Composite structural

The performance of the classifier has been verified using a number of practical applications, such as civil engineering [3], inspection of aerospace composite structures, ball bearings and aircraft multi-layer structures. Here we present shortly some results, focusing on detection of disbonds in adhesively joint multi-layer aerospace structures using Fokker Bond Tester resonance instrument, details can be found in [1]. 

We have presented a neural network based spectrum classifier (NSC) aimed at ultrasonic resonance spectroscopy. The ultrasonic spectroscopy and the NSC has been evaluated in many industrial applications, such as concrete inspection, testing of aerospace composite structures, ball bearings, and aircraft multi-layer structures. The latter application has been presented in some detail. 

In wide sectors of industry there is a growing need of inspection methods which go without liquid coupling media. The excitation of bulk and surface waves by means of air-coupled ultrasonic probes is therefore an attractive tool for NDE. This is tme e.g. for the rapid scanning of large composite structures in the aerospace industry [1]. In other cases, the use of liquid couplants is prohibitive like the thickness measurement of powder layers. 

The abrasion resistance of ionomers is outstanding, and ionomer Aims exhibit optical clarity. In composite structures ionomers serve as a heat-seal layer. 

The lack of homogeneity and the friable nature of FRP composite structures dictate that caution be followed in mechanical design, vendor selection, inspection, shipment, installation, and use. 

Table 11.2 Composite structures produced during the slow cooling of Fe-C alloys...

Zhu, T. L. 1993 A Reliability Based Safety Factor for Aircraft Composite Structures. Computers and Structures, 48(4), 745-748. 

In photoluminescence one measures physical and chemical properties of materials by using photons to induce excited electronic states in the material system and analyzing the optical emission as these states relax. Typically, light is directed onto the sample for excitation, and the emitted luminescence is collected by a lens and passed through an optical spectrometer onto a photodetector. The spectral distribution and time dependence of the emission are related to electronic transition probabilities within the sample, and can be used to provide qualitative and, sometimes, quantitative information about chemical composition, structure (bonding, disorder, interfaces, quantum wells), impurities, kinetic processes, and energy transfer. 

Polymerisation casting involves mixing monomer or low molecular weight polymer with a polymerisation initiator, pouring the mix into the mould and allowing polymerisation to occur in situ. A variation is to impregnate fibres with initiated monomer or other low molecular weight material and polymerise to produce composite structures. The main problem is due to the heat of polymerisation. Unless heat transfer distances are kept short or unless the reaction is carried out very slowly it can easily get out of hand. 

The commercial grades available in the 1970s used either zinc or sodium as the cross-linking ion and ranged in melt flow index from 0.4 to 14. The main application of the ionomer resins has been for packaging film. The polymer is particularly useful in composite structures to provide an outer layer with good heat sealability. The puncture resistance of film based on ionomer film has the puncture resistance of a LDPE film of twice the gauge. 

Since weight is frequently a factor in the applications of composite structures, values for eleetrical and thermal conductivity, and tensile strength and modulus are even more impressive when normalized by the mass of the fiber. 

Table 3 lists the selected properties [16] that we have measured for several commercially available acrylate resins manufactured by the Sartomer Company and the Rohm and Haas Company. The resins were cured in an AECL Gammacell Model 240. The temperature rise was measured for an 8-g sample using Acsion s (formerly AECL Radiation Applications Branch) Gamma Calorimetry method [17]. All of this information is being used to evaluate the applicability of EB-cured acrylate adhesives for repairing composite structures. Combinations of these adhesives can be used to create electron-curable adhesives suitable for composite repair. 

There are three options for remote repair of composite structures using electron curing a portable accelerator. X-rays generated from such an accelerator and radioisotopic sources, such as Co . 

The technology to routinely cure applied adhesives for repairing damaged composite structures at remote repair stations is currently available. There are already systems that use portable accelerators for X-ray radiographic inspection of aircraft components [43]. Fig. 6 shows a conceptual picture of a portable accelerator unit that would contain the power unit, vacuum systems, and computer... 

Adhesive bonding is an integral part of virtually all composite structure. Early composite matrix resins could in some cases act as an adhesive, such as with self-filleting systems used for honeycomb sandwich fabrication. As composite systems became more optimized for minimum resin content and limited flow, supplementary adhesives became more common. Modern-day composite structure relies on adhesives almost as much as bonded metallic structure. 

Fig. 40. Composite structure locations on Boeing 111. Reproduced by permission of the Boeing Company.

Labor cost in a structure is directly related to part count. If part count can be reduced, then labor costs (and inventory costs) wili decrease. Composite structures are generally composed of many fewer parts than are metal structures. Integral part design and fabrication techniques reduce fastener count and bonding operations. Thus, composite structures can have cost elements that are considerably lower than those for metal structures. 

Often, the manufacturing processes involved for composite structures fabrication are greatly simplified as compared to those for metal structures. Reduced part count results in a much lower assembly cost and overall reduction in the factory labor hours. 

In contrast, with composite materials, the materials utilization factor is rarely higher than 1.2 to 1.3. That is, only a maximum of 20-30% of the material is wasted with composite structures. Whereas obviously with a materials utilization factor for some metal parts of 15-25, the waste is 1500-2500% Those are not individually typical numbers, but are the worst cases in both situations, i.e., for metals and composite materiais. For metals, there are many, many operations for which the waste factor is very iow. And for composite materials there are also many situations where the waste factor is much lower than 20-30%. The point is that the worst-case situations are totaliy different for these two kinds of materials based on the way objects are inherently created with the two different types of materials. Composite materials are built up until the limits of the desired geometry are reached. At that point, the layup operation simpiy ceases. Composite materials and structures are fabricated in as ciose to the final configuration as possible, i.e., so-calied near-net shape. 

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