Arturo Montoya

Finite-element sensitivity for plasticity using complex variable methods

AbstractThe complex variable FEM (ZFEM) has been enhanced in this research to compute derivatives with respect to shape, material properties (elastic modulus, yield stress, plastic modulus, hardening parameters), and loads for a nonlinear solid mechanics model undergoing plastic deformation. This method presents a new and novel approach that uses complex variables to estimate derivatives within an incremental-iterative procedure for the solution of nonlinear finite-element equations. ZFEM offers significant advantages over real-valued finite-element analysis in that highly accurate derivative information may be obtained from a single analysis. The method has been implemented within a commercial finite-element software package using the user element and user material options. A strategy was developed to allow the software’s solver algorithm to handle complex variable operations needed by ZFEM to perform sensitivity analysis. Numerical results confirm the high accuracy of the method through the analysis of ...

Energy Harvesting from Roadways

This paper presents a preview of an ongoing study to develop an energy harvesting system based on piezoelectric elements embedded into the pavements structure. The system development involved designing and testing a number of prototypes in the laboratory under controlled stress conditions. In addition, it involved numerical modeling of the stress distribution in the power generation module and economic analysis of the value of the electric power generated, under a given traffic composition scenario. The results available to date suggest that this technology shows promise in powering LED traffic lights and wireless sensors embedded into pavement structures.

Sensitivity analysis in thermoelastic problems using the complex finite element method

ABSTRACT This article presents the complex finite element method (ZFEM) for the sensitivity analysis of thermoelastic systems. ZFEM, based on the complex Taylor series approach, performs finite element procedures using complex variables such that the response variables (temperature, stress) and their sensitivities with respect to an input parameter of interest (shape, mechanical and thermal properties, loading) are obtained simultaneously. ZFEM offers significant advantages over alternative sensitivity analyses that require direct derivations of the sensitivity formulae, multiple runs, and/or remeshing. To verify the numerical implementation, a hollow cylinder with convective boundary conditions on the inside and outside surface was considered. First-order derivatives of the stress fields were compared with exact solutions to demonstrate the accuracy of ZFEM sensitivities. The results indicate that the ZFEM-based derivatives are of high accuracy, thereby showing its applicability in the design and analysis of thermoelastic problems.

Theoretical and experimental evaluation of two roadway piezoelectric-based energy harvesting prototypes

AbstractThis paper presents the results of a theoretical and experimental study aiming to develop a stress-based roadway energy harvesting system. It describes two prototypes using piezoelectric el...

Development and Evaluation of Piezoelectric Prototypes for Roadway Energy Harvesting

AbstractThis paper describes the development of several piezoelectric prototypes capable of harvesting energy from the action of traffic on roadways. It provides a brief overview of piezoelectric t...

Experimental and finite element assessment of three energy harvesting prototypes for roadways

The transportation infrastructures serve a critical societal need to rapidly move goods and people across the nation. Using these infrastructures as a source of renewable energy by harvesting them from the roadways is a novel idea that has not been fully explored yet. Highway pavements are exposed to energy-potential resources from vehicle vibrations and traffic loading strains. Energy harvesting is a process that captures unused ambient energy such as heat, vibration, stress or movement that would otherwise be lost. Piezoelectric transducers are considered materials for harvesting energy in pavement structures as they convert mechanical strain into low voltage. For this purpose, two types of piezoelectric geometry were evaluated; cylindrical disks and thin film, suitable for compression and bending state of stresses, respectively. Two prototypes including piezoelectric disks connected in series and parallel were evaluated to study the effect of loading frequency and magnitude on output power under compression. Another prototype containing thin piezoelectric film was developed to investigate the potential of energy harvesting in bending condition. Finite element (FE) analysis was conducted to simulate prototypes’ response under loading. The evaluation of the prototypes involves laboratory testing of their power output as a function of stress and FE simulation of their mechanical behavior. The results showed that the energy harvesting modules should be designed to capture vertical compressive stress in pavement instead of tensile stress. Results suggested that voltage is highly dependent on loading magnitude. It was also concluded that piezoelectric stack connected in parallel produces higher current output under similar loading conditions.

