ARTICOLI SU ALTRI ARGOMENTI RELATIVI AI MATERIALI COMPOSITI
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’02
Draping of engineered prepregs and reinforced
thermoplastics http://www-mech.eng.cam.ac.uk/ccm/projects/mpfs/depart.html
’01 Experimental Investigation of Tow Deformation During Draping of Woven Fabricshttp://www-mech.eng.cam.ac.uk/ccm/projects/mpfs/departabs1.html 01 'Draping of woven composites over irregular surfaces' http://www-mech.eng.cam.ac.uk/ccm/projects/mpfs/departabs2.pdf ********************************************************************* - '02 - - - Structural Efficiency of Stitched Composite Panels With Stiffener Crippling ,43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Denver, Colorado, AIAA 2002-1728, April 22-25, 2002, pp. 12, (5.2MB PS; 4.5MB PDF). Format(s):Postscript, or PDF Abstract: The structural efficiency of blade-stiffened stitched specimens is compared to determine their weight saving potential if blades were allowed to buckle at less than or equal to design ultimate load. Analytical and experimental results from four configurations of crippling specimens are presented. Specimen skin and blades were held together with through-the-thickness stitches prior to curing. No mechanical fasteners were used for the assembly. Tests were conducted with and without low-speed impact damage. Failure modes are discussed. Finite element and experimental results agree for the response of the structures. For some specimen configurations, improved structural efficiency can be obtained by allowing stiffeners to buckle at design limit load rather than requiring that buckling not occur prior to design ultimate load. A parametric study is presented herein which describes the possible weight savings with this approach. ‘02 3D FINITE ELEMENT UNIT CELL STUDY OF PARTICLE FAILURE IN BRITTLE PARTICLE REINFORCED DUCTILE MATRIX COMPOSITES A. Eckschlager and H.J. Böhm http://ilfb.tuwien.ac.at/ilfb/ilfb_ra3e.html Full PaperAbstract - The aim of the present contribution is the modeling of the brittle failure of particles embedded in a ductile matrix subjected to global uniaxial loading. The study is based on three-dimensional multi-particle unit cells and uses the Finite Element method. Appropriate microgeometries are generated by randomly arranging a number of spherical particles within the unit cell, a variant of the Random Sequential Adsorption (RSA) method modified for compatibility with periodic boundary conditions being employed. Elastic material properties are used for the particles and the matrix is described by J2 plasticity. Predefined fracture surfaces, which are assumed to be perpendicularly oriented with respect to the overall uniaxial load, are provided for within the reinforcements. Brittle failure of the reinforcements, which is modeled as an instantaneous cleavage at these surfaces, is implemented by a node release technique. Failure in a given particle is controlled by Weibull-type fracture probabilities in combination with a Monte Carlo algorithm. The fracture probabilities are evaluated for the whole particle on the basis of the current stress distribution. Within the modeling assumptions used, which include neglecting other local failure mechanisms such as ductile damage of the matrix and decohesion at the interface between the constituents, successive particle cleavage and the resulting stress redistribution effects are simulated. Results are presented in terms of predictions for the overall stress vs.~strain behavior and for damage relevant fields at the microscale - '02 - - - Adhesive and Composite Properties of a New Phenylethynyl Terminated Imide , C. M. Thompson, J. W. Connell, P. M. Hergenrother and R. Yokota, 47th International SAMPE Symposium and Exhibition, Long Beach, California, May 12-16, 2002, (270KB PS, 154BK PDF).http://wais-gw.larc.nasa.gov:81/techreports.larc.nasa.gov:210/ltrs_index/HTML/2451/1=techreports.larc.nasa.gov%3A210;2=/usr/local/web/waissrc/ltrs_index;3=0%202451%20/usr/local/web/htdocs/ltrs/refer/2002/mtg/NASA-2002-47sampe-cmt.refer.html;4=techreports.larc.nasa.gov%3A210;5=/usr/local/web/waissrc/ltrs_index;6=0%202451%20/usr/local/web/htdocs/ltrs/refer/2002/mtg/NASA-2002-47sampe-cmt.refer.html;7=%00; Format(s):Postscript, or PDF Abstract: A relatively new phenylethynyl terminated imide oligomer (PETI) from the reaction of 2,3,3',4- biphenyltetracarboxylic dianhydride, 4,4'-oxydianiline and endcapped with 4-phenylethynylphthalic anhydride at a calculated number average molecular weight of 5000 g/mole was evaluated as an adhesive and composite matrix. The asymmetric dianhydride imparts a low melt viscosity to the oligomer and a high glass transition temperature to the cured resin. Preliminary adhesive work with titanium (6Al-4V) adherend gave good room temperature (RT) tensile shear strengths and excellent retention of RT strength at 260 degrees C. Preliminary composite work using unsized IM7 carbon fiber provided moderate to high mechanical