Papers by Daniel Segalman
A discretization strategy for elastic contact on a half plane has been devised to explore the sig... more A discretization strategy for elastic contact on a half plane has been devised to explore the significance of different friction models on joint-like interface mechanics. It is necessary to verify that discretization and accompanying contact algorithm on known solutions. An extensive comparison of numerical predictions of this model with corresponding 2-D elastic, frictional contact solutions from the literature is presented.
Journal of Intelligent Material Systems and Structures, Nov 1, 1994
The design and analysis of a series of linear actuators based on polymer hydrogel is presented. T... more The design and analysis of a series of linear actuators based on polymer hydrogel is presented. The actuators use arrays of pH sensitive gel fibers together with a fluid irrigation system to locally and rapidly regulate the composition of the solution. A dynamic model is constructed for one of the linear actuators, which includes the polymer gel, fluidic system, and transmission mechanics. Emphasis in the design and mechanical modeling of the actuators is placed on the com plete system including not only the polymer gel, but also on the containment system, irrigation scheme, and servo valving system.
Proceedings of the American Mathematical Society, Sep 1, 1972
Fan has proven an inequality relating the arithmetic and geometric means of (x¡, • • • , x") and ... more Fan has proven an inequality relating the arithmetic and geometric means of (x¡, • • • , x") and (1-*,, • • •, 1-x"), where 0<x,^|, i=l, ■ ■ ■ ,n. Levinson has generalized Fan's inequality; his result involves functions with positive third derivatives on (0, 1). In this paper, the above condition that requires 0<JC¡ísi has been replaced by a condition which only weights the x¡ to the left side of (0, 1) in pairs, and Levinson's differentiability requirement has been replaced by the analogous condition on third differences. 2 Pif(2a-x,.)/ 2Pi-f(l Pi(2a-*i)/t ft) ■ Furthermore, if/"(x)>0 on (0, 2a), then the above inequality reduces to equality if and only if all the x¡ are equal. Ky Fan's inequality is Levinson's inequality with p¡=l, a=\, and f(x) = \ogx. Popoviciu [2] has slightly weakened the differentiability assumption in Levinson's theorem.
When the Morton Salt Mine in Weeks Island, Louisiana was converted into a strategic Petroleum Res... more When the Morton Salt Mine in Weeks Island, Louisiana was converted into a strategic Petroleum Reserve oil reservoir, massive concrete bulkheads were installed to seal the access shafts against oil or water leakage. Recent inspection of these bulkheads has raised questions about their ability to perform satisfactorily in the event of a catastrophic water leak into the mine. Calculations are reported here which examine the response of the five bulkheads to a worst-case scenario of flooding by brine from the surface into the oil reservoir below the bulkheads. These calculations show that, under conservative analysis assumptions, factors of safety under such a load for the bulkheads sealing the service shaft and the two raisebores are close to 1. The Markel incline and production shaft bulkheads exhibit safety factors in excess of 2 and 3, respectively. 10 refs., 24 figs., 3 tabs.
Frictional energy dissipation in joints is an issue of long-standing interest in the effort to pr... more Frictional energy dissipation in joints is an issue of long-standing interest in the effort to predict damping of built up structures. Even obtaining a qualitative understanding of how energy dissipation depends on applied loads has not yet been accomplished. Goodman[].] postulated that in harmonic loading, the energy dissipation per cycle would go as the cube of the amplitude of loading. Though experiment does support a power-law relationship, the exponent tends to be lower than Goodman predicted. Recent calculations discussed here suggest that the cause of that deviation has to do with reshaping of the contact patch over each loading period.
