Sandwich cores

What kinds of configurations are possible for composite structures The most obvious is that of a fiber-reinforced laminate. With a laminate, we can change laminae orientations, stacking sequence, and laminae materials to arrive at a suitable structure. We can stiffen the laminate, or we can put a sandwich core in the middle of those laminae. We can do all of those possibilities, but recognize that we will also have, in vir-tuaiiy any structure, some kind of hoie or a cutout for some reason. Thus, we must have a procedure to place an appropriate amount of reinforcement around those cutouts so that ioad can be transferred around them. Without that reinforcement, the structure cannot do the job it is required to do. These various possibie configurations are shown in Figure 7-38. 

Abstract The unique and readily tunable electronic and spatial characteristics of ferrocenes have been widely exploited in the field of asymmetric catalysis. The ferrocene moiety is not just an innocent steric element to create a three-dimensional chiral catalyst enviromnent. Instead, the Fe center can influence the catalytic process by electronic interaction with the catalytic site, if the latter is directly coimected to the sandwich core. Of increasing importance are also half sandwich complexes in which Fe is acting as a mild Lewis acid. Like ferrocene, half sandwich complexes are often relatively robust and readily accessible. This chapter highlights recent applications of ferrocene and half sandwich complexes in which the Fe center is essential for catalytic applications. 

PVC foams used as sandwich cores generally have ... 

The typical failure sequence observed in the experiments of Xu and Rosakis [1] is sketched in Fig. 7. One of the major conclusions of Xu and Rosakis is that shear-dominated inter-layer (or interfacial) cracks are the ones that initiate first and that such cracks grow very dynamically, their speeds and shear nature being enhanced by the large wave mismatch between the core and the face-sheets (the ratio of shear wave speeds of steel to Homalite is 2.6, Table 2). It is the kinking of these cracks into the sandwich core that triggers the complex mechanisms of intralayer failure. 

It is interesting to note that foamed composites are suitable sandwich core materials for FRP boats (8). Cross-ties (or sleepers) for railroads, especially for use in tunnels and subways, are very promising applications. Japanese National raUways carried out a long-term test in a tunnel, and the results were excellent. 

ASTM C 273-61 (1988) Standard Method of Shear Test in Flatwise Plane of Flat Sandwich Constructions or Sandwich Cores, 3 pp (DOD Adopted) (FSC Area FACR) (YD) (Comm F-7)... 

Shear properties of sandwich core materials can be determined by a similar technique described in ASTM C273-94 [24]. In this method the support plates may be adhered directly to the facings of the sandwich or the core materials. The recommended speed of jaw separation is 0.50 mm/minute. 

ASTM C275 94. Shear properties of sandwich core materials. 

ASTM-Intemational, editor. Standard practice for shearography of polymer matrix composites, sandwich core materials and filament-wound pressure vessels in aerospace apphcations 2007. 

Balageas et al. [107] and Bocherens et al. [108] describe the use of optical time-domain reflectometry (OTDR) and FBG to detect impact damage in GFRP sandwich specimens. The optical fibers were embedded in the sandwich core at various depths (Figure 16.49). The principle of the detection method is that deformation and damage due to impact leave areas of permanent strain around the impact zone. The OTDR and FBG methods were employed to detect such changes in comparison with the... 

Table 7.1 6 Properties and relative cost of structural sandwich cores...

Ji, G. and Li, G. (2013) Impact tolerant and healable aluminum miUitube reinforced shape memory polymer composite sandwich core. Materials and Design, 51, 79-87. 

The cross sections of the control sample (standard market sample which is the sandwich one) and die developed absorbent core (i.e. developed carded web sandwiched between two layers of nonwoven fabrics) are shown Figs. 2 and 3 respectively. The absorbent core of the controlled sample is a mixture of wood pulp and fte granules of super absorbent polymer (SAP). The developed absorbent core was then inserted within the polymeric cover stock (one side perforated sheet and other side impermeable sheet) of an available sample (market sample). Fig. 4 shows the cross sectional view of n ikin with developed sandwiched core. 

In a sanitary napkin, along with the mass per unit area and absorbency, the thickness is also very important characteristics. A thicker napkin is not at all desirable. The thickness values of the developed samples and the control sample are given in Table 2. For samples of both types A and B, we noticed a signifieant increase in thickness with an increase in the mass of blended web portion of the absorbent core. It is evident from the Table 2 that the thickness of the prq>ared samples is significantly lower, in most cases (A1-A9, and B1-B3), compared to the control sample, > ch would be an added advantage for an ultra-thin sanitary napkin. It has also been observed that a change in content of SAF in the web does not affect the thickness of the sample gnilicantly. So, the mean thicknesses for the same mass of sandwiched core samples have been reported. 

Table 3.4 Properties of PVC foam cores (Divinycell H Sandwich Core Material, reference 3.6).

Wood is the most appropriate material for a solid sandwich core and has been used extensively for many applications, such as doors and partitions. For lightweight constructions flat or end grain balsa is still used, although this is being superseded by synthetic materials. Bonded microspheres of inorganic materials, glass, ceramics, etc. to form syntactic foams are useful core materials. 

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