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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Behaviour of plate elements based on the first-order shear deformation theory

A new analytical technique to assess the performance of shear deformable elements is presented, which makes it possible to determine a priori whether a given element will lock when used to model thin structures. The role that shear constraints play in determining the behavior of thin elements was established by comparing the results of key numerical tests with the predictions of element behavior made by studying the form of the shear constraints. Conclusions regarding locking behavior and the effects of reduced integration in thin shear deformable elements are presented, including the findings (1) that singularity of the shear stiffness matrix is not sufficient to avoid locking; (2) that the effect of mesh refinement on an element that contains spurious constraints is two-fold; and (3) that reduced integration does not remove spurious constraints but rather relaxes them. The results of the study are in agreement with previous studies of Mindlin plate elements in regarding Lagrangian elements as superior to serendipity elements when either full or reduced integration is employed.

Averill, R. C.↗
NASA NTRS1989

Assessment of shear deformation theories for multilayered composite plates

A review is made of the different approaches used for modeling multilayered composite plates. Discussion focuses on different approaches for developing two-dimensional shear deformation theories; classification of two-dimensional theories based on introducing plausible displacement, strain and/or stress assumptions in the thickness direction; and first-order shear deformation theories based on linear displacement assumptions in the thickness coordinate. Extensive numerical results are presented showing the effects of variation in the lamination and geometric parameters of simply supported composite plates on the accuracy of the static and vibrational responses predicted by six different modeling approaches (based on two-dimensional shear deformation theories). The standard of comparison is taken to be the exact three-dimensional elasticity solutions. Some of the future directions for research on the modeling of multilayered composite plates are outlined.

Noor, Ahmed K.↗
NASA NTRS1976

The Effects of Variable Mass and Geometry, Pretwist, Shear Deformation and Rotatory Inertia on the Resonant Frequencies of Intact Long Bones: A Finite Element Model Analysis

The influence of pretwist, nonuniformities in mass and flexural stiffness, rotatory inertia and shear deformation on the natural frequencies of intact bones is evaluated by means of a linear elastic, finite-element model which has been programmed for solution on the digital computer. Theoretical results are compared to the results on the forced vibration of intact canine radii obtained experimentally by Thompson. Surprisingly, inclusion of fairly large pretwist angles (from -14 to 12 deg for one specimen) had little affect on the first three frequencies of transverse vibration in either the cranial or lateral directions. Inclusion of shear deformation reduced the third-mode frequency in the stiffest (lateral) direction by about six percent, otherwise shear deformation played a minor role in determining natural frequencies. Similarly. rotatory inertia had negligible influence up to the third natural frequency. The predominant influence on the first three natural frequencies of transverse vibration could be attributed to the variations in mass and flexural stiffness along the length of the test specimens. Different effective moduli of elasticity are required to yield correct absolute values for the frequencies which correspond to experimental findings. thus implying the presence of some inhomogeneities in material properties around the bone cross-section and/or along its length.

Young, Donald R.↗
NASA NTRS1992

Vibration of compressively loaded shear deformable flat panels exhibiting initial geometric imperfections

Numerical study results are presented which indicate that, in the prebuckling range, the natural frequency predicted by the shear-deformable plate theory is smaller than that associated with its transverse-shear rigid counterpart. The opposite behavior occurs in the postbuckling/postcritical range. With increasing transverse shear flexibility, greater differences between frequencies predicted by shear deformation and infinitely rigid transverse shear theories emerge. The character of in-plane boundary conditions is a determinant of both increasing/decreasing buckling loads and increasing/decreasing vibratory frequencies.

Librescu, L.↗
NASA NTRS1990

A technique for predicting mode I energy release rates using a first-order shear deformable plate theory

Utilizing a first order shear deformable plate theory, a technique is described for predicting the distribution of the energy release rate along a curved or straight mode I planar crack in the plane of a plate (such as a delamination crack). Accuracy of the technique is assessed by comparing the distributions of energy release rate with those predicted by two- and three-dimensional finite element analyses of double cantilever beam specimens with straight crack fronts.

Davidson, B. D.↗
DOE OSTI2023

A study of adhesive bonding in metal–metal, metal–CFRP, and CFRP–CFRP material combinations under shear deformation: Fracture morphologies and damage mechanisms

