SEARCH · Search NASA

Results for “Poisson ratio”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Solid Rocket Motor Case (SRMC) dynamic sensitivity to changes in composite properties

Traditional composite lamination theory was used to compute the constitutive matrices using a potential range of lamina properties. Sensitivity of vibrational frequencies was examined for variations in constituent materials and geometric properties. The material component interactions examined were the lamina longitudinal and transverse Young's modulus, the lamina Poisson's ratio, and the shear modulus. Fiber and resin properties were related to the frequency response through lamina properties. Geometric properties examined are void ratio and helical wind angle. Capabilities and applications of the SPAR and NASTRAN computer codes are examined for laminated cylindrical shells.

Tolbert, R. N.↗

NASA NTRS1986

Thermal barrier coating life prediction model

This is the second annual report of the first 3-year phase of a 2-phase, 5-year program. The objectives of the first phase are to determine the predominant modes of degradation of a plasma sprayed thermal barrier coating system and to develop and verify life prediction models accounting for these degradation modes. The primary TBC system consists of an air plasma sprayed ZrO-Y2O3 top coat, a low pressure plasma sprayed NiCrAlY bond coat, and a Rene' 80 substrate. Task I was to evaluate TBC failure mechanisms. Both bond coat oxidation and bond coat creep have been identified as contributors to TBC failure. Key property determinations have also been made for the bond coat and the top coat, including tensile strength, Poisson's ratio, dynamic modulus, and coefficient of thermal expansion. Task II is to develop TBC life prediction models for the predominant failure modes. These models will be developed based on the results of thermmechanical experiments and finite element analysis. The thermomechanical experiments have been defined and testing initiated. Finite element models have also been developed to handle TBCs and are being utilized to evaluate different TBC failure regimes.

Hillery, R. V.↗

NASA NTRS1985

Thermal barrier coating life prediction model

This is the first report of the first phase of a 3-year program. Its objectives are to determine the predominant modes of degradation of a plasma sprayed thermal barrier coating system, then to develop and verify life prediction models accounting for these degradation modes. The first task (Task I) is to determine the major failure mechanisms. Presently, bond coat oxidation and bond coat creep are being evaluated as potential TBC failure mechanisms. The baseline TBC system consists of an air plasma sprayed ZrO2-Y2O3 top coat, a low pressure plasma sprayed NiCrAlY bond coat, and a Rene'80 substrate. Pre-exposures in air and argon combined with thermal cycle tests in air and argon are being utilized to evaluate bond coat oxidation as a failure mechanism. Unexpectedly, the specimens pre-exposed in argon failed before the specimens pre-exposed in air in subsequent thermal cycles testing in air. Four bond coats with different creep strengths are being utilized to evaluate the effect of bond coat creep on TBC degradation. These bond coats received an aluminide overcoat prior to application of the top coat to reduce the differences in bond coat oxidation behavior. Thermal cycle testing has been initiated. Methods have been selected for measuring tensile strength, Poisson's ratio, dynamic modulus and coefficient of thermal expansion both of the bond coat and top coat layers.

Hillery, R. V.↗

NASA NTRS1987

Finite-element analysis of corner cracks in rectangular bars

Stress intensity factors for a wide range of quarter-elliptical corner cracks in rectangular bars are presented. Cracked configurations were subjected to remote tension, in-plane bending, or out-of-plane bending. Results were compared with other numerical results for a quarter-circular corner crack configuration. The present results along the interior of the crack generally agreed within 3 percent with those from the literature. Some larger differences (3 to 13 percent) were observed near the intersection of the crack front and the free surfaces in the boundary layer region. Analyses were performed to study the effect of mesh refinement in the boundary layer region and the influence of Poisson's ratio on the distribution of stress-intensity factors.

Raju, L. S.↗

NASA NTRS1987

Cell model and elastic moduli of disordered solids - Low temperature limit

The cell theory has been previously employed to compute the equation of state of a disordered condensed system. It is now generalized to include anisotropic stresses. The condition of affine deformation is adopted, transforming an orginally spherical into an ellipsoidal cell. With a Lennard-Jones n-m potential between nonbonded centers, the formal expression for the deformational free energy is derived. It is to be evaluated in the limit of the linear elastic range. Since the bulk modulus in this limit is already known, it is convenient to consider a uniaxial deformation. To begin with, restrictions are made to the low-temperature limit in the absence of entropy contributions. Young's modulus and Poisson's ratio then follow.

