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Dive into the research topics where David E. Bowles is active.

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Featured researches published by David E. Bowles.


Journal of Composite Materials | 1989

Prediction of Coefficients of Thermal Expansion for Unidirectional Composites

David E. Bowles; Stephen S. Tompkins

Several analyses for predicting the longitudinal, α1, and transverse, α2, coefficients of thermal expansion of unidirectional composites were compared with each other, and with experimental data on different graphite fiber reinforced resin, metal, and ceramic matrix composites. Analytical and numerical analyses that accurately accounted for Poisson re straining effects in the transverse direction were in consistently better agreement with ex perimental data for α2 than the less rigorous analyses. All of the analyses predicted similar values of α1, and were in good agreement with the experimental data. A sensitivity analysis was conducted to determine the relative influence of constituent properties on the predicted values of α1 and α2. As would be expected, the prediction of α1 was most sensi tive to longitudinal fiber properties and the prediction of α2 was most sensitive to matrix properties.


Journal of Composite Materials | 1984

Effect of Microcracks on the Thermal Expansion of Composite Laminates

David E. Bowles

A finite element analysis was used to quantitatively predict the effect of matrix microcracks in the 90° plies of graphite/epoxy composites on the coefficient of ther mal expansion in the 0° direction, α y (perpendicular to the cracks). Results were generated for [0 m/90n]s, [0/±45/90]s and [0/90/±45] s graphite/epoxy laminate con figurations. Analytical predictions were compared with experimental results for the two quasi-isotropic laminate configurations. Both analytical and experimental results showed that microcracks reduced the effective stiffness of the 90° plies, thus causing the laminates, thermal response to be more like that of a [0] laminate. The change in αy was a function of lamina material properties, microcrack density, fiber orientation, and stacking sequence. A combination of classical lamination theory and finite element analysis was used to predict the effect of microcracks in both the 90° and 0° plies. Analytical results showed that the addition of microcracks in the 0° plies do affect αy, but to a lesser extent than those in the 90° plies.


Journal of Reinforced Plastics and Composites | 1996

Prediction of thermal cycling induced matrix cracking

Hugh McManus; David E. Bowles; Stephen S. Tompkins

Thermal fatigue has been observed to cause matrix cracking in laminated composite materials. A method is presented to predict transverse matrix cracks in a composite laminate subjected to cyclic thermal load. Shear lag stress approximations and a simple energy-based failure criteria are used to predict crack density as a function of temperature. Prediction of crack density as a function of thermal cycling is accomplished by assuming that fatigue degrades the materials inherent resistance to cracking. The method is implemented as a computer program. Simple experiments provide data on progressive cracking of a laminate with decreasing temperature, and on cracking induced by thermal cycling. Correlation of the analytical predictions to the data is very good. A parametric study using the analytical method is presented which provides insight into material behavior under cyclical thermal loads.


Experimental Mechanics | 1986

A laser-interferometric dilatometer for thermal-expansion measurements of composites

S. S. Tompkins; David E. Bowles; W. R. Kennedy

A high-precision, Fizeau-type laser-interferometric dilatometer system has been developed for low-expansion composite materials. The strain resolution is about one microstrain. The system is automated to operate over a large temperature range and record data during the test. A technique has been developed to reduce the data in real time. The dilatometer system is described and thermal-expansion measurements for several fiber-reinforced and particle-filled composites are presented.


Journal of Spacecraft and Rockets | 1986

Electron radiation effects on the thermal expansion of graphite/resin composites

David E. Bowles; Stephen S. Tompkins; George F. Sykes

The effects of 1 MeV electron radiation on the thermal expansion characteristics of two graphite reinforced resin matrix composite systems were studied. Specimens of both graphite/epoxy (T300/5208) and graphite/polyimide (C6000/PMR15) were irradiated to a total dose of 6 x 10/sup 9/ rads at two different rates. Unidirectional, cross-ply, and quasi-isotropic laminate configurations were examined. Thermal expansion measurements were made over the temperature range of -250/sup 0/F to +280/sup 0/F with a laser interferometer. Dynamic mechanical analyses (DMA) were performed to study changes in resin chemistry. Thermal expansion results indicate that radiation did produce permanent residual strains of up to -70 x 10/sup -6/ for the graphite/epoxy when exposed to temperatures up to +280/sup 0/F. However, no permanent changes in the coefficient of thermal expansion (CTE) were observed. No permanent residual strains or changes in the CTE attributable to radiation were observed for the graphite/polyimide specimens. No significant effects of radiation dose rate on the thermal expansion of either composite system were observed. DMA results indicate that electron radiation caused chemical changes in the epoxy matrix. These changes resulted in a lower glass transition temperature and broader rubbery region which extended into the temperature range of the thermal expansion tests.


Proceedings of SPIE | 1992

Composite materials for precision space reflector panels

Stephen S. Tompkins; Joan G. Funk; David E. Bowles; Timothy W. Towell; John W. Connell

One of the critical technology needs of large precision reflectors for future astrophysical and optical communications satellites lies in the area of structural materials. Results from a materials research and development program at NASA Langley Research Center to provide materials for these reflector applications are discussed. Advanced materials that meet the reflector panel requirements are identified and thermal, mechanical and durability properties of candidate materials after exposure to simulated space environments are compared. Results from analytical studies to define material properties that control laminate properties and reflector deformation are discussed. A parabolic, graphite-phenolic honeycomb composite panel having a surface accuracy of 70.8 microinches RMS and an areal weight of 1.17 lbm/ft2 was fabricated with T50/ERL1962 facesheets, a PAEI thermoplastic surface film, and Al and SiOx coatings.


Advances in Optical Structure Systems | 1990

Development of composite materials for spacecraft precision-reflector panels

Stephen S. Tompkins; David E. Bowles; Joan G. Funk; J. Andre Lavoie; Timothy W. Towell

One of the critical technology needs for large precision reflectors required for future astrophysics and optical communications is in the area of structural materials. Therefore, a major area of the Precision Segmented Reflector Program at NASA is to develop light-weight composite reflector panels with durable, space environmentally stable materials which maintain both surface figure and required surface accuracy necessary for space telescope applications. Results from the materials research and development program at NASA Langley Research Center are discussed. Advanced materials that meet the reflector panel requirements are identified. Thermal, mechanical and durability properties of candidate materials after exposure to simulated space environments are compared to the baseline material.


Experimental Mechanics | 1989

Experimental/analytical characterization of composite tubes under combined loading

Mark S. Derstine; Marek-Jerzy Pindera; David E. Bowles

The paper outlines the results of an investigation to characterize the response of P75/934 graphite/epoxy tubes with a stacking sequence of [15/0/±10/0/−15]s under pure torsion and combined axial/torsion loading. The experimentally observed nonlinear response and path-dependent failure are discussed in terms of material nonlinearities at the ply level and first-ply failure loads with the help of an analytical model.


Archive | 1988

Combined mechanical loading of composite tubes

Mark S. Derstine; Marek-Jerzy Pindera; David E. Bowles


Archive | 1995

From LDEF to a national Space Environment and Effects (SEE) program: A natural progression

David E. Bowles; Robert L. Calloway; Joan G. Funk; William H. Kinard; Arlene S. Levine

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Joan G. Funk

Langley Research Center

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Hugh McManus

Massachusetts Institute of Technology

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