Delamination

Delamination means the external layer of the moulding peeling away. See Table 11.8 for some causes and means of correction of delamination. 

Contamination by other material Check purity of granules. Check cylinder and HR for presence of another plastic. 

Inadequate mixing Check homogeneity of melt and plasticisation capacity of cylinder. 

Damp on granules Use dry granules. Use heated charging hopper. Reduce amoimt of plastic placed in hopper at a time. 

Zawistowski and Sz. Zieba, Setting up an injection moulding process. 

As corrosion proceeds the corrosion product formed takes up a larger volume than the steel consumed. This builds up tensile stresses around the rebars. 

EfI Crack with efflorescence ER Exposed reinforcement ERI0 Exposed reinforcement original cover 10 mm ES Efflorescence stains FD Frost damage F or FV Fine or very fine cracks 0.4 Crack 0.4 mm wide GL Grout loss 

W Weathering WS Water stain CS Core sample EW Excess washers SS Short stud on bearing TW Tie wire B Bottom plate T Top plate NW No washer LS Long stud FP Flaking paint PF Poor finish WD Water deposits 

Radar records changes in the dielectric constants associated with the concrete/air phase change. However, the radar also senses the dielectric changes at the steel concrete interface, the presence of water and, to a small amount, chlorides. This makes interpretation of radar images a difficult process. In North America the main use of radar and infrared has been for bridge deck surveys with vehicle mounted systems. In Europe and the 

United Kingdom hand-held systems have been used for surveys of building and other structures. The reader is recommended to review the literature for further information (Cady and Gannon, 1992 Bungey, 1993 Titman, 1993 Concrete Society, 1997b Matthews, 1998 ASTM D6087-05, 2005). There is further discussion of this topic in Section 4.15. 

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It has been observed [4], that the effect of mean stress on the damage rate is much smaller than that of the stress range when delamination is the dominant failure mode. 

However, it is possible that the constant rate of AE activity is interrupted by local peaks of high rate of AE. This is due to the formation of local (internal) delaminations because of interlaminar stresses arising due to the presence of transverse cracks. This is more accentuated in less severe loading conditions. Under severe loading conditions = 80% CTu, R = 0.1) the rate of damage development (delamination growth) is so fast that leads to an overall high rate of AE emission. 

O Brien, T.K., Characterization of Delamination Onset and Growth in a Composite Laminate in Damage in Composite Materials, ASTM STP 775, p. 140-167,1982 Poursartip, A. Ashby, M. F., Beaumont P.W.R., The Fatigue Damage Mechanics of Fibrous Laminates in Proceedings of the European Workshop on Nondestructive Evaluation of Polymers and Polymer Matrix Composites, Polymer NDE (edited by Khg. Ashbee), Technomic Publishing, p. 250-260, 1984... 

For the examination of the applied metallic or ceramic layer, the test object is heated up from the outside The heat applying takes place impulse-like (4ms) by xenon-flash lamps, which are mounted on a rack The surface temperature arises to approx 150 °C Due to the high temperature gradient the warmth diffuses quickly into the material An incorrect layer, e g. due to a delamiation (layer removal) obstructs the heat transfer, so that a higher temperature can be detected with an infrared camera. A complete test of a blade lasts approximatly 5 minutes. This is also done automatically by the system. In illustration 9, a typical delamination is to be recognized. 

With this testing method an evaluation is possible within shortest time, i.e. directly after the heat impulse. The high temperature difference between a delamination and sound material is affected - among other parameters - by the thickness of the layer. Other parameters are size and stage of the delamination Generally, a high surface temperature refers to a small wall thickness and/or layer separation [4],... 

Figure I represents a two-dimensional damage distribution of an impact in a 0/90° CFRP laminate of 3 mm thickness. Unlike in ultrasonic testing, which is usually the standard method for this problem, there is no shadowing effect on the successive layers by delamination echos. With the method of X-ray refraction the exact concentration of debonded fibers can be calculated for each position averaged over the wall thickness. Additionally the refraction allows the selection of the fiber orientation. The presented X-ray refraction topograph detects selectively debonded fibers of the 90° direction.

Many of the inspection problems posed by composites can be dealt with effectively by ultrasonic. Delaminations, bonding defects, impact damage, cavities and porosities are among the typical defects which can de detected by ultrasonic inspection. 

Today the coin-tap test is a widely used technique on wind turbine rotor blades for inspection of thin GFRP laminates for disbonded and delaminated areas. However, since the sensitivity of this technique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, there has been an increasing demand for alternative non-destmctive testing techniques which is less operator dependent and also more sensitive to delaminations and disbonded areas situated beyond thicker GFRP-laminates. 

After the performance demonstration a number of damaged rotor blades were scanned followed by a number of destructive verifications of the results achieved by ultrasonic scanning. Based on this examination it was concluded that the wind turbine rotor blade scanner is capable of detecting defects such as delaminations, inclusions, missing adhesion, lack of adhesive, porosities and variations in thickness. 

A close inspection under normal illumination reveals many indications of the condition of the painting and previous repairs. Also, because oil paints become more transparent with age, pentimenti, which originally would have been invisible after the overpainting, can be observed. Raking light illumination is very useful to determine the extent of cracking, distortions of the support, delaminations of the paint layers, etc. This stage of the examination is often done in close cooperation with styHstic experts. Thus, obvious problematic areas can be identified before the other tests are started. 

Muscovite mica formed as a primary mineral in pegmatites and granodiorite differs in physical properties compared to muscovite mica formed by secondary alteration (mica schist) (Table 2). The main differences are in flexibiUty and abiUty to be delaminated. Primary muscovite is not as brittle and delaminates much easier than muscovite formed as a secondary mineral. Mineralogical properties of the principal natural micas are shown in Table 3. The make-up of muscovite, phlogopite, and biotite are as follows ... 

Nondestmctive testing (qv) can iaclude any test that does not damage the plastic piece beyond its iatended use, such as visual and, ia some cases, mechanical tests. However, the term is normally used to describe x-ray, auclear source, ultrasonics, atomic emission, as well as some optical and infrared techniques for polymers. Nondestmctive testing is used to determine cracks, voids, inclusions, delamination, contamination, lack of cure, anisotropy, residual stresses, and defective bonds or welds in materials. 

Refining and Fractionation. These processes are used to alter and select cellulose properties so the final sheet has the desired properties (51). Properties of recycled fibers differ from those of fibers prepared directly from wood. For example, recovered chemical fibers have lower freeness, an apparent viscosity leading to different water drainage characteristics on paper machines. Recovered fibers also have iacreased apparent density, lower sheet strength, iacreased sheet opacity, inferior fiber—fiber bonding properties, lower fiber sweUiag, lower fiber flexibiUty, lower water reteatioa, reduced fiber fibrillatioa, and much lower internal fiber delamination. 

Newer high velocity thermal spray coating processes produce coatings in compression rather than tension because of the shot peening effect of the supersonic particles on impact. This has permitted coating as thick as 12,500 p.m without delamination as compared to older processes limited to 1,250 p.m. The reduced residence time of particles at temperature minimises decomposition of carbides present in conventional d-c plasma. This improves wear and hardness (qv) properties. 

Inter-ply shear is prominently featured in cord—mbber composite laminates, and may relate to delamination-induced failures. Studies utilizing experimental, analytical, and finite element tools, with specific apphcation to tires, are significant in compliant cord—mbber composites (90—95). 

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