bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Levels of Intervention in Low-Income Women With Depressive Symptoms: Compliance and Programme Assessment
Authors: Lara M. A. , Navarro C. , Rubí N. A. , Mondragón L.
Published: April 2003

Aims: This study reports on the evaluation of a brief group intervention for women of limited means with depressive symptoms.

Method: A comparison design was used with pre-, post-and four-month follow-up assessments for 93 women in the group intervention condition who were given six two-hour sessions of psycho-educational intervention, and 42 women in a minimum individual condition who received a 20-minute explanation in addition to the educational material, which yielded the following results.

Results: Both conditions were effective in motivating participants to engage in self-help activities (making time for themselves every week, using writing as a means of sorting out problems, talking to someone about their problems and carrying out the reflection and cognitive behavioural exercises) and to seek further professional help when necessary. The intervention condition was more positively evaluated since participants regarded it as having a greater influence on their life and problems. Influence was related to better understanding and coping with problems, mood improvement, changes in the way they thought about things, knowing themselves better and being more accepting of themselves.

Conclusions: The results suggest that both interventions tackle important issues related to depression in women but further data are needed for a better understanding of this relationship.
Attitudes of Hospital Staff Toward Mentally Ill Patients in a Teaching Hospital, Turkey
Authors: Aydin Nazan , Yigit Arzu , Inandi Tacettin , Kirpinar Ismet
Published: April 2003

The aim of this study was to examine the attitudes of hospital staff toward major mental diseases: schizophrenia and depression. Negative attitudes were common among all of the hospital staff, and were more common among academicians, resident physicians and nurses. Causes of attitude variations were discussed.

Background: Attitudes of hospital staff are important for admission, early diagnosis and treatment, and the rehabilitation process of mentally ill patients.

Aims: The main objective of this study was to investigate and compare hospital workers' attitudes toward and knowledge of schizophrenia and depression.

Methods: In 2001, a total of 160 hospital staff (40 academicians, 40 resident physicians, 40 nurses and 40 hospital employees) in a teaching hospital were interviewed with a questionnaire. The questionnaire included items about background information, a one-paragraph vignette, questions on social distance and expected burden, recognition of mental illness, hospitalization, prognostic outcome, and to whom and where the patient should be admitted.

Results: Although academicians, resident physicians, and nurses have sufficient knowledge about schizophrenia and depression, the frequency of their negative attitudes towards mentally ill subjects was more than that for uneducated hospital employees.

Conclusions: It was commented that this difference might be as a result of negative effects of the medical education system.
Fruitful Partnerships in a Rural African American Community
Authors: Boddie Stephanie C.
Published: April 2003

Rural African American congregations often have been pitted against their urban counterparts, with the urban churches viewed as superior social agents with a wider range of community services. An examination of social service provision in rural areas is necessary because both policy and programmatic responsibilities increasingly are delegated to state and local governance and ultimately to local communities. Legislation referred to as Charitable Choice encourages the government to contract with faith-based and community-based social service providers. This legislation also increases the importance of understanding the role that rural congregations play as the social service system favors private delivery of such services over public avenues. In this study, an in-depth examination of 17 congregations in an historically all-Black town revealed the distinct patterns of African American congregations providing a unified network of collaborative social services with secular organizations on behalf of their communities.
The Glass Ceiling is the Floor My Boss Walks on
Authors: Zane Nancie C.
Published: April 2003

This article analyzes layers of meaning that are embedded in the concept of diversity in a financial institution. It examines the discourses about diversity that emerged over 21/2 years, during which a CEO was intentionally trying to change his organization’s cultural norms and to become more sensitive to “valuing people. ” By tracking the conversational patterns between the CEO and the organizational “discourse communities, ” this research highlights the processes by which meaning gets ascribed to the concept of organizational diversity and its impact on organizational structures and culture across time.
Executive Coaching
Authors: Orenstein Ruth L.
Published: April 2003

This article challenges the prevailing understanding of executive coaching as an exclusively individual intervention. It discusses executive coaching as a complex and demanding process that encompasses multidimensional interrelationships among the individual, the organization, and the consultant. It presents four premises that guide the process, including the role of the unconscious in individual and group behavior, the interaction between the individual and the organization, multilevel organizational forces, and the consultant’s use of self as tool. It describes and analyzes three illustrative excerpts from actual executive coaching cases conducted by the author in the manner proposed by the article.
Finding the Thou in the I
Authors: Sullivan Chatham Clarke
Published: April 2003

Countertransference and parallel processes have become a newly appreciated facet of organizational research and consultation. These phenomena arise as the consultant and client relate and tend to complement or reflect dynamics that exist within the organization under study. In this article, the author provides an examination of countertransference and parallel processes, a historical review of their theoretical and methodological evolution, and an application to three cases according to an embedded intergroup relations perspective.
Battling The Serpent
Authors: Akinyela Makungu M.
Published: April 2003

