular network offers the potential for a

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

2007-01-01

77

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

78

MODAL DENSITY OF COMPOSITE HONEYCOMB SANDWICH PANELS  

Microsoft Academic Search

Honeycomb sandwich panels with composite face sheets are widely used in spacecraft applications. It is necessary to obtain the modal density of such panels to study their behaviour under acoustic excitation. The governing differential equation, with consideration of the shear flexibility of the core, is derived. From this equation the expression for the modal density is derived. Experimental results for

K. Renji; P. S. Nair; S. Narayanan

1996-01-01

79

Blast Impact on Aluminum Foam Composite Sandwich Panels  

Microsoft Academic Search

Sandwich aluminum foam structures are being considered for energy absorption applications, crashworthiness, protection of transformer housings, and structural safety. Blast loading is one such phenomenon that is a potential threat to such structures. This study examines LS-DYNA modeling for aluminum foam sandwich composites subjected to blast loads. The sandwich composite was designed using polymer composite facesheets and aluminum foam as

Rajan Sriram; Uday K. Vaidya

80

Mechanical properties of an extruded pyramidal lattice truss sandwich structure  

E-print Network

and electrodischarge machining has been used to fabricate pyramidal lattice sandwich structures from 6061 alu- minum reserved. Keywords: 6061; Lattice truss structure; Cellular material Lightweight sandwich panel structures to solid face- sheets to form a sandwich structure. The lattice topol- ogy, core relative density

Wadley, Haydn

81

Structural performance of metallic sandwich beams with hollow truss cores  

E-print Network

; Lightweight structures; Hollow tube core 1. Introduction Metallic sandwich panels with various honeycomb, latStructural performance of metallic sandwich beams with hollow truss cores H.J. Rathbun a , F.W. Zok of sandwich beams with hollow truss lattice cores made from a ductile stainless steel. The trusses

Wadley, Haydn

82

The Impulse Response of Extruded Corrugated Core Aluminum Sandwich Structures  

E-print Network

#12;Abstract Stainless steel sandwich structures with honeycomb cellular cores have demonstratedThe Impulse Response of Extruded Corrugated Core Aluminum Sandwich Structures A Thesis Presented sandwich structures from a 6061-T6 aluminum alloy. The core relative density was 25% and was strongly

Wadley, Haydn

83

Structurally graded core junctions in sandwich beams: fatigue loading conditions  

Microsoft Academic Search

Sandwich beams with inclusion of different core materials were the subject of the experimental study [Bozhevolnaya E, Thomsen OT. Structurally graded core junctions in sandwich beams: quasi-static analysis. Compos Struct, in press], which focused on the static performance of such sandwich elements. The concept of structurally graded core junctions, suggested in [Bozhevolnaya E, Thomsen OT. Structurally graded core junctions in

Elena Bozhevolnaya; Ole Thybo Thomsen

2005-01-01

84

Experimental study of acoustical behavior of flat honeycomb sandwich panel  

Microsoft Academic Search

Honeycomb (HC) sandwich composites have lightweight and excellent mechanical properties, but have poor acoustic properties. This work was done to improve the acoustical performance of HC sandwich composites used in airplane floors. Transmission loss (TL) is one of the metrics used to assess acoustical performance of HC sandwiches and requires a TL suite. A small-scale sound transmission loss (TL) test

Shankar Rajaram

2005-01-01

85

Timing resolution of Shisk-Kebab'' lead scintillator sandwich calorimeters  

SciTech Connect

We have constructed lead scintillator sandwich calorimeters with 1/4 [chi][sub o] sampling frequency and total thickness [approximately]16[chi][sub o]. The 4 mm thick scintillator plates are read out by wavelength shifter fibers 1 mm in diameter which pass through holes penetrating the plates on a .95 cm [times] .95 cm grid (Shish-Kebab geometry). We tested these modules in the A2 test beam at Brookhaven using low energy electrons and hadrons. Results are here presented on electron energy and time-of-flight resolution obtained with various combinations of scintillators and wavelength shifters. We also describe results on e/[pi] separation obtained with a new technique for the longitudinal segmentation.

Kistenev, E.; White, S. (Brookhaven National Lab., Upton, NY (United States)); Pischalnikov, Y.; Protopopov, Y.; Rykalin, V. (Institut Fiziki Vysokikh Ehnergij, Protvino (Russian Federation))

1992-01-01

86

Timing resolution of ``Shisk-Kebab`` lead scintillator sandwich calorimeters  

SciTech Connect

We have constructed lead scintillator sandwich calorimeters with 1/4 {chi}{sub o} sampling frequency and total thickness {approximately}16{chi}{sub o}. The 4 mm thick scintillator plates are read out by wavelength shifter fibers 1 mm in diameter which pass through holes penetrating the plates on a .95 cm {times} .95 cm grid (Shish-Kebab geometry). We tested these modules in the A2 test beam at Brookhaven using low energy electrons and hadrons. Results are here presented on electron energy and time-of-flight resolution obtained with various combinations of scintillators and wavelength shifters. We also describe results on e/{pi} separation obtained with a new technique for the longitudinal segmentation.

Kistenev, E.; White, S. [Brookhaven National Lab., Upton, NY (United States); Pischalnikov, Y.; Protopopov, Y.; Rykalin, V. [Institut Fiziki Vysokikh Ehnergij, Protvino (Russian Federation)

1992-12-31

87

Sound Transmission through a Cylindrical Sandwich Shell with Honeycomb Core  

NASA Technical Reports Server (NTRS)

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 transmission loss is derived in terms of modal impedance of the fluids and the shell. The results show the effects of (a) the incident angles of the plane wave; (b) the flight conditions of Mach number and altitude of the aircraft; (c) the ratios between the core thickness and the total thickness of the shell; and (d) the structural loss factors on the transmission loss. Comparisons of the transmission loss are made among different shell constructions and different shell theories.

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

1996-01-01

88

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

89

Flexural vibration of delaminated composite sandwich beams  

SciTech Connect

Consider a sandwich plate with anisotropic composite laminated faces and an ideally-orthotropic honeycomb core. In this paper, a one-dimensional model for the free vibration analysis of a plate with an across the width delamination located at the interface between the upper face and core is proposed. with this model the natural frequencies and mode shapes of the delaminated composite sandwich beams can be found by solving the eigenvalues and eigenvectors of twelve simultaneous linear homogeneous algebraic equations. For the purpose of verification, the solutions are reduced to the case of delaminated composite beams by letting the terms containing the core properties vanish, which show that the results match well with the experimental results done by other researchers.

Hwu, C.; Hu, J.S. [National Cheng Kung Univ., Tainan (Taiwan, Province of China). Institute of Aeronautics and Astronautics

1993-12-31

90

Thermographic Inspection of Metallic Honeycomb Sandwich Structures  

NASA Technical Reports Server (NTRS)

The X-33/VentureStar has a Thermal Protection System (TPS) consisting mainly of brazed metallic honeycomb sandwich structures. Inspection of these structures is changing as a result of the extremely thin (less than 200 microns) skins, the small critical defect size (less than 2 mm long by 100 microns wide) and the large number (more than 1000) of parts to be inspected. Pulsed Infrared Thermography has been determined to be the most appropriate inspection method for manufacturing inspection based on performance comparison with other methods, cost, schedule and other factors. The results of the assessment of the different methods will be summarized and data on the performance of the final production inspection system will be given. Finite difference thermal methods have been used to model the whole inspection process. Details of correlation between the models and experimental data will be given and data on the use of pulsed infrared thermography on other metallic honeycomb sandwich structures will be given.

Taylor, John O.; Dupont, H. M.

1998-01-01

91

Fiber Composite Sandwich Thermostructural Behavior: Computational Simulation  

NASA Technical Reports Server (NTRS)

Several computational levels of progressive sophistication/simplification are described to computationally simulate composite sandwich hygral, thermal, and structural behavior. The computational levels of sophistication include: (1) three-dimensional detailed finite element modeling of the honeycomb, the adhesive and the composite faces; (2) three-dimensional finite element modeling of the honeycomb assumed to be an equivalent continuous, homogeneous medium, the adhesive and the composite faces; (3) laminate theory simulation where the honeycomb (metal or composite) is assumed to consist of plies with equivalent properties; and (4) derivations of approximate, simplified equations for thermal and mechanical properties by simulating the honeycomb as an equivalent homogeneous medium. The approximate equations are combined with composite hygrothermomechanical and laminate theories to provide a simple and effective computational procedure for simulating the thermomechanical/thermostructural behavior of fiber composite sandwich structures.

Chamis, C. C.; Aiello, R. A.; Murthy, P. L. N.

1986-01-01

92

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

93

The durability of structural sandwich elements  

Microsoft Academic Search

Structural sandwich elements typically have two thin metal faces and a lightweight core. The core may be polyurethane or polyisocyanurate\\u000a foamedin situ, or it may be formed from either rigid plastic foam or mineral wool slabstock. It is particularly in the latter case that\\u000a durability problems may arise which have not been properly addressed by the industry. This paper considers

K. Berner; J. M. Davies; A. Helenius; L. Heselius

1994-01-01

94

Modeling the combustion of propellant sandwiches  

Microsoft Academic Search

A two-dimensional, steady-state model of a burning composite solid propellant is developed to study the characteristics of the combustion process. The solid composite is a periodic sandwich unit comprised of two oxidizer laminates (ammonium perchlorate, AP) separated by a fuel binder layer (hydroxyl-terminated polybutadiene, HTPB). Included in the model are essential features for simulating composite propellant combustion: (1) a free

G. M. Knott; M. Q. Brewster

2002-01-01

95

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

96

Moisture ingression in honeycomb core sandwich panels  

Microsoft Academic Search

Moisture ingression was studied in several composite sandwich panels, in which hydration was applied over a large surface\\u000a area at the panel edges. Significant moisture ingression occurred in panels with cores of Korex (based on a substrate of a\\u000a fiber pulp paper) and HRP (consisting of a woven-glass-fiber substrate with a polymer coating) of different density. Ingression\\u000a was more rapid

D. Cise; R. S. Lakes

1997-01-01

97

Indentation failure behavior of honeycomb sandwich panels  

Microsoft Academic Search

The failure behavior of simply supported honeycomb sandwich panels subjected to indentation loading on the top skin has been studied. A plate-on-elastic-foundation approach based on distributed load and panel-specific considerations (finite thickness and transverse shear) is developed to analyze the panel stress distribution. Panels with various glass-fibre\\/epoxy skins and aramid cores are analyzed by using this approach together with the

Shaw M. Lee; Thomas K. Tsotsis

2000-01-01

98

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

99

Self-healing sandwich composite structures  

NASA Astrophysics Data System (ADS)

Previous research demonstrated that a thin self-healing layer is effective in recovering partial sandwich composite performance after an impact event. Many studies have been conducted that show the possibility of using Fiber Bragg Grating (FBG) sensors to monitor the cure of a resin through strain and temperature monitoring. For this experiment, FBG sensors were used to monitor the curing process of a self-healing layer within a twelve-layer fiberglass laminate after impact. First, five self-healing sandwich composite specimens were manufactured. FBG sensors were embedded between the fiberglass and foam core. Then the fiberglass laminate was impacted with the use of a drop tower and the curing process was monitored. The collected data was used to compare the cure of the resin and fiberglass alone to the cure of the resin from a self-healing specimen. For the low viscosity resin system tested, these changes were not sufficiently large to identify different polymerization states in the resin as it cured. These results indicate that applying different resin systems might increase the efficiency of the self-healing in the sandwich composites.

Fugon, D.; Chen, C.; Peters, K.

2012-04-01

100

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

101

EVALUATION OF THE MATERIAL PROPERTIES OF RESIN-IMPREGNATED NOMEX PAPER AS BASIS FOR THE SIMULATION OF THE IMPACT BEHAVIOUR OF HONEYCOMB SANDWICH  

Microsoft Academic Search

Driven by stringent weight saving requirements composite sandwich construction has evolved as one of the basic structural design concepts for load-carrying components of advanced aeroplanes and helicopters. Particularly, sandwich using laminated carbon fibre reinforced plastics (CFRP) as face sheets and NOMEX honeycombs as core material is increasingly used due to features such as high strength-to-weight and stiffness-to-weight ratios as well

Falk Hähnel; Klaus Wolf

102

Mode I Toughness Measurements of Core/Facesheet Bonds in Honeycomb Sandwich Structures  

NASA Technical Reports Server (NTRS)

Composite sandwich structures will be used in many future applications in aerospace, marine and offshore industries due to the fact that the strength and stiffness to mass ratios surpass any other structural type. Sandwich structure also offers advantages over traditional stiffened panels such as ease of manufacturing and repair. During the last three decades, sandwich structure has been used extensively for secondary structure in aircraft (fuselage floors, rudders and radome structure). Sandwich structure is also used as primary structure in rotorcraft, the most common example being the trailing edge of rotor blades. As with other types of composite construction, sandwich structure exhibits several types of failure mode such as facesheet wrinkling, core crushing and sandwich buckling. Facesheet/core debonding has also been observed in the marine and aerospace industry. During this failure mode, peel stresses applied to an existing facesheet/core debond or an interface low in toughness, results in the facesheet being peeled from the core material, possibly leading to a significant loss in structural integrity of the sandwich panel. In an incident during a test on a liquid hydrogen fuel tank of the X-33 prototype vehicle, the outer graphite/epoxy facesheet and honeycomb core became debonded from the inner facesheet along significant areas, leading to failure of the tank. As a consequence of the accident; significant efforts were made to characterize the toughness of the facesheet/core bond. Currently, the only standardized method available for assessing the quality of the facesheet/core interface is the climbing drum peel test (ASTM D1781). During this test a sandwich beam is removed from a panel and the lip of one of the facesheets is attached to a drum, as shown in Fig. 1. The drum is then rotated along the sandwich beam, causing the facesheet to peel from the core. This method has two major drawbacks. First, it is not possible to obtain quantitative fracture data from the test and so the results can only be used in a qualitative manner. Second, only sandwich structure with thin facesheets can be tested (to facilitate wrapping of the facesheet around the climbing drum). In recognition of the need for a more quantitative facesheet/core fracture test, several workers have devised experimental techniques for characterizing the toughness of the facesheet/core interface. In all of these cases, the tests are designed to yield a mode I-dominated fracture toughness of the facesheet/core interface in a manner similar to that used to determine mode I fracture toughness of composite laminates. In the current work, a modified double cantilever beam is used to measure the mode I-dominated fracture toughness of the interface in a sandwich consisting of glass/phenolic honeycomb core reinforced with graphite epoxy facesheets. Two specimen configurations were tested as shown in Fig 2. The first configuration consisted of reinforcing the facesheets with aluminum blocks (Fig. 2a). In the second configuration unreinforced specimens were tested (Fig. 2b). Climbing drum peel tests were also conducted to compare the fracture behavior observed between this test and the modified double cantilever beam. This paper outlines the test procedures and data reduction strategies used to compute fracture toughness values from the tests. The effect of specimen reinforcement on fracture toughness of the facesheet/core interface is discussed.

Nettles, Alan T.; Ratcliffe, James G.

2006-01-01

103

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

104

Development of a theory for optimising sandwich composites  

SciTech Connect

In this investigation, the bending stiffness and strength of GRP/pvc foam sandwich beams have been determined analytically and compared with experimentally determined values. Accurate correlation enables justification of theory to predict dimensions for a sandwich beam that will provide suitable bending stiffness or strength for minimum weight. Experimental measurements of sandwich beam bending stiffness, shear stiffness, failure mode and load have been made. The theoretical analysis is in good agreement with the results of these tests.

Lingard, J.R. [DSTO Materials Research Lab., Ascot Vale, Victoria (Australia)

1993-12-31

105

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

106

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.

107

CFRP sandwiched facesheets inspected by pulsed thermography  

NASA Astrophysics Data System (ADS)

Carbon fiber reinforced polymer (CFRP) has been always used in aerospace, Sandwiched structures composed by a honeycomb core between two multi-layer CFRP facesheets are very common on aerospace parts. As to the application of the CFRP sandwiched facesheets is extended, The demand for quality control of CFRP sandwiched composites is increasing, Infrared thermography is one of several non-destructive testing techniques which can be used for defect detection in aircraft materials such as carbon-fibre-reinforced composites. Infrared thermography can be potentially useful, as it is quick, real time, non-contact and can examine over a relatively large area in one inspection procedure. The technique is based on heating the sample surface with different heat sources and monitoring the surface temperature of the sample with an IR camera, any abnormal behavior of the surface temperature distribution indicates the subsurface defect. This kind of structure is normally affected by anomalies such as delaminations, disbonding, water ingressing to the core. in this paper, several different kinds of defects which are of various size and depth below the test surface are planted in the CFRP composites, the Teflon inserts between the plies in the facesheet represents the delaminations, the Teflon inserts between the inner facesheet and adhensive or between adhensive and core are simulated disbonding in the composites, they are all tested by pulsed thermography, meanwhile, these samples are also inspected by ultrasonic testing, compare with each characteristic and the results got by these two different methods, it shows that pulsed thermography is an effective nondestructive technique for inspecting CFRP composites.

Li, Huijuan; Huo, Yan; Cai, Liangxu; Huang, Zhenhua

2010-10-01

108

Microwave nondestructive evaluation of thick sandwich composites  

SciTech Connect

Two microwave nondestructive testing techniques were used to inspect thick, stratified sandwich composites consisting of fiberglass epoxy laminates, foam and honeycomb constituents. Several different defects were embedded in these samples during their production. Each technique relies on the measurement of the reflected microwave energy from the composite samples using an open-ended rectangular waveguide as the inspection probe. The experiments were done at different frequencies and standoff distances based on the results of measurement parameter optimization conducted for each separate defect. The results of measurement parameter optimization conducted for each separate defect. The results of these measurements (presented in image formats) provide impressive detailed information about each defect, such as the raised edges associated with the manufacturing of the delaminations, the shape of the indentations caused by the impact fatigue defects, and surface skin fiber bundle orientations. As expected, higher frequencies provided better spatial resolutions. The importance of optimization as it pertains to successful defect detection and characterization was demonstrated both experimentally and theoretically. The results of this study clearly demonstrate the potential of microwaves as non-destructive tools for inspecting thick composite sandwich structures.

Ganchev, S.I.; Runser, R.J.; Qaddoumi, N.; Ranu, E. [Colorado State Univ., Ft. Collins, CO (United States); Carriveau, G. [Nondestructive Testing Information Analysis Center, Austin, TX (United States)

1995-04-01

109

Design, fabrication and test of 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 panel construction, were fabricated and tested. The designs utilize two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and potassium or sodium as the working fluid. Panels were tested by radiant heating, and the results indicate successful heat pipe operation at temperatures of approximately 922 K (1200 F). These panels, in addition to solving potential thermal stress problems in an Airframe-Integrated Scramjet Engine, have potential applications as cold plates for electronic component cooling, as radiators for space platforms, and as low distortion, large area structures.

Basiulis, A.; Camarda, C. J.

1982-01-01

110

Design, fabrication and test of 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 panel construction, were fabricated and tested. The designs utilize two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and potassium or sodium as the working fluid. Panels were tested by radiant heating, and the results indicate successful heat pipe operation at temperatures of approximately 922K (1200F). These panels, in addition to solving potential thermal stress problems in an Airframe-Integrated Scramjet Engine, have potential applications as cold plates for electronic component cooling, as radiators for space platforms, and as low distortion, large area structures.

Basiulis, A.; Camarda, C. J.

1983-01-01

111

A multifunctional heat pipe sandwich panel structure Douglas T. Queheillalt a,*, Gerardo Carbajal b  

E-print Network

upon a truncated, square honeycomb sandwich structure. In closed cell hon- eycomb structuresA multifunctional heat pipe sandwich panel structure Douglas T. Queheillalt a,*, Gerardo Carbajal b June 2007 Abstract A multifunctional sandwich panel combining efficient structural load support

Wadley, Haydn

112

Experimental investigation and constitutive modeling of metallic honeycombs in sandwich structures  

E-print Network

Traditionally, honeycomb sandwich structures are designed in the elastic range, but recent studies on the crushing of sandwich profiles have shown their potential in crashworthiness applications. Thin sandwich sheets also ...

Mohr, Dirk, 1976-

2003-01-01

113

Insitu expanding foam based carbon/epoxy sandwich jackets for column retrofit  

E-print Network

foam core sandwich panel jacket applied to the two (2) reinforced concretefoam core sandwich panel jacket applied to each of the continuously reinforced flexure concretefoam core sandwich panel jacket applied to each of the lapped reinforced flexure concrete

Danyeur, Alicia

2008-01-01

114

Homogenized elastic properties of honeycomb sandwich with skin effect  

Microsoft Academic Search

The adaptation of homogenization theory to periodic plates is presented and extended to include transverse shear deformation theory for a honeycomb sandwich. Based on the scaling asymptotic expansions about plate thickness ? for sandwiches with comparable characteristic periodicity ?, the homogenization functions ?, U, and V are formulated implicitly in 3-D elliptical equations corresponding to the modes of transverse shear,

X. Frank Xu; Pizhong Qiao

2002-01-01

115

Response of sandwich composites with nanophased cores under flexural loading  

Microsoft Academic Search

It is well known that in a sandwich structure, the core plays an important role in enhancing the flexural rigidity and by controlling the failure mechanisms. If the core is made from foam, the strength of the core material and the debond strength at the core–skin interface almost entirely dictate the performance of structural sandwich composites especially under flexure. In

Hassan Mahfuz; Muhammad S. Islam; Vijaya K. Rangari; Mrinal C. Saha; Shaik Jeelani

2004-01-01

116

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

117

Development, testing, and numerical modeling of a foam sandwich biocomposite  

NASA Astrophysics Data System (ADS)

This study develops a novel sandwich composite material using plant based materials for potential use in nonstructural building applications. The face sheets comprise woven hemp fabric and a sap based epoxy, while the core comprises castor oil based foam with waste rice hulls as reinforcement. Mechanical properties of the individual materials are tested in uniaxial compression and tension for the foam and hemp, respectively. The sandwich composite is tested in 3 point bending. Flexural results are compared to a finite element model developed in the commercial software Abaqus, and the validated model is then used to investigate alternate sandwich geometries. Sandwich model responses are compared to existing standards for nonstructural building panels, showing that the novel material is roughly half the strength of equally thick drywall. When space limitations are not an issue, a double thickness sandwich biocomposite is found to be a structurally acceptable replacement for standard gypsum drywall.

Chachra, Ricky

118

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

119

Structural properties of superplastically formed/diffusion-bonded orthogonally corrugated core sandwich plates  

NASA Technical Reports Server (NTRS)

This paper describes a new superplastically formed/diffusion-bonded (SPF/DB) orthogonally corrugated sandwich structure, and presents formulae and the associated plots for evaluating the effective elastic constants for the core of this new sandwich structure. Comparison of structural properties of this new sandwich structure with the conventional honeycomb core sandwich structure was made under the condition of equal sandwich density. It was found that the SPF/DB orthogonally corrugated sandwich core has higher transverse shear stiffness than the conventional honeycomb sandwich core. However, the former has lower stiffness in the sandwich core thickness direction than the latter.

Ko, W. L.

1980-01-01

120

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.

121

Thermochemical response of honeycomb sandwich panels  

NASA Technical Reports Server (NTRS)

A simple study aimed at predicting the thermochemical response of honeycomb sandwich panels is presented. The overall thermal conductivity coefficient for the panel is obtained through a consideration of the convective gas movement within the cell spaces. The earlier correlations of Catton and Edwards are used. The analytical solution for the one-dimensional approximation is quoted from an earlier study. In comparison with three data points obtained at JPL at heat fluxes of 2.5, 5 and 8 W/sq cm, the char penetration depth is well predicted, especially when the debonding of the face sheet is considered. Re-radiation of incident heat flux from the debonded face sheet plays an important role in this model.

Ramohalli, K.

1983-01-01

122

Standard Test Method for Sandwich Corrosion Test  

E-print Network

1.1 This test method defines the procedure for evaluating the corrosivity of aircraft maintenance chemicals, when present between faying surfaces (sandwich) of aluminum alloys commonly used for aircraft structures. This test method is intended to be used in the qualification and approval of compounds employed in aircraft maintenance operations. 1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information. 1.3 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements appear in Section 9.

American Society for Testing and Materials. Philadelphia

2009-01-01

123

Tethered-bead, immune sandwich assay.  

PubMed

We describe a proof-of-principle, immune sandwich assay in which immune complexes link micron-size beads via DNA tethers to a sensor surface. The number of tethered beads, counted using low-magnification microscopy, provides a measure of the concentration of analyte. The prototype assay was sensitive to pM concentration of analyte. In theory, the assay could be sensitive to sub-fM analyte because beads attached via single-immune complexes and DNA strands form tethers, and tether formation in the absence of analyte is extremely rare. The limiting step at present is binding of streptavidin at the end of DNA to biotin on capture beads. Potential advantages of this type of sensor are discussed. PMID:25064819

Silver, Jonathan; Li, Zhenyu; Neuman, Keir

2015-01-15

124

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

125

Optimization of Sandwich Composites Fuselages Under Flight Loads  

NASA Astrophysics Data System (ADS)

The sandwich composites fuselages appear to be a promising choice for the future aircrafts because of their structural efficiency and functional integration advantages. However, the design of sandwich composites is more complex than other structures because of many involved variables. In this paper, the fuselage is designed as a sandwich composites cylinder, and its structural optimization using the finite element method (FEM) is outlined to obtain the minimum weight. The constraints include structural stability and the composites failure criteria. In order to get a verification baseline for the FEM analysis, the stability of sandwich structures is studied and the optimal design is performed based on the analytical formulae. Then, the predicted buckling loads and the optimization results obtained from a FEM model are compared with that from the analytical formulas, and a good agreement is achieved. A detailed parametric optimal design for the sandwich composites cylinder is conducted. The optimization method used here includes two steps: the minimization of the layer thickness followed by tailoring of the fiber orientation. The factors comprise layer number, fiber orientation, core thickness, frame dimension and spacing. Results show that the two-step optimization is an effective method for the sandwich composites and the foam sandwich cylinder with core thickness of 5 mm and frame pitch of 0.5 m exhibits the minimum weight.

Yuan, Chongxin; Bergsma, Otto; Koussios, Sotiris; Zu, Lei; Beukers, Adriaan

2012-02-01

126

Evaluation of Analysis Techniques for Fluted-Core Sandwich Cylinders  

NASA Technical Reports Server (NTRS)

Buckling-critical launch-vehicle structures require structural concepts that have high bending stiffness and low mass. Fluted-core, also known as truss-core, sandwich construction is one such concept. In an effort to identify an analysis method appropriate for the preliminary design of fluted-core cylinders, the current paper presents and compares results from several analysis techniques applied to a specific composite fluted-core test article. The analysis techniques are evaluated in terms of their ease of use and for their appropriateness at certain stages throughout a design analysis cycle (DAC). Current analysis techniques that provide accurate determination of the global buckling load are not readily applicable early in the DAC, such as during preliminary design, because they are too costly to run. An analytical approach that neglects transverse-shear deformation is easily applied during preliminary design, but the lack of transverse-shear deformation results in global buckling load predictions that are significantly higher than those from more detailed analysis methods. The current state of the art is either too complex to be applied for preliminary design, or is incapable of the accuracy required to determine global buckling loads for fluted-core cylinders. Therefore, it is necessary to develop an analytical method for calculating global buckling loads of fluted-core cylinders that includes transverse-shear deformations, and that can be easily incorporated in preliminary design.

Lovejoy, Andrew E.; Schultz, Marc R.

2012-01-01

127

Performance of polymer-steel sandwich structures under blast loads  

NASA Astrophysics Data System (ADS)

The applicability of the polymer-steel sandwich structures has become a topic of interest over the last few years. To study the effect of polymers (which are well-known energy absorbers) on the performance of sandwich structures under blast loads, a set of experiments were carried out on circular polyurea-steel sandwich samples in a 3 Hopkinson bar setup. Using a physics-based material model for polyurea, the test was numerically modeled in LS-DYNA and verified by comparing to experimental results.

Samiee, Ahsan; Isaacs, Jon; Nemat-Nasser, Sia

2009-03-01

128

The behavior of bonded doubler splices for composite sandwich panels  

NASA Technical Reports Server (NTRS)

The results of an investigation into the behavior of adhesively bonded doubler splices of two composite material sandwich panels are presented. The splices are studied from three approaches: analytical; numerical (finite elements); and experimental. Several parameters that characterize the splice are developed to determine their influence upon joint strength. These parameters are: doubler overlap length; core stiffness; laminate bending stiffness; the size of the gap between the spliced sandwich panels; and room and elevated temperatures. Similarities and contrasts between these splices and the physically similar single and double lap joints are discussed. The results of this investigation suggest several possible approaches to improving the strength of the sandwich splices.

Zeller, T. A.; Weisahaar, T. A.

