Modeling of elastic-viscoplastic bahavior and its finite element implementation

A state variable approach is developed to simulate the isothermal quasi-static mechanical behavior of elastic- viscoplastic materials subject to small deformations. Modeling of monotonic/cyclic loading, strain-rate effect, work hardening, creep, and stress relaxation are investigated. Development of the constitutive equations is based upon Hooke\u27s law, the separation of the total strain into elastic and plastic quantities, and the separation of work hardening into isotropic and kinematic quantities. The formulation consists of three coupled differential equations; a power law measuring viscoplastic strain-rate and two first order equations for isotropic and kinematic hardening. Derivation of, behavior of, and use of the model are discussed. Actual material data from uniaxial monotonic and cyclic tests is simulated numerically. The formulation, excluding kinematic hardening, is also expanded into multiple dimensions and the compression of a cylinder with constrained ends is solved using the finite element method

Study of three-dimensional nonlinear nip mechanics

An understanding of nip pressure and deformed nip geometry is of vital importance to the design of web handling equipment. Axial variations in nip pressure and deformed nip geometry can lead to poor product performance and customer dissatisfaction. This study evaluates these axial variations for two general cases: an identical-hollow-drum design and a classic calendaring design. Both cases include the effects of elastomeric coverings. Comparisons between modelling the resulting axial variations in nip parameters by beam effects or shell effects are evaluated. Evaluations of nip pressure and overdrive/underdrive are performed. Approximate boundary conditions for the study of web wrinkling are proposed based on deformed nip geometry

Empowering Learners to Choose the Difficulty Level of Problems Based on Their Learning Needs

ABSTRACT Research has found that increasing learner control offers several benefits, including increased motivation, attitude, and learning. The goal of the present study was to determine how prior math achievement influences students' selection of the difficulty level of problems within Math Pursuits, a hypermedia learning program. Math Pursuits was designed to help children understand mathematics by discovering how it relates to the world around them. The program presented each learner with an adjustable level of challenge, along with the necessary scaffolding to support success. The researchers hypothesized that students with lower math skills would choose to start with a lower difficultly level; whereas, students with higher math skills would begin the program by choosing a question with a higher level of difficulty. Results supported these hypotheses. This research also examined the motivational framework guiding students' selection of problem difficulty

Applications of DSP to Explicit Dynamic FEA Simulations of Elastically-Dominated Impact Problems

Explicit Dynamic Finite Element techniques are increasingly used for simulating impact events of personal electronic devices such as portable phones and laptop computers. Unfortunately, the elastically-dominated impact behavior of these devices greatly increases the tendency of Explicit Dynamic methods to calculate noisy solutions containing high-frequency ringing, especially for acceleration and contact-force data. For numerous reasons, transient FEA results are often improperly recorded by the analyst, causing corruption by aliasing. If aliasing is avoided, other sources of distortion can still occur. For example, filtering or decimating Explicit Dynamic data typically requires extremely small normalized cutoff frequencies that can cause significant numerical problems for common DSP programs such as MATLAB. This paper presents techniques to combat the unique DSP-related challenges of Explicit Dynamic data and then demonstrates them on a very challenging transient problem of a steel ball impacting a plastic LCD display in a portable phone, correlating simulation and experimental results

Empowering Learners to Choose the Difficulty Level of Problems Based on Their Learning Needs

Research has found that increasing learner control offers several benefits, including increased motivation, attitude, and learning. The goal of the present study was to determine how prior math achievement influences students' selection of the difficulty level of problems within Math Pursuits, a hypermedia learning program. Math Pursuits was designed to help children understand mathematics by discovering how it relates to the world around them. The program presented each learner with an adjustable level of challenge, along with the necessary scaffolding to support success. The researchers hypothesized that students with lower math skills would choose to start with a lower difficultly level; whereas, students with higher math skills would begin the program by choosing a question with a higher level of difficulty. Results supported these hypotheses. This research also examined the motivational framework guiding students' selection of problem difficulty

Achieving sub electron noise in CCD systems by means of digital filtering techniques that lower 1/f pixel correlated noise

Scientific CCDs designed in thick high resistivity silicon (Si) are excellent detectors for astronomy, high energy and nuclear physics, and instrumentation. Many applications can benefit from CCDs ultra low noise readout systems. The present work shows how sub electron noise CCD images can be achieved using digital signal processing techniques. These techniques allow 0. 4 electrons of noise at readout bandwidths of up to 10 Kpixels per second while keeping the full CCD spatial resolution and signal dynamic range. © 2012 Springer Science+Business Media B.V. (outside the USA).Fil: Cancelo, Gustavo Indalecio Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fermi National Accelerator Laboratory; Estados UnidosFil: Estrada, Juan Cruz. Fermi National Accelerator Laboratory; Estados UnidosFil: Fernández Moroni, Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages"; ArgentinaFil: Treptow, Ken. Fermi National Accelerator Laboratory; Estados UnidosFil: Zmuda, Ted. Fermi National Accelerator Laboratory; Estados UnidosFil: Diehl, H. Thomas. Fermi National Accelerator Laboratory; Estados Unido