Recent advances in nonlinear passive vibration isolators

Characterization and analysis of delamination fracture in composites: An overview of developments from 1990 to 2001

This paper presents an interlaboratory test campaign organized by the RILEM 182-PEB Technical Committee. In the campaign, 11 different test methods, comprising uniaxial tension/compression, 2-, 3- and 4-point bending and indirecttension tests, were utilized in order to investigate fatigue characteristics of a dense graded asphalt concrete mixture. The testing conditions specified were sinusoidal excitation at 10Hz and 10°C using controlled strain and stress modes. In total, more than 150 fatigue tests were carried out during the investigation. The fatigue test results were analyzed using both classical as well as continuum damage mechanics approaches. The fatigue test results obtained using the classical fatigue approach are considerably influenced by test type and mode of loading (controlled stress or strain) used. Consequently, this approach has limited use in realistic fatigue characterization of bituminous materials and pavement structures. In contrast to the classical approach, models founded on continuum damage theory may serve to isolate intrinsic fatigue characteristics from the influence of so-called biased effects, which are largely caused by the accelerated laboratory testing. The continuum damage models investigated may constitute steps, towards a rational mechanistic fatigue characterization model, which are important for effective future pavement design.

Fatigue of bituminous mixtures

Current asphalt binder specifications lack the ability to characterize asphalt binder damage resistance to fatigue loading. Multiple accelerated testing procedures that attempt to efficiently and accurately characterize the contribution of asphalt binders to mixture fatigue are under investigation. One of these tests, which has received significant acceptance by experts and has been submitted as a draft AASHTO standard, is the linear amplitude sweep (LAS) test. This procedure uses viscoelastic continuum damage mechanics to predict binder fatigue life as a function of strain in the pavement. The LAS test uses cyclic loading with systematically increasing load amplitudes to accelerate damage and provides sufficient data for analysis in less than 30 min. Although results of the current LAS testing protocol are promising, the time and the complex numerical procedures required for the analysis have raised concern. In addition, insufficient damage accumulation was observed when the strain amplitudes proposed in...

Modification and Validation of Linear Amplitude Sweep Test for Binder Fatigue Specification

An efficient method of fitting Prony-series models to viscoelastic experimental data with power-law presmoothing is presented. A direct fitting of a Prony-series function to experimental data without appropriate presmoothing is difficult when the data have significant variance. A power-law series comprising multiple power-law terms is found capable of portraying a globally smooth, broadband viscoelastic behavior with minimal impact from local variance in the data. However, from a computational point of view, a Prony series representation is preferred to a power-law series representation because of the computational efficiency associated with the exponential basis functions of a Prony series. In this paper, a procedure involving presmoothing of experimental data via power-law-series representation followed by fitting of a Prony-series model to the presmoothed data is discussed and illustrated. Discussion focuses on how experimental data with significant variance can be effectively presmoothed through power...

Fitting Prony-Series Viscoelastic Models with Power-Law Presmoothing

A viscoelastic continuum damage model and its application to uniaxial behavior of asphalt concrete

An Analytical Crack-Tip Element for Layered Elastic Structures

A comprehensive constitutive model for asphalt concrete was calibrated that included viscoelasticity, viscoplasticity, and irreversible microstructural damage in unconfined compression. Three different types of laboratory tests were designed and performed to calibrate each of these response components. Small-strain dynamic modulus tests were used to calibrate the undamaged linear viscoelastic properties. Cyclic creep and recovery tests to failure were performed to calibrate the viscoplastic properties. Constant-rate-of-strain tests to failure were used to calibrate the damage behavior. These tests were performed at a wide range of temperatures, loading rates, and stress levels. Upon calibration of each individual response, the model was validated by predicting the results of other constant-rate-of-strain tests at temperatures and strain rates different from those used in the calibrations. The predictions for these different conditions indicate that the comprehensive model can realistically simulate a wide range of asphalt concrete behavior.

Viscoelastic, Viscoplastic, and Damage Modeling of Asphalt Concrete in Unconfined Compression

A study was performed to evaluate whether time-temperature superposition principles would continue to apply to the behavior of asphalt concrete beyond the commonly assumed small strain (<100 μe) limits. A series of unconfined uniaxial compression constant crosshead displacement rate tests were performed to large-strain values. The measured axial stress versus axial strain data were cross-plotted to produce stress versus reduced time master curves and corresponding temperature shift functions at various strain levels to determine the maximum strain level at which time-temperature superposition remains valid. The results suggest that asphalt concrete remains a thermorheologically simple material well into the postpeak region (i.e., that time-temperature superposition is valid throughout the useful stress-strain response). The results further suggest that the temperature shift function aT may be only a weak function of strain level. For many practical engineering purposes, however, the differences between th...

Time-Temperature Superposition for Asphalt Concrete at Large Compressive Strains

A constitutive model based on an extended form of the Schapery continuum damage formulation is currently being evaluated and developed as a comprehensive material model for asphalt concrete. This model considers the viscoelastic, damage, and viscoplastic components of asphalt concrete behavior over the full range conditions of interest for the mechanistic prediction of flexible pavement distresses. The focus of the present paper is limited to the viscoplastic response component at intermediate and high temperatures. The results confirm earlier findings that asphalt concrete in compression is a thermorheologically simple material well into the large strain viscoplastic regime at elevated temperature. The study demonstrates that the proposed viscoplastic model component provides a good representation of the viscoplastic response of asphalt concrete in uniaxial unconfined compression. Given the validity of time-temperature superposition for viscoplastic response, the viscoplastic material parameters can be calibrated from a limited number of uniform time and uniform load creep and recovery tests. Typical viscoplastic material parameters are derived for a representative asphalt concrete mixture.

Richard A. Schapery

Papers

A viscoelastic continuum damage model and its application to uniaxial behavior of asphalt concrete

An Analytical Crack-Tip Element for Layered Elastic Structures

Viscoelastic, Viscoplastic, and Damage Modeling of Asphalt Concrete in Unconfined Compression

Time-Temperature Superposition for Asphalt Concrete at Large Compressive Strains

Viscoplasticity Modeling of Asphalt Concrete Behavior