A stochastic finite element approach to determine the safety of suspension bridge cables

A new methodology to determine the safety of suspension bridge main cables is proposed and illustrated on a corrosion-deteriorated cable composed of 9061 wires. The approach is the first one incorporating a finite element (FE) model to predict the cable’s failure load, accounting for load recovery due to friction in broken wires and simulating the reduced cables strength as a three dimensional random field. In order to obtain the breaking load of a cable, the load is increased gradually (quasi-static loading) in a cable’s FE model, having wires break a few at a time according to their residual strength. Because of the load transfer to surrounding wires, the breakage of an individual wire affects the stress state inside the surrounding wires. This local damage eventually causes a global reduction in the load carrying capacity of the cable, up to a complete failure. The safety of the cable is determined through a Monte Carlo simulation, in which the reduced strength of the cable is generated for every realization through the Spectral Representation Method (SRM) and is input as a material parameter in the FE model. The statistics of the load that will drive a suspension bridge cable to failure under a hypothetical deterioration state are obtained at the end of the simulation. INTRODUCTION The structural function of the main cables in suspension bridges is to transfer the tension load, derived by supporting the roadway, to the towers. The main cables are composed of thousands of high strength parallel steel wires with a diameter of approximately 5 mm bundled together in strands either built in situ or prefabricated. These strands are then compacted and tightened together and eventually the cross section of the cable becomes semi-circular. The wires in pristine conditions have a strength ranging from 1570 MPa to 1800 MPa. However with aging, fatigue loading, and harsh environmental conditions, the wires strength reduces significantly (Shi et al., 2007). Field observations of aging suspension bridges indicate serious distress of

Development and Finite Element Analysis of Piezoelectric-Based Prototypes for Harvesting Energy from Roadway Pavement

Energy harvesting is a process that captures unused ambient energy such as heat, vibration, stress or movement that would otherwise be lost. Highway pavements infrastructure exposed to energy-potential resources from vehicle vibrations and traffic loading strains that could be harvested. Piezoelectric transducers (PZT) are potential materials for harvesting energy from pavements as they convert mechanical loading strains into electric voltage. For this purpose, this study is aimed to evaluate two types of piezoelectric prototypes integrated within asphalt mix; cylindrical disks and thin film sheet, suitable for compression and bending state of stresses, respectively. Finite element (FE) analysis was conducted to simulate prototype response in different geometry under dynamic loading. The evaluation of the prototype involves laboratory testing of their power output as a function of stress, and FE simulation of their mechanical behavior. Results suggested that power output is highly dependent on loading frequency and magnitude and PZT geometry but could be promising in powering low-watt LED traffic lights and wireless sensors embedded in pavement particularly in remote areas.

Physics-Based Stochastic Model to Determine the Failure Load of Suspension Bridge Main Cables

A new methodology to determine the safety of suspension bridge main cables is proposed in this paper and illustrated by simulating the failure of a corrosion-deteriorated cable composed of 9,061 wires. The approach is the first to use a finite-element (FE) model to predict the failure load, account for load recovery due to friction in broken wires, and simulate the reduced strength of the cable as a three-dimensional random field. To obtain cable failure load, the load is increased gradually, causing individual wires break according to their residual strength variability. Because of the load transfer to surrounding wires, the breakage of an individual wire affects the stress state of its surrounding wires. Consequently, as the load is increased, this local damage spreads to its immediate vicinity, and eventually the entire cable fails. Because of the complexity of the problem, the critical failure load is determined through a Monte Carlo simulation approach that accounts for the uncertainty in the spatial variability of the residual strength of the individual wires. The probability distribution of the load that will drive a suspension bridge cable to failure is reported and investigated in the paper.