Krishna Kannan

Comprehensive molecular dynamics simulations are conducted to identify material modifications which can improve strength and reduce hysteresis losses at the nanointerfaces formed between silica, silane coupling agent (SCA) and styrene-butadiene rubber (SBR), all of which are important ingredients of green tyres. Improving strength and reducing hysteresis losses at such interfaces are expected to reduce rolling resistance (RR), consequently lowering greenhouse emissions. Various modifications considered in this work include a variety of SBR blends, several SCA and surface occupancies of SCA on the silica surface. To tackle a large number of combinations possible and identify modifications which may improve the nature of the interfaces, a hierarchical computational framework is developed. The reduced sample space of such material modifications may be more amenable to comprehensive and computationally or experimentally expensive studies. It was found that some amino-based SCA in combination with certain blends of SBR can improve the interfaces strength and lower hysteresis losses, when compared to the commonly used bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), which is a sulphur-based SCA.

Single body models of tracked vehicles are used for mobility and steerability studies in soft terrains. Modelling of soft soil-track interaction forces is a major area of interest in these studies. Accuracy of soil track interaction model depends on prediction of shear deformation at soil track interface and modelling of resistance of soil to deformation. In this paper a novel method for calculating the dynamic distribution of shear displacement at the soil track interface, for studying 3-D motion in soft terrains is discussed. The proposed method uses position and orientation information of tracked vehicle, with respect to a coordinate system fixed in soil, to calculate the shear displacement distribution. The shear displacement distribution over the entire area of track can be calculated using the proposed method. Simulation results are compared with results of existing method which uses a differential equation approach. Results are in agreement for straight line motion simulation and differ for turning motion as expected.

This paper presents the tractive performance of different grouser shapes in extremely soft seabed soil using finite element analysis (FEA). Consequently, the deformation characteristics and pattern of shear failure in the seabed soil can be predicted, eliminating expensive full-scale experiments. A three-dimensional FEA with the incorporation of geometric nonlinearity of shear rheometry is performed using coupled Eulerian–Lagrangian (CEL) technique in ABAQUS Explicit. The Mohr–Coulomb criterion is used to define the constitutive behaviour of the seabed soil sample used. To validate the model, the CEL simulation results are corroborated with experimental observations. The study reveals that the Mohr–Coulomb model with the governing parameters is able to capture the maximum rotational moment obtained from the experimental results with a maximum error of 3.5%. The Mohr–Coulomb model is therefore used to determine the maximum traction developed from two distinct grouser profiles to evaluate their tractive efficiency. It is observed that a triangular grouser offers better traction than an involute grouser.

Polyamide 66/hectorite nanocomposites exhibit superior mechanical properties compared with pure polymers and are promising for structural applications. X-ray diffraction results revealed reduced degree of exfoliation with increase in organoclay content. Flexural fatigue characteristics of polyamide 66/hectorite nanocomposites containing different quantities of clay content were investigated, under deflection control mode, using a custom built flexural fatigue test rig. Addition of organoclay improved the moduli of the material. An enhanced resistance to cyclic softening was noticed at high temperatures with the incorporation of organoclay. Nanocomposite samples exhibited a significant improvement in fatigue life compared with pure polymers; however, the degree of enhancement is governed by the nanostructure of organoclay in polymer matrix. The fatigue life of nanocomposite samples is strongly affected by specimen temperature and induced stress. Macroscopic fracture surfaces changed from flat featureless structure to a highly perturbed structure with increase in organoclay content. © 2010 Society of Plastics Engineers.

The objective of the present work is to predict the degree of curing for a rectangular slab of rubber, which was subjected to non-uniform thermal history. As the thermal conductivity of rubber is very low, the temperature gradient across a slab is quite large, which leads to non-uniform vulcanization, and hence non-uniform mechanical properties-an inhomogeneous material. Since curing is an exothermic reaction, heat transfer and chemical reactions are solved in a coupled manner. The effect of heat generation on curing is also discussed. © 2009 Elsevier B.V. All rights reserved.