Peng, S. T. J.↗

NASA NTRS1987

Mechanical and electrical properties of graphite fiber-epoxy composites made from pristine and bromine intercalated fibers

The mechanical and electrical properties of pristine and bromine intercalated graphite fiber-epoxy composites were compared. The two types of composite were similar in terms of tensile modulus, tensile strength, and Poisson's Ratio. However, the interlaminar shear strength of the brominated composite was 18 percent greater than its pristine counterpart. Only slight differences were observed in flexural properties. A five-fold decrease was observed in the electrical resistivity of the brominated composite parallel to the axis of the fibers, resulting in a unidirectional resistivity of about 90 microOmega/cm. Transverse resistivity was unaffected. Both types of composite were subjected to a simulated lightning strike of 10 KJ (at a peak current of 150 kA), and the composite with the intercalated graphite exhibited less damage.

Jaworske, Donald A.↗

NASA NTRS1985

Investigation of instability, dynamic forces, and effect of dynamic loading on strength of cages for the bearings in the high pressure oxygen turbopumps for the space shuttle main engine

Experiments were performed to determine the effect of cyclic loading on bearing cage strength. A long term working tensile load of approximately 1300 N (300 lbs) was found to be the likely maximum. Higher loads caused a decrease in cage tensile strength after the 125,000 cycle testing period. Poisson's ratio in compression was found to be highly dependent upon the direction of the fiberglass plies. At room temperature the value was 0.15 with the plies and 0.68 across the plies. At -196 C (-321 F), the value with the plies was 0.20. The results of the analyses conducted have again demonstrated the critical need for improved lubrication in the high pressure oxygen turbopump bearings. Lubricant films with low shear strength and low friction coefficients promote cage stability and decrease ball/cage forces during marginal operating conditions. The analysis of the effect of combined bearing loads on ball/cage loads has identified a radial load of 3600 N (800 lbs) as the maximum for the current clearance of the balls and cage pockets. Liquid oxygen impinging on the cage in the direction of rotation was found to enhance cage stability.

Dufrane, K. F.↗

NASA NTRS1988

An exactly solvable model for calculating critical misfit and thickness in epitaxial superlattices - Layers of equal elastic constants and thicknesses

A parabolic interaction potential has been used to develop a model for calculating the misfit dislocation (MD) energy in the case of a superlattice of alternating layers of materials with equal elastic constants and thicknesses. The model, which is believed to be a good one for small misfits and to have some merit for covalent bonded materials, is exactly solvable for the critical thickness above which it is energetically favorable to lose coherency by the introduction of MDs into the interfaces. It was found, for a given misfit f, that the critical thickness for epitaxial superlattices free from their substrate is somewhat more than four times that for a single epilayer on a thick substrate. Furthermore, the critical thickness varies almost inversely with misfit to the power 1.22 when Poisson's ratio is 1/3. It was also shown that the critical misfit f(c) obtained by equating maximal misfit strain and MD energies is a significant overestimate of f(c). The results for a superlattice are compared with those of a thin layer on a thick substrate.

Van Der Merwe, Jan H.↗

NASA NTRS1989

An analytical and experimental investigation of edge delamination in laminates subjected to tension, bending, and torsion

An integrated two-dimensional finite element was developed to calculate interlaminar stresses and strain energy release rates for the study of delamination in composite laminates subjected to uniaxial tension, bending, and torsion loads. Addressed are the formulation, implementation, and verification of the model. Parametric studies were conducted on the effect of Poisson's ratio mismatch between plies and the stacking sequence on interlaminar stress, and on the effect of delamination opening height and delamination length, due to bending, on strain energy release rate for various laminates. A comparison of strain energy release rates in all-graphite and graphite/glass hybrid laminates is included. The preliminary results of laminates subjected to torsion are also included. Fatigue tension tests were conducted on Mode 1 and mixed mode edge-delamination coupons to establish the relationship between fatigue load vs. onset of delamination cycle. The effect on the fatigue delamination onset of different frequencies (1 and 5 Hz) was investigated for glass, graphite,and their hybrid laminates. Although a 20 percent increase in the static onset-of-delamination strength and a 10 percent increase in ultimate strength resulted from hybridizing the all-graphite laminate with a 90 deg glass ply, the fatigue onset is lower in the hybrid laminate than in the all-graphite laminate.