1980-01-01

129

Thermal behavior of a titanium honeycomb-core sandwich panel  

NASA Technical Reports Server (NTRS)

Finite element thermal stress analysis was performed on a rectangular titanium honecomb-core sandwich panel which is subjected to thermal load with a temperature gradient across its depth. The distributions of normal stresses in the face sheets and the face-sheet/sandwich-core interfacial shear stresses are presented. The thermal buckling of the heated face sheet was analyzed by assuming the face sheet to be resting on an elastic foundation representing the sandwich core. Thermal buckling curves and thermal buckling load surface are presented for setting the limit for temperature gradient across the panel depth.

Ko, William L.; Jackson, Raymond H.

1991-01-01

130

Multifunctional composite sandwich structures utilizing embedded microvascular networks  

NASA Astrophysics Data System (ADS)

Sandwich composites possess exceptional specific flexural strengths, but currently lack the capability for multifunctional use of the volumes encapsulated within their cores. The objectives of this research are to (1) fabricate sacrificial fiber with increased production rates and decreased degradation times, (2) integrate sacrificial fibers into sandwich composite skins, and (3) transport, store, and recover fluid from cells within a honeycomb composite core. Melt-mixing and extrusion of PLA and tin (II) oxalate catalyst is used to increase production rates by five orders of magnitude and reduce evacuation times by a factor of four, while substantially lowering costs and eliminating hazardous chemical waste. Sacrificial fibers are woven into and fully evacuated from sandwich composite structures. Finally, fluid is successfully transported via the patterned microvascular pathways and stored within the core compartments, enabling sandwich composites suitable for applications such as structural fluid storage, heat dissipation, and damage sensing.

Tye, Jordan

131

Debonding detection of honeycomb sandwich structures using frequency response functions  

NASA Astrophysics Data System (ADS)

A vibration-based non-destructive evaluation (NDE) method is proposed to determine the location and size of debonding in honeycomb sandwich beams. Although most of the existing vibration-based NDE methods need many measurement points, the method proposed here only utilizes the frequency response function (FRF) measured at one point. A parameterized damaged Timoshenko beam model is developed with the method of reverberation-ray matrix (MRRM) for the first time, and combined with the genetic algorithm (GA) to inverse the damage parameters from the measured FRF. The detection of a honeycomb sandwich beam can be divided into two steps: (1) identifying the equivalent elastic moduli and other parameters of the intact sandwich beam. (2) Identifying the debonding location and size of the damaged sandwich beam with the predetermined parameters. It is demonstrated experimentally that the method can inverse damage parameters with acceptable precision.

Zhu, Kaige; Chen, Mingji; Lu, Qiuhai; Wang, Bo; Fang, Daining

2014-10-01

132

Sandwich Lunch Please select four fillings from the following  

E-print Network

water and orange juice One round of sandwiches per person £4.50 One and a half rounds of sandwiches per juice 70p per person Blenheim still or sparkling water £1.50 per bottle Canned drinks 70p each Breakfast meal Blenheim still or sparkling water and orange juice £10.50 per person Please ask us about our hot

Oxford, University of

133

Low-velocity impact failure of aluminium honeycomb sandwich panels  

Microsoft Academic Search

In this paper, the failure response of aluminium sandwich panels subjected to low-velocity impact is discussed. A three-dimensional geometrically correct finite element model of the honeycomb sandwich plate and a rigid impactor was developed using the commercial software, ABAQUS. This discrete modelling approach enabled further understanding of the parameters affecting the initiation and propagation of impact damage. Strain-hardening behaviour of

C. C. Foo; L. K. Seah; G. B. Chai

2008-01-01

134

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

135

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

136

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

137

The fatigue behaviour and damage development of 3D woven sandwich composites  

Microsoft Academic Search

In this paper, the bending fatigue behaviour and damage development during fatigue of polyurethane (PUR)-epoxy 3D woven sandwich composites is investigated. 3D sandwich fabrics are produced by a velvet weaving technique. It allows relatively easy production of delamination-resistant sandwich panels, compared to more traditional sandwich structures with honeycomb or foam cores. In this paper, the 3D sandwich fabrics made of

H. Judawisastra; J. Ivens; I. Verpoest

1998-01-01

138

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

139

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. PMID:24722502

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

2014-01-01

140

REIS, ENGIN MURAT. Characteristics of Innovative 3-D FRP Sandwich Panels. Foam and honeycomb core sandwich composites are widely used in structural  

E-print Network

and honeycomb core sandwich composites are widely used in structural applications. Nevertheless, possibilitiesABSTRACT REIS, ENGIN MURAT. Characteristics of Innovative 3-D FRP Sandwich Panels. Foam encountered in traditional FRP panels. The panels consist of GFRP laminates and foam core sandwich where top

141

FRANKL, BERNARD ANTHONY. Structural Behavior of Insulated Precast Prestressed Concrete Sandwich Panels Reinforced with CFRP Grid. (Under the direction of Sami H.  

E-print Network

. Such panels consist of two layers of concrete separated by a layer of rigid foam insulation. PanelsABSTRACT FRANKL, BERNARD ANTHONY. Structural Behavior of Insulated Precast Prestressed Concrete prestressed concrete sandwich wall panels are typically used for the construction of building envelopes

142

Formation and electronic structures of organoeuropium sandwich nanowires.  

PubMed

Organoeuropium sandwich clusters, comprising europium (Eu) and 1,3,5,7-cyclooctatetraene (COT) (Eu(n)(COT)(m)), were produced in the gas phase using a laser vaporization synthesis method. Photoionization mass spectra revealed an exclusive Eu(n)(COT)(m) formation with three compositions: m = n + 1, m = n, and m = n - 1, which, we propose, correspond to full-sandwich, half-sandwich, and inverted-sandwich structures, respectively. The charge distributions, metal-ligand bonding characteristics, and electronic structures of the clusters were comprehensively investigated by photoionization measurements of Eu(n)(COT)(m) neutrals and by photoelectron spectroscopy of Eu(n)(COT)(m)(-) and isoelectronic Ba(n)(COT)(m)(-) anions. The results confirmed that (1) highly ionic metal-ligand bonding is formed between Eu(2+) and COT(2-) within the sandwich structure (at the termini, ionic forms are Eu(+) and COT(-)) and (2) size dependence of orbital energy can be explained by the Coulombic interaction of simple point charge models between the detaching electrons and dipoles/quadrupoles. When the terminus of the sandwich clusters is Eu(2+), COT(2-), or Eu(0), the orbital energy of the electron detachment channel at the opposite terminus strongly depends on the cluster size. In this case, the molecular stack behaves as a one-dimensionally aligned dipole; otherwise, it behaves as a quadrupole, and the relationship between cluster size and electron detachment energy is much weaker. The study also reports on the 4f orbital energy in Eu ions and the formation mechanism of organoeuropium sandwich nanowires up to 12 nm in length. The nanowires are formed by successive charge transfer at the terminal part, Eu(+) and COT(-), which reduces the ionization energy and increases the electron affinity, respectively. PMID:24725191

Hosoya, Natsuki; Takegami, Ryuta; Suzumura, Jun-ichi; Yada, Keizo; Miyajima, Ken; Mitsui, Masaaki; Knickelbein, Mark B; Yabushita, Satoshi; Nakajima, Atsushi

2014-09-18

143

Microbiological quality and risk factors related to sandwiches served in bakeries, cafés, and sandwich bars in South Korea.  

PubMed

The objective of this study was to investigate the microbiological quality of sandwiches produced on site and served in bakeries, cafés, and sandwich bars in South Korea and to determine the major risk factors affecting the sanitation level in each store (n = 1,120). The microbiological quality of the sandwiches was analyzed, and the sanitation level of each store was evaluated as satisfactory or unsatisfactory based on sanitation guidelines. Total coliforms were detected in 906 samples (80.9%), but only 3 samples (0.3%) contained confirmed Escherichia coli contamination. The detection rate was highest for Bacillus cereus (10.0%), followed by Staphylococcus aureus (1.3%) and Salmonella (0.2%). Vibrio parahaemolyticus was not detected in any samples. The microbial contamination level was significantly lower in winter (P < 0.05) and in stores with a higher sanitation grade. Factors related to the microbiological quality of sandwiches were evaluated as the relative risk (RR) of coliform contamination, and the higher risk factors for sandwich contamination were improper holding temperature (RR = 8.75), cross-contamination (RR = 6.30), lack of proper ventilation systems (RR = 6.16), and the absence of clean and/or suitable outer garments (RR = 5.73). Most factors were related to the failure of food handlers to adhere to sanitation guidelines rather than to unsanitary environments. This study provides a comprehensive analysis of the relationship between the microbiological quality of sandwiches served on-site and various risk factors. These results will help researchers establish guidelines for the sanitary management of sandwich shops. PMID:23433370

Jang, Hong Geun; Kim, Nam Hee; Choi, Young Min; Rhee, Min Suk

2013-02-01

144

Experimental study on mechanical properties of aircraft honeycomb sandwich structures  

NASA Astrophysics Data System (ADS)

Mechanical behaviour of sandwich panels under different conditions have been exprimentally studied in this research to increase the knowledge of aircraft sandwich panel structures and facilitate design criteria for aircraft structures. Tests were concentrated on the honeycomb sandwich structures under different loads including flexural, insert shear, flat wise tension and compression loads. Furthermore, effect of core density and face material on mechanical behavior of different samples were investigated and compared with analytical and FEM method. Effects of skin thickness on strength of honycomb sandwhich panels under shear pull out and moments have also been considerd in this study. According to this investigation, insert strength and flexural test under different load conditions is strongly affected by face thickness, but compression and tearoff (falt wise tensile) properties of a sandwich panel depends on core material. The study concludes that the correlation between experimental results and the analytical predictions will enable the designer to predict the mechanical behaviour and strength of a sandwich beam; however, applied formula may lead engineers to unreliable results for shear modulus.

Zakeri, A. A.; Talebi Mazraehshahi, H.

2010-06-01

145

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

146

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

147

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

148

Sandwich panel of veneer-overlaid low-density fiberboard  

Microsoft Academic Search

Low-density sandwich panels of veneer-overlaid fiberboards of 12 mm thickness for structural use were manufactured at densities\\u000a of 0.3–0.5g\\/cm3 using an isocyanate compound resin adhesive and steam injection pressing method. The effects of board density, veneer thickness,\\u000a and resin content on the fundamental properties of sandwich panels were examined, with the following results: (1) The dry\\u000a moduli of rupture and

Tarnami Kawasaki; Min Zhang; Shuichi Kawai

1999-01-01

149

A sandwich model for engineering cartilage with acellular cartilage sheets and chondrocytes.  

PubMed

Acellular cartilage can provide a native extracellular matrix for cartilage engineering. However, it is difficult for cells to migrate into acellular cartilage because of its non-porous structure. The aim of this study is to establish a sandwich model for engineering cartilage with acellular cartilage sheets and chondrocytes. Cartilage from adult pig ear was cut into a circular cylinder with a diameter of approximately 6 mm and freeze-sectioned at thicknesses of 10 ?m and 30 ?m. The sheets were then decellularized and lyophilized. Chondrocytes isolated from newborn pig ear were expanded for 2 passages. The acellular sheets and chondrocytes were then stacked layer-by-layer, in a sandwich model, and cultured in dishes. After 4 weeks of cultivation, the constructs were then either maintained in culture for another 12 weeks or implanted subcutaneously in nude mouse. Histological analysis showed that cells were completely removed from cartilage sheets after decellularization. By re-seeding cells and stacking 20 layers of sheets together, a cylinder-shaped cell sheet was achieved. Cartilage-like tissues formed after 4 weeks of culture. Histological analyses showed the formation of cartilage with a typical lacunar structure. Cartilage formation was more efficient with 10 ?m-thick sheets than with 30 ?m sheets. Mature cartilage was achieved after 12 weeks of implantation, which was demonstrated by histology and confirmed by Safranin O, Toluidine blue and anti-type II collagen antibody staining. Furthermore, we achieved cartilage with a designed shape by pre-shaping the sheets prior to implantation. These results indicate that the sandwich model could be a useful model for engineering cartilage in vitro and in vivo. PMID:21194746

Gong, Yi Yi; Xue, Ji Xin; Zhang, Wen Jie; Zhou, Guang Dong; Liu, Wei; Cao, Yilin

2011-03-01

150

Synthesis and crystal structure of pseudo-sandwich-type heteropolytungstates functionalized by organometallic ruthenium(II).  

PubMed

The reaction between [XW(9)O(34)](9-) (X = As, P) and [RuC(6)H(6)Cl(2)](2) in aqueous buffer solution (pH 6.0) leads to the isolation of two pseudo-sandwich-type heteropolytungstates KNa(6)[(RuC(6)H(6))AsW(9)O(34)] x 17 H(2)O (As-1) and Na(7)[(RuC(6)H(6))PW(9)O(34)] x 14 H(2)O (P-2). Single-crystal X-ray diffraction analyses reveal that the two compounds have the following features: (1) in two polyanions [(RuC(6)H(6))XW(9)O(34)](7-) (X = As, 1; P, 2), the (RuC(6)H(6)) unit is linked via three Ru-O(W) bridges to the side of the trilacunary polyanion, while the lacunary site is still free; (2) the units 1 and 2 are connected exclusively by a central Na cation cluster to form the pseudo-sandwich-type heteropolytungstates; and (3) the pseudo-sandwich-type heteropolytungstates are further connected by Na or K cations to construct the 2D and 3D structures. Furthermore, the electrochemical behaviours of As-1 and P-2 in aqueous solution (1.0 M LiCl + HCl, pH 3.0) have been investigated. Two compounds exhibit the expected reduction processes of the W atoms in a negative potential range and the oxidation of the Ru center in a positive potential range. The results of the electrocatalytic experiments reveal that the compound P-2 has electrocatalytic activity towards the reduction of nitrate. PMID:19655068

Bi, Li-Hua; Hou, Guang-Feng; Li, Bao; Wu, Li-Xin; Kortz, Ulrich

2009-08-28

151

Experimental investigation and constitutive modeling of metallic honeycombs in sandwich structures.  

E-print Network

??Includes bibliographical references (p. 207-214).Traditionally, honeycomb sandwich structures are designed in the elastic range, but recent studies on the crushing of sandwich profiles have shown… (more)

Mohr, Dirk, 1976-

2003-01-01

152

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

153

Gravity sag of sandwich panel assemblies as applied to precision cathode strip chamber structural design  

SciTech Connect

The relationship between gravity sag of a precision cathode strip chamber and its sandwich panel structural design is explored parametrically. An algorithm for estimating the dominant component of gravity sag is defined. Graphs of normalized gravity sag as a function of gap frame width and material, sandwich core edge filler width and material, panel skin thickness, gap height, and support location are calculated using the gravity sag algorithm. The structural importance of the sandwich-to-sandwich ``gap frame`` connection is explained.

Horvath, J. [Lawrence Livermore National Lab., CA (United States)

1993-09-16

154

Drug metabolism in hepatocyte sandwich cultures of rats and humans  

Microsoft Academic Search

Adult hepatocytes from rat and man were maintained for 2 weeks between two gel layers in a sandwich configuration to study the influence of this culture technique on the preservation of basal activities of xenobiotic-metabolizing phase I and phase II enzymes. The response of these enzyme activities to an enzyme inducer was investigated using rifampicin (RIF). Basal levels of cytochrome

A Kern; A Bader; R Pichlmayr; K.-F Sewing

1997-01-01

155

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

156

A la Carte Entres and Sandwiches Chicken Dijon 55  

E-print Network

A la Carte Entr�es and Sandwiches Entr�es Chicken Dijon 55 Beef Lasagna 50 Spinach Lasagna 50 Chili 34 1/4 Sheet Cake 22 Beverages Soft Drinks (six pack) 6.50 Coke Sprite Diet Coke Dasani Water Juices

157

Shell - house steel\\/polyurethane sandwich systems ready to build  

Microsoft Academic Search

A shell formed architecture can be quickly obtained by a light steel bearing structure holding insulated polyurethane sandwich panels, shaped in shell form or straight. Lightweight façades could be shaded, in hot climates, with textile extentions and double roofs. Methodology follows very strict design phases which have brought to different systems with different, but a very simple, final shapes. Some

Marco Imperadori

158

Damage detection of fiber-reinforced polymer honeycomb sandwich beams  

Microsoft Academic Search

In a framework of developing a structural health monitoring for civil infrastructure, the damage identification procedure based on dynamic response for fiber reinforced polymer (FRP) sandwich composites is evaluated. In this paper, an experimental damage identification procedure based on structural dynamic responses and using smart sensors is conducted. Damage identification is estimated from comparison of dynamic responses of healthy and

Wahyu Lestari; Pizhong Qiao

2005-01-01

159

Stiffness and strength properties for basic sandwich material core types  

SciTech Connect

Three basic core material types for sandwich structure applications are studied. The three two-dimensional pattern types are: honeycomb, triangular cells, and a new configuration involving star type cells. The specific critical properties of stiffness and strength type are identified and studied, both theoretically and experimentally.

Beomkeun, K; Christensen, R M

1999-08-03

160

Failure initiation and propagation characteristics of honeycomb sandwich composites  

Microsoft Academic Search

The energy absorbed during the failure of a variety of structural shapes is influenced by material, geometry and the failure mode. Failure initiation and propagation of the honeycomb sandwich under loading involves not only non-linear behavior of the constituent materials, but also complex interactions between various failure mechanisms. Therefore, there is a need for an improved understanding of the material

A. R. Othman; D. C. Barton

2008-01-01

161

Impact behavior and energy absorption of paper honeycomb sandwich panels  

Microsoft Academic Search

Dynamic cushioning tests were conducted by free drop and shock absorption principle. The effect of paper honeycomb structure factors on the impact behavior was analyzed. Results of many experiments show that the dynamic impact curve of paper honeycomb sandwich panel is concave and upward; the thickness and length of honeycomb cell-wall have a great effect on its cushioning properties; increasing

Dongmei Wang

2009-01-01

162

Hybrid processing of thick skins for honeycomb sandwich structures  

Microsoft Academic Search

Carbon–epoxy prepregs are generally used to form the skins of honeycomb sandwich structures used in aerospace or racing yachts. For some applications, it is desirable to increase the thickness of the skins. In order to achieve an ideal core pressure level during cure for maximal skin–core bonding, the issue of air extraction from the honeycomb cells through the skin during

S. Sequeira Tavares; Y. Roulin; V. Michaud; J.-A. E. Månson

2011-01-01

163

Fatigue analysis of honeycomb-composite sandwich beams  

Microsoft Academic Search

The fatigue behaviour of honeycomb sandwich beams is experimentally investigated through four-point bending tests. Two kinds of specimens, initially undamaged and damaged by interface debonding, have been tested. The fatigue tests results are presented in standard SN diagrams with a best curve fit of the experimental data, while the fatigue limit is evaluated through a stair-case procedure. Two different failure

G. Belingardi; P. Martella; L. Peroni

2007-01-01

164

Assessment of semi-impregnated fabrics in honeycomb sandwich structures  

Microsoft Academic Search

Semi-impregnated fabrics, or semipregs, are fabrics alternating dry and resin impregnated areas along the fibre bed surface. Due to their increased initial through thickness permeability to gas flow, these could constitute an alternative to prepreg in the skins of vacuum-bagged honeycomb sandwich structures, reducing the pressure in the honeycomb. The semipreg through thickness air permeability before cure is measured and

S. Sequeira Tavares; V. Michaud; J.-A. E. Månson

2010-01-01

165

Sound radiation from a line forced perforated elastic sandwich panel  

E-print Network

Sound radiation from a line forced perforated elastic sandwich panel I. David Abrahams Department INTRODUCTION Sound transmission through panels has long been a sub- ject of importance in a variety- plates separated by stiffeners or ribs in between.2 The trans- mission and reflection of sound waves

Abrahams, I. David

166

Control of Wave Propagation in Sandwich Beams with Auxetic Core  

Microsoft Academic Search

The wave propagation in sandwich beams with cellular core is analyzed and controlled. The material properties of cellular cores are highly dependent on the geometry of the cell composing the honeycomb structure. Core materials of different geometry placed periodically along the beam length introduce the proper impedance mismatch necessary to impede the propagation of waves along the beam. A theoretical

MASSIMO RUZZENE; FABRIZIO SCARPA

2003-01-01

167

The dynamic response of composite sandwich beams to transverse impact  

E-print Network

configuration with composite face- sheets and a core made from PVC foam or end-grain balsa wood. High is such that a low density PVC foam core outperforms a higher density PVC foam core. End-grain balsa wood has a superior stiffness and strength to that of PVC foam in compression and in shear. Consequently, sandwich

Fleck, Norman A.

168

Methods for Assessing Honeycomb Sandwich Panel Wrinkling Failures  

NASA Technical Reports Server (NTRS)

Efficient closed-form methods for predicting the facesheet wrinkling failure mode in sandwich panels are assessed. Comparisons were made with finite element model predictions for facesheet wrinkling, and a validated closed-form method was implemented in the HyperSizer structure sizing software.

Zalewski, Bart F.; Dial, William B.; Bednarcyk, Brett A.

2012-01-01

169

Hepatocytes in collagen sandwich: evidence for transcriptional and translational regulation  

PubMed Central

The influence of extracellular matrix configuration on the tissue- specific function of cultured hepatocytes was investigated. Adult rat hepatocytes sandwiched between two layers of collagen gel were compared to cells cultured on a single layer of collagen gel for differences in the total RNA content, the level of albumin-specific mRNA, the rate of albumin gene transcription, and the rate of albumin mRNA translation. Adult hepatocytes in the sandwich system maintained the level of albumin mRNA similar to that found in the normal liver for at least six weeks, whereas the level of albumin mRNA declined rapidly in the single gel system. After one week of culture, hepatocytes in the single gel system could be induced to recover the high level of albumin mRNA and albumin production when a second layer of collagen gel was overlaid at that time. Furthermore, sandwiched hepatocytes maintained significantly higher transcriptional activity compared to cells in the single gel system. In addition to transcriptional control, the ultimate rate of albumin production was shown to depend on the rate of translation, which increased with culture time and reached a plateau in one to two weeks. This increase in translational activity over time in culture was observed in both the sandwich and the single gel systems and, thus, appeared to be independent of the configuration of extracellular matrix. PMID:1734019

1992-01-01

170

A comparative study of impulse-resistant metal sandwich plates  

Microsoft Academic Search

The performance of metal sandwich plates under impulsive blast loads is compared to that of solid plates made of the same material and having the same weight. Three core geometries are considered: pyramidal truss, square honeycomb and folded plate. Plates of infinite length and clamped along their sides are subject to uniform impulsive load. The momentum impulse is applied to

Zhenyu Xue; John W. Hutchinson

2004-01-01

171

A comparative studyof impulse-resistant metal sandwich plates  

Microsoft Academic Search

The performance of metal sandwich plates under impulsive blast loads is compared to that of solid plates made of the same material and having the same weight. Three core geometries are considered: pyramidal truss, square honeycomb and folded plate. Plates of infinite length and clamped along their sides are subject to uniform impulsive load. The momentum impulse is applied to

Zhenyu Xue; John W. Hutchinson

172

Star cell type core configuration for structural sandwich materials  

DOEpatents

A new pattern for cellular core material used in sandwich type structural materials. The new pattern involves star shaped cells intermixed with hexagonal shaped cells. The new patterned cellular core material includes star shaped cells interconnected at points thereof and having hexagonal shape cells positioned adjacent the star points. The new pattern allows more flexibility and can conform more easily to curved shapes.

Christensen, Richard M. (Danville, CA)

1995-01-01

173

Electronic transport in nanoparticle monolayers sandwiched between graphene electrodes.  

PubMed

Graphene/CdSe nanoparticle monolayer/graphene sandwich structures were fabricated to explore the interactions between these layered materials. Electrical transport across these heterostructures suggests that transport is limited by tunneling through the nanoparticle (NP) ligands but not the NP core itself. Photoconductivity suggests ligands may affect the exciton separation efficiency. PMID:25319544

Lu, Chenguang; Zhang, Datong; Zande, Arend van der; Kim, Philip; Herman, Irving P

2014-11-01

174

On using corrugated skins to carry shear in sandwich beams  

Microsoft Academic Search

A simplified approach is used to study the potential of using a corrugated skin in a sandwich to carry shear loads. Shear carrying capability is a major requirement for ship bottom panels, among other structures. The simplifications in the paper are quite major and in particular the corrugated skin is modeled as a conventional material with a homogenized stiffness. The

Matthew Kampner; Joachim L. Grenestedt

2008-01-01

175

Design of Sandwich Composite Panels with Enhanced Passive Damping  

Microsoft Academic Search

Sandwich composite panels are being used increasingly in transportation vehicles including aircraft, spacecraft, ships, road and rapid transit vehicles. This is because their strength-to-weight ratios are generally superior to those of metals including aluminum and steel. Their structural strength properties are fairly well known. However their fatigue, vibration and acoustic properties are known less. This is a problem since such

John Smith; Ann Brown

176

Fabrication and structural performance of periodic cellular metal sandwich structures  

Microsoft Academic Search

Metallic sandwich panels with periodic, open-cell cores are important new structures, enabled by novel fabrication and topology design tools. Fabrication protocols based on the sheet forming of trusses and shell elements (egg-boxes) as well as textile assembly have allowed the manufacture of robust structures by inexpensive routes. Topology optimization enables control of failure mechanisms at the truss length scale, leading

Haydn N. G. Wadley; Norman A. Fleck; Anthony G. Evans

177

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

178

Carbon foam characterization: sandwich flexure, tensile and shear response  

E-print Network

to determine the mechanical properties and failure modes of the carbon foam. Sandwich beams composed of open cell carbon foam cores and carbon-epoxy laminate face sheets are tested in the flexure condition using a four point setup. The primary failure mode...

Sarzynski, Melanie Diane

2004-09-30

179

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

180

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

181

Underwater blast response of free-standing sandwich plates with metallic lattice cores  

E-print Network

-standing sandwich plates with a square honeycomb core and a corrugated core has been measured. The total momentumUnderwater blast response of free-standing sandwich plates with metallic lattice cores G.J. Mc 19 May 2010 Accepted 29 May 2010 Available online 12 June 2010 Keywords: Sandwich structures Lattice

Fleck, Norman A.

182

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

183

Metallic sandwich panels subjected to multiple intense shocks Hamid Ebrahimi, Ashkan Vaziri  

E-print Network

Available online 11 January 2013 Keywords: Sandwich panels Honeycomb core Folded plate core Multiple shocks out to find the optimum core density of a square honeycomb core sandwich panels under two shocks strength and ductility. In this set of simulations, square honeycomb sandwich panels made of four steels

Vaziri, Ashkan

184

Identification of honeycomb sandwich properties by high-resolution modal analysis  

E-print Network

Identification of honeycomb sandwich properties by high-resolution modal analysis M. R´ebillat X and core materials of honeycomb sandwich. All the elastic coefficients and loss-factors that matter the problem of the identification of elastic and damping properties of sandwich panels [1, 2]. The honeycomb

Paris-Sud XI, Université de

185

TEMPERATURE DEPENDENT CREEP EXPANSION OF Ti-6Al-4V LOW DENSITY CORE SANDWICH STRUCTURES  

E-print Network

TEMPERATURE DEPENDENT CREEP EXPANSION OF Ti-6Al-4V LOW DENSITY CORE SANDWICH STRUCTURES Douglas T The application of lightweight, structurally efficient metal based honeycomb structures has been limited for the low cost manufacture of porous metal sandwich structures. These porous cored sandwich structures

Wadley, Haydn

186

Non Destructive Testing of sandwich composites: adhesion defects evaluation; Experimental and Finite  

E-print Network

was introduced at different locations in sandwich composite by insertion of a Teflon film between honeycomb This paper deals with Non Destructive Testing NDT of sandwich honeycomb structures which are widely used detection [5, 6]. This experimental study is carried out at 550 kHz in real sandwich honeycomb by evaluating

Paris-Sud XI, Université de

187

Performance of metallic honeycomb-core sandwich beams under shock loading  

E-print Network

Performance of metallic honeycomb-core sandwich beams under shock loading H.J. Rathbun a , D honeycomb core sandwich and solid monolithic beams have been subjected to high-pressure, short. The experiments have been designed to achieve two objectives: (i) to demonstrate the benefits of sandwich

Hutchinson, John W.

188

8th International Conference on Sandwich Structures A. J. M. Ferreira (Editor)  

E-print Network

, 2008 DAMAGE TOLERANCE OF A SANDWICH PANEL WITH A CRACKED SQUARE HONEYCOMB CORE LOADED IN SHEAR I toughness, elastic behaviour, honeycomb Summary. We explore the shear fracture strength of a sandwich panel, the honeycomb core is loaded in a sandwich panel configuration with stiff and strong face-sheets. The damage

Fleck, Norman A.

189

International Journal of Mechanical Sciences 47 (2005) 545569 Metal sandwich plates optimized for pressure impulses  

E-print Network

loading; Sandwich plates; Honeycomb cores; Optimal design ARTICLE IN PRESS wwwInternational Journal of Mechanical Sciences 47 (2005) 545­569 Metal sandwich plates optimized and shear-off at supports and webs. All-metal sandwich plates have distinct advantages over comparable

Hutchinson, John W.