This article posits that the spread of Christianity among enslaved Africans hastened the development of a common ethnic identity among ethnically diverse peoples who were the first generations of enslaved Africans on American shores. The article focuses on this notion of Black religion as a primary source of the logic of Black resistant/resilience and as the spiritual source for the development of a collective Black consciousness. It is further argued that resistant/resilience organically developed in the process of the construction of an authentically African theology as exemplified in the document that has come to be known as "Nat Turner's confession." The author assumes that the African-Christian hybrid cosmology seen in the confession is an example of the worldview of enslaved Africans generally in the 19th century. This Africanized Christianity forms the basis for the common ethnic identity, with its motivating cultural value (self-determination) and central organizing theme (resistant/resilience) seen in the ethos of Africans in America today.
Race-Specific College Student Experiences On A Predominantly White Campus
Authors: Cureton Steven R.
Published: April 2003

The purpose of this study was to assess the extent to which African American students enrolled at a predominantly White educational institution may or may not be experiencing unique, racially exclusive social situational circumstances that could potentially affect academic performance. The findings indicate that general attitudes concerning the college experience, adverse situations or circumstances unrelated to the university, perceptions of self, perceptions of the campus's social climate, and perceptions of the campus police are not racially exclusive, as both Black and White students expressed similar attitudes about the university setting and had experienced similar personal and social issues related and nonrelated to college.
Careers In The British Armed Forces
Authors: Hussain Asifa
Published: April 2003

In the past 4 years, the Ministry of Defence has embarked on a concerted effort to encourage ethnic minorities living in the United Kingdom to consider a career in the British Armed Forces. In view of the diverse nature of Britain's minorities, there has been an emphasis on targeting specific groups rather than treating ethnic minorities as one distinct group. Among those targeted have included Blacks of African and Caribbean origin. This article identifies the perceptions that the main Black groups in Britain have of the British Armed Forces. More significantly, the article aims to extract opinions on areas such as the extent to which respondents would consider a military career, factors that influenced the propensity to join, the extent of a family history of military service, and the degree of awareness among respondents of Ministry of Defence initiatives aimed at attracting minorities.
African American Women And Their Quest For Congress
Authors: Clayton Dewey M.
Published: April 2003

As many barriers to Black electoral success were removed during the latter half of the 20th century, Black representation in Congress increased dramatically from 2 in 1949 to 38 in 2000. Many of these Black congresspersons (particularly from southern states) were first elected from majority Black districts but were subsequently reelected from majority White districts. However, the percentage of Blacks in Congress remains low. Black females face a double disadvantage when running for Congress because of race and gender biases. The 2000 congressional election in the third district of Louisville, Kentucky, provides an excellent case study to examine what obstacles Black females running for Congress outside the South encounter in forming multiracial coalitions to win election. This race pitted Eleanor Jordan, a Black female challenger, against Anne Northup, a White female incumbent.
Up From The Grave
Authors: Foster Gary S. , Eckert Craig M.
Published: April 2003

Sociohistorical reconstructions of African American communities in the Midwest are often dependent on diaries and letters that provide a wealth of detail but may not represent the collective pattern. Cemetery and burial records data are used to reconstruct a sociodemographic profile of a small 19th- and 20th-century African American community in the rural Midwest. Surnames of African Americans (and their ancestors) were disproportionately British, suggesting association with or ownership by those of British heritage. Although the mean age of the Black community was significantly younger than that of the White community, childhood mortality was no greater. Rather, Blacks generally did not live as long as Whites in adulthood. However, racial crossover was present. The Black community was disproportionately male, suggesting a frontier phenomenon and instability, and disproportionately experienced violent mortality. Seasonal death patterns among Blacks typified a younger population. Finally, familial measures suggest the Black community was tentative and tenuous.
Social Justice Versus Social Equality
Authors: Grant Otis B.
Published: April 2003

During the 1920s, the Garvey movement challenged Black intellectualism, which at the time was in the midst of a renaissance. Influenced by the philosophy of Booker T. Washington and considered irreparably idealistic, Garveyism, nevertheless, remains the largest sociopolitical race movement in history. Throughout his legal quandaries, Garvey accurately articulated that the American legal system was highly bureaucratized and that the efficient processing of legal matters was the system's paramount concern. Garvey's ideology eerily resembles the law and economics paradigm of contemporary American justice, and his embrace of social justice over social equality is now realized in the rational choice framework of the American legal system. Consequently, Garvey remains relevant because he correctly surmised that capitalism is the cornerstone of righteousness and thus social justice should be evaluated by a capitalistic yardstick rather than by a social justice paradigm.
Glycolysis of Rigid Polyurethane Foam under Various Reaction Conditions
Authors: Murai M. , Sanou M. , Fujimoto T. , Baba F.
Published: April 2003

