Preparing the material:  The specimens may be of any convenient size, though beams 2” X 2” X 30” tested over a 28-inch span, are considered best.  The beams are surfaced on all four sides, care being taken that they are not damaged by the rollers of the surfacing machine.  Material for these tests is sometimes cut from large beams after failure.  The specimens are carefully weighed in grams, and all dimensions measured to the nearest 0.01 inch.  If to be tested in a green or fresh condition the specimens should be kept in a damp box or covered with moist sawdust until needed.  No defects should be allowed in these specimens.

Marking and sketching:  Sketches are made of each end of the specimen to show the character of the growth, and after testing, the manner of failure is shown for all four sides.  In obtaining data regarding the rate of growth and the proportion of late wood the same procedure is followed as with large beams.

Adjusting specimen in machine:  The beam should be correctly centred in the machine and each end should have a plate with roller bearings between it and the support.  Centre loading is used.  Between the movable head of the machine and the specimen is placed a bearing block of maple or other hard wood, the lower surface of which is curved in a direction along the beam, the curvature of which should be slightly less than that of the beam at rupture, in order to prevent the edges from crushing into the fibres of the test piece.

Measuring the deflection:  The method of measuring deflection of large beams can be used for small sizes, but because of the shortness of the span and consequent slight deformation in the latter, it is hardly accurate enough for good work.  The special deflectometer shown in Fig. 31 allows closer reading, as it magnifies the deflection ten times.  It rests on two small nails driven in the beam on the neutral plane and vertically above the supports.  The fine wire on the wheel at the base of the indicator is attached to another small nail driven in the beam on the neutral plane midway between the end nails.  All three nails should be in place before the beam is put into the machine.  The indicator is adjustable by means of a thumb-screw at the base and is set at zero before the load is applied.  Deflections are read to the nearest 0.001 inch.  For rate of application of load see SPEED OF TESTING MACHINE, above.  The speed should be uniform from start to finish without stopping.  Readings must be made “on the fly.”

Log of the test:  The log sheets used for small beams (see Fig. 32) are the same as for large sizes and the procedure is practically identical.  The stress-strain diagram is continued to or beyond the maximum load, and in a portion of the tests should be continued to six-inch deflection or until the specimen fails to support a load of 200 pounds.  Deflection readings for equal increments of load are taken until well beyond the elastic limit, after which the scale beam is kept balanced and the load read for each 0.1 inch deflection.  The load and deflection at first failure, the maximum load, and any points of sudden change should be shown on the diagram, even though they do not occur at one of the regular points.  A brief description of the failure and the nature of any defects is entered on the log sheet.