The SNL/AWE joint mechanics workshop, held in Dartington Hall, Totnes, Devon, UK 26-29 April 2009... more The SNL/AWE joint mechanics workshop, held in Dartington Hall, Totnes, Devon, UK 26-29 April 2009 was a follow up to another international joints workshop held in Arlington, Virginia, in October 2006. The preceding workshop focused on identifying what length scales and interactions would be necessary to provide a scientific basis for analyzing and understanding joint mechanics from the atomistic scale on upward. In contrast, the workshop discussed in this report, focused much more on identification and development of methods at longer length scales that can have a nearer term impact on engineering analysis, design, and prediction of the dynamics of jointed structures. Also, the 2009 meeting employed less technical presentation and more break out sessions for developing focused strategies than was the case with the early workshop. Several "challenges" were identified and assignments were made to teams to develop approaches to address those challenges.
AIAA Journal, May 1, 2012
ABSTRACT A reduced order model (ROM) of linearized compressible fluid flow coupled with a von Kar... more ABSTRACT A reduced order model (ROM) of linearized compressible fluid flow coupled with a von Karman plate is developed. Separate ROMs for both the fluid and structure are derived and are coupled through a solid wall boundary condition at the interface boundary. The structural ROM is formulated using the method of quadratic components, which postulates that the full kinematics of the plate can be represented using linear and quadratic terms. The fluid ROM is constructed via a proper orthogonal decomposition method. Both ROMs are further reduced via a Galerkin discretization, and the coupled system is implicitly integrated in time. The coupled model is subsequently compared with previously validated models that used either a linearized plate model with the linearized compressible fluid model or a quasi-static fluid model with the von Karman plate model. The comparisons are conducted in high-Mach-number regimes where the comparison is admissible, and excellent agreement is found. Analysis of the resulting limit cycles shows two sets of discontinuities in the limit cycle amplitudes. These discontinuities have two salient features: a snap through phenomenon in phase space is observed in the higher modes, and the coalescing of several of the lower modes is observed below the critical dynamic pressures followed by a sudden separation above the critical dynamic pressures.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 1993
Springer eBooks, Jul 12, 2017
One of the most frustrating features of joint mechanics is that all the important processes take ... more One of the most frustrating features of joint mechanics is that all the important processes take place precisely where they cannot be seen or measured directly — the interface between contacting bodies. In order to achieve some insight into the mechanisms that give rise to the nonlinearities of joints one naturally turns to analytic or numerical models of interface mechanics. With such models, one can explore the significance of different assumptions of kinematics or surface mechanics and compare those with laboratory experiments on the integrated joints. Among the limitations of such modeling strategies are the twin problems of 1) employing suitable models for friction and 2) solving the resulting equations. There is evidence that the commonly used Coulomb friction model is inconsistent with the experimentally observed behavior of lap joints; it is necessary to explore the use of more complex models. Additionally, even when computing contact and sliding with the relatively simple Coulomb friction model, capturing the evolution of traction fields from one load set to the next in a physically plausible manner has been a continuing challenge. Obtaining fidelity to such path dependence for more complex models would be consequently more difficult. This issue has motivated the research reported here on the source of the difficulty in modeling path-dependent contact and possible solutions. A two-parameter Coulomb friction model is used to test a conventional contact algorithm and a newer one devised specifically to capture path dependence correctly. The evolution of lateral traction during cyclic loading is used to illustrate how the shear traction distribution at each load step evolves from that of the previous.