The dissolution time of rigid polyurethane foam (PUF) under various glycolysis conditions was examined in a detailed investigation of the glycolysis reactivity of PUF. PUF dissolution depended on the molecular weight of glycol. Dipropylene glycol and tetraethylene glycol dissolved PUF in the shortest time among polypropylene glycols and polyethylene glycols, respectively. PUF dissolution time was reduced to one-half for each 10 C rise in the range of 170–200 C. Also PUF dissolution time was inverselyproportional to KOH (catalyst) concentration. Dibutyltindilaurate concentration had less influence on PUF dissolution time than KOH concentration. Smaller PUF particles dissolved in a shorter time. Especially, the initial glycolysis conversion of PUF was proportional to the total surface area of PUF particles.
Effect of Viscosity on Low Density Foaming of Poly(Ethylene-Co-Octene) Resins
Authors: Gendron Richard , Vachon Caroline
Published: April 2003

Foaming of low density poly(ethylene-co-octene) resins by injection molding is the result of various reactions occurring during the process. This includes simultaneous decomposition of the chemical blowing agent and cross-linking of the polymer matrix during curing in the mold, followed by foaming after mold opening. Dynamicrheology as well as elongational viscosity were investigated for compounds prepared from resins with different melt indices and various cross-linking agent levels, and these results were linked to the morphology and density of the corresponding foams. Rheological requirements were finally defined quantitatively for this set of conditions.
Moisture Sorption Effects on and Properties of a Carbon Fiber-reinforced Phenylethynyl-terminated Poly(etherimide)
Authors: Bullions Todd A. , Loos A. C. , McGrath J. E.
Published: April 2003

This paper reports the results of anin vestigationof moisture sorption effects on the properties of a carbon fiber-reinforced high-performance phenylethynyl-terminated poly(etherimide). Due to the relative newness of this material, minimal information regarding its performance under the duress of environmental effects is known. Composite and neat resin specimens were cycled to effective moisture equilibrium during exposure to a 85% relative humidity/90 C environment followed by exposure to a 10% relative humidity/90 C environment. The composite through-the-thickness moisture diffusion coefficients (Dz) ranged from 2.3 × 10 -6 to 6 mm2/s. The value of Dz for moisture absorptionwas measured to be about 67% greater thanthe value of Dz for moisture desorption; residual stress-accelerated diffusion, void-assisted diffusion, and diffusion hindered by moisture–matrix interactions are discussed as possible explanations for this difference. At 85% relative humidity, the effective moisture equilibrium content of the composite and neat resin were 0.52 ± 0.02% and 1.60 ± 0.01%, respectively. The average transverse moisture expansion coefficient of the composite was 1.1 × 10 -3±0.7 × 10-3. The 1.2% retention (85% 7.0% retention (10% relative humidity) of the control 9.5 MPa. No conclusive results were obtained from open-hole compression strength and apparent interlaminar shear strength tests. The majority of the surfaces of the TFS specimens displayed moisture sorption induced damage. The dramatic impact that inadequate matrix cure can have on a composite’s ability to transverse flexural strength (TFS) specimens exhibited 60.7 ± relative humidity) and 83.6 ± value of 135.9 ± endure a single moisture sorption cycle is illustrated by comparison with a previous moisture exposure study of this material.
Impact Damage of Partially Foam-filled Co-injected Honeycomb Core Sandwich Composites
Authors: Vaidya U. K. , Ulven C. , Pillay S. , Ricks H.
Published: April 2003

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 weight is partial filling of the cells, without losing the advantage of VARTM processing of the core. Two cores are considered, a polyurethane foam for full filling of honeycomb cells, and syntactic foam for partial filling, in conjunction with carbon–epoxy facesheets. Their impact response was investigated under low and high velocity impact (LVI and HVI respectively). For both cores, the foam filling was found to provide confinement to the cells. The resistance to penetration, energy absorbed and damage modes in LVI and HVI were a function of core stiffness, extent of filling and number of facesheet plies. The results illustrate that partial syntactic foam filled sandwich plate (with reduced weight penalty in comparison to full filling) can provide LVI response improvement in the order of 56% increase in peak load, and for HVI about 74% improvement in ballistic limit.
Failure Modes and Optimization of Sandwich Structures for Load Resistance
Authors: Swanson Stephen R. , Kim Jongman
Published: April 2003

Sandwich construction using foam cores is used in applications, and an understanding offailure loads is an important part ofthe design process. Tests on sandwich beam specimens with embedded strain gages show that the simpler analysis procedures can be in error by large factors, while an elasticity solution from the literature gives good agreement with the experiments. Comparisons with laboratory tests on sandwich bend specimens with carbon–epoxy faces and polyurethane foam cores ofseveral densities show that the elasticity solution, in conjunction with criteria for failure of the faces and yield of the core give good agreement with the data, and show that the mode of failure and the load at failure could be predicted. Optimization ofsandwich structures for strength/weight is considered, and it is shown that the laboratory strength data support the theoretical optimization results.
Effects of Moisture and Temperature on High Strain Rate Behavior of S2-Glass–Vinyl Ester Woven Composites
Authors: Haque A. , Hossain M. K.
Published: April 2003

