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We discuss the decomposition of the tensorial relaxation function for isotropic and transversely isotropic (TI) modified quasi-linear viscoelastic (MQLV) models. We show how to formulate the constitutive equation using a convenient decomposition of the relaxation tensor into scalar components and tensorial bases. We show that the bases must be symmetrically additive, i.e., they must sum up to the symmetric fourth-order identity tensor. This is a fundamental property both for isotropic and anisotropic bases that ensures the constitutive equation is consistent with the elastic limit. We provide two robust methods to obtain such bases. Furthermore, we show that, in the TI case, the bases are naturally deformation-dependent for deformation modes that induce rotation or stretching of the fibres. Therefore, the MQLV framework allows to capture the non-linear phenomenon of strain-dependent relaxation, which has always been a criticised limitation of the original quasi-linear viscoelastic theory. We illustrate this intrinsic non-linear feature, unique to the MQLV model, with two examples (uni-axial extension and perpendicular shear). [ABSTRACT FROM AUTHOR]

Fibre-reinforced composites laminates (FRCLs) are employed in various applications such as in marine, aerospace, automotive, and civil industries due to their lightweight nature, design tailorability, and superior specific mechanical properties. However, they possess extremely low flame resistance mainly due to the inherent flammability of the polymer matrix. Various treatments have been applied to improve the fire resistance of FRCLs. In particular, hybridisation (fibre hybridisation and polymer hybridisation) is an important technique which is becoming very popular to enhance the thermal performance and flame resistance of FRCLs. This article is a comprehensive review of the recent developments that broadly cover the improvements in fire resistance of composite laminates via multi-scale hybridisation; the characteristics of thermal decomposition of FRCLs have been presented to comprehend the need for flame retardancy. Approaches for improving the fire resistance of FRCLs and thermal stability, both in polymer and in fibre systems, are discussed. Enhancing the fire resistance has been significant through additives to the matrix, use of flame-retardant modified fibres at interfacial regions and by way of multi-layered hybrid laminates besides hybridization at fibre, yarn and layer level. Finally, a review is presented on the modelling of fire resistance of composite laminates by considering thermo-mechanical models for the prediction of decomposition and failure of laminates at elevated temperatures. [ABSTRACT FROM AUTHOR]

Metamaterials exploit sub-wavelength microstructures to yield novel macroscopic material properties. Recently, the notion of a metacluster has emerged, which is a collection of resonators that interact in order to modify and possibly enhance the resonance. They can also be employed to modify and tune the far-field scattered response. This is particularly important with regard to metamaterial design. In the context of elastodynamics, Cotterill et al. [Proc. R. Soc. A 478(2263), 20220026 (2022)] considered the case of void metaclusters, thus permitting the modification of the so-called giant monopole resonance in elastodynamics. Here, we consider one of the original resonant configurations of metamaterial science in Liu et al. [Science 289, 1734 (2000)]; this structure consists of coated cylinders of circular cross section and gives rise to a strong dipole resonance for sufficiently soft coatings. We consider the nature of the interaction of two such identical resonators in close proximity, which we term the co-dipole metacluster. We show that, contrary to the giant monopole case, the frequency at which the resonance occurs is unchanged as compared to a single resonator. The amplitude of the resonance itself is enhanced significantly, however, by up to 5.7 times the enhancement observed when considering two non-interacting resonators. Furthermore, although the nature of the resonance remains dominated by a dipole response, both the enhancement and the far-field scattered response are now significantly affected by the incidence angle, in contrast to the single resonator. [ABSTRACT FROM AUTHOR]

We present a unified framework for the study of wave propagation in homogeneous linear thermo-visco-elastic (TVE) continua, starting from conservation laws. In free-space such media admit two thermo-compressional modes and a shear mode. We provide asymptotic approximations to the corresponding wavenumbers which facilitate the understanding of dispersion of these modes, and consider common solids and fluids as well as soft materials where creep compliance and stress relaxation are important. We further illustrate how commonly used simpler acoustic/elastic dissipative theories can be derived via particular limits of this framework. Consequently, our framework allows us to: (i) simultaneously model interfaces involving both fluids and solids and (ii) easily quantify the influence of thermal or viscous losses in a given configuration of interest. As an example, the general framework is appliedto the canonical problem of scattering from an interface between two TVE half spaces in perfect contact. To illustrate, we provide results for fluid–solid interfaces involving air, water, steel and rubber, paying particular attention to the effects of stress relaxation. [ABSTRACT FROM AUTHOR]