190

Collapse mechanism maps for the hollow pyramidal core of a sandwich panel under transverse shear  

E-print Network

alternatives to prismatic (corrugated) and honeycomb structures when configured as the core of a sandwich panel concerns associated with the use of traditional closed cell honeycomb sandwich panels (Blitzer, 1997Collapse mechanism maps for the hollow pyramidal core of a sandwich panel under transverse shear S

Fleck, Norman A.

191

Sound transmission loss of damped honeycomb sandwich Portia Peters and Steven Nutt  

E-print Network

Sound transmission loss of damped honeycomb sandwich panels Portia Peters and Steven Nutt Honeycomb be a base for further enhancements in the acoustical behavior of honeycomb sandwich structures. #12; sandwich panels are widely used in aerospace applications because of the high stiffness-to-weight ratios

Southern California, University of

192

Metal sandwich plates subject to intense air shocks Ashkan Vaziri, John W. Hutchinson *  

E-print Network

­structure interaction in the design and assessment of sandwich plates subject to water shocks. Square honeycomb 2006 Elsevier Ltd. All rights reserved. Keywords: Sandwich plates; Honeycomb core; Folded plate coreMetal sandwich plates subject to intense air shocks Ashkan Vaziri, John W. Hutchinson * Division

Hutchinson, John W.

193

Static and fatigue bending behavior of pultruded GFRP sandwich panels with through-thickness fiber insertions  

E-print Network

of the core material. For sandwich panels with honeycomb cores the overall panel behavior is gov- ernedStatic and fatigue bending behavior of pultruded GFRP sandwich panels with through-thickness fiber) sandwich panel pro- posed for civil infrastructure and transportation applications. The research consists

194

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

195

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

SciTech Connect

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, W.L.; Jackson, R.H.

1993-06-01

196

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

197

Materials Science and Engineering A 472 (2008) 242250 Shear behavior of aluminum lattice truss sandwich panel structures  

E-print Network

and more than 40% stiffer and stronger than flexible honeycombs used for the cores of curved sandwich honeycomb structures when configured as the core of a sandwich panel. These lattice sandwich structures and corrosion concerns associated with the use of traditional closed cell honeycomb sandwich panels [22

Wadley, Haydn

198

Cryogenic optical testing of sandwich-type silicon carbide mirrors.  

PubMed

The experimental cryogenic performance of 160-mm-diameter silicon carbide (SiC) mirrors, one of which, a 700-mm-diameter mirror, is to be used as a primary mirror of the Japanese Infrared Astronomical Satellite ASTRO-F, is described. The mirrors are made from a sandwich-type SiC material that comprises a light porous core and a dense chemical-vapor-deposited coat of SiC. Three mirrors were manufactured consecutively, and changes in their surface contours related to temperature were measured with an interferometer when the mirrors were placed in a liquid-helium cryostat. Owing to significant improvements in manufacturing, the third SiC mirror showed only slight deformation as the temperature decreased from 300 to 6 K, which indicates high thermal strain homogeneity for a well-controlled sandwich-type SiC mirror. PMID:12564490

Kaneda, Hidehiro; Onaka, Takashi; Kawada, Mitsunobu; Murakami, Hiroshi

2003-02-01

199

Detection of ?-Lactamase Residues in Milk by Sandwich ELISA  

PubMed Central

?-Lactamase residues in milk represent a public health risk. The cylinder plate detection method, which is based on bacterial growth, is laborious and time consuming. In this study, 15 monoclonal antibodies (mAbs) were selected against Temoneira (TEM) 1 ?-lactamase. A sandwich enzyme-linked immunosorbent assay (ELISA) based on an optimum mAb pair was developed and validated for the detection of ?-lactamase. The limit of detection and linear dynamic range of the method were 4.17 ng/mL and 5.5–100 ng/mL, respectively. ?-Lactamase recovery in pure milk was 96.82–103.13%. The intra- and inter-assay coefficients of variation were 6.21–7.38% and 12.96–13.74%, respectively. Our developed sandwich ELISA can be used as a rapid detection method of ?-lactamase in milk. PMID:23812026

Wang, Wenbing; Liu, Liqiang; Xu, Liguang; Ma, Wei; Kuang, Hua; Xu, Chuanlai

2013-01-01

200

Metal/dielectric/metal sandwich film for broadband reflection reduction  

PubMed Central

A film comprising randomly distributed metal/dielectric/metal sandwich nanopillars with a distribution of cross-sectional diameters, displayed extremely low reflectance over the blue-to-red regime, when coated on glass and illuminated normally. When it is illuminated by normally incident light, this sandwich film (SWF) has a low extinction coefficient, its phase thickness is close to a negative wavelength in the blue-to-red spectral regime, and it provides weakly dispersive forward and backward impedances, so that reflected waves from the two faces of the SWF interfere destructively. Broadband reflection-reduction, over a wide range of incidence angles and regardless of the polarization state of the incident light, was observed when the SWF was deposited on polished silicon. PMID:23591704

Jen, Yi-Jun; Lakhtakia, Akhlesh; Lin, Meng-Jie; Wang, Wei-Hao; Wu, Huang-Ming; Liao, Hung-Sheng

2013-01-01

201

High-performance sandwich panels made from braided tubes  

SciTech Connect

A light weight, high-performance sandwich panel was developed using thin walled braided tubes as the core material. The panels have certain specific advantages over conventional honeycomb sandwich panels including superior skin-core bonding, integral conduit systems and self-draining thereby avoiding moisture accumulation. A short manufacturing process leads to a cost effective product. The technology of the tube production is not material-specific, so any reinforcing fiber can used in conjunction with a large number of resin systems including thermoplastic resins. The braided tubes used as the core can be produced in a wide variety of cross-sectional shapes and sizes so the panels can be designed to meet various specific functions. 6 figures, 1 table.

Williams, D.J.; Ajibade, F.

1988-07-01

202

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

203

Laparoscopic Mesh Splenopexy (Sandwich Technique) for Wandering Spleen  

PubMed Central

Background: Wandering spleen is a rare clinical condition caused by incomplete fusion of the 4 primary splenic ligaments, allowing the spleen to be mobile within the abdomen, predisposing to splenic torsion along the vascular pedicle leading to splenomegaly and infarction, often diagnosed in an emergency setting. Methods: The wandering spleen diagnosis was achieved by ultrasound in our case. We successfully treated the patient with laparoscopic splenopexy because the size was almost normal, and no infarction or evidence of hypersplenism was present. We used the sandwich technique in which 2 meshes sandwich the spleen. Results: This technique was found to be highly satisfactory as a treatment for wandering spleen. The patient was discharged on the third postoperative day with no intra-operative or postoperative complications. Conclusion: Laparoscopy usually confirms the diagnosis.Recommended surgical procedures are splenopexy or splenectomy. Splenopexy is feasible, less invasive, and does not diminish splenic function. PMID:17761090

Palanivelu, Chinnusamy; Senthilkumar, Rangaswamy; Parthasarathi, Ramakrishnan; Kavalakat, Alfie J.

2007-01-01

204

The measurement of residual stresses by sandwich holographic interferometry  

NASA Astrophysics Data System (ADS)

Sandwich holographic interferometry was first proposed by Prof. N. Abramson in 1974. There are many advantages in using this method. One of its most important virtues is that it can compensate for rigid body displacements between the two exposures and is very convenient in practical operation. The authors have already made a detailed theoretical analysis of in-plane and out-of-plane displacements. This paper describes experimental measurements of the residual stresses in welds, by studying the curvature or the second-order derivative of the fringes of in-plane or out-of-plane displacements, using sandwich holographic interferometry. The stresses are obtained quantitatively, and are verified by an experiment involving measurements of the stresses of a flat plate.

Wang, Lingli; Ke, Jingtang

205

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

206

Fatigue Life Analysis of Small Composite Sandwich Wind Tuebine Blades  

Microsoft Academic Search

The present fatigue life analysis of the small composite sandwich wind turbine blades (SCSWTBs) can be certified by IEC 61400-2:Wind Turbines - Part2: Design requirements of small wind turbines (IEC 61400-2 2006). The paper will establish an analytical method for the fatigue life analysis of SCSWTBs. Microsoft Office EXCEL is used to calculate the maximum stress, minimum stress, and stress

J. H. Wu; F. M. Lai

2011-01-01

207

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

208

Novel stacked folded cores for blast-resistant sandwich beams  

E-print Network

compression, and the exploitation of fluid-structure interaction effects to reduce the momentum imparted by a blast (Fleck and Deshpande, 2004; McShane et al., 2007; Xue and Hutchinson, 2004). A wide range of metallic cellular cores have been investigated... ., 2012; Radford et al., 2007; Vaughn and Hutchinson, 2006). In this paper we describe the first analysis of a novel sandwich core suitable for blast miti- gation: the Stacked Folded Core. The concept is sketched in Fig. 1: individual folded sheets...

Schenk, M.; Guest, S. D.; McShane, G. J.

2014-08-23

209

Analysis of Thermal Deformation on a Honeycomb Sandwich CFRP Mirror  

Microsoft Academic Search

Thermal deformation analysis was performed on a carbon fiber reinforced plastic (CFRP) mirror with sandwich structure. To obtain unexpected asymmetry of the surface sheet, we investigated the deformation of a quasi-isotropic laminate under hot and humid conditions. Despite the symmetric lay-up, quasi-isotropic laminate deforms into twisted saddle shape with time, and this deformation could be simulated by assuming ply angle

Yoshihiko Arao; Jun Koyanagi; Shin Utsunomiya; Hiroyuki Kawada

2010-01-01

210

Moisture Ingression In Honeycomb Core Sandwich Panels: Directional Aspects  

NASA Technical Reports Server (NTRS)

Moisture ingression was studied in several composite sandwich panels.No observable ingression was found in a panel with HRP core of density 0.13 g/cc (8.0 lb/ft'). Significant moisture ingression occurred in a panel with Korex 3.0-lb core with density 0,048 g/cc, (3.0 lb/cu ft). It was as faster in the Y-axis (core ribbon) direction, per unit distance than in other directions.

Cise, D. M.; Lakes, R. S.

1997-01-01

211

Impact energy absorption of sandwich plates with crushable core  

SciTech Connect

The objective of this paper is to derive a closed-form solution for deformations, resisting forces, and energy absorption of a metal honeycomb with face plating subjected to localize static and dynamic loads. Two load cases are considered: a quasi-static indentation by a circular punch and dynamic impact by a cylindrical projectile with a velocity in the range of 20 {divided_by} 40 m/sec. The present analysis is building-up on the earlier solution obtained by one of the authors in which the crash resistance of a bare honeycomb was predicted from a known geometry of the cell and material properties. The face plating increases crush resistance of the honeycomb by spreading deformation outside the loading area and invoking considerable membrane action in the plate. Each of the above contributions is quantified and is shown that the resisting force and the radial extent of deformation are increasing functions of punch displacement. The present analytical predictions are compared with measurements taken on seven impact tests on sandwich plates, reported by Goldsmith and Sackman. A correlation of final plate deflections under the projectile was very good for lower impact velocities (less that 6.3% error) and good for higher impact velocities (between 2.08% and 8.9% error). This exceeds the accuracy of a purely numerical solution presented. Three mechanisms limiting the energy absorbed by a sandwich plate are identified: densification of the honeycomb, punch-through shear of the facing plates, and reaching deformation of the outer boundary of the sandwich plate. The present theory provides the necessary background information for optimum designing of sandwich plates against impact loads.

Wierzbicki, T.; Fatt, M.H.; Alvarez, A.L. [Massachusetts Institute of Technology, Cambridge, MA (United States)

1995-12-31

212

Star cell type core configuration for structural sandwich materials  

DOEpatents

A new pattern for cellular core material used in sandwich type structural materials is disclosed. The new pattern involves star shaped cells intermixed with hexagonal shaped cells. The new patterned cellular core material includes star shaped cells interconnected at points thereof and having hexagonal shape cells positioned adjacent the star points. The new pattern allows more flexibility and can conform more easily to curved shapes. 3 figs.

Christensen, R.M.

1995-08-01

213

Monitoring for Heterosigma akashiwo using a sandwich hybridization assay  

Microsoft Academic Search

Field testing of a ribosomal RNA (rRNA)-targeted sandwich hybridization assay (SHA) for Heterosigma akashiwo (Raphidophyceae) in Puget Sound, WA, USA, has showed that the lower limit of detection is well below the level at which cells pose a danger to fish. Moreover, the assay has proven to be both rapid and easy-to-use. Isolates of H. akashiwo from Australia, Japan, New

John V Tyrrell; Laurie B Connell; Chris A Scholin

2002-01-01

214

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

215

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.

216

Shaped Pd-Ni-Pt core-sandwich-shell nanoparticles: influence of Ni sandwich layers on catalytic electrooxidations.  

PubMed

Shape-controlled metal nanoparticles (NPs) interfacing Pt and nonprecious metals (M) are highly active energy conversion electrocatalysts; however, there are still few routes to shaped M-Pt core-shell NPs and fewer studies on the geometric effects of shape and strain on catalysis by such structures. Here, well-defined cubic multilayered Pd-Ni-Pt sandwich NPs are synthesized as a model platform to study the effects of the nonprecious metal below the shaped Pt surface. The combination of shaped Pd substrates and mild reduction conditions directs the Ni and Pt overgrowth in an oriented, layer-by-layer fashion. Exposing a majority of Pt(100) facets, the catalytic performance in formic acid and methanol electro-oxidations (FOR and MOR) is assessed for two different Ni layer thicknesses and two different particle sizes of the ternary sandwich NPs. The strain imparted to the Pt shell layer by the introduction of the Ni sandwich layer (Ni-Pt lattice mismatch of ?11%) results in higher specific initial activities compared to core-shell Pd-Pt bimetallic NPs in alkaline MOR. The trends in activity are the same for FOR and MOR electrocatalysis in acidic electrolyte. However, restructuring in acidic conditions suggests a more complex catalytic behavior from changes in composition. Notably, we also show that cubic quaternary Au-Pd-Ni-Pt multishelled NPs, and Pd-Ni-Pt nanooctahedra can be generated by the method, the latter of which hold promise as potentially highly active oxygen reduction catalysts. PMID:24896733

Sneed, Brian T; Young, Allison P; Jalalpoor, Daniel; Golden, Matthew C; Mao, Shunjia; Jiang, Ying; Wang, Yong; Tsung, Chia-Kuang

2014-07-22

217

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

218

Thermomechanical response of metal foam sandwich panels for structural thermal protection systems in hypersonic vehicles  

NASA Astrophysics Data System (ADS)

Sandwich panels with metal foam cores are proposed for load-bearing structural components in actively cooled thermal protection systems for aerospace vehicles. Prototype acreage metal foam sandwich panels (MFSP's) are constructed and analyzed with the central goal of characterizing the thermomechanical response of the system. MFSP's are subjected to uniform temperature fields and equibiaxial loading in a novel experimental load frame. The load frame exploits the mismatch of coefficients of thermal expansion and allows for thermostructural experimentation without the endemic conflict of thermal and mechanical boundary conditions. Back-to-back strain gages and distributed thermocouples capture the in-plane response of the panels, including buckling and elastic-plastic post-buckling. The out-of-plane response is captured via moire interferometry, which provides a visualization of evolving mode shapes throughout the post-buckling regime. The experimental results agree with an analytical prediction for critical temperatures in sandwich panels based on a Rayleigh-Ritz minimization of the energy functional for a Reissner-Mindlin plate. In addition, a three-dimensional finite element model of the non-linear thermomechanical response of the panel-frame experimental system is developed and the results are shown to agree well with the experimentally identified response of MFSP's. Central to analytical and numerical characterization of MFSP's is an understanding of the response of metal foam under shear loading. The shear response of metal foam is captured experimentally, providing density-dependent relationships for material stiffness, strength, and energy absorption. Speckle photography is employed to identify microstructural size effects in the distribution of strain throughout metal foam under shear loading. In addition, a micromechanical model is established for the density-dependent shear modulus of metal foam, which allows for the coupling of cell-level imperfections with unit cell response. Through experiments, MFSP's are subjected to dynamic through-the-thickness thermal gradients, constrained deformation, and active cooling. In capturing the response of the cooled and uncooled panels, control and actuation of thermostructural deformation in actively cooled MFSP's is demonstrated. The finite element model of the panel-frame system is extended to the actively cooled experiments and is shown to agree well with the experimental results.

Rakow, Joseph F.

219

Vibrational analysis of rectangular sandwich plates resting on some elastic point supports  

SciTech Connect

An approximate solution of forced-vibration for rectangular sandwich plate resting on some elastic point supports is presented. The sandwich plate has thin, anisotropic composite laminated faces and a thick orthotropic core. The simplified sandwich plate model is used in the analysis. The governing equation of elastically point supported rectangular sandwich plate is obtained by using the Lagrange equation. The steady state response solution to a sinusoidally varying point force is also derived. The response curves of rectangular sandwich plates having CFRP laminated faces and aluminum honeycomb core is calculated. Application examples illustrate the effects of laminate lay-up of face sheets, core material properties and core thickness ratio on the vibration characteristics of rectangular sandwich plate.

Ichinomiya, Osamu; Maruyama, Koichi; Sekine, Kouji [Hokkaido Inst. of Tech., Sapporo (Japan). Dept. of Mechanical engineering

1995-11-01

220

Numerical Simulation On Dynamic Indentation Behavior of Sandwich Plates With Aluminum Foam Cores  

NASA Astrophysics Data System (ADS)

Dynamic indentation behavior of sandwich plates with aluminum alloy skins and aluminum foam cores has been simulated by using LS-DYNA. The simulation results were compared with the experimental data in each specimen group for validating the effectiveness and reliability of the FEM model. The numerical simulation results were discussed and several typical failure modes were summarized. An evaluation approach of energy-absorbing ability was proposed based on the deformation mechanism of the sandwich plates. The energy-absorbing ability varied with different structural geometry parameters of sandwich plates was evaluated, which revealed that the energy-absorbing ability of sandwich plates was sensitive to structural geometry parameters.

Zhang, H.; Huang, X. Q.; Tang, L. Q.

2010-05-01

221

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

222

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

223

Combined-load buckling behavior of metal-matrix composite sandwich panels under different thermal environments  

SciTech Connect

Combined compressive and shear buckling analysis was conducted on flat rectangular sandwich panels with the consideration of transverse shear effects of the core. The sandwich panel is fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that the square panel has the highest combined load buckling strength, and that the buckling strength decreases sharply with the increases of both temperature and panel aspect ratio. The effect of layup (fiber orientation) on the buckling strength of the panels was studied in detail. The metal matrix composite sandwich panel was much more efficient than the sandwich panel with nonreinforced face sheets and had the same specific weight.

Ko, W.L.; Jackson, R.H.

1991-09-01

224

Stable high-order molecular sandwiches: Hydrocarbon polyanion pairs with multiple lithium ions inside and out  

SciTech Connect

Stable ten-component sandwich compounds have been characterized in which four lithium ions reside between two tetraanions derived from corannulene or its alkyl-substituted derivatives and four additional lithium ions decorate the exterior. In tetrahydrofuran solution, the four lithium ions inside the sandwich can exchange environments with the four external lithium atoms, but the two tetraanion decks of the sandwich never separate from one another on the time scale of nuclear magnetic resonance. Theoretical calculations point to a [open quotes]stacked bowl[close quotes] conformation and a low energy barrier for synchronous double inversion of the tetraanion bowls in the solvated sandwich compounds.

Ayalon, A.; Rabinovitz, M. (Hebrew Univ. of Jerusalem (Israel)); Sygula, A.; Rabideau, P.W. (Louisiana State Univ., Baton Rouge, LA (United States)); Cheng, P.C.; Scott, L.T. (Boston College, Chestnut Hill, MA (United States))

1994-08-19

225

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

226

Preparation and PhysicoChemical Study of Sandwich Glass-Jute-Bisphenol-C-Formaldehyde Resin Composites  

Microsoft Academic Search

Glass-Jute-bisphenol-C-formaldehyde (Glass-Jute-BCF) sandwich composites were prepared by hand lay-up technique at 150°C under 30.4 MPa pressure for 2 h. The resin, glass and jute fiber content in the sandwich composite were 33.3, 10.4 and 56.3 wt%, respectively. 10 prepregs containing 8 inner prepregs of jute mats sandwiched between 2 outer prepregs of glass mats. Glass-Jute-BCF sandwich composite has 23 MPa tensile strength, 119 MPa flexural

J. P. Patel; N. M. Mehta; P. H. Parsania

2010-01-01

227

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

228

Low Velocity Blunt Impact on Lightweight Composite Sandwich Panels  

NASA Astrophysics Data System (ADS)

There is an increased desire to incorporate more composite sandwich structures into modern aircrafts. Because in-service aircrafts routinely experience impact damage during maintenance due to ground vehicle collision, dropped equipment, or foreign object damage (FOD) impact, it is necessary to understand their impact characteristics, particularly when blunt impact sources create internal damage with little or no external visibility. The objective of this investigation is to explore damage formation in lightweight composite sandwich panels due to low-velocity impacts of variable tip radius and energy level. The correlation between barely visible external dent formation and internal core damage was explored as a function of impact tip radius. A pendulum impactor was used to impact composite sandwich panels having honeycomb core while held in a 165 mm square window fixture. The panels were impacted by hardened steel tips with radii of 12.7, 25.4, 50.8, and 76.2 mm at energy levels ranging from 2 to 14 J. Experimental data showed little dependence of external dent depth on tip radius at very low energies of 2 to 6 J, and thus, there was also little variation in visibility due to tip radius. Four modes of internal core damage were identified. Internal damage span and depth were dependent on impact tip radius. Damage depth was also radius-dependent, but stabilized at constant depth independent of kinetic energy. Internal damage span increased with increasing impact energy, but not with increasing tip radius, suggesting a relationship between maximum damage tip radius with core density/size.

Chan, Monica Kar

229

A note concerning the Lighthill “sandwich model” of tropical cyclones  

PubMed Central

The basic element of Lighthill's “sandwich model” of tropical cyclones is the existence of “ocean spray,” a layer intermediate between air and sea made up of a cloud of droplets that can be viewed as a “third fluid.” We propose a mathematical model of the flow in the ocean spray based on a semiempirical turbulence theory and demonstrate that the availability of the ocean spray over the waves in the ocean can explain the tremendous acceleration of the wind as a consequence of the reduction of the turbulence intensity by droplets. This explanation complements the thermodynamic arguments proposed by Lighthill. PMID:16049097

Barenblatt, G. I.; Chorin, A. J.; Prostokishin, V. M.

2005-01-01

230

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

231

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

232

Optimized analysis of geometry parameters for honeycomb sandwich mirror  

NASA Astrophysics Data System (ADS)

The relationship of geometry parameters, specific stiffness, surface figure and natural frequency was investigated based on modified Gibson theory, sandwich theory, Hoff theory and vibration theory. By theoretical analysis and finite element method, we demonstrated the geometric parameters had non-linear influence on dimensionless specific stiffness in different directions with the honeycomb core was equivalent as modified solid material. Approximate expressions of deformation, natural frequency and geometric parameters were obtained. The results showed the optimal solidity ratio and face plate thickness ratio were in the range of 0.03 ~ 0.1 and 0.02 ~0.05, respectively.

Chen, Xiao'an; Cheng, Yuntao; Zeng, Qingna; Liu, Hong; Fang, Jingzhong; Rao, Changhui

2014-07-01

233

Sandwich-accretion disk models for active galactic nuclei.  

NASA Astrophysics Data System (ADS)

The author uses "sandwich-accretion disk" models to describe the inner part of active galactic nuclei. He examines by means of analytical and numerical methods the vertical structure of sandwich accretion disks from the central plane to the coronal phase including a transition region. Standard theory is applied to the cool disk and the coronal phase. A parameter Fq is included which represents the fraction of energy dissipated in the corona in relation to the total amount of dissipated energy. The author assumes that accretion takes place both in the disk and in the corona. He strongly suggests that majority of accretion occurs in the cool disk: Fq ? 1. The extension of the coronal phase is determined by the accretion rate for a given central mass. The coronae are described as one-temperature (1-T) and two-temperature (2-T) plasma both for hydrostatic equilibria and expanding coronae. The author takes local dissipation of kinetic energy as heating mechanism. Cooling is due to blackbody radiation for the disk and bremsstrahlung and inverse Compton scattering of soft photons for the corona. One obtains higher intensities in the high-frequency range for analytical models compared to numerical calculations.

Walter, T. M.

1998-01-01

234

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

235

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

236

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

237

Mechanical behavior of sandwich panels with hollow AlSi tubes core construction Jian Xiong a  

E-print Network

adhesive. The out- of-plane compression (i.e. core crushing), in-plane compression, and three-point bending. The Al­Si alloys are widely used in aerospace, marine, automotive and other engineering applications due

Vaziri, Ashkan

238

Standard test method for water absorption of core materials for structural sandwich constructions  

SciTech Connect

This method covers the determination of the relative rate of absorption of water by various types of core materials when immersed. The method is intended to apply to the testing of all types of core materials, including honeycomb structures, wood, cellulated materials, resin-impregnated reinforcing materials, etc. but does not apply to loose mineral fillers. The test specimen shall be in the form of a square 7.62 cm (3 in.) in length by 7.62 cm (3 in.) in width by the thickness of the material. The dimensions shall be measured to an accuracy of +-0.5 percent. Three specimens are weighed individually and conditioned as prescribed before immersion in a container of distilled water maintained at a temperature of 23 +- 3/sup 0/C. At the end of 24 hour, specimens are removed from the water, wiped dry, weighed and calculations are made from data.

Not Available

1980-01-01

239

Low-energy impact response of composite and sandwich composite plates with piezoelectric sensory layers  

E-print Network

stone or the fall of a composite cell-phone case from a table to the floor, where the damage caused mayLow-energy impact response of composite and sandwich composite plates with piezoelectric sensory xxxx Keywords: Low-energy impact Piezoelectric Composite Sandwich Plates Layerwise mechanics

Papadopoulos, Evangelos

240

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

241

Optimization of a Sandwich Panels by Using the Simulated Annealing Method  

Microsoft Academic Search

The mass reduction of space structures is of great importance, since it allows the payload and\\/or space vehicles lifetime increase. As a consequence, the use of sandwich panels has been growing in the last years, since these panels have a high stiffness\\/weight ratio. The problem presented in this work is about mass minimization of sandwich panels facesheets. The panel facesheets

Renato Correa Ribeiro Bustamante

2002-01-01

242

Honeycomb Sandwich Material Modeling for Dynamic Simulations of Aircraft Interior Components  

Microsoft Academic Search

An approach for modeling sandwich structures with a Nomex ® honeycomb core and phenolic composite faces in the commercial finite element code LS-DYNA with solid elements for the core and shell elements for the thin faces is presented, which accounts for the major sandwich failure modes. Extensive material testing was conducted to determine the parameters for the composite face material

S. Heimbs; P. Middendorf; M. Maier

243

Structural analysis of the adhesive bond in a honeycomb core sandwich panel  

Microsoft Academic Search

Detailed finite element models are used to examine the effect of the adhesive joint between the honeycomb core and the face sheets on the load transfer and static response of sandwich panels. The square-cell honeycomb core panels considered have simply supported edges and are subjected to static uniform pressure loading. The sandwich core, face sheets and adhesive joint are modeled

W. Scott Burton; A. K. Noor

1997-01-01

244

Torsion of honeycomb FRP sandwich beams with a sinusoidal core configuration  

Microsoft Academic Search

A combined analytical, numerical and experimental investigation of honeycomb fiber-reinforced polymer (HFRP) sandwich beam samples subjected to torsion loads is conducted. The sandwich panel considered in this study has unique sinusoidal core geometry in the plane extending vertically between face laminates, and it has been used primarily as decking systems in highway bridges. Using a homogenization process and mechanics of

Julio F. Davalos; Pizhong Qiao; Vinod Ramayanam; Luyang Shan; Justin Robinson

2009-01-01

245

Effect of debonding on natural frequencies and frequency response functions of honeycomb sandwich beams  

Microsoft Academic Search

The natural frequencies of honeycomb sandwich beams having debonding or delamination embedded between the face-layer laminates and the honeycomb core are studied herein. A theoretical analysis of the effect of the extent of debonding on the flexural stiffness and on the natural frequency is compared with experimental observations. In this analysis the free vibration of the delaminated sandwich beams is

Hyeung-Yun Kim; Woonbong Hwang

2002-01-01

246

Evaluating bending fatigue strength of aluminum honeycomb sandwich beams using local parameters  

Microsoft Academic Search

This study analyzed the four-point bending fatigue strengths of aluminum honeycomb sandwich beams with cores of various relative densities. The debonding of the adhesive between the face sheet and the core was identified to be the major failure mode. Several global parameters and local parameters were considered to evaluate the fatigue life of the studied sandwich structures. The finite element

Yi-Ming Jen; Li-Yen Chang

2008-01-01

247

International Journal of Impact Engineering 35 (2008) 10631074 Mechanical response of metallic honeycomb sandwich panel structures  

E-print Network

honeycomb sandwich panel structures to high-intensity dynamic loading Kumar P. Dharmasenaa,Ã?, Haydn N many of the phenomenological details of the core deformation behavior. The honeycomb sandwich panels Explosive tests were performed in air to study the dynamic mechanical response of square honeycomb core

Hutchinson, John W.

