Publications
Authors: M. A. Castellucci, A. T. Hughes, W. V. Mars
Published: 13/07/2007
Journal: Experimental Mechanics, 48, 1-8, 2008.
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Comparison of Test Specimens for Characterization of Dynamic Properties of Rubber
Abstract
Dynamic material properties inferred via experiment can be strongly influenced by the choice of test specimen geometry unless care is taken to ensure that mechanical fields (stress, strain, etc.) within the specimen adequately reflect the ideal homogeneous deformation state. In this work, finite element models of simple shear, cylindrical compression, simple tension, and bi-conical shear test specimens were analyzed in order to quantify the relative conformity of each specimen to its correspondi...
Dynamic material properties inferred via experiment can be strongly influenced by the choice of test specimen geometry unless care is taken to ensure that mechanical fields (stress, strain, etc.) within the specimen adequately reflect the ideal homogeneous deformation state. In this work, finite element models of simple shear, cylindrical compression, simple tension, and bi-conical shear test specimens were analyzed in order to quantify the relative conformity of each specimen to its corresponding ideal. Three metrics of conformity were evaluated, based respectively on the distributions of stress, strain, and strain energy density. The results show that a simple shear specimen provides superior conformity. Other factors involved in the selection of test specimen geometry are also discussed. Such factors include relative linearity and symmetry of measured stress–strain data, grip slip, and heat build up.
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Authors: W. V. Mars, A. Fatemi
Published: 01/07/2004
Journal: Rubber Chemistry and Technology
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Factors that Affect the Fatigue Life of Rubber: A Literature Survey
Abstract
Many factors are known to influence the mechanical fatigue life of rubber components. Four major categories of factors are reviewed here: the effects of mechanical loading history, environmental effects, effects of rubber formulation, and effects due to dissipative aspects of the constitutive response of rubber. For each category, primary factors are described, and existing literature is presented and reviewed. Rubber's fatigue behavior is extremely sensitive to both the maximum and minimum cycl...
Many factors are known to influence the mechanical fatigue life of rubber components. Four major categories of factors are reviewed here: the effects of mechanical loading history, environmental effects, effects of rubber formulation, and effects due to dissipative aspects of the constitutive response of rubber. For each category, primary factors are described, and existing literature is presented and reviewed. Rubber's fatigue behavior is extremely sensitive to both the maximum and minimum cyclic load limits. Other aspects of the mechanical load history are also discussed, including the effects of static loaded periods (“annealing”), load sequence, multiaxiality, frequency, and loading waveform. Environmental factors can affect both the short and long term fatigue behavior of rubber. The effects of temperature, oxygen, ozone, and static electrical charges are reviewed. A great range of behavior is available by proper manipulation of formulation and processing variables. Effects of elastomer type, filler type and volume fraction, antidegradants, curatives, and vulcanization are discussed. The role of dissipative constitutive behavior in the improvement of fatigue properties of rubber is also reviewed. Four distinct dissipative mechanisms are identified, and their effects on fatigue behavior are described.
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Authors: William Mars, Kevin Barbash, Matthew Wieczorek, Scott Braddock, Joshua Goossens, Ethan Steiner
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Durability of Elastomeric Bushings Computed from Track-Recorded Multi-Channel Road Load Input
Abstract
The qualification requirements of automakers derive from track testing in which road load and moment inputs to a part in x, y and z directions are recorded over a set of driving conditions selected to represent typical operation. Because recorded histories are lengthy, often comprising many millions of time steps, past industry practice has been to specify simplified block cycle schedules for purposes of durability testing or analysis. Simplification, however, depends on imprecise human judgemen...
The qualification requirements of automakers derive from track testing in which road load and moment inputs to a part in x, y and z directions are recorded over a set of driving conditions selected to represent typical operation. Because recorded histories are lengthy, often comprising many millions of time steps, past industry practice has been to specify simplified block cycle schedules for purposes of durability testing or analysis. Simplification, however, depends on imprecise human judgement, and risks fidelity of the inferred life and failure mode relative to actual. Fortunately, virtual methods for fatigue life prediction are available that are capable of processing full, real-time, multiaxial road load histories. Two examples of filled natural rubber ride bushings are considered here to demonstrate. Each bushing is subject to a schedule of 11 distinct recorded track events. Endurica EIETM map building procedures are first used together with a finite element solution to map the 6 channel loading space and to obtain stress/strain solutions at each gridpoint in the load space. EIE is then used with the recorded histories to interpolate from the recorded road load inputs on the bushing to stress-strain history at each element centroid in the finite element model. The interpolated stress-strain histories are then used to compute damage accrual and fatigue life across all 11 events. The computational requirements of this workflow are benchmarked with the outcome that the entire schedule in full detail can be analyzed on a timescale well suited for use at the earliest stages of business development and engineering.
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