A study of acoustic emission-rate behavior in glass fiber-reinforced plastics

This study examines acoustic emission (AE) rate behavior of specific glass fiber-reinforced plastics (GFRP) systems under static and stair-step loading. Coupons of glass fiber (GF)-polyester and GF-epoxy are taken to failure under static tensile loading. The AE-rate behavior is examined under ranges of temperature (-50°C to 140°C) and strain rates (0.01-10%/min). The AE behavior under stair-step load is studied for comparison. For stair-step load programs, specimens of different types (test coupons, square profile tubes, GFRP-foam sandwich shell) and scales (overall length between 210 and 5500 mm) are tested with varying loading direction : test coupons under tension, filament wound tubes under torsion and the sandwich shell under compression. In static tensile tests, glass fiber reinforced epoxy and polyester respond with exponential AE-rate behavior, i. e., AE = ke αt . Determining the exponential factor a for each material by superimposing the rate (differential) and cumulative AE curve is found to be simultaneously a convincing method for establishing exponential behavior and efficient quantitative analysis. The exponential factor a was found to be a function of strain rate and invariant within a certain temperature range. In stair-step tests, cumulative AE curves were compared at different scales and found to be similar in shape at all scales.