Safe design of adhesive joining in multi-materials in engineered structures requires the accumulation of numerous experimental data on the failure behavior of various adhesively-bonded material combinations under different loading conditions. The deep understanding of mechanical performance, fracturing morphologies, and main damage mechanisms is also quintessential for accelerating the development of proper physics-based and multi-scale models for assisting the design. Towards this goal, this work presents a comprehensive characterization of the failure behavior of adhesively-bonded metal–metal, metal–CFRP, and CFRP–CFRP material combinations under global shear deformation via single lap shear testing. Thanks to a synergistic combination of measurement methods by using Digital Imaging Correlation (DIC) and 3D optical profilometry, adhesive features on the adherend after failure were quantified and the main progressive damage mechanisms were identified. The characterization performed in this work provides quantitative data that contributes to a better understanding of shear failure in adhesive bonding across different bi-material combinations. Finally, the obtained results have practical implications, including the potential to enhance adhesive bonding design, identify failure causes in adhesive joints, and develop or validate computational models capable of capturing the observed behavior in various adhesively-bonded materials under global shear deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mass transport in a highly immiscible alloy on extended shear deformation

Forced mixing to a single phase or supersaturated solid solution (SSS) and its prerequisite microstructure evolution in immiscible systems has been a focus of research for both fundamental science and a variety of applications. Controlling the formation of SSS by shear deformation assisted processing could enable a material design beyond conventional equilibrium microstructure in immiscible systems. Here, a highly immiscible (mixing enthalpy of ~ 20 kJ·mol -1 ) Cu-50 at. % Cr binary alloy was employed to investigate the microstructure evolution and localized tendencies of SSS during severe shear deformation. The present results demonstrate distinctive microstructure refinement process in each phase and how they lead to localized SSS as a function of shear strain. Preferential dynamic recrystallization occurs in the softer Cu phase due to strain localization, leading to substantial grain refinement. The refinement of Cr phase in the top-most layer, however, is enabled by the progressive evolution of grain lamination, splitting, and fragmentation as a function of shear strain. The eventual SSS is found to be strongly dependent on the local environments that affect the dislocation activity, including the level of microstructure refinement, the interfacial orientation relationship, hardness difference, and supposed stability of oxidation. Ab initio simulations comfirm that it is more favorable to oxidize Cr than Cu at incoherent Cu/Cr interfaces which then limits the mass transport on an incoherent boundary. Our results shed light on the underpinning mechanism for non-equilibrium mass transport in immiscible systems upon severe deformation that can be applicable to a variety of processing techniques aimed at producing immiscible alloys with superior mechanical properties.

36 MATERIALS SCIENCE↗
NASA NTRS1989

A shear deformable theory of laminated composite shallow shell-type panels and their response analysis. I - Free vibration and buckling

This paper deals with the substantiation of a shear deformable theory of cross-ply laminated composite shallow shells. While the developed theory preserves all the advantages of the first order transverse shear deformation theory it succeeds in eliminating some of its basic shortcomings. The theory is further employed in the analysis of the eigenvibration and static buckling problems of doubly curved shallow panels. In this context, the state space concept is used in conjunction with the Levy method, allowing one to analyze these problems in a unified manner, for a variety of boundary conditions. Numerical results are presented and some pertinent conclusions are formulated.

Librescu, L.↗
NASA NTRS1981

An improved transverse shear deformation theory for laminated antisotropic plates

An improved transverse shear deformation theory for laminated anisotropic plates under bending is presented. The theory eliminates the need for an arbitrarily chosen shear correction factor. For a general laminate with coupled bending and stretching, the constitutive equations connecting resultants with average displacements and rotations are derived. Simplified forms of these relations are also obtained for the special case of a symmetric laminate with uncoupled bending. The governing equation for this special case is obtained as a sixth-order equation for the normal displacement requiring prescription of the three physically natural bounday conditions along each edge. For the limiting case of isotropy, the present theory reduces to an improved version of Mindlin's theory. Numerical results are obtained from the present theory for an example of a laminated plate under cylindrical bending. Comparison with results from exact three-dimensional analysis shows that the present theory is more accurate than other theories of equivalent order.

Murthy, M. V. V.↗
DOE OSTI2022

The Roles of Interface, Adherend, and Adhesive in Plasma- and Other-treated Joints of Metals and FRP Materials Under Shear Deformation

This work investigated the role of interface, adherend, and adhesive in adhesively-bonded metal-metal, metal-CFRTP, and CFRTP-CFRTP combinations with plasma-treated surfaces under shear deformation. To this end, aluminum alloys (AA5052 and AA6061) and short-carbon-fiber-reinforced polyamide 66 (CFRPA66) were used as examples and performed through single lap shear testing. The results showed that air plasma surface treatment can improve the shear behavior of adhesively-bonded AA5052-CFRPA66 and CFRPA66-CFRPA66 joints with about 20% enhanced lap shear strength compared to non-treated cases. Failure surface morphology of plasma-treated CFRPA66 adherend confirmed this improvement by showing an increased amount of adhesive failure than interfacial failure between CFRPA66 and adhesive. But this is not true for AA5052-AA6061 joints with plasma-treated surfaces exhibiting almost no enhanced lap shear strength. This study also showed the importance of selecting a proper surface modification method for the enhancement of adhesive-bonded structures under shear deformation through the analysis of the results in this study and in the literature. For fiber-reinforced polymers (FRPs), improving FRP/adhesive interface may be prioritized via different surface modification methods (e.g., plasma, chemical coating, etc.) than adhesive modification methods. However, for surface-cleaned metals, toughening adhesive via different enhancement methods (e.g., nano-particles, chemical enhancement, etc.) may be more important than improving metal/adhesive interface. These insightful results are valuable in the area of multi-materials joining.

