bluuebunny/crossref_metadata_2025 huggingface dataset:
Gender dysphoria: recognition and assessment
Authors: Eden Kate , Wylie Kevan , Watson Emily
Published: January 2012

The role of the mental health professional, and of the psychiatrist in particular, is evolving and changing. As the recognition of transsexualism and gender identity disorder expands across the transgender spectrum, it has been recommended that gender dysphoria should replace existing diagnostic terminology. Patient-focused care is evolving and this article considers the limitations of current healthcare settings and how the mental health professional can support patients undergoing the real-life experience. Differentiation from other mental health conditions that may present as gender dysphoria is outlined, as well as specific clinical situations.
Gender dysphoria: treatment and outcomes
Authors: Wylie Kevan , Eden Kate , Watson Emily
Published: January 2012

Once a formal diagnosis of gender dysphoria is established and comorbid disorders addressed, it is the role of the gender specialist to facilitate treatment according to agreed goals. This article reviews the treatment of gender dysphoria, including psychotherapy, and how eligibility and readiness for surgery are assessed. It considers issues facing transgender individuals detained in prison or psychiatric hospital, the factors that affect patients' satisfaction with gender reassignment surgery and how the specialist can ensure a satisfactory outcome.
Schizoaffective disorder
Authors: Castle David J.
Published: January 2012

The term ‘schizoaffective disorder’ has meant different things to different people over the 80 years since Kasanin described a series of cases with an admixture of schizophrenia-like and mood-like symptoms. This article provides a brief overview of the history of the concept, and suggests a parsimonious approach for clinicians.
Nocturnal enuresis with antipsychotic medication
Authors: Barnes Thomas R. E. , Drake Marcus J. , Paton Carol
Published: January 2012

Nocturnal enuresis can be discomfiting and troublesome. There is increasing evidence that as a side-effect of second-generation antipsychotics, particularly clozapine, it may be underrecognised. Direct but sensitive questioning may be required to elicit this side-effect. We briefly review possible mechanisms of this problem, and management and treatment options.
Transcranial direct current stimulation for depression: 3-week, randomised, sham-controlled trial
Authors: Loo Colleen K. , Alonzo Angelo , Martin Donel , Mitchell Philip B. , Galvez Veronica , Sachdev Perminder
Published: January 2012

Background

Preliminary evidence suggests transcranial direct current stimulation (tDCS) has antidepressant efficacy.

Aims

To further investigate the efficacy of tDCS in a double-blind, sham-controlled trial (registered at www.clinicaltrials.gov: NCT00763230).

Method

Sixty-four participants with current depression received active or sham anodal tDCS to the left prefrontal cortex (2 mA, 15 sessions over 3 weeks), followed by a 3-week open-label active treatment phase. Mood and neuropsychological effects were assessed.

Results

There was significantly greater improvement in mood after active than after sham treatment (P<0.05), although no difference in responder rates (13% in both groups). Attention and working memory improved after a single session of active but not sham tDCS (P<0.05). There was no decline in neuropsychological functioning after 3–6 weeks of active stimulation. One participant with bipolar disorder became hypomanic after active tDCS.

Conclusions

Findings confirm earlier reports of the antidepressant efficacy and safety of tDCS. Vigilance for mood switching is advised when administering tDCS to individuals with bipolar disorder.
Compulsion under the Mental Health Act 1983: audit of the quality of medical recommendations
Authors: Mason Julian , Roberts Hannah , Northridge Rebecca , Fountoulaki Garyfallia , Andrews Emma , Watcyn-Jones Cassie , Manion Terri , Chalmers Julie , Davison Phil
Published: January 2012

Aims and method

To audit the quality of medical recommendations for detention under the Mental Health Act 1983, Section 2 and 3. The recommendations were tested against a gold standard based on the statutory criteria. Two cycles were completed, the first containing 214 recommendations, the second 202. Relevant education took place after the first cycle.

Results

The percentage of medical recommendations containing clear statements of why each of the statutory criteria was met increased in the second cycle. It reached 87% for mental disorder; 87% for nature and/or degree; 75% for why community treatment was not possible; 64% for why detention was in the interests of health; 60% for safety; 55% for protection of others; and 70% why informal admission was not possible.

