Robert Mullen

University of South Carolina | USC · Department of Civil & Environmental Engineering

States, counties, and municipalities rely on pavement performance models to forecast future pavement conditions in their jurisdictions. Accurate prediction is essential for budget planning and the identification of candidates for rehabilitation. This study compares the performance of three different approaches to predict pavement conditions: (1) a...

State departments of transportation recognize the need to incorporate pavement structural condition in their pavement performance models and/or decision processes used to select candidate projects for preservation, rehabilitation, or reconstruction at the network level. However, pavement structural condition data are costly to obtain. To this end,...

In construction project management, scheduling plays a crucial role in a project"s success. Construction scheduling and monitoring schemes are used to predict the project"s total duration. For this prediction, the Critical Path Method (CPM) and the Program Evaluation and Review Technique (PERT) are widely used. These methods predict the overall pro...

This paper presents a novel, non-iterative, general formulation for the transient analysis of interacting elastodynamic systems in contact that may exhibit relative motion with respect to each other. The overall system consists of a collection of individual structures (subsystems). Each of the structure is solved at first independently of the other...

A new method to determine the dynamic interaction between the train and track has been presented. The train and the track are considered as different subsystems. The subsystems are solved independently assuming no contact force exists, and the overall solution of the system is obtained enforcing displacement compatibility and dynamic force equilibr...

A new strategy for the mass matrix lumping of enriched elements for explicit transient analysis is presented. It is shown that to satisfy the kinetic energy conservation, the use of zero or negative masses for enriched degrees of freedom of lumped mass matrix may be necessary. For a completely cracked element, by lumping the mass of each side of th...

Several methodologies to count and classify vehicles from video recordings were explored in this research to provide transportation agencies with a safer alternative to collect these data which are needed for traffic engineering and planning studies. In this study, three approaches for detecting and classifying vehicles were investigated: Haar-like...

Video object detection and classification have been a relevant feature in computer science. The primary objective is to train computers to gather and interpret visual information through different discriminant functions. In transportation engineering, monitoring the performance of the transportation system network provides relevant and critical inf...

A major shortcoming to interval uncertainty approaches in computational mechanics is the lack of an interval field to represent uncertainty. This paper introduces the supervised interval field (SIF), a model to quantify spatially and temporally dependent uncertainty using machine learning. We introduce deep learning model architectures that are use...

A well-posed problem in analysis of elastic bodies requires the definition of appropriate constrains of the boundary to prevent rigid body motion. However, one is sometimes presented with the problem of non-self-equilibrated tractions on an elastic body that will cause rigid body motion, while the boundary should remain unconstrained. One such case...

This paper focuses on the analysis of thin plates with uncertain structural parameters modelled as intervals. The plate is assumed to be orthotropic. Interval uncertainty is associated with the Young's modulus of the plate and also with the applied load. Interval Finite Element Method (IFEM) developed in the earlier work for line elements of the au...

A static analysis of structural systems with uncertain parameters is presented. Uncertain load and material parameters of the system are modeled by probability-boxes (or p-boxes), which do not require complete information about the statistical nature of the underlying random process. Arithmetic operations on p-boxes yield guaranteed lower and upper...

The present study focuses on the development of Nonlinear Interval Finite Elements (NIFEM) for beam and frame problems. Three constitutive models have been used in the present study viz. bilinear, Ramberg-Osgood, and cubic models, to illustrate the development of Nonlinear Interval Finite Elements (NIFEM). Interval Finite Element Method (IFEM) has...

We analyze the frequency response of structural dynamic systems with uncertainties in load and material properties. We introduce uncertainties in the system as interval numbers, and use Interval Finite Element Method (IFEM). Overestimation due to dependency is reduced using a new decomposition for the stiffness and mass matrices, as well as for the...

We present a new interval-based formulation for the static analysis of plane stress/strain problems with uncertain parameters in load, material and geometry. We exploit the Interval Finite Element Method (IFEM) to model uncertainties in the system. Overestimation due to dependency among interval variables is reduced using a new decomposition strate...

In this work, the issue of predicting structural behaviour in the presence of geometric uncertainty arising out of fabrication errors and/or thermal changes in trusses and frames is addressed. Geometric uncertainty is expressed as deviations of actual dimensions of system components from their corresponding nominal dimensions (misfitting) and is ex...