248

EXPERIMENTAL TEST AND FINITE ELEMENT MODELLING OF PEDESTRIAN HEADFORM IMPACT ON HONEYCOMB SANDWICH PANEL  

Microsoft Academic Search

This paper represents a Finite Element model of Cel lbond's aluminium honeycomb sandwich panel and proposes an original technique to develop the mater ial characteristics which realistically simulate a child headform impacting on a sandwich panel. As part of a major study to develop a pedestrian friendly car bonnet design, this investigation has been carried out with the requirement as

M. Asadi; A. C. Vollaire; M. Ashmead; H. Shirvani

249

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

250

Mechanical response of metallic honeycomb sandwich panel structures to high-intensity dynamic loading  

Microsoft Academic Search

Explosive tests were performed in air to study the dynamic mechanical response of square honeycomb core sandwich panels made from a super-austenitic stainless steel alloy. Tests were conducted at three levels of impulse load on the sandwich panels and solid plates with the same areal density. Impulse was varied by changing the charge weight of the explosive at a constant

Kumar P. Dharmasena; Haydn N. G. Wadley; Zhenyu Xue; John W. Hutchinson

2008-01-01

251

The role of the resin fillet in the delamination of honeycomb sandwich structures  

Microsoft Academic Search

In this study, the mechanism of peel fracture (or core\\/skin delamination) in honeycomb-core sandwich panels was investigated, and the role of resin fillets on energy absorption was elucidated. Fillet deformation and fracture were shown to control the delamination resistance of sandwich panels, to a great extent. In fact the area fraction of fillets on the fracture surface proved to be

Ryo Okada; M. T Kortschot

2002-01-01

252

Performance of sandwich plates with truss cores Nathan Wicks *, John W. Hutchinson  

E-print Network

Performance of sandwich plates with truss cores Nathan Wicks *, John W. Hutchinson Division in revised form 30 January 2003 Abstract Sandwich plates with truss cores fashioned from straight struts have distinct advantages relative to other con- structions, including those with honeycomb cores. In addition

Hutchinson, John W.

253

Structurally optimized sandwich panels with prismatic cores L. Valdevit a,*, J.W. Hutchinson b  

E-print Network

Structurally optimized sandwich panels with prismatic cores L. Valdevit a,*, J.W. Hutchinson b , A sandwich panels with corrugated and prismatic diamond cores have been analyzed and their behavior compared with panels designed using truss and honeycomb cores. Failure mechanism maps have been devised that account

Hutchinson, John W.

254

Wave propagation in a sandwich structure Liping Liu a,*, Kaushik Bhattacharya b  

E-print Network

online 6 May 2009 Keywords: Wave propagation Transfer matrix Sandwich structure Mindlin plate theory a b equation to a Hamiltonian system and then using a transfer matrix approach for solving the Hamiltonian s t r a c t The propagation of elastic waves in a sandwich structure with two thin stiff face

Bhattacharya, Kaushik

255

Wave propagation in a sandwich structure Liping Liu a,*, Kaushik Bhattacharya b  

E-print Network

online xxxx Keywords: Wave propagation Transfer matrix Sandwich structure Mindlin plate theory a b s t r equation to a Hamiltonian system and then using a transfer matrix approach for solving the Hamiltonian a c t The propagation of elastic waves in a sandwich structure with two thin stiff face

Liu, Liping

256

Thermal response of a flat heat pipe sandwich structure to a localized heat flux  

E-print Network

Thermal response of a flat heat pipe sandwich structure to a localized heat flux G. Carbajal a , C The temperature distribution across a flat heat pipe sandwich structure, subjected to an intense localized thermal to the evaporator side of the flat heat pipe, while the condenser side was cooled via natural convective

Wadley, Haydn

257

Mechanical response of carbon fiber composite sandwich panels with pyramidal truss cores  

E-print Network

of light carbon fiber reinforced polymer (CFRP) composite materials with structurally efficient sandwich-predicts the measurements. The CFRP pyramidal cores investigated here have a similar mechanical performance to CFRP (e.g. so that cooling fluid can pass through a sandwich core), the CFRP pyramidal cores offer

Wadley, Haydn

258

Response of metallic pyramidal lattice core sandwich panels to high intensity impulsive loading in air  

E-print Network

blast Fluidestructure interaction Pyramidal core Sandwich panels a b s t r a c t Small scale explosive face as a result of a fluid-structure inter- action (FSI) effect [3,4,8e10] and the higher flexural the large scale bending and fracture response of a model sandwich panel system in which the core has little

Hutchinson, John W.

259

Analysis and interpretation of a test for characterizing the response of sandwich panels to water blast  

Microsoft Academic Search

Metallic sandwich panels are more effective at resisting underwater blast than monolithic plates at equivalent mass\\/area. The present assessment of this benefit is based on a recent experimental study of the water blast loading of a sandwich panel with a multilayered core, using a Dyno-crusher test. The tests affirm that the transmitted pressure and impulse are significantly reduced when a

Z. Wei; K. P. Dharmasena; H. N. G. Wadley; A. G. Evans

2007-01-01

260

Deformation and fracture modes of sandwich structures subjected to underwater impulsive loads  

Microsoft Academic Search

Sandwich panel structures with thin front faces and low relative density cores offer significant impulse mitigation possibilities provided panel fracture is avoided. Here steel square honeycomb and pyramidal truss core sandwich panels with core relative densities of 4% were made from a ductile stainless steel and tested under impulsive loads simulating underwater blasts. Fluid-structure interaction experiments were performed to (i)

Lapo Mori; S. Lee; Zhenyu Xue; A. Vaziri; D. T. QUEHEILLALT; K. P. DHARMASENA; Haydn Wadley; J. W. HUTCHINSON; H. D. ESPINOSA

2007-01-01

261

Underwater blast response of free-standing sandwich plates with metallic lattice cores  

Microsoft Academic Search

The underwater blast response of free-standing sandwich plates with a square honeycomb core and a corrugated core has been measured. The total momentum imparted to the sandwich plate and the degree of core compaction are measured as a function of (i) core strength, (ii) mass of the front face sheet (that is, the wet face) and (iii) time constant of

G. J. McShane; V. S. Deshpande; N. A. Fleck

2010-01-01

262

Dynamic properties of sandwich structures with integrated shear-thickening fluids  

Microsoft Academic Search

The integration of shear-thickening fluids (STFs) into composite structures has been investigated with the aim of tuning part stiffness and damping capacity under dynamic deformation. Results from oscillatory rheological measurements for a STF based on concentrated fused silica in polypropylene glycol were correlated with results from vibrating beam tests on model sandwich structures containing layers of the same STF sandwiched

C. Fischer; S. A. Braun; P.-E. Bourban; V. Michaud; C. J. G. Plummer; J.-A. E. Månson

2006-01-01

263

Natural Cork Agglomerate Employed as an Environmentally Friendly Solution for Quiet Sandwich Composites  

PubMed Central

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

264

Static and dynamic response of a sandwich structure under axial compression  

NASA Astrophysics Data System (ADS)

This thesis is concerned with a combined experimental and theoretical investigation of the static and dynamic response of an axially compressed sandwich structure. For the static response problem of sandwich structures, a two-dimensional mechanical model is developed to predict the global and local buckling of a sandwich beam, using classical elasticity. The face sheet and the core are assumed as linear elastic orthotropic continua in a state of planar deformation. General buckling deformation modes (periodic and non-periodic) of the sandwich beam are considered. On the basis of the model developed here, validation and accuracy of several previous theories are discussed for different geometric and material properties of a sandwich beam. The appropriate incremental stress and conjugate incremental finite strain measure for the instability problem of the sandwich beam, and the corresponding constitutive model are addressed. The formulation used in the commercial finite element package is discussed in relation to the formulation adopted in the theoretical derivation. The Dynamic response problem of a sandwich structure subjected to axial impact by a falling mass is also investigated. The dynamic counterpart of the celebrated Euler buckling problem is formulated first and solved by considering the case of a slender column that is impacted by a falling mass. A new notion, that of the time to buckle, "t*" is introduced, which is the corresponding critical quantity analogous to the critical load in static Euler buckling. The dynamic bifurcation buckling analysis is extended to thick sandwich structures using an elastic foundation model. A comprehensive set of impact test results of sandwich columns with various configurations are presented. Failure mechanisms and the temporal history of how a sandwich column responds to axial impact are discussed through the experimental results. The experimental results are compared against analytical dynamic buckling studies and finite element based simulation of the impact event.

Ji, Wooseok

265

A Novel Sandwich Electrochemical Immunosensor Based on the DNA-Derived Magnetic Nanochain Probes for Alpha-Fetoprotein  

PubMed Central

One novel electrochemical immunosensor was constructed by immobilizing capture antibody of alpha-fetoprotein (AFP Ab1) on a nafion/nanogold-particle modified glassy carbon electrode. With a sandwich immunoassay, one DNA-derived magnetic nanoprobe, simplified as DNA/(ZMPs—HRP-AFP Ab2)n, was employed for the detection of AFP. The fabricated procedure of the proposed biosensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The performance and factors influencing the performance of the biosensor were also evaluated. Under optimal conditions, the developed biosensor exhibited a well-defined electrochemical behavior toward the reduction of AFP ranging from 0.01 to 200?ng/mL with a detection limit of 4?pg/mL (S/N = 3). The biosensor was applied to the determination of AFP in serum with satisfactory results. It is important to note that the sandwich nanochainmodified electro-immunosensor provided an alternative substrate for the immobilization of other tumor markers. PMID:22013390

Gan, Ning; Jia, Liyong; Zheng, Lei

2011-01-01

266

Published: Journal of Sandwich Structures and Materials,16, 22-41 (2014) (doi:10.1177/1099636213502980) Corresponding author  

E-print Network

as other sandwich composites (e.g. foams and honeycomb cores), namely ultra low weight and considerablePublished: Journal of Sandwich Structures and Materials,16, 22-41 (2014) (doi:10 for cores of sandwich composites Meisam Shir Mohammadi and John A Nairn Wood Science & Engineering, Oregon

Nairn, John A.

267

European Journal of Mechanics A/Solids 25 (2006) 215229 The response of clamped sandwich plates with lattice cores  

E-print Network

resistance than monolithic plates of equal mass, and the square-honeycomb sandwich plates outperformEuropean Journal of Mechanics A/Solids 25 (2006) 215�229 The response of clamped sandwich plates circular monolithic and sandwich plates of equal areal mass and thickness has been measured by loading

Fleck, Norman A.

268

International Journal of Impact Engineering 35 (2008) 920936 Impact response of sandwich plates with a pyramidal lattice core  

E-print Network

), prismatic sandwich cores such as the corrugated and Y-frame cores [7] and various honeycomb cores. The trussInternational Journal of Impact Engineering 35 (2008) 920­936 Impact response of sandwich plates The ballistic performance edge clamped 304 stainless-steel sandwich panels has been measured by impacting

Wadley, Haydn

269

Sandwich-walled cylindrical shells with lightweight metallic lattice truss cores and carbon fiber-reinforced composite face sheets  

E-print Network

, sandwich panels traditionally made from foam and honeycomb cores with close-cells [9] cannot accom- modateSandwich-walled cylindrical shells with lightweight metallic lattice truss cores and carbon fiber manufactured sandwich-walled cylindrical shells with aluminum pyramidal truss core of constant curvature

Vaziri, Ashkan

270

Influence of skin\\/core debonding on free vibration behavior of foam and honeycomb cored sandwich plates  

Microsoft Academic Search

The dynamic behavior of partially delaminated at the skin\\/core interface sandwich plates with flexible cores is studied. The commercial finite element code ABAQUS is used to calculate natural frequencies and mode shapes of the sandwich plates containing a debonding zone. The influence of the debonding size, debonding location and types of debonding on the modal parameters of damaged sandwich plates

Vyacheslav N. Burlayenko; Tomasz Sadowski

2010-01-01

271

Damage monitoring in sandwich beams by modal parameter shifts: A comparative study of burst random and sine dwell  

E-print Network

response of honeycomb sandwich beams, damaged by two different ways i.e., impact damage and core Parameters, Structural Health Monitoring, Honeycomb Sandwich Beams 1. Introduction Laminated honeycomb1 Damage monitoring in sandwich beams by modal parameter shifts: A comparative study of burst

Mailhes, Corinne

272

Multi-physics modeling of the fabrication and dynamic performance of all-metal auxetic-hexagonal sandwich-structures  

E-print Network

-metal sandwich structures containing auxetic honeycomb cores. Consequently, the following three rele- vant topics-hexagonal sandwich-structures M. Grujicic , R. Galgalikar, J.S. Snipes, R. Yavari, S. Ramaswami Department-metal sandwich-structures with an auxetic-hexagonal core. Specific fabrication processes analyzed in the present

Grujicic, Mica

273

“Segment-wise model” for theoretical simulation of barely visible indentation damage in composite sandwich beams: Part I – Formulation  

Microsoft Academic Search

When localized transverse loading is applied to a sandwich structure, the facesheet locally deflects and the core crushes. A residual dent induced by the core crushing significantly degrades the mechanical properties of the sandwich structure. The authors establish a “segment-wise model” for theoretical simulation of static indentation loading and unloading responses in honeycomb sandwich beams with composite facesheets. The model

Shu Minakuchi; Yoji Okabe; Nobuo Takeda

2008-01-01

274

Room Temperature and Elevated Temperature Composite Sandwich Joint Testing  

NASA Technical Reports Server (NTRS)

Testing of composite sandwich joint elements has been completed to verify the strength capacity of joints designed to carry specified running loads representative of a high speed civil transport wing. Static tension testing at both room and an elevated temperature of 350 F and fatigue testing at room temperature were conducted to determine strength capacity, fatigue life, and failure modes. Static tension test results yielded failure loads above the design loads for the room temperature tests, confirming the ability of the joint concepts tested to carry their design loads. However, strength reductions as large as 30% were observed at the elevated test temperature, where all failure loads were below the room temperature design loads for the specific joint designs tested. Fatigue testing resulted in lower than predicted fatigue lives.

Walker, Sandra P.

1998-01-01

275

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

276

Boratabenzene-vanadium sandwich molecular wire and its properties.  

PubMed

Different from all reported sandwich molecular wires (SMWs), a novel class of SMW including vanadium boratabenzene (HBBz) clusters and their related one-dimensional (1D) SMWs are explored by using a density functional theory approach. The uniqueness of this class of SMWs lies in the boron heterocycles, where they possess a reactive functional atom. These features may overcome the limitation of existing SMWs which are inert and are difficult to be absorbed stably on surfaces. Theoretical calculations of the novel vanadium boratabenzene clusters indicated that they are energetically stable, with the rings having a restricted degree of rotation. In addition, its metallic 1D analog shows great promise in the applications of molecular electronics and spintronics. PMID:23108175

Tan, Wee Boon; Hongmei, Jin; Yang, Shuo-Wang; Xu, Guo Qin

2012-12-01

277

Microbiological investigation of an antibacterial sandwich layer system.  

PubMed

To allow medical application of an artificial bladder made of biocompatible polyurethane, a long-term stable antibacterial coating is required. Alone, the artificial bladder exhibits no defense against microorganisms. Silver coating provides long-term antibacterial protection by the continuous release of silver ions into aqueous solutions. To control and to prolong the rate of silver ion release, the deposited silver film has to be protected by an inert film of biocompatible polyparylene by means of chemical vapor deposition. In this study, an antibacterial artificial bladder surface was developed by the formation of a sandwich structure consisting of silver and a biocompatible polymer (polyparylene) as a diffusion barrier. Specifically, this study analyzed the correlation between polyparylene thickness and silver release to determine optimal concentrations to combat common bacteria in vitro. The release of silver from sandwich structures was investigated in vitro by testing different thicknesses of polyparylene (0, 190, 540, and 1000 nm) as a diffusion barrier. The best result was demonstrated with a thickness of 190 nm of polyparylene, which yielded a silver dispense rate of 650?pg/(cm(2)?min), which would yield bacteriozidal concentrations above 30??g/l in the bladder volume. The authors confirmed the antibacterial effect in vitro against common urinary tract infection pathogens, namely, Escherichia coli and Staphylococcus cohnii. Inhibition of bacterial growth could be detected within 8 h. A diffusion assay with spherical silver spots showed concentric zones free of bacterial growth. Our results suggest the possible utility of silver-polyparylene coatings as antibacterial agents. PMID:25280843

Heidari Zare, Hamideh; Sudhop, Stefanie; Schamberger, Florian; Franz, Gerhard

2014-09-01

278

Probabilistic Structural Evaluation of Uncertainties in Radiator Sandwich Panel Design  

NASA Technical Reports Server (NTRS)

The Jupiter Icy Moons Orbiter (JIMO) Space System is part of the NASA's Prometheus Program. As part of the JIMO engineering team at NASA Glenn Research Center, the structural design of the JIMO Heat Rejection Subsystem (HRS) is evaluated. An initial goal of this study was to perform sensitivity analyses to determine the relative importance of the input variables on the structural responses of the radiator panel. The desire was to let the sensitivity analysis information identify the important parameters. The probabilistic analysis methods illustrated here support this objective. The probabilistic structural performance evaluation of a HRS radiator sandwich panel was performed. The radiator panel structural performance was assessed in the presence of uncertainties in the loading, fabrication process variables, and material properties. The stress and displacement contours of the deterministic structural analysis at mean probability was performed and results presented. It is followed by a probabilistic evaluation to determine the effect of the primitive variables on the radiator panel structural performance. Based on uncertainties in material properties, structural geometry and loading, the results of the displacement and stress analysis are used as an input file for the probabilistic analysis of the panel. The sensitivity of the structural responses, such as maximum displacement and maximum tensile and compressive stresses of the facesheet in x and y directions and maximum VonMises stresses of the tube, to the loading and design variables is determined under the boundary condition where all edges of the radiator panel are pinned. Based on this study, design critical material and geometric parameters of the considered sandwich panel are identified.

Kuguoglu, Latife; Ludwiczak, Damian

2006-01-01

279

Transient Dynamic Response and Failure of Sandwich Composite Structures under Impact Loading with Fluid Structure Interaction  

NASA Astrophysics Data System (ADS)

The objective of this study is to examine the Fluid Structure Interaction (FSI) effect on transient dynamic response and failure of sandwich composite structures under impact loading. The primary sandwich composite used in this study consisted of a 6.35 mm balsa core and a multi-ply symmetrical plain weave 6 oz E-glass skin. Both clamped sandwich composite plates and beams were studied using a uniquely designed vertical drop-weight testing machine. There were three impact conditions on which these experiments focused. The first of these conditions was completely dry (or air surrounded) testing. The second condition was completely water submerged. The final condition was also a water submerged test with air support at the backside of the plates. The tests were conducted sequentially, progressing from a low to high drop height to determine the onset and spread of damage to the sandwich composite when impacted with the test machine. The study showed the FSI effect on sandwich composite structures is very critical such that impact force, strain response, and damage size are generally much greater with FSI under the same impact condition. As a result, damage initiates at much lower impact energy conditions with the effect of FSI. Neglecting to account for FSI effects on sandwich composite structures results in very non-conservative analysis and design. Additionally, it was observed that the damage location changed for sandwich composite beams with the effect of FSI.

Kwon, Y. W.; Violette, M. A.; McCrillis, R. D.; Didoszak, J. M.

2012-12-01

280

Combined compressive and shear buckling analysis of hypersonic aircraft structural sandwich panels  

NASA Technical Reports Server (NTRS)

The combined-load (compression and shear) buckling equations were established for orthotropic sandwich panels by using the Rayleigh-Ritz method to minimize the panel total potential energy. The resulting combined-load buckling equations were used to generate buckling interaction curves for super-plastically-formed/diffusion-bonded titanium truss-core sandwich panels and titanium honeycomb-core sandwich panels having the same specific weight. The relative combined-load buckling strengths of these two types of sandwich panels are compared with consideration of their sandwich orientations. For square and nearly square panels of both types, the combined load always induces symmetric buckling. As the panel aspect ratios increase, antisymmetric buckling will show up when the loading is shear-dominated combined loading. The square panel (either type) has the highest combined buckling strength, but the combined load buckling strength drops sharply as the panel aspect ratio increases. For square panels, the truss-core sandwich panel has higher compression-dominated combined load buckling strength. However, for shear dominated loading, the square honeycomb-core sandwich panel has higher shear-dominated combined load buckling strength.

Ko, William L.; Jackson, Raymond H.

1991-01-01

281

Combined compressive and shear buckling analysis of hypersonic aircraft sandwich panels  

NASA Technical Reports Server (NTRS)

The combined-load (compression and shear) buckling equations were established for orthotropic sandwich panels by using the Rayleigh-Ritz method to minimize the panel total potential energy. The resulting combined-load buckling equations were used to generate buckling interaction curves for super-plastically-formed/diffusion-bonded titanium truss-core sandwich panels and titanium honeycomb-core sandwich panels having the same specific weight. The relative combined-load buckling strengths of these two types of sandwich panels are compared with consideration of their sandwich orientations. For square and nearly square panels of both types, the combined load always induces symmetric buckling. As the panel aspect ratios increase, antisymmetric buckling will show up when the loading is shear-dominated combined loading. The square panel (either type) has the highest combined buckling strength, but the combined load buckling strength drops sharply as the panel aspect ratio increases. For square panels, the truss-core sandwich panel has higher compression-dominated load buckling strength. However, for shear dominated loading, the square honeycomb-core sandwich panel has higher shear-dominated combined load buckling strength.

Ko, William L.; Jackson, Raymond H.

1992-01-01

282

Damage-Tolerance Characteristics of Composite Fuselage Sandwich Structures with Thick Facesheets  

NASA Technical Reports Server (NTRS)

Damage tolerance characteristics and results from experimental and analytical studies of a composite fuselage keel sandwich structure subjected to low-speed impact damage and discrete-source damage are presented. The test specimens are constructed from graphite-epoxy skins borided to a honeycomb core, and they are representative of a highly loaded fuselage keel structure. Results of compression-after-impact (CAI) and notch-length sensitivity studies of 5-in.-wide by 10-in.long specimens are presented. A correlation between low-speed-impact dent depth, the associated damage area, and residual strength for different impact-energy levels is described; and a comparison of the strength for undamaged and damaged specimens with different notch-length-to-specimen-width ratios is presented. Surface strains in the facesheets of the undamaged specimens as well as surface strains that illustrate the load redistribution around the notch sites in the notched specimens are presented and compared with results from finite element analyses. Reductions in strength of as much as 53.1 percent for the impacted specimens and 64.7 percent for the notched specimens are observed.

McGowan, David M.; Ambur, Damodar R.

1997-01-01

283

Elastic constants for superplastically formed/diffusion-bonded corrugated sandwich core  

NASA Technical Reports Server (NTRS)

Formulas and associated graphs for evaluating the effective elastic constants for a superplastically formed/diffusion bonded (SPF/DB) corrugated sandwich core, are presented. A comparison of structural stiffnesses of the sandwich core and a honeycomb core under conditions of equal sandwich core density was made. The stiffness in the thickness direction of the optimum SPF/DB corrugated core (that is, triangular truss core) is lower than that of the honeycomb core, and that the former has higher transverse shear stiffness than the latter.

Ko, W. L.

1980-01-01

284

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

285

Elastic and plastic buckling of simply supported solid-core sandwich plates in compression  

NASA Technical Reports Server (NTRS)

A solution is presented for the problem of the compressive buckling of simply supported, flat, rectangular, solid-core sandwich plates stressed either in the elastic range or in the plastic range. Charts for the analysis of long sandwich plates are presented for plates having face materials of 24s-t3 aluminum alloy, 76s-t6 alclad aluminum alloy, and stainless steel. A comparison of computed and experimental buckling stresses of square solid-core sandwich plates indicates fair agreement between theory and experiment.

Seide, Paul; Stowell, Elbridge Z

1950-01-01

286

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

287

Passively Q-switched and mode-locked Nd:YVO4 laser with sandwich structured wallpaper graphene oxide absorber  

NASA Astrophysics Data System (ADS)

We report on a passively Q-switched and mode-locked Nd:YVO4 laser using a novel low-cost wallpaper graphene oxide absorber. Sandwich structured wallpaper graphene oxide absorber was constructed by a high transmission mirror, a piece of wallpaper graphene oxide absorber and a reflective mirror. The average output power of 310 mW of passively Q-switched and mode-locked laser was successfully achieved. The repetition rate and pulse width of the Q-switched envelope were 213 kHz and 770 ns, respectively. The repetition rate of passively mode-locked pulse within the Q-switched envelope was 81.3 MHz with the pulse energy of 3.8 nJ.

Zhang, L.; Wang, Y. G.; Yu, H. J.; Sun, W.; Han, Z. H.; Zhang, S. B.; Hou, W.; Lin, X. C.; Li, J. M.; Tang, J.

2011-11-01

288

The soft impact of composite sandwich beams with a square-honeycomb core B.P. Russell, T. Liu, N.A. Fleck, V.S. Deshpande*  

E-print Network

The soft impact of composite sandwich beams with a square-honeycomb core B.P. Russell, T. Liu, N that the sandwich beams outperformed both monolithic composite beams and steel sandwich beams with a square-honeycomb-clamped monolithic beams and sandwich beams of equal areal mass have been measured by loading the beams at mid

Fleck, Norman A.

289

An Investigation on Low Velocity Impact Response of Multilayer Sandwich Composite Structures  

PubMed Central

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

290

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

291

Thick sandwich panel fabrication for bridge deck structure and its joint strength  

NASA Astrophysics Data System (ADS)

The purpose of this study is to evaluate the static strength of thick plate laser welded lap joint and the performance of thick sandwich panel for bridge deck structure. The strength of thin sheet laser welded lap joint whose thickness is less than 1.6 mm have been already reported, but the strength of thick plate laser welded lap joint whose thickness is more than 10 mm is not known. The authors believe this thick laser welded lap jont enable heavy industries to make a revolution on applying it for sandwich panel fabrication. Then, they have conducted mechanical tests of 10 mm + 6 mm thick laser welded lap joints to grasp their static strength. According to the obtained data, they fabricate a thick sandwich panel model of newly designed bridge deck structure for evaluation. The static lading test, cyclic loading test and collapsing test show that the thick sandwich panel has enough performance for the practical application.

Kitagawa, Akikazu; Fukuda, Naoaki; Takeda, Shinnosuke; Matsunawa, Akira

2003-03-01

292

Multiple debondings' detection in honeycomb sandwich structures using multi-frequency elastic guided waves  

NASA Astrophysics Data System (ADS)

Due to the complex nature of sandwich structures, damage detection in honeycomb sandwich structures inherently imposes many challenges. In this study, leaky guided wave properties generated by piezoelectric wafer actuators/sensors in honeycomb sandwich structures are first simulated by the finite element method. In the numerical model, the detailed honeycomb core geometry is considered. Differential features due to presence of debonding are determined through an appropriate damage index analysis of the signals at the normal and debonded conditions. The image of the debonding is formed by using a probability analysis of the leaky guided wave at each frequency. The final image of the structure can be fused from multi-frequency leaky guided waves. A new method for multi-debonding detection is proposed. Based on the analysis, information about the debondings in the honeycomb sandwich structures can be quantitatively characterized.

Song, F.; Huang, G. L.; Kim, J. H.; Haran, S.

2010-03-01

293

Pulsed thermography detection of water and hydraulic oil intrusion in the honeycomb sandwich structure composite  

NASA Astrophysics Data System (ADS)

Water and hydraulic oil intrusion inside honeycomb sandwich Structure Composite during service has been linked to in-flight failure in some aircraft. There is an ongoing effort to develop nondestructive testing methods to detect the presence of water and hydraulic oil within the sandwich panels. Pulsed thermography(PT) represents an attractive approach in that it is sensitive to the change of thermal properties. Using a flash lamp PT, testing can be applied directly to the surface of the panel. The viability of PT is demonstrated through laboratory imaging of both water and hydraulic oil within sandwich panels. The detection of water and hydraulic oil intrusion using a one-sided flash lamp PT is presented. It is shown that simple detection, as well as spatial localization of water and hydraulic oil within sandwich panels, and assign the quantity of water and hydraulic oil is possible.

Zhao, Shi-bin; Zhang, Cun-lin; Wu, Nai-ming

2011-08-01

294

Metal-graphene-metal sandwich contacts for enhanced interface bonding and work function control.  

PubMed

Only a small fraction of all available metals has been used as electrode materials for carbon-based devices due to metal-graphene interface debonding problems. We report an enhancement of the bonding energy of weakly interacting metals by using a metal-graphene-metal sandwich geometry, without sacrificing the intrinsic ?-electron dispersions of graphene that is usually undermined by strong metal-graphene interface hybridization. This sandwich structure further makes it possible to effectively tune the doping of graphene with an appropriate selection of metals. Density functional theory calculations reveal that the strengthening of the interface interaction is ascribed to an enhancement of interface dipole-dipole interactions. Raman scattering studies of metal-graphene-copper sandwiches are used to validate the theoretically predicted tuning of graphene doping through sandwich structures. PMID:22540140

Gong, Cheng; Hinojos, David; Wang, Weichao; Nijem, Nour; Shan, Bin; Wallace, Robert M; Cho, Kyeongjae; Chabal, Yves J

2012-06-26

295

Development of bonding methods and energy absorption of sandwich panels for thermoplastic advanced composites.  