Clinical implications

Doctors, scrutineers and approved mental health practitioners welcomed clear guidance about what is expected in a medical recommendation for detention and endorsed the gold standard described. Armed with a better understanding of what is expected and a template to follow, there was an improvement in the reasons given for detention.
An innovative service but will it work in practice? Commentary on … Fair Horizons
Authors: Tyrer Stephen Patrick
Published: January 2012

This commentary discusses the proposed service, Fair Horizons, a new development designed to ensure comprehensive mental healthcare coverage. Although the aims of the new service are laudable and derive from recent seminal papers on changes in the National Health Service, the proposed initiatives are so far untested and there is uncertainty about how far costs will be reduced under this new system. Success is more likely to result if clinicians are committed to the new service and work harder.
Introduction
Authors: Steven Yurenka
Published: January 2012

The purpose of the American Society for Testing and Materials Conference on Composite Materials: Testing and Design was to provide a forum for the discussion of analytical and experimental studies of advanced composites. Emphasis was on the development of a basic understanding of the mechanical and structural behavior of both organic and metal matrix composites. The program brought together for the first time, comprehensive, detailed, and significant work in the areas of mechanical properties testing, as well as examples of design application. The ultimate aim of the society, speakers, and participants was uniformly the same one; to pave the way for quicker and more widespread utilization of the use of composite materials in military and commercial aircraft, missiles, and space vehicles, and naval and other structural component applications. In recent years advanced composite materials reinforced with high-strength, high-modulus filaments have received increasing attention. This activity has been motivated by the potential for superior performance in structural and other applications afforded by the unique capabilities of such composite materials. The very nature of these advanced composites, namely, the heterogeneity and the high stiffness and strengths, however, has been introducing new problems in both testing and in the development of appropriate design procedures. Thus, innovations in testing techniques and design philosophy have been needed urgently. A short range goal of the sponsoring ASTM Subcommittee on Composites, D-30, has been to derive ideas for new test methods and design and analysis procedures from the technological fallout of this conference. The technical papers which were presented at the conference and which are included in this volume were divided into four sessions and were in some cases given in simultaneous presentations over a period of three days. The four sessions were entitled “Testing, Fatigue and Creep, Design and Application, and Fracture Mechanics,” and each session was opened with a keynote address by an outstanding expert in his field. Although questions and answers were not recorded and published, a lively question and answer period followed each paper.
Composite Materials' Testing
Authors: Prosen S. P.
Published: January 2012

This paper will discuss some of the tests now being used in composites testing. The problems of testing, getting the information sought after, the pitfalls, and some of the controversy surrounding testing will be presented in detail. The added difficulty of testing brought about by the use of high-modulus (advanced) fibers is composites will be discussed thoroughly. For instance, the shear strength test for composite materials has become an extremely controversial subject now that we are dealing with high-modulus fibers. We thought we understood shear testing when we tested glass filament reinforced plastics—at least we all understood one another—now we do not understand shear in this complex advanced composites field.
Special Problems Associated with Boron-Epoxy Mechanical Test Specimens
Authors: Hadcock R. N. , Whiteside J. B.
Published: January 2012

Boron-epoxy composite material specimens were developed and tested to provide basic mechanical property data for design of the Grumman R&D FB-111 boron composite wing box extension. Special problems associated with tension, compression, and shear tests are presented in this paper. Considerable development was required to achieve consistent results even in the apparently simple case of the tension of a unidirectional laminate. Specimen geometry and loading tab configuration have a considerable effect upon the failure stress and the location of the fracture origin, and several designs were tried before consistent failures were produced in the central portions of the specimens. Problems were encountered also in testing compression coupon specimens. “Brooming” failures occurred when the specimen ends were not encapsulated securely. Considerable scatter evident in early tests indicated that compression specimens failed prematurely due to combined flexure-transverse shear and eccentric loading effects. This was confirmed by theoretical analysis. The testing of flat panels in shear by the standard picture frame method presented difficulties. An anisotropic finite element analysis yielded stresses which were in good agreement with strain gage readings but indicated a isevere stress concentration at the corner radius. Additional shear data were obtained from a modified picture frame method, the rail shear test. Experience gained in these programs indicates that the testing of high-strength, high-modulus, anisotropic composites with low normal shear properties and negligible ductility lead to special problems in the design and analysis of specimens.
Characterization of Anisotropic Composite Materials
Authors: Halpin J. C. , Pagano N. J. , Whitney J. M. , Wu E. M.
Published: January 2012

Characterization procedures for aniso tropic composite materials are examinec critically with reference to obtaining a uniform procedure for both stiffness and ultimate property characterization. An experimental procedure employing thin-walled anisotropic cylinders for both uniaxial and multiaxial characterization is proposed.
Test Methods for High-Modulus Carbon Yarn and Composites
Authors: Hoggatt J. T.
Published: January 2012

Several test methods used for the evaluation of carbon filaments and composites are presented. Included are methods for determining tensile, compressive, interlaminar shear, and bearing strength properties of flat and tubular carbon composites. The tensile and compressive properties of composite materials having varying fiber volume functions are reported. The use of both tubular and flat specimens made it possible to determine the effect of narrow (flat) specimens versus wide (cylindrical) specimens on the strength properties of the composite. Interlaminar shear strength (ILS) studies of carbon composites, using flat short-beam specimens, indicated that the strength and the mode of failure obtained are very sensitive to the selected span-to-depth ratio (SDR). Results also show that the apparent ILS increases approximately 25 percent by changing the SDR from eight to four. The bearing strength of a multidirectional composite was found to be 38,000 psi, which is 90 percent of the tensile strength. In addition to methods for composite properties evaluation, material control test methods are described. These include a yarn tension test, resin content, and void content determination.
The Effect of Geometry on the Mode of Failure of Composites in Short-Beam Shear Test
Authors: Sattar S. A. , Kellogg D. H.
Published: January 2012

