A comparison of impact tests for assessment of fiberglass reinforced plastic toughness

Abstract

AbstractAll measures of impact resistance have shortcomings. The ASTM tests, Izod, Charpy, and drop‐dart, measure impact at a single velocity. Furthermore, the Izod and Charpy tests impose an unrealistic unidimensional stress on the test specimen. Indirect gauges of impact toughness, such as the area under the tensile stress‐strain curve (tensile work), flexural modulus, or resin cracking in mandrel bend tests, are normally conducted at unrealistically low straining rates. Variable‐rate impact testers have been developed to overcome these shortcomings. In this paper, results obtained from a variable‐rate tester are compared with those from other methods for assessing composite toughness. Data are reported for flexible and brittle low profile press molding resins, tested as SMC (sheet molding compound) moldings by Izod, drop‐dart and variable‐rate impact. Indirect measures of impact resistance, mandrel bend and flexural modulus, are also discussed. The effects of resin flexibility and the composite glass content are demonstrated. The glass content affects the ultimate failure strength of the composite but not the failure of the resin matrix. The resin flexibility affects the initial stages of failure.