A Handbook of Testing

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Excerpt from A Handbook of Testing: MaterialsThe properties of materials used by engineers vary owing to many causes. If we take a pound of almost any gas and measure its temperature, pressure, and volume, we can estimate with accuracy the behaviour of the gas, if it is to be compressed, under certain conditions, to a new pressure and volume. If, however, we take a pound of steel we cannot forecast with any accuracy the behaviour of the material under load if we know nothing more about it than the fact that it is called steel. It is of some assistance if we know the chemical. Composition of the steel, but, even with such information, we cannot estimate with accuracy the load which the material will carry at the point of fracture.Experience has taught engineers that the only satisfactory method of estimating suitable loads in design works is to subject samples of the actual material to be used, to tests, which reproduce, as nearly as is possible, the conditions met with in actual practice. Thus, if a quantity of steel is made for a purpose in which the material is subjected to a direct pull, the most satisfactory way of deciding the maximum value of the pull to be allowed in practice is to test samples of the material under similar conditions, and obtain a record of the physical properties of these samples. Of course it is possible that all of the steel from which the samples have been selected will not behave in a similar fashion to the specimens tested. In general, however, we can obtain suffi cient data to assist us to estimate with considerable certainty the safe loads to which the materials may be subjected.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.