E-print Network

??Given their high strength-to-weight and stiffness-to-weight ratios, sandwich composites continue to be considered for automotive applications. Thermoplastic materials, while difficult to bond, have an increased… (more)

Haslam, Erik Bravant

2012-01-01

296

Structural design and analysis of a lightweight composite sandwich space radiator panel  

E-print Network

models to validate the predictions of finite element analysis. The optimum dimensions of the sandwich panel are determined and structural and thermal response of the Poco foam is compared with existing aluminum honeycomb core....

Mukundan, Sudharsan

2005-02-17

297

ANALYSES OF DEFORMATION IN VISCOELASTIC SANDWICH COMPOSITES SUBJECT TO MOISTURE DIFFUSION  

E-print Network

Sandwich composites with polymer foam core are currently used in load-bearing components in buildings and naval structures due to their high strength to weight and stiffness to weight ratios, excellent thermal insulation, and ease of manufacturing...

Joshi, Nikhil P.

2010-01-16

298

An Analytical and Experimental Evaluation of the Damping Capacity of Sandwich BEAMS with Viscoelastic Cores.  

National Technical Information Service (NTIS)

A study is made of the free vibrations of sandwich beams with viscoelastic cores. The study includes formulation of the equations of motion and natural boundary conditions, derivation of expressions for the modal distribution of damping based upon small d...

I. W. Jones, V. L. Salerno, A. Savacchio

1966-01-01

299

Experimental Investigation of Strain Concentrations Caused by Inserts in Sandwich Beams  

Microsoft Academic Search

This paper presents an experimental study of the strain concentrations developing across the insert-core junctions in a sandwich beam with an implanted stiff insert into its core. Strain measurements were carried out at several positions on the skins and across the insert-core junc- tion, for several sandwich beam specimens loaded in 3-points bending and having inserts with various geometries. The

N. G. Tsouvalis; M. J. Kollarini

2008-01-01

300

A numerical model for bird strike of aluminium foam-based sandwich panels  

Microsoft Academic Search

Experimental bird-strike tests have been carried out on double sandwich panels made from AlSi7Mg0.5 aluminium foam core and aluminium AA2024 T3 cover plates. The bird-strike velocity varied from 140 to 190m\\/s. The test specimens were instrumented with strain gauges in the impacted area to measure the local strains of the rear sandwich plate. A numerical model of this problem has

A. G. Hanssen; Y. Girard; L. Olovsson; T. Berstad; M. Langseth

2006-01-01

301

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

302

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

Microsoft Academic Search

This paper introduces a simple method for engineering analysis of ply drop-off induced local bending effects in CFRP\\/honeycomb sandwich panels. The model constituent parts are the base-line face laminate of a CFRP\\/sandwich panel, a dropped sub-laminate, a supporting honeycomb core material, and an adhesive\\/resin layer interfacing the laminates. The interaction between the core material and the face laminates is modelled

O. T. Thomsen; W. Rits; D. C. G. Eaton; S. Brown

1996-01-01

303

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

Microsoft Academic Search

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

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

2007-01-01

304

Preparation and microwave absorption properties of foam-based honeycomb sandwich structures  

Microsoft Academic Search

Radar-absorbing structures having foam-based honeycomb sandwich structures (FBHSS) were fabricated through a conventional foaming technique. Conductive fillers such as carbonyl iron\\/nickel fibers (CINF) and magnetic metal micropowder (MMP) were added to polyurethane foams so as to efficiently increase the absorbing capacity of FBHSS. A honeycomb sandwich structure, which was made of composite face sheets and foam cores, was used as

Yanfei He; Rongzhou Gong

2009-01-01

305

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

306

Experimental research on the bearing capacity of polyurethane foam sandwich concrete wallboard  

Microsoft Academic Search

In order to study the bearing capacity of polyurethane foam sandwich concrete wall-board, 6 bending specimens and 3 axial compression specimens were designed. According to the experiment, the failure patterns, loading-displacement curves and the stress-strain curves of the specimens were obtained. The results show that polyurethane foam sandwich concrete wall-board average strain of bending normal cross-section does not conform to

Yi-sheng Su; Zong-ping Chen; Xiao-jun Ke; Guo-hong Xiong

2010-01-01

307

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

308

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

309

Simulations of backgate sandwich nanowire MOSFETs with improved device performance  

NASA Astrophysics Data System (ADS)

We propose a novel backgate sandwich nanowire MOSFET (SNFET), which offers the advantages of ETSOI (dynamic backgate voltage controllability) and nanowire FETs (good short channel effect). A backgate is used for threshold voltage (Vt) control of the SNFET. Compared with a backgate FinFET with a punch-through stop layer (PTSL), the SNFET possesses improved device performance. 3D device simulations indicate that the SNFET has a three times larger overdrive current, a ~75% smaller off leakage current, and reduced subthreshold swing (SS) and DIBL than those of a backgate FinFET when the nanowire (NW) and the fin are of equal width. A new process flow to fabricate the backgate SNFET is also proposed in this work. Our analytical model suggests that Vt control by the backgate can be attributed to the capacitances formed by the frontgate, NW, and backgate. The SNFET devices are compatible with the latest state-of-the-art high-k/metal gate CMOS technology with the unique capability of independent backgate control for nFETs and pFETs, which is promising for sub-22 nm scaling down.

Hengliang, Zhao; Huilong, Zhu; Jian, Zhong; Xiaolong, Ma; Xing, Wei; Chao, Zhao; Dapeng, Chen; Tianchun, Ye

2014-10-01

310

Characterizing Facesheet/Core Disbonding in Honeycomb Core Sandwich Structure  

NASA Technical Reports Server (NTRS)

Results are presented from an experimental investigation into facesheet core disbonding in carbon fiber reinforced plastic/Nomex honeycomb sandwich structures using a Single Cantilever Beam test. Specimens with three, six and twelve-ply facesheets were tested. Specimens with different honeycomb cores consisting of four different cell sizes were also tested, in addition to specimens with three different widths. Three different data reduction methods were employed for computing apparent fracture toughness values from the test data, namely an area method, a compliance calibration technique and a modified beam theory method. The compliance calibration and modified beam theory approaches yielded comparable apparent fracture toughness values, which were generally lower than those computed using the area method. Disbonding in the three-ply facesheet specimens took place at the facesheet/core interface and yielded the lowest apparent fracture toughness values. Disbonding in the six and twelve-ply facesheet specimens took place within the core, near to the facesheet/core interface. Specimen width was not found to have a significant effect on apparent fracture toughness. The amount of scatter in the apparent fracture toughness data was found to increase with honeycomb core cell size.

Rinker, Martin; Ratcliffe, James G.; Adams, Daniel O.; Krueger, Ronald

2013-01-01

311

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

312

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

313

Bending Behavior of Simply Suppoted Metallic Sandwich Plates with Dimpled Cores  

NASA Astrophysics Data System (ADS)

Metallic sandwich plates are lightweight structural materials with load-bearing and multi-functional characteristics. Previous analytic studies have shown that the bendability of these plates increases as the thickness decreases. Due to difficulty in the manufacture of thin sandwich plates, dimpled cores (structures called egg-box cores) are employed as a sandwich core. High-precision dimpled cores are easily fabricated in a sectional forming process. The cores are then bonded with skin sheets by multi-point resistance welding. The bending characteristics of simply supported plates were observed by the defining measure, including the radius ratio of the small dimple, the thickness of a sandwich plate, and the pattern angle (0°/90°, 45°). Experimental results revealed that sandwich plates with a thickness of 2.2 mm and a pattern angle of 0°/90° showed good bendability as the punch stroke under a collapse load was longer than other cases. In addition, the gap between attachment points was found to be an important parameter for the improvement of the bendability. Finally, sandwich plates with dimpled cores were bent with a radius of curvature of 330 mm for the sheet thickness of 2.2 mm using an incremental bending apparatus.

Seong, Dae-Yong; Jung, Chang Gyun; Yang, Dong-Yol; Ahn, Dong Gyu

314

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

315

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

316

An Analysis of Nondestructive Evaluation Techniques for Polymer Matrix Composite Sandwich Materials  

NASA Technical Reports Server (NTRS)

Structural sandwich materials composed of triaxially braided polymer matrix composite material face sheets sandwiching a foam core are being utilized for applications including aerospace components and recreational equipment. Since full scale components are being made from these sandwich materials, it is necessary to develop proper inspection practices for their manufacture and in-field use. Specifically, nondestructive evaluation (NDE) techniques need to be investigated for analysis of components made from these materials. Hockey blades made from sandwich materials and a flat sandwich sample were examined with multiple NDE techniques including thermographic, radiographic, and shearographic methods to investigate damage induced in the blades and flat panel components. Hockey blades used during actual play and a flat polymer matrix composite sandwich sample with damage inserted into the foam core were investigated with each technique. NDE images from the samples were presented and discussed. Structural elements within each blade were observed with radiographic imaging. Damaged regions and some structural elements of the hockey blades were identified with thermographic imaging. Structural elements, damaged regions, and other material variations were detected in the hockey blades with shearography. Each technique s advantages and disadvantages were considered in making recommendations for inspection of components made from these types of materials.

Cosgriff, Laura M.; Roberts, Gary D.; Binienda, Wieslaw K.; Zheng, Diahua; Averbeck, Timothy; Roth, Donald J.; Jeanneau, Philippe

2006-01-01

317

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

318

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

319

Sandwich-type structure for economical MEMS and MOEMS assembly  

NASA Astrophysics Data System (ADS)

A new fabrication method suitable for cheap assembling of MEMS and MOEMS is described. As a present, the very expensive methods for assembling and packaging, applied in the case of MEMS and MOEMS, make almost prohibit the final cost of a new prototype. For this reason it is so important to reduce the prize of the assembling techniques, and to find a way for batch mounting and packaging. The proposed method consists of generating a high aspect ratio structure, by means of soldering some different shaped metallic foils. The technological process consists of the following steps. In the first step, the desired 3D structure is divided into N different levels, while maintaining the thickness of each of them between 10-300 micrometers. Next, the pattern for each level is achieved by applying, to the copper metallic substrates, a double side lithography, commonly used in printed circuits fabrication, such as: solid negative resist lamination; UV exposure; alkaline spray developing, and acid spray etching. After a double side Sn-Pb electroplating of each metallic foil, all of them are properly stacked and aligned in a frame, by means of some special etched holes. The resulting stack is pressed and heated at soldering alloy's melting temperature, preferably by using a vacuum system. Finally, the temperature is ramped down and the pressure is released, resulting in the desired 3D arbitrary shaped sandwich type structure. This new technique opens wide perspectives to replace some expensive assembling methods, in a variety of prototypes containing MEMS and MOEMS, being also recommended for metal can packaging in special applications and microfluidic devices assembling too.

Dumbravescu, Niculae

1999-10-01

320

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

321

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

322

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

323

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.

324

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

325

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

326

Network architecture design of an agile sensing system with sandwich wireless sensor nodes  

NASA Astrophysics Data System (ADS)

Wireless sensor network (WSN) is recently emerged as a powerful tool in the structural health monitoring (SHM). Due to the limitations of wireless channel capacity and the heavy data traffic, the control on the network is usually not real time. On the other hand, many SHM applications require quick response when unexpected events, such as earthquake, happen. Realizing the need to have an agile monitoring system, an approach, called sandwich node, was proposed. Sandwich is a design of complex sensor node where two Imote2 nodes are connected with each other to enhance the capabilities of the sensing units. The extra channel and processing power, added into the nodes, enable agile responses of the sensing network, particularly in interrupting the network and altering the undergoing tasks for burst events. This paper presents the design of a testbed for examination of the performance of wireless sandwich nodes in a network. The designed elements of the network are the software architecture of remote and local nodes, and the triggering strategies for coordinating the sensing units. The performance of the designed network is evaluated through its implementation in a monitoring test in the laboratory. For both original Imote2 and the sandwich node, the response time is estimated. The results show that the sandwich node is an efficient solution to the collision issue in existing interrupt approaches and the latency in dense wireless sensor networks.

Dorvash, S.; Li, X.; Pakzad, S.; Cheng, L.

2012-04-01

327

The flame structure of AP/HTPB sandwiches  

NASA Astrophysics Data System (ADS)

Ultraviolet emission imaging experiments have been used to study the combustion of sandwiches of ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB) in nitrogen at pressures up to 32 atm, with binder layers from 50 to 450 mum in thickness. An ICCD camera system has been used to image the flame emission near 310 nm, and a backlighting technique has been developed that allows determination of the corresponding surface shape during combustion. The results indicate the AP/HTPB interface regression rate of IPDI cured samples undergoing low power (100W) laser-assisted deflagration is nearly independent of the binder thickness for binders thicker than 100 mum. The pressure exponent of the regression rate is 0.31 up to 15 atm, increasing with pressure from 15 to 32 atm. Two primary regimes of flame behavior have been identified: a split flame base regime which occurs with high Peclet and Damkohler numbers, and a merged flame base regime which occurs with low Peclet and Damkohler numbers. A secondary regime, exhibiting a "lifted" flame, occurs with low Damkohler numbers and high Peclet numbers. The ultraviolet flame emissions observed in the experiments show a correspondence with the fuel-rich region of the flame, as determined with a Schvab-Zeldovich model. This is reasonable since the primary sources of ultraviolet emission in the 305--315 nm region, electronically excited OH and the CO + O reaction, are dependent on fuel related species. The growth of the fuel-rich region with increasing Peclet number, predicted by the model, is qualitatively matched by the experimental results. The predicted shrinkage of the fuel-rich region when the binder layer is diluted with fine AP is also qualitatively matched by the experiments. Comparison of the experimental results with a single-reaction model with finite rate kinetics shows a weak qualitative agreement on the influence of Damkohler number. A large increase in Damkohler number (factor of 20) leads to a strong splitting of the calculated reaction zone and a splitting of the base of the high temperature region. This seems to correspond to the splitting of the ultraviolet emission flame base observed in the experiments.

Chorpening, Benjamin Todd

2000-10-01

328

Construction Technologies.  

ERIC Educational Resources Information Center

This document contains materials developed for and about the construction technologies tech prep program of the South-Western City Schools in Ohio. Part 1 begins with a map of the program, which begins with a construction technologies program in grades 11 and 12 that leads to entry-level employment or one of five 2-year programs at a community…

Columbus State Community Coll., OH.

329

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

330

Optimisation of Composite Sandwich Structures Subjected to Combined Torsion and Bending Stiffness Requirements  

NASA Astrophysics Data System (ADS)

This research is motivated by the rapidly increasing use of composite sandwich structures to reduce weight and improve energy efficiency in a wide range of industries such as automotive, aerospace and civil infrastructure. The paper presents a minimum-weight optimization method for sandwich structures to meet both torsion and bending rigidity requirements. This multiple inequality-constrained optimisation problem is formulated using the Lagrange multiplier method. Solving the resulting equations reveals the optimum solution that can satisfy both flexural and torsion stiffness requirements depend on the stiffness ratio relative to elastic modulus ratio. To illustrate the newly developed optimum design solutions, numerical examples are presented for sandwich structures made of either isotropic face skins or orthotropic composite face skins.

Li, Xiang; Li, Gangyan; Wang, Chun H.

2012-06-01

331

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

NASA Astrophysics Data System (ADS)

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.

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

332

Bending and vibration of functionally graded material sandwich plates using an accurate theory  

E-print Network

In this paper, the bending and the free flexural vibration behaviour of sandwich functionally graded material (FGM) plates are investigated using QUAD-8 shear flexible element developed based on higher order structural theory. This theory accounts for the realistic variation of the displacements through the thickness. The governing equations obtained here are solved for static analysis considering two types of sandwich FGM plates, viz., homogeneous face sheets with FGM core and FGM face sheets with homogeneous hard core. The in-plane and rotary inertia terms are considered for vibration studies. The accuracy of the present formulation is tested considering the problems for which three-dimensional elasticity solutions are available. A detailed numerical study is carried out based on various higher-order models to examine the influence of the gradient index and the plate aspect ratio on the global/local response of different sandwich FGM plates.

Natarajan, S

2012-01-01

333

Tests of graphite/polyimide sandwich panels in uniaxial edgewise compression  

NASA Technical Reports Server (NTRS)

The local and general buckling behavior of graphite/polyimide sandwich panels simply supported along all four edges and loaded in uniaxial edgewise compression were investigated. Material properties of sandwich panel constituents (adhesive and facings) were determined from flatwise tension and sandwich beam flexure tests. Buckling specimens were 30.5 by 33 cm, had quasi-isotropic, symmetric facings, and a glass/polyimide honeycomb core. Core thicknesses were varied and three panels of each thickness were tested at room temperature to investigate failure modes and corresponding buckling loads. Specimens 0.635 cm thick failed by overall buckling at loads close to the analytically predicted buckling load; all other panels failed by face wrinkling. Results of the wrinkling tests indicated that several buckling formulas were unconservative and therefore not suitable for design purposes; a recommended wrinkling equation is presented.

Camarda, C. J.

1980-01-01

334

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

335

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

336

Low-Velocity Impact Response of Sandwich Beams with Functionally Graded Core  

NASA Technical Reports Server (NTRS)

The problem of low-speed impact of a one-dimensional sandwich panel by a rigid cylindrical projectile is considered. The core of the sandwich panel is functionally graded such that the density, and hence its stiffness, vary through the thickness. The problem is a combination of static contact problem and dynamic response of the sandwich panel obtained via a simple nonlinear spring-mass model (quasi-static approximation). The variation of core Young's modulus is represented by a polynomial in the thickness coordinate, but the Poisson's ratio is kept constant. The two-dimensional elasticity equations for the plane sandwich structure are solved using a combination of Fourier series and Galerkin method. The contact problem is solved using the assumed contact stress distribution method. For the impact problem we used a simple dynamic model based on quasi-static behavior of the panel - the sandwich beam was modeled as a combination of two springs, a linear spring to account for the global deflection and a nonlinear spring to represent the local indentation effects. Results indicate that the contact stiffness of thc beam with graded core Increases causing the contact stresses and other stress components in the vicinity of contact to increase. However, the values of maximum strains corresponding to the maximum impact load arc reduced considerably due to grading of thc core properties. For a better comparison, the thickness of the functionally graded cores was chosen such that the flexural stiffness was equal to that of a beam with homogeneous core. The results indicate that functionally graded cores can be used effectively to mitigate or completely prevent impact damage in sandwich composites.

Apetre, N. A.; Sankar, B. V.; Ambur, D. R.

2006-01-01

337

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

338

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

339

Impact damage detection in sandwich composite structures using Lamb waves and laser vibrometry  

NASA Astrophysics Data System (ADS)

This experimental study explores the feasibility of impact damage detection in composite sandwich structures using Lamb wave excitation and signals acquired with a laser Doppler vibrometer. Energy maps are computed from the transient velocity wave fields and used to highlight defect areas in impacted coupons of foam core and honeycomb core sandwich materials. The technique performs well for the detection of barely visible damage in this type of material, and is shown to be robust in the presence of wave reverberation. Defect extent information is not always readily retrieved from the obtained defect signatures, which depend on the wave - defect interaction mechanisms.

Lamboul, B.; Passilly, B.; Roche, J.-M.; Osmont, D.

2013-01-01

340

Impact damage detection in composite chiral sandwich panels using nonlinear vibro-acoustic modulations  

NASA Astrophysics Data System (ADS)

This paper reports an application of nonlinear acoustics to impact damage detection in a composite chiral sandwich panel. The panel is built from a chiral honeycomb and two composite skins. High-frequency ultrasonic excitation and low-frequency modal excitation were used to observe nonlinear modulations in ultrasonic waves due to structural damage. Low-profile, surface-bonded piezoceramic transducers were used for ultrasonic excitation. Non-contact laser vibrometry was applied for ultrasonic sensing. The work presented focuses on the analysis of the modulation intensities and damage-related nonlinearities. The paper demonstrates that the method can be used for impact damage detection in composite chiral sandwich panels.

Klepka, Andrzej; Staszewski, Wieslaw J.; di Maio, Dario; Scarpa, Fabrizio

2013-08-01

341

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

342

Behaviour of cellular foam core materials in GRP sandwich under fatigue  

SciTech Connect

This paper concerns four point bend testing of sandwich beams with PVC foam cores, representative of hull panels in high speed light craft. The study focuses on the long term behavior of cellular foam core materials when the sandwich beam is subjected to fatigue loading until the specimen fails due to shear fracture or excessive shear deformations in the core. The core materials tested include the partially cross-linked PVC Divinycell H100 and H200 and the linear PVC Airex R63.80. Results from the program are presented and discussed.

Aamlid, O.; Echtermeyer, A.T.; McGeorge, D.; Buene, L. [Det Norske Veritas Research AS, Hoevik (Norway)

1993-12-31

343

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

344

Constructing Phylogenies.  

ERIC Educational Resources Information Center

Introduces a method for constructing phylogenies using molecular traits and elementary graph theory. Discusses analyzing molecular data and using weighted graphs, minimum-weight spanning trees, and rooted cube phylogenies to display the data. (DDR)

Bilardello, Nicholas; Valdes, Linda

1998-01-01

345

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

346

The low velocity impact response of sandwich beams with a corrugated core or a Y-frame core  

E-print Network

. The AISI 304 stainless steel sandwich beams comprised two identical face sheets and represented scaled-down versions of ship hull designs. No significant rate effects were observed at impact speeds representative are needed in ship hull designs that do not employ a back face. Keywords: Drop-weight test, Sandwich beam

Fleck, Norman A.

347

Shock loading response of sandwich panels with 3-D woven E-glass composite skins and stitched foam core  

Microsoft Academic Search

Sandwich composite are used in numerous structural applications, with demonstrated weight savings over conventional metals and solid composite materials. The increasing use of sandwich composites in defense structures, particularly those which may be exposed to shock loading, demands for a thorough understanding of their response to suc highly transient loadings. In order to fully utilize their potential in such extreme

Srinivasan Arjun Tekalur; Alexander E. Bogdanovich; Arun Shukla

2008-01-01

348

Migration patterns and moult of Common Terns Sterna hirundo and Sandwich Terns Sterna sandvicensis using Teesmouth in late summer  

Microsoft Academic Search

Count, recovery and biometric data were analysed to assess the conservation status and use of Teesmouth by Common Terns Sterna hirundo and Sandwich Terns Sterna sandvicensis in late summer. The recognition of the international importance of Teesmouth to migratory Sandwich Terns was endorsed. Peak late summer counts for 1990–1997 averaged 1,835, over 1% of the international population. Analysis of information

Robin M. Ward

2000-01-01

349

A study of damage development in a weft knitted fabric reinforced composite. Part 1: Experiments using model sandwich laminates  

Microsoft Academic Search

Coupons consisting of single layers of Milano weft knitted glass fabric reinforced epoxy resin have been tested with the knitted fabric oriented at various angles to the loading direction, alone and sandwiched between outer layers of unidirectional glass\\/epoxy reinforcement. The sandwich coupons enable the initiation of damage to be observed directly. Tensile tests have shown that the first damage occurs

C. R. Rios; S. L. Ogin; C. Lekakou; K. H. Leong

2007-01-01

350

FRP Shear Transfer Mechanism for Precast Prestressed Concrete Sandwich Load Bearing Panels Sami Rizkalla, Tarek Hassan and Gregory Lucier  

E-print Network

of concrete penetrating the foam core, as detailed in Figure 1. Increasing the degree of composite actionFRP Shear Transfer Mechanism for Precast Prestressed Concrete Sandwich Load Bearing Panels Sami prestressed concrete sandwich wall panels reinforced with carbon fiber reinforced polymer (CFRP) shear grid

351

An examination of nondestructive evaluation techniques for polymer matrix composite sandwich materials  

NASA Astrophysics Data System (ADS)

Structural sandwich materials composed of triaxially braided polymer matrix composite material face sheets sandwiching a foam core are being utilized for applications including aerospace components and recreational equipment. Since full scale components are being made from these sandwich materials, it is necessary to develop proper inspection practices for their manufacture and in field use. Specifically, nondestructive evaluation (NDE) techniques need to be investigated for analysis of components made from these materials. Hockey blades made from sandwich materials were examined with multiple NDE techniques including thermographic, radiographic, and laser based methods to investigate the manufactured condition of blades and damage induced from play. Hockey blades in an as received condition and damaged blades used in play were investigated with each technique. NDE images from the blades were presented and discussed. Structural elements within each blade were observed with radiographic imaging. Damaged regions and some structural elements of the hockey blades were identified with thermographic imaging. With shearography, structural elements, damaged regions, and other material variations were detected in the hockey blades. Each technique's advantages and disadvantages were considered in making recommendations for inspection of components made from these types of materials.

Cosgriff, Laura M.; Roberts, Gary D.; Averbeck, Timothy; Jeanneau, Philippe; Quddus, Michael

2006-03-01

352

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

353

A robust high-throughput sandwich cell-based drug screening platform.  

PubMed

Hepatotoxicity evaluation of pharmaceutical lead compounds in early stages of drug development has drawn increasing attention. Sandwiched hepatocytes exhibiting stable functions in culture represent a standard model for hepatotoxicity testing of drugs. We have developed a robust and high-throughput hepatotoxicity testing platform based on the sandwiched hepatocytes for drug screening. The platform involves a galactosylated microfabricated membrane sandwich to support cellular function through uniform and efficient mass transfer while protecting cells from excessive shear. Perfusion bioreactor further enhances mass transfer and cellular functions over long period; and hepatocytes are readily transferred to 96-well plate for high-throughput robotic liquid handling. The bioreactor design and perfusion flow rate are optimized by computational fluid dynamics simulation and experimentally. The cultured hepatocytes preserved 3D cell morphology, urea production and cytochrome p450 activity of the mature hepatocytes for 14 days. When the perfusion-cultured sandwich is transferred to 96-well plate for drug testing, the hepatocytes exhibited improved drug sensitivity and low variability in hepatotoxicity responses amongst cells transferred from different dates of perfusion culture. The platform enables robust high-throughput screening of drug candidates. PMID:20971505

Zhang, Shufang; Tong, Wenhao; Zheng, Baixue; Susanto, Thomas A K; Xia, Lei; Zhang, Chi; Ananthanarayanan, Abhishek; Tuo, Xiaoye; Sakban, Rashidah B; Jia, Ruirui; Iliescu, Ciprian; Chai, Kah-Hin; McMillian, Michael; Shen, Shali; Leo, Hwaliang; Yu, Hanry

2011-02-01

354

Hepatocyte function and extracellular matrix geometry: long-term culture in a sandwich configuration  

Microsoft Academic Search

Adult rat hepatocytes cultured in a collagen sandwich system maintained normal morphology and a physiolog- ical rate of albumin secretion for at least 42 days. Hep- atocytes cultured on a single layer of collagen gel essen- tially ceased albumin secretion within I wk but could recover function with the overlay of a second layer of collagen gel. This culture configuration

JAMES C. Y. DUNN; MARTIN L. YARMUSH; HANS G. KOEBE; RONALD G. TOMPKINS

355

Magnetic measurements of monolayer-thickness films of Cr sandwiched by Au  

Microsoft Academic Search

Calculations show ferromagnetic moments (3.1muB) in Au-Cr-Au sandwiches, for monolayers of Cr. The measured moment (0.41muB at 2 K) is larger in Cr monolayers than for thicker Cr samples. Results are discussed in terms of other studies of this system including those which showed superconductivity.

M. B. Brodsky; L. R. Sill; C. H. Sowers

1986-01-01

356

Magnetic measurements of monolayer-thickness films of Cr sandwiched by Au  

Microsoft Academic Search

Calculations show ferromagnetic moments (3.1(MU) sub B) in Au-Cr-Au sandwiches, for monolayers of Cr. The measured moment (0.41(MU) sub B at 2(0)K) is larger in Cr monolayers than for thicker Cr samples. Results are discussed in terms of other studies of this system including those which showed superconductivity.

M. B. Brodsky; L. R. Sill; C. H. Sowers

1985-01-01

357

Probing Enzymatic Activity inside Living Cells Using a Nanowire-Cell "Sandwich" Assay  

E-print Network

of an intracellular signal transduction pathway requires minimally invasive methods for probing enzyme activity in situ. Here, we describe a new method for monitoring enzyme activity in living cells by sandwiching live cell assay, enzyme activity Enzymes mediate a wide range of cellular processes, and dynamic control

Heller, Eric

358

Mechanical properties of chemically-treated hemp fibre reinforced sandwich composites  

Microsoft Academic Search

In this study, hemp fabrics were used as reinforcements with polyester resin to form composite skins while short hemp fibres with polyester as a core for making composite sandwich structures. To improve the fibre matrix adhesion properties, alkalisation, silane and acetylation treatments on the fibres surface were carried out. Examinations through fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM),

M. M. Kabir; H. Wang; K. T. Lau; F. Cardona; T. Aravinthan

359

The response of clamped sandwich plates with metallic foam cores to simulated blast loading  

E-print Network

projectiles. The sandwich plates comprise AISI 304 stainless steel face sheets and aluminium alloy metal foam of AISI 304 stainless steel plays a significant role in increasing the shock resistance of the monolithic. Introduction Clamped monolithic plates are commonly used in the design of commercial and military vehicles

Fleck, Norman A.

