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Durability considerations after composite repair

posted time:2019-01-23 09:57:27 | browse:31次

The full protection to achieve the grade, the erosion from environment including: mixer temperature (infrared radiation) and ultraviolet (UV) radiation would erode pieces resin and fiber wet environment, if undertake airtight good performance of coated fiber without prior or mold is not full, pieces will suffer erosion from fuel or gasoline, hydraulic fluid, antifreeze, acid, solvent coating decoloring agent, and other chemical attack against heat and UV radiation is the best measure to use proper protective coating UV inhibitors to repair the surface, form the surface of light color is enough to reflect infrared radiation.In the 20th century, according to a study conducted in the 70 s black coating of composite material surface temperature can be higher than the surrounding temperature of 115 ° F to 120 ° F (i.e., 29 ℃ to 35 ℃).High temperature specialty resins and adhesives must also be used for repairs near exhaust pipes or other high temperature areas.Galvanic corrosion also needs to be taken into account. For example, carbon fibers in direct contact with aluminum layers may show rapid aging, especially when bolts are used for repair.The direct current from the two materials at opposite poles causes the current to corrode, but the corrosion occurs only in the metal layer, not the carbon fiber, and the humidity makes the corrosion worse.Another way to resist galvanic corrosion is to isolate the carbon fiber from the aluminum using a boundary layer, which can be made of glass fiber, bonded soft film or other non-resistant materials.Bonding repair surface pretreatment though bolt repair sometimes used in composite material structure, but the most common of the durability of the bonded repair repair solution or scour Angle cutting, this way can effectively keep the strength and hardness of material, at the same time to ensure the smooth surface in the aerodynamic environment, if you need a radar site performance, can also have the repair effect.The durability of the adhesive repair depends on the performance of the adhesive used between the patch and the surface of the repaired site, and the main variables that affect the performance of the adhesive include proper selection, adhesive processing, uniform adhesive thickness (neither too thin nor too thick), and surface pretreatment of the bonded site.In the 1950s, Fokker F27 twin-turboprop airliners used a phenolic binder to bond the aluminum surfaces.R.J. Schliekelmann, a durability adhesion expert at Schiphol Fokker of the Netherlands, mentioned this point in his report at the 15th annual meeting of the international federation of airworthiness technology and engineering, Amsterdam, Netherlands, November 4-6, 1985.Pressure heaters are used for adhesive repair at elevated temperatures and pressures.The structural properties of the repair site were good, and the adhesive repair effect did not weaken with the change of temperature and humidity. Many of the repair results lasted for decades.Epoxy adhesives were developed in the aerospace industry in the 1960s and were expected to achieve the same satisfactory results, but the adhesion repair joints subsequently showed the first aging due to high temperature/humidity in the 1970s, which was a great disappointment.Over the next 20 years, numerous studies have established the now widely accepted fact that surface pretreatment processes are the root cause of several days and decades of poor adhesion durability.The goal of this field is to achieve effective and powerful adhesive repair, and the cause of repair failure only exists in the adhesive itself, such as the common adhesive failure, adhesive from the repair patch or repair surface peeling, namely adhesive failure.It should be noted that although the research in the field of adhesion joint repair has focused on the failure of adhesion, in practice, there may still be a failure of adhesion without successful adhesion repair.For example, if the adhesive is not adequately treated, this may be due to inadequate treatment temperature.The failure of the adhesive connection is mainly caused by gluing, without proper treatment of the adhesive will fall off, so the failure of the reason is still in its own.Therefore, if the adhesive is properly treated and gives full play to its performance, the adhesive failure is often caused by insufficient adhesion of the adhesive repair surface, and the focus is pointed to the surface pretreatment.

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