Publications
Authors: W.V. Mars, M. Isasi, and A. Arriaga
Published: 01/10/2013
Journal: Constitutive Models for Rubber VIII – Gil-Negrete and Alonso, Editors, Pages 355-360, 2013 Taylor & Francis Group, London, ISBN 978-1-138-00072-8
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Loss of stiffness during fatigue and the development of crack precursors
Abstract
Jago (2012) recently reviewed techniques useful for imaging and surveying crack precursors, not only on the surface of a specimen, but also in the bulk. Crack precursors are seen to occur in a range of sizes, with smaller precursors occurring more frequently, and larger precursors occurring less frequently. For example, Mars & Fatemi (2006) reported observations in which precursors of size 20 microns occurred at a volume density of 5000/mm3, and precursors of size 100 microns occurred at a volum...
Jago (2012) recently reviewed techniques useful for imaging and surveying crack precursors, not only on the surface of a specimen, but also in the bulk. Crack precursors are seen to occur in a range of sizes, with smaller precursors occurring more frequently, and larger precursors occurring less frequently. For example, Mars & Fatemi (2006) reported observations in which precursors of size 20 microns occurred at a volume density of 5000/mm3, and precursors of size 100 microns occurred at a volume density of 3/mm3.
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Authors: W.V. Mars, X.Z. Cheng, H. Yang, and L.Q. Zhang,
Published: 01/10/2013
Journal: Constitutive Models for Rubber VIII – Gil-Negrete and Alonso, Editors, Pages 371-376, 2013 Taylor & Francis Group, London, ISBN 978-1-138-00072-8
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Influence of cyclic softening on the energy release rate of an edge crack under simple tension
Abstract
Prior to the advent of finite element analysis for nonlinearly elastic materials at finite strains, the problem of computing the mechanical fields surrounding the tip of a crack in an elastomer was considered completely intractable (Gent and Mars 2013). This limitation, along with recognition that the stress-concentrating power of the crack tip is responsible for crack growth, inspired Rivlin and Thomas (1953) to develop an energetic theory for the analysis of cracks, following Griffith’s orig...
Prior to the advent of finite element analysis for nonlinearly elastic materials at finite strains, the problem of computing the mechanical fields surrounding the tip of a crack in an elastomer was considered completely intractable (Gent and Mars 2013). This limitation, along with recognition that the stress-concentrating power of the crack tip is responsible for crack growth, inspired Rivlin and Thomas (1953) to develop an energetic theory for the analysis of cracks, following Griffith’s original concept (Griffith 1921). The approach considers the supply of energy associated with growth of a crack, and it avoids the need to understand crack tip fields in detail. It has proven so elegant and powerful that it has been widely adopted into practice. For a general overview of fracture mechanics in elastomers, see Lake (2003) or Thomas (1994).
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Authors: WV Mars, D Ostberg
Published: 03/10/2012
Journal: ENDURICA LLC FINDLAY OH (2012)
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Fatigue Damage Analysis of an Elastomeric Tank Track Component
Abstract
Abstract: The backerpad on the Abrams tank track system is an elastomeric cushion that protects the track and has direct contact with the tank’s wheels. The backerpad’s service life is limited by harsh operating conditions, and system designers are challenged to extend that limit. Accordingly, an analysis is demonstrated here of an experimental backerpad’s fatigue performance under the action of a tank roadwheel epeatedly rolling over the pad. First, the elastomer is characterized via tes...
Abstract: The backerpad on the Abrams tank track system is an elastomeric cushion that protects the track and has direct contact with the tank’s wheels. The backerpad’s service life is limited by harsh operating conditions, and system designers are challenged to extend that limit. Accordingly, an analysis is demonstrated here of an experimental backerpad’s fatigue performance under the action of a tank roadwheel epeatedly rolling over the pad. First, the elastomer is characterized via tests that define its fatigue behavior. Next, the multiaxial, variable amplitude duty cycle of the pad through a representative rollover event is computed in ABAQUS/Explicit. Finally, the material characterization and duty cycle are analyzed via the fe-safe/Rubber fatigue life solver to estimate damage accumulation in each finite element of the model. The calculation identifies the location and number of duty cycle repeats associated with the first appearance of 1 mm cracks for the selected duty cycle, providing an example of how fatigue analysis may be applied to understand damage development in elastomeric components.