This paper presents the adaptation of a semi-implicit time integration scheme that has been reported in the literature and its implementation for use in discrete element methods (DEM). The computational efficiency of DEM methods is primarily associated with the selection of time increment sizes, as dictated by stability requirements, and other fact...

The present study focuses on the development of Nonlinear Interval Finite Elements (NIFEM) for beam and frame problems. Three constitutive models have been used in the present study viz. bilinear, Ramberg-Osgood, and cubic models, to illustrate the development of Nonlinear Interval Finite Elements (NIFEM). The Interval Finite Element Method (IFEM)...

A new class of interval-based computational algorithms for parameter identification under uncertainty in structural engineering problems is presented. The iterative method allows passing directly from uncertain raw measurements to sharp (tight) bound estimates of the unknown parameters by exploiting interval FEMs and adjoint-based optimization tech...

In this work, the issue of predicting structural behaviour in the present of geometric uncertainty arising out of fabrication errors and/or thermal changes in engineering systems is addressed. Geometric uncertainty is expressed as the deviations of actual dimensions of the system components from their corresponding nominal dimensions (misfitting) a...

This paper presents the development of a semi-implicit time integration scheme, originally developed for structural dynamics in the 1970’s, and its implementation for use in Discrete Element Methods (DEM) for rigid particle interaction, and interaction of elastic bodies that are modeled as a cluster of rigid interconnected particles. The method is...

A new method for dynamic response spectrum analysis of a structural system with interval uncertainty is developed. This interval finite-element-based method is capable of obtaining the bounds on dynamic response of a structure with interval uncertainty. The present method is performed using a set-theoretic (interval) formulation to quantify the unc...

When available information on uncertain system parameters is scarce or limited, intervals might be considered a natural way for uncertainty modeling. Interval Finite Element Methods (IFEM) have been developing in the past decades. In this work, a new IFEM for frame structures is presented. The new formulation aims to further reduce overestimation d...

Finite element models of structures using interval numbers to model parameters uncertainty are presented. The difficulties with simple replacement of real numbers by intervals are reviewed. Methods to overcome these difficulties are presented. Recent advances in providing sharp solution bounds for linear static, linear dynamic, and non-linear stati...

The organization of this conference is supported by the Czech Scientific Foundation, under project No. P105/10/J028 – Development and implementation of a simulation framework for quasi-ductile composites combining short fibers and aligned continuous reinforcement.

This paper describes the reliability analysis of a concrete containment for NPP under a high internal overpressure. There is showed summary of calculation models and calculation methods for the probability analysis of the structural integrity considering degradation effects and high internal overpressure. The probabilistic safety assessment (PSA) l...

Probability-box (p-box) is a rigorous and practical way to represent epistemic sources of uncertainty where the available knowledge is insufficient to construct the required probability distributions. In this paper, interval finite element (FE) methods are combined with the concept of p-box to analyse structures subjected to uncertain loads modelle...

This paper addresses the main challenge in interval computations, which is to minimise the overestimation in the target quantities. When sharp enclosures for the primary variables are achievable in a given formulation, such as the displacements in interval finite elements, the calculated enclosures for secondary or derived quantities, such as stres...

Determination of the mechanical properties of MEMS (microelectromechanical systems) materials is necessary for accurate device design and reliability prediction. This is most unambiguously performed using MEMS-fabricated test specimens and MEMS loading devices. We describe here a wafer-level technique for measuring the bend strength, fracture tough...

Polycrystalline silicon is the most widely used structural material for surface micromachined microelectromechanical systems (MEMS). There are many advantages to using thick polysilicon films; however, due to process equipment limitations, these devices are typically fabricated from polysilicon films less than 3 μm thick. In this work, microelectro...

This paper describes the interval boundary element method treatment of the pointwise discretization error for systems with geometrically generated flux singularities. Worst-case interval bounds are provided for the local discretization error for all elements except for the element with a singular flux solution, for which the flux intensity factor i...

This paper considers structural reliability assessment when statistical parameters of distribution functions can not be determined precisely due to epistemic uncertainty. Uncertainties in parameter estimates are modeled by interval bounds constructed from confidence intervals. Reliability analysis needs to consider families of distributions whose p...

Imprecise probability identifies a number of various mathematical frameworks for making decisions when precise probabilities (or PDF) are not known. Imprecise probabilities are normally associated with epistemic sources of uncertainty where the available knowledge is insufficient to construct precise probabilities. While there is no "unified theory...

