SEARCH · Engineering Papers

Results for “DEFORMATION”

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 793 records · Page 44

All sources NASA NTRS DOE OSTI

NASA NTRS1982

The use of baseline measurements and geophysical models for the estimation of crustal deformations and the terrestrial reference system

Four possible estimators are investigated for the monitoring of crustal deformations from a combination of repeated baseline length measurements and adopted geophysical models, particularly an absolute motion plate model. The first estimator is an extension of the familiar free adjustment. The next two are Bayesian type estimators, one weak and one strong. Finally, a weighted constraint estimator is presented. The properties of these four estimators are outlined and their physical interpretations discussed. A series of simulations are performed to test the four estimators and to determine whether or not to incorporate a plate model for the monitoring of deformations. The application of these estimations to the maintenance of a new conventional terrestrial reference system is discussed.

Bock, Y.↗

NASA NTRS1983

Plastic deformation and wear process at a surface during unlubricated sliding

The plastic deformation and wear of a 304 stainless steel surface sliding against an aluminum oxide rider with a spherical surface (the radius of curvature: 1.3 cm) were observed by using scanning electron and optical microscopes. Experiments were conducted in a vacuum of one million Pa and in an environment of fifty thousandth Pa of chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step shaped proturbances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. The mechanism for tearing away of the surface layer from the contact area and sliding track contour is explained assuming the simplified process of material removal based on the adhesion theory for the wear of materials. Previously announced in STAR as N82-32735

Yamamoto, T.↗

NASA NTRS1983

Molecular deformation and stress-strain behavior of poly(bisphenol-A-diphenyl sulfone)

The strain-birefringence response of poly(bisphenol-A-diphenyl sulfone) is found to be independent of temperature at temperatures below -100 C; at higher temperatures, the response becomes slightly dependent on temperature, with lower birefringence seen at higher temperatures. The stress-strain behavior and the stress-birefringence response both depend on temperature over the entire testing temperature range (-179 C to 150 C) studied; this dependence, however, is not pronounced. The evidence is seen as suggesting that the polymer molecules respond to deformation by undergoing conformational rearrangements; the mode of the molecular deformation remains unchanged for temperatures of -100 C or lower. At higher temperatures, the average length of the chain segments involved in the rearrangement increases. The stress-strain response is attributed mainly to chain orientation. The entropic contribution deriving from chain orientation at temperatures below -100 C is still substantial. The modest temperature dependence of the stress-strain response suggests that the energy barriers for the chain segments involved in the rearrangement are relatively low.

Hong, S.-D.↗

NASA NTRS1983

Structural variation of proterozoic dikes in central Superior Province: A possible reflection of post-Archean shield deformation

Preliminary work is reported on the use of two structural parameters, dike dip and thickness, as possible depth-of-exposure indicators in the Central Superior Province. The data demonstrate systematic variations in the dip and thickness of 2.6 and 1.14 Ga. dikes across the Central Superior Province and are tentatively interpreted to result from post intrusion deformation. Combination of these results with additional structural and paleomagnetic data from dikes of all gas may permit detailed mapping both spatially and temporally of crustal deformation in this part of the Canadian Shield. Although dike dip and thickness data apparently reflect crustal exposure level as given by host rock metamorphic grade (ranging from subgreenschist to granulite), these post-orogenic dikes themselves are at most only weakly metamorphosed. This requires that regional isotherms dropped dramatically after the Kenoran orogeny (2.65 Ga.) and prior to emplacement of the earlist post-orogenic swarm (Matachewan-Hearst) at 2.6 Ga.

Ernst, R. E.↗

NASA NTRS1984

Geodynamics of crustal deformation and seismotectonic block movements in central Europe

Geological observations reveal the style of neotectonic near-surface stresses and deformations in central Europe. Seismic activity, focal depths and fault plane solutions of earthquakes indicate kinematic reactions within the crust. A crustal deformation model which may account for the Rhine graben systems and the associated seismotectonic block movements in Europe is presented. A computer aided tomography to gravity anomalies is used in determining the crustal stresses in central Europe. Tomographical interpretations of gravity data with respect to seismic stresses are discussed. Kinematics and dynamics are integrated to show that the measured regional stresses in central Europe are derivable from the convection generated traction on the boundary of the elastic spherical shell of the crust as inferred from satellite derived gravity data.