The interlaminar shear strength of composite materials is often determined by the short-beam shear test method. This type of test is satisfactory only so long as a pure shear failure occurs. Nonshear or mixed-mode failures, hence invalid data, can result if the interlaminar shear strength is too high with respect to the ultimate flexure strength, or if span-to-depth ratio or width-to-depth ratio is improperly chosen. Since the flexural stress is dependent on span length, various span-to-depth ratios of interest were investigated using beam theory to determine the interaction of shear and flexure stresses present in the short-beam specimen. These interactions are shown as a function of the direct stress in the short beam. Examination of the shear-flexure interaction was made by employing a failure criterion based on distortion energy. Failure was found limited to either shear mode at the center of the beam or flexural mode at the outer fiber. The combination of shear and flexure at intermediate locations is not of sufficient magnitude to cause failure. Since the probability of nonshear failure increases as interlaminar shear strength is improved without accompanying increases in flexural strength a means of choosing proper length-to-depth ratios knowing the approximate flexural-to-shear strength ratio is presented. The possibility of a flexural failure is minimized by incorporating a flexural stress to flexural strength ratio which will not be exceeded at the chosen length-to-depth ratio. The effect of the width-to-depth ratio on the shear stresses in the specimen is developed by a theory of elasticity solution. The formula currently being used to calculate the shear stresses is based on beam theory and assumes that the shear stresses are constant along the width of the specimen. The exact solution for an ortho-tropic beam shows a significant effect of the width-to-depth ratio on the magnitude and distribution of shear stresses in the short beam. The inter-laminar shear stress is highest at the edges of the specimen and lowest at the middle. Calibration curves for graphite-polymer, boron-polymer, and boron-aluminum have been developed to correct the shear stresses as given by the conventional beam theory formula for various values of width-to-depth ratios. Experimental data has been obtained on a graphite-polymer system for fiber orientations of both zero and ±45 deg. Conventional beam theory calculations show the interlaminar shear strength of the ±45-deg cross ply to be reduced significantly over that of the unidirectional specimens. Application of the theory of elasticity correction factors to these data indicate that the actual interlaminar shear strength for both orientations are approximately equal.
Characterization of the Mechanical Properties of a Unidirectional Carbon Fiber Reinforced Epoxy Matrix Composite
Authors: Rothman E. A. , Molter G. E.
Published: January 2012

An exploratory characterization program was conducted on one high-modulus unidirectional composite, carbon fiber reinforced epoxy. Existing test methods were used with minimum modification except in the cases of dynamic moduli and flexural fatigue strength where new methods were developed. The test methods were generally satisfactory. Two notable exceptions were the short-beam shear test for determining interlaminar shear strength and the flat plate test for static shear modulus.
Angle-Plied Boron/Epoxy Test Methods—A Comparison of Beam-Tension and Axial Tension Coupon Testing
Authors: Lantz R. B. , Baldridge K. G.
Published: January 2012

A discussion of necessary considerations for tension test specimen design of laminated angle-plied composite materials is presented. Particular attention is paid to the straight-sided axial coupon and the long-beam flexure test. A large amount of test data, including strain gage measurements, has been compiled to provide a basis of comparisons of tensile strengths and elastic properties of angle-plied boron/epoxy laminates by the two test methods.
Compression Testing of Aluminum-Boron Composites
Authors: Adsit N. R. , Forest J. D.
Published: January 2012

This paper presents methods for obtaining the mechanical behavior of aluminum-boron composites in compression. The property data obtained is compared with tensile data, and then used to predict the failure of simple structural elements. The analytical predictions are then confirmed by structural element tests.
Preliminary Evaluation of Test Standards for Boron Epoxy Laminates
Authors: Lenoe E. M. , Knight M. , Schoene C.
Published: January 2012

This paper describes the first phase of a program of critical evaluation and development of test standards for advanced composite materials. Emphasis is on flat laminates, and the work deals primarily with boron epoxy laminates fabricated using the 3M three-inch wide preimpregnated (prepreg) tape system. The results of approximately 1800 experiments are reported, and specific recommendations concerning specimen geometries and testing techniques are presented. Four types of experiments were investigated, namely, tension, compression, flexure, and shear tests. Tension test variables examined were ply thickness, orientation of reinforcement, gage length and width, type of grip, specimen edge finish, loading rate, specimen alignment, and method of strain measurement. In compression testing, the controlling features investigated were number of plies, specimen width and length, unsupported gage length and end cap, and specimen cross-sectional geometry. The flexural experiments considered the effects of orientation of reinforcement, number of plies, load contact radii, span and type, and spacing of loads. Interlaminar (short-beam) shear tests were considered, and the effects of span-to-depth ratio were determined. Torsion test data for rods of boron epoxy materials are discussed also with regard to the observed shear response of the resin system.
Shear-Modulus Determination of Isotropic and Composite Materials
Authors: Greszczuk L. B.
Published: January 2012

