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The purpose of this paper is to study the damage induced in “green” and synthetic composites under impact loading.

The study was focussed on epoxy-based composites reinforced with woven hemp or glass fibres. Six assessment techniques were employed in order to analyse and compare impact damages: eye observation, back face relief, terahertz spectroscopy, laser vibrometry, x-ray micro-tomography and microscopic observations.

Different damage detection thresholds for each material and technique were obtained. Damage induced by mechanical and laser impacts showed relevant differences, but the damage mechanisms are similar in both types of impact: matrix cracks, fibre failure, debonding at the fibres/matrix interface and delamination. Damage shape on back surfaces is similar after mechanical or laser impacts, but differences were detected inside samples.

The combination of these six diagnoses provides complementary information on the damage induced by mechanical or laser impacts in the studied green and synthetic composites.

The indentation behaviour of sandwich panels is significant to incipient damage and is known to be affected by a number of dominant parameters. However, it is challenging not only to demonstrate how those few dominant parameters influence the indentation behaviour but also to ascertain that such influence was coupled to the variation of the other dominant parameters. The paper aims to discuss these issues.

In this work, the authors adopted a controllable quasi-static testing to carry out a diagnostic interrogation on the nature of incipient damage in laminate-skinned sandwich panels using hemispherical indenter and used photographs taken from the cross-sections of all the cut-up tested specimens, which were stopped both just before and after the initial critical loads, respectively, to confirm the mechanism of the incipient damage. Sandwich panels with aluminium honeycomb core had carbon/epoxy skins of two different thicknesses and lay-ups and hemispherical nosed indenter had three different diameters.

The authors found that: the incipient damage mechanism in all the panels was combined delamination in the skin and core crushing without debonding; doubling the skin thickness had the significant enhancement on critical load and indentation and this enhancement became greater for the larger indenter diameters; the indenter diameter had the moderate effect on critical load in the thick panels from 8 to 14 mm but had the negligible effect on thin panels and no effect on the thick panels from 14 to 20 mm; varying the skin lay-up or support had little effect on the indentation behaviour.

These findings were limited to the constant core density and core thickness. Varying the former significantly could alter the findings accordingly.

The results of this work should be tremendously useful to design and analysis in industrial applications of sandwich structures in aircraft, vehicles, marine vessels and transport carriages for situations involving localised loading and deformation.

The results of this research work is one of the very few that demonstrated a systematic understanding of the indentation behaviour characteristics of sandwich construction, which is vital to the establishment of indentation law for sandwich structures in future.

The Civil Aviation Authority (CAA) has in the past declared ‘lives’ for some nominally ‘fail safe’ aeroplane types pending further evidence. This Notice offers structural review and inspection as an alternative to such ‘lifing’ provided that the constructor provides a document describing the inspections necessary to ensure that damage and incipient failure can be found before unacceptable structural weakening occurs.

THE breakdown of any kind of machinery always causes additional expense, not only because repairs are costly, but also because of the loss of operating time and production. Bearings are a particularly critical component and their serviceability is usually essential for the operation of any machine into which they are fitted. Thus it is important that bearing damage should be detected early enough to replace the bearing during a scheduled servicing period, and that unscheduled servicing of the machine should be prevented. This is particularly so where safety is a factor, as in aircraft engines, and certain parts of the process industries.

An investigation of the use of ultrasonic agitation for cleaning printed circuit boards using CFC‐based solvents has shown that, under the standard conditions required to produce clean assemblies, no damage will occur to the components studied. Damage can only be induced by use of anomalously longer times or higher power densities. In all cases in which damage has been induced, it is of a purely mechanical nature due to fatigue, and is located on the device bond‐wires and/or the package legs. Cleaning using CFC‐based solvents under standard ultrasonic conditions of power density and time etc. is readily achieved within 2 minutes, even with a minimum stand‐off height.

FEW engineering products receive the abuse to which aero engines are subjected in wartime and few mechanical devices are produced in which the margin of safety and failure is so small and yet so vital. Failures on a large scale are, therefore, inevitable and their consideration in detail would present a task of prohibitive magnitude but what little is known with any completeness and certainty can offer some useful data. Consideration of a large number of different makes of engines overhauled during wartime has revealed an amazing complexity of facts; it has shown that failures have developed from almost every conceivable cause which, in turn, have produced every conceivable result. There are few tangible pronouncements which can be made on the subject but nevertheless distinct common tendency has been observed which is sufficiently consistent to be worth consideration. This concerns the general trend of failures and will be referred to later; but with regard to failures in detail, the only safe statement to make is that invariably different parts‐fail on different types of engines subjected to similar conditions of severity in operation. The reason for this is not hard to find, and complexity of design in modern aero engines prohibits the mechanical ideal of simultaneous failure of adjacent parts subjected to a given overload. Not only is the exact functional strength of each individual part hardly known but the loadings which it has to endure cannot be foreseen.

THE STATIC AND FATIGUE TESTS on the A300B Airbus structure are being performed simultaneously at a number of sites in Europe. The main static test specimen is located in Toulouse. The fatigue test specimens are undergoing tests in Munich, Bremen and Hamburg. Detailed testing of major components such as the wing movable control surfaces and items such as the flap tracks has been carried out in Amsterdam and Hatfield respectively.

The purpose of this paper is to report the results of a recent project of complex tests on the survival of structural health monitoring (SHM) technology with piezo wafer active sensors (PWAS) and electromechanical impedance spectroscopy (EMIS) at simulating the concomitant action of harsh conditions of outer space: extreme temperatures, radiations, vacuum.

The tests were conducted on PWAS, consists in adhesive and aluminium discs as structural specimens, with PWAS bonded on them. The substantiating of PWAS-EMIS-based SHM technique consists the fact that real part of the PWAS electromechanical impedance spectrum follows with fidelity the resonance behaviour of the structure vibrating under the PWAS excitation. This EMIS signature is very sensitive to any structural changes and, on this basis, can be monitored the onset and progress of structural damages such as fatigue, cracks, corrosion, etc.

The conclusion of the tests is that the cumulative impact of severe conditions of temperature, radiation and vacuum has not generated decommissioning of sensors or adhesive, which would have meant the compromise of the methodology. A second important outcome is linked to the capability of this methodology to distinguish between the damages of mechanical origin and the false ones, caused by environmental conditions, which are, basically, harmless.

The question of transfer of PWAS-EMIS-based SHM technology to space vehicles and applications received, as a novelty, a first and encouraging response.

The purpose of this paper is to espouse Triggernomic Repair Process Analysis (TRAP), a nonlinear theoretical methodology employed to stress the importance of an informed approach to the diagnosis and prognosis of structural building defects at the owner‐occupier level.

TRAP analysis focuses on the diagnosis limitations relating to house repair and maintenance among owner‐occupiers in the UK, based on a stratified random survey of owner‐occupiers' maintenance decisions.

It is concluded that lack of technical skills‐knowledge awareness is one of the main deterrents to efficient defect diagnosis. The failing on defect diagnosis is broadly defined as resulting from Chronic Deficiency of Defects Diagnosis (CD³). CD³ is furthermore conceptualised as a theoretical dichotomy construct which persists due to Chronic Diagnosis Failure (CDF) and Chronic Misapplication of Maintenance Remedies (CMMR).

The constructs identified help to explain why owner‐occupier housing disrepair remains high and a source of concern among practitioners in the UK. A pro‐maintenance housing regeneration agenda is imminent in order to promote technical skill‐knowledge awareness and the effectiveness of the maintenance decision making among owner‐occupiers.