Solutions to partial differential equations describing behavior of physical systems are often imprecise. This uncertainty is due to numerical approximations and uncertainty in physical parameters. In elastostatics, these parameters include uncertain material behavior, uncertain boundary conditions, and uncertain geometry of the system. This paper a...

In this work, point-wise discretization error is bounded via interval approach for the elasticity problem using interval boundary element formulation. The formulation allows for computation of the worst case bounds on the boundary values for the elasticity problem. From these bounds the worst case bounds on the true solution at any point in the dom...

In this paper, a method to account for the point-wise discretization error in the solution for boundary element method is developed. Interval methods are used to enclose the boundary integral equation and a sharp parametric solver for the interval linear system of equations is presented. The developed method does not assume any special properties b...

In engineering, most governing partial differential equations for physical systems are solved using finite element or finite difference methods. Applications of interval methods have been explored in finite element analysis to model systems with parametric uncertainties and to account for the impact of truncation error on the solutions. An alternat...

Static analysis is an essential procedure to design a structure. Using static analysis, the structure's response to the applied external forces is obtained. This response includes internal forces/moments and internal stresses that are used in the design process. However, the mechanical characteristics of the structure possess uncertainties that alt...

In engineering most partial differential equations are solved using numerical methods. Throughout the years finite element method emerged as the most widely used numerical technique to obtain discrete solutions to partial differential equations. An alternative method to the finite element method is the boundary element method. In boundary element f...

Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. The associated stresses produce spalling in ceramics, e.g., plasma-sprayed ZrO2-Y2O3, Al2O3-TiO2, and porcelain enamel. The off-axis effec...

High quality Sicceramic foams, which have only recently become available, have for the first time made possible the construction of low density ceramic fiber-ceramic foam sandwiches for high temperatureapplications. This report describes the construction of some ceramic fiber-ceramic foam structures and the preliminary measurement of strength a tel...

A set of 12.7 mm (0.5 in.) diameter stainless steel tubes were coated with ceramic and expanded. The bond cast was 0.08 to 0.13 mm (0.003 to 0.005 in.) NiCrAlY with 0.38 mm (0.015 in.) of ZrO28Y2O3ceramic. Upon pressurization, the tube-substrate yielded and overstressed the coatings in tension. The coatings cracked (i.e., they failed) but did not c...

Predicting outcomes based on a variety of fixation techniques remains problematic in the treatment of mandible fractures. There is inherent difficulty in comparing the hundreds of published articles on the subject because of the large number of variables, including injury patterns, assessment techniques, treatment approach, device selection and app...

This paper presents a new approach for the treatment of parameter uncertainty for linear static structural mechanics problems. Parameter uncertainties are introduced as interval numbers. Interval arithmetic is applied to finite-element method to analyze the structural responses due to uncertain loading, axial and bending stiffness. However, a naive...

Reliable design is dependent on reliable engineering simulation. Many problems of engineering analysis rely on numerical techniques for solving partial differential equations. The foremost method of obtaining approximate solution to partial differential equations is the finite element method. However, alternate approaches, such as the boundary elem...

Latest scientific and engineering advances have started to recognize the need for defining multiple types of uncertainty. Probabilistic modeling cannot handle situations with incomplete or little information on which to evaluate a probability, or when that information is nonspecific, ambiguous, or conflicting [12], [47], [50]. Many interval-based u...

Frequency analysis of a structural system with bounded uncertainty is presented. An interval (set-theoretic) formulation is used to quantify the uncertainty present in the structure's parameters such as material properties. Independent variations for each element are considered. Using the developed interval finite-element method, it is proven that,...

Nickel/graphite cells consisting of graphite cores and nickel cell walls were formed into form lightweight cell composite samples by hot-pressing in reducing atmosphere. In the composite samples, the cells walls were diffusion-bonded to form a continuous metal-matrix. The composite density ranged from 2 to 4 g/cm3. Mechanical properties of the comp...

In engineering, most governing partial differential equations of physical systems are solved using finite element or finite difference methods. Applications of interval methods have been explored in finite element analysis to model systems with uncertainty in parameters and to account for the impact truncation error on solutions. An alternative to...

In this paper we discuss the benefits of using rubber-modified asphalt concrete in high-speed railway foundations. We present the results from a series of three-dimensional finite element simulations modeling a high-speed train foundation utilizing various trackbed materials. Four trackbed materials were tested for their relative vibration attenuat...

