Test Methods to Establish Strength and Reliability

Three main subjects are presented in this paper: (i) A description of tests made for the purpose of determining design data; (ii) a discussion of the problems arising in the establishment of the approval procedures necessary to ensure safety and reliability; and (iii) a discussion of proposals for cyclic reliability tests. In the first section, tests to provide design data for glazing materials are described with particular emphasis placed on glasses. Types of specimen and apparatus for obtaining data at room temperature are mentioned and illustrations given of apparatus and specimens used in long term elevated temperature tests. In the second section, the overall level of reliability of complete components is discussed both in terms of structural safety and satisfactory service. While the current requirements have proved satisfactory for the past generation of aircraft, proposals are now put forward for patterns of testing that are more closely linked to the various design conditions now in use with both high‐speed and low‐speed aircraft, in order to place equal importance on the effects of temperature. In the third section, proposals are put forward for cyclic testing to overcome what appears to be an increasingly unsatisfactory record of reliability. The purpose of the tests is not to establish a safe life for any particular design but to reveal design deficiencies occurring from repeated applications of flight and thermal loadings.