The effects of moisture and temperature on high strain rate responses of S2-glass–vinyl ester woven composites have been studied in this work. Compressive properties and micro-structural damage progression under high strain rate loading have been investigated using the Split Hopkinson Pressure Bar technique. The compressive stress pulse is applied through the thickness direction (TD) as well as through the filler direction. The stress strain responses at strain rates ranging 490–1470s−1 under various environmental conditions have been investigated and the relevant failure modes have also been identified by optical and scanning electron microscopic examinations.

The results indicate that moisture and temperature degrade the compressive failure strength under high strain rate loading. The level of such degradation is seen to vary with strain rates and loading direction. In general, the failure strength and failure strain of both dry and wet samples are seen to be increased under high strain rate loading. The strain rate sensitivity of the woven composites is more significant if the failure is dominated by the resin materials. High temperature tests were conducted at temperatures ranging 23–204°C. The maximum rate effect is observed below the glass transition temperature, Tg (121°C) specifically for TD specimens. Microbuckling of the fiber, kinking and fiber splitting are the major failure modes for the specimens loaded in filler direction. The specimens loaded in the thickness direction mostly failed under matrix cracking.
Burst Tests of Filament-wound Graphite-epoxy Tubes
Authors: Chang D. J.
Published: April 2003

A test program was conducted to investigate the failure modes of undamaged and damaged graphite-epoxy cylindrical tubes subjected to internal pressure. Some tubes were intentionally damaged by either a longitudinal-line cut or a single-point impact. Both types of damage were intended to simulate fiber breakage caused by a local damage. The objectives of the program were to investigate the failure modes of graphite-epoxy cylindrical tubes subjected to internal pressure, with and without local damage, and to qualitatively determine the relative burst pressure degradation associated with preexisting local damage to the tubes. A high-speed motion analyzer was used to record images of the fractures. The images provide the failure mode information that was not available in existing literature. Testing was conducted under three conditions: hydraulic pressurization, pneumatic pressurization with solid inserts, and pneumatic pressurization with inert propellant inserts. A tube with a longitudinal cut can fail by three different modes: a local leakage mode, a bursting mode with fracture initiating from the cut, or a bursting mode with complete tube disintegration. In testing of impact-damaged tubes, the results show that the burst pressure decreases with increasing impact load. At an impact load of 1493N (335 lb), the burst pressure decreases by 33% compared to the undamaged condition.
Triaxial Woven Fabric (TWF) Composites with Open Holes (Part I): Finite Element Models for Analysis
Authors: Zhao Qi , Hoa S. V.
Published: April 2003

Two finite element models (Superelement 1 and Superelement 2)are developed for prediction of mechanical behavior of triaxial woven fabric (TWF) composites with open holes. Superelement 1 is a 15-node superelement constructed of six identical 8-node 3-D isoparametric elements and three identical 4-node 2-D isoparametric laminate elements. Superelement 2 is similar to the first element except that this element takes into account the geometric and material properties of the twisted yarns. The assembly is done by the pseudo element technique suggested herein and the static condensation procedure. The availability of these elements allows for the analysis of complex structures of the triaxial fabric with open holes. Superelement 1 can be used for the vibration analysis with some economy of computer space and time. Superelement 2 can be used for detailed stress analysis and for strength prediction. Although these two elements are developed for the TWF composites with open holes, they can be applicable for analytical models for other materials and structures made of other types of textile composites.
Determination of Residual Stress in Composite Laminates Using the Incremental Hole-drilling Method
Authors: Sicot O. , Gong X. L. , Cherouat A. , Lu J.
Published: April 2003

The cooling conditions used in the forming process of composite materials play an important role in the creation ofresidual stress. In this study, a new method for measuring residual stress in composite laminates is presented. Three cooling conditions were used to produce different residual stress levels. Residual stresses in [02/902]s and [08] laminate have been measured by the incremental holedrilling method combined with 3-D finite element modelling. A software which quickly calculates all the coefficients for each increment was developed. The automatic procedure can be used to calculate the calibration coefficient for any type oflaminate (ply number, mechanic characteristics,...) and whatever the number of increments and their depths. The different results show that this method provides access to the in-depth distribution and through thickness ofresidual stress in the laminate with a good accuracy and practicality.
Viscoelastic Analysis of Composite Cylinders Subjected to Rotation
Authors: Tzeng Jerome T.
Published: April 2003

