Michelin (France)

In this paper, the study of helical buckling is extended, for the first time, to slender structures with a complex architecture: textile cords. This phenomenon is investigated experimentally through in-situ X-ray tomography compression tests and numerically through filament-scale finite element simulations, which are then compared with the experimental results. Additionally, a parametric study is performed on the matrix stiffness, exploring configurations beyond the experiment’s domain. The results highlight that the buckling amplitude is inversely related to the stiffness of the matrix and the twist of the cord. These findings are discussed in relation to the theory for buckling in single filaments. The consequences of the buckled configuration on strain distribution at the filament scale are analyzed, highlighting how helical buckling influences load redistribution within the cord. In this sense, this work could open the field towards a conscious design of textile cords around the buckling point. • First study extending helical buckling to textile cord-elastomer composites. • Helical buckling analyzed via in-situ X-ray tomography and numerical simulations. • Revealed relationship between buckling behavior, matrix stiffness and cord twist. • Buckling alters filament-scale strain distribution, redistributing the load.

ABSTRACTThe U.S. automotive tire industry consumes more than 3.6 million tons of materials to manufacture 300 million tires annually. To ensure materials‐related sustainability, it is important to enable the use of a greater recycling rate of steel scrap in the manufacturing of new tires. However, impurities like copper compromise the performance of steel wires that are cold‐drawn from ~5.5 mm diameter rods. This article investigates copper precipitation in sensitized steel wire rods and their mechanical properties subjected to varying heat treatment procedures. The amount of copper precipitated in sensitized zones as a function of Cu concentration in the steel samples is quantified using scanning electron microscopy. Preliminary findings indicate that an increase in cooling rate during the heat treatment procedure increases the amount of Cu precipitated in the sensitized zones and increases the geometric footprint of the sensitized zones. Tensile tests on heat‐treated 5 mm‐diameter wire rods showed a higher strain and slightly lower peak stress as the cooling rate decreased. This research thus contributes to a better understanding of the influence of Cu concentration on the microstructure and performance of steel wires used in tire manufacturing, thereby allowing for the enhanced use of scrap steel.

We present an extension of the SLIPLINK technology introduced by A. Likhtman to polymer nanocomposites in order to model explicitly free and grafted chains. Entanglements are explicitly modeled by slip-springs (SS) and follow the constraint release algorithm of destruction/recreation when reaching the chain end. Following the birth/death process, one can compute the age of slip-springs and the entire population age pyramid. We varied nanoparticle volume fraction, grafting density, and polymer/particle interactions to determine structural and dynamic properties of the nanocomposite materials. Scaling laws for slip-springs average age versus chain length have been obtained. While the dynamics of slip-springs between free chains in the nanocomposite is almost identical to that of a pure polymer melt, a characteristic exponent close to 3.7 has emerged governing the average age of slip-springs between grafted chains. The number of inter-particle graft-graft entanglements and their increased average lifetimes have a strong impact on the viscoelastic response of the material and the nanoparticle cluster formation. The emergence of polymer network elasticity will be discussed for high grafting density and high-volume fraction.

The iron and steel manufacturing sector significantly adds to global greenhouse gas emissions, caused primarily by the carbothermic reduction of iron ore. Recycling scrap steel offers an effective decarbonization strategy but introduces impurities like copper (Cu) that can negatively impact mechanical properties. This study investigates the effects of Cu content and heat treatment on the mechanical performance and sensitization of steel wire rods for tire manufacturing. Steel rods with 0.04 and 0.21 wt% Cu are heated to 1050 or 1200 °C, then air quenched, or furnace cooled. Tensile testing coupled with microscopic analysis is used to evaluate mechanical properties and assess the sensitization effects. Higher Cu content leads to larger sensitized zones with increased Cu precipitation along grain boundaries. Ductility and toughness, crucial for wire drawability, are found to be reduced, despite higher ultimate strength. Slower furnace cooling is seen to result in smaller sensitized zones compared to air quenching, suggesting a pivotal role of cooling rate in sensitization control. The findings provide insights into optimize heat treatment parameters and Cu content limits, balancing mechanical performance and maintaining drawability for enhanced scrap steel recycling in tire production.

Molecular simulations were conducted to provide a better description of the poly(glycerol sebacate) (PGS)-water interface. The density and the glass-transition temperature as well as their dependencies on the degree of esterification were examined in close connection with the available experimental data. The work of adhesion and water contact angle were calculated as a function of the degree of esterification. A direct correlation was established between the strength of the hydrogen bond network in the interfacial region and the change in the water contact angle with respect to the degree of esterification. The interfacial region was described by local density profiles and orientations of the water molecules.

Polymer nanocomposites (PNCs) are known to display exceptional nonlinear mechanical properties, even for a deformation amplitude as low as a few percent. One of the most studied phenomena is the so-called Payne effect, a drop in storage modulus with increasing amplitude. Several mechanisms have been put forward to rationalize such an effect, including filler network breaking, polymer chain desorption, and yielding of the polymer confined between the nanofillers. In this contribution, we demonstrate that for PNCs involving fractal-like aggregates, the Payne effect may originate from the shear-induced alignment of the aggregates. We reach this conclusion by using a coarse-grained model, which combines an explicit representation of fillers with an implicit description of the polymer matrix. We systematically characterize the effects of the aggregate size and polydispersity in the amplitude of the Payne effect. Moreover, we probed the mechanical response of the model PNCs after the first cycle of deformation. We observe slow recovery kinetics of the original storage modulus of the PNCs and relate this memory effect to the alignment of the aggregates. Our findings should contribute to clarifying the relation between the macroscopic mechanical response of the PNCs and the mesoscopic state of the filler.