Chan, Wen S.↗

NASA NTRS1989

Weld stresses beyond elastic limit: Materials discontinuity

When welded structures depend on properties beyond the elastic limit to qualify their ultimate safety factor, and weld-parent materials abruptly change at the interface, then stress discontinuity is inevitable. The stress concentration is mildly sensitive to material relative strain hardening and acutely sensitive to applied stress fields. Peak stresses occur on the weld surface, at the interface, and dissipate within a 0.01-inch band. When the stress is intense, the weld will always fracture at the interface. The analysis incorporates a classical mechanics model to more sharply define stress spikes within the bandwidth, and suggests a relative material index and Poisson's ratio related to strain hardening. Implications are discussed which are applicable to industries of high performance structures.

Verderaime, V.↗

NASA NTRS1989

Three-dimensional stress analysis of plain weave composites

Techniques were developed and described for performing three-dimensional finite element analysis of plain weave composites. Emphasized here are aspects of the analysis which are different from analysis of traditional laminated composites, such as the mesh generation and representative unit cells. The analysis was used to study several different variations of plain weaves which illustrate the effects of tow waviness on composite moduli, Poisson's ratios, and internal strain distributions. In-plane moduli decreased almost linearly with increasing tow waviness. The tow waviness was shown to cause large normal and shear strain concentrations in composites subjected to uniaxial load. These strain concentrations may lead to earlier damage initiation than occurs in traditional cross-ply laminates.

Whitcomb, John D.↗

NASA NTRS1988

Prediction of high temperature metal matrix composite ply properties

The application of the finite element method (superelement technique) in conjunction with basic concepts from mechanics of materials theory is demonstrated to predict the thermomechanical behavior of high temperature metal matrix composites (HTMMC). The simulated behavior is used as a basis to establish characteristic properties of a unidirectional composite idealized an as equivalent homogeneous material. The ply properties predicted include: thermal properties (thermal conductivities and thermal expansion coefficients) and mechanical properties (moduli and Poisson's ratio). These properties are compared with those predicted by a simplified, analytical composite micromechanics model. The predictive capabilities of the finite element method and the simplified model are illustrated through the simulation of the thermomechanical behavior of a P100-graphite/copper unidirectional composite at room temperature and near matrix melting temperature. The advantage of the finite element analysis approach is its ability to more precisely represent the composite local geometry and hence capture the subtle effects that are dependent on this. The closed form micromechanics model does a good job at representing the average behavior of the constituents to predict composite behavior.

Caruso, J. J.↗

NASA NTRS1989

Development of a finite element based delamination analysis for laminates subject to extension, bending, and torsion

Delamination is a common failure mode of laminated composite materials. This type of failure frequently occurs at the free edges of laminates where singular interlaminar stresses are developed due to the difference in Poisson's ratios between adjacent plies. Typically the delaminations develop between 90 degree plies and adjacent angle plies. Edge delamination has been studied by several investigators using a variety of techniques. Recently, Chan and Ochoa applied the quasi-three-dimensional finite element model to the analysis of a laminate subject to bending, extension, and torsion. This problem is of particular significance relative to the structural integrity of composite helicopter rotors. The task undertaken was to incorporate Chan and Ochoa's formulation into a Raju Q3DG program. The resulting program is capable of modeling extension, bending, and torsional mechanical loadings as well as thermal and hygroscopic loadings. The addition of the torsional and bending loading capability will provide the capability to perform a delamination analysis of a general unsymmetric laminate containing four cracks, each of a different length. The solutions obtained using this program are evaluated by comparing them with solutions from a full three-dimensional finite element solution. This comparison facilitates the assessment of three dimensional affects such as the warping constraint imposed by the load frame grips. It wlso facilitates the evaluation of the external load representation employed in the Q3D formulation. Finally, strain energy release rates computed from the three-dimensional results are compared with those predicted using the quasi-three-dimensional formulation.