A viscoelastic analysis has been developed to investigate stress relaxation and creep in a multi-layered composite cylinder subjected to rotation. The analysis accounts for ply-by-ply variation of material properties, fiber orientations, and density gradients through the thickness of cylinders. A closed form solution based on the corresponding elastic problem is derived for a generalized plane strain state in a thick-walled multi-layered cylinder. Laplace transform is then applied to obtain the numerical solution of the viscoelastic problem. The paper illustrates the derivation of the analytical model and solution procedure. A numerical simulation shows substantial creep and stress relaxation in thick-walled cylinders at an elevated temperature. Viscoelastic effects of composite can result in a drastic change of stress and strain profiles in a cylinder over a period of time, which is critical in terms of structural durability for application suchas energy storage flywheels.
Modeling Analysis of Tensile Tests of Bundled Filaments with a Bimodal Weibull Survival Function
Authors: Creasy T. S.
Published: April 2003

A convolution model applied to single mode Weibull fiber bundle experiments was extended to predict the response of bimodalmodel bundles. Published data for bimodal SiC fibers predicted the sensitivity of bundle test as a function of gauge length. A bundle test could rapidly determine the modality of a bundle from experiments at two gauge lengths. Next, the method checked the applied strain rate bimodality of Kevlar. The analysis indicates that a bundle test cannot determine the parameters of a modelthat predicts variation in apparent modulus or strain to failure since slack in the bundle generates these effects.
Torsion of Thin Orthotropic Open Sections
Authors: Camomile Alan , Swanson Stephen R.
Published: April 2003

Torsion of thin rectangular laminated rods is considered. Although thin open sections are inefficient in torsion, a predictive capability for stiffness and strength is often required in design. An existing theory for torsion of laminated cross-sections is reviewed, and the effects of warping restraint are developed for thin sections. Experiments are reported for torsion of IM6/3501-6 carbon/epoxy laminated specimens with both thin rectangular and angle shapes. The experiments correlate well with the theory for stiffness and strain, and demonstrate the effects of lamination sequence and the equivalence of the rectangular and angle shapes. Pronounced nonlinear response is seen for certain layups. Failure is generally in accord with predictions based on interlaminar shear stress.
Interlaminar Stresses Due to In-Plane Gradient Stress Fields
Authors: Saeger Kevin J. , Lagace Paul A. , Shim Dong Jin
Published: April 2003

Interlaminar stresses that arise in composite laminates where gradients exist in in-plane stress fields are investigated. Two distinct mechanisms give rise to interlaminar stresses in generic problems, the presence of free edges and in-plane gradients. It is shown that the latter mechanism should be considered separately from the former and that interlaminar stresses from such in-plane gradients can be significant. A methodology to approximate these stresses through direct integration of the equilibrium equations is presented. The methodology involves the use of closed-form expressions of the in-plane stress field obtained by solving two-dimensional elasticity problems using homogenized material properties. As an example, the methodology is applied to the case of a laminate with a circular hole through which the importance of interlaminar stresses from in-plane gradients is demonstrated. The results show that the characteristics of the interlaminar stresses from in-plane gradients are very different from those of interlaminar stresses arising from free edges. Specifically, the parameters that affect the decay rates and magnitudes of the interlaminar stresses from the two mechanisms are found to be different. The current investigation provides new insights into interlaminar stress problems, in general, and offers a simple method for calculating the interlaminar stresses due to in-plane gradients.
Thermal Response and Ablation Characteristics of Carbon Fiber Reinforced Composite with Novel Silicon Containing Polymer MSP
Authors: Ogasawara Toshio , Ishikawa Takashi , Yamada Tetsuya , Yokota Rikio , Itoh Masayoshi , Nogi Shigeru
Published: April 2003

Polymer composites are widely used for high temperature thermal protection (TPS)materials for spacecraft heat shields, and nozzle liners for solid propellant rocket motors. Newly developed silicon containing polymer, abbreviated MSP (Mitsui Silicon Containing Polymer), possesses high decomposition temperature (500 C), and high char yield (>94% at 1000 C)after pyrolysis. Therefore, the MSP polymer has potential as matrix resin of high performance ablative composites compared with conventional phenolic resins. In this study, thermal performance and ablation characteristics of a carbon composite with the MSP polymer (CF/MSP) were investigated under supersonic plasma air stream. The cold wall heat fluxes ranged from 1.2 to 11.0MW/m2. Conventional carbon fiber phenolic (CF/PR) composite was tested at the similar conditions for direct comparison. The mass loss of the CF/MSP composite was far less than that of the CF/PR composite, which is due to higher char yield and consequent high density of char layer. On the other hand, higher internal temperature was measured in the CF/MSP composite.
Static and Dynamic Fatigue of Glass–Carbon Hybrid Composites in Fluid Environment
Authors: Shan Ying , Lai Kian-Fong , Wan Kai-Tak , Liao Kin
Published: April 2003