Carbon black filled natural and synthetic rubbers used in automobile tires have to sustain a very large hydrostatic tensile stress between the two steel belts, especially near the belt edge. In addition, the rate effect of the volumetric and the distortional response of filled elastomers becomes significant for vehicles running at high speeds. In other words, by limiting the volumetric and distortional response and making it rate dependent, one can emulate the high stresses observed in tires. There are a number of constitutive equations of the rate and integral type for filled elastomers, but none of the available models employ a rate-dependent dilatational limit. In this paper, we propose a new non-linear rate-type compressible viscoelastic incorporating individual limits for dilatation, contraction, and distortion. The rate type thermodynamic framework of Rajagopal and Srinivasa (2000) is extended to include such limits. By establishing the physical meaning of various parameters used in the constitutive equation, we show that they are tightly correlated with the certain type of experiments and can be determined from the available data in the literature. Only a few parameters need to be determined by curve fitting. The proposed model is validated using in-house as well as the other experimental data available in the literature. In Part B of the paper, extensive validation of the proposed constitutive equation for cyclic barreling and cyclic inhomogeneous planar extension will be demonstrated.

A rigorous, comprehensive, and thermodynamically consistent theory has been developed for the fused deposition modelling (FDM) of semi-crystalline polymers. It is sufficiently general in that it can accommodate multiple phase transition mechanisms (crystallization, glass transition, and melting) during the heating and cooling cycles of the process encountered during FDM. The theory predicts the residual stresses and the resulting warpage in the polymer part due to the temperature-dependent, spatially varying specific volumes of each phase, precipitated by the inhomogeneous distribution of temperature. The theory treats the semi-crystalline polymer as a constrained mixture of multiple phases, where glass is assumed to be a new phase of the polymer. The statistically based Avrami kinetics for crystallization, modified for non-isothermal processes, is recovered as a particular case of our non-equilibrium thermodynamic analysis. Moreover, the theory predicts the temperature corresponding to the local free energy minima as the ideal glass transition temperature analogous to that of Franz and Parisi's mean field theory with a statistical basis.

This paper presents the development of a constitutive model for describing the nonlinear viscoelastic behavior of deep-seabed sediments. To quantify the nonlinear response, shear rheological tests are carried out on deep-sea sediments substitute at different shear rates. These substitute samples are prepared by mixing bentonite with water based on the in-situ vane shear strength of deep-sea sediments. A compressible viscoelastic fluid model is formulated based on the thermodynamic framework developed by Rajagopal and Srinivasa (2000) to describe the experimental response of bentonite–water mixture. Experimental responses indicate that the effects of slip are significant in the shear rheometry of bentonite–water mixture. Hence a slip model is proposed, which relates the shear stress to slip velocity at the wall and the imposed shear rate values. The slip boundary conditions coupled with the viscoelastic model is validated using experimental data and is observed to be in good agreement. Further, the influence of shear rate on interfacial slip has been numerically analyzed and slip effects are found to be significant in defining rheological behavior with increasing shear rates.

Based on a Gibbs potential formulation for implicit elastic bodies, we propose a new strain limiting constitutive relation using Lode invariants of stress, and numerically study a non-dimensionalized problem of a plate with radiused V-notch subjected to tensile traction. The stress predicted by the new relation agrees with the linearized elastic model beyond a certain distance from the notch-tip. As we approach the tip, the stress associated with the new constitutive relation increases rapidly, and it is nonlinear in the vicinity of the radiused-tip, unlike bounded stress predicted by the linearized elastic model.

Fatigue and damage are the least understood phenomena in the mechanics of solids. Recently, Alagappan et al. (“On a possible methodology for identifying the initiation of damage of a class of polymeric materials”, Proc R Soc Lond A Math Phys Eng Sci 2016; 472(2192): 20160231) hypothesized a criterion for the initiation of damage for a certain class of compressible polymeric solids, namely that damage will be initiated at the location where the derivative of the norm of the stress with respect to the stretch starts to decrease. This hypothesis led to results that were in keeping with the experimental work of Gent and Lindley(“Internal rupture of bonded rubber cylinders in tension. Proc. R. Soc. Lond. A 1959; 249, 195–205 :10.1098) and agrees qualitatively with the results of Penn (“Volume changes accompanying the extension of rubber”, Trans Soc Rheol 1970; 14(4): 509–517) on compressible polymeric solids. Alagappan et al. considered a body wherein there is a localized region in which the density is less than the rest of the solid. In this study, we show that the criterion articulated by Alagappan et al. is still applicable when bodies have multiple localized regions of lower density, thereby lending credence to the notion that the criterion might be reasonable for a large class of bodies with multiple inhomogeneities. As in the previous study, it is found that damage is not initiated at the location where the stresses are the largest but instead at the location where the densities tend to the lowest value. These locations of lower densities coincide with locations in which the deformation gradient is very large, suggesting large changes in the local volume, which is usually the precursor to phenomena such as the bursting of aneurysms.