The ability to predict potential strength degradation of a filament wound sphere was developed using an incremental finite element model of the composite during fabrication. The sphere was modeled taking into account the winding/loading pattern and the resulting internal layer boundaries. The thickness profile of the sphere's layers were computed using a thickness profile/pattern simulation program. This thickness profile was used by the mesh generating program to ensure that the elements generated did not cross , layer boundaries. The elements used were four noded isoparametric quadrilateral elements and these were collapsed to triangular elements for transitions. The input to the finite element program was prepared by an interface program which combines the mesh generator output with the loading and option control data. The main feature of the finite element program was the incremental construction and loading of the model. Strength degradation definitely occurs when the average fiber layer strain is negative. The negative strain means that all the winding tension has been lost from the layer and the fibers in uncured resin will buckle when they try to support compressive loading. Then when the resin cures the buckled region of fibers are degraded in strength. This model gives a layer-by-layer analysis of the potential strength loss of the composite. / Ph. D.

The effect of laminate thickness on the fracture behavior of laminated graphite/epoxy (T300/5208) composites has been studied. The predominantly experimental research program included the study of the [0/±45/90]_ns and [0/90]_ns laminates with thicknesses of 8, 32, 64, 96 and 120 plies and the [0/±45]_ns laminate with thicknesses of 6, 30, 60, 90 and 120 plies. The research concentrated on the measurement of fracture toughness utilizing the center-cracked tension, compact tension and three point bend specimen configurations. Fracture toughness was computed using the stress intensity factor results of a finite element stress analysis of each specimen geometry which treated the composite as homogeneous but anisotropic. The development of subcritical damage at the crack tip was studied nondestructively using enhanced x-ray radiography and destructively using the laminate deply technique. The test results showed fracture toughness to be a function of laminate thickness. The fracture toughness of the [0/±45/90]_ns and [0/90]_ns laminates decreased with increasing thickness and asymptotically approached lower bound values of 30 ksi√in (1043 MP a√mm) and 25 ksi√in (869 √mm) respectively. The fracture toughness of the [0/±45/90]_ns laminate was independent of crack length at 8 and 120 plies. The fracture of the thin and thick [0/±45/90]_ns laminates were self-similar, macroscopically. However, the [0/90]_2s laminate (8 plies) exhibited fracture toughness values that increased sharply as a function of increasing crack size. This was attributed to large axial splits which formed perpendicular to the crack tip in the 0° plies and extended in the direction of applied load. The fracture toughness of the [0/90]_ns laminate was independent of crack length at 90 plies. The axial splits in the 0° plies of the thicker specimens were confined to the surface and the final fracture was self-similar. For both the [0/±45/90]_ns and [0/90]_ns laminates, the center-cracked tension, three-point bend and compact tension specimens gave comparable results. In contrast to the other two laminates, the fracture toughness of the [0/±45]_ns laminate increased sharply with increasing thickness but reached an upper plateau value of 40 ksi√in (1390 MP a√mm) at 30 plies. Fracture toughness was independent of crack size at 6 and 90 plies. The 6 ply specimens failed by an apparent uncoupling mechanism where the two interior -45° plies delaminated from the adjacent +45° plies and failed by matrix splitting parallel to the fibers. The surface 0° plies failed by broken fibers along a +45° line in association with matrix splitting parallel to the fibers in the +45° plies. The thick [0/±45]_ns laminates exhibited a surface boundary layer in which 45° fiber breaks and splits were evident along with delaminations. However, the interior of the specimens failed in a self-similar manner with fibers in the 0° plies breaking along a line collinear with the starter notch. The compact tension and three-point bend specimens defined a constant fracture toughness at about 15% below the plateau exhibited by the center-cracked tension specimens. The general toughness parameter model, a strain criterion developed by C. C. Poe, Jr. of NASA Langley, was the only candidate thin laminate failure criterion that was successful in using thin laminate parameters to predict the fracture of thick laminates. The "universal” general toughness parameter value of 1.5 √mm quite closely predicted the fracture of the thick laminates. / Ph. D.

The elements of production typewriting, including production time and production quality, for the first-time typing of business letters originated by machine dictation and longhand and typed on correcting electric and text-editing typewriters, were analyzed. Students typed four business letters, one under each of four conditions: on the correcting electric from machine dictation, on the text-editing from machine dictation, on the correcting electric from longhand, and on· the text-editing from longhand. Analyses were done for the elements of production time and for the elements of production quality. A two-factor ANOVA in a randomized block design was used to analyze the data for types of equipment when methods of origination were pooled and for methods of origination when types of equipment were pooled. When types of equipment and methods of origination were examined separately, the model was a randomized block design. Analyses of the elements of production time showed that (1) students took longer to produce copy when they typed on the text-editing typewriter than when they typed on the correcting electric typewriter and (2) students took longer to produce copy when they transcribed from machine dictation than when they transcribed from longhand. Analyses of the elements of production quality showed that students made more errors when they transcribed from machine dictation than when they transcribed from longhand. / Ed. D.