Unidirectional glass fiber reinforced and glass-carbon fiber reinforced epoxy matrix composite samples (% glass to carbon fiber volume ratio 90: 10 and 75: 25)were subject to two-point bend rupture test in distilled water at 75 C and tension-tension cyclic test in both air and distilled water at 25 C. In the rupture test, while no obvious difference in rupture time was observed at larger deflections, glass– carbon hybrid samples showed prolonged rupture time in comparison to all-glass samples when loaded at 10% maximum deflection. When compared to samples tests in air, cyclic loading in water resulted in shorter fatigue lives for both all-glass and hybrid composite samples. However, hybrid samples showed better environmental fatigue resistance in water than all-glass samples, to 10 7 cycles. By incorporating appropriate amount of carbon fibers in glass fiber composite, long-term performance of glass–carbon hybrid composites under static and dynamic fatigue is substantially enhanced. It is demonstrated by the present study that the intra-ply hybrid approach is effective and economical in improving the durability of fiber reinforced polymer composites for long term applications.
Damage Evolution in Quasi-Isotropic SCS-6/Timetal 21S under Quasi-Static and Dynamic Bending
Authors: Bedouet S. , Neu R. W. , Fitoussi J. , Forsythe K. M.
Published: April 2003

Damage initiation and evolution in SCS-6/Timetal 21S with quasiisotropic layup loaded under quasi-static and dynamic bending is investigated. When the axes of the fibers in the outer ply are transverse to the bending stress ([90/ 45/0] s layup), the bending strength is significantly lower and damage in the form of fiber-matrix separation initiates sooner than when the fibers in the outer ply are parallel to the bending stress ([0/ 45/90] s). The damage process and plasticity for dynamic bending is similar to quasi-static bending with the asymptotic damage level being the same for both. However, the rate of increase of damage with strain is smaller for dynamic bending compared to quasi-static bending. The energy dissipated in this titanium matrix composite under dynamic loading is smaller than either a graphite-fiber polymide-matrix composite or a glass-fiber bismaleimidematrix composite.
Conceptual Design Principles for Non-Circular Pressurized Sandwich Fuselage Sections – a Design Study Based on a High-Order Sandwich Theory Formulation
Authors: Thomsen Ole T. , Vinson Jack R.
Published: April 2003

Results obtained as part of a design study regarding a non-circular pressurized sandwich fuselage section are presented. The originating problem is associated with preliminary studies for the “Global Range Transport” envisaged by the “New World Vistas” program of the United States Air Force. The modeling and analysis is conducted usinga high-order sandwich theory formulation in which the elastic response of each face laminate is accounted for, includingbending-stretching couplingand transverse shear deformations, and where the transverse flexibility of the core is included. The sandwich fuselage envisaged may contain flat, tapered and curved sandwich elements, and a high-order sandwich theory formulation is developed to analyze each of these configurations. The paper includes a presentation of the adopted high-order sandwich theory with special emphasis on the application for the analysis of sandwich panels with variable core thickness, and for the analysis of curved sandwich panels. Numerical results obtained for two different mid-plane asymmetric fuselage sections are presented and compared; one with constant core thickness, and one with varyingcore thickness.
The Influence of Internal Stresses on the Microbond Test – I: Theoretical Analysis
Authors: Mendels D. -A. , Leterrier Y. , Manson J. -A.E.
Published: April 2003

The present work focuses on the interfacial mechanical behaviour of a model composite consisting of a solid droplet on a fibre, generally referred to as the microbond test. The interfacial adhesion is derived from the modelling of stress transfer in the microbond geometry including process-induced internal stresses, following two alternative approaches, namely the numerical discretisation of the droplet profile, and the equivalent cylinder analytical solution. This is in contrast to previous approaches, which mainly consider approximate geometry of the droplet. The numerical derivation provides comprehensive stress field data, whereas the equivalent cylinder approach is less accurate. However, these two approaches are shown to be equivalent as they result in the determination of the same interfacial shear strength. Numerical results clearly demonstrate that the maximum shear strength is located at the inflection point of the droplet profile. This provides an insight into the commonly observed remaining cone of resin on the fibre after debonding. It is further shown that the shear strength obtained by this method is independent of the location of the applied force, provided that the load isapplied between the droplet end and itsprofile inflection point. The model isgeneralis ed to the case of a symmetric loading and therefore includes internal stresses. It is then used to predict experimental interfacial shear strength versus droplet length for epoxy/glass, epoxy/Kevlar and epoxy/carbon systems at different levels of internal stresses and contact angle values.
Biaxial Failure Envelope and Creep Testing of Fibre Reinforced Plastic Pipes in High Temperature Aqueous Environments
Authors: Hale J. M. , Gibson A. G. , Speake S. D.
Published: April 2003

Results are presented for a series of tests on filament wound glass fibre reinforced pipes which have been subject to prolonged exposure to high temperature water. Two materials systems in common use in offshore piping applications are tested: continuous fibre e-glass in a phenolic and an epoxy resin matrix, respectively. This is the first work on this type on water saturated GRP at very high temperatures up to 160 C.