properties. The chemistry, mechanical, and physical properties of the new PETI in neat resin, adhesive and composite form are presented. ‘01 Composite Materials with Multifunctional Structure-Power Capabilities http://www.argreenhouse.com/papers/tony2/ASC01_Preprint.pdf ABSTRACT We describe our efforts to develop new design strategies, analysis methods, performance indices, and prototypes for multifunctional structure-battery materials for unmanned air-vehicle applications. The technology is being demonstrated by the design and testing of a structure-battery system for AeroVironment Inc.’s Black-Widow Micro-Air Vehicle (MAV) consisting of Telcordia Technologies’ PLiONTM battery cell material with structural polymers and/or composite materials added for tailoring mechanical Failure Analysis of Stiffened CFRP Panels with an Open Hole Under Compressive Loading C Soutis, I Guz and Y Zhuk http://www.cm.ic.ac.uk/docs/research/resapubs/mechpropchart.html#mpc1 Carbon fibre composite materials are sensitive to open holes, defects, and low-velocity impact damage that can significantly reduce their stiffness and strength properties. To develop structures which are more damage-tolerant, it is necessary to understand how the damage is caused and how it can affect residual performance. A typical aircraft structure such as a fuselage shell or a wing surface usually consists of a skin reinforced with stiffeners. Many investigations of open holes and impact damage in carbon fibre composites are based on testing of small laminates rather than structural elements or full-scale structures. The aim of this work is to examine the failure mechanisms under in-plane compression in stiffened thin-skinned plates with an open hole and apply the cohesive zone model developed by the principal investigator to predict damage initiation, growth, and residual strength. This investigation will increase further our understanding of the factors that control notch sensitivity in composite structures. Theoretical computer modelling will be used to examine particularly the effects of geometry and sub-structure. The structural elements examined will be representative of currently built aircraft structures. - '99 - - - - Advanced Modeling Strategies for the Analysis of Tile-Reinforced Composite Armor , Carlos G. Davila and Tzi-Kang Chen, NASA/TM-1999-209352, ARL-TR-1978, July 1999, pp. 21, (799KB).http://wais-gw.larc.nasa.gov:81/techreports.larc.nasa.gov:210/ltrs_index/HTML/2458/1=techreports.larc.nasa.gov%3A210;2=/usr/local/web/waissrc/ltrs_index;3=0%202458%20/usr/local/web/htdocs/ltrs/refer/1999/tm/NASA-99-tm209352.refer.html;4=techreports.larc.nasa.gov%3A210;5=/usr/local/web/waissrc/ltrs_index;6=0%202458%20/usr/local/web/htdocs/ltrs/refer/1999/tm/NASA-99-tm209352.refer.html;7=%00; Format(s): Postscript, or PDF Abstract: A detailed investigation of the deformation mechanisms in tile-reinforced armored components was conducted to develop the most efficient modeling strategies for the structural analysis of large components of the Composite Armored Vehicle. The limitations of conventional finite elements with respect to the analysis of tile-reinforced structures were examined, and two complementary optimal modeling strategies were developed. These strategies are element layering and the use of a tile-adhesive superelement. Element layering is a technique that uses stacks of shear deformable shell elements to obtain the proper transverse shear distributions through the thickness of the laminate. The tile-adhesive superelement consists of a statically condensed substructure model designed to take advantage of periodicity in tile placement patterns to eliminate numerical redundancies in the analysis. Both approaches can be used simultaneously to create unusually efficient models that accurately predict the global response by incorporating the correct local deformation mechanisms. - '98 - - - - Chemistry, Adhesive and Composite Properties of Low Molecular Weight Phenylethynyl Terminated Oligomers , 21st Annual Adhesion Society Meeting, Savannah, Georgia, February 22-25, 1998, (448KB).John W. Connell, Format(s): Postscript,
or PDF
Abstract: As part of an on-going effort to develop high performance/high temperature structural resins, the chemistry, adhesive and composite properties of relatively low molecular weight phenylethynyl terminated oligomers are under investigation. PETI-5 is a phenylethynyl terminated oligomer that was developed at the NASA Langley Research Center and has undergone extensive evaluation as an adhesive and composite matrix resin. This material is prepared at a calculated number average molecular weight (Mn) of 5000 g/mole from 3.3', 4,4'-tetracarboxylic biphenyl dianhydride (BPDA), 85 mole percent 3,4'-oxydianiline (3,4'-ODA), 15 mole percent 1,3-bis(3-aminophenosy)benzene (APB) and endcapped with 4-phenylethynylphthalic anhydride (PEPA) in N-methyl-2-pyrrolidinone (NMP). PETI-5 has displayed excellent processability and outstanding mechanical