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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.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Deformation of a metal-matrix tensile coupon with a central slot - An experimental study

A metal-matrix specimen was investigated using high-sensitivity moire interferometry. In-plane displacement fields were analyzed at various load levels from 15 to 95 percent of the failure load. Normal and shear strains were determined from displacement gradients. Highly localized plastic slip zones occured in the ductile aluminum matrix tangent to the ends of the slot. Shear strains in the slip zone were an order of magnitude greater than the largest normal strains in the specimen. The shear-strain concentration factor rose dramatically with the onset of plastic slip and continued to rise gradually with load to 95 percent of the failure load. Upon unloading, shear strains in the slip zone remained precariously high.

Post, Daniel↗
DOE OSTI2020

Transport of coexisting Ni-Cu sulfide liquid and silicate melt in partially molten peridotite

Transport of coexisting sulfide and silicate melts in partially molten peridotite contributes to the redistribution of chalcophile elements within the upper mantle as well as the genesis of magmatic Ni-Cu sulfide deposits, but has not been investigated systematically. Using laboratory experiments, theoretical calculations, and X-ray synchrotron microtomography, this study documents the topology and considers controls on the extraction of two immiscible liquids during partial melting of mantle peridotite. Under hydrostatic conditions, the measured dihedral angle at silicate melt-mineral-mineral junctions is 13.7–21.3°. Silicate melt is distributed along grain edges forming incompletely interconnected melt channels that disconnected by some dead ends at melt fractions ~7–9 vol%. Application of theoretically predicted permeability (k ~10 -14 -10 -16 m 2 ) permits estimation of the extraction velocity of silicate melt of 0.7-11.1 μm/day within a single interconnected melt channel. In the absence of silicate melt, isolated sulfide droplets (3.77 vol%) show a sulfide-olivine-olivine dihedral angle of 91.5–101.3°. However, in the presence of silicate melt, sulfide droplets (average size ~2.53±2.14μm, 1σ) are partially surrounded by silicate melt and stranded in triple junctions or melt pockets due to the limitation of the smallest dimension (0.3μm) of melt channels. Thus, the extraction of sulfide liquid is highly restricted by these dead ends and the smallest dimension of melt channels during porous flow of silicate melt. In contrast, during large-strain shear deformation (strain ~1.6–2.5), initially stranded sulfide droplets were elongated and extracted with silicate melt into liquid-rich sheets with a length of several hundred microns, constantly oriented at 14.3±4.5°to the shear plane and antithetic to the shear direction. The angle is lower than that (18-30°) of those sheets containing sulfide liquid only, indicating that silicate melt dominates liquid-rich sheets. Driven by stress, silicate melt-dominated liquid-rich sheets open the appropriately oriented grain boundaries between silicate minerals, thus providing an efficient pathway for the extraction of sulfide liquid during deformation. When such sheet-like channels remain open, sulfide droplets (> millimeter-scale) can be potentially mobile through high strain domains of the upper mantle, contributing to the addition of chalcophile elements and the fertilization of the lithospheric mantle.

high P-T experiment↗
NASA NTRS1987

Moire interferometry, 1986

Current capabilities of moire interferometry are described. Several examples illustrate this whole-field optical technique for measurements of in-plane displacements. Sensitivity corresponds to moire measurements with gratings of 2400 lines/mm. The examples are taken from studies of composite members, material anomalies, plasticity, joints, micromechanics and strain concentrations. The abundance of high-sensitivity displacement information permits calculation of normal strains and shear strains in the field, including critical zones of very high gradients.

Post, D.↗
NASA NTRS1986

Geodetic measurement of deformation in the central Mojave Desert, California

Data from triangulation and trilateration surveys made during 1934-1982 are used to calculate shear strain rates in the central Mojave Desert of California. For the region between the Helendale and Camp Rock faults the shear strain rate was determined to be 0.16 + or - 0.03 microstrain/yr, with maximum right-lateral shear strain occurring on a plane oriented N41 deg W + or - 5 deg. If this deformation is due to right-lateral motion across the northwest trending local faults, the average shear straining corresponds to a relative displacement of 6.7 + or - 1.3 mm/yr across this portion of the network, accounting for about 12 percent of the predicted 56 mm/yr of relative motion between the North Atlantic and Pacific plates. From the Camp Rock fault eastward across the network there is a transition from significant to very low strain rates. Examination of nine focal mechanisms and their relation to the local geology and the strain data suggests that most of the long-term displacement occurs on the major northwest trending faults oriented nearly along the direction of relative motion between the North American and Pacific plates. Secondary faulting, controlled by a Coulomb-Anderson failure mechanism or by slip on preexisting faults can account for the occurrence of earthquakes on faults of other orientations.