Optimal flight in the vertical plane with a vehicle model intermediate in complexity between the point-mass and energy models is studied. Flight-path angle takes on the role of a control variable. Range-open problems feature subarcs of vertical flight and singular subarcs as previously studied. The class of altitude-speed-range-time optimization problems with fuel expenditure unspecified is investigated and some interesting phenomena uncovered. The maximum-lift-to-drag glide appears as part of the family, final-time-open, with appropriate initial and terminal transient maneuvers. A family of, climb-range paths appears for thrust exceeding level-flight drag, some members exhibiting oscillations. Oscillatory paths generally fail the Jacobi test for durations exceeding a period and furnish a minimum only for short-duration problems. Minimizing paths of long duration follow a certain corridor in the V-h chart. The features of the family sharpen for the special case of thrust and drag independent of altitude, and considerable analytical attention is accorded to this for the insight it provides to the more general model. The problem of "steepest climb" is found to be ill-posed with the vehicle model under consideration, straight-vertically-upward maneuver sequences being furnished by a family of paths alternating between upward and downward vertical flight and including a limiting "chattering" member. / Ph. D.

The knowledge of particle size and size distribution are important parameters for understanding the behavior of numerous colloid systems. These areas include for example, clays, viruses, paints and blood. Until recently this information could be obtained only by the use of expensive, slow and complex instrumentation. Hydrodynamic chromatography provides a means of investigating particles in the submicron and micron region. The separation mechanism of this method is based upon the flow parameters with which the solute particles interact as they pass through a packed column. In the past the interpretation of these chromatograms has been based upon the mathematical modeling of the column parameters. We have developed a new multiwavelength detector system to be used in conjunction with hydrodynamic chromatography which provides size and concentration information of the eluant directly. The result is a rugged system that provides size and size distribution information rapidly and at low cost. / Ph. D.

In this paper we analyze the relationships between the flows of customers in a queueing network whose queue length process is a Markov process. A flow is a stochastic process formed by embedding the queue length process at transitions corresponding to: customers arriving to the network at a node; customers departing the network from a node; customers moving from one node to another node; all customers entering a node; all customers leaving a node; superpositions and decompositions of the flows described above. We show that flow processes in queueing networks are Markov renewal processes. In fact, we construct two Markov renewal processes corresponding to a flow. One Markov renewal process is formed by embedding the queue length process just before transitions of interest. The other Markov renewal process is formed by embedding the queue length process just after the transitions of interest. If a queueing network is a Jackson network and if the queue length process is reversible then the Markov renewal process formed by embedding the queue length process just before inputs to a node is the reverse process of the Markov renewal process formed by embedding the queue length process just after outputs from the node. Similar results hold for other flows in the network. We extend the above results to networks of symmetric queues where the service times are restricted to the Erlang distributed. To do this we need to introduce the concept of the quasi-reversed process of a Markov renewal process. A closed queueing network is constructed where the queue length process is not reversible yet the input process is the reverse process of the output process at each node. Another closed network is constructed where the queue length process is not reversible and the input process is not the reverse process of the output process at a node. From these two examples we conclude that reversibility is not a necessary condition for the input process to be the reverse process of the output process at a node and that the input process is not always the reverse process of the output process. Some implications of these results when applied to the decomposition or recomposition of stochastic processes are discussed. / Ph. D.

The process analysis approach was chosen for modeling the joint product nature of timber supply. Considerable emphasis was placed upon defining model components that would be required for developing a positivistic model of timber supply. An empirical application of the proposed linear programming model to Eastern Virginia simulated the impacts of increased fuelwood prices on the timber market system in 1976. The empirical application of the model indicated an ability to simulate many of the complex market interactions inherent in timber supply. Fuelwood was found to act as both a production complement and a production competitor with the conventional forest products, depending upon the range of prices analyzed. Fuelwood price was also found to act as a demand shifter for roundwood outputs of the forest. / Ph. D.

The controversy regarding commercial thinning continues to intensify as pine plantation acreage in the south increases. This controversy has caused industrial and nonindustrial landowners to re-examine the economic returns from their plantation investments. This study was undertaken to develop investment guidelines for the management of loblolly pine plantations. Computer simulation was used to evaluate the effect on present value that four future price/market scenarios, three management regimes, and three mechanized thinning systems can have on current thinning investments. When the economic returns from thinning are compared with a no-thin management regime, simulation results indicate that long-term investment advantages favor thinning only slightly, regardless of the future price/market scenario assumed. This slight difference suggests that individual forest product companies may find other reasons such as wood flow, tax advantages, and future product requirements of their manufacturing facilities to be overriding factors for engaging in commercial thinning. Generally, short-run cost and production differences between thinning systems are more significant than the long-term investment effects. Consequently, the type of mechanized thinning system employed has a negligible impact on the total investment. / Ph. D.

