Experimental investigation of the Mullins effect in swollen elastomers

International audienceNatural rubber distinguishes itself by its particular mechanical properties. It has become an almost irreplaceable important component part in industrial applications such as vibration isolator, sealing system, flexible piping or structural bearing. During the service, these components are subjected to fluctuating mechanical loading. Under cyclic loading conditions, rubber exhibits strong inelastic responses such as stress-softening due to Mullins effect. It is believed that such inelastic response plays major role in determining the durability in service of rubber component. In engineering applications where the components are concurrently exposed to aggressive solvent, further material degradation in the form of swelling occurs. Thus, it is essential to investigate the effect of swelling on the stress-softening due to Mullins effect in rubber like materials for durability analysis. In this study, the Mullins effect in swollen carbon black-filled natural rubber under cyclic loading conditions is investigated. The swollen rubbers are obtained by immersing initially dry rubber in solvent at room temperature for various immersion durations. The stress-strain responses for both dry and swollen rubber are found qualitatively similar. However, the stress-softening in swollen rubbers are notably lower compared to that in the dry one. This work is later extended for future modelling purpose by adapting the concept of Continuum Damage Mechanics (CDM) [Chagnon, G., Verron,E., Gornet, L., Markmann, G., Charrier, P., 2004. On the relevance of Continuum Damage Mechanics as applied to the Mullins effect in elastomers. J. Mech. Phys. Sol. 52, 627-1650] and pseudo-elastic model [Ogden, R.W., Roxburgh, D.G., 1999. A pseudo-elastic model for the Mullins effect in filled rubber.Proc. R. Soc. A. 455, 2861-2877]

Fatigue of swollen elastomers

International audienceThe compatibility of the properties of elastomer with conventional diesel fuel has made it favourable in many engineering applications. However, due to global energy insecurity issues, there is an urgent need to find alternative renewable sources of energy as replacements to conventional diesel. In this respect, biodiesel appears to be a promising candidate. Hence, research into the compatibility and fatigue characteristics of elastomers exposed to biodiesel becomes essential. The present paper introduces the first attempt to investigate the effect of different solvents on the fatigue of swollen elastomers. The filled nitrile rubbers are immersed in the palm biodiesel and conventional diesel to obtain the same degree of swelling prior to the application of uniaxial fatigue loading. Field Emission Scanning Electron Microscopy (FESEM) analysis is carried out to observe the fracture surfaces. Stretch-N curves are plotted to illustrate the fatigue life duration. These curves showed that the fatigue lifetime of rubber is the longest for dry rubber and the least for rubber swollen in biodiesel. FESEM micrographs reveal that the loading conditions have no effect on the crack initiation and propagation patterns regardless of the swelling state

Mechanical response of swollen elastomers under short and long-terms cyclic loading conditions / Loo Mei Sze

Conventional petroleum-derived fuels are no longer considered as futuristic sources of fuel because of their ever-increasing cost and continuous diminution in supply. These energy insecurity issues have motivated the government of Malaysia to explore intensively the prospect of biodiesel as a renewable energy alternative for future substitution of the current depleting energy resources. While the introduction of biodiesel such as palm biodiesel is proven to be environmentally friendly, the compatibility between biodiesel and elastomeric components remains as a major challenge up to this date. Indeed, it is found that the exposure of elastomeric components to biodiesel leads to a material degradation in the form of swelling which reduces their performance in service. Hence, the investigation and modeling of the mechanical responses of elastomers swollen by biodiesel are essential for durability analysis of the components. In this thesis, the mechanical responses of swollen elastomers under short-term and long-term cyclic loading conditions are addressed. The cyclic loading is considered as a short-term loading if the number of loading cycles is less then ten cycles. To this end, the thesis is divided into two parts. The first part of the thesis focuses on the mechanical response under short-term cyclic loading. For this purpose, both dry and swollen elastomeric specimens are subjected to various modes of short-term cyclic loading. The swollen elastomeric specimens are obtained by immersing initially dry specimens in solvents (palm biodiesel and conventional diesel fuel) in the absence of mechanical stress until various desired degrees of swelling are obtained (stress-free swelling). It is found that swollen elastomers show inelastic responses such as stress-softening due to Mullins effect, hysteresis and permanent set which decrease as the degree of swelling increases. Moreover, a first attempt toward the modeling of the Mullins effect taking into consideration swelling is proposed by extending phenomenologically the well-known Continuum Damage Mechanics model and Pseudo-Elastic model. The second part of the thesis deals with the mechanical response of swollen elastomers under long-term cyclic (fatigue) loading. For this purpose, the fatigue tests are conducted at various maximum strains and at constant zero strain ratio. The physical mechanism of fatigue damage is studied by observing the specimen fracture surfaces through FESEM analysis coupled with EDS. Two definitions of end-of-life are adopted: (i) The number of cycles required for a crack to reach 1 mm in length and (ii) The number of cycles required for a complete rupture to occur in the specimens. The Wöhler curves are plotted using the maximum principal stretch as the predictor. It is found that the swollen elastomers have a shorter lifetime compared to the dry ones. More precisely, the elastomers swollen by biodiesel appears to have the shortest lifetime. Moreover, FESEM results revealed that the solvent type and swelling level has no effect on the morphology of crack nucleation and propagation, regardless of the loading condition