The results of water absorption tests on the two material systems at 95 C are presented. It is shown that saturated conditions can be achieved within seven days at this temperature.

Creep modulus test results for the two material systems as a function of temperature up to 160 C are presented. The reduction in TG for the epoxy material in the saturated state is quantified and it is shown that the phenolic material is largely unaffected by water absorption.

The results of biaxial tensile loading tests for the two material systems are presented in the form of failure envelopes at temperatures from 20to 160 C. The considerable weakening of the epoxy system, particularly under the matrix dominated loading conditions, is quantified and it is shown that the failure envelope for the phenolic system is largely unaffected by temperature.

Finally, a comparison is made between the two materials as a function of loading condition and temperature as a design guide.
Phase Shift Effect on the Stress Distribution for Satin Weave Composites
Authors: Woo Kyeongsik , Suh Young W. , Whitcomb John D.
Published: April 2003

In this study, the stacking phase shift effect on the stress distribution was investigated for eight-harness satin weave textile composites. Simply stacked two-layer configurations with phase shifts were modeled by unit cells and repeating boundary conditions were applied at the outer surfaces. Detailed stresses were calculated by macro-element post-processing. Results were assessed to investigate the variation of stress distributions according to the manner how the adjacent tows were arranged. The changes in the failure initiation at the matrix and tows were also examined.
Influence of Particle Size Distribution of Preformed Rubber on the Structure and Properties of Composite Systems
Authors: Hayes Brian S. , Seferis James C.
Published: April 2003

Four different size distributions of preformed rubber particles were used to interlayer toughening carbon fiber composites. Prepregs were made using single pass impregnation with model epoxy resins containing the different preformed particle distributions at two concentrations. The particle distributions and average particle sizes were selected to investigate the effect on laminate structure and fracture toughness. It was found that the average particle size affected the interlayer formation in the cured laminate. A significant difference in the fracture toughness of the laminates was found due to a change in the particle size distribution, average particle size, concentration, and resultant laminate structures. In this study, it is shown that the particle size distribution must be taken into account when designing interlayer toughened composites so that mode I and mode II toughness can be optimized.
Fracture Micromechanisms of Fibre-Metal Laminates: In-Situ SEM Observations
Authors: Castrodeza E. M. , Bastian F. L. , Yawny A. , Ipiña J. E.Perez
Published: April 2003

The monotonic fracture micromechanisms of an aramid-aluminum laminate were studied using very small single edge bend specimens, SE(B) tested in a small-instrumented testing machine inside a scanning electron microscope. Thefracture process was followed by simultaneous observation of the sample and recording the loading variables. The instability fracture toughness was strongly dependent on the fibre-reinforced epoxy layer and the crack-growth in the external aluminum layers, prior to fracture instability, was influenced by the notch acuity. The load versus loadline displacement behaviourand load instabilities were similar to the ones obtained by conventional testing procedures. The technique implemented proved to be a powerful tool to study the fracture micromechanisms of aramid-aluminum laminates or other fibre-metal laminates and to correlate them with the recorded macro events.
Measuring the Bending Stiffnesses of Orthotropic and Symmetric Laminates from Flexural Vibrations
Authors: Berthelot J. -M. , Angoulvant F.
Published: April 2003

The paper develops an extensive analysis of the problem of determining the bending stiffnesses of orthotropic and symmetric laminates from flexural vibrations of rectangular plates with different boundary conditions consisting of clamped or free edges. Rayleigh’s approximation and Ritz method are considered for evaluating the flexural vibrations of plates. The experimental results and an analysis of the sensibility show clearly the tendency for the evaluation of the bending stiffnesses from the natural frequencies of the flexural vibrations of an orthotropic or symmetric plate to be an ill conditioned problem. It results that iterative procedures associated with Ritz method or with numerical method as finite element analysis cannot be used for evaluating the bending stiffnesses from the natural frequencies of a single plate in industrial applications. For orthotropic laminates, the paper shows how the Rayleigh’s approximation allows to overcome the problem of the divergence of the iterative processes. This approximation suggests another methods for evaluating the bending stiffnesses and their variations with the frequency. Next for symmetric laminates, the evaluation of the stiffnesses from the flexural vibrations of plates is implemented using the measurement of the mode shapes deduced from experimental modal analysis.
Modelling Interlaminar and Intralaminar Damage in Filament-Wound Pipes under Quasi-Static Indentation
Authors: Zou Z. , Reid S. R. , Li S. , Soden P. D.
Published: April 2003