Qiao, Yao↗
DOE OSTI2020

Solid Cylinder Torsion for Large Shear Deformation and Failure of Engineering Materials

Using a thin-walled tube torsion test to characterize a material’s shear response is a well-known technique; however, the thin walled specimen tends to buckle before reaching large shear deformation and failure. An alternative technique is the surface stress method (Nadai 1950; Wu et al. J Test Eval 20:396–402, 1992), which derives a shear stress-strain curve from the torque-angular displacement relationship of a solid cylindrical bar. The solid bar torsion test uniquely stabilizes the deformation which allows us to control and explore very large shear deformation up to failure. However, this method has rarely been considered in the literature, possibly due to the complexity of the analysis and experimental issues such as twist measurement and specimen uniformity.

42 ENGINEERING↗
NASA NTRS1985

A higher-order shear deformation theory of laminated elastic shells

A higher-order shear deformation theory of elastic shells is developed for shells laminated of orthotropic layers. The theory is a modification of the Sanders' theory and accounts for parabolic distribution of the transverse shear strains through thickness of the shell and tangential stress-free boundary conditions on the boundary surfaces of the shell. The Navier-type exact solutions for bending and natural vibration are presented for cylindrical and spherical shells under simply supported boundary conditions.

Reddy, J. N.↗
NASA NTRS1937

Stress Analysis of Beams with Shear Deformation of the Flanges

This report discusses the fundamental action of shear deformation of the flanges on the basis of simplifying assumptions. The theory is developed to the point of giving analytical solutions for simple cases of beams and of skin-stringer panels under axial load. Strain-gage tests on a tension panel and on a beam corresponding to these simple cases are described and the results are compared with analytical results. For wing beams, an approximate method of applying the theory is given. As an alternative, the construction of a mechanical analyzer is advocated.

Kuhn, Paul↗
DOE OSTI2021

Revealing extreme twin-boundary shear deformability in metallic nanocrystals

Metals containing abundant coherent twin boundaries (TBs) are able to sustain substantial plastic deformation without fracture due to shear-induced TB migration and sliding. Retaining ductility in these metals, however, has proven difficult because detwinning rapidly exhausts TB migration mechanisms at large deformation, whereas TB sliding was only evidenced for loading on very specific crystallographic orientations. Here, we reveal the intrinsic shear deformability of twins in nanocrystals using in situ nanomechanical testing and multiscale simulations and report extreme shear deformability through TB sliding up to 364%. Sliding-induced plasticity is manifested for orientations that are generally predicted to favor detwinning and shown to depend critically on geometric inhomogeneities. Normal and shear coupling are further examined to delineate a TB orientation-dependent transition from TB sliding to TB cracking. These dynamic observations reveal unprecedented mechanical properties in nanocrystals, which hold implications for improving metal processing by severe plastic deformation.

36 MATERIALS SCIENCE↗
NASA NTRS1979

Note on the effect of transverse shear deformation in laminated anisotropic plates

The paper describes the development of some computer methods in applied mechanics. It begins with a distribution of primary stresses in laminated plates, followed by a determination of the associated statically consistent transverse shearing stress. The last section deals with the use of an energy principle for the utilization of these expressions for primary and transverse stresses. The purpose of this is to obtain two-dimensional constitutive equations involving transverse shear deformations and transverse shear stress resultants.

Reissner, E.↗
NASA NTRS1986

On mixed and displacement finite element models of a refined shear deformation theory for laminated anisotropic plates

An improved plate theory that accounts for the transverse shear deformation is presented, and mixed and displacement finite element models of the theory are developed. The theory is based on an assumed displacement field in which the inplane displacements are expanded in terms of the thickness coordinate up to the cubic term and the transverse deflection is assumed to be independent of the thickness coordinate. The governing equations of motion for the theory are derived from the Hamilton's principle. The theory eliminates the need for shear correction factors because the transverse shear stresses are represented parabolically. A mixed finite element model that uses independent approximations of the displacements and moments, and a displacement model that uses only displacements as degrees of freedom are developed. A comparison of the numerical results for bending with the exact solutions of the new theory and the three-dimensional elasticity theory shows that the present theory (and hence the finite element models) is more accurate than other plate-theories of the same order.

Reddy, J. N.↗