Experimental investigation and theoretical modelling of induced anisotropy during stress-softening of rubber

International audienceThe Mullins effect refers to a stress-softening phenomenon of rubber-like materials during cyclic loading. Anisotropy of the material behaviour is generally observed after stretching. In this paper, a large set of original suitable experiments are reported to characterise this effect under several deformation conditions. Then, a phenomenological model is derived to capture the anisotropic distribution. For that, the affine micro-sphere model (Miehe et al., 2004) is amended with a directional network alteration in order to describe anisotropy. The alteration process, involving the breakage and the slippage of the links embedded in the macromolecular network, is modeled by the evolution of the average number of monomer segments per chain during stretching. The average chain length and the chain density are incrementally described by functions to allow both softening and stiffening, depending to the maximum and the minimum stretch rates and levels endured in each direction. The good capacity of the model to reproduce experimental observations validates the above assumptions

Capilano College Fall 1986 Reading Series

Poster with dates and times of the Fall 1986 Reading Series, featuring Sharon Pollock, Sandra Birdsell, and Fred Wah

A theory of network alteration for the Mullins effect

International audienceThis paper reports on the development of a new network alteration theory to describe the Mullins effect. The stress-softening phenomenon that occurs in rubber-like materials during cyclic loading is analysed from a physical point of view. The Mullins effect is considered to be a consequence of the breakage of links inside the material. Both filler-matrix and chain interaction links are involved in the phenomenon. This new alteration theory is implemented by modifying the eight-chains constitutive equation of Arruda and Boyce (J. Mech. Phys. Solids 41 (2) (1993) 389). In the present method the parameters of the eight-chains model, denoted C-R and N in the bibliography, become functions of the maximum chain stretch ratio. The accuracy of the resulting constitutive equation is demonstrated on cyclic uniaxial experiments for both natural rubbers and synthetic elastomers

A new modelling of the Mullins'effect and viscoelasticity of elastomers based on physical approach

The mechanical behaviour of elastomers is known to be highly non-linear, time-dependent and to exhibit hysteresis and stress-softening known as the Mullins effect (Mullins, 1948) upon cyclic loading. These phenomena are classically studied and modelled independently. Some studies are based on physical approaches (Arruda and Boyce, 1993; Bergström and Boyce, 1998; Marckmann et al., 2002) in which macroscopic constitutive equations are build in regards with the physics of polymeric chains. In this context of physical considerations, the aim of the present paper is to study independently each phenomenon involved in rubber-like materials and to assemble them in a global constitutive equation. First, the hyperelastic behaviour of elastomers is modelled by the physical approach of Arruda and Boyce (1993), widely known as the eight-chains model. This model accurately reproduces the large strains elastic behaviour of elastomers under different types of deformation. Second, the hysteretic time dependent behaviour is approached by the model developed by Bergström and Boyce (1998) that considers the separation of the network in two phases: an elastic equilibrium network and a viscoelastic network that captures the nonlinear rate-dependent deviation from equilibrium. This model is quite simple and successfully reproduces the rate-dependent hysteretic properties of elastomers. Last, as shown in the bibliography, the Mullins stress-softening effect can be considered as a damage phenomenon which only depends on the maximum stretch attained during the deformation history (Govindgee and Simo, 1992). In the present approach, the physical theory of Marckmann et al. (2002) based on an alteration of the polymeric network is adopted. This theory was introduced in the eight-chains hyperelastic model and successfully simulates the decrease of the material stiffness between the first and the second loading curves under cyclic loading. As these three models are based on the physics of the polymeric network, they are gathered in a new efficient constitutive equation. This model is able to reproduces imultaneously the Mullins effect and the time-dependent hysteretic behaviour of elastomers. Finally, the constitutive parameters of this new model are identified by fitting experimental data

Theoretical and numerical limitations for the simulation of crack propagation in natural rubber components

International audienceIn this paper, two commercial software packages dedicated to the simulation of crack propaga-tion in elastomer components were tested: FLEXPAC and MSC-MARC. Firstly, the theoretical limitations ofclassical crack propagation laws were examined to demonstrate that actual numerical predictions are limitedto very simple loading conditions. Secondly, crack propagation approaches implemented in both softwareswere analysed. In order to compare their performances, fatigue experiments are performed. Different rubbercomponents with different pre-cracks were tested under several loading conditions. Crack propagation, i.e.size and direction of the crack, was measured as a function of the number of cycles. Then, these results werecompared with crack direction criteria proposed by the two models. It was demonstrated that loading ampli-tude highly influenced the crack direction and that the models must take this into account in their solver. Fi-nally, limitations of this type of numerical analysis to predict the duration life of rubber components werehighlighted

Population Genetic Structure is Unrelated to Shell Shape, Thickness and Organic Content in European Populations of the Soft-Shell Clam Mya Arenaria.

The soft-shell clam Mya arenaria is one of the most ancient invaders of European coasts and is present in many coastal ecosystems, yet little is known about its genetic structure in Europe. We collected 266 samples spanning a latitudinal cline from the Mediterranean to the North Sea and genotyped them at 12 microsatellite loci. In parallel, geometric morphometric analysis of shell outlines was used to test for associations between shell shape, latitude and genotype, and for a selection of shells we measured the thickness and organic content of the granular prismatic (PR), the crossed-lamellar (CL) and the complex crossed-lamellar (CCL) layers. Strong population structure was detected, with Bayesian cluster analysis identifying four groups located in the Mediterranean, Celtic Sea, along the continental coast of the North Sea and in Scotland. Multivariate analysis of shell shape uncovered a significant effect of collection site but no associations with any other variables. Shell thickness did not vary significantly with either latitude or genotype, although PR thickness and calcification were positively associated with latitude, while CCL thickness showed a negative association. Our study provides new insights into the population structure of this species and sheds light on factors influencing shell shape, thickness and microstructure

RAD sequencing sheds new light on the genetic structure and local adaptation of European scallops and resolves their demographic histories.