Sauber, Jeanne↗
NASA NTRS1984

Free edge strain concentrations in real composite laminates: Experimental-theoretical correlation

The magnitude of the maximum shear strain at the free edge of axially loaded theta (2)/-theta(2)(s) and (+ or - theta(2) (s) composite laminates was investigated experimentally and numerically to ascertain the actual value of strain concentration in resin matrix laminates and to determine the accuracy of finite element results. Experimental results using moire interferometry show large, but finite, shear strain concentrations at the free edge of graphite-epoxy and graphite-polyimide laminates. Comparison of the experimental results with those obtained using several different finite element representations showed that a four node isoparametric finite element provided the best and most trouble free numerical results. The results indicate that the ratio of maxium shear strain at the free edge to applied axial strain varies with fiber orientation and does not exceed nine for the most critical angle which is 15 deg.

Herakovich, C. T.↗
NASA NTRS1985

Free edge strain concentrations in real composite laminates Experimental-theoretical correlation

The magnitude of the maximum shear strain at the free edge of axially loaded theta (2)/theta(2)(s) and (+ or - theta(2) (s) composite laminates was investigated experimentally and numerically to ascertain the actual value of strain concentration in resin matrix laminates and to determine the accuracy of finite element results. Experimental results using moire interferometry show large, but finite, shear strain concentrations at the free edge of graphite-epoxy and graphite-polyimide laminates. Comparison of the experimental results with those obtained using several different finite element representations showed that a four node isoparametric finite element provided the best and most trouble free numerical results. The results indicate that the ratio of maximum shear strain at the free edge to applied axial strain varies with fiber orientation and does not exceed nine for the most critical angle which is 15 deg.

Herakovich, C. T.↗
NASA NTRS1984

Deformation measurements of composite multi-span beam shear specimens by Moire interferometry

Experimental analyses were performed for determination of in plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight ply beams were subjected to 5 point and 3 point flexure. Whole field measurements were recorded at load levels from about 20% to more than 90% of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole field contour maps of shear strains were obtained by a method developed for these tests. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin rich zones in regions of shear tractions; free edge shear strains in quasi-isotropic specimens in regions of normal stresses; and shear stresses associated with cyclic shear compliances of quasi-isotropic plies in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of relaxation; influence of contact stress distribution; specimen failure; effect of specimen overhang; nonlinearity; and qualities of 5 and 3 point flexure tests.

Post, D.↗
NASA NTRS2003

Viscoelastic Vibration Dampers for Turbomachine Blades

Simple viscoelastic dampers have been invented for use on the root attachments of turbomachine blades. These dampers suppress bending- and torsion-mode blade vibrations, which are excited by unsteady aerodynamic forces during operation. In suppressing vibrations, these dampers reduce fatigue (thereby prolonging blade lifetimes) while reducing noise. These dampers can be installed in new turbomachines or in previously constructed turbomachines, without need for structural modifications. Moreover, because these dampers are not exposed to flows, they do not affect the aerodynamic performances of turbomachines. Figure 1 depicts a basic turbomachine rotor, which includes multiple blades affixed to a hub by means of dovetail root attachments. Prior to mounting of the blades, thin layers of a viscoelastic material are applied to selected areas of the blade roots. Once the blades have been installed in the hub and the rotor is set into rotation, centrifugal force compresses these layers between the mating load-bearing surfaces of the hub and the blade root. The layers of viscoelastic material provide load paths through which the vibration energy of the blade can be dissipated. The viscoelasticity of the material converts mechanical vibration energy into shear strain energy and then from shear strain energy to heat. Of the viscoelastic materials that have been considered thus far for this application, the one of choice is a commercial polyurethane that is available in tape form, coated on one side with an adhesive that facilitates bonding to blade roots. The thickness of the tape can be chosen to suit the specific application. The typical thickness of 0.012 in. (.0.3 mm) is small enough that the tape can fit in the clearance between the mating blade-root and hub surfaces in a typical turbomachine. In an experiment, a blade was mounted in a test fixture designed to simulate the blade-end conditions that prevail in a turbocompressor. Vibrations were excited in the blade by use of an impact hammer, and damping of the vibrations was measured by use of a dynamic signal analyzer. Tests were performed without and with viscoelastic dampers installed in the dovetail root attachment. The results of the measurements, some of which are presented in Figure 2, show that the viscoelastic dampers greatly increased the rate of damping of vibrations. Accordingly, dynamic stresses on rotor blades were significantly reduced, as shown in Figure 2.