Hooper, Steven J.↗

NASA NTRS1990

Evaluation of EA-934NA with 2.5 percent Cab-O-Sil

Currently, Hysol adhesive EA-934NA is used to bond the Field Joint Protection System on the Shuttle rocket motors at Kennedy Space Center. However, due to processing problems, an adhesive with a higher viscosity is needed to alleviate these difficulties. One possible solution is to add Cab-O-Sil to the current adhesive. The adhesive strength and bond strengths that can be obtained when 2.5 percent Cab-O-Sil is added to adhesive EA-934NA are examined and tested over a range of test temperatures from -20 to 300 F. Tensile adhesion button and lap shear specimens were bonded to D6AC steel and uniaxial tensile specimens (testing for strength, initial tangent modulus, elongation and Poisson's ratio) were prepared using Hysol adhesive EA-934NA with 2.5 percent Cab-O-Sil added. These specimens were tested at -20, 20, 75, 100, 125, 150, 200, 250, and 300 F, respectively. Additional tensile adhesion button specimens bonding Rust-Oleum primed and painted D6AC steel to itself and to cork using adhesive EA-934NA with 2.5 percent Cab-O-Sil added were tested at 20, 75, 125, 200, and 300 F, respectively. Results generally show decreasing strength values with increasing test temperatures. The bond strengths obtained using cork as a substrate were totally dependent on the cohesive strength of the cork.

Caldwell, Gordon A.↗

NASA NTRS1989

On modelling the residual strength of impact damaged, compression loaded laminates

A methodology is presented to predict the residual compression strength of impact damaged composite laminates by considering the competing failure modes of local delamination buckling and compression failure. The minimum delamination buckling load and the location of the first local region to buckle are determined by a Rayleigh-Ritz analysis. The Rayleigh-Ritz analysis is formulated to account for the multiple delamination locations, Poisson's ratio mismatch between sublaminates and possible bending-stretching coupling behavior of the delaminated regions. The compression failure load is determined by a modified maximum strain criterion applied in the delaminated region. The minimum delamination buckling and compression failure loads may be compared to the global buckling load to predict initial failure. For non-catastrophic failures, failure sequences are predicted in an iterative manner. Analytical predictions for sequential failure modes and loads are shown to correlate well with experimental results. A comparative evaluation of various delamination buckling models and their accuracy in predicting experimental results is also presented.

Davidson, B. D.↗

NASA NTRS1991

Deflection And Stress In Preloaded Square Membrane

Theoretical analysis yields equations for transverse deflection of, and stresses in, square membrane subject to both uniform transverse load and tension preloads applied uniformly along the edges. Follows energy/virtual-displacement approach. Basic equation expresses strain energy in membrane as double integral, over x and y coordinates of square, of function of longitudinal strains, shear strain, thickness of membrane, and Young's modulus and Poissons's ratio of membrane material.

Hermida, Alfonso↗

NASA NTRS1991

Estimation of the engineering elastic constants of a directionally solidified superalloy for finite element structural analysis

The temperature-dependent engineering elastic constants of a directionally solidified nickel-base superalloy were estimated from the single-crystal elastic constants of nickel and MAR-MOO2 superalloy by using Wells' method. In this method, the directionally solidified (columnar-grained) nickel-base superalloy was modeled as a transversely isotropic material, and the five independent elastic constants of the transversely isotropic material were determined from the three independent elastic constants of a cubic single crystal. Solidification for both the single crystals and the directionally solidified superalloy was assumed to be along the (001) direction. Temperature-dependent Young's moduli in longitudinal and transverse directions, shear moduli, and Poisson's ratios were tabulated for the directionally solidified nickel-base superalloy. These engineering elastic constants could be used as input for performing finite element structural analysis of directionally solidified turbine engine components.

Abdul-Aziz, Ali↗

NASA NTRS1991

METCAN updates for high temperature composite behavior: Simulation/verification

The continued verification (comparisons with experimental data) of the METCAN (Metal Matrix Composite Analyzer) computer code is updated. Verification includes comparisons at room and high temperatures for two composites, SiC/Ti-15-3 and SiC/Ti-6-4. Specifically, verification of the SiC/Ti-15-3 composite includes comparisons of strength, modulus, and Poisson's ratio as well as stress-strain curves for four laminates at room temperature. High temperature verification includes comparisons of strength and stress-strain curves for two laminates. Verification of SiC/Ti-6-4 is for a transverse room temperature stress-strain curve and comparisons for transverse strength at three temperatures. Results of the verification indicates that METCAN can be used with confidence to simulate the high temperature nonlinear behavior of metal matrix composites.

Lee, H.-J.↗