Applications where O-rings are used to isolate atmospheric environments within a structure are cr... more Applications where O-rings are used to isolate atmospheric environments within a structure are critical to weapon reliability. Failure occurs when gasses are able to travel from one side of the oring to the other. The anticipated cause of failure is the relaxation of the rubber over decades, the reduction in closure force, and the O-ring's consequent inability to offer a barrier to gas transport. A predictive model with tractable complexity has been developed to predict the time over which an O-ring is able to maintain an acceptable value of closure force. c9 W 1. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000. c9 cr, W €33 €33 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United. States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or respolm'bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclared, or represents that its use would not infringe privately ow& rights. Reference herein to any specific commercial product, process, or sem'ce by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
Analytic predictions for damped natural frequencies of a simple viscoelastic structure are compar... more Analytic predictions for damped natural frequencies of a simple viscoelastic structure are compared with measured values. The structure studied is an aluminum channel incorporating a constrained layer of highly viscoelastic polymer. The predictive technique employs a general and systematic method for calculating damping and stiffness matrices using only measured material properties and structure geometry. These matrices are then used to predict the dynamic properties of the structure. This work constitutes the first step in the experimental verification of the analytic method. Future work will demonstrate and test some of the unique capabilities of the analytic method including the ability to predict even the complex modes of viscoelastic structures. The experimental and analytic results are in the form of frequency response functions, and the frequencies and damping of the natural modes. The natural frequencies agreed to within 5%, as expected, and the damping values agreed to within the uncertainty in the properties of the viscoelastic damping material. The measured and predicted mode shapes, as compared using the Modal Assurance Criterion (MAC), also agreed closely. Agreement between the predicted and measured response of the structure studied is very good, and indicating that the analytic technique used is a viable method for modelingmore » viscoelastically damped structures. 10 refs., 6 figs., 6 tabs.« less
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Sep 1, 1998
The von Mises stress is often used as the metric for evaluating design margins, particularly for ... more The von Mises stress is often used as the metric for evaluating design margins, particularly for structures made of ductile materials. For deterministic loads. both static and dynamic, the calculation of von Mises stress is straightforward, as is the resulting calculation of reliability. For loads modeled as random processes, the task is different; the response to such loads is itself a random process and its properties must be determined in terms of those of both the loads and the system. This has been done in the past by Monte Carlo sampling of numerical realizations that reproduce the second order statistics of the problem. Here, we present a method that provides analytic expressions for the probability distributions of von Mises stress which can be evaluated efficiently and with good precision numerically. Further, this new approach has the important advantage of providing the asymptotic properties of the probability distribution.
Iwan models have had some exposure recently in modeling the nonlinear response of individual join... more Iwan models have had some exposure recently in modeling the nonlinear response of individual joints. This popularity can be ascribed to their mathematical simplicity, their versatility, and their ability to capture the important responses of mechanical joints under unidirectional loads. There is a lot of history to this category of model. Masing explored kinematic hardening of metals with a model consisting of ten Jenkins elements in series. Soon after, Prandtl explored the behavior of a continuous distribution of such elements. Ishlinskii explored the mathematical structure of such continuous distributions. Much more recently, Iwan demonstrated practical application of such models in capturing various sorts of metal plasticity. Among the features that make such models interesting is a simple relationship between the asymptotic nature of the integral kernel at small values and the power-law relation between force amplitude and dissipation per cycle in harmonic loading. Iwan provided several differential equations for deducing the kernel from force-displacement relations. Segalman and Starr devised methods for deducing kernels from force-displacement curves of arbitrary Masing models. This is illustrated to generate a BPII model equivalent to the Ramberg-Osgood plasticity model. The Segalman-Starr relationship is used to find relationships among several other plasticity models.
The problem of understanding and modeling the complicated physics underlying the action and respo... more The problem of understanding and modeling the complicated physics underlying the action and response of the interfaces in typical structures under dynamic loading conditions has occupied researchers for many decades. This handbook presents an integrated approach to the goal of dynamic modeling of typical jointed structures, beginning with a mathematical assessment of experimental or simulation data, development of constitutive models to account for load histories to deformation, establishment of kinematic models coupling to the continuum models, and application of finite element analysis leading to dynamic structural simulation. In addition, formulations are discussed to mitigate the very short simulation time steps that appear to be required in numerical simulation for problems such as this. This handbook satisfies the commitment to DOE that Sandia will develop the technical content and write a Joints Handbook. The content will include: (1) Methods for characterizing the nonlinear stiffness and energy dissipation for typical joints used in mechanical systems and components. (2) The methodology will include practical guidance on experiments, and reduced order models that can be used to characterize joint behavior. (3) Examples for typical bolted and screw joints will be provided.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 2014
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Papers by Daniel Segalman