A new approach for achieving guaranteed reliable results within the context of finite-element approximation of mechanical systems is developed. A reliable analysis requires that all the sources of uncertainty and errors be accommodated. The appropriateness of a partial differential equation to a given physical problem is beyond the scope of this wo...

In a few critical applications, mechanical transmission of power by rotation at low speed is required without leakage at an interface. Herein we examine a device that enables torque to be transmitted across a sealed environmental barrier. The barrier represents the restraint membrane through which the torque is transmitted. The power is transferred...

Future reusable launch vehicles will require advanced structural seals. This includes propulsion seals along edges and hinge lines in hypersonic engines, and control surface seals for movable flaps and elevons on proposed reentry vehicles. Seals must remain in sealing engagement with opposing surfaces, for multiple missions, even though the seal ga...

In order to ensure the safety of a structure, one must provide for adequate strength of structural elements. In addition, one must prevent large unstable deformations such as buckling. In most analyses of buckling, structural properties and applied loads are considered certain. This approach ignores the fact that imperfections and unknown changes i...

This chapter explores the use of interval numbers to account for uncertainties in engineering models. We concentrate on models based on finite element discretization of partial differential equations. Results of such models are used ubiquitously in engineering design. Uncertainties in the results of finite element models can be attributed to the fo...

Rubber disks bonded between flat parallel metal plates are often used as adhesion test specimens; for example, ASTM D 429 1999, Method A. However, the mechanics of adhesion failure (debonding) for this geometry have not previously been fully analyzed. Therefore, a study was conducted to determine the strain energy release rate (tearing energy) for...

Rubber disks bonded between flat parallel metal plates are often used as adhesion test specimens such as ASTMD 429 1999, Method A. However, the mechanics of adhesion failure (debonding) for this geometry have not been fully analyzed previously. Therefore, a study has been conducted of the strain energy release rate (tearing energy) for bonded rubbe...

Accounting for uncertainties in mechanics problems has been accomplished previously by probabilistic methods that may require highly repetitive and time-consuming computations to analyze the behavior of mathematical models. In addition to the repetitions, knowledge of the probability distribution of state variables is often incomplete. This article...

An efficient method for including the impact of uncertain input data along with the impact of truncation errors in finite element calculations is presented. This method is based on the theory of interval numbers. The formulation involves a predictor-corrector approach that allows for wide interval values as input and maintains sharp results during...

A videotape presentation of the flow field in a packed bed of 48 twisted tapes which can be simulated by very thin virtual cylinders has been assembled. The indices of refraction of the oil and the Lucite twisted tapes were closely matched, and the flow was seeded with magnesium oxide particles. Planar laser light projected the flow field in two di...

This paper presents a nontraditional uncertainty treatment for mechanics problems. Uncertainties are introduced as bounded possible values (intervals). Interval finite-element methods, developed by the authors, are used in the present formulation. To account for different types of uncertainties in linear static problems an interval linear system of...

Polysilicon fracture mechanics specimens have been fabricated using standard microelectro-mechanical systems (MEMS) processing techniques, with characteristic dimensions comparable to typical MEMS devices. These specimens are fully integrated with simultaneously fabricated electrostatic actuators that are capable of providing sufficient force to en...

Polysilicon fracture mechanics specimens have been fabricated using standard microelectromechanical systems (MEMS) processin techniques, and thus have characteristic dimensions comparable with typical MEMS devices. These specimens are fully integrate with simultaneously fabricated electrostatic actuators which are capable of providing sufficient fo...

The authors are introducing a new treatment of uncertainty in mechanics problems in a form of intervals. The formulation of interval finite element methods (IFEMs), follows the conventional finite element methods. However, loads nodal geometry and element materials are expressed as interval quantities. In addition, integration of stiffness and load...

: This work presents a new interval based approach for uncertainty treatment in mechanics problems. The paper concentrates on geometric and material uncertainty in static problems. Uncertainty is introduced in a form of interval (tolerance), where the value could be any number between the lower and upper limits of the interval. Obtaining sharp resu...

Accounting for uncertainties in mechanics problems has been accomplished previously by probabilistic methods that may require highly repetitive and time-consuming computations to analyze the behavior of mathematical models. In addition to the repetitions, knowledge of the probability distribution of state variables is often incomplete. This article...