360

The dynamic response of clamped rectangular Y-frame and corrugated core sandwich plates  

E-print Network

projectiles. All plates are made from AISI 304 stainless steel, and the sandwich topologies comprise two..................................................................................................................Introduction Clamped plates are representative of the structures used in the design of commercial and military decade there have been substantial changes in ship design, see for example the review by Paik et al

Fleck, Norman A.

361

Active Vibration Suppression of Sandwich Beams using Piezoelectric Shear Actuators: Experiments and  

E-print Network

. These types of actuators, where the electric field is applied parallel to the poling direction to cause normal extension actuators are usually placed at the extreme thickness positions of a plate-like structureActive Vibration Suppression of Sandwich Beams using Piezoelectric Shear Actuators: Experiments

Vel, Senthil

362

Ultra-Lightweight Nanocomposite Foams and Sandwich Structures for Space Structure Applications  

NASA Technical Reports Server (NTRS)

Microcellular nanocomposite foams and sandwich structures have been created to have excellent electrical conductivity and radiation-resistant properties using a new method that does not involve or release any toxicity. The nanocomposite structures have been scaled up in size to 12 X 12 in. (30 X 30 cm) for components fabrication. These sandwich materials were fabricated mainly from PE, CNF, and carbon fibers. Test results indicate that they have very good compression and compression-after-impact properties, excellent electrical conductivity, and superior space environment durability. Compression tests show that 1000 ESH (equivalent Sun hours) of UV exposure has no effect on the structural properties of the sandwich structures. The structures are considerably lighter than aluminum alloy (= 36 percent lighter), which translates to 36 percent weight savings of the electronic enclosure and its housing. The good mechanical properties of the materials may enable the electronic housing to be fabricated with a thinner structure that further reduces the weight. There was no difficulty in machining the sandwich specimens into electronic enclosure housing.

Tan, Seng

2012-01-01

363

Effect of core topology on projectile penetration in hybrid aluminum/alumina sandwich structuresq  

E-print Network

: Received 25 February 2013 Received in revised form 6 May 2013 Accepted 30 May 2013 Available online 20 June panels made from Al 6061-T6. The panels were subjected to impact tests using hard steel spheres over,16] on extruded 6061-T6 aluminum sandwich panels with a strong triangular corrugated core [17] have shown

Wadley, Haydn

364

Heavy-gage bonded honeycomb sandwich as primary load-bearing structure  

NASA Technical Reports Server (NTRS)

Heavy-gage bonded honeycomb sandwich is used as a primary load-bearing structural material in large-diameter boosters. Theoretical investigations based on a small deflection theory for prediction of stress fields and buckling loads, and structural testing were made. This structure is a potential weight saver for compression load-critical components.

1967-01-01

365

Identification of complex crack damage for honeycomb sandwich plate using wavelet analysis and neural networks  

Microsoft Academic Search

In this study, crack damage detection for a honeycomb sandwich plate is studied using the energy spectrum of dynamic response decomposed by wavelet transform and the artificial neural network (NN). The results show that taking the energy spectrum of the decomposed wavelet signals of dynamic responses as the inputs of the NN can simplify the NN design for structural damage

L H Yam; Y J Yan; L Cheng; J S Jiang

2003-01-01

366

Dynamic and quasi-static deformation of aluminium honeycomb sandwich panel in three point bending  

Microsoft Academic Search

In this research, the dynamic and quasi-static deformations of aluminium honeycomb sandwich panels in three point bending were investigated experimentally. The load, the deflection of a loading point and the strain response of the rear surface plate at various locations were measured. A peak load caused by local plastic buckling of the cores just under the loading point appeared in

H. Kobayashi; M. Daimaruya; Y. Takaya

2003-01-01

367

Local buckling of honeycomb sandwich plates under action of transverse shear forces  

Microsoft Academic Search

We evaluate the critical transverse shear forces for the local buckling of honeycomb sandwich plates subjected to lateral loads. The evaluation is based on the stress field accounting for the stresses on the microscale in the honeycomb's hexagonal cells. These microscale stresses are computed by the two-scale method of homogenization theory for periodic media. The elastic restraints resulting from neighboring

Guangyu Shi; Pin Tong

1994-01-01

368

An investigation of the skin\\/core bond in honeycomb sandwich structures using statistical experimentation techniques  

Microsoft Academic Search

Experimental design has been used to investigate the effect of processing parameters on the peel strength of Nomex honeycomb core\\/carbon fibre-epoxy prepreg skin sandwich panels, manufactured by vacuum bagging. The four processing parameters considered were: (i) consolidation pressure; (ii) temperature cure cycle; (iii) temperature ramp rate and (iv) vacuum pressure application time. Each parameter was considered at three levels. It

S. M. Grove; E. Popham; M. E. Miles

2006-01-01

369

Vacuum Bag Only Prepreg Processing of Honeycomb Sandwich Panels James Kratz  

E-print Network

Vacuum Bag Only Prepreg Processing of Honeycomb Sandwich Panels James Kratz Department. This technique can be very effective for laminates, but extremely lightweight honeycomb structures introduce two to solve the manufacturing problems for honeycomb structures. Biography James Kratz recently defended his

Dawson, Jeff W.

370

Dynamic response of doubly curved honeycomb sandwich panels to random acoustic excitation. Part 1: Experimental study  

Microsoft Academic Search

A set of four doubly curved, composite honeycomb sandwich panels has been tested with broad band, random acoustic excitation in a progressive wave tube facility. This paper presents the experimental results in the form of dynamic face plate strain measurements taken from various points close to the centre of the panels, on both the inner and outer face plates. The

P. R. Cunningham; R. G. White

2003-01-01

371

Optimization of a metal honeycomb sandwich beam-bar subjected to torsion and bending  

Microsoft Academic Search

In this paper, we analyze a metal honeycomb sandwich beam\\/torsion bar subjected to combined loading conditions. The cell wall arrangement of the honeycomb core is addressed in the context of maximizing resistance to either bending, torsion, or combined bending and torsion for given dimensions, face sheet thicknesses and core relative density. It is found that the relative contributions of the

A.-J. Wang; D. L. McDowell

2003-01-01

372

Non-autoclave processing of honeycomb sandwich structures: Skin through thickness air permeability during cure  

Microsoft Academic Search

In non-autoclave processing of sandwich structures, the pressure level inside the honeycomb becomes a critical process parameter, which depends on the permeability to air of the upper skin. In this work, prepreg and adhesive permeabilities were determined separately and in combination through a falling pressure method. We showed that a range of initial skin through thickness air permeability could be

S. Sequeira Tavares; N. Caillet-Bois; V. Michaud; J.-A. E. Månson

2010-01-01

373

Guided wave propagation in honeycomb sandwich structures using a piezoelectric actuator\\/sensor system  

Microsoft Academic Search

Due to the complex nature of such composite structures, an understanding of the guided wave propagation mechanism in honeycomb composite panels with different frequencies inherently imposes many challenges. In this paper, a numerical simulation is first conducted to investigate the wave propagation mechanism in honeycomb sandwich structures using piezoelectric actuators\\/sensors. In contrast to most of the previous work, elastic wave

F. Song; G. L. Huang; K. Hudson

2009-01-01

374

Theoretical design and analysis of a honeycomb panel sandwich structure loaded in pure bending  

Microsoft Academic Search

This paper discusses the theoretical and quantitative design and analysis of a honeycomb panel sandwich structure. The initial design is based on specific requirements that the panel must achieve prior to failure under load. Materials to be used for the facing and core are selected based on the given requirements. With the materials chosen, the facing sheets and core are

Gaetano G. Galletti; Christine Vinquist; Omar S. Es-Said

2008-01-01

375

Modelling of low-energy\\/low-velocity impact on Nomex honeycomb sandwich structures with metallic skins  

Microsoft Academic Search

In the aircraft industry, manufacturers have to decide quickly whether an impacted sandwich needs repairing or not. Certain computation tools exist at present but they are very time-consuming and they also fail to perfectly model the physical phenomena involved in an impact. In a previous publication, the authors demonstrated the possibility of representing the Nomex™ honeycomb core by a grid

B. Castanié; C. Bouveta; Y. Aminanda; J.-J. Barrau; P. Thevenet

2008-01-01

376

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

377

Strength reduction behavior of honeycomb sandwich structure subjected to low-velocity impact  

Microsoft Academic Search

The paper deals with the effect of constituent materials on impact damage and strength reduction of a sandwich structure, composed of laminated facesheets and Nomex® honeycomb core. Low-velocity impact tests were performed and damage was inspected by scanning acoustic microscopy. In addition, static tests were conducted under flexural loading. The damage behavior is characterized through the energy absorbed during impact.

Ki-Weon Kang; Heung Seob Kim; Man Sig Kim; Jung-Kyu Kim

2008-01-01

378

PARAMETER IDENTIFICATION FOR ALUMINUM HONEYCOMB SANDWICH PANELS BASED ON ORTHOTROPIC TIMOSHENKO BEAM THEORY  

Microsoft Academic Search

The present paper deals with parameter identification of aluminum honeycomb sandwich panels with the assumption that they can be treated as orthotropic continua. Elastic constants and modal damping ratios are considered as the identified parameters, and the basic equations of Timoshenko beam theory are employed in this paper. The numerical identification problem of minimizing the errors between the experimental and

T. Saito; R. D. Parbery; S. Okuno; S. Kawano

1997-01-01

379

Dynamic response of doubly curved honeycomb sandwich panels to random acoustic excitation. Part 2: Theoretical study  

Microsoft Academic Search

In this paper a single-degree-of-freedom model is developed to predict the dynamic response of an acoustially excited doubly curved sandwich panel. Three variants of the model are investigated, based on differing assumptions regarding the spatial distribution of the applied loading. When the loading is assumed to be uniform then the model reduces to the Miles approach, and when the loading

P. R. Cunningham; R. S. Langley; R. G. White

2003-01-01

380

Tensile mechanical properties of metal honeycomb sandwich structure with interface connection defects  

NASA Astrophysics Data System (ADS)

Thermal protection system is one of the key technologies of reusable launch vehicle (RLV). The ARMOR TPS is one of important candidate structure of RLV. ARMOR TPS has many advantages, for example: fixing easily, longer life, good properties, short time of maintenance and service. In comparison with traditional TPS, the ARMOR TPS will be the best selection for all kinds of RLV. So the ARMOR thermal protection system will be used in aviation and spaceflight field more and more widely because of its much better performance. ARMOR TPS panel is above the whole ARMOR TPS, and the metal honeycomb sandwich structure is the surface of the ARMOR TPS panel. So the metal honeycomb sandwich structure plays an important role in the ARMOR TPS, while it bears the flight dynamic pressure and stands against the flight dynamic calefaction. Because the active environment of metal honeycomb sandwich structure is very formidable, it can produce interface connection defects which can exist in the process of manufacture as well. Tensile mechanical properties of the metallic honeycomb sandwich structure with defects are analyzed to obtain damage tolerance of the structure. The effect of shape, dimension and location of defects on the tensile mechanical properties is conducted by experimental study. Then finite element analysis is performed to validate the experimental results. Haynes214 which is a kind of super alloy materials with high performances is chosen as both face sheet and core in this paper.

He, Xiaodong; Kong, Xianghao

2010-04-01

381

Modal analysis and acoustic transmission through offset-core honeycomb sandwich panels  

NASA Astrophysics Data System (ADS)

The work presented in this thesis is motivated by an earlier research that showed that double, offset-core honeycomb sandwich panels increased thermal resistance and, hence, decreased heat transfer through the panels. This result lead to the hypothesis that these panels could be used for acoustic insulation. Using commercial finite element modeling software, COMSOL Multiphysics, the acoustical properties, specifically the transmission loss across a variety of offset-core honeycomb sandwich panels, is studied for the case of a plane acoustic wave impacting the panel at normal incidence. The transmission loss results are compared with those of single-core honeycomb panels with the same cell sizes. The fundamental frequencies of the panels are also computed in an attempt to better understand the vibrational modes of these particular sandwich-structured panels. To ensure that the finite element analysis software is adequate for the task at hand, two relevant benchmark problems are solved and compared with theory. Results from these benchmark results compared well to those obtained from theory. Transmission loss results from the offset-core honeycomb sandwich panels show increased transmission loss, especially for large cell honeycombs when compared to single-core honeycomb panels.

Mathias, Adam Dustin

382

Establishment of a sandwich ELISA for human megsin, a kidney-specific serine protease inhibitor  

Microsoft Academic Search

Background. We previously identified a novel serine protease inhibitor (serpin), megsin, which is predomi- nantly expressed in the kidney. Megsin expression is up-regulated in human and experimental renal diseases associated with mesangial proliferation and expansion, suggesting that urinary megsin may be a novel diagnostic marker for some renal diseases. Methods. We established a specific and sensitive sandwich enzyme-linked immunosorbent assay

Reiko Inagi; Yuko Izuhara; Naoto Tominaga; Masaomi Nangaku; Kiyoshi Kurokawa; Toshio Miyata

383

Ferrocene analogues of sandwich B12·Cr·B12: a theoretical study.  

PubMed

The bowl B(12) cluster was previously reported to be analogous to benzene and predicted to be one of the best candidates to be new inorganic ligands. The structural stability and electronic properties of a new sandwich compound Cr(B(12))(2) (D(3d)) have been investigated by using density functional theory. It is found that the sandwich Cr(B(12))(2) (D(3d)) is a stable complex with large binding energy (-5.93 eV) and HOMO-LUMO gap (2.37 eV), as well as Fe(C(5)H(5))(2) and Cr(C(6)H(6))(2), following the 18-electron principle. The detailed molecular orbitals and aromaticity analyses indicate that the sandwich compound Cr(B(12))(2) (D(3d)) is electronically very stable. The natural bond orbital analysis suggests that spd-? interaction plays an important role in the sandwich compounds. PMID:23320677

Yuan, Yuan; Cheng, Longjiu

2013-01-14

384

Deformation and Fracture of Impulsively Loaded Sandwich Panels H.N.G. Wadleya,*  

E-print Network

reduced the strength and ductility in the welds and a narrow heat affected zone on either side of the weld of these fractures always lay within the heat affected zone of the longitudinal welds. For the most intensively alloy system fabricated by friction stir weld joining extruded sandwich panels with a triangular

Hutchinson, John W.

385

Experimental investigation of graphite/polyimide sandwich panels in edgewise compression. M.S. Thesis  

NASA Technical Reports Server (NTRS)

The local and general buckling of graphite/polyimide sandwich panels simply supported along all four edges and loaded in uniaxial edgewise compression is investigated. Material properties of sandwich panel constituents (adhesive and facings) were determined from flatwise tension and sandwich beam flexure tests. An adhesive bond study resulted in the selection of a suitable cure cycle for FM 34 polyimide film adhesive and, a bonding technique using a liquid cell edge version of that adhesive resulted in considerable mass savings. Tensile and compressive material properties of the facings, quasiisotropic, symmetric, laminates (0, +45,90,-45)s of Celion/PMR-15, were determined at 116, R.T., and 589 K (-250, R.T., and 600 F) usng the sandwich beam flexure test method. Results indicate the Gr/PI is a usable structural material for short term use at temperatures as high as 589 K (600 F). Buckling specimens were 1006.5 sq cm. 156 sq in., had quasiisotropic symmetric facings (0, + or - 45,90)s and a glass/polyimide honeycomb core (HRH-327-3/8-4).

Camarda, C. J.

1980-01-01

386

Deformation and fracture of impulsively loaded sandwich panels H.N.G. Wadley a,n  

E-print Network

cores have attracted interest for multifunctional applications which exploit their high bend strength method Finite element simulation a b s t r a c t Light metal sandwich panel structures with cellular and impact energy absorption. This concept has been explored here using a model 6061-T6 aluminum alloy system

Wadley, Haydn

387

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

388

An analytic model for the response to water blast of unsupported metallic sandwich panels  

Microsoft Academic Search

A prior assessment of the response of a metallic sandwich panels to water blast has identified soft and strong core responses and outlined the advantages of softness. Ensuing analysis has provided mechanism maps that distinguish these responses. The present article extends these assessments by developing an analytic model for the wet face response, inclusive of fluid\\/structure interaction, that can be

R. M. McMeeking; A. V. Spuskanyuk; M. Y. He; V. S. Deshpande; N. A. Fleck; A. G. Evans

2008-01-01

389

International Journal of Mechanical Sciences 46 (2004) 585608 Collapse mechanisms of sandwich beams with composite faces  

E-print Network

sandwich beams with composite faces and a PVC foam core subjected to three point bending. The faces Divinycell PVC foam of relative density 6.6% and 13.3%. The mechanical properties of the face sheets and core manufactured from woven glass ÿbre-epoxy face sheets and a PVC foam core, and loaded in three-point bending

Steeves, Craig A

390

Effects of processing variables on the quality of co-cured sandwich panels  

NASA Astrophysics Data System (ADS)

This paper summarizes basic studies conducted to compare the effects of various processes and materials on the quality of co-cured honeycomb sandwich panels with carbon-epoxy facings. Manipulation of the vacuum-pressure-temperature schedules of those processes resulted in improved facing surface quality, compaction, and sealing. The mechanical properties of those panels also improved.

Jouin, Pierre; Pollock, David; Rudisill, Ed

391

Thermal characteristics of composite sandwich structures for machine tool moving body applications  

Microsoft Academic Search

The thermal deformation affects the accuracy of a precision machine tool. There are various heat sources in machine tools such as motors, spindle units, and friction in LM-guide systems. In this work, the thermal characteristics of composite sandwich structures for machine tool parts were investigated both by FEM analysis and experiment. Then the machine tool slide of a high speed

Jung Do Suh; Dai Gil Lee

2004-01-01

392

Structural–acoustic optimization of sandwich cylindrical shells for minimum interior sound transmission  

Microsoft Academic Search

This paper presents an optimization study of cylindrical sandwich shells to minimize the transmitted sound into the interior induced by the exterior acoustic excitations. The boundary elements and finite elements are, respectively, used to model the interior and exterior acoustics and the vibration of the shell. The design parameters of the optimization are the reinforcement angles of the orthotropic composite

H. Denli; J. Q. Sun

2008-01-01

393

Vibration and sound radiation of sandwich beams with honeycomb truss core  

Microsoft Academic Search

The vibrations of and the sound radiation from sandwich beams with truss core are analyzed. The structure of the core is composed of a sequence of identical unit cells repeating along the beam length and across the core thickness. Each cell is composed of beam elements assembled to form a frame structure. Layouts with the typical honeycomb pattern arranged through

M. Ruzzene

2004-01-01

394

Indentation of Foam-Based Polymer Composite Sandwich Beams and Panels Under Static Loading  

NASA Astrophysics Data System (ADS)

Foam core composite sandwich structures are highly susceptible to damage when subjected to localized loading. Therefore, thorough study of the role of factors such as face sheet thickness, indentor diameter value, and crosshead displacement rate in indentation events is important. The objective of the present work is to investigate experimentally and numerically the influence of these factors on the nonlinear static indentation behavior of sandwich beams and panels consisting of glass fiber/resin face sheets and PVC (polyvinylchloride) foam core. Static indentation tests are carried out on sandwich composite beam and panel specimens using steel cylindrical and spherical indentors, respectively. Numerical models are developed for simulating the mechanical response of sandwich structures subjected to localized indentation beyond the limit of elastic deformation in the foam core. In this relation, the *CRUSHABLE FOAM and the *CRUSHABLE FOAM HARDENING options in the ABAQUS finite element program system are used. The numerical analysis results demonstrate good agreement with experimental data. It is found that increasing the face sheet thickness and indentor diameter value leads to increase in the load (for a given displacement). It is shown also that the indentation behavior does not exhibit sensitivity to crosshead displacement rate over the conditions considered in the present work.

Rizov, V.

2009-06-01

395

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

NASA Astrophysics Data System (ADS)

A Dynamic Finite Element (DFE) model for the vibration analysis of three-layered sandwich beams is presented. The governing differential equations of motion of the sandwich beam for the general case, when the properties of each layer are dissimilar, are exploited. Displacement fields are imposed such that the face layers follow the Rayleigh beam assumptions, while the core is governed by Timoshenko beam theory. The DFE model is then used to examine the free-vibration characteristics of an asymmetric soft-core sandwich beam with steel face layers and a rubber core. The natural frequency results for the first four modes, in this case, show the exact match between the DFE and ‘exact’ Dynamic Stiffness Matrix (DSM) formulations, using only a one-element mesh, justifying the use of Q uasi-Exact ( QE-DFE) title. Convergence-wise, the QE-DFE formulation also outperforms the conventional FEM, which makes it useful in benchmarking other studies or the examination of high frequency response where FEM requires the use of large number of elements in order to achieve better accuracy. The application of the DFE to a lead-core sandwich beam is also discussed.

Hashemi, Seyed M.; Adique, Ernest J.

2010-04-01

396

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

397

Thermo-structural optimization of all-metallic prismatic sandwich panels  

NASA Astrophysics Data System (ADS)

All-metallic sandwich panels with prismatic cores offer tremendous potential for thermostructural applications, due to their exceptional bending response together with the possibility of driving a fluid through their open cores, thus enabling active cooling. This thesis offers a complete thermo-mechanical characterization of prismatic panels with both corrugated and diamond cores, with main emphasis on geometric optimization. For the mechanical study, the panel geometry is analytically optimized for minimum weight under any combination of bending and transverse shear force. For longitudinal loadings (i.e. bending axis parallel to the core corrugation direction), corrugated panels show excellent performance, equivalent to the best concepts available; for transverse loadings (i.e. bending axis perpendicular to the corrugation direction), this goal is achieved with diamond core designs. Failure maps are constructed based on the analytical model to provide easy visualization of the failure modes and allow immediate identification of optimal designs. Such maps are used to design a selected number of experiments, with the three-fold goal of (i) validating the analytical model, (ii) exploring the behavior subsequent to failure initiation (thus assessing the robustness of the chosen designs), and (iii) check the reliability of numerical simulations in capturing limit loads and deformation modes. Good agreement is achieved among analytical, computational and experimental results. In order to assess the active cooling performance of prismatic panels, a scenario is envisioned where a uniform heat flux is impinging on one face, with the rest of the panel being thermally insulated; under these conditions, all the heat flux is transferred to a cooling fluid flowing through the core channels. At any given level of the pressure drop, the panel geometry is optimized for maximum transferred heat flux subject to a temperature constraint on the structure. Although very large optimal core densities emerge (typically an order of magnitude higher than mechanical optima), good thermal performance can be achieved by much lighter structures; in particular, structurally optimized panels often show active cooling performance within a factor two of thermally optimized structures. This is a promising result for the design and fabrication of multi-functional plates.

Valdevit, Lorenzo

398

Metal Foam Analysis: Improving Sandwich Structure Technology for Engine Fan and Propeller Blades  

NASA Technical Reports Server (NTRS)

The Life Prediction Branch of the NASA Glenn Research Center is searching for ways to construct aircraft and rotorcraft engine fan and propeller blades that are lighter and less costly. One possible design is to create a sandwich structure composed of two metal faces sheets and a metal foam core. The face sheets would carry the bending loads and the foam core would have to resist the transverse shear loads. Metal foam is ideal because of its low density and energy absorption capabilities, making the structure lighter, yet still stiff. The material chosen for the face sheets and core was 17-4PH stainless steel, which is easy to make and has appealing mechanical properties. This material can be made inexpensively compared to titanium and polymer matrix composites, the two current fan blade alternatives. Initial tests were performed on design models, including vibration and stress analysis. These tests revealed that the design is competitive with existing designs; however, some problems were apparent that must be addressed before it can be implemented in new technology. The foam did not hold up as well as expected under stress. This could be due to a number of issues, but was most likely a result of a large number of pores within the steel that weakened the structure. The brazing between the face sheets and the foam was also identified as a concern. The braze did not hold up well under shear stress causing the foam to break away from the face sheets. My role in this project was to analyze different options for improving the design. I primarily spent my time examining various foam samples, created with different sintering conditions, to see which exhibited the most favorable characteristics for our purpose. Methods of analysis that I employed included examining strut integrity under a microscope, counting the number of cells per inch, measuring the density, testing the microhardness, and testing the strength under compression. Shear testing will also be done to examine the strengths of different types of brazes.

Fedor, Jessica L.

2004-01-01

399

Construction Work  

USGS Multimedia Gallery

Construction work taking place at the Theodore Roosevelt National Park in North Dakota. Funding for the road project at Theodore Roosevelt National Park comes from the $170 million appropriated for the Federal Highway Administration to spend on roads in national parks....

2009-07-24

400

CONSTRUCTION PROFESSIONAL  

E-print Network

CONSTRUCTION Management HUMAN RESOURCE Management NEW! PROFESSIONAL SOCIAL MEDIA Certificate NEW about this program go to: http://www.sonoma.edu/exed/htp/ PROFESSIONAL SOCIAL MEDIA CERTIFICATE The Professional Social Media Certificate provides participants with training and experience developing a social

Ravikumar, B.

401

Airship construction  

NASA Technical Reports Server (NTRS)

Forty-four years ago the first successful metal airship was completed and delivered to the United States Navy, the ZMC-2. Between those years and the present, very little effort or serious consideration has been given to the manufacture, design, construction, or economic impact of airships. It is important to retain and exploit the small but continually diminishing pool of airship talent that will expedite the success of the United States in what is now a pioneering venture. The relative simplicity of airship construction, utilizing the tremendous technical advances of the last 44 years, leads to the conclusion that this form of transportation holds great promise for reducing costs of military missions and improving the international competitive position of the United States in commercial applications.

Roda, J.

1975-01-01

402

Electromagnetic waves reflection, transmission and absorption by graphene - magnetic semiconductor - graphene sandwich-structure in magnetic field: Faraday geometry  

E-print Network

Electrodynamic properties of the graphene - magnetic semiconductor - graphene sandwich-structure have been investigated theoretically with taking into account the dissipation processes. Influence of graphene layers on electromagnetic waves propagation in graphene - semi-infinte magnetic semiconductor and graphene - magnetic semiconductor - graphene sandwich-structure has been analyzed. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such structure have been calculated. The size effects associated with the thickness of the structure have been analyzed. The possibility of efficient control of electrodynamic properties of graphene - magnetic semiconductor - graphene sandwich structure by an external magnetic field has been shown.

Kuzmin, Dmitry A; Shavrov, Vladimir G

2014-01-01

403

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

404

Graduate Studies Construction Engineering  

E-print Network

funded by the National Science Foundation (NSF), Construction Industry Institute (CII), Georgia engineering, building construction, and industrial and systems engineering. SELECTED COURSES · ConstructionGraduate Studies Construction Engineering CONSTRUCTION ENGINEERING The construction engineering

Jacobs, Laurence J.

405

Clay Nanocomposite/Aerogel Sandwich Structures for Cryotanks  

NASA Technical Reports Server (NTRS)

GRC research has led to the development of epoxy-clay nanocomposites with 60-70% lower gas permeability than the base epoxy resin. Filament wound carbon fiber reinforced tanks made with this nanocomposite had a five-fold lower helium leak rate than the corresponding tanks made without clay. More recent work has produced new composites with more than a 100-fold reduction in helium permeability. Use of these advanced, high barrier composites would eliminate the need for a liner in composite cryotanks, thereby simplifying construction and reducing propellant leakage. Aerogels are attractive materials for use as cryotank insulation because of their low density and low thermal conductivity. However, aerogels are fragile and have poor environmental stability, which have limited their use to certain applications in specialized environments (e.g., in certain types of nuclear reactors as Cerenkov radiation detectors, and as thermal insulators aboard space rovers on Mars). New GRC developed polymer crosslinked aerogels (X-Aerogels) retain the low density of conventional aerogels, but they demonstrate a 300-fold increase in their mechanical strength. Currently, our strongest materials combine a density of approx. 0.45 g/cc, a thermal conductivity of approx. 0.04 W/mK and a compressive strength of 185 MPa. Use of these novel aerogels as insulation materials/structural components in combination with the low permeability of epoxy-clay nanocomposites could significantly reduce cryotank weight and improve durability.

Miller, Sandi; Leventis, Nicholas; Johnston, J. Chris; Meador, Michael

2006-01-01

406

Simulation of giant magnetoimpedance in single layer and sandwiched thin films  

NASA Astrophysics Data System (ADS)

The giant magnetoimpedance (GMI) effect implies a strong dependence of the impedance of a conductor on the external magnetic field and has been observed in a wide range of soft magnetic materials. The impedance values of magnetic thin films and magnetic/conductor/magnetic sandwiched structures with different thickness are simulated using the finite element method (FEM). The giant magneto-impedance (GMI) is calculated from the difference of the impedance values with high and low permeability of the magnetic material. The application of extra magnetic field can be simulated by change the value of permeability. It is shown that the GMI ratio of films is significantly influenced by the geometry. And the conductor layer can obviously increase the sensitivity of GMI effect. The skin effect combined with the lack of shielding of the central conductor at the edge produce the high GMI effect of sandwiched structure thin films.

