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shearing strength developed at the elastic limit and the maximum load, using formula

Es lp
Par

e Calculate the modulus of elasticity in shear from the formula

aps Ip * Pa

Using the coördinates of any point on the corrected curve of the magnified scale.

Compute also the modulus of elastic resilience and the modulus of rupture-work.

Report.- The report will contain (1) a brief description of the specimen and method of test, (2) a tabulated statement of the computed and observed results (rule a form to suit the requirements), (3) a description of the fractured specimen, (4) plotted curves on coördinate paper, (5) an ink copy of the running log of loads and deformation.

INSTRUCTIONS FOR TESTING CEMENT.

(Short Course.) The work will include two days in the laboratory, and during this time the student will determine the time of setting, the fineness on No. 100 and No. 80 sieve, and the strength of three to one mortar in the case of a standard brand of Portland cement.

Time of Setting.-Mix up neat cement with enough water to render a paste of such consistency that when placed on a glass plate it will retain its form, and at the same time by striking the glass against the hand

See Church's Mechanics of Engineering.

the paste can be spread out without cracking on the suface.

Trowel the paste on the glass to thin edges, and set the pat thus made aside in a damp chamber, and observe the time that elapses until (1) it will bear the quarter pound standard needle without appreciable indentation; (2), the weight of the one pound standard needle without appreciable indentation.

Tests for Strength. - Mix up the mortar consisting of three parts standard crushed quartz stone and one part Portland cement, proportion being taken by weight. Mix the sand and cement thoroughly until the mixture presents a uniform color. Gauge with about eight per cent. of water and work over the mixture thoroughly about six times. Tamp in molds in layers, and finish the surface of the briquette. Record the initials on one corner of the briquettes, and leave the briquettes in the molds. They will be taken therefrom by the instructor and placed under water after twenty-four hours.

SECOND DAY's WORK. At the laboratory period one week following, the briquettes are to be taken from the water and tested for strength.

Tests for Fineness of Grinding.- Sift about four ounces of cement through No. 100 and No. 80 sieve and weigh the residue left on the sieves.

The Report.- Each student should report the results of the tests made by him as an individual to determine the fineness of grinding, the time of setting, and the strength of the five briquettes. Reports should be made on blank forms provided for that purpose.

Special instructions are issued to civil engineers.

AN ELEMENTARY COURSE IN PROPERTIES OF

MATERIALS.

BY GEORGE L. CHRISTENSEN, Assistant Professor of Mechanical Engineering, Michigan College

of Mines.

Instruction in the properties of engineering materials should have the following objects in view:

1. To illustrate the behavior of materials under stress.

2. To establish clear and definite conceptions as to the meaning of such fundamental terms as elastic limit, yield point, ultimate strength, percentage of elongation, modulus of elasticity, resilience.

3. To familiarize the student as far as possible with the methods by which materials are tested to obtain numerical results indicating their qualities.

4. To fix in the memory a few of the average numerical values for the more common materials such as cast iron, wrought iron, steel, timber, stone and concrete; thus establishing a very convenient mental standard of reference for the more detailed study of these and kindred materials, and at the same time forming the basis for that ready judgment so essential to the engineer.

5. To illustrate the use of these numerical values in simple problems of designing, thus associating and connecting the material itself, and the mathematical considerations involved, and laying the foundation for that habit of thought which must ever recognize the material in its various strengths and elasticities, in every problem of design.

6. To study the processes of manufacture, in so far as these give name to the product or modify its qualities.

7. To study methods of protecting and preserving materials under conditions of use.

The class-room instruction should be fundamental, keeping before the student the underlying principles and truths, and guiding him through the maze of experimental facts to habits of clear, discerning, independent thought; the laboratory, a means of illustration, going hand in hand with the class-room, supplementing, reviewing, clearing up, fixing the ideas. It is the purpose of this paper to outline briefly some features of the instruction in this subject as developed at the Michigan College of Mines under the increasing influence of this idea of using the laboratory as a means of illustration in conjunction with the class-room work. The course as given runs through twenty-three weeks, three recitations of fifty-five minutes each per week. The text-book is Johnson's “The Materials of Construction.” The class, numbering sixty students, is divided into three sections of twenty each for recitations, and each of these sections is again divided into two laboratory divisions of ten students each, making in all six laboratory divisions. During a portion of the course, , the first recitation period of each week is set aside for laboratory illustration work, when, instead of the whole section meeting in the class-room, one of the small laboratory divisions of ten students meets in the laboratory, the other division taking some other hour of the same day. With this organization of the class it is possible to undertake a series of tests, the whole class being made familiar with the plan and scope, but each laboratory division doing only a small part of the work.

Beginning the course, the first week is devoted to a class-room consideration of definition of terms and the behavior of materials under tensile stress. In the laboratory period of the second week, tensile tests are made of two specimens both cut from the same wrought iron or mild steel bar, one being rough, one inch in diameter, and the other turned down to a smaller size (Fig. 1). The group of ten students gathers around the testing machine, there is room enough for all to note everything that takes place—and each student is

No 21

No. 21

Rerested Specimens

Fig. 1.

required to keep full records just as though he were making the test individually. This being the first test, the construction and operation of the testing machine is explained. The rough bar is tested first. It is marked off in the presence of the class, with punch marks an inch apart, and placed in the machine. As the test proceeds, attention is first directed to the detection of the yield point by noting the drop of the beam, then the breaking down action is watched as shown by the loosening of the mill scale, then interest centers in the rapid stretching of the bar, readily noted with a pair of dividers, and finally, in turn, the ultimate load, the

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