Liu, H. S.↗

NASA NTRS1984

A numerical analysis of contact and limit-point behavior in a class of problems of finite elastic deformation

Finite element methods for the analysis of bifurcations, limit-point behavior, and unilateral frictionless contact of elastic bodies undergoing finite deformation are presented. Particular attention is given to the development and application of Riks-type algorithms for the analysis of limit points and exterior penalty methods for handling the unilateral constraints. Applications focus on the problem of finite axisymmetric deformations, snap-through, and inflation of thick rubber spherical shells.

Endo, T.↗

NASA NTRS1984

Numerical analysis of some problems related to the mechanics of pneumatic tires: Finite deformation/rolling contact of a viscoelastic cylinder and finite deformation of cord-reinforced rubber composites

The formulation and numerical analysis of several problems related to the behavior of pneumatic tires are considered. These problems include the general rolling contact problem of a rubber-like viscoelastic cylinder undergoing finite deformations and the finite deformation of cord-reinforced rubber composites. New finite element models are developed for these problems. Numerical results obtained for several representative cases are presented.

Oden, J. T.↗

NASA NTRS1984

Strain localization during deformation of Westerly granite

A specimen of Westerly granite was cyclically loaded to near failure at 50 MPa confining pressure. Holographic interferometry provided detailed measurements of localized surface deformations during loading and unloading. The data are consistent with deformation occurring primarily elastically at low differential stress; in conjunction with one incipient fault zone between approximately 350 and 520 MPa differential stress; and in conjunction with a second incipient fault zone above 580 MPa and/or during creep. During unloading only one fault zone, that which is active at the intermediate stress levels during loading, is seen to recede.

Brodsky, N. S.↗

NASA NTRS1985

Stability and vibration of isotropic, orthotropic and laminated plates according to a higher-order shear deformation theory

A higher-order shear deformation theory is used to demonstrate the natural frequencies and buckling loads of elastic plates. The theory accounts for parabolic distribution of the transverse shear strains through the thickness of the plate and rotary inertia. Exact solutions of simply supported plates are obtained and the results are compared with the exact solutions of three-dimensional elasticity theory, the first-order shear deformation theory, and the classical plate theory. The present theory predicts the frequencies and buckling loads more accurately when compared to the first-order and classical plate theories.

Reddy, J. N.↗

NASA NTRS1984

Plastic deformation of silicon dendritic web ribbons during the growth

The distribution of slip dislocations in silicon dendritic web ribbons due to plastic deformation during the cooling phase of the growth was studied. The results show the existence of two distinguishable stress regions across the ribbon formed during the plastic deformation stage, namely, shear stress at the ribbon edges and tensile stress at the middle. In addition, slip dislocations caused by shear stress near the edges appear to originate at the twin plane.

Cheng, L. J.↗

NASA NTRS1985

Neogene compressional deformation and possible thrust faulting in southwest Dominican Republic

Analysis of regional and high resolution remote sensing data coupled with detailed field investigations indicates Neogene compressional deformation in the southwest Dominican Republic. Airborne synthetic aperture radar data and high resolution near infrared photography show folds in Tertiary sediments and possible thrust fault scarps implying NE to SW compression in the region. Large road cuts through the scarps allow study of otherwise poorly accessible, heavily vegetated karst terrain. Deformation increases toward scrap fronts where small bedding-plane thrust faults become more numerous. Analysis of mesoscopic faults with slickensides indicates compression oriented between N to S and E to W. The lowermost scarp has highly sheared fault breccia and undeformed frontal talus breccias implying it is the basal thrust into which the higher thrust faults sole. Thus, the scarps probably formed in a regional NE to SW compressional stress regime and are the toes of thrust sheets. Previous workers have suggested that these scarps are ancient shorelines. However, the gross morphology of the scarps differs substantially from well known erosional terraces on the north coast.

Golombek, M. P.↗

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 NTRS1985

Thermal deformation of concentrators in an axisymmetric temperature field

Axisymmetric thermal deformations of paraboloid mirrors, due to heating, are examined for a mirror with a optical axis oriented toward the Sun. A governing differential equation is derived using Mushtari-Donnel-Vlasov simplifications, and a solution is presented which makes it possible to determine the principal deformation characteristics.