A model is developed for quantifying the size effect due to heterogeneity and anisotropy in polycrystalline films. The Monte Carlo finite element calculations predict the average and standard deviation of the microscopic (local) stress intensity factors and energy release rate of a crack in a columnar aggregate of randomly orientated, perfectly bon...

The authors present a model of the electromechanical performance of bimetallic cantilever microactuators by deriving the relationship between the tip deflection and change in temperature using a simple analytical approach. The model is verified by comparison with finite element analysis and published experimental data. The maximum tip force generat...

In this paper, a new treatment of load uncertainties in structural problems based on fuzzy set theory is introduced. A fuzzy finite-element method (FFEM) for treating uncertain loads in static structural problems is developed. First, the problem is discretized, which results in a system of fuzzy algebraic equations. An efficient algorithm for calcu...

Polysilicon fracture mechanics specimens have been fabricated using standard MEMS (microelectromechanical systems) processing techniques, and as a result, have characteristic dimensions comparable to typical MEMS devices. These specimens are fully integrated with simultaneously fabricated electrostatic actuators which are capable of providing suffi...

A post-test analysis of a set of inside-diameter/outside-diameter (ID/OD) bidirectional brush seals used in three-port wave rotor tests was undertaken to determine brush bristle and configuration wear, pullout, and rotor coating wear. The results suggest that sharp changes in the pressure profiles were not well reflected in bristle tip configuratio...

Despite their mobility differences under occlusal loads, a natural tooth and an implant are often used together to support fixed prostheses. In some situations, tooth/implant-supported partial prostheses include cantilever extensions, especially in the posterior region where the bone is inadequate for placement of an additional implant. In this stu...

A Monte Carlo finite element model is developed for predicting the scatter in the nominal elastic constants of a thin film aggregate of cubic crystals. Universal results for the nominal plane strain Young's modulus and Poisson's ratio are presented as functions of the number of grains within a unit volume, acid two parameters that quantify the leve...

Polysilicon microfracture specimens were fabricated using surface micromachining techniques identical to those used to fabricate microelectromechanical systems (MEMS) devices. The nominal critical J-integral (the critical energy release rate) for crack initiation, Jc, was determined in specimens whose characteristic dimensions were of the same orde...

Attachment clips are commonly used to provide retention for removable implant-supported overdentures. In this study, the effects of attachment clips on occlusal force transmission in four implant-supported overdentures with cantilever extensions were investigated using beam theory. Distributions of moments and of forces in overdenture, clips, canti...

Composites composed of closed solid wall cells enclosing a fluid are examined in this paper. The analysis of their stiffness in compression includes the effects of fluids in the cell interiors. A specialized finite element program is developed to account for the internal pressure. Both two-dimensional and three-dimensional geometries are considered...

Composites of closed metal cells, in which the cells have uniform wall thickness and which confine a fluid in their interior, are modeled using cylindrical cells with square, hexagonal and circular cross sections. The analysis of their predicted mechanical behaviors in compression includes the effects of fluids and pressure in the cell interiors. A...

Polycrystalline silicon is the most widely used structural material for surface micromachined microelectromechanical systems (MEMS). There are many advantages to using thick polysilicon films; however, due to process equipment limitations, these devices are typically fabricated from polysilicon films less than 3 μm thick. In this work, microelectro...

Multiple cracking dissipates energy and thus enhances the toughness of materials and structures composed of relatively brittle constituents. In this paper a biomimetic example is studied, i.e. the fracture behavior of the conch shell (Strombus Gigas). We focus on multiple cracking which occurs in the macroscopic layer on the tensile side of 4-point...

Accounting for uncertainties in mechanics problems has previously been accomplished by probabilistic methods. Such methods can require highly repetitive computations to analyze the behavior of mathematical models. In addition, knowledge of the probability distribution of state variables is often incomplete. In this paper, a new treatment of uncerta...

A fundamental component of computer-based video image analysis for pavement distress evaluation is identification of the type of distress from geometric and textural properties of an area of interest identified during image analysis. This study describes the algorithms used to identify and classify the most common pavement distress types once a pos...

A transient analysis, using the finite element method, is presented to study the behavior of piezoelectric materials, including non-linear plasticity effects. The analysis involves the development of an elastic-plastic constitutive law for piezoelasticity. A mixed implicit-explicit integration scheme is constructed to solve the finite element equat...