Methods of testing reinforced plastics, parts I and II

Abstract

PART I. Measurement of Tensile Strength. An experimental comparison has been made between five types of tensile tests including novel types designed to enable axial loading conditions to be approached more readily than is the case with established methods. Examination of the results of two hundred and forty tests indicates that significant differences can occur between the results of different tests and that there is also a significant variation between the properties of material cut from different parts of the same sheet. It is concluded that the results, obtained when testing paper-base material by novel methods, are sufficiently good to justify development of a simplified apparatus of similar type for general use. PART II. Measurement of Interlaminar Strength. The strength of reinforced plastics depends almost entirely on their fibrous reinforcement, and when, as in laminated plastics, this reinforcement is arranged to lie in parallel planes, there is marked interlaminar weikness. For example, the tensile strength measured in a direction at right-angles to the laminations is shown to be from one-sixth to one-ninth of the corresponding value measured in the direction of the laminations. In spite of the obvious concern of the designer in tile value of interlaminar strength and of the indication of previous research that this quantity is markedly affected by variations in manufacturing conditions, measurements of this quantity are not generally made in this country: It has been the practice in the National Physical Laboratory however to carry out certain tests of interlaminar strength and it was considered desirable to compare and to assess the accuracy of these tests together with those used in U.S.A. and Germany. Besides providing the basis for the rational interpretation of the results, it was hoped that the investigation would enable one particular type of test to be selected for further work.