FOR most of the uses to which timber is put, reasonably good resistance to impact is an advantage for many uses, such as aircraft construction, sports goods, or tool handles, it is an overriding requisite. Its measurement is, therefore, an important part of the routine testing of timber. Since conditions of service as regards this property are seldom, if ever, known with exactitude, and since, moreover, the size and shape of the member receiving the impact bear an important but undefined relationship to its resistance, the laboratory tests for the property are essentially empirical. The resulting figures from such tests in themselves mean little they cannot be translated into design figures as are, for instance, modulus of elasticity or maximum compressive strength and their value lies almost entirely in their use for comparisons. As with most empirical tests, one of the essentials is that the character of the test, i.e. testpiece and testing conditions, shall be rigidly defined and adhered to. Unfortunately there are in more or less common use in the various timber testing laboratories several different methods of measuring impact resistance and the lack of a universal standard impact test is a serious drawback to the usefulness of the results, since one of the greatest advantages of the standardized test, viz., the interchangeability of results between one laboratory and another, is at once nullified. It is hoped that when circumstances permit the interested research institutions will take up the study of impact testing and agree upon a uniform standard test.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Sep 1, 1942