# Soft impacts on aerospace structures

TL;DR: In this paper, the authors provide an overview of the literature dealing with three types of soft impacts of concern for the aerospace applications, namely impacts of rain drops, hailstones and birds against aircraft.

About: This article is published in Progress in Aerospace Sciences.The article was published on 2016-02-01 and is currently open access. It has received 56 citations till now. The article focuses on the topics: Aerospace.

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01 Nov 2009

TL;DR: In this paper, the authors theoretically and numerically study the events within the time scale of about 1 μs over which the coupled dynamics between the gas and the droplet becomes important, and show that the solution is overtaken by initially subdominant physical effects such as the surface tension of the liquid-gas interface or viscous forces in the liquid.

Abstract: A high-velocity (≈1 ms−1) impact between a liquid droplet (≈1 mm) and a solid surface produces a splash. Classical observations traced the origin of this splash to a thin sheet of fluid ejected near the impact point, though the fluid mechanical mechanism leading to the sheet is not known. Mechanisms of sheet formation have heretofore relied on initial contact of the droplet and the surface. In this paper, we theoretically and numerically study the events within the time scale of about 1 μs over which the coupled dynamics between the gas and the droplet becomes important. The droplet initially tries to contact the substrate by either draining gas out of a thin layer or compressing it, with the local behaviour described by a self-similar solution of the governing equations. This similarity solution is not asymptotically consistent: forces that were initially negligible become relevant and dramatically change the behaviour. Depending on the radius and impact velocity of the droplet, we show that the solution is overtaken by initially subdominant physical effects such as the surface tension of the liquid–gas interface or viscous forces in the liquid. At low impact velocities surface tension stops the droplet from impacting the surface, whereas at higher velocities viscous forces become important before surface tension. The ultimate dynamics of the interface once droplet viscosity cannot be neglected is not yet known.

122 citations

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TL;DR: In this article, the capability of a vertical tail leading edge to withstand bird strike was investigated and general considerations on the improvement of such capability with respect to the mass saving and to the required structural performances by considering different material systems.

32 citations

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TL;DR: In this paper, a method of strength calculations for laminated aircraft cockpit windows influenced by different operating factors (bird strike, pressurization) is devised, based on embedding the initial uncanonical shell in the auxiliary one of canonical form in plan with the boundary conditions, which permit of a simple analytical problem solution as a trigonometric series.

Abstract: The method of strength calculations for laminated aircraft cockpit windows influenced by different operating factors (bird strike, pressurization) is devised. The method is based on embedding the initial uncanonical shell in the auxiliary one of canonical form in plan with the boundary conditions, which permit of a simple analytical problem solution as a trigonometric series. For satisfying the initial boundary conditions, the auxiliary shell is supplemented with compensating loads, which are continuously distributed over the contour of the initial shell. The compensating loads enter in the equations of motion for the auxiliary shell as integral relations. The system of motion equations is rearranged in the system of ordinary differential equations of second order, which is integrated by the solution expansion in the Taylor series. The windows are treated as a laminated open-ended cylindrical shell consisting of isotropic layers of constant thickness. The laminated window model is based on the modified theory of first order that accounts for transverse shear strains, thickness reduction, rotary inertia, and compression of the normal element in each layer. For the composition, the hypothesis of broken line is valid. The model of pressure pulse that apparently represents the effect of the bird impact on the windows was constructed on the basis of experimental studies. The stress-strain state of the window element in AN aircrafts was evaluated, set on the bird strike and cockpit pressurization. Five window alternatives are examined. Calculation results are in good agreement with experimental data. The results become theoretical and practical backgrounds for engineering calculations and optimum design of laminated aircraft window elements influenced by different operating factors. Thus, the advanced method can be applied to estimation of the lifetime of existing window elements and development of the new ones.

28 citations

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TL;DR: In this paper, the influence of laminates' layups on damage modes and energy variations of bird impact on a square laminated plate were numerically investigated by means of Smoothed Particle Hydrodynamics (SPH) and finite element method (FEM) analysis.

24 citations

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TL;DR: In this paper, the authors compared the performance of pulsating water jet and continuous water jet technologies on granite samples at three pressure levels of 20MPa, 40MPa and 60MPa.

24 citations

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TL;DR: The mating of Brazilian and Guatemalan flies is, therefore, selective rather than random; however, the particular type of selectivity here observed does not constitute a barrier to gene exchange.

6,273 citations

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01 Apr 1998TL;DR: In this article, the authors present contact laws, contact dynamics, low velocity impact damage, residual properties, and ballistic impact on sandwich structures, as well as the impact on the sandwich structure.

Abstract: 1. Introduction 2. Contact laws 3. Impact dynamics 4. Low velocity impact damage 5. Damage prediction 6. Residual properties 7. Ballistic impact 8. Repairs 9. Impact on sandwich structures References.

1,146 citations

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TL;DR: The fluid dynamic phenomena of liquid drop impact are described and reviewed in this article, and specific conditions under which the above phenomena did occur in experiments are analyzed and the characteristics of drop impact phenomena are described in detail.

1,081 citations

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TL;DR: In this article, a general flow law is used throughout, and the equations for steady flow, with r allowed to be non-zero, are found, with different variations of density, temperature or flow law with depth.

Abstract: A block of ice resting upon a rough slope forms a theoretical model of a glacier or an ice-sheet, the sides of the glacier valley being ignored. Previous papers have described two types of steady flow in this model: ( a ) laminar flow, in which the longitudinal velocity gradient r is zero, and ( b ) extending or compressive flow, in which r is non-zero, ( a ) was derived under the assumption of a general flow law for ice, but ( b ) was only derived under the assumption of perfect plasticity. In the present paper a general flow law is used throughout, and the equations for steady flow, with r allowed to be non-zero, are found. The previous results ( a ) and ( b ) appear as special cases. Possible variations of density, temperature or flow law with depth are allowed for. If the density and the flow law are known as functions of depth in any region, and if the surface slope, the surface velocity, and the value of r are known, the equations give the stresses and velocity as functions of depth. The borehole experiment on the Jungfraufirn (1948-50) allows an experimental test. From the observed value of r , and Glen’s laboratory flow law for ice, a theoretical curve for the result of the experiment is calculated which is compared with the experimental curve. At a depth of 50 m the effect of ignoring r , as has been done hitherto, is to underestimate the shear rate by a factor of 50; on the present theory it is overestimated by a factor of 1∙33. The remaining discrepancy is probably mainly due to the effect of the glacier sides.

457 citations