Engineering topics

Hyer, M. W.

Publications and source records attributed to Hyer, M. W..

At least 91 records · Page 5

NASA NTRS1984

Residual thermal stresses in cross-ply graphite-epoxy tubes

Elasticity solutions for the residual stress state in cross-ply graphite-epoxy tubes subjected to a spatially uniform temperature below the cure temperature are derived. The solutions are valid away from the ends of the tube. Numerical results are presented for three tubes. It is seen that stacking arrangement can affect the residual stresses and that the radial stresses are smaller than the other stress components. The results show that classical lamination theory is in considerable error when the tube radius to wall thickness ratio is less than 20.

Hyer, M. W.↗

NASA NTRS1983

Stresses in a quasi-isotropic pin loaded connector using photoelasticity

Birefringent glass-epoxy and a numerical stress separation scheme are used to compute the stresses in the vicinity of a pin-loaded hole. The radial and circumferential stresses at the hole edge, and the net section and shear-out stresses are computed. The numerical and experimental results are compared with the computed stresses. The fixture used to load the connector is discussed and typical isochromatic and isoclinic fringe patterns are presented. The stress-separation scheme is briefly discussed.

Hyer, M. W.↗

NASA NTRS1983

Temperature dependence of mechanical and thermal expansion properties of T300/5208 graphite/epoxy

The 116-394 K temperature range elastic constants, ultimate strengths and thermal expansion behavior of T300/5208 graphite/epoxy laminates of various different lay-up types have been determined. It is noted that most properties exhibit nearly linear temperature dependencies, although the transverse modulus and axial thermal expansion vary nonlinearly with temperature, and change in value by an order of magnitude over the present temperature range.

Hyer, M. W.↗

NASA NTRS1983

The response of cylindrical panels fabricated from symmetrically and unsymmetrically laminated composite materials

Equations are developed which govern the deflection response of long cylindrical panels subjected to a line load. The line load is directed toward the center of curvature of the panel, is located at an arbitrary point along the arc length of the panel, and is included at an arbitrary angle relative to the radial direction. Only the geometrically linear problem is considered and the spatial dependence in the problem is reduced to one independent variable, specifically, the arc length along the panel. The problem is thus solvable in closed form. Both symmetrically laminated and the less common unsymmetrically laminated simply supported panels are studied. The unsymmetrically laminated case was considered because the natural shape of an unsymmetric laminate is cylindrical. Results are presented which show the influence of the location and inclination of the line load on panel deflection. Shallow and deep panels are considered. Both the symmetric and unsymmetric panels exhibit similar behavior, the unsymmetric configurations being less stiff. Limited experimental results are presented.

Carper, D. M.↗

NASA NTRS1983

Nonlinear effects of elastic coupling in unsymmetric laminates

Classical lamination theory predicts the room-temperature shape of all unsymmetrically laminated, elevated-temperature cure composites to be a saddle shape. Experimental observation indicates, however, that in many cases the room-temperature shape is cylindrical. In addition, a second cylindrical shape can often be obtained from the first by a simple snap-through action. It is the elastic couplings between inplane and out-of-plane deformations which are inherent in unsymmetric laminates that are responsible for the room-temperature shape. However, the couplings are so strong that geometrically nonlinear effects are produced. These are not accounted for in the classical theory. This paper reviews a theory developed to explain the effects of the coupling on laminate shape. The theory is based on a minimization of the laminate's total potential energy. The theory accounts for geometric nonlinearities. Because the problem is nonlinear, approximate solutions are sought by using a Rayleigh-Ritz procedure. Because of the observed snap-through of some laminates, stability of the predicted shapes is examined. Numerical results and some limited experimental data are presented for several laminates.

Hyer, M. W.↗

NASA NTRS1982

Solution Accounts for Structural Damping

New analytical technique determines dynamic response of damped structures dominated by internal structural damping mechanisms. Though structural damping is often negligible compared with damping due to air friction and friction in joints, structural damping can be of major importance in structures having heavy damping treatments or in outer-space structures. Finite-element model includes nonlinear, nonviscous internal damping.

