Strategies For Nde Of Fiber Reinforced Polymer Structural Components
- PDF / 1,601,383 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 19 Downloads / 170 Views
Typically damage modes in composite materials are "documented" during quasi-static, or cyclic loading to failure regimes where the extent of damage is severe and progresses rapidly to the final event. For design applications such as bridge structures with desired services lives of seventy five years, the deterioration is likely to be due to both loading and the environment. Since the service loading, is designed to remain nominally inthe elastic range subtle damage due to stresses that locally exceed the strength of the material system may be exacerbated by thermal cycles, moisture variation, and exposure to ultraviolet radiation. These additional factors may degrade the material system, which in turn may result in mechanically induced damage to the weakened material. These forms of deterioration ultimately progress and degrade the component to a condition that falls below the safe operating factor for the structure. Consequently it is essential that such deterioration be identified at as early a stage inthe progression as possible to avoid having it reach the critical level, and to either mitigate the cause of the deterioration or to facilitate its repair by locating and identifying the deterioration. STRATEGY FOR SELECTING NDE METHODS The strategy for selecting NDE methods for assessment of composite materials structural components in infrastructure applications must involve three main areas of consideration. It is necessary to determine the nature of the deterioration modes, establish a means of assessing the effects of the deterioration, and overcome the constraints associated with examination of the components in the field. Unfortunately the determination of the nature of the deterioration mechanisms infiber reinforced polymer composites is complicated for applications such as infrastructure because the exposure to the environment is a time dependent process for which no satisfactory accelerated test procedure has been established. It is however, clear that moisture, ultraviolet radiation exposure, in the presence of thermal mechanical loading will ultimately affect the matrix material, the reinforcement fibers, and the interface between these elements. NDE methods that are sensitive to changes in the properties of these elements are appropriate candidates for consideration. Many infrastructure applications are stiffiess critical, which of course is why composite materials with high specific stiffness are receiving consideration. Consequently it is necessary to be able to determine the effects of the deterioration on the stiffness of the components. As with most fiber reinforced polymers deterioration that is in part mechanically induced is distributed throughout the component. The nature of the environmental deterioration is such that it is not uniformly distributed and is likely to be more concentrated near the surfaces of the component, regions of high mechanical stress or more severe thermal exposure. Candidate NDE methods must be able to quantify the extent of this deterioration, and perhaps differentiat
Data Loading...