Bairamov, R.↗

NASA NTRS1986

Deformational sequence of a portion of the Michipicoten greenstone belt, Chabanel Township, Ontario

Detailed mapping at a scale of one inch = 400 feet is being carried out within a fume kill, having excellent exposure, located in the southwestern portion of the Michipicoten Greenstone Belt near Wawa, Ontario. The rocks are metasediments and metavolcanics of lower greenschist facies. U-Pb geochronology indicates that they are at least 2698 + or - 11 Ma old. The lithologic packages strike northeast to northwest, but the dominant strike is approximately east-west. Sedimentary structures and graded bedding are well preserved, aiding in the structural interpretation of this multiply deformed area. At least six phases of deformation within a relatively small area of the Michipicoten Greenstone Belt have been tentatively identified. These include the following structural features in approximate order of occurrence: (0) soft-sediment structures; (1) regionally overturned rocks, flattened pebbles, bedding parallel cleavage, and early, approximately bedding parallel faults; (2) northwest to north striking cleavage; (3) northeast striking cleavage and associated folds, and at least some late movement on approximately bedding parallel faults; (4) north-northwest and northeast trending faults; and (5) diabase dikes and associated fracture cleavages. Minor displacement of the diabase dikes occurs on faults that appear to be reactivated older structures.

Shrady, C. H.↗

NASA NTRS1986

Abrasion and deformed layer formation of manganese-zinc ferrite in sliding contact with lapping tapes

Wear experiments were conducted using replication electron microscopy and reflection electron diffraction to study abrasion and the deformed layers produced in single-crystal Mn-Zn ferrite simulated heads during contact with lapping tapes. The crystaline state of the head is changed drastically during the abrasion process. Crystalline states ranging from nearly amorphous to highly textured polycrystalline can be produced on the wear surface of a single-crystal Mn-Zn ferrite head. The total thickness of the deformed layer was approximately 0.8 microns. This thickness increased as the load and abrasive grit size increased. The anisotropic wear of the ferrite was found to be inversely proportional to the hardness of the wear surface. The wear was lower in the order 211 111 10 0110. The wear of the ferrite increased markedly with an increase in sliding velocity and abrasive grit size.

Miyoshi, K.↗

NASA NTRS1986

Synsedimentary deformation and thrusting on the eatern margin of the Barberton Greenstone belt, Swaziland

Mapping on the eastern margin of the 3.6 to 3.3 Ga Barberton Greenstone Belt NW Swaziland has revealed a tectonic complex which is more than 5 km thick. The area consists of fault bound units made up of three lithological associations. Some of these were affected by four phases of deformation. Fold structures, foliations, and lineations are associated with the deformation. Sedimentation, geological structures, and evolutionary history of the area are explained.

Lamb, S. H.↗

NASA NTRS1986

An approach to modeling present-day deformation in southern California

This paper presents an approach to modeling the complete, time-dependent deformation in southern California. A variety of techniques are used to include the far-field plate motion, stress relaxation in the asthenosphere, aseismic fault slip within the elastic lithosphere, and the complex, three-dimensional nature of the faults within the southern California region. Among the conclusions of the work here are the following: (1) the data exibit a marginal preference for a relatively thin lithosphere in southern California: (2) the most sensitive determinant for lithospheric thickness and viscosity of the asthenosphere is the rotation rate of the motion vectors toward or away from major faults; (3) the major faults in southern California are slipping at depth, at or near their average Holocene rates; (4) a shallow, active decollement beneath the Transverse Ranges is apparently needed to realistically model the strain changes observed there; and (5) this modeling technique offers the best approach for understanding the complex deformation field in southern California.

Rundle, J. B.↗

NASA NTRS1986

Finite strain calculations of continental deformation. I - Method and general results for convergent zones. II - Comparison with the India-Asia collision zone

The present investigation has the objective to perform numerical experiments on a rheologically simple continuum model for the continental lithosphere. It is attempted to obtain a better understanding of the dynamics of continental deformation. Calculations are presented of crustal thickness distributions, stress, strain, strain rate fields, latitudinal displacements, and finite rotations, taking into account as basis a model for continental collision which treats the litoshphere as a thin viscous layer subject to indenting boundary conditions. The results of this paper support the conclusions of England and McKenzie (1982) regarding the role of gravity in governing the deformation of a thin viscous layer subject to indenting boundary conditions. The results of the experiments are compared with observations of topography, stress and strain rate fields, and palaeomagnetic latitudinal displacements in Asia.

Houseman, G.↗