Publications
Authors: R. Stocek, W. V. Mars, R. Kipscholl, and C. G. Robertson
Published: 10/10/2017
Journal: Presented at the Fall 192nd Technical Meeting of the Rubber Division, ACS, Cleveland, Ohio
DOI/URL:
Open Link
Characterizing Rubber’s Resistance Against Chip and Cut Behavior
Abstract
Tires in service - especially in rough terrain - show a behavior which is well known as the cut and chip (CC) effect. This work describes unique analytical methods to characterize the fracture in rubber occurring during lab-simulated operation of the tire tread in rough terrain. The new test device controls and records multiple applied loads and displacements during cyclic impact to the surface of a solid rubber wheel to mimic and quantify the cut and chip damage experienced by tire tread compo...
Tires in service - especially in rough terrain - show a behavior which is well known as the cut and chip (CC) effect. This work describes unique analytical methods to characterize the fracture in rubber occurring during lab-simulated operation of the tire tread in rough terrain. The new test device controls and records multiple applied loads and displacements during cyclic impact to the surface of a solid rubber wheel to mimic and quantify the cut and chip damage experienced by tire tread compounds on off-road and poor road conditions. To demonstrate the testing capabilities, characterization results are examined for carbon black filled rubber
compounds suitable for tire tread applications. The instrument provides a reliable method for evaluating the resistance of rubber against CC damage, and it can also be used in full contact mode for measurement of friction and wear.
Read More
Authors: A. Ramachandran, R. P. Wietharn, S.I. Mathew, W. V. Mars, and M. A. Bauman
Published: 10/10/2017
Journal: Presented at the Fall 192nd Technical Meeting of the Rubber Division, ACS, Cleveland, Ohio
DOI/URL:
Open Link
Critical Plane Selection Under Nonrelaxing Simple Tension with Strain Crystallization
Abstract
The orientation of cracks initiating under cyclic loading is normally set by the maximum principal direction of the applied stress. In simple tension, this causes cracks to appear perpendicular to the tension direction. In contrast, for a strain-crystallizing natural rubber compound, we have observed an exception that occurred during nonrelaxing simple tension fatigue tests. In this case, cracks initiated in a markedly different orientation. The specimen used for experimentation was a rectangula...
The orientation of cracks initiating under cyclic loading is normally set by the maximum principal direction of the applied stress. In simple tension, this causes cracks to appear perpendicular to the tension direction. In contrast, for a strain-crystallizing natural rubber compound, we have observed an exception that occurred during nonrelaxing simple tension fatigue tests. In this case, cracks initiated in a markedly different orientation. The specimen used for experimentation was a rectangular flat dumbbell prepared according to the ASTM D4482 Standard. Critical plane analysis of this case, with and without strain crystallization, was
performed with Endurica CL to predict the plane on which crack nucleation is favored. The analysis shows that the nonrelaxation ratio R, and therefore the degree of strain crystallization and associated crack growth rate, depend on plane orientation in a way that predicts the effect. This information is useful as additional validation when comparing fatigue life predictions to experiments, or as a first step towards understanding the loading experienced at the failure location. Nonrelaxing cycles in a rubber that strain crystallizes improve fatigue life, and also cause crack initiation in a direction not perpendicular to the maximum tension direction.
Read More
Authors: C. G. Robertson, R. Stocek, C. Kipscholl, and W. V. Mars
Published: 12/09/2017
Journal: Presented at the Annual Business Meeting and Conference on Tire Science and Technology, Akron, Ohio
DOI/URL:
Open Link
Characterizing the Intrinsic Strength of Natural Rubber / Butadiene Rubber Blends
Abstract
Tires require rubber compounds capable of enduring more than 108 deformation cycles without crack growth. One strategy for evaluating candidate compounds is to measure the intrinsic strength. The intrinsic strength is the residual strength remaining in the material after the strength-enhancing effects of energy dissipation in crack tip fields are removed. If loads stay always below the intrinsic strength (taking proper account of the possibility that the intrinsic strength may degrade with aging...
