Lightning strike damage behavior of carbon fiber reinforced epoxy, bismaleimide, and polyetheretherketone composites

Experimental work has shown that a component of lightning strike damage is caused by a mechanical loading. As the profile of the pressure loading is unknown a number of authors propose different pressure loads, varying in form, application area and magnitude. The objective of this paper is to investigate the potential contribution of pressure loading to composite specimen damage. This is achieved through a simulation study using an established modelling approach for composite damage prediction. The study examines the proposed shockwave loads from the literature. The simulation results are compared with measured test specimen damage examining the form and scale of damage. The results for the first time quantify the significance of pressure loading, demonstrating that although a pressure load can cause damage consistent with that measured experimentally, it has a negligible contribution to the overall scale of damage. Moreover the requirements for a pressure to create the damage behaviours typically witnessed in testing requires that the pressure load be within a very precise window of magnitude and loading area.

/pdf/quantifying-the-influence-of-lightning-strike-pressure-30ad8fji4b.pdf

Quantifying the Influence of Lightning Strike Pressure Loading on Composite Specimen Damage

Delamination analysis of CFRP laminates exposed to lightning strike considering cooling process

Increased electrification of aircraft power systems has been widely presented as a route toward meeting environmental and emissions targets for aircraft performance, via more-electric aircraft and future hybrid-electric aircraft concepts. In parallel, the superior mechanical performance of carbon fiber reinforced polymer (CFRP) has resulted in its increasing use for aircraft structures. The relatively low electrical conductivity of CFRP compared to traditional aluminum structures and copper conductors limits the use of structural CFRP structures as electrical elements, so separate systems are needed. This adds structural mass and volume to a system, negating some of the benefits of using CFRP. Closer integration of the composite structure and electrical power system (EPS), with an ultimate goal of achieving components with multifunctionality (combined thermal, electrical, and structural functionality), offers a route toward the light-weighting of these systems, thus supporting improvements in aircraft performance. This article presents a roadmap to achieve this multifunctionality, supported by the combination of introducing definitions for different levels of multifunctionality, associated design thresholds, and trades between the EPS and CFRP materials/structures. Existing multifunctional (MF) electrical–thermal–structural CFRP-based solutions are contextualized within this roadmap. This enables the realization of viable routes for developing MF systems for the strategic focus of future research efforts.

/pdf/a-route-to-sustainable-aviation-a-roadmap-for-the-3w3ly0vox4.pdf

A Route to Sustainable Aviation: A Roadmap for the Realization of Aircraft Components With Electrical and Structural Multifunctionality

Our research into the formation of a functional copper-containing surface layer on parts of automobile engines by using an alignment tribotechnology has established a decrease in the wear of parts during their operation. It was found that the formed coating creates an elastic layer that reduces strains in a material of engine parts. Our experimental study of the coercive force of parts' working surfaces has confirmed a decrease in the accumulation of destructive stresses in the near-surface layers of a components' material. In turn, a comparative analysis of the obtained results by using a coercimetric method confirms that the proposed aligning tribotechnology leads to reduction of the stressed-strained state and makes it possible to improve wear resistance and enhance the technical condition of diesel engine cylinder liners: the magnitude of coercive force reduces by 7.5 %, while operating time increases by 16 %. In this case, at larger operating time: 254.8 thousand km against 220.5 thousand km, according to data on the coercive force (14.2…9.1) A/cm and (13.2…9.0) А/cm, it is almost in the same condition.The functional surface layer forms when introducing a composite oil to the tribotechnology of cold alignment of an automobile powertrain. We have proposed and implemented a circuit to connect electric current to components at an engine's cylinder-piston group as a result of studying the developed tribotechnology of alignment. The features of this scheme are that the constant electric current is supplied by the plus polarity, through the brush-collector node, to the crankshaft, and by the minus polarity, through the clamping contact, to the crankcase block.The research results suggest a possibility to control the internal strains and the subsequent magnitude of wear in a material of working heavily-loaded components of automobile powertrains provided they are serviced properly. The proposed tribotechnology of alignment could be of interest for both service departments at trucking companies and for car service stations.

/pdf/exploring-a-possibility-to-control-the-stressed-strained-267aqq02uh.pdf

Exploring a possibility to control the stressed­strained state of cylinder liners in diesel engines by the tribotechnology of alignment

https://hal-univ-tlse3.archives-ouvertes.fr/hal-01940478/document

A method to replace lightning strike tests by ball impacts in the design process of lightweight composite aircraft panels

The increased use of carbon fiber reinforced plastics (CFRP) in aeronautic industry and the large scale installation of electrical systems in new aircrafts have led to the development of specific models to understand current distributions into composite materials. For instance, the analysis of a short circuit on a carbon structural element inside an aircraft cannot be analysed using standard methods supposing linear behaviour of the composite. Thus, this paper presents an innovative approach to model the dynamic electrical behaviour of a CFRP material during a short circuit.

http://ieeexplore.ieee.org/iel5/6064642/6078493/06078540.pdf

Dynamic electrical behaviour of a composite material during a short circuit

Assemblies representative of aircraft junctions made of two materials and a fastener have been subjected to lightning current waveforms in laboratory. Current distributions on the different parts of the assemblies have been measured. An electrical equivalent circuit of the assemblies has been built. An inverse method has been designed to extract the dynamical in-strike electrical parameters (resistances, inductances, generators) of the circuit from the measured current distributions. It is shown in particular that the in-strike contact resistances between the different parts are systematically very small, even when the pre- or post-strike values are large. This effect is related to the appearance of internal discharges in the gaps of the assembly.

In-strike dynamical measurements of contact resistances

Lightning strikes of composite materials induce two distinct kinds of direct effects: surface and bulk mechanical damage Bulk damage includes fiber-resin debonding, transverse cracks, fiber rupture and ply delamination It results from the mechanical stresses associated to physical processes which come with lightning strikes such as surface explosion or magnetic force generation We propose a method to design mechanical impact tests representative of lightning tests in the sense that strains and stresses applied to the material in both experimental situations are comparable A campaign of actual equivalent mechanical test and has been designed using a simulation driven procedure and performed in the maboratory The procedure of the method of equivalence is demonstrated trough the comparison of numerical and real impact tests observations with lightning strikes measurements of rear face displacements and internal damaged areas

Equivalent impact set-up for lightning strike damage on composite coupons

Lightning strikes on thin monolithic composite materials such as aircraft fuselage skin induce two distinct kinds of direct effects: surface and bulk mechanical damage. Bulk damage includes fibre-resin debonding, transverse cracks, fibre rupture and ply delamination which are caused by mechanical stresses resulting from physical processes induced by lightning strikes such as surface explosion or magnetic force generation. We propose here a method to design mechanical impact tests wanted to be representative of lightning ones in the sense that strains and stresses applied to the material in both situations are comparable. The criterion of equivalence we rely on is thus the temporal evolution of the rear face deflection. Mechanical impact tests leading to deflections quite similar to the ones obtained during lightning tests have been designed using a simulation driven procedure and performed experimentally. A comparison between these two kinds of tests is then achieved, based on the two observables: rear face deflection for which we have a quite good matching for the first 100 µs and internal damage (delamination area and profile) for which we obtain an acceptable matching for the total delaminated area but very poor matching for the distribution of the delamination in the laminate.

How to define a mechanical impact equivalent to a lightning strike

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