A new test technique that uses split rings to determine the shear modulus of isotropic and composite materials is described. In this test, two concentrated loads that are equal in magnitude but opposite in direction and act normal to the plane of the ring are applied at the point where the ring is split. Pertinent equations which relate the resultant ring deformation to the physical and mechanical properties are given. The out-of-plane deflection is predominantly due to shear deformation, which makes this test an ideal one for shear-modulus determination. Tests are conducted on steel and aluminum rings to demonstrate the accuracy of the new test method. The measured shear moduli are shown to agree within 2 percent of the values reported in the literature. The test then is used to measure the shear moduli of epoxy resin, unidirectional fiber glass composites, bidirectional fiber glass composites, unidirectional boron-epoxy composites, and unidirectional Thornel 40-epoxy composites. The experimental results are compared with theoretically predicted values, and a good agreement is found. Finally, a discussion of existing test method's for shear determination is presented, and the shear moduli obtained by various tests are compared.
Strength Theories of Failure for Anisotropic Materials
Authors: Kaminski B. E. , Lantz R. B.
Published: January 2012

A discussion of several failure criteria from their initial application to homogeneous, orthotropic materials to their extension to “quasi-homogeneous,” anisotropic materials is presented. Also discussed are the assumptions, general limitations, and the physical and analytical significance of the respective “material constants.” The basic criteria include the Lame'-Navier maximum stress theory, Henky-von Mises distortional energy theory, Tresca maximum shear stress theory, and the St. Venant maximum strain stream theory.
Optimization of a Boron Filament Reinforced Composite Matrix
Authors: Juneau P. W. , Shenker L. H. , Saffire V. N.
Published: January 2012

Most polymeric matrix materials currently in use with boron filaments are based on epoxy resins having limited strength retention characteristics at elevated temperatures. In order to provide materials capable of fulfilling the requirements for a matrix having the optimum properties necessary for short time, elevated temperature composite application in the aerospace field, an intensive development program was undertaken. An effective evaluation of resin systems for composite applications was undertaken by choosing a test configuration which imposed major stresses in the weak direction of the matrix and matrix-fiber interface. This testing concept made it necessary to compare materials having low flexural modulus and tensile values. The evaluation configuration chosen for this study was a 9-ply boron-resin laminate, with the filaments oriented in the ±45 deg direction. Evaluation consisted of determining the flexural modulus of a 1-in.-wide by 4.5-in.-long plate over a temperature range up to 600 F, and observing the reduction in modulus as the temperature increased. One plate could tnus be used to test the entire range of temperatures, and could then be reconfigured for a tension test, permitting maximum utilization of materials. In addition, through other laboratory evaluation techniques and fabrication studies, it was possible to evaluate a considerable number of resin formulations and modifications. In general, it was found that toughness is the key property required of the resin matrix, rather than high modulus and high strength alone. Unmodified phenolic resins were found to be brittle and subject to crazing under thermal stress on cooldown from cure temperatures. Epoxies have relatively low heat distortion temperatures and are not necessarily compatible with heat shield materials cured simultaneously. A phenolic resin modified with epoxy and polyvinyl formal was found to have a combination of properties that approaches an optimum for a moderate elevated temperature (500 F) resin matrix for boron filaments.
Defining the Adhesion Characteristics in Advanced Composites
Authors: Hanna G. L. , Steingiser Samuel.
Published: January 2012

The object of this study was to develop testing techniques that would permit a valid measure of the in-plane shear properties of advanced filament reinforced composites. The shear properties of glass and graphite reinforced epoxy materials were measured by short-beam shear and torsion tests. The specimen geometries and testing procedures necessary to make valid measures of shear properties were established for each of the tests and were found applicable to all materials studied. The torsion tube and torsion rod tests are the best available methods to accurately measure shear modulus, G, and shear strength, τu, by a single determination. The short-beam shear test at a span-to-depth ratio of 4 is capable of giving the same shear strength value as the torsion tests on composites only if a shear failure occurs. However, short-beam shear specimens of composites possessing good adhesion often fail in tension, and no correlation can be made between the calculated shear strengths obtained from short-beam shear testing and torsion testing. Torsion specimens then are required to measure shear strength. The theory that the maximum inter-facial shear strength that can be achieved in a composite is equal to the shear strength of the matrix material was examined. Torsion tests were conducted on unreinforced epoxy resin as well as on glass and graphite reinforced composites fabricated to achieve maximum adhesion. In no instance did the composite shear strength exceed that of the matrix resin (that is, about 14 ksi).
Fatigue Testing and Thermal-Mechanical Treatment Effects on Aluminum-Boron Composites
Authors: Shimizu H. , Dolowy J. F.
Published: January 2012

