Different from conventional materials, materials with negative Poisson's ratios expand laterally when stretched longitudinally. Known as ‘auxetic’ materials, the effect means they possess particularly fascinating properties, which have recently attracted considerable attention in the literature. A range of auxetic materials has been discovered, theoretically designed and fabricated. Developments in additive manufacturing (AM) techniques enable fabrication of materials with intricate cellular architectures. This paper outlines recent progress in the development of auxetic materials and structures, and their mechanical properties under quasi-static and dynamic loading are analysed and summarised. Limited experimental studies on 3D printed auxetic materials and structures are given more attention, ahead of extensively finite element (FE) simulations. A special focus is dedicated to their large, plastic deformation behaviour and energy absorption performance, which should be stressed in their engineering applications; no review paper has yet been found regarding this. Finally, this paper provides an overview of current study limitations, and some future research is envisaged in terms of auxetic materials and structures, nano-auxetics and additive manufacturing.

Large deformation and energy absorption of additively manufactured auxetic materials and structures: A review

Finite element modeling strategies for 2D and 3D delamination propagation in composite DCB specimens using VCCT, CZM and XFEM approaches

A review of phase-field models, fundamentals and their applications to composite laminates

On cohesive element parameters and delamination modelling

Enhancement of impact toughness and damage behaviour of natural fibre reinforced composites and their hybrids through novel improvement techniques: A critical review

A three-dimensional separable cohesive element (SCE) is proposed to enable the modelling of interaction between matrix cracking and interfacial delamination in laminated fibre-reinforced composite materials. It is demonstrated that traditional cohesive elements are incapable of modelling the coupled failure mechanisms accurately if partitioning is not allowed. The SCE may be partitioned according to the configuration and geometry of matrix cracks in adjacent plies, thus maintaining appropriate connection between plies. Physically, the original interface is split and new interfaces are formed to bond the homologous cracked solids during fracturing process. The stress concentration induced by matrix cracks and the load transfer from cracked solid elements to interface cohesive element are effectively modelled. A comprehensive set of cases of multiple matrix crack configurations from plies of different fiber angles is considered. The proposed SCE is applied to model progressive failure in composite laminates and the results are found to agree with experiments.

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A separable cohesive element for modelling coupled failure in laminated composite materials

Adaptive floating node method for modelling cohesive fracture of composite materials

Apart from major cracks and delamination, extensive and diffused short matrix micro-cracks are generally observed in composite laminates. In principle, discrete crack models (DCM) offer greatest fidelity to the mechanics of crack growth, including interactions between different failure modes, but it is impractical to model numerous cracks explicitly beyond coupon-sized laminates. Smeared crack models (SCM), on the other hand, treat diffused damage by effective material degradation. However, homogenization of cracks does not model strong discontinuities and delamination-matrix crack interactions. An adaptive discrete-smeared crack model is proposed here to preserve fidelity to the fracturing process while maintaining efficiency and simplicity in modelling distributed damage. DCM is used to model individual matrix cracks at the initial stages of propagation. Subsequently, adaptive transition from DCM to coupled DCM/SCM is performed. Critical cracks are explicitly retained, while non-critical ones are modelled by dispersed damage. The method is demonstrated with off-axis and open-hole tension tests.

X. Lu

Papers

On cohesive element parameters and delamination modelling

A separable cohesive element for modelling coupled failure in laminated composite materials

Adaptive floating node method for modelling cohesive fracture of composite materials

Adaptive discrete-smeared crack (A-DiSC) model for multi-scale progressive damage in composites

Auxeticity of monoclinic tetrachiral honeycombs