Laboratory manual of testing materials

This manual is the outcome of the operation, through eighteen years, of the Laboratory for Testing Materials of Purdue University. During this time several instructors, temporarily serving the laboratory, have improved its practice. Especial mention should be made of the services of the late Professor Hancock, whose untimely death deprived the science of testing materials of a very able and patient investigator, and his colleagues of a good friend. Professor Yeoman, now of Valparaiso University, did valuable service in the organization of the work of the cement laboratory. The authors are indebted to Professor Poorman of Purdue University, for valuable suggestions.

In its original form the manual was published by the senior author of this volume; and later, with the assistance of Professor Scofield, the manual was enlarged, and was found useful in several universities. Now the authors have availed themselves of the assistance of the present publishers to enlarge the work. The list of experiments has been increased, and a more complete treatment of machines and apparatus added.

One purpose of the manual is to relieve the instructor from the necessity of explaining the details of mechanical procedure, and so to free his time for matters of greater educational importance. It is also hoped by the authors that the practitioner will find the volume of convenient use.

1. The student should obtain a knowledge of materials by handling them and watching their behavior under stress. From the appearance before and after test, he is led to recognize the nature of normal and defective samples. This knowledge will give character to the work of engineering design, and will be of service in work of inspection.

2. A knowledge of the technique of testing materials should be gained, by which he may know afterwards if proper methods are being used in cases that come under his inspection, and by which he may judge the significance of results of the tests of material submitted to him.

3. A training should result in precise methods of observation.

4. The class-room instruction in Applied Mechanics which precedes or accompanies this course, is reinforced with concrete knowledge of things and properties, which are otherwise only words defined in text-books. The application of theoretical analysis to the tests performed in the laboratory becomes of individual interest and is fixed in the mind. Discrepancies between theoretical deductions and results of tests of actual material as supplied to the market also become evident. Many of the fundamental facts relating to metals, such as the relative stiffness of hard and soft steel, the elevation of the yield point, and the lowering of the elastic limit through overstrain can also be brought to the student's notice by a few well-selected experiments.

5. Work is assigned from day to day according to the progress of the student. The laboratory work is self contained, i.e., the work is all to be performed during the time assigned by the faculty. From time to time lectures are ^iven explaining the manufacture and properties of the common materials tested, and the technique of testing.

6. The student should refer to standard text-books and specifications to compare the results obtained with recorded data.

7. Thesis work in testing materials presents a ready and attractive medium by which students can receive some training in proper methods of planning and executing experimental investigations. The work may be individual, or performed by groups of students, and the expense of material is small. “If the professor is interested in some one field of investigation and systematically plans for a term of years, the theses in time are of use in extending knowledge.”

The method of administering thesis work in general involves the following steps: A list of problems, to which, on account of limitations of equipment and the desire to concentrate, the work of the laboratory should be confined, is prepared early in the year. These subjects are generally chosen from this list by students. When a subject is chosen by a student, a thesis outline is prepared by the professor in consultation with the student, in which the problem is clearly stated; the authorities, if any, cited; a list of literature, or directions to main source of information given; and the main plan of attack fairly definitely indicated. Details of apparatus, etc., are generally left to the student. A student may present a subject of his own choice. The written thesis covers a clear and logical account of the purpose of the thesis; the material tested; the methods and machines, with a discussion or error; the actual results; the analysis and presentation of the results; and the conclusions there from. All data remain the property of the university and publication of the results may only be made by the student with the consent of the University authorities.


CHAPTER II - General Instructions

Preliminary Notes. - In all tests, first carefully examine the material. Measure, and note characteristics and defects, if any. If this is not done before the specimen is broken, the test is useless. Note the serial number if any.

The character of the log sheet will be considered in grading the report.

The student should understand the manipulation and reading of all instruments used in each test.

Enough readings should be taken to accurately determine the stress-strain curve. Calculate from table of average strengths of materials, see appendix, the increment of loading required to give at least 18 readings. When quantities being measured are changing rapidly, intervals must be shortened.

Specimens upon which further observations are to be made should be carefully marked and placed in assigned case.

All laboratory notes and data, together with unfinished reports, must be left in the folio case.

Operation of Machines During Test. - Preliminary to every test, each student should become familiar with the operation and mechanism of the testing machine to be used.

Balance poise at zero with test piece in the machine but not clamped.

All readings upon test piece for a certain load should be taken when the beam is balanced at the load and at no other time. The finger may be used to lift the beam slightly and so give warning which will prevent the loads being exceeded.

The speed of applying the load should be such that the beam may be kept balanced, otherwise the readings will be of doubtful accuracy.

Often after the elastic limit has been reached a faster speed may be used and much time saved. Any consistent speed is allowable if the load readings are accurate, except in experiments for which the machine speed to be used is stated in the instructions. Students should be sure that machines are properly thrown out of gear when the test is finished.

Caution. - Testing machines have upon different occasions been left by the operators with countershaft running and the friction clutches thrown in, so that the machines continued running. The result has usually been that some part of the machine was broken. The operator will take special care that this does not occur with machines for which he is responsible. He will be charged with all the repairs made necessary by careless handling.

Reports. - Reports will be written on Form B paper and placed in the regular manila cover. On th6 outside of the cover will appear the number of the experiment, folio number, name of student and his co-workers, title of experiment and the day and date performed, all in lettering.

Clearness and order of statement, legibility of writing, lettering and neatness will receive due attention in marking the report.

In plotting stress-strain curves, select such a scale as can easily be read by inspection, in decimals. State plainly the scale of coordinates. Use the bow pen to circle the points plotted^ and draw curves with instruments. Pencil in curve first and submit to instructor, then ink in. Use India ink for curves and lettering on the curve sheets. Avoid broken lines from point to point.