Recent developments in genomics are advancing our understanding of the processes shaping population structure in wild organisms. In particular, reduced representation sequencing has facilitated the generation of dense genetic marker datasets that provide greater power for resolving population structure, investigating the role of selection and reconstructing demographic histories. We therefore used RAD sequencing to study the great scallop Pecten maximus and its sister species P. jacobeus along a latitudinal cline in Europe. Analysis of 219 samples genotyped at 82,439 single nucleotide polymorphisms clearly resolved an Atlantic and a Norwegian group within P. maximus as well as P. jacobeus, in support of previous studies. Fine-scale structure was also detected, including pronounced differences involving Mulroy Bay in Ireland, where scallops are commercially cultured. Furthermore, we identified a suite of 279 environmentally associated loci that resolved a contrasting phylogenetic pattern to the remaining neutral loci, consistent with ecologically mediated divergence. Finally, demographic inference provided support for the two P. maximus groups having diverged during the last glacial maximum and subsequently expanded, whereas P. jacobeus diverged around 95,000 generations ago and experienced less pronounced expansion. Our results provide an integrative perspective on the factors shaping genome-wide differentiation in a commercially important marine invertebrate

Population Genetic Structure Is Unrelated to Shell Shape, Thickness and Organic Content in European Populations of the Soft-Shell Clam Mya Arenaria

The soft-shell clam Mya arenaria is one of the most ancient invaders of European coasts and is present in many coastal ecosystems, yet little is known about its genetic structure in Europe. We collected 266 samples spanning a latitudinal cline from the Mediterranean to the North Sea and genotyped them at 12 microsatellite loci. In parallel, geometric morphometric analysis of shell outlines was used to test for associations between shell shape, latitude and genotype, and for a selection of shells we measured the thickness and organic content of the granular prismatic (PR), the crossed-lamellar (CL) and the complex crossed-lamellar (CCL) layers. Strong population structure was detected, with Bayesian cluster analysis identifying four groups located in the Mediterranean, Celtic Sea, along the continental coast of the North Sea and in Scotland. Multivariate analysis of shell shape uncovered a significant effect of collection site but no associations with any other variables. Shell thickness did not vary significantly with either latitude or genotype, although PR thickness and calcification were positively associated with latitude, while CCL thickness showed a negative association. Our study provides new insights into the population structure of this species and sheds light on factors influencing shell shape, thickness and microstructure

Reconciling differences in natural tags to infer demographic and genetic connectivity in marine fish populations

Processes regulating population connectivity are complex, ranging from extrinsic environmental factors to intrinsic individual based features, and are a major force shaping the persistence of fish species and population responses to harvesting and environmental change. Here we developed an integrated assessment of demographic and genetic connectivity of European flounder Platichthys flesus in the northeast Atlantic (from the Norwegian to the Portuguese coast) and Baltic Sea. Specifically, we used a Bayesian infinite mixture model to infer the most likely number of natal sources of individuals based on otolith near core chemical composition. Simultaneously, we characterised genetic connectivity via microsatellite DNA markers, and evaluated how the combined use of natural tags informed individual movement and long-term population exchange rates. Individual markers provided different insights on movement, with otolith chemistry delineating Norwegian and Baltic Sea sources, whilst genetic markers showed a latitudinal pattern which distinguished southern peripheral populations along the Iberian coast. Overall, the integrated use of natural tags resulted in outcomes that were not readily anticipated by individual movement or gene flow markers alone. Our ecological and evolutionary approach provided a synergistic view on connectivity, which will be paramount to align biological and management units and safeguard species’ biocomplexityFundação para a Ciência e a Tecnologia | Ref. UID/MAR/04292/2013Fundação para a Ciência e a Tecnologia | Ref. PTDC/AAG-GLO/5849/2014Fundação para a Ciência e a Tecnologia | Ref. PTDC/MAR-EST/2098/201

New insights on the population genetic structure of the great scallop (Pecten maximus) in the English Channel coupling microsatellite data and demogenetic simulations.

International audienceThe great scallop (Pecten maximus) is a commercially important bivalve in Europe, particularly in the English Channel, where fisheries are managed at regional and local scales through the regulation of fishing effort. In the long term, knowledge about larval dispersal and gene flow between populations is essential to ensure proper stock management. Yet, previous population genetic studies have reported contradictory results. In this study, scallop samples collected across the main fishing grounds along the French and English coasts of the English Channel (20 samples with temporal replicates for three sites,n= 1059 individuals), and the population genetic structure was analysed using 13 microsatellite loci. Coupling empirical genetic data with demogenetic modelling based on a biophysical model simulating larval exchanges among scallop beds revealed a subtle genetic differentiation between south-west English populations and the rest of the English Channel, which was consistent with larval dispersal simulations. The present study provides a step forward in the understanding of great scallop population biology in the English Channel, underlining the fact that even in a context of potentially high gene flow and recent divergence times since the end of the last glacial maximum, weak but significant spatial genetic structure can be identified at a regional scale