Roussos, L. A.↗

NASA NTRS1982

Development of a Priest interferometer for measurement of the thermal expansion of a graphite epoxy in the temperature range 116-366 K

The thermal expansion behavior of graphite epoxy laminates between 116 and 366 degrees Kelvin was investigated using as implementation of the Priest interferometer concept. The design, construction and use of the interferometer along with the experimental results it was used to generate are described. The experimental program consisted of 25 tests on 25.4 mm and 6.35 mm wide, 8 ply pi/4 quasi-isotropic T300-5208 graphite/epoxy specimens and 3 tests on a 25.4 mm wide unidirectional specimen. Experimental results are presented for all tests along with a discussion of the interferometer's limitations and some possible improvements in its design.

Short, J. S.↗

NASA NTRS1982

The room-temperature shapes of four-layer unsymmetric cross-ply laminates

A geometrically nonlinear extension of classical lamination theory developed by Hyer (1981) for predicting the room-temperature shapes of unsymmetric laminates is reformulated using relaxed restrictions regarding the inplane strains. The inplane residual strains of unsymmetric laminates which have cooled from curing into a cylindrical room-temperature shape are examined numerically. Results show that the residual strains are compressive and practically independent of spatial location on the laminate. In addition, the room temperature shapes of the four-layer unsymmetric cross-ply laminates are predicted, and it is shown that the temperature shapes are a strong function of their size and their stacking arrangement. It is demonstrated that, depending on the parameters selected, the room-temperature shape of a four-layer cross-ply unsymmetric laminate can be a unique saddle shape, a unique cylindrical shape, or a cylindrical shape that can be snapped through to another cylindrical shape.

Hyer, M. W.↗

NASA NTRS1982

Thermal expansion of graphite-epoxy between 116 K and 366 K

A Priest laser interferometer was developed to measure the thermal strain of composite laminates. The salient features of this interferometer are that: (1) it operates between 116 K and 366 K; (2) it is easy to operate; (3) minimum specimen preparation is required; (4) coefficients of thermal expansion in the range of 0-5 micro epsilon/K can be measured; and (5) the resolution of thermal strain is on the order of micro epsilon. The thermal response of quasi-isotropic, T300/5208, grahite-epoxy composite material was studied with this interferometer. The study showed that: (1) for the material tested, thermal cycling effects are negligible; (2) variability of thermal response from specimen to specimen may become significant at cryogenic temperatures; and (3) the thermal response of 0.6 cm and 2.5 cm wide specimens are the same above room temperature.

Short, J. S.↗

NASA NTRS1982

Advances in Moire interferometry for thermal response of composites

An experimental technique for the precise measurement of the thermal response of both sides of a laminated composite coupon specimen uses Moire interferometry with fringe multiplication which yields a sensitivity of 833 nm (32.8 micro in.) per fringe. The reference gratings used are virtual gratings and are formed by partially mirrorized glass prisms in close proximity to the specimen. Results are compared with both results obtained from tests which used Moire interferometry on one side of composite laminates, and with those predicted by classical lamination theory. The technique is shown to be capable of producing the sensitivity and accuracy necessary to measure a wide range of thermal responses and to detect small side to side variations in the measured response. Tests were conducted on four laminate configurations of T300/5208 graphite epoxy over a temperature range of 297 K (75 F) to 422 K (300 F). The technique presented allows for the generation of reference gratings for temperature regimes well outside that used in these tests.

Brooks, E. W., Jr.↗

NASA NTRS1982

Load distributions in photoeleastic bolted-joint models

An attempt is made to study the stresses in multiple-bolt connectors, focusing on the stress distribution in a two-pin connector, the two pins being in line and in parallel with the direction of the applied load. The photoelastic modeling approach with two-dimensional transmission photoelasticity is used. The joint models and model fringe patterns are discussed, with special attention given to the existence of a photoelastic isotropic point and to the separation of stresses.

Hyer, M. W.↗

NASA NTRS1982

Thermal expansion of graphite epoxy

Two optical techniques to measure the thermal expansion of fiber-reinforced composites are discussed. These techniques are moire interferometry and Fizeau interferometry. The pertinent features of each setup are presented and the preparation of the composite specimens discussed. Thermal expansion measurements in the range 116 to 422 K for 0 deg, 90 deg, and quasi-isotropic graphite-epoxy composite laminates are presented.