Jin, Fang; Mo, Wenqin; Sun, Huajun; Cheng, Weiming

2009-08-01

407

Development of lightweight graphite/polyimide sandwich panels, phases 3, 4 and 5  

NASA Technical Reports Server (NTRS)

Work performed in the last three phases of the program included: (1) face sheet processing; (2) honeycomb core manufacture; (3) face sheet-to-core bonding development; and (4) sandwich panel fabrication and testing. Resin cure studies were a major portion of this effort since processing problems traced to the polyimide matrix resin had to be resolved before quality core and face sheets could be fabricated. Honeycomb core fabrication and testing were conducted by Hexcel Corporation. A total of four graphite/polyimide resin composite cores were fabricated, tested, and reported. Two sandwich panels weighing .48 and .58 lb/sq ft, respectively were designed and fabricated which meet the support structure loads for the shuttle orbiter thermal protection system.

Merlette, J. B.

1972-01-01

408

Flexural effects of sandwich beam with a plate insert under in-plane bending  

NASA Astrophysics Data System (ADS)

The local stress concentrations in sandwich beam with a plate insert under in-plane bending are concerned in the study. An improved six-step phase shifting method in digital photoelasticity is employed to calculate the whole-field shear stress.The shear load transfer is realized by shear bands which connect the top and bottom sheet faces through adhesively-bonded interfaces. The plate insert plays a role in load transfer in the sandwich structure, and the fact that debonding might occur at more sites of the interfaces may also leads to the failure of the structure. The local stress concentrations at the insert end change with the load under three-point bending loads, while they remain as the initial residual shear stress under four-point bending loads. The local stress concentration effects generated by the plate insert is essentially caused by the mismatch of elastic properties of the core materials and the irrational geometry of the insert.

Zhenkun, Lei; Wei, Qiu; Libo, Deng

2012-07-01

409

Study of structurally efficient graphite-thermoplastic trapezoidal-corrugation sandwich and semisandwich panels  

NASA Astrophysics Data System (ADS)

The structural efficiency of compression-loaded trapezoidal-corrugation sandwich and semisandwich composite panels is studied to determine their weight savings potential. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them, and semisandwich panels with a corrugation attached to a single skin are considered. An optimization code is used to find the minimum weight designs for critical compressive load levels ranging from 3000 to 24,000 lb/in. Graphite-thermoplastic panels based on the optimal minimum weight designs were fabricated and tested. A finite-element analysis of several test specimens was also conducted. The results of the optimization study, the finite element analysis, and the experiments are presented.

Jegley, Dawn C.

1994-03-01

410

Structural Response of Aluminium Foam Hybrid Sandwich Panels Under Three-Point Bending Loading  

NASA Astrophysics Data System (ADS)

The present study focuses on the structural response of sandwich panels consisting of a commercial closed-cell foam core and thin aluminium sheet skins under static three-point bending loading. Panels of different thicknesses and span lengths were tested, and the influence of the foam density, core thickness and skin type on the response was revealed. The failure modes in bending were greatly dependent on the span length but independent on the foam thickness. For short spans, the deformed shape at failure was asymmetric, as opposed to a symmetric mode for long spans. The density and thickness of the foam core, the presence of reinforcing face sheets and the beam span determined the failure load and bending strength of the sandwich panels.

Kabir, Kaveh R.; Vodenitcharova, Tania; Hoffman, Mark

411

High-Fidelity Modeling for Health Monitoring in Honeycomb Sandwich Structures  

NASA Technical Reports Server (NTRS)

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 propagation in the structure before and after the impact. Results of modeling of the wave propagation, impact, and damage detection in sandwich honeycomb plates using piezoelectric actuator/sensor scheme are reported. The results of the simulations are compared with the experimental results. It is shown that the model is suitable for analysis of the physics of failure due to the impact and for testing structural health monitoring schemes based on guided wave propagation.

Luchinsky, Dimitry G.; Hafiychuk, Vasyl; Smelyanskiy, Vadim; Tyson, Richard W.; Walker, James L.; Miller, Jimmy L.

2011-01-01

412

Identification of honeycomb sandwich properties by high-resolution modal analysis  

NASA Astrophysics Data System (ADS)

A method is proposed to identify the mechanical properties of the skin and core materials of honeycomb sandwich. All the elastic coefficients and loss-factors that matter in the dynamics of a panel in the thick-plate approximation are identified. To this end, experimental natural modes (i.e. eigenmodes of the damped system) are compared to the numerical modes of a large sandwich panel (lx,y/h ? 80). The chosen generic model for the visco-elastic behaviour of the materials is E (1 + j?). The numerical modes are computed by means of a Rayleigh-Ritz procedure and their dampings are predicted according to the visco-elastic model. The frequencies and dampings of the natural modes of the panel are estimated experimentally by means of a high-resolution modal analysis technique. An optimisation procedure yields the desired coefficients. A sensitivity analysis assess the reliability of the method.

Rebillat, M.; Boutillon, X.

2010-06-01

413

Stress intensity factors for multiple cracks in an adhesively bonded sandwich sheet  

SciTech Connect

A new method is proposed for analyzing stress intensity factors of multiple cracks in an adhesively bonded metallic sandwich sheet. Using a basic solution of a single crack and taking unknown density of surface tractions and adhesive shear stresses, Fredholm integral equations and compatibility equations are formulated based upon stress free condition along each crack and displacement continuity between the sheets and adhesive layers, respectively. These equations are solved simultaneously, and the stress intensity factors of multiple cracks are determined from the derived density of tractions. It is shown that the mutual interaction of multiple cracks in a sandwich sheet is smaller than that in a monolithic sheet. Also, mutual interaction of cracks in the same sheet is smaller than that of cracks in the different sheets.

Nishimura, T. (Mitsubishi Heavy Industries, Ltd., Nagoya (Japan))

1993-01-01

414

Vibration and sound radiation from a sandwich cylindrical shell with prismatic core  

NASA Astrophysics Data System (ADS)

The vibration and the sound radiation of cylindrical shells with cellular core is here analyzed. The considered structure is composed of a repeated unit cell and can be classified as a Linear Cellular Alloy (LCA) core. The unit cells are of a tetrahedral configuration, arranged according to a honeycomb lay-out. The considered configuration has previously been proposed for core designs of sandwich beams with superior structural properties. In here, the effects of the core configuration on the structural-acoustic behavior of the considered sandwich shell is investigated through a FE model. The FE model is created with ANSYS, a commercially available Finite Element Analysis (FEA) package. The sensitivity of the shell's dynamic characteristics to changes in the geometric properties of the core is investigated. An optimization problem is formulated to determine the core configuration which minimizes, within a target frequency range, the sound radiation of the shell in an unbounded fluid environment.

Jeong, Sang M.; Ruzzene, Massimo

2004-07-01

415

Multilayer Roll-Bonded Sandwich: Processing, Mechanical Performance, and Bioactive Behavior  

NASA Astrophysics Data System (ADS)

Multifunctionality and improving the properties of materials make it necessary to use hybrid systems such as combinations of metals with polymers. Their applications can be found in all areas where light weight and improved and adapted mechanical properties as well as high functionality are needed. Moreover, tailored types of hybrids can be interesting for biomedical applications, as under specific conditions they show, e.g., good strength combined with high elasticity. Herein, we present preliminary tests on the biomimetic behavior of AISI SS316L/polypropylene copolymer/AISI SS316L sandwich. Biomimetic coatings were produced by inducing a calcium phosphate layer in a way similar to the process of natural bone formation. Knowledge of the formability of three-layered sandwich sheets and their biomimetic behavior is presented.

Palkowski, Heinz; Stanic, Vesna; Carradò, Adele

2012-04-01

416

Sandwich-like compounds based on bare all-boron cluster B(6)(2-).  

PubMed

Here, we theoretically predict antiaromatic double-decked compounds [DMB(6)](q-) (D = B(6)(2-), Cp(-); M = Li, Na, K, Be, Mg, Ca) as well as the triple-decked sandwich-like species. Being energetically higher than the fusion isomers, the homo-decked assembly species [B(6)MB(6)](q-) without and with counterions are less likely to be observed experimentally. The hetero-decked sandwich species are low-lying minima containing double-fold antiaromatic B(6)(2-) building blocks. Additionally, the well-retained double antiaromaticity is mainly ascribed to the ionic electrostatic interaction and the protection of rigid Cp-deck in order to avoid the fusion of B(6)(2-). Our results represent the first example that the antiaromaticity is well retained in assembled compounds as in the free B(6)(2-) cluster. Realization of the double antiaromatic B(6)(2-)-incorporated assembled compound is very promising. PMID:18414723

Yang, Li-ming; Wang, Jian; Ding, Yi-hong; Sun, Chia-chung

2008-05-01

417

Resistive switching of Pt/ZrO2/YBa2Cu3O7 sandwiches  

NASA Astrophysics Data System (ADS)

Resistive switching characteristics of Pt/ZrO2/YBa2Cu3O7 sandwiches are investigated for nonvolatile memory applications. Reproducible bipolar resistance switching with an on/off current ratio about 60 and long data retention are achieved. The conduction mechanism obeys Schottky emission in the low resistance state, while Poole-Frankel conduction is predominant in the high resistance state. The resistance switching of Pt/ZrO2/YBa2Cu3O7 sandwiches can be ascribed to migration and redistribution of oxygen vacancies around the ZrO2/YBa2Cu3O7 interface, which switches the conduction between the interface-controlled and the bulk-controlled mechanisms.

Wen, Zheng; Li, Kun; Wu, Di; Li, Aidong

2014-03-01

418

Compressive response of a sandwich plate containing a cracked diamond-celled lattice  

NASA Astrophysics Data System (ADS)

The compressive strength is determined for a sandwich plate containing a centre-cracked core made from an elastic-brittle, diamond-celled lattice. It is assumed that the lattice fails when the major component of principal stress anywhere in the lattice attains the compressive or tensile strength of the solid, or when local buckling intervenes. First, analytical and numerical predictions are given for the unnotched strength of the core and for the compressive fracture toughness of the lattice K IC. Second, finite element simulations and analytical models are reported for the fracture response of the sandwich plate with cracked core. The active failure mechanism in the cracked core is sensitive to core height, crack length, lattice geometry and material choice; this is illustrated by means of material-property charts.

Quintana Alonso, I.; Fleck, N. A.

2009-09-01

419

Analysis of a ceramic filled bio-plastic composite sandwich structure  

SciTech Connect

Design and analysis of a ceramic-filled bio-plastic composite sandwich structure is presented. This proposed high-dielectric structure is used as a substrate for patch antennas. A meandered-strip line-fed fractal-shape patch antenna is designed and fabricated on a copper-laminated sandwich-structured substrate. Measurement results of this antenna show 44% and 20% of bandwidths with maximum gains of 3.45 dBi and 5.87 dBi for the lower and upper bands, respectively. The half-power beam widths of 104° and 78° have been observed from the measured radiation pattern at the two resonance frequencies 0.9 GHz and 2.5?GHz.

Habib Ullah, M. [Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, Bangi Selangor 43600 (Malaysia) [Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, Bangi Selangor 43600 (Malaysia); Department of Electrical, Electronic and System Engineering, Universiti Kebangsaan Malaysia, Bangi 43600 (Malaysia); Islam, M. T. [Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, Bangi Selangor 43600 (Malaysia)] [Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, Bangi Selangor 43600 (Malaysia)

2013-11-25

420

A Finite Element Analysis for Predicting the Residual Compressive Strength of Impact-Damaged Sandwich Panels  

NASA Technical Reports Server (NTRS)

A simple analysis method has been developed for predicting the residual compressive strength of impact-damaged sandwich panels. The method is tailored for honeycomb core-based sandwich specimens that exhibit an indentation growth failure mode under axial compressive loading, which is driven largely by the crushing behavior of the core material. The analysis method is in the form of a finite element model, where the impact-damaged facesheet is represented using shell elements and the core material is represented using spring elements, aligned in the thickness direction of the core. The nonlinear crush response of the core material used in the analysis is based on data from flatwise compression tests. A comparison with a previous analysis method and some experimental data shows good agreement with results from this new approach.

Ratcliffe, James G.; Jackson, Wade C.

2008-01-01

421

Analysis of a ceramic filled bio-plastic composite sandwich structure  

NASA Astrophysics Data System (ADS)

Design and analysis of a ceramic-filled bio-plastic composite sandwich structure is presented. This proposed high-dielectric structure is used as a substrate for patch antennas. A meandered-strip line-fed fractal-shape patch antenna is designed and fabricated on a copper-laminated sandwich-structured substrate. Measurement results of this antenna show 44% and 20% of bandwidths with maximum gains of 3.45 dBi and 5.87 dBi for the lower and upper bands, respectively. The half-power beam widths of 104° and 78° have been observed from the measured radiation pattern at the two resonance frequencies 0.9 GHz and 2.5 GHz.

Habib Ullah, M.; Islam, M. T.

2013-11-01

422

Analysis of an Aircraft Honeycomb Sandwich Panel with Circular Face Sheet/Core Disbond Subjected to Ground-Air Pressurization  

NASA Technical Reports Server (NTRS)

The ground-air pressurization of lightweight honeycomb sandwich structures caused by alternating pressure differences between the enclosed air within the honeycomb core and the ambient environment is a well-known and controllable loading condition of aerospace structures. However, initial face sheet/core disbonds intensify the face sheet peeling effect of the internal pressure load significantly and can decrease the reliability of the sandwich structure drastically. Within this paper, a numerical parameter study was carried out to investigate the criticality of initial disbonds in honeycomb sandwich structures under ground-air pressurization. A fracture mechanics approach was used to evaluate the loading at the disbond front. In this case, the strain energy release rate was computed via the Virtual Crack Closure Technique. Special attention was paid to the pressure-deformation coupling which can decrease the pressure load within the disbonded sandwich section significantly when the structure is highly deformed.

Rinker, Martin; Krueger, Ronald; Ratcliffe, James

2013-01-01

423

Unprecedented bending and rearrangement of f-element sandwich complexes induced by superbulky cyclooctatetraenide ligands.  

PubMed

The use of the superbulky cyclooctatetraenide dianion ligand [C(8)H(6)(SiPh(3))(2)](2-) (= COT(BIG)) in organo-f-element chemistry leads to unprecedented effects such as the formation of a significantly bent anionic Ce(III) sandwich complex, a novel cerocene formed by sterically induced SiPh(3) group migration, as well as the first example of a bent uranocene. PMID:21214176

Lorenz, Volker; Schmiege, Benjamin M; Hrib, Cristian G; Ziller, Joseph W; Edelmann, Anja; Blaurock, Steffen; Evans, William J; Edelmann, Frank T

2011-02-01

424

Tailoring materials properties of UFG aluminium alloys by accumulative roll bonded sandwich-like sheets  

Microsoft Academic Search

Accumulative roll bonding (ARB) as a method of severe plastic deformation is a well-established process to produce ultrafine-grained\\u000a (UFG) sheet materials with extraordinary mechanical properties. In this work ARB is applied to combine different sheet materials\\u000a in order to tailor the materials properties by producing sandwich-like structures. The high strength aluminium alloy AA5754,\\u000a after 4 ARB cycles (N4), is used

Tina Hausöl; Heinz Werner Höppel; Mathias Göken

2010-01-01

425

Energy-absorption performance of porous materials in sandwich composites under hypervelocity impact loading  

Microsoft Academic Search

This study presents the results of an experimental investigation concerning composite structure models for hypervelocity impact-resistant composites. Sandwich models were investigated for their abilities to prevent perforation subjected to 1–7 km\\/s projectile hypervelocity impact loading. The models involve several material systems, dual-wall configurations, fabric-reinforced silicon carbide ceramic-matrix composite as impact-facing sheet, hollow sphere energy-absorption materials, carbon fabric and Kevlar fabric

Yi Li; Jian Bao Li; RouQi Zhang

2004-01-01

426

Free vibration and stability of angle-ply laminated composite and sandwich plates under thermal loading  

Microsoft Academic Search

A two-dimensional global higher-order deformation theory is presented for the free vibration and stability problems of angle-ply laminated composite and sandwich plates subjected to thermal loading. By using the method of power series expansion of continuous displacement components, a set of fundamental governing equations which can take into account the effects of both transverse shear and normal stresses is derived

Hiroyuki Matsunaga

2007-01-01

427

Study of Cellular Materials Sandwich Under Dynamic Loading for Bird Strike Application  

Microsoft Academic Search

This paper reports an original inverse perforation tests on foam core sandwich panels under impact loading. The key point\\u000a is the use of an instrumented Hopkinson pressure bar as a perforator and at the same time a measuring device. It aims at a\\u000a high quality piercing force record during the whole perforation process, which is not available in common free-flying

Y. Girard; I. Elnasri; H. Zhao

428

Double antibody sandwich enzyme linked immunoassay and rapid Immunoswab assay for detection of gliadin in food  

Microsoft Academic Search

Celiac (gluten intolerant) sprue is a life-long threatening disease. The only effective treatment thus far is to maintain a gluten-free diet. Sensitive and reliable double antibody sandwich enzyme-linked immunosorbent assay (ELISA) and Immunoswab assay were developed by using chicken egg yolk anti-gliadin immunoglobulin Y as capturing antibody and monoclonal anti-gliadin IgG (HYB-314) antibody as detecting antibody for the detection of

Hoon H. Sunwoo; Naiyana Gujral; Susan Lutz; Mavanur Suresh

2011-01-01

429

Double antibody sandwich enzyme linked immunoassay and rapid Immunoswab assay for detection of gliadin in food  

Microsoft Academic Search

Celiac (gluten intolerant) sprue is a life-long threatening disease. The only effective treatment thus far is to maintain a gluten-free diet. Sensitive and reliable double antibody sandwich enzyme-linked immunosorbent assay (ELISA) and Immunoswab assay were developed by using chicken egg yolk anti-gliadin immunoglobulin Y as capturing antibody and monoclonal anti-gliadin IgG (HYB-314) antibody as detecting antibody for the detection of

Hoon H. Sunwoo; Naiyana Gujral; Susan Lutz; Mavanur Suresh

2012-01-01

430

Fabrication and compressive performance of plain carbon steel honeycomb sandwich panels  

Microsoft Academic Search

Plain carbon steel Q215 honeycomb sandwich panels were manufactured by brazing in a vacuum furnace. Their characteristic parameters, including equivalent density, equivalent elastic modulus, and equivalent compressive strength along out-of-plane (z-direction) and in-plane (x- and y-directions), were derived theoretically and then determined experimentally by an 810 material test system. On the basis of the experimental data, the compressive stress-strain curves

Yu'an Jing; Shiju Guo; Jingtao Han; Yufei Zhang; Weijuan Li

2008-01-01

431

Low-velocity impact damage initiation in graphite\\/epoxy\\/Nomex honeycomb-sandwich plates  

Microsoft Academic Search

Low-velocity impact and static indentation tests on sandwich plates composed of 4- to 48-ply graphite\\/epoxy cross-ply laminate facesheets and Nomex honeycomb cores have been performed to characterize damage initiation as a function of facesheet thickness and loading rate. Force histories during low-velocity impact are measured by using an instrumented impactor and integrated to produce energy histories. Energy histories are shown

Eric J Herup; Anthony N Palazotto

1998-01-01

432

Vibration control of honeycomb sandwich panel using multi-layer piezoelectric actuator  

Microsoft Academic Search

A novel multi-layer piezoelectric actuator (MPA) is developed and used to control the vibration of honeycomb sandwich panel (HSP). The governing equation of the system is derived with the Hamilton principle considering third-order shearing deformation of HSP. The formulation of the actuation force is obtained and indicates the actuation force is a fourth-order polynomial function of the piezoelectric layers number.

Yajun Luo; Shilin Xie; Xinong Zhang

2008-01-01

433

Compressive response of notched glass-fiber epoxy\\/honeycomb sandwich panels  

Microsoft Academic Search

The quasi-static uniaxial compressive response of E-glass\\/epoxy-Nomex™ sandwich panels containing circular through-holes was studied experimentally. Specimens with four and eight-harness satin weave fabric face-sheets were tested. In both materials the principal failure mechanism consisted of linear damage zones (LDZs) emanating from the hole edge. LDZs are macroscopically similar to fiber-bridged cracks in tension, and propagated in a stable manner. Cross-sectioning

M. G Toribio; S. M Spearing

2001-01-01

434

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

Microsoft Academic Search

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

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

2008-01-01

435

Effective elastic characteristics of honeycomb sandwich composite shells made of generally orthotropic materials  

Microsoft Academic Search

This paper works on the analytical development of the method of two-scale asymptotic homogenization. The technique is used to determine the effective elastic stiffnesses of hexagonal honeycomb-cored structural sandwich composite shells made of generally orthotropic materials. Orthotropy of the constituent materials leads to much more complex unit-cell problems and is considered in the present paper for the first time. At

Gobinda C. Saha; Alexander L. Kalamkarov; Anastasis V. Georgiades

2007-01-01

436

The low velocity impact response of an aluminium honeycomb sandwich structure  

Microsoft Academic Search

The low velocity impact response of two aluminium honeycomb sandwich structures has been investigated by conducting drop-weight impact tests using an instrumented falling-weight impact tower. Initially, the rate-sensitivity of the glass fibre reinforced\\/epoxy skins and aluminium core was investigated through a series of flexure, shear and indentation tests. Here, it was found that the flexural modulus of the composite skins

W. J. Cantwell

2003-01-01

437

NON-DESTRUCTIVE TESTING OF HONEYCOMB SANDWICH STRUCTURES USING ELASTIC WAVES  

Microsoft Academic Search

A new method for accurately measuring localized phase velocities in reverberant panels in the frequency range 5–50 kHz is applied to the problem of the non-destructive testing of honeycomb sandwich structures. First, a brief description of the elastic and vibration properties of these materials is given. With access to only one side of the panel, the method is shown to

S. Thwaites; N. H. Clark

1995-01-01

438

Misura dell'eccesso positivo a bassa energia mediante sandwich di lastre nucleari in campo magnetico  

Microsoft Academic Search

Riassunto  Lastre Ilford G5 di 400 micron di spessore sono state esposte in sandwich con un'intercapedine d'aria di 3,2 mm in un campo\\u000a magnetico di 30000 oersted al livello del mare. Se ne ricava un valore per l'eccesso positivo dei mesoni ? a fine range: ?=0±0,27.\\u000a Viene discussa la sensibilità del metodo sia per la determinazione della massa che per quella

M. Merlin; B. Vitale; Y. Goldschmidt-Clermont

1952-01-01

439

The Underwater Blast Resistance of Metallic Sandwich Beams With Prismatic Lattice Cores  

Microsoft Academic Search

The finite element method is used to evaluate the underwater blast resistance of mono- lithic beams and sandwich beams containing prismatic lattice cores (Y-frame and corru- gated core) and an ideal foam core. Calculations are performed on both free-standing and end-clamped beams, and fluid-structure interaction effects are accounted for. It is found that the degree of core compression in the

G. J. McShane; V. S. Deshpande; N. A. Fleck

2007-01-01

440

A group-specific, indirect sandwich ELISA for the detection of equine encephalosis virus antigen  

Microsoft Academic Search

A polyclonal antibody-based, group-specific, indirect, sandwich ELISA (S-ELISA) for the detection of equine encephalosis virus (EEV) antigen was developed. Purified EEV particles were titrated in the S-ELISA and the limit of detection was determined to be approximately 9.0 ng of antigen\\/ml (0.45 ng\\/well). Positive S-ELISA reactions were recorded with seven serologically distinct EEV serotypes. No cross-reactions were recorded with other

J. E. Crafford; A. J. Guthrie; M. van Vuuren; P. P. C. Mertens; J. N. Burroughs; P. G. Howell; C. Hamblin

2003-01-01

441

Dynamic analysis of sandwich panels and topological design of cores considering the size effect  

Microsoft Academic Search

A typical sandwich panel is composed of the upper and lower skins separated by a lightweight core, for instance, foams, trusshoneycombs and corrugated cores (1-4). And each kind of cores has various structural forms. For example, the foam cores have polymer and metallic ones with open-cell and close- cell ones; the truss cores have tetrahedral, pyramidal, 3D Kagome and diamond

K. Qiu; W. Zhang; P. Duysinx

442

Contact transparency inducing low bias negative differential resistance in two capped carbon nanotubes sandwiching ? barrier  

NASA Astrophysics Data System (ADS)

A first-principles study of the transport properties of two capped (5, 5) carbon nanotubes sandwiching ? barrier is reported. Contact transparency at zero bias is obtained. Strong negative differential resistance effect with large peak-to-valley ratio of 1,124 % is present under very low bias, which may promise the potential applications in nano-electronic devices with low power dissipation in the future.

Min, Y.; Fang, J. H.; Zhong, C. G.; Dong, Z. C.; Li, J. F.; Yao, K. L.; Zhou, L. P.

2014-08-01

443

Sandwich ELISA for detecting urinary Survivin in bladder cancer  

PubMed Central

Objective Survivin as a tumor marker in the diagnosis of bladder cancer has not been completely confirmed yet and there are few reports about using Survivin enzyme-linked immunosorbent assay (ELISA) kit to detect the urine of bladder cancer patients. This study aimed to develop a Survivin ELISA and validate its value in the detection of bladder cancer. Methods Through square matrix titration, different combinations of coating antibody and detecting antibody, a Survivin ELISA was constructed. This assay was evaluated according to intra-assay precision, inter-assay precision and minimum detectable dose (MDD). Survivin levels were detected and analyzed in 102 bladder cancer patients and 102 healthy people by established ELISA. Then cutoff value was defined according to the analysis of receiver operating characteristic (ROC) curve. The sensitivity and specificity of detection were calculated on the basis of cutoff value to diagnose bladder cancer patients. Furthermore, the value of Survivin expression detected by ELISA among different clinicopathological characteristics of patients was also compared. Results Through optimization of different conditions, intra-assay precision was 8.39%, inter-assay precision 8.57% and MDD 0.0625 ng/mL in this assay. When the optical density at 450 nm (OD450) was 0.09, it could get the optimized diagnostic cutoff value. According to this value, the sensitivity and specificity of diagnosis in bladder cancer patients were 70.6% and 89.2%, respectively. The associations between patients’ clinical variables and OD450 were not significant except tumor numbers in patients. Conclusions This experiment has preliminarily developed a Survivin ELISA and confirmed Survivin as a biomarker which owned a practical and significant value in the diagnosis of bladder cancer. PMID:23997523

Li, Xuefeng; Wang, Yaming; Xu, Jianjun

2013-01-01

444

Shape-dependent surface-enhanced Raman scattering in gold–Raman-probe–silica sandwiched nanoparticles for biocompatible applications  

Microsoft Academic Search

To meet the requirement of Raman probes (labels) for biocompatible applications, a synthetic approach has been developed to sandwich the Raman-probe (malachite green isothiocyanate, MGITC) molecules between the gold core and the silica shell in gold–SiO2 composite nanoparticles. The gold–MGITC–SiO2 sandwiched structure not only prevents the Raman probe from leaking out but also improves the solubility of the nanoparticles in

Ming Li; Scott K Cushing; Jianming Zhang; Jessica Lankford; Zoraida P Aguilar; Dongling Ma; Nianqiang Wu

2012-01-01

445

Efficient Design and Analysis of Lightweight Reinforced Core Sandwich and PRSEUS Structures  

NASA Technical Reports Server (NTRS)

Design, analysis, and sizing methods for two novel structural panel concepts have been developed and incorporated into the HyperSizer Structural Sizing Software. Reinforced Core Sandwich (RCS) panels consist of a foam core with reinforcing composite webs connecting composite facesheets. Boeing s Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) panels use a pultruded unidirectional composite rod to provide axial stiffness along with integrated transverse frames and stitching. Both of these structural concepts are ovencured and have shown great promise applications in lightweight structures, but have suffered from the lack of efficient sizing capabilities similar to those that exist for honeycomb sandwich, foam sandwich, hat stiffened, and other, more traditional concepts. Now, with accurate design methods for RCS and PRSEUS panels available in HyperSizer, these concepts can be traded and used in designs as is done with the more traditional structural concepts. The methods developed to enable sizing of RCS and PRSEUS are outlined, as are results showing the validity and utility of the methods. Applications include several large NASA heavy lift launch vehicle structures.

Bednarcyk, Brett A.; Yarrington, Phillip W.; Lucking, Ryan C.; Collier, Craig S.; Ainsworth, James J.; Toubia, Elias A.

