Material defects laminations

This index describes the potential of the tablet to cap and laminate, and is related to the ability to relieve shear stresses within the compact via material flow. In Equation (1), TS equals the tensile strength of the normal tablet and TSo is measured from a tablet with a hole in its center, which simulates a defect. 

Microspectroscopy applies the identification power of infrared spectroscopy to the microscopic realm. Contaminants on printed circuit boards, blemishes in coatings, and other production defects can be isolated in situ and analyzed (see Electronics, coatings). Analysis of flaws that develop during use illuminates the method of failure. Microscopic samples, such as particulates filtered from air, can be analyzed individually. The forensic applications are many paint chips, single fibers, explosive residues, and inks on currency can all be identified nondestmctively (see Forensic chemistry). The structures of layered materials, such as laminated polymer films, are studied via microspectroscopy by cross-sectioning the materials and examining the individual layers edge on (47). 

Three modes are clearly defined for crack propagation from a very thin (radius of the order of 10 gm) notch-machined in the specimen (Fig. 12.3). This notch induces a stress concentration effect, higher than those produced by all the other defects already present in the specimen, which governs the fracture initiation. For isotropic materials, mode I (the most severe) is generally used and gives the lowest value of toughness. In the case of adhesives and laminates, modes II and III are also performed. 

A technique generally applied to characterize and prevent the capping and lamination of a material intended to be compacted is using the brittle fracture index (BFI). The BFI was designed by Hiestand et al. [31] and measures the ability of a material to relieve stress by plastic deformation around a defect. It is obtained by applying Equation (8) and compares the tensile strength of a tablet with a hole in its center (To), which acts as a built-in stress concentrator defect, with the tensile strength of a similar tablet without a hole (T), both at the same relative density ... 

Reddy, A.D. Rehfield, L.W. Haag, R.S. Influence of prescribed delamination on stiffness-controlled behavior of composite laminates. Effects of defects in composite materials. ASTM STP 1984, 863, 71-83. 

The tendency to have a pack component specification which is all-embracing is also changing. A simpler procedure utilises a series of information documents which lay out the procedures that a supplier has to follow for selective package forms, i.e. glass bottles, plastic bottles, laminates, labels, collapsible tubes, etc. It is then possible to have an abbreviated specification document which covers critical, major and minor defect classifications, advice on delivery and identification, and basic information on the material to be employed, etc. The specification therefore cross-references to its respective information (component manual) document and becomes considerably simplified in terms of both layout and detail. This is particularly important now that specifications are being computerised in conjunction with stock control and purchasing. 

It is now fairly normal procedure to have a general support document, i.e. packaging material manual, issued under specific headings such as bottle glass bottle plastic laminations labels leaflets. These broadly describe the requirements of the items including reject (defect) terminology and possibly associated AQL. Such manuals provide suppliers with a broader view of the quality expected, and may cross-reference the details of the test procedures, including performance, to be applied (see below). 

The two major techniques in ultrasonic testing arc the pulse-echo mode and the through-transmission mode. In pulse-echo mode, the same transducer is used to emit and receive ultrasonic waves and requires access to only one side of the structure inspected (Fig. 12). The pulse-echo technique is effective on the near side skin laminate only, and the sensitivity decreases as a function of depth [29]. With the through-transmission mode, access to both sides of a structure is required as an emitter probe is placed on one side and a receiver on the other (Fig. 13). This technique measures the signal amplitude of ultrasonic waves transmitted through the material tested and is more sensitive to small defects than the pulse-echo mode. The detection of flaws throughout the whole depth of a... 

Oblique ultrasonic waves sent to a composite at frequencies that excite plate wave modes induce the leaky lamb wave phenomenon. When the leaky Lamb wave is generated, the specular reflection is distorted. When the specular reflection and the leaky Lamb wave interfere, a phase cancellation occurs, and two components are generated with a phase between them. Because each type of defect has a unique response, this technique can be used to determine material eleastic constants and to estimate the volume content of resin as well as porosity content. Detection of transverse cracking and delamination in a 24-layer unidirectional graphite-epoxy laminate has also been reported [140], and oblique incidenee back-scattering techniques give accurate fiber orientation of the first composite layers [15],... 

To finalize this section, I would like to mention that some papers delve into the studies of radiation tolerance of laminated composites with the thickness of layers not increasing tens of nanometers. By varying the thickness of such materials, we can investigate the main mechanisms of influence produced by interphase boundaries on the behavior of radiation defects. The irradiation of multilayered structures with the ions of inert gases first of all with helium allows for the modeling of processes that may arise during the reactor-induced irradiation of oxide dispersion-strengthened steels and alloys. 

It is of utmost importance to design all areas of the extruder, from body infeed right through to the column exit, in the best possible way in respect of fluidics. All components must be shaped in such manner that the complete body mass flows through freely. The properties of any plastic body which sticks or stops (at dead corners ) will alter in the course of time, whereby the flow behaviour is the first thing to be affected. Such bits of material, possibly dried out especially within the vacuum chamber, may eventually move again and be extruded with the column. This leads to inhomogeneity of the column and can possibly cause laminations or other defects. 

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