The Nail Penetration Behaviour of Carbon Nanotube Composite Electrodes for Energy Storage

The high surface area, electrical and mechanical properties of carbon nanotube (CNT) composites has rendered them promising candidates for structural power composites. Nevertheless, it is important to understand their mechanical behaviour before they are applied in energy storage devices amid the safety concerns. This work explores the nail penetration behaviours of supercapacitor specimens consisting of CNT electrodes and pseudocapacitor specimens with carbon nanotube-polyaniline (CNT/PANI) electrodes. Specimens with and without electrolyte were tested. The dry cells without electrolyte follow a power law behaviour, while the wet cells with the electrolyte exhibit a piece-wise nonlinear relationship. The force, voltage and temperature of the supercapacitor were recorded during the nail penetration test. No temperature change or overheating was observed after short-circuit. Moreover, electrochemical testing is performed before and after the specimen penetration. The cyclic voltammetry shows the dramatic loss of capacitance, changing the cell behaviour from capacitor to resistor-like manner. Johnson-Cook model was used to predict the nail penetration behaviour. The coefficients of Johnson-Cook model are calibrated from the experimental load-displacement curves. The finite element model predictions are in a good agreement with the experimental results.

Johnson–Cook Parameter Identification for Commercially Pure Titanium at Room Temperature under Quasi-Static Strain Rates

Background: To simulate mechanical shocks on an intracranial implant called WIMAGINE®, Clinatec chose a Johnson–Cook model to account for the viscoplastic behavior of grade 2 titanium in a dynamic study using Radioss©. Methods: Thirty tensile specimens were subjected to tensile tests at room temperature, and the influence of the strain rate (8 × 10−3 and 8 × 10−2 s−1) and sandblasting was analyzed. Relaxations were included in the tests to analyze viscosity phenomena. Results: A whole set of parameters was identified for the elastic and plastic parts. Strain rate influence on stress was negligible at these strain rates. As expected, the sandblasting hardened the material during the tests by decreasing the hardening parameters, while local necking occurred at an earlier strain. Conclusions: This article provides the parameters of a Johnson–Cook model to simulate the elastoplastic behavior of pure titanium (T40, grade 2) in Finite Element Model (FEM) software.

Combined Laser Shock and Micro-Compression Approach to the Mechanical Behavior of Powders for Cold Spray

In cold spray, particles undergo large plastic deformation upon impact in a rapid dynamic regime (up to 109 s-1) at solid state. The simulation of this impact is key to understanding the cold spray process. In this study, an approach based on laser shock and micro-compression testing was developed to characterize the mechanical behavior of powders and fit parameters of the Johnson-Cook material behavior model. In situ micro-compression particle testing was performed in a SEM equipped with a microindentation stage. From subsequent FEM simulations of the test, static coefficients of the Johnson-Cook model were identified. A laser shock powder launcher (LASHPOL) was also developed to accelerate single particles and measure their corresponding velocity using high-speed imaging. In addition, image analysis of the particles before and after impact, together with FEM simulation, were used to determine strain rate hardening coefficients for the Johnson-Cook model.