2012-01-01

446

Hypervelocity Impact Performance of Open Cell Foam Core Sandwich Panel Structures  

NASA Technical Reports Server (NTRS)

Open cell metallic foam core sandwich panel structures are of interest for application in spacecraft micrometeoroid and orbital debris shields due to their novel form and advantageous structural and thermal performance. Repeated shocking as a result of secondary impacts upon individual foam ligaments during the penetration process acts to raise the thermal state of impacting projectiles ; resulting in fragmentation, melting, and vaporization at lower velocities than with traditional shielding configurations (e.g. Whipple shield). In order to characterize the protective capability of these structures, an extensive experimental campaign was performed by the Johnson Space Center Hypervelocity Impact Technology Facility, the results of which are reported in this paper. Although not capable of competing against the protection levels achievable with leading heavy shields in use on modern high-risk vehicles (i.e. International Space Station modules), metallic foam core sandwich panels are shown to provide a substantial improvement over comparable structural panels and traditional low weight shielding alternatives such as honeycomb sandwich panels and metallic Whipple shields. A ballistic limit equation, generalized in terms of panel geometry, is derived and presented in a form suitable for application in risk assessment codes.

Ryan, S.; Ordonez, E.; Christiansen, E. L.; Lear, D. M.

2010-01-01

447

Monoclonal Antibody-Based Sandwich ELISA for the Detection of Staphylococcal Enterotoxin A  

PubMed Central

A sensitive and specific monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (ELISA) was established and validated for the detection of staphylococcal enterotoxin A (SEA). After routine fusion and selection, 10 monoclonal antibodies showed high affinity for SEA. An optimal pair for sandwich ELISA was selected by pairwise interaction analysis. After optimization, the limit of detection (LOD) and linear dynamic range of the method were established, and were found to be 0.0282 ng/mL and 0.06–2 ng/mL, respectively. The recovery in pure milk ranged from 82.67% to 111.95% and the intra- and inter-assay coefficients of variation ranged from 3.16% to 6.05% and from 5.16% to 10.79%, respectively. Cross-reactivity with staphylococcal enterotoxin B (SEB), staphylococcal enterotoxin C (SEC), staphylococcal enterotoxin D (SED), and staphylococcal enterotoxin E (SEE) in this method were insignificant. These results indicate that the sandwich ELISA method developed in our study is effective for routine identification of SEA in food samples. PMID:23603865

Kuang, Hua; Wang, Wenbing; Xu, Liguang; Ma, Wei; Liu, Liqiang; Wang, Libing; Xu, Chuanlai

2013-01-01

448

Use of the skin sandwich technique to probe the role of the hair follicles in sonophoresis.  

PubMed

The human skin sandwich technique was used to explore the effect of brief ultrasound exposure on the transfollicular pathway of absorption. Hydrocortisone was used as a model drug. In order to calculate the permeability coefficient of hydrocortisone, its concentration at saturation in the PBS donor solution was determined. Skin samples were prepared by sandwich technique with total hydration of the epidermal and sandwich membranes. The skin was sonicated for 0 s (control), 30 s or 45 s using a pulsed mode (10% duty cycle) with the spatial and temporal average intensity (SATA) of 3.7 W/cm(2). The transducer was then removed and permeation was allowed to proceed for 52 h. Then the percentage follicular contribution was determined. It was determined that without ultrasound, drug entry into follicles accounted for 46% of total penetration. As the duration of sonication increased, the follicular contribution fell to zero even though total transepidermal flux dramatically increased. This is explained by ultrasound exposure causing sloughing off of the uppermost stratum corneum. This permeabilises the continuous surface but at the same time the disturbed cornceocytes will plug hair follicle orifices. PMID:22209999

Sarheed, Omar; Frum, Yakov

2012-02-28

449

Factors influencing hydrocortisone permeation into human hair follicles: use of the skin sandwich system.  

PubMed

The aim of the present study was to use the in vitro human skin sandwich system in order to quantify the influence of formulation variables on intrafollicular hydrocortisone permeation. The investigated variables were the pH and the viscosity of the topical formulation as well as the presence of chemical enhancers (carvone, menthone, oleic acid and sodium lauryl sulphate). Furthermore, skin sandwich hydration was also varied in order to determine if the method itself can be run using only partially hydrated skin tissues. It was determined that the follicular contribution to hydrocortisone flux decreased marginally with increasing alkalinity in the pH range 3-8.8. Intrafollicular penetration was markedly reduced when HPMC gels were used instead of an aqueous solution. Pretreating the skin with chemical enhancers also reduced the follicular contribution to flux, probably due to permeabilisation of the continuous stratum corneum. Furthermore, it was not possible to satisfactorily modify the skin sandwich method so that it could be deployed using less hydrated skin. PMID:18406085

Frum, Yakov; Eccleston, Gillian M; Meidan, Victor M

2008-06-24

450

Process Factors and Edgewise Compressive Properties of Scarf-repaired Honeycomb Sandwich Structures  

NASA Astrophysics Data System (ADS)

Bonded repairs were conducted on flat and edge-closed composite sandwich panels that had undergone different levels of initial damage, and edgewise compression behaviors of repaired panel were tested. Experimental results indicate that these repair techniques can restore the compression performance of damaged panels effectively. The repaired specimens recovered an average of over 83 % of their strength. A k-sample Anderson-Darling test was used to analyze the influence of various parameters, including curing temperature, curing pressure, and repair configurations. After a thorough comparison, it was concluded that a high-temperature, high-pressure treatment can improve the mechanical performance of repaired panels, but the improvement is closely related to the structural complexity of the repaired region. A double-side repair scheme could be used to prevent the degradation of mechanical performance caused by the additional bending moment. The conclusions drawn in the present study provide further insight into the mechanical performance of repaired sandwich panels under edgewise compressive loads. These data facilitate the improved design methodology on bonded repair of composite sandwich structures.

Liu, Sui; Guan, Zhidong; Guo, Xia; Sun, Kai; Kong, Jiaoyue; Yan, Dongxiu

2013-11-01

451

Numerical comparison of patch and sandwich piezoelectric transducers for transmitting ultrasonic waves  

NASA Astrophysics Data System (ADS)

Guided wave ultrasonic inspection is becoming an important method of non-destructive testing for long, slender structures such as pipes and rails. Often it is desirable to use transducers that can strongly excite a specific mode of wave propagation in the waveguide. Piezoelectric patch transducers are frequently employed, by researchers, for exciting waves in beam like structures. Sonar systems frequently make use of resonant transducers, such as sandwich transducers, for acoustic wave generation and this principle has been used to excite waves in a rail. This paper compares the two transduction approaches, for launching bending waves in rectangular waveguides, with numerical modeling. The numerical modeling combined a waveguide finite element model, of the waveguide, with conventional three-dimensional piezoelectric finite element models of the transducers. The waveguide finite elements were formulated using a complex exponential to describe the wave propagation along the structure and conventional finite element interpolation over the area of the element. Consequently, only a two-dimensional finite element mesh covering the cross-section of the waveguide is required. The harmonic forced response of the waveguide was used to compute a complex dynamic stiffness matrix which represented the waveguide in the transducer model. The effects of geometrical parameters of patch and sandwich transducers were considered before the comparison was made. It appears that piezoelectric patch transducers offer advantages at low frequencies while sandwich transducers are superior at high frequencies, where resonance can be exploited, at the cost of more complex design.

Loveday, Philip W.

2006-03-01

452

Study on the cell size effect of steady state thermal performance of metallic honeycomb sandwich panels  

NASA Astrophysics Data System (ADS)

In this paper, numerical study is performed to reveal the influences of the cell size on the steady state thermal performance of hexagonal metallic honeycomb sandwich panel, by using the semi-empirical Swann and Pittman formula and the Finite Element Method (FEM), respectively. Based on the same material volume of honeycomb core, two types of hexagonal honeycomb core, i.e., size variation of core cell with a constant core height and height variation of core with a constant side length of hexagonal cell, are considered to establish the panel's thermal analysis model, which including the conduction and radiation coupling. Comparisons between the temperature distribution results from both methods show that FEM can reveal the size effect of the honeycomb cell on the thermal performances of sandwich panel while the Swann and Pittman formula can not. At the same time, numerical results show that for the core with constant height, the panel thermal performance analyzed by FEM has a tendency of being close to the results obtained from Swann and Pittman formula as the core cell size decreases; whereas, if the hexagonal cell with constant side length is concerned, the greater the core height, the worse the thermal conductive performance of sandwich panel. Besides, analyses based on both methods also show that the temperature distribution of the lower surface of panel becomes gradually uniform when the wall thickness of hexagonal cell decreases.

Lai, Yu-dong; Sun, Shi-ping

2011-11-01

453

Non-destructive inspection of drilled holes in reinforced honeycomb sandwich panels using active thermography  

NASA Astrophysics Data System (ADS)

The aerospace industry is in constant need of ever-more efficient inspection methods for quality control. Product inspection is also essential to maintain the safe operation of aircraft components designed to perform for decades. This paper proposes a method for non-destructive inspection of drilled holes in reinforced honeycomb sandwich panels. Honeycomb sandwich panels are extensively employed in the aerospace industry due to their high strength and stiffness to weight ratios. In order to attach additional structures to them, panels are reinforced by filling honeycomb cells and drilling holes into the reinforced areas. The proposed procedure is designed to detect the position of the holes within the reinforced area and to provide a robust measurement of the distance between each hole and the boundary of the reinforced area. The result is a fast, safe and clean inspection method for drilled holes in reinforced honeycomb sandwich panels that can be used to robustly assess a possible displacement of the hole from the center of the reinforced area, which could have serious consequences. The proposed method is based on active infrared thermography, and uses state of the art methods for infrared image processing, including signal-to-nose ratio enhancement, hole detection and segmentation. Tests and comparison with X-ray inspections indicate that the proposed system meets production needs.

Usamentiaga, R.; Venegas, P.; Guerediaga, J.; Vega, L.; López, I.

2012-11-01

454

Study on the cell size effect of steady state thermal performance of metallic honeycomb sandwich panels  

NASA Astrophysics Data System (ADS)

In this paper, numerical study is performed to reveal the influences of the cell size on the steady state thermal performance of hexagonal metallic honeycomb sandwich panel, by using the semi-empirical Swann and Pittman formula and the Finite Element Method (FEM), respectively. Based on the same material volume of honeycomb core, two types of hexagonal honeycomb core, i.e., size variation of core cell with a constant core height and height variation of core with a constant side length of hexagonal cell, are considered to establish the panel's thermal analysis model, which including the conduction and radiation coupling. Comparisons between the temperature distribution results from both methods show that FEM can reveal the size effect of the honeycomb cell on the thermal performances of sandwich panel while the Swann and Pittman formula can not. At the same time, numerical results show that for the core with constant height, the panel thermal performance analyzed by FEM has a tendency of being close to the results obtained from Swann and Pittman formula as the core cell size decreases; whereas, if the hexagonal cell with constant side length is concerned, the greater the core height, the worse the thermal conductive performance of sandwich panel. Besides, analyses based on both methods also show that the temperature distribution of the lower surface of panel becomes gradually uniform when the wall thickness of hexagonal cell decreases.

Lai, Yu-dong; Sun, Shi-ping

2012-04-01

455

Experimental investigation of graphite/polyimide sandwich panels in edgewise compression  

NASA Technical Reports Server (NTRS)

The local and general buckling behavior of graphite/polyimide sandwich panels simply supported along all four edges and loaded in uniaxial edgewise compression was investigated. Material properties of adhesive and facings were determined from flatwise tension and sandwich beam flexure tests. Tensile and compressive material properties of the facings were determined at 116, R.T., and 589 K (-250, R.T., and 600 F) using the sandwich beam flexure test method. Results indicate that Gr/PI is a usable structural material for short term use at temperatures as high as 589 K (600 F). Buckling specimens were 30.5 X 33.0 cm (12 x 13 in.), had quasi-isotropic symmetric facings and a glass/polyimide honeycomb core. Core thicknesses varied and three panels of each thickness were tested in edgewise compression at room temperature to investigate failure modes and corresponding buckling formulas. Specimens 0.635 cm (0.25 in.) thick failed by overall buckling at loads close to the analytically predicted buckling load; all other panels failed by face wrinkling. Results of the winkling tests indicate that several buckling formulas were unconservative and therefore not suitable for design purposes; recommended wrinkling equations are presented.

Camarda, C. J.

1980-01-01

456

Signal amplification for thrombin impedimetric aptasensor: sandwich protocol and use of gold-streptavidin nanoparticles.  

PubMed

In this work, we report a highly specific amplification strategy demonstrated for the ultrasensitive biosensing of thrombin with the use of gold-streptavidin nanoparticles (strep-AuNPs) and silver reduction enhancement. The biotinylated aptamer of thrombin was immobilized onto an avidin-graphite epoxy composite (AvGEC) electrode surface by affinity interaction between biotin and avidin; electrochemical impedance measurements were performed in a solution containing the redox marker ferrocyanide/ferricyanide. The change in interfacial charge transfer resistance (Rct) experimented by the redox marker, was recorded to confirm aptamer complex formation with target protein, thrombin (Thr), in a label-free first stage. A biotinylated second thrombin aptamer, with complementary recognition properties was then used in a sandwich approach. The addition of strep-AuNPs and silver enhancement treatment led to a further increment of Rct thus obtaining significant signal amplification. The AptThrBio1-Thr-AptThrBio2 sandwich formation was inspected by confocal microcopy after incubation with streptavidin quantum dots. In order to visualize the presence of gold nanoparticles, the same silver enhancement treatment was applied to electrodes already modified with the nanoparticle-sandwich conjugate, allowing direct observation by scanning electron microscopy (SEM). Results showed high sensitivity and selectivity for thrombin detection, with an improvement from ca. 4.7 pM in a simple assay to 0.3 pM in the amplified reported scheme. PMID:24296061

Ocaña, Cristina; del Valle, Manel

2014-04-15

457

Finite element based stability-constrained weight minimization of sandwich composite ducts for airship applications  

NASA Astrophysics Data System (ADS)

High Altitude Long Endurance (HALE) airships are platform of interest due to their persistent observation and persistent communication capabilities. A novel HALE airship design configuration incorporates a composite sandwich propulsive hull duct between the front and the back of the hull for significant drag reduction via blown wake effects. The sandwich composite shell duct is subjected to hull pressure on its outer walls and flow suction on its inner walls which result in in-plane wall compressive stress, which may cause duct buckling. An approach based upon finite element stability analysis combined with a ply layup and foam thickness determination weight minimization search algorithm is utilized. Its goal is to achieve an optimized solution for the configuration of the sandwich composite as a solution to a constrained minimum weight design problem, for which the shell duct remains stable with a prescribed margin of safety under prescribed loading. The stability analysis methodology is first verified by comparing published analytical results for a number of simple cylindrical shell configurations with FEM counterpart solutions obtained using the commercially available code ABAQUS. Results show that the approach is effective in identifying minimum weight composite duct configurations for a number of representative combinations of duct geometry, composite material and foam properties, and propulsive duct applied pressure loading.

Khode, Urmi B.

458

Sizing Single Cantilever Beam Specimens for Characterizing Facesheet/Core Peel Debonding in Sandwich Structure  

NASA Technical Reports Server (NTRS)

This technical publication details part of an effort focused on the development of a standardized facesheet/core peel debonding test procedure. The purpose of the test is to characterize facesheet/core peel in sandwich structure, accomplished through the measurement of the critical strain energy release rate associated with the debonding process. Following an examination of previously developed tests and a recent evaluation of a selection of these methods, a single cantilever beam (SCB) specimen was identified as being a promising candidate for establishing such a standardized test procedure. The objective of the work described here was to begin development of a protocol for conducting a SCB test that will render the procedure suitable for standardization. To this end, a sizing methodology was developed to ensure appropriate SCB specimen dimensions are selected for a given sandwich system. Application of this method to actual sandwich systems yielded SCB specimen dimensions that would be practical for use. This study resulted in the development of a practical SCB specimen sizing method, which should be well-suited for incorporation into a standardized testing protocol.

Ratcliffe, James G.

2010-01-01

459

Failure Maps for Rectangular 17-4PH Stainless Steel Sandwiched Foam Panels  

NASA Technical Reports Server (NTRS)

A new and innovative concept is proposed for designing lightweight fan blades for aircraft engines using commercially available 17-4PH precipitation hardened stainless steel. Rotating fan blades in aircraft engines experience a complex loading state consisting of combinations of centrifugal, distributed pressure and torsional loads. Theoretical failure plastic collapse maps, showing plots of the foam relative density versus face sheet thickness, t, normalized by the fan blade span length, L, have been generated for rectangular 17-4PH sandwiched foam panels under these three loading modes assuming three failure plastic collapse modes. These maps show that the 17-4PH sandwiched foam panels can fail by either the yielding of the face sheets, yielding of the foam core or wrinkling of the face sheets depending on foam relative density, the magnitude of t/L and the loading mode. The design envelop of a generic fan blade is superimposed on the maps to provide valuable insights on the probable failure modes in a sandwiched foam fan blade.

Raj, S. V.; Ghosn, L. J.

2007-01-01

460

Diffuse field transmission into infinite sandwich composite and laminate composite cylinders  

NASA Astrophysics Data System (ADS)

This paper is concerned with the modelling of diffuse field transmission into composite laminate and sandwich composite infinite cylinders. Two models are presented and compared: Symmetrical Laminate composite and discrete thick laminate composite. The latter is shown to handle accurately, as a particular case, the first model, and the important case of sandwich composite shells. In both models, membrane, bending, transverse shearing as well as rotational inertia effects and orthotropic ply angle of the layers are considered. Starting from the dynamic equilibrium relations and stress-strain-displacement relations, a dispersion system is given in a wave approach context. Next, expressions for the matrix systems governing the structural impedance, critical frequencies and ring frequency are given. The developed equations are applied to the calculation of the diffuse field transmission of an infinite cylinder. Predictions with the presented models are compared to results presented in the literature for both laminate composite and sandwich composite configurations. They confirm the accuracy of both models and the general nature of the presented discrete thick laminate composite model.

Ghinet, Sebastian; Atalla, Noureddine; Osman, Haisam

2006-02-01

461

Elasticity Solutions for the Buckling of Thick Composite and Sandwich Cylindrical Shells Under External Pressure  

NASA Astrophysics Data System (ADS)

Thick composite and sandwich shells are used in many naval submersible structures and in other applications such as space vehicles. Stability under the prevailing high external pressure in deep ocean environments is of primary concern. In many other applications the loading involves a combination of external pressure and axial compression. It is well known that for these structures the simple classical formulas are in much error, due to both the large thickness and the large extensional over shear modulus ratios of modern composite and sandwich materials. Although there exist several advanced theories, such as first order shear and higher order shear theories, each based on a specific set of assumptions, it is not easy to determine the accuracy and range of validity of these advanced models unless an elasticity solution exists. This paper presents the research performed over the last 15 years on benchmark elasticity solutions to the problem of buckling of (i) orthotropic homogeneous cylindrical shells and (ii) sandwich shells with all constituent phases i.e., facings and core assumed to be orthotropic. The paper focuses on uniform external pressure loading. In this context, the structure is considered a three-dimensional body. The results show that the shell theory predictions can produce in many cases highly non-conservative results on the critical loads. A comparison with the corresponding formulas from shell theory with shear included, is also performed. The present solutions provide a means of accurately assessing the limitations of the various shell theories in predicting stability loss.

Kardomateas, George A.

462

Open-Mode Debonding Analysis of Curved Sandwich Panels Subjected to Heating and Cryogenic Cooling on Opposite Faces  

NASA Technical Reports Server (NTRS)

Increasing use of curved sandwich panels as aerospace structure components makes it vital to fully understand their thermostructural behavior and identify key factors affecting the open-mode debonding failure. Open-mode debonding analysis is performed on a family of curved honeycomb-core sandwich panels with different radii of curvature. The curved sandwich panels are either simply supported or clamped, and are subjected to uniform heating on the convex side and uniform cryogenic cooling on the concave side. The finite-element method was used to study the effects of panel curvature and boundary condition on the open-mode stress (radial tensile stress) and displacement fields in the curved sandwich panels. The critical stress point, where potential debonding failure could initiate, was found to be at the midspan (or outer span) of the inner bonding interface between the sandwich core and face sheet on the concave side, depending on the boundary condition and panel curvature. Open-mode stress increases with increasing panel curvature, reaching a maximum value at certain high curvature, and then decreases slightly as the panel curvature continues to increase and approach that of quarter circle. Changing the boundary condition from simply supported to clamped reduces the magnitudes of open-mode stresses and the associated sandwich core depth stretching.

Ko, William L.

1999-01-01

463

Development of an innovative sandwich common bulkhead for cryogenic upper stage propellant tank  

NASA Astrophysics Data System (ADS)

In the frame of the Future Launcher Preparatory Program (FLPP) investigating advancing technologies for the Next Generation of Launchers (NGL) a number of novel key technologies are presently under development for significantly improving vehicle performance in terms of payload capacity and mission versatility. As a respective ESA guided technology development program, Cryogenic Upper Stage Technologies (CUST) has been launched within FLPP that hosts among others the development of a common bulkhead to separate liquid hydrogen from the liquid oxygen compartment. In this context, MT Aerospace proposed an advanced sandwich design concept which is currently in the development phase reaching for TRL4 under MT Aerospace responsibility. Key components of this sandwich common bulkhead are a specific core material, situated in-between two thin aluminum face sheets, and an innovative thermal decoupling element at the equatorial region. The combination of these elements provides excellent thermal insulation capabilities and mechanical performance at a minimum weight, since mechanical and thermal functions are merged in the same component. This improvement is expressed by substantial performance figures of the proposed concept that include high resistance against reverse pressure, an optimized heat leak and minimized mass, involving the sandwich dome structure and the adjacent interface rings. The development of single sub-technologies, all contributing to maturate the sandwich common bulkhead towards the desired technology readiness level (TRL), is described in the context of the given design constraints as well as technical, functional and programmatic requirements, issued from the stage level. This includes the thermal and mechanical characterization of core materials, manufacturing issues as well as non-destructive testing and the thermal and structural analyses and dimensioning of the complete common bulkhead system. Dedicated TRL assessments in the Ariane 5 Mid-life Evolution (A5-ME) program track the progress of these technology developments and analyze their applicability in time for A5-ME. In order to approximate A5-ME concerned preconditions, activities are initiated aiming at harmonization of the available specifications. Hence, a look-out towards a further technology step approaching TRL6 in a subsequent phase is given, briefly addressing topics of full scale manufacture and appropriate thermo-mechanical testing of an entire sandwich common bulkhead.

Szelinski, B.; Lange, H.; Röttger, C.; Sacher, H.; Weiland, S.; Zell, D.

2012-12-01

464

Alternatives to lumber and plywood in home construction  

SciTech Connect

The diminished supply and unstable price of lumber is compelling designers, builders, and developers to explore alternative materials for residential construction. The report discusses several commercially available alternative materials or building systems that may be used in framing and sheathing, including: engineered wood products; laminated fiberboard that can be used for sheathing walls; light-gauge structural steel components for floors, walls and roof systems; foam core structure sandwich panels for walls and roofs; and a variety of concrete and concrete block systems, many of which include insulation material.

Lund, E.

1993-04-01

465

phenogram construction  

NSDL National Science Digital Library

Prior to this exercise, I introduce some fundamental concepts regarding systematics and phylogenetic reconstruction. I do it early in the semester because I like to have the students thinking about these things while we are discussing the major fossil groups later in the semester. The exercise is simple: students construct a phenogram using a collection of objects â could be fossils, or toy animals, or whatever. I use about ten things. At first, students think it'll be easy. They soon realize how difficult it is to identify characters that group some taxa but exclude others. Obviously, the particular taxa you choose can make the exercise more or less difficult. I should also mention that I require the students to produce a dendrogram with strictly dichotomous branching. I explicitly refer to it as a phenogram because I allow students to use whatever characters they wish, and it isn't even necessary that they be able to recognize the organisms. Inevitably, this exercise leads to discussions about the importance of phylogenetically informative characters.

Stephen, Dan

466

Construction research  

SciTech Connect

The papers in this volume report information on fast-track paving, statistically based specifications, bridge rehabilitation, contracts management, and automation in hot in-place asphalt pavement recycling. Hossain and Wojakowski discuss the construction and performance of a fast-track concrete pavement in Kansas. Weed presents the use of composite pay equations as a means of eliminating the confusion and difficulty in administering the acceptance testing of various quality characteristics. He uses an example based on portland cement concrete pavement to illustrate the practicality of this method. Taavoni describes the upgrading and recycling of an 1879 wrought-iron pin connected truss bridge by replacing the pins. Abdul-Malak and Abou-Assaly investigate innovative concepts of contract management to improve the execution of contracts in Lebanon. They present an integrated contract management approach directed toward understanding the interactions, interrelationships, and interdependencies that exist among candidate concepts and strategies. Pagdadis and Ishai discuss the use of automated equipment used for hot in-place asphalt resurfacing and the breakthroughs that have been achieved toward improving this particular site process through real-time data handling.

NONE

1994-12-31

467

[Echinococcus granulosus infection in dogs and livestock from Xinjiang production and construction corps].  

PubMed

The prevalence of Echinococcus granulosus infection in dogs and livestock was investigated in Xinjiang Production and Construction Corps by stratified random sampling. A total of 5 391 dog feces were detected by double antibody sandwich ELISA, and the positive rate of dog coproantigen was 0.69% (37/5 391). The livestock were subjected to necropsy, inspection and palpation. The prevalence of E. granulosus infection in livestock was 3.88% (431/11 122). PMID:25223066

Han, Fei; Wang, Bing-Quan; Wang, Li-Jie; Xiong, Jun; Xi, Yi; Wu, Li-Wen; Ma, Fu-Rong; Li, Fan-Ka

2014-06-01

468

SIMULATION OF THE DAMAGE TOLERANCE BEHAVIOUR OF CFRP\\/HONEYCOMB SANDWICH BASED ON MEASURED PROPERTIES OF THE RESIN IMPREGNATED CORE PAPER  

Microsoft Academic Search

Structural sandwich is widely used as a lightweight design solution for load-carrying components. In aircraft structures particularly sandwich using carbon fibre reinforced plastics (CFRP) as face sheets and non-metallic honeycombs as core material is applied due to features such as high strength-to-weight and stiffness-to-weight ratios as well as excellent fatigue behaviour. Owing to the rather weak core material, sandwich is

F. Hähnel; K. Wolf

469

Comparison of mersilene mesh-methyl metacrylate sandwich and polytetrafluoroethylene grafts for chest wall reconstruction.  

PubMed

We report the outcomes of patients who underwent reconstruction with Mersilene mesh-methyl methacrylate (MM-MM) sandwich and polytetrafluoroethylene (PTFE) grafts after a large chest wall resection. Between June 1990 and September 2001, 59 consecutive patients (37 men, 22 women; mean age, 48.1 +/- 11.8 years; range 22-74 years) underwent large chest wall resection (greater than 5 cm diameter) and reconstruction with prosthetic material in our department. Twenty-one patients (33%) underwent reconstruction with a PTFE graft (group 2) between 1990 and 1994, and 38 patients (67%) underwent reconstruction with an MM-MM sandwich graft (group 1) between 1994 and 2001. Operative morbidity ratios were 5.2% (2/38) in group 1 and 24% (5/21) in group 2 (p = .036). The paradoxical respiration ratio was significantly higher (p = .018) in group 2 (5/21: 24%) than it was in group 1 (1/38: 2.6%). The operative mortality ratio was 4.5% (1/21) in group 2 and 0% in group 1. Mean hospital stay was 10.6 days (range 5-21 days) in group 1 and 13.3 days (range 7-36 days) in group 2 (p = .015). The MM-MM graft is inexpensive and easy to apply, provides better cosmetic options, and offers minimal morbidity. We therefore recommend that the MM-MM sandwich graft be used rather than the PTFE graft for large defects of the anterolateral chest wall and sternum where successful prevention of paradoxical respiration is required. PMID:17101604

Kilic, Dalokay; Gungor, Adem; Kavukcu, Sevket; Okten, Ilker; Ozdemir, Nezih; Akal, Murat; Yavuzer, Sinasi; Akay, Hadi

2006-01-01

470

Guided waves propagating in sandwich structures made of anisotropic, viscoelastic, composite materials.  

PubMed

The propagation of Lamb-like waves in sandwich plates made of anisotropic and viscoelastic material layers is studied. A semi-analytical model is described and used for predicting the dispersion curves (phase velocity, energy velocity, and complex wave-number) and the through-thickness distribution fields (displacement, stress, and energy flow). Guided modes propagating along a test-sandwich plate are shown to be quite different than classical Lamb modes, because this structure does not have the mirror symmetry, contrary to most of composite material plates. Moreover, the viscoelastic material properties imply complex roots of the dispersion equation to be found that lead to connections between some of the dispersion curves, meaning that some of the modes get coupled together. Gradual variation from zero to nominal values of the imaginary parts of the viscoelastic moduli shows that the mode coupling depends on the level of material viscoelasticity, except for one particular case where this phenomenon exists whether the medium is viscoelastic or not. The model is used to quantify the sensitivity of both the dispersion curves and the through-thickness mode shapes to the level of material viscoelasticity, and to physically explain the mode-coupling phenomenon. Finite element software is also used to confirm results obtained for the purely elastic structure. Finally, experiments are made using ultrasonic, air-coupled transducers for generating and detecting guided modes in the test-sandwich structure. The mode-coupling phenomenon is then confirmed, and the potential of the air-coupled system for developing single-sided, contactless, NDT applications of such structures is discussed. PMID:12765380