Fatigue strength data are presented in the form of constant lifetime curves over a short ratio range, principally for a tension/tension mode with a low minimum stress and a maximum stress closely approaching the full tensile strength of the material. A brief description of the complex stress distribution within the matrix and its consequences are given, and the effects of thermal/or mechanical treatments or both are discussed in terms of the stress state modifications and the effects on longitudinal tensile strength. Regions of high triaxial stress within the matrix results in a higher than predicted Young's modulus, with a fracture stress which approaches and occasionally exceeds the rule of mixtures at strain levels less than the strain capability of the filaments. Under these circumstances, it was suspected that the strength of the composite was limited by the early fracture initiation in the matrix. Thus, composite material strength should be optimized by decreasing the initial or residual matrix stress level to the point where fracture is initiated simultaneously in the matrix and the filament. Stress modifications and resultant strength improvements were accomplished by selective thermal and mechanical treatments to the composities after fabrication.
Mechanical Testing of Metal Matrix Composites
Authors: Kreider K. G.
Published: January 2012

Testing techniques were developed for the mechanical testing of metal matrix, high-modulus filament composites. The testing of boron-aluminum composites was emphasized using both unidirectional reinforcement and multidirectional reinforcement. Tension, compression, shear, fatigue, and creep testing are discussed. Because of the anisotropy of the material, certain adaptations of standard tension testing techniques were developed in the gripping, specimen design, and extensometry. The tension test at temperatures up to 500 C of materials with room-temperature tensile strengths in the reinforced direction of up to 200,000 psi and shear strengths in nonreinforced directions of 10,000 psi required specimens of modified geometry. These specimens had long grip lengths to prevent delaminating shear failures and only mildly reduced sections to prevent longitudinal shear from the shoulder into the grip. The gripping of the materials required abrasive paper or doublers to eliminate slippage in the grips without making indentations in the brittle boron fiber as occurs with serrated grips. Strain measurement was accomplished with both strain gages and clip on linear variable differential transducer extensometers. Both methods required special considerations due to anisotropy and the brittle nature of the fibers. Similarly, in compression and shear tests particular specimen designs and loading point constraints were found superior. The recommended material information input and reportable information from the tests will be discussed. The input information is more complex than is the case for isotropic materials and includes the properties of the constituent phases of the composite, the geometry of their combination, and the thermal and mechanical history of the part which lead to internal stresses between the constituents. The axial unidirectionally reinforced elastic properties of the composites can be predicted from the rule of mixtures, and the stress strain curve demonstrated three regions; elastic-elastic behavior, elastic-plastic behavior, and fiber breakage similar to that observed by McDanels et al. It was found that the rule of mixtures prediction of strength could be applied better if the statistical nature of the fiber strength and the critical reinforcing length were taken into consideration. An analysis of the state of stress of the composite structures in the tests described is presented together with a discussion of the value and limitations of the tests in determining engineering properties.
Characterizing Strength of Unidirectional Composites
Authors: Ishai O. , Lavengood R. E.
Published: January 2012

This study was made to determine the effect of test variables on the strength of unidirectional composites. Specimens of glass fiber reinforced epoxy of varying geometry were tested in tension and flexure at several strain rates. Both experimental and theoretical results show that specimen geometry strongly influences strength measurements for off-axis specimens having a small length-to-width ratio. This is a result of nonsymmetrical anisotropy in the specimens which causes twisting in flexure tests and shear coupling in tension tests. For slender specimens, having a free length-to-width ratio greater than six, both strength and stiffness measurements are almost unaffected by the boundary conditions of the test. A normalization procedure was used successfully to relate the strength of an off-axis composite to its transverse strength. While changes in loading mode, strain rate, and specimen geometry may produce significant changes in absolute strength values, normalized strengths proved to be essentially invariant.
Practical Influence of Fibrous Reinforced Composites in Aircraft Structural Design
Authors: Schjelderup H. C. , Jones B. H.
Published: January 2012

Practical design problems which have become evident as a result of current DOD-industry composite development programs are discussed. Design problems related to residual stresses beween matrix and filaments are reviewed, and the significance of thermal effects on the interface between filament and matrix is out-lined. Local failure and strength properties, as influenced by filament diameter, and the ever-present problem of interlaminar shear are studied. The concept of balanced and minimum gage laminates is considered together with its interaction with design. The influence of design criteria, allowables, and joints on composite structures design is discussed. Detail design problems related to thermoelasticity and fatigue highlight some of the potential design problems which are unique to composites. As experience in the design of composite structures is gained, many requirements for the future evolve. The requirements are basically a need for uniformity of practice in order for composites to become cost competitive with conventional materials. Suggestions and recommendations for future standards in composite design are presented.
Determination of Design Allowables for Composite Materials
Authors: Jones B. H.
Published: January 2012

