1,720,993 research outputs found
Sub-surface damage location and identification using infra-red techniques
No full textThe paper presents a new methodology for identifying sub-surface damage in composite components using a combination of Pulse Phase Thermography (PPT) and Thermoelastic Stress Analysis (TSA)
Dynamic response of doubly curved honeycomb sandwich panels to random acoustic excitation. Part 1: Experimental study
No full textA set of four doubly curved, composite honeycomb sandwich panels has been tested with broad band, random acoustic excitation in a progressive wave tube facility. This paper presents the experimental results in the form of dynamic face plate strain measurements taken from various points close to the centre of the panels, on both the inner and outer face plates. The panels were tested at overall sound pressure levels up to 164 dB (ref. 2×10?5 Pa, over a frequency bandwidth of 60–600 Hz). The response was found to be linear, with a maximum measured root mean square strain of 250?. The doubly curved geometry was found to have a profound effect on the ratio of inner-to-outer face plate strain, which was compared with ratios reported for flat and singly curved geometries. The second part of this study concentrates on three methods for predicting the response of the doubly curved panels to random acoustic excitation
Free vibration of doubly curved composite honeycomb rectangular sandwich panels
No full textSandwich panels have a wide variety of applications in many branches of engineering including aerospace, marine, civil and motorsport. Their very high stiffness-to-weight ratio make them particularly useful in aircraft and typical applications include floor panels, fairings and inlet cowl panels. In the latter case, the geometry of the panels can be considered doubly curved and they are usually constructed with carbon fibre reinforced plastic face plates and a lightweight resin impregnated paper honeycomb core. The free vibration of such panels both experimentally, and theoretically using a commercially available finite element code, has been investigated. Results are presented for the natural frequencies, and the theoretical investigation is extended to cover a variety of configurations in terms of the radius of curvature
A new measurement technique for the estimation of core shear strain in closed sandwich structures
No full textSandwich structures have been widely used for many years in applications such as aircraft panels, marine-craft hulls, racing car bodies and spacecraft solar arrays. Most sandwich panel designs include a lightweight core such as paper honeycomb or closed cell foam encased between two face plates, and in the case of aircraft panels constructed from carbon fibre reinforced plastics, the core is bevelled and edge pan plies are included to totally enclose the core. This type of design restricts access to the core making it almost impossible for the engineer to measure the shear strain developed in the core during in-service static or dynamic loading. This paper introduces a new measurement technique whereby the shear strain in the core can be estimated from face plate measurements using a linear finite difference approximation. The estimation method is presented and supported by calculations on a statically loaded sandwich beam. Static and dynamic experiments were conducted in order to validate the technique using a honeycomb sandwich beam instrumented with strain gauges on the core and face plates. The results showed excellent agreement between measured and estimated core shear strain for sandwich configurations with thin face plates, such as those encountered in aircraft and marine-craft constructions
Dynamic response of doubly curved honeycomb sandwich panels to random acoustic excitation. Part 2:Theoretical study
No full textIn this paper a single-degree-of-freedom model is developed to predict the dynamic response of an acoustically excited doubly curved sandwich panel. Three variants of the model are investigated, based on differing assumptions regarding the spatial distribution of the applied loading. When the loading is assumed to be uniform then the model reduces to the Miles approach, and when the loading is assumed to conform to the structural mode shape then the method is very similar to the Blevins approach. The third variant involves a more detailed consideration of the travelling wave characteristics of the applied loading, and this is found to give much improved agreement with experimental results obtained in a progressive wave tube facility. In addition, an approach using the finite element method is presented in which the response to grazing incidence excitation is computed, and this is also found to yield good agreement with the experimental results
Experimental verification of various modelling techniques for piezoelectric actuated panels
No full textThe scientific equipment being used on-board satellites sometimes requires a high degree of pointing accuracy and a minimum level of disturbances i.e. vibrations. To this end, actively controlled structures are employed and one of the best methods of achieving this degree of control with the minimum of impact on the structure itself is to employ piezoelectric patches as sensors/actuators. In this paper, various techniques for the mathematical modelling of the dynamics of a piezoelectric actuated panel are presented. The results obtained via the numerical simulations are then compared with test results in order to assess the accuracy of the various modelling techniques. Attention is focused on a simply supported panel, with twin patches of piezoelectric material bonded on opposite faces of the panel, which act as actuators. The equations governing the dynamics of the system, which includes the panel and the actuators driven by electrical signals, are derived using Lagrange’s equations of motion with vibration mode shapes of the bare panel as the Ritz functions. Other techniques, such as Mechanical Impedance based method and Finite Element method are also used to produce mathematical models of the system
Honeycomb elastic properties: a review of some existing theories and a new dynamic approach
No full textThe influence of the nine orthotropic material properties of honeycomb on the dynamic response of a finite
element model of a simple supported sandwich plate are examined. Fifteen available theories from the
literature for the material properties of honeycomb are reviewed and their values calculated for a HexWeb
5.2-1/4-25(3003) Aluminium core. The agreement between the theoretical material properties and the major
ASTM(American Society for Testing andMaterials) standard test methods is investigated. A new and simple
technique is described for measuring the dynamic shear moduli of honeycomb materials and its values are
compared with those presented in the literature
On predicting the response of acoustically-excited doubly curved sandwich panels
No full textThis paper presents a recent programme of research, which has concentrated on the measurement and prediction of the dynamic response of doubly curved composite honeycomb sandwich panels to high intensity, random acoustic excitation. Four panels with varying radii of curvature were tested in a progressive wave tube (PWT) facility at overall sound pressure levels up to 164 dB (re 2×10?5 Pa). Several methods are presented to predict the dynamic response of the panels to random acoustic excitation. The first of these was the single-degree-of freedom (SDOF) approximation method, where different assumptions with regard to the spatial characteristics of the pressure loading are made. Finite element analysis (FEA) was also used to predict the response, where the pressure loading was assumed to consist of a series of travelling waves at grazing incidence to the structure.
The results presented for both the SDOF approximation method and the FEA method show good agreement between predicted and measured strain values, which are also presented
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