A pragmatic modelis proposed to predict interlaminar and intralaminar damage, i.e., delamination and matrix cracking, in filament wound pipes. The pipe is modelled as an assembly of sublaminates connected along their interfaces. The initiation of delamination and transverse matrix cracking is predicted based on stress-based failure criterion. Delamination propagation is governed by the energy release rates. After the occurrence of damage, constraint between sublaminates is removed to model the delamination and a ply discount model is used to account for the materialdegradation effects of matrix cracking. The establishment of a leakage path is comprised by jointed matrix cracking in each layer and delamination at each interface. Finite element analysis has been carried out to simulate the quasi-static indentation of filament-wound composite pipes. Despite the simplification of treating each damage mechanism independently (i.e., no direct interactions), good agreement has been achieved between experimentalresul ts and the predictions of the model for the load–indentation relationship, the evolution of multiple delaminations and the formation of a leakage path.
Recurring Cost Minimization of Composite Laminated Structures – Optimum Part Size as a Function of Learning Curve Effects and Assembly
Authors: Apostolopoulos Panayotis , Kassapoglou* Christos
Published: April 2003

The cost of a laminated composite plate is examined in detail. The fabrication process is broken out into individual steps and simple equations to estimate the cost on the basis of part size and complexity are developed. The option to divide the plate into modulesisals o included in the approach. The effectsof learning curve and assembly are also incorporated. The cost equations developed are implemented in a simple optimization algorithm that minimizes the fabrication cost as a function of module size, overall plate size, thickness, learning curve, and fastener type and spacing. It isfound that there isa range of valuesfor these parametersfor which the total cost of the plate is lower if it is made by assembling smaller identical modules instead of making it in a single piece. There is a module size that minimizes the total fabrication and assembly cost and results in cost values significantly lower than the cost of the plate if it were fabricated in one piece. The modular approach is also compared to an approach where the plate is made of pieces optimized locally for minimum weight based on local applied loads. The cost of the plate made by identical modules (at the optimum size found by the analysis) is found to be lower than that for a plate assembled with pieces each of which is optimized for weight. On the other hand, the weight of the plate made by identical modulesishigher than the weight of the plate made by assembling pieces locally optimized for weight.
FRP Strengthened Masonry Beams. Part I – Model
Authors: Kiss Rita M. , Kollar Laszlo P. , Jai John , Krawinkler Helmut
Published: April 2003

This paper presents a simple model to predict the load-deflection curve of a fiber-reinforced plastic (FRP) reinforced masonry beam subjected to bending and axial loads. Delamination growth is modeled by using an energy balance approach. It is shown that continuously growing delamination results in highly nonlinear behavior.
Optimizing the Weld Strength of Ultrasonically Welded Nylon Composites
Authors: Liu Shih-Jung , Chang I-Ta
Published: April 2003

Ultrasonic welding of thermoplastic composites has become an important process in industry because of its relatively low cost and high quality resultant joints. However, the optimization of this technique has been essentially based on a trial-and-error process. In this report, an L18 orthogonal array design based on the Taguchi method was conducted to optimize the joint strength of ultrasonically welded thermoplastic composites. The materials used were 15 and 35% glass-fiber filled nylon-6 composites. Specimens for ultrasonic welding were welded on a 2000-watt welder and their joint strengths were determined by a tensile tester. The experimental result suggests that the amplitude of vibration, hold time and geometry of the energy directorsare the principal factorsaffecting the joint property of ultrasonically welded nylon composites. Semicircular energy directors were found to weld products of the highest strength. In addition, the joint strength of the parts increases with the fiber content in the composites, but decreases with the moisture of the materials.
Predicting the Strength of Diamond Braided Composites
Authors: Aggarwal A. , Ramakrishna S. , Ganesh V. K.
Published: April 2003

The strength of diamond braided composites is examined and the experimentally observed trends from the braid architectures are simulated using the micromechanics models. The effect of continuity of yarns at the edge of specimen is also studied. Standard tensile tests performed on both types of specimens showed a significant difference in failure strength and failure strain along with the failure mode between the specimens with continuous and discontinuous yarn reinforcement. A micromechanical model is developed to predict the failure strength of the above mentioned composites under uniaxial tensile loading. The model predicts with fair degree of accuracy the stress–strain response for the specimens with yarn discontinuity at the edges.
Thermal Residual Stress and Interphase Effects on Crack-Inclusion Interactions
Authors: Cheeseman Bryan A. , Santare Michael H.
Published: April 2003

An analytical investigation is conducted into the problemof a matrix crack interacting with an inclusion possessing an interphase and subjected to a thermal load. The interphase is modeled as a third, homogeneous phase surrounding the circular inclusion. By using a dislocation based approach to model the crack, along with an analytical solution to the thermal stress problem, a set of singular integral equations are formulated and then solved using established numerical techniques. The solution is applied to a glass fiber–epoxy composite system having either radial or circumferential matrix cracks and undergoing a uniform temperature change. This solution gives a quantitative and analytical method to evaluate the influence of interphase properties on the stress intensity factors of nearby, thermally loaded microcracks.