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Authors: WV Mars
Published: 01/09/2012
Journal: Rubber Chemistry and Technology 85 (2012)(3), 493
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Book Review: Engineering with Rubber, Edited by AN Gent
Abstract
When a text has influenced a large enough audience, for a long enough time, it becomes a classic. We expect that newcomers to the field will enter through this text, and that established professionals will have a well-worn copy in their personal library. Alan Gent's Engineering with Rubber: How to Design Rubber Components is such a classic. It has just been published by Hanser in a 3rd edition, offering a valuable guide to the fundamentals of rubber component mechanical design.
Authors: M Aït-Bachir, WV Mars, E Verron
Published: 01/05/2012
Journal: International Journal of Non-Linear Mechanics 47 (2012)(4), 22-29
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Energy release rate of small cracks in hyperelastic materials
Abstract
The energy release rate of a small crack in an infinite hyperelastic medium, and subjected to large strain multiaxial loading conditions, is derived by considering the balance of configurational stresses acting on two planes: one cutting the center of the crack face, and the other at an infinite distance in front of the crack tip. The analysis establishes that the energy release rate of a small crack is always proportional to the size of the crack, irrespective of the loading conditions and the ...
The energy release rate of a small crack in an infinite hyperelastic medium, and subjected to large strain multiaxial loading conditions, is derived by considering the balance of configurational stresses acting on two planes: one cutting the center of the crack face, and the other at an infinite distance in front of the crack tip. The analysis establishes that the energy release rate of a small crack is always proportional to the size of the crack, irrespective of the loading conditions and the crack orientation. The balance of configurational stresses is illustrated for several benchmark cases including simple extension, pure shear and equibiaxial extension, and for perpendicular and inclined cracks.
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Authors: WV Mars
Published: 01/06/2011
Journal: Rubber Chemistry and Technology 84 (2011)(2), 178-186
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Analysis of Stiffness Variations in Context of Strain-, Stress-, and Energy-Controlled Processes
Abstract
In compounded material systems, such as rubber, a wide range of properties can be achieved by design. This flexibility poses a challenge–how to balance stiffness against other considerations, such as energy dissipation under dynamic loading, fatigue, etc. Negotiating this balance requires that adequate account be taken of how a given mechanical input (i.e., strain, stress, energy) is controlled, and how other mechanical outputs vary as the stiffness changes. We outline here a simple analysis b...
In compounded material systems, such as rubber, a wide range of properties can be achieved by design. This flexibility poses a challenge–how to balance stiffness against other considerations, such as energy dissipation under dynamic loading, fatigue, etc. Negotiating this balance requires that adequate account be taken of how a given mechanical input (i.e., strain, stress, energy) is controlled, and how other mechanical outputs vary as the stiffness changes. We outline here a simple analysis by which these considerations can be managed. The analysis is based on a novel split of the elasticity law into work-conjugate parts: one representing generally that which is to be held constant, and the other representing that which occurs in reaction to imposed control. The split gives rise to a scalar parameter suitable for quantifying the degree to which a given 1D mechanical process is strain-, energy-, or stress-controlled. The physical sense of the parameter is illustrated through the example of a two-spring system, where one spring represents the subject material, and the other represents the mechanical environment in which the material operates. The example shows that the parameter concisely summarizes the effects of the environment on the operating conditions of the material. We also provide a simple example illustrating how the parameter can be used to rank the fatigue performance of a set of compounds, taking into account the stiffness and the test control mode.
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Authors: B Näser, M Kaliske, WV Mars
Published: 01/09/2010
Journal: Tire Science and Technology 38 (2010)(3), 194-212
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Fatigue investigation of elastomeric structures
Abstract
Fatigue crack growth can occur in elastomeric structures whenever cyclic loading is applied. In order to design robust products, sensitivity to fatigue crack growth must be investigated and minimized. The task has two basic components: (1) to define the material behavior through measurements showing how the crack growth rate depends on conditions that drive the crack, and (2) to compute the conditions experienced by the crack. Important features relevant to the analysis of structures include tim...
Fatigue crack growth can occur in elastomeric structures whenever cyclic loading is applied. In order to design robust products, sensitivity to fatigue crack growth must be investigated and minimized. The task has two basic components: (1) to define the material behavior through measurements showing how the crack growth rate depends on conditions that drive the crack, and (2) to compute the conditions experienced by the crack. Important features relevant to the analysis of structures include time-dependent aspects of rubber’s stress-strain behavior (as recently demonstrated via the dwell period effect observed by Harbour et al.), and strain induced crystallization. For the numerical representation, classical fracture mechanical concepts are reviewed and the novel material force approach is introduced. With the material force approach at hand, even dissipative effects of elastomeric materials can be investigated. These complex properties of fatigue crack behavior are illustrated in the context of tire durability simulations as an important field of application.
