Kirigami inspired shape programmable and reconfigurable multifunctional nanocomposites for 3D structures

The ability to shape and program remotely and contactlessly from two-dimensional (2D) flat multilayer materials into three-dimensional (3D) structures and functional devices could be ideal for applications like space missions, environmental remediation and minimally invasive surgery. However, achieving a fast and accurate deployment of complex 3D shapes contaclessly at low energy consumption, while embedding a number of physical properties and functionalities, remains very challenging. Herein, a strategy to widen the complexity space of 3D shapes and functions achievable is demonstrated, by enabling a controlled sequential folding while incorporating nano-reinforcements. Sequential folding was successfully achieved and a honeycomb structure was developed by designing multilayer polymer films with different kirigami patterns - each responding at a different rate upon heating. A finite element method (FEM) model was developed to better understand the main underlying physical mechanism as well as to feedback into materials and structure design. Moreover, a shape-programmed CNT veil-based honeycomb structure was developed, triggered remotely by thermal stimuli, with capability to self-sense the folding state through the electrical resistance change (ΔR/R0 = 100–300 %). Overall, it was demonstrated that designing layered nanocomposites with different 2D patterns allows an accurate sequential folding into 3D structures, with bespoke physical properties and integrated sensing–actuating functionalities

Hemp fibre as alternative to glass fibre in sheet moulding compound. Part 1 : influence of fibre content and surface treatment on mechanical properties

Original article can be found at : http://www.iom3.org/ Copyright ManeyHemp fibre mat reinforced unsaturated polyester composites were fabricated using a conventional sheet moulding compound process. The influence of fibre and CaCO3 filler content on strength and stiffness of these hemp fibre reinforced sheet moulding compounds is reported and compared with data for chopped glass fibre reinforced sheet moulding compounds. In addition the influence of alkaline and silane treatments of the hemp fibres is evaluated. The experimental data are compared to modified versions of the Cox-Krenchel and Kelly-Tyson models, supplemented with parameters of composite porosity to improve the prediction of composite tensile properties. A good agreement was found between the modified models and experimental data for strenght and stiffness. The results indicate that hemp fibre reinforced sheet moulding compounds are of interest for low cost engineering applications that require high stiffness to weight ratios.Peer reviewe

Comparative assessment of stress transfer efficiency in tension and compression

Raman spectroscopy is used to get an insight into the microstructural aspects of the compressional behaviour of carbon fibre composites. This is done by a comparative assessment of the stress transfer efficiency in tension and compression in single-fibre discontinuous model geometries. It was found that the axial stress is transferred in the fibre through the generation of shear stresses at the interface. The mechanism of stress transfer is independent of the loading mode. Furthermore, the values of maximum interfacial shear stress are a function of the applied strain for both tension and compression loading. Significant differences were found, however, in the mode of failure of the two systems. In tension, interfacial failure initiates from the fibre ends at relatively high applied strains and the stress transfer efficiency is affected by the onset of matrix plasticity. On the other hand, in compression, deterioration of the stress transfer efficiency occurs prior to any noticeable interfacial failure at the fibre ends due to fibre collapse at low strains. Finally, it is worth noting that in compression, the fibre fragments remain in contact, and thus can still bear load. (C) 2002 Published by Elsevier Science Lt

Mechanisms of stress transfer and interface integrity in carbon/epoxy composites under compression loading Part I : experimental investigation

Raman spectroscopy is used to get an insight into the microstructural aspects of the compressional behavior of carbon fiber composites. This is done by a comparative assessment of the stress transfer efficiency in tension and compression in single-fiber discontinuous model geometries. It was found that axial stress is transferred in the fiber through the generation of shear stresses at the interface for both tension and compression loading. Experimental evidence is presented to verify that the values of the maximum interfacial shear stress that the system sustains is a function of the applied strain and independent of the type of loading. However, compressive failure is quite different as fiber fragments remain in contact, thus can still bear load. (C) 2002 Published by Elsevier Science Lt

Extraction of mix-mode cohesive laws of a unidirectional composite undergoing delamination with large-scale fibre bridging

A novel method is proposed for extracting the mixed-mode cohesive laws of composite materials undergoing delamination with large-scale fibre bridging. In the approach, the mixed-mode cohesive laws are derived from a potential function expressed in cylindrical coordinates with the magnitude and phase angle between the normal and tangential end-openings. The potential function is mapped using experimental R-curves in terms of the J-integral and the end-openings. The mixed-mode cohesive laws describe both the crack tip (high tractions, small separations) and bridging region (small tractions, high separations). The extracted mixed-mode cohesive tractions are fully coupled, i.e., both the normal and shear traction depend on the normal and tangential openings. The peak normal and shear tractions were found to be at a mixed mode opening