Recent advances on fatigue of rubber after the literature survey by Mars and Fatemi in 2002 and 2004

Subjected to multiaxial mechanical loading and hostile environment, rubber experiences degradation over a period of time. Therefore, it is of utmost importance to prevent failure of rubber components during the service. As highlighted in Mars and Fatemi [Mars, W.V, Fatemi, A., 2002. A literature survey on fatigue analysis approaches of rubbers. Int. J. Fatigue 24, 949–961; Mars, W.V, Fatemi, A., 2004. Factors that affect the fatigue life of rubber: A literature survey. Rubber Chem. Technol. 77, 391–412], a large number of works focused on the durability of rubber. Furthermore, it has been expanding rapidly until today. For this reason, the present work focuses on collecting and analyzing the vast amount of works on fatigue of rubber conducted in the last 15 years since the review of Mars and Fatemi in 2002 and 2004. To this end, three bibliographic databases are consulted: Google Scholar, Scopus and Web of Science. The collected works are analyzed with the objective to identify the current and future trends and needs in the study of rubber fatigue

Continuum mechanical model for the Mullins effect in swollen rubber

International audienceThe present paper deals with the continuum mechanical modeling of Mullins effect observed in swollen rubber under cyclic loading conditions. For this purpose, the concept of Continuum Damage Mechanics (CDM) applied to rubber materials is adopted and extended in order to take into account the swelling level. The damage exhibited by the material due to Mullins effect is assumed to be isotropic and is described by a scalar damage parameter which depends on the swelling level and on the maximum deformation experienced by the material during loading history. Results show that the proposed model is qualitatively in good agreement with experimental observations

Continuum mechanical model for the Mullins effect in swollen rubber

International audienceThe present paper deals with the continuum mechanical modeling of Mullins effect observed in swollen rubber under cyclic loading conditions. For this purpose, the concept of Continuum Damage Mechanics (CDM) applied to rubber materials is adopted and extended in order to take into account the swelling level. The damage exhibited by the material due to Mullins effect is assumed to be isotropic and is described by a scalar damage parameter which depends on the swelling level and on the maximum deformation experienced by the material during loading history. Results show that the proposed model is qualitatively in good agreement with experimental observations

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INELASTIC RESPONSES OF SWOLLEN NITRILE RUBBER UNDER CYCLIC LOADING

International audiencePalm biodiesel is deemed a promising future fuel substitute for conventional diesel fuel. In line with this perspective, necessary changes in the existing diesel engine system are expected in order to address the issue of material compatibility. One typical degradation observed in rubber components exposed to aggressive solvent such as palm biodiesel during the service is swelling. Thus, the investigation of the effect of swelling on the mechanical response under cyclic loading is prerequisite for durability analysis of such components. In this study, filled and unfilled swollen nitrile rubbers are immersed in conventional diesel and palm biodiesel baths until a 5% swelling level is achieved. Both dry and swollen rubbers are subjected to uniaxial cyclic loading tests. The analysis of the mechanical responses has shown that swelling decreases inelastic effects such as hysteresis, stress softening, and permanent set. For both dry and swollen rubbers, fillers are found to have significant effects in the inelastic responses, whereas the effects of solvent and loading rate are comparable

Effect of swelling level on fatigue lifetime of filled nitrile rubber

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Experimental investigations of swollen nitrile rubber under fatigue loading

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