Exposure durability

Classification—a review of exposure durability in terms of interior and exterior grades of plywood... 

The addition of certain inorganic ion trapping agents to the encapsulant resin improves the high temperature exposure durability of encapsulant resin. 

Cyclic tensile testing was done after exposure durability testing [16]. The as-received and an exposed curve (similar time and stress of exposed fiber push out sanqile) are shown in Figure 10. As can be seen from the cyclic tensile tests performed at room temperature both as received and post exposed that the exposed sample has a smaller hysteresis consistent with scenario 2 above. 

Figure 20-8 shows the crystal structure of a thiazine indigo compared to a diketo-pyrrolopyrrole with very similar molecular size, shape and particularly intermolecu-lar hydrogen bondings, which are mainly responsible for their pigmentary character such as insolubility, heat stability and exposure durability. 

Figure 20-17 shows the crystal structure of the N,N-diethyl derivative, further confirming the linearity of the molecule as well as the intermolecular hydrogen bondings responsible for the high insolubility, heat stability and exposure durability. 

Durability. Grass-like surfaces intended for heavy-duty athletic use should have a service life of at least eight years, a common warranty period provided by suppHers. Lifetime is more or less proportional to the ultraviolet (uv) exposure (sunlight) and to the amount of face ribbon available for wear, but pile density and height also have an effect. Color is a factor generally uv absorption is highest with red fabrics and least with blue. In addition, different materials respond differendy to abrasive wear. These effects caimot be measured except in simulated field use and controlled laboratory experiments, which do not necessarily redect field conditions. 

Catalyst Durability. Automobile catalysts last for the life of the vehicle and still function well at the time the vehicle is scrapped. However, there is potential for decline in total catalytic performance from exposure to very high temperatures, accumulation of catalyst poisons, or loss of the active layer (29,64—68). 

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

Redux was soon extended to other aircraft including the DeHavilland civilian airliner Dove and the jetliner Comet [202]. In the Fokkcr F27/F50 Friendship , it accounted for about 70% of stmctural bonds (about 550 parts). Over 1000 F27/F50 aircraft were constructed and were in service for over 30 years, indicating high fatigue resistance and durability ([198], pp. 80-81). When attempts were used to substitute low-temperature curing epoxies for PVF, joint corrosion due to salt spray exposure required expensive repairs. 

In-service issues. As mentioned previously, many early service failures of bonded structure were due to adherend surface treatments that were unstable in long-term exposure to water. A majority of these problems were resolved by the adoption of surface treatments such as chromic and phosphoric acid anodize for aluminum details. The remaining few were alleviated by the adoption of phosphoric acid anodized honeycomb core and foaming adhesives resistant to water passage. Other service durability issues such as the cracking of brittle potting compound used to seal honeycomb sandwich assemblies, and subsequent delamination, have been minor in scope. 

It is thus important to consider all types of exposure. If a building is to be durable and of good appearance, special attention must be paid to the design of details, especially those involving metals, and precautions must be taken against corrosion, since failure which is not due to general exposure to the external atmosphere often occurs in components within or structurally part of the building. 

Since the individual members of this group of media differ considerably in properties, so also do the finishes that can be made from them. As a class, however, they are generally inferior to the better alkyds for durability under normal conditions. A particular exception is the tung-oil 100% phenolic type of medium, which produces finishes with very good resistance to water and mildly acidic or alkaline conditions pale colours, however, discolour by yellowing on exposure. 

Cross-linking the fibers with radiation lead to durable-stretch fabrics. The fabrics can be made by any process, such as weaving and knitting, and from any combination of cross-linked, heat-resistant olefin elastic and inelastic (hard) fibers, e.g., cotton and wool. These fabrics exhibit excellent chemical resistance (e.g., chlorine or caustic resistance) and durability, that is, they retain their shape and feel (hand) over repeated exposure to processing conditions, such as stone-washing, dye-stripping, and PET-dyeing. 

Resistance to acid erosion depends on brand and varies from 0 04 to 0-54% per hour (Setchell, Teo Kuhn, 1985 Wilson et al, 1986a Walls, McCabe Murray, 1988). It would appear that cements based on copolymers of acrylic and maleic acids are less durable than those based on poly(acrylic acid). The extent of erosion varies inversely with the time allowed for the cement to cure prior to exposure (Walls, McCabe Murray, 1988). 

Concrete is a composite material composed of cement paste with interspersed coarse and fine aggregates. Cement paste is a porous material with pore sizes ranging from nanometers to micrometers in size. The large pores are known as capillary pores and the smaller pores are gel pores (i.e., pores within the hydrated cement gel). These pores contain water and within the water are a wide variety of dissolved ions. The most common pore solution ions are OH", K+ and Na+ with minor amounts of S042" and Ca2+. The microstructure of the cement paste is a controlling factor for durable concrete under set environmental exposure conditions. 

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