The problems of establishing design allowables and factors of safety for filamentary composites are considered. A method is recommended for determining design data when small sample sizes are employed to establish basic laminate properties. It is advocated that the traditional factor of safety of 1.5 should not be employed without some reference to the coefficient of variation of the strength data. The concept of reliability is introduced. Methods for predicting design allowables under multiaxial stress are discussed in general terms. The influence of lamina failure is considered together with means for predicting this. Results presented indicate that a linear analysis, based on the distortional energy criterion, can predict progressive lamina failure adequately for design purposes. A description of the phenomenon of crazing is included, and it is suggested that this is generally due to initial lamina failures. The paper concludes with some comments on the effects of testing and processing variables.
Characterization of Graphite Fiber/Resin Matrix Composites
Authors: Elkin R. A. , Fust G. , Hanley D. P.
Published: January 2012

The strength properties of a unidirectional lamina are essential inputs to the design of efficient composite airframe structural elements. To achieve the reliability required for such structures, these properties must be determined experimentally. A program was undertaken to characterize the static tensile, compressive, and in-plane shear strengths of Thornel-50, Morganite Type II, and HMG-50 unidirectional graphite fiber/resin matrix laminates. Test results show that the Morganite fiber composites have significantly higher compressive, shear, and transverse tensile strengths than Thornel or HMG fiber composites. However, for longitudinal tension, the Thornel laminates have a slight strength advantage over the other two materials. Calculated strength envelopes for a typical airframe component laminate are presented as a convenient means of material comparison. Correlations of laminate strengths with fiber content are shown, and optimum fiber contents for Thornel-50 laminates are estimated. Test methods used are reported, and differences in observed failure modes with the various materials are discussed. Test panel fabrication procedures, materials acceptance, and nondestructive inspection techniques are reviewed also. Composite strengths plotted as a function of qualitative ultrasonic inspection ratings show a promising correlation.
Failure Criteria for Filamentary Composites
Authors: Chamis C. C.
Published: January 2012

A two-level, linear, semiempirical theory for a failure criterion is described. The theory predicts the strength behavior of unidirectional filamentary composites under uniaxial and combined stress from basic constituent material properties and fabrication process considerations. Application of the theory to several filament-nonmetallic matrix composites are presented, and comparisons are made with experimental data. These results show good agreement between theory and experiment. Simple and combined strength envelopes are generated to illustrate the versatility of the theory and to point up problem areas in experimental work and design.
Shear Stability of Laminated Anisotropic Plates
Authors: Ashton J. E. , Love T. S.
Published: January 2012

An analytical and experimental study of the shear stability of laminated anisotropic plates is presented. The plates considered are rectangular, have clamped edges, and are fabricated with laminated construction of boron-epoxy composite material. Such plates, when the laminates are midplane symmetric, are anisotropic in nature. The analytical solutions are obtained by means of the principle of stationary potential energy, using the Ritz method. The deflected shape is approximated with beam characteristic functions. Experimental results are presented for 14 boron-epoxy plates and for 2 aluminum plates, and the results compared with the theory. Good agreement is shown.
Behavior of Fiber-Reinforced Plastic Laminates under Biaxial Loading
Authors: Bert C. W. , Mayberry B. L. , Ray J. D.
Published: January 2012

This paper reports on 54 biaxial-loading tests on fiber glass-epoxy laminates of three lamination schemes: parallel ply, cross ply, and quasi-isotropic. The tests were conducted on a specially designed fixture using a cable-pulley system in conjunction with a universal testing machine. The loadings were biaxial tension with 1:1 and 1:2 principal-load ratios. The contours of the reduced-thickness test sections of the flat specimens were designed to achieve a uniform-stress field.
Methods of Joining Advanced Fibrous Composites
Authors: Dallas R. N.
Published: January 2012