Hyer, M. W.↗

NASA NTRS1982

Unsymmetrically laminated composites

Classical lamination theory predicts that the room-temperature shapes of all elevated-temperature cure, unsymmetrically laminated composites are saddles. However, experimental observation indicates that the shapes are often cylindrical. In addition, a second cylindrical can sometimes be obtained from the first by a simple snap-through action. A geometrically nonlinear extension to classical lamination theory is used to explain this behavior. Approximate solutions to the nonlinear extension are obtained by using a Rayleigh-Ritz minimization of the laminate's total potential energy. A stability analysis explains the dual cylindrical shapes.

Hyer, M. W.↗

NASA NTRS1981

Use of two-dimensional transmission photoelastic models to study stresses in double-lap bolted joints

The stress distribution in two hole connectors in a double lap joint configuration was studied. The following steps are described: (1) fabrication of photoelastic models of double lap double hole joints designed to determine the stresses in the inner lap; (2) assessment of the effects of joint geometry on the stresses in the inner lap; and (3) quantification of differences in the stresses near the two holes. The two holes were on the centerline of the joint and the joints were loaded in tension, parallel to the centerline. Acrylic slip fit pins through the holes served as fasteners. Two dimensional transmission photoelastic models were fabricated by using transparent acrylic outer laps and a photoelastic model material for the inner laps. It is concluded that the photoelastic fringe patterns which are visible when the models are loaded are due almost entirely to stresses in the inner lap.

Hyer, M. W.↗

NASA NTRS1981

Calculation of the room-temperature shapes of unsymmetric laminates

A theory explaining the characteristics of the cured shapes of unsymmetric laminates is presented. The theory is based on an extension of classical lamination theory which accounts for geometric nonlinearities. A Rayleigh-Ritz approach to minimizing the total potential energy is used to obtain quantitative information regarding the room temperature shapes of square T300/5208 (0(2)/90(2))T and (0(4)/90(4))T graphite-epoxy laminates. It is shown that, depending on the thickness of the laminate and the length of the side the square, the saddle shape configuration is actually unstable. For values of length and thickness that render the saddle shape unstable, it is shown that two stable cylindrical shapes exist. The predictions of the theory are compared with existing experimental data.

Hyer, M. W.↗

NASA NTRS1981

A finite element model with nonviscous damping

A constitutive law by which structural damping is modeled as a relationship between stress, strain, and strain rate in a material is used in conjunction with the finite element method to develop general integral expressions for viscous and nonviscous damping matrices. To solve the set of nonlinear equations resulting from the presence of nonviscous damping, a solution technique is developed by modifying the Newmark method to accommodate an iterative solution and treat the nonviscous damping as a pseudo-force. The technique is then checked for accuracy and convergence in single- and multi-degree-of-freedom problems, and is found to be accurate and efficient for initial-condition problems with small nonviscous damping.

Roussos, L. A.↗

NASA NTRS1981

An inherent instability in fiber-reinforced composite laminates

Presented is a theory to predict the room-temperature shape of unsymmetric laminates. The theory is an extension of classical lamination theory and includes the effects of geometric nonlinearities. It is shown that the saddle shape predicted by the classical theory can actually be an unstable shape and a laminate will assume a cylindrical shape instead. The phenomena is coupled to the length, width, and thickness of the laminate.

Hyer, M. W.↗

NASA NTRS1980

Use of two-dimensional transmission photoelastic models to study stresses in double-lap bolted joints: Load transfer and stresses in the inner lap

The determination of the stress distribution in the inner lap of double-lap, double-bolt joints using photoelastic models of the joint is discussed. The principal idea is to fabricate the inner lap of a photoelastic material and to use a photoelastically sensitive material for the two outer laps. With this setup, polarized light transmitted through the stressed model responds principally to the stressed inner lap. The model geometry, the procedures for making and testing the model, and test results are described.

Hyer, M. W.↗