Modelling the crush behaviour of thermoplastic composites

Thermoplastic composites are likely to emerge as the preferred solution for meeting the high-volume production demands of passenger road vehicles. Substantial effort is currently being directed towards the development of new modelling techniques to reduce the extent of costly and time consuming physical testing. Developing a high-fidelity numerical model to predict the crush behaviour of composite laminates is dependent on the accurate measurement of material properties as well as a thorough understanding of damage mechanisms associated with crush events. This paper details the manufacture, testing and modelling of self-supporting corrugated-shaped thermoplastic composite specimens for crashworthiness assessment. These specimens demonstrated a 57.3% higher specific energy absorption compared to identical specimen made from thermoset composites. The corresponding damage mechanisms were investigated in-situ using digital microscopy and post analysed using Scanning Electron Microscopy (SEM). Splaying and fragmentation modes were the primary failure modes involving fibre breakage, matrix cracking and delamination. A mesoscale composite damage model, with new non-linear shear constitutive laws, which combines a range of novel techniques to accurately capture the material response under crushing, is presented. The force-displacement curves, damage parameter maps and dissipated energy, obtained from the numerical analysis, are shown to be in a good qualitative and quantitative agreement with experimental results. The proposed approach could significantly reduce the extent of physical testing required in the development of crashworthy structures

Resistance welding of carbon fibre reinforced PEKK by means of CNT webs

Single lap shear specimens were manufactured using resistance welding of carbon fibre reinforced substrates by means of CNT web-based heating elements. Heating elements were manufactured by embedding the CNT web layers between layers of PEKK/glass fibre and connecting them to copper electrodes. An experimental campaign explored their electrothermal behaviour influencing the welding process. Single lap shear specimens were then welded at a pressure of 0.05 MPa and different levels of power and duration. An optimum bond was obtained with a specific power of 80–90 kW/m2 and a time of 150 s, achieving a shear strength of 30 MPa. Post-mortem analysis revealed that fracture propagated within the substrates. This work represents a further step in the integration of CNT web-based heating elements in an industrial welding process

On the mechanical properties of melt-blended nylon 6/ethylene-octene copolymer/graphene nanoplatelet nanocomposites.

Ethylene-octene copolymer (EOC) with a loading level of 20 wt%, maleated EOC (EOC-g-MA) with a loading level of 3 wt% and graphene nanoplatelets (GnPs) at four different loading levels, i.e., 3 wt%, 5 wt%, 10 wt% and 15 wt% were added to nylon 6 to prepare nanocomposites using a twin-screw extruder with a high shear rate screw running at 300 rpm. Increased stiffness was observed with the addition of GnPs while tensile strength of nanocomposites was only slightly influenced. Addition of GnPs into nylon 6 and nylon 6/EOC blend caused either a reduction in the Charpy impact strength or it remained unaffected. Similarly, the Izod impact strength of compatibilized nylon 6/EOC blend increased while that of nylon 6/EOC blend-based nanocomposites decreased. An increase was observed in the compressive Izod impact strength of compatibilized nylon 6/EOC blend. Addition of GnPs to nylon 6/EOC blend caused an increase in the fracture toughness due to their influence on the morphology and fracture mechanisms. This study shows that simultaneous addition of high surface area GnPs and an impact modifier to neat nylon 6 can help achieve enhancement and tailoring of stiffness and toughness

A highly efficient ergonomic approach for the bonded repair of composite aerostructures utilising a virtual environment

This work presents an innovative approach to produce standardised procedures for a specific type of damage and subsequent repair of a Carbon Fibre Reinforced Plastic Composite (CFRP) aerostructure, along with an analysis of the process based on ergonomic methodologies and digital tools. A case study is presented to illustrate the approach's unique ability to increase the operator efficiency and reduce the opportunities for injury. The key benefit of this research is the demonstration of the potentialities of using 3D environments to highlight process issues and to provide design suggestions that will reduce the time and cost of the repair

A highly efficient ergonomic approach for the bonded repair of composite aerostructures utilising a virtual environment

This work presents an innovative approach to produce standardised procedures for a specific type of damage and subsequent repair of a Carbon Fibre Reinforced Plastic Composite (CFRP) aerostructure, along with an analysis of the process based on ergonomic methodologies and digital tools. A case study is presented to illustrate the approach's unique ability to increase the operator efficiency and reduce the opportunities for injury. The key benefit of this research is the demonstration of the potentialities of using 3D environments to highlight process issues and to provide design suggestions that will reduce the time and cost of the repair

Financial incentives for open source development: the case of Blockchain

Unlike traditional open-source projects, developers of open-source blockchain-based projects can reap large financial rewards thanks to a modern form of seigniorage. I consider a developer working on an open-source blockchain-based software that can be used only in conjunction with a specific crypto-token. This token is first sold to investors via an Initial Coin Offering (ICO) and then traded on a frictionless financial market. In all equilibria of the game, in each post-ICO period there is a positive probability that the developer sells all of his tokens on the market and, as a consequence, no development occurs

Comparison of different quasi-static loading conditions of additively manufactured composite hexagonal and auxetic cellular structures

Auxetic cellular structures have the potential to revolutionise sandwich panel cores due to their potential superior energy absorption capability. Because of their negative Poisson's ratio, auxetics behave counterintuitively and contract orthogonally under an applied compressive force, resulting in a densification of material in the vicinity of the applied load. This study investigates three cellular structures and compares their compressive energy absorbing characteristics under in-plane and axial loading conditions. Three unit cell topologies are considered; a conventional hexagonal, re-entrant and double arrowhead auxetic structures. The samples were additively manufactured using two different materials, a conventional Nylon and a carbon fibre reinforced composite alternative (Onyx). Finite element simulations are experimentally validated under out of and in-plane loading conditions and the double arrowhead (auxetic) structure is shown to exhibit comparatively superior energy absorption. For the carbon fibre reinforced material, Onyx, the specific energy absorbed by the double arrowhead geometry was 125% and 244% greater than the hexagonal (non-auxetic) and re-entrant (auxetic) structures respectively