Ply drops

To decrease the thickness of a laminate, some of the laminae must be selectively stopped, dropped, or terminated. Moreover, the stopped laminae are covered with at least one continuous lamina as in Figure 7-31. There, resin-rich zones occur naturally in the vicinity of the ply drop. Such regions are also local stress-concentration sites. However, the tapered laminate creates a globally lessened stress concentration. 

Resin flow models are capable of determining the flow of resin through a porous medium (prepreg and bleeder), accounting for both vertical and horizontal flow. Flow models treat a number of variables, including fiber compaction, resin viscosity, resin pressure, number and orientation of plies, ply drop-off effects, and part size and shape. An important flow model output is the resin hydrostatic pressure, which is critical for determining void formation and growth. 

Agastra, P. Mandell, J. F. Testing and Simulation of Damage Growth at Ply Drops in Wind Turbine Blade Laminates. Presented at the Society lor the Advancement of Material and Process Engineering, Seattle, Washington (USA), May 17-20,2010 Paper 398. 

More recent data on carbon-epoxy composites AS4/3501-6 (an amine cured epoxy resin reinforced with in-plane fiber tow waviness AS4 carbon fibers designed for structural applications) were reported [221]. Composites stmctural details (ply drops, ply joints, etc.) can produce significant fiber deviation. The in-plane fiber tow waviness may create areas with high resin content which... 

Populations of soil mites were reduced in the Chernobyl area, but no population showed a catastrophic drop in numbers. By 1987, soil microfauna — even in the most heavily contaminated plots — were comparable to controls. Plies Drosophila spp.) from various distances from the accident site and bred in the laboratory had higher incidences of dominant lethal mutations (14.7%, estimated dose of 0.8 mGy/h) at sites nearest the accident than controls (4.3%). Fish populations seemed unaffected in July/August 1987, and no grossly deformed individuals were found. However, 134+137( 5 levels were elevated in young fishes. The most heavily contaminated teleost in May 1987 was the carp (Carassius carassius). But carp showed no evidence of mutagenesis, as judged by incidence of chromosomal aberrations in cells from the corneal epithelium of carp as far as 60 km from Chernobyl (Sokolov et al. 1990). 

If, as in the fracture surface type shown in Fig. 3 on the left hand side, the width of the featureless delamination is increasing with delamination length this is also reflected in the R-curve (Fig. 5). There, values are dropping from relatively high cross-ply -values to a value typical of the unidirectional laminate. This could be a hint that energy release rates determined for the cross-ply laminates using the analysis developed for the unidirectional material are valid in the sense that relative proportions are conserved. 

A. Triethyl 2-methyl-l,1,3-propanetricarboxylale (not isolated). A 1-1. three-necked flask is fitted with a mechanical stirrer, a reflux condenser protected by a calcium chloride tube, and a 250-ml. dropping funnel. All parts of the apparatus should be scrupulously dry. Three hundred milliUters of anhydrous ethanol (Note 1) is placed in the flask, and 14.1 g. (0.61 g. atom) of clean sodium, cut in pieces as large as wiU easily pass through a neck of the flask, is added rapidly. The neck of the flask is immediately closed, and the mixture is stirred until all the sodium has dissolved the cooling bath is removed, and heat is a[)plied if the reaction becomes sluggish at the end. 

This property of rebound resilience is very rarely specified, but it is a useful, fast, simple test that can be carried out quantitatively to assign the foam type to conventional or high-resilicncc types. The test is described in ASTM D. 574 95, Test H and consists of dropping a 16 mm diameter steel ball of weight 16.3 g onto the specimen, which preferably is in the form of the end product, or onto the foam at a minimum thickness of 50 mm. Plied-up samples are permitted without the use of cement. 

Karasek et al. [66] conducted drop-weight impact tests on IM7 carbon fibre/ epoxy resin laminates after sea water exposure. Four resin systems (Table 7.2) were used, three of them being based on the same Shell Epikote 828 with different hardeners and/or impact modifiers. The volume fractions were in the range 60-69% fibre and the lay-up was [0/ 45/90°]js. Samples were about 6.35 mm thick for all materials (different cured ply thicknesses necessitated the use of differing numbers of plies) and cut to 100 x 100 mm squares for testing. The samples were saturated with ASTM D1141-52 Formula A synthetic sea water at 95°C, and then conditioned at ambient... 

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