Nguyen, Nhan↗
DOE OSTI2020

Dislocation density-based plasticity model from massive discrete dislocation dynamics database

In this work, we present a dislocation density-based strain hardening model for single crystal copper through a systematic coarse-graining analysis of more than 200 discrete dislocation dynamics (DDD) simulations of plastic deformation under uniaxial tension. The proposed constitutive model has two components: a generalized Taylor relation connecting resolved shear stresses to dislocation densities on individual slip systems, and a generalized Kocks-Mecking model for dislocation multiplication. The DDD data strongly suggests a logarithmic dependence of flow stress on the plastic shear strain rate on each slip system, and, equivalently, an exponential dependence of the plastic shear strain rate on the resolved shear stress. Hence the proposed generalized Taylor relation subsumes the Orowan relation for plastic flow. The DDD data also calls for a correction to the Kocks-Mecking model of dislocation multiplication to account for the increase of dislocation density on slip systems with negligible plastic shear strain rate. This is accomplished by allowing the multiplication rate on each slip system to include contributions from the plastic strain rates of the two coplanar slip systems. The resulting constitutive model successfully captures the strain hardening rate dependence on the loading orientation as predicted by the DDD simulations, which is also consistent with existing experiments.

36 MATERIALS SCIENCE↗
NASA NTRS1978

The Application of Strainrange Partitioning Method to Multiaxial Creep-Fatigue Interaction

The method of strain range partitioning was applied to a series of torsional fatigue tests conducted on tubular 304 stainless steel specimens at 1200 F (649 C). Creep strain was superimposed on cycling strain, and the resulting strain range was partitioned into four components: (1) completely reversed plastic shear strain, (2) plastic shear strain followed by creep strain, (3) creep strain followed by plastic strain, and (4) completely reversed creep strain. Each strain component was related to the cyclic life of the material. The experimental procedure used to achieve strain partitioning is described, and the torsional test results are compared to those obtained from axial tests. The damaging effects of the individual strain components were expressed by a linear life fraction rule.

Zamrik, S. Y.↗
NASA NTRS2001

Fracture Behavior of a Stitched Warp-Knit Carbon Fabric Composite

Tests were conducted on several types of fracture specimens made from a carbon/epoxy composite. The composite material was stitched prior to introducing epoxy resin. Boeing, used this material to develop a composite wing box for a transport aircraft in the NASA Advanced Composites Transport Program. The specimens included compact, extended compact, and center notched tension specimens. The specimens were cut from panels with three orientations in order to explore the effects of anisotropy. The panels were made with various thicknesses to represent a wing, skin from tip to root. All fractures were not self-similar depending on specimen type and orientation. Unnotched tension specimens were also tested to measure elastic constants and strengths. The normal and shear strains were calculated on fracture planes using a series representation of strain fields for plane anisotropic crack problems. The fracture parameters were determined using a finite element method. Characteristic distances for critical tension and shear strains were calculated for each specimen and a failure criterion based on the interaction of tension and shear strains was proposed.

Poe, Clarence C., Jr.↗
NASA NTRS1988

Geodetic Measurement of Deformation East of the San Andreas Fault in Central California

Triangulation and trilateration data from two geodetic networks located between the western edge of the Great Valley and the San Andreas fault have been used to calculate shear strain rates in the Diablo Range and to estimate the slip rate along the Calaveras and Paicines faults in Central California. Within the Diablo Range the average shear strain rate was determined for the time period between 1962 and 1982 to be 0.15 + or - 0.08 microrad/yr, with the orientation of the most compressive strain at N 16 deg E + or - 14 deg. The orientation of the principal compressive strain predicted from the azimuth of the major structures in the region is N 25 deg E. It is inferred that the measured strain is due to compression across the folds of this area: the average shear straining corresponds to a relative shortening rate of 4.5 + or - 2.4 mm/yr. From an examination of wellbore breakout orientations and the azimuths of P-axes from earthquake focal mechanisms the inferred orientation of maximum compressive stress was found to be similar to the direction of maximum compressive strain implied by the trend of local fold structures. Results do not support the hypothesis of uniform fault-normal compression within the Coast Ranges. From trilateration measurements made between 1972 and 1987 on lines that are within 10 km of the San Andreas fault, a slip rate of 10 to 12 mm/yr was calculated for the Calaveras-Paicines fault south of Hollister. The slip rate of the Paicines fault decreases to 4 mm/yr near Bitter.

Sauber, Jeanne M.↗
DOE OSTI2025

Machine-learning-informed scattering correlation analysis of sheared colloids

We have carried out theoretical analysis, Monte Carlo simulations and machine-learning analysis to quantify microscopic rearrangements of dilute dispersions of spherical colloidal particles from coherent scattering intensity. Both monodisperse and polydisperse dispersions of colloids were created and underwent a rearrangement consisting of an affine simple shear and non-affine rearrangement using the Monte Carlo method. We calculated the coherent scattering intensity of the dispersions and the correlation function of intensity before and after the rearrangement and generated a large data set of angular correlation functions for varying system parameters, including number density, polydispersity, shear strain and non-affine rearrangement. Singular value decomposition of the data set shows the feasibility of machine-learning inversion from the correlation function for the polydispersity, shear strain and non-affine rearrangement using only three parameters. A Gaussian process regressor is then trained on the data set and can retrieve the affine shear strain, non-affine rearrangement and polydispersity with relative errors of 3%, 1% and 6%, respectively. Altogether, our model provides a framework for quantitative studies of both steady and non-steady microscopic dynamics of colloidal dispersions using coherent scattering methods.

