Narayanaswami Ranganathan

MULTIAXIAL FATIGUE CRITERIA APPLIED TO A POLYCHLOROPRENE RUBBER

Abstract Due to their interesting mechanical behavior and their diversity, rubber materials are more and more used in industry. Indeed, formulating a multiaxial fatigue criterion to predict fatigue lives of rubber components constitutes an important objective to conceive rubber products. An experimental campaign is developed here to study the multiaxial fatigue behavior of polychloroprene rubber. To reproduce multiaxial solicitations, combined tension–torsion tests were carried out on a dumbbell-type specimen (an axisymmetric rubber part bonded to metal parts with a reduced section at mid-height), with several values of phase angles between tension and torsion. A constitutive model is needed to calculate multiaxial fatigue criteria, and then analyze fatigue results. A large strain viscoelastic model, based on the tension–torsion kinematics, is then used to determine the materials stress–strain law. Dissipated energy density is introduced as a multiaxial fatigue criterion, and compared with those usually ...

The Energy Based Approach to Fatigue

This paper presents the energy based approaches developed to describe different aspects of fatigue. Different topics covered include fatigue crack initiation, crack initiation at a notch, multiaxial fatigue and fatigue crack propagation. Specific examples treated include, crack initiation at a notch, cracking at solder joint in electronic application, fatigue life estimation in a synthetic rubber and fatigue crack propagation in a metallic material.

Variable Amplitude Fatigue

Fatigue crack growth behavior of selected aluminum alloys under variable amplitude loading is discussed in this study, based principally on experimental observations. The tests include single overloads tests in different environments, block load tests and tests using an aircraft wing loading spectrum. It is shown that conditions favoring a planar slip behavior lead to very high delays as opposed to conditions leading to multiple slip behavior. The Aluminium Liithium alloy studied here, has the best fatigue crack growth resistance in almost all test conditions studied here as compared to other conventional alloys. Under the spectrum loading studied here, the same alloy exhibits a change in micromechanism leading to a four fould acceleration of growth rates. Acceptable life predictions can be made, by taking into account this crack acceleration effect.

Tensile Creep Studies on Filled Polychloroprene Elastomer

Tensile creep data on an elastomeric material, polychloroprene, are presented in this paper. The data were collected at four temperatures, 20, 40, 80, and 110°C and four stress levels, 0.4, 0.6, 0.8, and 1 MPa. Each experiment was conducted over a time period of about twelve hours. Two different mechanisms seem to operate for the creep behavior in these ranges. At the lower temperatures, 20 and 40°C, the data are fitted with a new four-parameter equation; the data at different stress levels are combined into a single curve, which can be called a master plot. At the higher temperatures, 80 and 110°C, for the time period used, a single equation cannot fit the data and two equations are used, a four-parameter equation for the initial time, and the Findley equation for the later time.

An Overview of the Fatigue of Polychloroprene Rubber

Some fundamental studies carried in a synthetic rubber - Chloroprene CR29 are presented in the first part of the paper. A critical analysis of test results, shows that an energy based approach permits the determination of fatigue lives in this material. This aspect is further enhanced by biaxial fatigue tests in the same material. These tests covering a life range from 10000 to 1000000 cycles show that the energy based model is very efficient to describe the fatigue behavior. Some evidence of strain induced crystallization (previously observed in natural rubber) with associated life enhancement at high load ratios is also presented. A comprehensive model based on the determination of the constitutive laws taking into account the viscoelastic behavior is developed showing excellent correlation with experimental data.

Rubber fatigue — the intrinsic Intricacies

This paper brings out the salient fractographic features that can be found on the fracture surface of some selected rubbers. It is shown that the presence of a specific feature — called the tongues can be correlated to the effect of load ratio and hence the fatigue lives in a synthetic rubber.

Determination of the energy necessary for creating fatigue cracks by measurement of microhardness

The growth of cracks is related to the existence of a plastic zone at the crack tip, the formation and growth of which are accompanied by an energy dissipation. The estimation of this energy is generally made by global measures. In our study, we have used microhardness measurements at the crack tip for estimating energy. The results obtained are more accurate near the crack tip than those estimated by other methods.