ASTM Service Fluids

Third Monomers. In order to achieve certain property improvements, nitrile mbber producers add a third monomer to the emulsion polymerization process. When methacrylic acid is added to the polymer stmcture, a carboxylated nitrile mbber with greatly enhanced abrasion properties is achieved (9). Carboxylated nitrile mbber carries the ASTM designation of XNBR. Cross-linking monomers, eg, divinylbenzene or ethylene glycol dimethacrylate, produce precross-linked mbbers with low nerve and die swell. To avoid extraction losses of antioxidant as a result of contact with fluids duriag service, grades of NBR are available that have utilized a special third monomer that contains an antioxidant moiety (10). FiaaHy, terpolymers prepared from 1,3-butadiene, acrylonitrile, and isoprene are also commercially available. 

For these tests, the service liquids (solvent, oil, hydraulic fluid, acid, base. ..) can be used but, to ease the establishment of specifications and comparative tests, reference solvents, oils or fuels are often used. The most current are IRM 901,902 or 903 oils (which replace ASTM 1,2 and 3 oils), fuels or solvents ASTM A, B, C. 

F ow P/LOpcAtlei Under this heading come the viscosity of the fluid and the effect of temperature on viscosity. The latter might be a theoretically derived function, or an arbitrary function such as the viscosity index, or even a grossly empirical evaluation of the viscosity at two or more selected temperatures. Low temperature flow properties are frequently evaluated by the ASTM pour point determination [5], but the inadequacies of this method of evaluation have led to the use of pumpability tests which have a better empirical relation to service conditions. 

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. 

Aging changes in mechanical behavior of PNF elastomers were reported with time, temperature, degree of cross-linking (radiation and chemical), and fluid and other environmental conditions for in-service evaluations ASTM and other practical tests were employed. Property changes and conditions are detailed in several references. ... 

Immersion Corrosion—Accelerated Tests To simulate service of components that will be immersed in fluids, ASTM G 31 should be followed. This standard includes many precautions relating to how laboratory testing environments may differ from actual service. Issues such as immersion solution composition, temperature, aeration, velocity, and volume must be addressed thoroughly before the design of the test can be considered complete. For tests involving corrosion in water, two ASTM D 2688 and ASTM D 2776 should be referenced, which determine corrosivity by weight loss and electrical methods, respectively. 

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