Advanced fibrous composites have a high potential for aircraft structural applications; joint design limits this potential. How to transfer loads efficiently from composite components to supporting structures is a difficult problem. The approach taken in this study is to measure the strengths of adhesive bonded joints, riveted joints, and joints containing both rivets and bonds. The data generated have contributed to defining design allowables and have given a basis for the design of composite parts. A significant variable has been found to be fiber orientation of the adherend. Three orientations of boron epoxy laminates have been bonded to titanium alloy Ti 6Al-4V: unidirectional, isotropic, and modified isotropic. By careful joint design it has been found possible to transfer over 90 percent of the tensile load carrying capability of the laminate through the joint. Both ductile and semirigid adhesives have been tested, with the former giving higher shear stresses at ½ in. overlap distances. Shear stresses of 7000 psi have been measured, which equal metal-to-metal bonds with the same adhesive system. However, when the overlap is increased to 1½ in. the semirigid type will carry approximately 20 percent more load than the ductile type. Adding rivets to bonded joints was found to have no effect on the static strength properties of composite-to-metal joints. This result is unexpected and may be because of nonoptimum design. It is anticipated that fatigue strengths would be improved by the combination joints. Composite components have been designed, built, and tested. The joints did not fail when loaded up to over 4000 psi in shear.
Diffusion Bonded Scarf Joints in a Metal Matrix Composite
Authors: Olster E. F. , Jones R. C.
Published: January 2012

Joints, approaching 100 percent efficiency, have been obtained in a 2024 aluminum alloy reinforced with type 355 stainless steel wires using a deformation diffusion bonding technique. A scarf joint, whose geometry is dependent upon the critical fiber length and the distance between layers of fibers, was developed for this study. The effect of an aluminum oxide coating on the joining surfaces was investigated, and it was concluded that within the range of bonding parameters used in this study sound joints could be obtained only if the oxide coating was removed immediately before joining. A wide range of joining parameters provided sound joints; however, the ultimate tensile strength of the joined specimen decreased as bonding times increased. The high-strength scarf joint specimens failed with massive debonding along the diffusion bond planes resulting from the composite fabrication technique. These fracture surfaces examined with a scanning electron microscope and appeared nearly identical to fracture surfaces in unjoined, untreated material. The lower-strength scarf joint specimens fractured with little or no debonding along these original bond planes, and when subjected to flexure tests could undergo massive deformation with no indication of macroscopic failure.
Composite Materials for High-Temperature Magnetic Applications
Authors: Pavlovic D. M. , Towner R. J.
Published: January 2012

Different types of composite materials containing dispersoids, fibers, or aligned-eutectic structure in a matrix of either cobalt or iron or their alloys were investigated for potential use as solid-rotor core materials operating at 1200 to 1600 F under stress. Composite-strengthening methods deteriorated the soft-magnetic quality of the matrix material. Magnetic saturation induction (Bs) decreased in direct proportion to the volume fraction of nonmagnetic phase present. In regard to structure-sensitive magnetic properties, such as coercive force (Hc) and d-c magnetization curve, the effects of matrix composition, amount and distribution of secondary phase, internal stress, demagnetization effects, and temperature were studied experimentally and interpreted by reference to theory. The overall consideration of both magnetic and mechanical performance, as well as ease of processing and thermal stability, favored dispersion-strengthened iron + 27 weight percent cobalt-base material for further development.
Cryogenic Boron-Filament-Wound Pressure Vessels
Authors: Morris E. E. , Alfring R. J.
Published: January 2012

Filament tensile strengths and pressure-strain characteristics for a high-modulus, boron-filament-wound/resin composite, pressure vessel were obtained. Five 8-in.-diameter by 13-in.-long boron-filament-wound, metallined pressure vessels were fabricated and burst tested (three at 75 F and two at −320 F) with the following results : 1. The average ultimate boron-filament strength at room temperature was 236,600 psi. The values obtained were highly consistent, varying only 1.9 percent from the average. 2. At −320 F, the boron-filament strength increased about 16 percent to 273,800 psi. 3. Naval Ordnance Laboratory (NOL) rings fabricated from the same boron-filament tape used in the test vessels had an average ultimate filament strength of 309,000 psi at room temperature. The vessels achieved 77 percent of this value. 4. Good correspondence was obtained between the expected and the measured pressure strain characteristics at 75 and −320 F. At the vessel burst points, the strains were about 0.30 to 0.40 percent, roughly one tenth of the strain encountered in glass-filament-wound vessels. 5. The resin content in the boron filament-wound composite ranged from 37 to 47 volume percent. The vessels displayed very low biaxial strains and high strength-to-weight ratios. Such low strains permit strong metal liners (for example, titanium) to work elastically up to the ultimate stress of boron filament. The present strength and potential strength of boron are high enough to ensure that boron-filament-wound, metal-lined vessels will be lighter than competing homogeneous metal tanks for cryogenic service.
Structural Synthesis of Composite Materials for Ablative Nozzle Extensions
Authors: Au N. N. , Scheyhing E. R. , Summers G. D.
Published: January 2012

