Ricardo L. Actis

Ricardo L. Actis
Washington University in St. Louis | WUSTL , Wash U · Department of Mechanical Engineering and Materials Science

DSc

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41
Publications
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Publications

Publications (41)
Article
The effects of small notches on the predicted fatigue life of mechanical and structural components are examined. It is shown that the classical results of Neuber, Peterson and others can be interpreted to mean integral averages of stresses or strains over small volumes that depend on the solution of a problem of elasticity. This interpretation perm...
Article
Simulation governance is discussed from the perspectives of formulation and application of design rules in structural, mechanical and aerospace engineering. The key technical requirements are described in the context of what is variously called validation pyramid, building block method and validation experiment hierarchy and illustrated by an examp...
Article
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The global maritime operating environment of U.S. Naval Aviation assets necessitates their prolonged exposure to severe corrosive environments. The resulting corrosion damage on flight critical structural components has a significant adverse impact on fleet readiness and total ownership costs. To address these issues, NAVAIR has initiated a multiye...
Article
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There is evidence that appropriate footwear is an important factor in the prevention of foot pain in otherwise healthy people or foot ulcers in people with diabetes and peripheral neuropathy. A standard care for reducing forefoot plantar pressure is the utilization of orthotic devices such as total contact inserts (TCI) with therapeutic footwear. M...
Article
a b s t r a c t An overview of the general considerations underlying the selection of mathematical models and the methods used for estimation and control of the associated errors and the requisite technical capabilities are presented. An example that illustrates the main points of the paper is presented.
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Full-text available
The primary objective of conservative care for the diabetic foot is to protect the foot from excessive pressures. Pressure reduction and redistribution may be achieved by designing and fabricating orthotic devices based on foot structure, tissue mechanics, and external loads on the diabetic foot. The purpose of this paper is to describe the process...
Article
Procedures for verification and validation through adaptive control of the errors of discretization and idealization in finite element analysis (FEA), guided by feedback information, are discussed. A hierarchic framework for the construction of sequences of finite element spaces and working models is outlined and an example is presented.
Conference Paper
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
Article
The development of efficient and reliable methods for the design and analysis of fastened structural connections and bonded joints is among the most important and most challenging problems in aerospace applications because these connections are common sites of failure initiation and there is a complicated nonlinear interaction between the fasteners...
Article
This paper illustrates an example of a very fruitful effort of an industry research team in identifying and filling an analysis tool requirement in the area of composite bonded joints. The Composites Affordability Initiative, an Air Force sponsored joint aeronautics industry program, identified an analysis need for the rapid sizing of composite bon...
Article
The solution to the Laplace operator in three-dimensional domains in the vicinity of straight edges is presented as an asymptotic expansion involving eigenpairs with their coefficients called edge flux intensity functions (EFIFs). The eigenpairs are identical to their two-dimensional counterparts over a plane perpendicular to the edge. Extraction o...
Conference Paper
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Higher order (p-version) finite element methods have been shown to be clearly superior to low order finite element methods when properly applied. However, realization of the full benefits of p-version finite elements for general 3-D geometries requires the careful construction and control of the mesh. A 2-D elasticity problem with curved boundary i...
Article
The definition, essential properties and formulation of hierarchic models for laminated plates and shells are presented. The hierarchic models satisfy three essential requirements: approximability; asymptotic consistency, and optimality of convergence rate. Aspects of implementation are discussed and the performance characteristics are illustrated...
Article
Background: Magnetic resonance imaging tissue tagging is a relatively recent methodology that describes ventricular systolic function in terms of intramyocardial ventricular deformation. Because the analysis involves the use of many intramyocardial points to describe systolic deformation, it is theoretically more sensitive at describing subtle dif...
Article
Full-text available
The principal objective of this investigation was to provide a reliable and efficient prototype software for the engineering design and analysis of multilayered composite shells, capable of modeling linear and nonlinear behavior in three dimensions. In addition, it should be capable of assessing the quality of the solution and providing feedback on...
Article
Prediction and measurement of residuum shape change inside the prosthesis under various loading conditions is important for prosthesis design and evaluation. Residual limb surface measurements with the prosthesis in situ were used for construction of a finite element model (FEM). These surface measurements were obtained from volumetric computed tom...
Article
Objectives: To determine nonlinear material properties of passive, diastolic myocardium using magnetic resonance imaging (MRI) tissue-tagging, finite element analysis (FEA) and nonlinear optimization. Background: Alterations in the diastolic material properties of myocardium may pre-date the onset of or exist exclusive of systolic ventricular dy...
Article
