The progress in mechanical engineering which has led in the past few years to much lighter designs of aircraft and land vehicles can be attributed to improvements in the materials used and to a much better adaptation of structural design to these materials. In cases where the temperature is low in aircraft and land conveyances, the engineer’s main problem has been alternating stresses. In applications where steels are used at high temperatures similar problems exist, but our knowledge is here less firmly founded than in the domain of alternating stress at room temperature. The test results described in the paper, however, point to a similar line of advance as has been followed in automobile and aircraft engineering. Here, too, it is important not only to develop better materials but also to improve designs if the strength properties of these materials are to be utilized fully. It has developed that an improvement in creep properties at high temperatures can only be attained, as a rule, at the price of an increase in embrittlement and sensitivity to notching. These considerations are particularly important in the attachment of blade roots to turbine disks. A large number of tests have been made with the aim of throwing some light on these problems and obtaining a clearer idea of the basic connection between structural design and strength.

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