Complexities associated with the application of composite materials for the thermal protection of aerospace structures are discussed in the light of a detailed investigation of the Titan III Stage II ablative nozzle extension. This paper describes the methods used in a structural evaluation of the nozzle extension that led to an understanding of several structural failures. Results of an experimental investigation of the composite material properties and analyses of the nozzle extension's response to mechanical and thermal loads are presented. Particular attention is focused on the challenges encountered in testing to obtain the properties of the liner and shell materials over their operating temperature ranges. The importance of individual material properties and fabrication variables is explored. The effect of moisture content on thermal expansion and stress levels is shown to be of primary importance. Also, the ability to vary stress levels by changing the tape wrap angle is demonstrated. The experience gained from this investigation is translated into a structural synthesis approach tailored to the specific requirements of current aerospace programs. The importance of integrating the various interacting technical disciplines in terms of the design configuration, environmental conditions, material thermal and mechanical properties, thermal and structural analyses, fabrication techniques, and process controls is discussed. Finally, conclusions drawn from the nozzle extension study are extended to other applications of composite materials.
Crack Phenomena in Cross-Linked Glassy Polymers
Authors: McGarry F. J. , Sultan J. N.
Published: January 2012

Previous work established that tensile stress cycling of fibrous glass reinforced resin composites degrades their macroscopic mechanical properties by inducing microcracks in the cross-linked glassy polymer matrix. While the greatest damage occurs in the first stress cycle, it continues to accumulate during subsequent loadings, and composite modulus reductions of 20 to 25 percent after 100 to 200 cycles are common. Detailed studies of unrein-forced matrices indicate that much of the work required to drive a crack is consumed by molecular cold drawing and partial orientation in the glassy material at the crack tip. Further, this work can be increased substantially by suspending small particles of certain elastomers throughout the cross-linked matrix material; increases in the fracture surface work term of an order of magnitude, or more, are possible. When such toughened epoxies or polyesters are reinforced with fibrous glass and then stress cycled, the internal microcracking previously observed in the composite material is eliminated. The degree of toughening conferred by the elastomer particles is related to their average size, the distribution of sizes, their composition, the composition of the matrix, the volume fraction of elastomer present, and the adhesion between particles and matrix. Recent work has revealed that other, additional factors are important. These latter include the initial molecular weight of the elastomer, the nature of elastomeric copolymers which can be used, the conditions of plane stress or plane strain under which toughness measurements are made, the detailed nature of the catalyst used to harden the glassy matrix, and the morphological features of the particles. All of these factors will be described and their significance discussed.
Fractography of Aluminum-Boron Composites
Authors: Jones R. C.
Published: January 2012

The basic objective of this study has been to relate the observed behavior of metal matrix eomposites to the micromechanical behavior of each component, as surveyed at the fracture surface. The principal method of investigation has been scanning electron microscopy. Scanning electron microscope examination of fracture surfaces of metal matrix composites has been found to be an extremely useful tool in interpreting micromechanical behavior. Application of the scanning microscope to the boron filament-aluminum alloy composite system has allowed detailed examination of the components and their interaction in situ. The boron filaments are observed to undergo substantial breakup in the compositing and loading sequence. Incomplete bonding at diffusion bond planes in the matrix metal is found to be a major problem in cross-ply aluminum-boron composites. Debonding of diffusion bond planes, observed at fracture surfaces, has been observed on a large scale in both cross-ply and unidirectionally reinforced composites. It is not yet clear whether such debonding cracks are a contributory cause or an effect of the final fracture process. Potential fracture initiation sites are discussed, and the effect of a triaxial stress state on failure of the matrix material between fibers is presented graphically. Observations made of fracture surfaces containing large amounts of incomplete bonding or debonding at diffusion bond planes lead to the conclusion that further optimization of fabrication parameters is needed to improve current state-of-the-art aluminum-boron materials.
Tensile Strength of Fiber-Reinforced Composites: Basic Concepts and Recent Developments
Authors: Zweben Carl
Published: January 2012

This paper presents a selective analysis of the subject of composite tensile strength, emphasizing basic principles including recent advances by the author. The importance of the statistical scatter in fiber strength and local fiber over-stress caused by fiber discontinuities are discussed. Recently developed failure criteria that give good correlation with experimental data are covered. The analysis of whisker-reinforced composites, in addition to giving good strength predictions, explains why predictions of previous theories are much higher than experimental values. The applicability of the “rule of mixtures” to composite strength is discussed, and the problem of notch sensitivity is mentioned briefly.
Fracture in Graphite Filament Reinforced Epoxy Loaded in Shear
Authors: Novak R. C.
Published: January 2012

The failure mode in graphite filament reinforced epoxy composites loaded in shear is dependent on the strength of the interfacial bond. Failure of composites made from untreated filaments occurs progressively by interfacial debonding and crack propagation through the resin. Shear strength of these composites is low and is inversely proportional to the filament volume fraction. Failure of composites made from treated filaments may occur at the interface, in the matrix, or in the filaments, and may be in shear or tension or a combination of both. Shear strength of these composites is high, but the factors leading to high shear strength also lead to brittle fracture of the material. Thus, the consequences of increasing shear strength on other properties such as impact strength must be studied carefully in light of the intended application.