The use of finite element analysis (FEA) software products in mechanical and structural design are examined. It is found that current FEA software products are being under-utilized because they do not satisfy the requirements of the design process well. Specifications for future FEA software products are outlined.
Article
A method is developed and validated for approximating continuous smooth distributions of finite strains in the ventricles from the deformations of magnetic resonance imaging (MRI) tissue tagging "tag lines" or "tag surfaces." Tag lines and intersections of orthogonal tag lines are determined using a semiautomated algorithm. Three-dimensional (3-D)...
Article
Until very recently, computer codes offering nonlinear capabilities were based on the h-version of the finite clement method. In this paper we describe an algorithm and its implementation based on the p-version of the finite element method The functionalities to be discussed are inelastic material behavior based on the deformation theory of plastic...
Article
Passive myocardial material properties have been measured previously by subjecting test samples of myocardium to in vitro load-deformation analysis or, in the intact heart, by pressure-volume relationships. A new method for determining passive material properties, described in this paper, couples a p-version finite element model of the heart, a non...
Article
A 3D, nonlinear finite element (FE) model of the diastolic canine heart was constructed from multislice magnetic resonance images (MRI). The model was solved using the p-version of the FE method to predict stress and deformation in diastole. Finite element models were employed in an 'inverse' problem to estimate the nonlinear material properties of...
Article
Prior to this project, the p-version of the finite element method was known to be effective for linear analyses, but had not been used for solving nonlinear problems. Computer codes offering inelastic analysis capabilities were based on the h-version of the finite element method exclusively. Proper use of these codes requires a very substantial eng...
Conference Paper
An algorithm is described to compute continuous, transmural distributions of finite strains from tagged magnetic resonance (MR) images of the heart. Validation is performed by constructing a finite element (FE) model from the undeformed image and simulating complex deformations of the undeformed tags and intersections. Strains are calculated from t...
Article
A surface peripheral crack of an annular plate is modelled as a local rotational flexibility for vibration analysis. Computed values of the local stiffness are very close to those computed by using strain energy arguments and data for beam-like structures. From the solution of the appropriate eigenvalue problem, the decrement of the fundamental nat...
Article
A new experimental method for the evaluation of myocardial constitutive models combines magnetic resonance (MR) radiofrequency (RF) tissue-tagging techniques with iterative two-dimensional (2-D) nonlinear finite element (FE) analysis. For demonstration, a nonlinear isotropic constitutive model for passive diastolic expansion in the in vivo canine h...
Article
The effects of direct ventricular interaction and interaction mediated by the pericardium on the diastolic left ventricle (LV) were quantified using idealized models of five pathologic conditions. Two-dimensional (2D) mathematical models were constructed in long and short axis views of four pathologic LV conditions and the normal heart (NL): dilate...
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Full-text available
This paper presents recent developments in advanced analysis methods for the computation of stress site damage. The method of solution is based on the p-version of the finite element method. Its implementation was designed to permit extraction of linear stress intensity factors using a superconvergent extraction method (known as the contour integra...
Article
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The solution of small-strain elastic-plastic stress analysis problems by the p-version of the finite element method is discussed. The formulation is based on the deformation theory of plasticity and the displacement method. Practical realization of controlling discretization errors for elastic-plastic problems is the main focus of the paper. Numeri...
Article
The formulation of a hierarchic sequence of models for bidirectional composites in cylindrical bending is presented and their performance is demonstrated on the basis of the degree to which the equilibrium equations of two-dimensional elasticity are satisfied. A numerical example is presented.
Article
The principles governing the formulation of hierarchic models for laminated composites are discussed. The essential features of the hierarchic models described herein are: (1) the exact solutions corresponding to the hierarchic sequence of models converge to the exact solution of the corresponding problem of elasticity for a fixed laminate thicknes...
Article
Full-text available
The research conducted in the formulation of hierarchic models for laminated plates is described. The work is an extension of the work done for laminated strips. The use of a single parameter, beta, is investigated that represents the degree to which the equilibrium equations of three dimensional elasticity are satisfied. The powers of beta identif...
Article
A crack in a vibrating beam produces a change in stiffness depending upon the crack is open or close. If the crack opens and closes with the vibration, a non-linear behavior takes place. The presence of closing cracks can be detected by analyzing the spectrum response for a given forcing function, even through the change in natural frequency associ...
Article
Full-text available
Key issues pertaining to the representation of geometrical features of solid bodies will be discussed from the perspective of design and development of finite element analysis (FEA) software for industrial applications. The authors' experience with quasi-regional mapping [1] in conjunction with the p-version will be summarized and illustrated by ex...
Article
Full-text available
INTRODUCTION Excessive localized peak plantar pressures (PPP) are known to contribute to skin breakdown in people with diabetes (DM) and peripheral neuropathy (PN). Previous work has shown a correlation between plantar soft tissue thickness (STT) under the metatarsal heads (where most ulcers occur) and PPP in subjects with DM and PN [1,2]. The purp...

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