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Authors: WV Mars
Published: 01/03/2009
Journal: Rubber Chemistry and Technology 82 (2009)(1), 51-61
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Computed dependence of rubber’s fatigue behavior on strain crystallization
Abstract
This work explores the consequences of strain crystallization on rubber's fatigue crack nucleation behavior over an extensive space of operating conditions, including tension and compression loading states, and relaxing and non-relaxing cycles. The study considers, via computation, how the nonlinear elastic stress-strain behavior, the fatigue crack growth characteristics, and the damage accumulation law combine to produce the Haigh diagram and the Cadwell diagram. Four hypothetical materials are...
This work explores the consequences of strain crystallization on rubber's fatigue crack nucleation behavior over an extensive space of operating conditions, including tension and compression loading states, and relaxing and non-relaxing cycles. The study considers, via computation, how the nonlinear elastic stress-strain behavior, the fatigue crack growth characteristics, and the damage accumulation law combine to produce the Haigh diagram and the Cadwell diagram. Four hypothetical materials are studied, which differ in their crystallization and associated fatigue crack growth behavior. The calculations demonstrate that a relatively simple idealization can credibly predict the unique shape and sensitivities of observed fatigue behavior over a wide range of conditions. They also clarify how features of the Haigh and Cadwell diagrams are linked to the occurrence of crystallization and to parameters such as the power-law slope and the fatigue threshold.
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Authors: R. Harbour, A. Fatemi, W. V. Mars
Published: 01/07/2008
Journal: International Journal of Fatigue Vol. 30, Issue 7, July 2008, pp. 1231-1247.
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Fatigue Life Analysis and Predictions in NR And SBR Under Variable Amplitude and Multiaxial Loading Conditions
Abstract
This paper investigates the effects of variable amplitude loading conditions on the fatigue lives of multiaxial rubber specimens. Two filled rubber materials were used and compared to investigate the effects of strain-crystallization on crack development NR, which strain crystallizes, and SBR, which does not. The applicability of Miner’s linear damage rule for predicting fatigue lives of variable amplitude tests in rubber and the use of both scalar and plane-specific equivalence parameters to ...
This paper investigates the effects of variable amplitude loading conditions on the fatigue lives of multiaxial rubber specimens. Two filled rubber materials were used and compared to investigate the effects of strain-crystallization on crack development NR, which strain crystallizes, and SBR, which does not. The applicability of Miner’s linear damage rule for predicting fatigue lives of variable amplitude tests in rubber and the use of both scalar and plane-specific equivalence parameters to characterize fatigue life results were also investigated. A fatigue life prediction approach that utilizes normal strain to find the critical plane and the cracking energy density on that plane to determine fatigue life is introduced and compared to other approaches. The effects of load sequence and temperature on fatigue life, as well as differences in fatigue lives using both stiffness and critical crack length failure criteria are discussed.
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Authors: R. Harbour, A. Fatemi, W. V. Mars
Published: 01/01/2008
Journal: ASME Journal of Engineering Materials and Technology, Vol. 130, 011005 (2008) (11 pages) DOI:10.1115/1.2806276
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Constitutive Behavior and Temperature Effects in NR and SBR Under Variable Amplitude and Multiaxial Loading Conditions
Abstract
Knowledge of the stress response of a material to the applied deformations is necessary for many engineering analysis and applications. This paper addresses the observed effects of load sequencing, Mullins effect, and multiaxial loading on the constitutive behavior of rubber under variable amplitude conditions for a series of experiments using multiaxial ring test specimens. Two filled rubber materials were used and compared in this study; natural rubber, which strain crystallizes, and styrene b...
Knowledge of the stress response of a material to the applied deformations is necessary for many engineering analysis and applications. This paper addresses the observed effects of load sequencing, Mullins effect, and multiaxial loading on the constitutive behavior of rubber under variable amplitude conditions for a series of experiments using multiaxial ring test specimens. Two filled rubber materials were used and compared in this study; natural rubber, which strain crystallizes, and styrene butadiene rubber (SBR), which does not. A pseudoelastic approach is used to model the cyclic stress-strain response for both materials. The implications of inelasticity when using hyperelastic material models are also discussed. Based on temperature results for the multiaxial ring specimen obtained via a thermal imaging system for SBR, a model capable of accurately predicting surface temperature for the multiaxial ring specimen as a function of hysteresis area and test frequency has been developed.
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