Tires require rubber compounds capable of enduring more than 108 deformation cycles without crack growth. One strategy for evaluating candidate compounds is to measure the intrinsic strength. The intrinsic strength is the residual strength remaining in the material after the strength-enhancing effects of energy dissipation in crack tip fields are removed. If loads stay always below the intrinsic strength (taking proper account of the possibility that the intrinsic strength may degrade with aging), then cracks cannot grow. Using the cutting protocol proposed originally by Lake and Yeoh, as implemented on a commercial Intrinsic Strength Analyzer, the intrinsic strength is determined for a series of carbon black (CB) reinforced blends of natural rubber (NR) and butadiene rubber (BR) typical of tire applications. The intrinsic strength benefits of the blends over the neat NR and BR compounds are only observed after aging at temperatures in the range from 50 °C to 70 °C, thus providing fresh insights into the widespread durability success of CB-filled NR/BR blends in tire sidewall compounds and commercial truck tire treads.
Read More
Authors: W.V. Mars and M.D. Ellul (2017)
Published: 01/06/2017
Journal: Rubber Chemistry and Technology
DOI/URL:
Open Link
Fatigue Characterization of a Thermoplastic Elastomer
Abstract
The capacity to resist crack development in an olefinic thermoplastic elastomer (TPE) has been measured via a set of experiments that quantify (1) the fracture mechanical strength of the material under quasi-static loads, (2) the rate of growth of a crack under dynamic solicitations as a function of the energy release rate, and (3) the size of crack precursors in new material. Because the subject TPE exhibited strong inelasticity in the stress–strain response, it also was necessary to characte...
The capacity to resist crack development in an olefinic thermoplastic elastomer (TPE) has been measured via a set of experiments that quantify (1) the fracture mechanical strength of the material under quasi-static loads, (2) the rate of growth of a crack under dynamic solicitations as a function of the energy release rate, and (3) the size of crack precursors in new material. Because the subject TPE exhibited strong inelasticity in the stress–strain response, it also was necessary to characterize the development of an inelastic set under cyclic loading as a function of the applied strain. Combined with the multiplicative kinematic split, this additional measurement yields the elastic part of the strain. It also enables engineering calculations to be made of fatigue life.
Read More
Authors: J. R. Goossens, W. V. Mars, G. Smith, P. Heil, S. Braddock, and J. Pilarski
Published: 01/01/2017
Journal: SAE Technical Paper, 2017-01-1857, 2017
DOI/URL:
Open Link
Durability Analysis of 3-Axis Input to Elastomeric Front Lower Control Arm Vertical Ride Bushing
Abstract
Fatigue life prediction of elastomer NVH suspension products has become an operating norm for OEMs and suppliers during the product quoting process and subsequent technical reviews. This paper reviews a critical plane analysis based fatigue simulation methodology for a front lower control arm. Filled natural rubber behaviors were measured and defined for the analysis, including: stress-strain, fatigue crack growth, strain crystallization, fatigue threshold and initial crack precursor size. A se...
Fatigue life prediction of elastomer NVH suspension products has become an operating norm for OEMs and suppliers during the product quoting process and subsequent technical reviews. This paper reviews a critical plane analysis based fatigue simulation methodology for a front lower control arm. Filled natural rubber behaviors were measured and defined for the analysis, including: stress-strain, fatigue crack growth, strain crystallization, fatigue threshold and initial crack precursor size. A series of four distinct single and dual axis bench durability tests were derived from OEM block cycle specifications, and run to end-of-life as determined via a stiffness loss criterion. The tested parts were then sectioned in order to compare developed failure modes with predicted locations of crack initiation. In all cases, failure mode was accurately predicted by the simulation, and predicted fatigue life preceded actual end-of-life by not more than a factor of 1.4 in life.
Read More
Authors: K. P. Barbash and W. V. Mars
Published: 04/04/2016
Journal: SAE Technical Paper, 2016.
DOI/URL:
Open Link
Critical Plane Analysis of Rubber Bushing Durability under Road Loads
Abstract
We demonstrate here an accounting of damage accrual under road loads for a filled natural rubber bushing. The accounting is useful to developers who wish to avoid the typical risks in development programs: either the risk of premature failure, or of costly overdesign. The accounting begins with characterization of the elastomer to quantify governing behaviors: stress-strain response, fatigue crack growth rate, crack precursor size, and strain crystallization. Finite Element Analysis is used to c...
