Voids and Porosity

Such tests can identify incorrect component dimensions, lack of adhesive, lack of filleting, edge voids and porosity at the manufacturing level, throughout the cross section of a laminate after the part has been cured [29]. Other in-service damages detectable include paint failure, lighting strikes, and peeled surfaces. 

The two major categories of polymer composite used in aerospace are laminates and sandwich stmctures, which require some differences in NDT inspection methods. The inspection of choice at the time of manufacture may be different from the inspection of choice for in-service assessments. The form of the stmcture determines the types of features of concern and the NDT techniques that may be apphed to detect and measure them. Table 15.1 summarizes some general thoughts and considerations on NDT of polymer composite stmctures. American Society for Testing and Materials (ASTM) also provides guidance on NDT for polymer composites [12]. The primary concerns in laminates are voids and porosity, inclusions, delamination, the fiber-to-resin ratio, and wrinkles (wavy or out-of-plane ply). Ultrasound is the predominate method for composite laminate inspection. In sandwich structures, the core material-to-facesheet bond, core condition, and fluid ingress are the usual concerns. 

Diffusion can result in the presence of voids and porosity [43]. There are, however, instances where inherent porosity (e.g., the formation of a diffusion coating on a sintered metal substrate) has been decreased by the formation of a diffusion coating. Some metals are sensitive to nonmetallic impurities in that they are hardened and embrittled by small amounts of carbon, oxygen, nitrogen, and so forth. The formation of compounds containing these elements during diffusion can result in a poorly bonded interlayer, a hard or brittle layer, or even a barrier to diffusion. Since these elements are present in the base metal and sometimes in the process atmosphere, diffusion coatings... 

The monitoring of ultrasonic echoes forms one of the most widely used methods of nondestructive testing for bonded joints and composites. The method is commonly used for the detection of disbonds, voids, and porosity. 

Geometrical factors - structure, void volume and porosity will affect the filler s ability to be wetted by the rubber into which it is incorporated. The shape of the particle will depend on the crystal structure of the mineral being used. 

A number of other parameters can be calculated from true, bulk, and tap density measurements. These include void volume, porosity, bulkiness, and compressibility. 

In a packed bed of unit volume, the volumes occupied by the voids and the solid particles are e and (1 — e) respectively where e is the voidage fraction or porosity of the bed. Let S0 be the surface area per unit volume of the solid material in the bed. Thus the total surface area in a packed bed of unit volume is (1 — e)S0. 

The volume fractions of both micropores and voids (intermicroglobule porosity) represent the total porosity (gj. This value, indicating a percentage of pores in the... 

In the 300-gallon-per-day plant the mean ice particle sizes have been calculated from measurements of ice bed permeability and porosity made on the ice harvested at the top of the column. From these results the important design parameters can be calculated, such as particle diameters, linear ice velocities, residence time of ice in the column, frictional losses in the wash water flowing down the column and in brine flowing toward the screens in the bottom of the coltam, and the fraction of voids occupied by air above the liquid level in the column. Typical ranges for some of these measured or calculated quantities are shown in Table III from measurements in the 12-inch diameter column. 

Void [52] developed a variety of ballistic deposition models to simulate sedimentation processes. Void used ballistic models to determine deposition densities for spherical particles which traveled via vertical paths and were deposited on horizontal surfaces. Recently, Schmitz et al. [53] used a ballistic aggregation model to describe particle aggregation at the surface of a crossflow microfiltration membrane. Schmitz and co-workers were able to account for interfacial forces empirically, and demonstrated the influence of physical and chemical variables on the resulting morphology of the fouling deposits (such as aggregate density variation with depth, and influence of shear flow and re-entrainment properties on fouling deposit density and porosity). 

Most solids of high surface area are to some extent porous. The texture of such materials is defined by the detailed geometry of the void and pore space. Porosity, , is a concept related to texture and refers to the pore space in a material. An open pore is a cavity or channel communicating with the surface of a particle, as opposed to a closed pore. Void is the space or interstice between particles. In the context of adsorption and fluid penetration powder porosity is the ratio of the volume of voids plus the volume of open pores to the total volume occupied by the powder. Similarly, particle porosity is the ratio of the volume of open pores to the total volume of the particle. It should be noted that these definitions place the emphasis on the accessibility of pore space to the adsorptive. 

Total porosity Ratio of volume of voids and pores (open and closed) to volume occupied by solid... 

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