Gaussian process regression↗
NASA NTRS1986

Plastic deformation - Its role in fatigue crack propagation

Recognizing the fact that the effective driving force Delta-K(eff) determines the fatigue crack propagation (FCP) rate and that the shear strain, which is considered to develop due to an occurrence of crack closure, primarily contributes to the plastic deformation, an effort is made here to elucidate the role of plastic deformation in FCP by developing a correlation between the Delta-K(eff) and the applied driving force (Delta-K) with shear strain as variable. The disparity between Delta(K)eff) and Delta-K, which apparently increases with shear strain level, persists at lower values of Delta-K. This suggests a strong influence of the degree of localized deformation on the FCP rates in the near threshold level. Hence, an improvement of FCP rates in the near threshold level should follow an effort that promotes the plastic deformation near the crack tip to a greater degree. This approach could explain the effect of the grain size, microstructure, environment, R-ratio and crack size on the near-threshold FCP rates.

Mazumdar, P. K.↗
NASA NTRS1985

Elastic-plastic deformation of a metal-matrix composite coupon with a center slot

A comprehensive experimental analysis of deformations of the surface of a metal-matrix specimen is reported. The specimen is a 6-ply 0 + or - 45 sub s boron-aluminum tensile coupon with a central slot. Moire interferometry is used for high-sensitivity whole-field measurements of in-plane displacements. Normal and shear strains are calculated from displacement gradients. Displacement fields are analyzed at various load levels from 15% to 95% of the failure load. Deformations of the boron fibers could be distinguished from those of the matrix. Highly localized plastic slip zones occur tangent to the ends of the slot. Shear strains and concurrent transverse compressive strains in the slip zones reach approximately 10% and 1%, respectively. Upon unloading, elastic recovery in surrounding regions causes a reverse plastic shear strain in the slip zone of about 4%. Longitudinal normal strains on the unslotted ligament peak at the slot boundary at about 1% strain. The strain concentration factor at the end of the slot decreases with load level and the advance of plasticity.

Post, D.↗
NASA NTRS1975

The application of 'strain range partitioning method' to torsional creep-fatigue interaction

The method of strain range partitioning was applied to a series of torsional fatigue tests conducted on tubular 304 stainless steel specimens at 1200 F (649 C). Creep strain was superimposed on cycling strain, and the resulting strain range was partitioned into four components; completely reversed plastic shear strain followed by creep strain, creep strain followed by plastic strain and completely reversed creep strain. Each strain component was related to the cyclic life of the material. The paper describes the experimental procedure used to achieve strain partitioning and the torsional test results are compared to those obtained from axial tests. The damaging effects of the individual strain components were expressed by a linear life fraction rule. The shear strain plastic component showed the least detrimental factor when compared to creep strain reversal by plastic strain. In the latter case, a reduction of torsional fatigue life in the order of magnitude of 1.5 was observed.

Zamrik, S. Y.↗
DOE OSTI2020

Slip band characteristics in the presence of grain boundaries in nickel-based superalloy

Shear strain profiles along slip bands in a modified Rolls-Royce nickel superalloy (RR1000) were analyzed for a tensile sample deformed by 2%. The strain increased with distance away from a grain boundary (GB), with maximum shear strain towards the center of the grain, indicating that dislocation nucleation generally occurred in the grain interior. The strain gradients in the neighborhood of the GBs were quantified and generally correlated with rotation about the active slip system line direction. This leads to an ability to determine the active slip system in these regions. The dislocation spacing and pileup stresses were inferred. The dislocation spacing closely follows an Eshelby analytical solution for a single ended pileup of dislocations under an applied stress. The distribution of pileup stress values for GBs of a given misorientation angle follows a log-normal distribution, with no correlation between the pileup stress and the GB misorientation angle. Furthermore, there is no observed correlation between various transmissivity factors and slip band pileup stress. Hence it appears that the obstacle strength of any of the observed GBs is adequate to facilitate the dislocation pileups present in the slip bands. However, slip band transmission does correlate with transmissivity factors, with the current study focusing on the Luster and Morris m’-factor. Observation of strain profiles of transmitted bands indicate dislocation nucleation locations.

36 MATERIALS SCIENCE↗