Delamination voids

It can provide the thickness of concrete slabs up to an accuracy of 3% and can determine the location and extent of flaws such as cracks, delaminations, voids, honeycombing and debonding in plain, reinforced and post-tensioned concrete structures It can also locate voids in the subgrade beneath slabs and pavements. For masonry it can determine thickness and locate cracks, voids and other defects where the brick or block units are bonded together with mortar. Impact-echo is not adversely affected by the presence of steel reinforcing bars. 

Ultrasonic C-scan n. A non-destructive inspection technique for reinforced plastics in which the energy absorbed from a short ultrasonic pulse is measured. This is quantitatively different for sample containing delaminations, voids, or too little or too much reinforcement, than for solid samples of the correct composition. 

Delamination, voids, and other hidden defects Impact echo, infrared thermography, pulse echo, and radar... 

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. 

The nondestructive temperature differential test by infrared is used. In this method, heat is applied to a product and the surface is scanned to determine the amount of infrared radiation is emitted. Heat may be applied continuously from a controlled source, or the product may be heated prior to inspection. The rate at which radiant energy is diffused or transmitted to the surface reveals defects within the product. Delaminations, unbonds, and voids are detected in this manner. This test is particularly useful with RPs. 

With nondestructive ultrasonic test back and forth scanning of a specimen is accomplished with ultrasonics. This NDT can be used to find voids, delaminations, defects in fiber distribution, etc. In ultrasonic testing the sound waves from a high frequency ultrasonic transducer are beamed into a material. Discontinuities in the material interrupt the sound beam and reflect the energy back to the transducer, providing data that can be used to detect and characterize flaws. It can locate internal flaws or structural discontinuities by the use of high frequency reflection or attenuation (ultrasonic beam). 

Of historical interest may be the use of a half dollar coin (the lighter weight 250 not as efficient). During the early 1940s the coin tap test was used very successfully in evaluating the performances of plastics, particularly RP primary aircraft structures. With a good ear (human hearing ear) there was (and is) a definite different sound between a satisfactory and unsatisfactory RP product. The unsatisfactory product would contain voids, delaminations, defects in fiber distribution, etc. In... 

Thermal imaging is sensitive to infrared radiation that detects temperature changes over the surface of a part when heat has been applied. Thermal diffusion in a solid is affected by variation in composition or by the presence of cracks, voids, delaminations, etc the effects are detected by surface temperature changes. Defects cannot be detected if their depth below the surface is more than two to three times their diameter. Nondestructive testing has been primarily used for composites and analysis of adhesive bonds or welds. Several studies are documented in the literature (322—327). 

Technologies, such as coextrusion and coinjection, allow PET and other plastics to package foods and other products.225 226> 227 Care must be taken to control the process so that the melt when blown will not have micro-voids in the container walls or will delaminate. Coextrusion and coinjection (or multilayer processes) are essential technique in the production of high performance BM products (Chapters 4 and 5). The parison or preform is coextruded with a number of different layers, each of which contributes an important property to the finished product. Increasingly, a mid layer may consist of recycled material which is encapsulated between inner and outer layers of virgin plastics. 

There is research underway to produce compatibilized blends of kenaf and jute with polypropylene. This research is directed at developing the technologies needed to combine dissimilar resources for improved bonding, impact resistance, moldability, and to decrease creep. The two materials remain as separate phases, but if delamination and/or void formation can be avoided, properties can be improved over those of either separate phase. 

For weak scale adherence and low substrate ductility, through-scale cracking is accompanied by a delamination and spalling of the scale. This was observed to a large extent on Fe-doped NiAl specimens after bending at RT (Fig. 6).The weak adherence in this case was caused by a pronounced formation of interfacial voids. Void formation at the oxidc-metal interface has often been observed for NiAl. It was studied in more detail by Brumm and Grabke in [32. ... 

SEM observations on a series of NiAl specimens showed that the formation of large interfacial voids at 1223 K is more the exception than the rule. Typically, small faceted voids of only a few micrometre size were found. Larger voids are formed by a coalescence of small voids which leads to a complicated shape of the voids. Such a void structure with high void density was found on the specimen shown in Fig. 6. The high density of voids diminished the effective scale adherence and affected the large-scale delaminations observed. 

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