The purpose of this study was to identify factors which influenced Virginia Superintendents in Region-Study Group VI between 1978 and 1982 to continue or to vacate the position of superintendent. The population for the study included 29 cases: 19 were classified as continuing superintendents and 10 were classified as non-continuing. The Region of Study included 12 counties and 7 cities. The focus is on the examination of turnover in this geographical region. In carrying out the purpose, the study examined the following research questions: (a) What factors, as perceived by the continuing superintendent, were responsible for or contributed to the decision to continue in the same position? (b) What factors, as perceived by the non-continuing superintendent, were responsible for or contributed to the decision to vacate the position? This descriptive research study used case study methodology to investigate the pertinent factors that influenced the decisions of superintendents in Region-Study Group VI to continue or to vacate their positions of leadership in Virginia School Systems. The study utilized personal confidential interviews as the primary method of data collection. An Interview Guide was developed as the data gathering instrument. Questions were designed to focus on major areas of responsibility of a superintendent. In addition to job competency factors, social, political, personal, community and system demographic factors were examined. A model was designed to check these factors against perceptions of job satisfaction. Data which could be quantified were key-punched for analysis. The chi square test was applied. Factors which appeared to be statistically significant from the chi square analysis of continuing and non-continuing categories included: Community Factors, Social Factors, Job Competencies--Board Relations, Business and Fiscal Management, Curriculum and Instruction, and student Personnel Services. Areas of the interview which could not be easily quantified were reported in narrative form with case specific data. The following case specific information was reported as reasons for staying on the job by the continuing superintendents: (a) positive board relations, (b) community support, (c) challenge and prestige of leadership, (d) personal preference for a particular commit. Case specific information reported by non-continuing superintendents as reasons for changing jobs or termination included: (a) unsatisfactory board relations, (b) health, (c) to avoid community conflict, (d) retirement age, (e) role of change agent, and (f) professional growth--the challenge of a larger school district. / Ed. D.

Job satisfaction has been the subject of a great deal of research by a variety of professional disciplines. However, in school psychology, more speculation than empirical data exists on the topic. Although speculation in the profession has suggested a relatively high degree of job dissatisfaction among school psychologists, a 1982 nationwide study of members of The National Association of School Psychologists failed to substantiate the claims of such speculation. The population of school psychologists in Virginia was chosen for the present study. The study was designed to answer the following four research questions: 1. What are the overall levels of job satisfaction among school psychologists in Virginia? 2. What degree of satisfaction do Virginia school psychologists express with each of 20 subfactors of job satisfaction? 3. What is the relationship between overall levels of job satisfaction and selected demographic variables? 4. How does the job satisfaction of Virginia school psychologists compare with school psychologists nationally? Data were collected via mailed surveys using a demographic data form and a modified form of the Minnesota Satisfaction Questionnaire {MSQ). Four hundred and thirty-nine school psychologists were initially mailed survey materials, and a response rate of 87.36% was obtained. Of this total, two hundred and sixty-seven met the requirements necessary to be included in data analysis. Frequency counts of modified MSQ responses revealed that 84.27% of the school psychologists indicated that they were either satisfied or very satisfied with their jobs. Subscale means and 95% confidence intervals on the modified MSQ indicated that Virginia school psychologists were satisfied with 18 of the 20 subfactors of job satisfaction measured. Only the scales of school system policies and practices, and advancement had means and confidence intervals which fell completely within the dissatisfied range. Multiple regression procedures were used to determine the relationships between overall job satisfaction scores and demographic variables. Three significant predictors of job satisfaction emerged: membership in the Virginia Association of School Psychologists (positively related), membership in the National Education Association (negative related), and contract length (negatively related). This model explained 9.25% of the total variance and overall job satisfaction scores. Analysis of variance procedures were used to compare the job satisfaction of Virginia school psychologists with that of a national sample of school psychologists. Results indicated that Virginia school psychologists were more satisfied with their job security but less satisfied with their compensation, than were their national counterparts. Results of multi-group comparisons of covariance structures available in the computer program LISREL indicated that for the demographic variables studied with the exception of age, no differences existed between Virginia school psychologists and the national sample regarding the relationship of that variable with total job satisfaction scores. Several implications were drawn from the results of the study leading to recommendations for school psychologists, trainers and employers of school psychologists, and professional school psychology organizations. The recommendations focused on development of advancement opportunities for school psychologists, methods for reducing dissatisfaction associated with school system policies and practices, and topics for additional research. / Ed. D.