We demonstrate here an accounting of damage accrual under road loads for a filled natural rubber bushing. The accounting is useful to developers who wish to avoid the typical risks in development programs: either the risk of premature failure, or of costly overdesign. The accounting begins with characterization of the elastomer to quantify governing behaviors: stress-strain response, fatigue crack growth rate, crack precursor size, and strain crystallization. Finite Element Analysis is used to construct a nonlinear mapping between loads and strain components within each element. Multiaxial, variable amplitude strain histories are computed from road loads. Damage accrues in this reckoning via the growth of cracks. Crack growth is calculated via integration of a rate law from an initial size to a size marking end-of-life. Multiaxiality is addressed via Critical Plane Analysis, in which damage accrual is computed for all potential crack plane orientations, prior to selecting the most critical orientation and its associated life. Variable amplitudes in the energy release rate history are considered via the application of rainflow counting, which is applied on each potential plane during the critical plane search. The analysis produces estimates of life for each element in the finite element model. These are visualized to identify bushing life and failure mode. Also, the analysis produces a diagnostic database enabling damage sources to be identified with respect to time, space, and orientation, and giving various details of the micromechanics of damage accumulation.
Read More
Authors: Enduirica
Published: 01/06/2015
Journal:
DOI/URL:
Open Link
Why do we call it the Pure Shear test?
Abstract
This experiment is useful for both hyperelastic and fracture mechanical characterizations of rubber. We explain the nomenclature.
Authors: Endurica
Published: 01/06/2015
Journal:
DOI/URL:
Open Link
Comparing Pure Shear and Simple Shear
Abstract
The spin and rate of deformation tensors for these two common testing scenarios are computed and compared.
Authors: A.N. Gent, W.V. Mars, In: James E. Mark, Burak Erman and Mike Roland, Editor(s)
Published: 01/10/2013
Journal: The Science and Technology of Rubber (Fourth Edition), Academic Press, Boston, 2013, Pages 473-516, ISBN 9780123945846, 10.1016/B978-0-12-394584-6.00010-8
DOI/URL:
Open Link
Chapter 10 – Strength of Elastomers
Abstract
This chapter seeks to answer such questions as where and under what conditions does fracture begin, and what laws govern the growth of a crack once it has been initiated? First considered is the initiation of fracture from crack precursors, followed by the rate of development of cracks after initiation. The phenomenon of accelerated growth under dynamic stressing is also discussed. Then the effects of applied stresses and temperature of measurement are discussed, as well as other effects of the ...
This chapter seeks to answer such questions as where and under what conditions does fracture begin, and what laws govern the growth of a crack once it has been initiated? First considered is the initiation of fracture from crack precursors, followed by the rate of development of cracks after initiation. The phenomenon of accelerated growth under dynamic stressing is also discussed. Then the effects of applied stresses and temperature of measurement are discussed, as well as other effects of the environment, notably the destructive action of ozone. Finally, a brief survey of abrasive wear is given.
Read More
Authors: William V. Mars, Marion G. Pottinger
Published: 01/10/2013
Journal: Tire Science and Technology
DOI/URL:
Open Link
John R. Luchini — Tire Science Giant
Abstract
Dr. John Remo Luchini, a giant among scientists in the tire industry and a past president of the Tire Society, passed away at his home on September 27, 2013, after a short illness. John was a passionate and dedicated scientist known for repeated contributions to experimental and computational tire science and for exceptional service to the professional community. He had retired in 2011 as senior research scientist after a 34 year career with the Cooper Tire & Rubber Company.
John was born...
Dr. John Remo Luchini, a giant among scientists in the tire industry and a past president of the Tire Society, passed away at his home on September 27, 2013, after a short illness. John was a passionate and dedicated scientist known for repeated contributions to experimental and computational tire science and for exceptional service to the professional community. He had retired in 2011 as senior research scientist after a 34 year career with the Cooper Tire & Rubber Company.
John was born September 2, 1949, in Detroit, Michigan, and raised in Dearborn Heights, Michigan. He earned his B.S., M.S., and Ph.D. degrees in engineering at the University of Michigan, where he also met and married his wife Tamara. His doctoral thesis was supervised by Professor Sam Clark, during a period of high demand for more energy efficient tires. Entitled “Mathematical Model for Rubber Hysteresis,” his thesis explored the problem of...
Read More
