Sandwich panels with a foldcore are of interest to the aerospace industry due to their promising properties. There is an increasing interest in the basic properties of such a core and response of ...these panels to low energy impact loading. In this paper experiments to determine quasi-static properties of such a core and a sequence of impact experiments using a drop tower and 4-point bending tests are presented. The aim of the latter is to assess the damage tolerance of sandwich panels with aramid paper foldcores and carbon fibre reinforced plastic (CFRP) skins under impact loading. The impact energy range in these experiments was chosen to investigate a variety of damage scenarios from barely visible damages (BVID) to fibre fractures in all plies of the impacted face sheet. 4-point bending tests were performed with the panels previously damaged by impact loadings to assess the residual bending strength of these samples. A numerical procedure has also been developed to reproduce these experiments (the impact as well as the 4-point bending tests). The method can also be employed to predict the results of the residual strength in other experiments like compression (CAI) or edgewise compression after the impact.
► Sensitivity of sandwiches with foldcores to impact damage were investigated. ► The static properties of the cores were acquired experientially. ► Impact and subsequent residual strength experiments were performed. ► Numerical simulations of impact and the residual strength were performed. ► Strength decreases significantly even if damaged by very low energy impacts.
The characterization of critical energy release rates of adhesive joints in laminated composite structures is a key issue when failure analyses have to be performed. Critical energy release rates, or ...fracture toughnesses, are known to be dependent on the mode mixing ratio, i.e. the portion of shear loading. It is thus useful to determine a criterion which gives the critical energy release rate as a function of the mode mixing ratio, which is the overall goal of this paper. For this purpose several experiments have been performed, for single mode I, single mode II, and mixed mode I/II loading conditions with pre-defined mode mixing ratios. Unfortunately, most of the experimental outcome cannot be used directly for least squares fitting of suitable fracture toughness criteria due to a couple of reasons, which will be discussed in detail. Hence, a numerical approach based on cohesive interface elements is employed to determine some of the critical energy release rates by fitting against experimental load–deformation curves. This combined numerical/experimental approach yields a useful database of discrete critical energy release rate values. These are utilized to fit suitable criteria which then allow the calculation of critical energy release rates for any given mode mixing ratio. The results are discussed in terms of convergence to the discrete values and physical plausibility, and a simple possibility to include mode III behavior is presented.
•Algorithm vertical stabilisation using a linear parametrisation of the current density.•Experimentally derived model of the vacuum vessel to account for vessel currents.•Real-time contouring ...algorithm for flux surface averaged 1.5 D transport equations.•Full real time implementation coded in Simulink runs in less than 200μs.•Applications: shape control, safety factor profile control, coupling with Raptor.
Equilibrium reconstruction consists in identifying, from experimental measurements, a distribution of the plasma current density that satisfies the pressure balance constraint. The LIUQE code adopts a computationally efficient method to solve this problem, based on an iterative solution of the Poisson equation coupled with a linear parametrisation of the plasma current density. This algorithm is unstable against vertical gross motion of the plasma column for elongated shapes and its application to highly shaped plasmas on TCV requires a particular treatment of this instability. TCV's continuous vacuum vessel has a low resistance designed to enhance passive stabilisation of the vertical position. The eddy currents in the vacuum vessel have a sizeable influence on the equilibrium reconstruction and must be taken into account. A real time version of LIUQE has been implemented on TCV's distributed digital control system with a cycle time shorter than 200μs for a full spatial grid of 28 by 65, using all 133 experimental measurements and including the flux surface average of quantities necessary for the real time solution of 1.5 D transport equations. This performance was achieved through a thoughtful choice of numerical methods and code optimisation techniques at every step of the algorithm, and was coded in Matlab and Simulink for the off-line and real time version respectively.
We present the first evidence for the existence of a neoclassical toroidal rotation driven in a direction counter to the plasma current by nonaxisymmetric, nonresonant magnetic fields. At high beta ...and with large injected neutral beam momentum, the nonresonant field torque slows down the plasma toward the neoclassical "offset" rotation rate. With small injected neutral beam momentum, the toroidal rotation is accelerated toward the offset rotation, with resulting improvement in the global energy confinement time. The observed magnitude, direction, and radial profile of the offset rotation are consistent with neoclassical theory predictions.
The main goal of the Divertor Tokamak Test facility (DTT), as indicated in the European Fusion Roadmap, is to explore and qualify alternative power exhaust solutions for DEMO. This paper illustrates ...its role and objectives.
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