properties in both adhesive and composite forms. However, in the processing of complex structural parts, improvements in resin flow are desirable. In an attempt to improve the processability of PETI-5 (5000 g/mole) while maintaining equivalent properties, lower molecular weight versions (2500 and 1250 g/mole) were evaluated as adhesives and composite matrix resins. - '97 - - - Thermal Conductivity Database of Various Structural Carbon-Carbon Composite MaterialsCraig W. Ohlhorst, Wallace L. Vaughn, Philip O. Ransone and Hwa-Tsu Tsou, T , NASA TM-4787, November 1997, pp. 94, (2MB). Format(s): Postscript, or PDF Abstract: Advanced thermal protection materials envisioned for use on future hypersonic vehicles will likely be subjected to temperatures in excess of 1811 K (2800F) and, therefore, will require the rapid conduction of heat away from the stagnation regions of wing leading edges, the nose cap area, and from engine inlet and exhaust areas. Carbon-carbon composite materials are candidates for use in advanced thermal protection systems. For design purposes, high temperature thermophysical property data are required, but a search of the literature found little thermal conductivity data for carbon-carbon materials above 1255 K (1800F). Because a need was recognized for in-plane and through-the-thickness thermal conductivity data for carbon-carbon composite materials over a wide temperature range, Langley Research Center (LaRC) embarked on an effort to compile a consistent set of thermal conductivity values from room temperature to 1922 K (3000F) for carbon-carbon composite materials on hand at LaRC for which the precursor materials and thermal processing history were known. This report documents the thermal conductivity data generated for these materials. In-plane thermal conductivity values range from 10 to 233 W/m-K, whereas through-the-thickness values range from 2 to 21 W/m-K. - '92 - - - Relationship Between Mechanical-Property and Energy-Absorption Trends for Composite Tubes http://wais-gw.larc.nasa.gov:81/techreports.larc.nasa.gov:210/ltrs_index/HTML/2264/1=techreports.larc.nasa.gov%3A210;2=/usr/local/web/waissrc/ltrs_index;3=0%202264%20/usr/local/web/htdocs/ltrs/refer/1992/rdp3284.tex.refer.html;4=techreports.larc.nasa.gov%3A210;5=/usr/local/web/waissrc/ltrs_index;6=0%202264%20/usr/local/web/htdocs/ltrs/refer/1992/rdp3284.tex.refer.html;7=%00; Gary L.
Farley , , NASA TP-3284 ARL-TR-29 , December 1992 , pp.
14 . Format(s):
Postscript,
or PDF
Abstract: U.S. Army helicopters are designed to dissipate prescribed levels of crash impact kinetic energy without compromising the integrity of the fuselage. Because of the complexity of the energy-absorption process, it is imperative for designers of energy-absorbing structures to develop an in-depth understanding of how and why composite structures absorb energy. A description of the crushing modes and mechanisms of energy absorption for composite tubes and beams is presented. Three primary crushing modes of composite structure including transverse shearing, lamina bending, and local buckling are described. The experimental data presented show that fiber and matrix mechanical properties and laminate stiffness and strength mechanical properties cannot reliably predict the energy-absorption response of composite tubes. - '92 - - - Properties of Five Toughened Matrix Composite Materials Roberto J. Cano and Marvin B. Dow , , NASA TP-3254 , October 1992 , pp. 58 , The paper is missing figures. Please see question 16 of the Frequently Asked Questions (FAQ) for information on how to obtain a hardcopy of this document.http://wais-gw.larc.nasa.gov:81/techreports.larc.nasa.gov:210/ltrs_index/HTML/2821/1=techreports.larc.nasa.gov%3A210;2=/usr/local/web/waissrc/ltrs_index;3=0%202821%20/usr/local/web/htdocs/ltrs/refer/1992/rdp3254.tex.refer.html;4=techreports.larc.nasa.gov%3A210;5=/usr/local/web/waissrc/ltrs_index;6=0%202821%20/usr/local/web/htdocs/ltrs/refer/1992/rdp3254.tex.refer.html;7=%00; Format(s):
Postscript,
or PDF
Abstract: The use of toughened matrix composite materials offers an attractive solution to the problem of poor damage tolerance associated with advanced composite materials. In this study, the unidirectional laminate strengths and moduli, notched (open-hole) and unnotched tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths of five carbon fiber/toughened matrix composites, IM7/E7T1-2, IM7/X1845, G40-800X/5255-3, IM7/5255-3, and IM7/5260, have been evaluated. The compression-after-impact (CAI) strengths were determined primarily by impacting quasi-isotropic laminates with the NASA Langley air gun. A few CAI tests were also made with a drop-weight impactor. For a given impact energy, compression-after-impact strengths were determined to be dependent on impactor velocity. Properties and strengths for the five materials tested are compared with NASA data on other toughened matrix materials (IM7/8551-7, IM6/1808I, IM7/977-2, IM7/F655, and T800/F3900). This investigation found that all five materials were stronger and more impact damage tolerant than more brittle carbon/epoxy composite materials currently used in aircraft structures. '92 NUMERICAL SIMULATION OF CRASH BEHAVIOR OF COMPOSITE STRUCTURES FOR AUTOMOTIVE APPLICATIONS http://www.esi-group.com/services/publications/composites/composites.htmlABSTRACT : The present paper evaluates
