AIN SHAMS UNIVERSITY

FACULTY OF ENGINEERING

NEW PROGRAMS IN MATERIALS ENGINEERING

Materials TestingMATL 352

Lab. 7

Procedure and Observations

Certain test parameters must be selected before the test is started:

☻ Type of load variation: sine, haversine, square, saw-tooth, and ramp, dual ramp triangular or trapezoidal function.

☻ Mean stress: for endurance tests, the mean stress is normally zeroed.☻ Alternating stress: the maximum stress results (alternating + mean stress) should

be close to the maximum static stress for the first specimen, and then be reduced by about 10% for the second one and so on.

☻ Frequency: ASTM E 466 specifies a maximum of 170 Hz

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AIN SHAMS UNIVERSITY

FACULTY OF ENGINEERING

NEW PROGRAMS IN MATERIALS ENGINEERING

Materials TestingMATL 352

Objective

To conduct a constant amplitude rotating bending fatigue test of steel and obtain one point on the S-N curve.

Specimen

A round fatigue specimen of steel.

Procedure

1- Carefully measure the dimensions of the specimen and make a drawing.2- Securely fasten the specimen in the chucks of the testing machine. Sketch the

set up of the specimen showing fixation and loading method.3- Set the load so that the maximum tension and compression equal each other and

about 80% of the ultimate strength.4- Adjust the frequency to about 150 Hz, set the counter to zero.5- Start the machine.6- Continue the test until the specimen fractures.

Test ResultsThe following fatigue strength test results were obtained for complete stress reversal in bending:

Stress (psi) Cycles of fracture92,000 41,00083,000 128,00074,000 590,00067,000 1,620,00065,000 5,500,00064,500 8,000,00064,000 14,000,00064,100 15,000,00063,900 specimen did not fracture

Bring half log scale paper and plot the S-N diagram on the S versus log N bases and determine the values of fatigue strength for N = 105, N = 106, and N = 5x106 cycles.

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AIN SHAMS UNIVERSITY

FACULTY OF ENGINEERING

NEW PROGRAMS IN MATERIALS ENGINEERING

Materials TestingMATL 352

Fatigue Life Curves Experiment

What you need:

4 Jumbo Paper Clips A Copy of Figure 6

What to do:

1. Bend four paper clips at each of the four bending angles indicated in figure below until each fails, counting the number of times the

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AIN SHAMS UNIVERSITY

FACULTY OF ENGINEERING

NEW PROGRAMS IN MATERIALS ENGINEERING

Materials TestingMATL 352

paper clip is bent. For instance, bend a paper clip 45, then bend it to -45, then back to zero. This is one cycle.

2. Record the data in attached table.3. Using a spreadsheet program, plot the number of cycles versus the

angle. The angle represents the stress amplitude.

Place paper clip in a vertical plate and bend in the middle using this guide to judge the angles.

Table for Experimental Data

Cycles to Failure Angle,

? 90

? 45

? 20

? 10Fig. 6 Bending angle guide

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