the crashworthiness simulation techniques of CFRP/honeycomb
composite structures for automotive applications. A basic
methodology for strenght and failure analyses of
CFRP/honeycomb sandwich materials is outlined. The new
material models have been implemented into a
crashworthiness simulation code, PAM-CRASH TM. After
calibration of the material models and parameters on
laboratory coupon tests and validation on simple
component crash tests, the models are extrapolated to the
numerical crash simulation of a full size composite
prototype passenger car main-frame. The numerical resultsare
satisfactorily correlated with experimental results. '?? TECNICHE DI LAMINAZIONE http://www.cfa-hq.org/documents/TeachingLaminatingTechniques.doc Teaching Laminating Techniques aminating is one of the foundational skills of the open molding process. The techniques for placement, saturation, and manual roll-out of fiberglass reinforcement, are used across the composites industry, where open molding produces a wide variety of composite products. Hand lay-up and chopping consumes most of the polyester resin produced in the U.S., and upward of 150,000 people are employed in open molding facilities across the country, where manual laminating is a mainstay proce '?? A Fundamental Study of the Compressive Failure of Polymer Matrix Composites Final Report Executive Summary Experiments and analysis reveal that microbuckling from random fibre waviness dictates the strength, with the length scale of the waviness on a tow-by-tow level for T800-924c carbon fibre-epoxy pre-preg material. A semi-automated digital imaging technique has been developed to measure the 2D in-plane distribution of fibre waviness, and the 2D power spectral density function has been determined for random waviness in commercial carbon fibre-epoxy composites. This technique has the important advantage of integrating fibre misalignment information from relatively large regions of the material. The distribution of compressive strength has been predicted using a finite element program, which includes the effect of fibre misalignment and the relative length scale of the waviness to the fibre diameter. It is found that the predicted, and measured, spread in compressive strength can be represented by a Weibull distribution. Thus, a methodology has been developed to predict the statistical distribution of compressive strength from the measured random waviness pattern. Additionally, the effect of processing conditions (notably the bobbin tension and the contact distance on the spreading rolls) on the waviness of pre-preg has been explored in collaboration with Hexcel. The tow tension was found to have very little effect over the range studied, but it was noted that increased spreading-roll contact (the ‘S-wrap’ technique) actually led to a slightly wider distribution of fibre misalignment. Measured compressive strengths were found to correlate consistently with misalignment data. A study of the effect of pultrusion conditions on fibre alignment was carried out in collaboration with Neptco (‘Graphlite’ rods). In general, such material exhibits a high degree of fibre alignment and correspondingly high compressive strengths. However, it was found that higher pultrusion speeds lead to poorer alignment and higher porosity levels, with associated reductions in compressive strength, in accordance with theoretical predictions. Finally, a new phenomenon of microbuckling tunnelling has been observed, and modelled by integral equation and finite element techniques. This 3D failure mode is by microbuckling of the load-bearing axial plies with concomitant delamination of the neighbouring off-axis plies. The steady state tunnelling stress is a using minimum strength parameter for the design of multi-directional thick laminates. '?? This program is designed to provide training guidelines for spray operators in the }{\i\f4\fs22 open molding composites industry}{\f3\fs22 ,\par where styrene based resin and gel coat materials are used.(articolo 1)http://www.cfa-hq.org/instguide.pdf ,ancora piu' completo(articolo 2)Controlled Spraying Training Program '?? Composite Materials Design http://callisto.my.mtu.edu/my472/ A free online course from MTU. The course aims to teach the mechanical behaviour of polymer composite materials. There are a number of problems that are set as part of the course and MathCad routines which can be downloaded and used as teaching aids. '?? compositi con fibre naturali http://www.hempology.org/CURRENT%20HISTORY/1996%20HEMP%20COMPOSITES.html |
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