Question

how does the fatigue testing machine work ? what does it give us ? and what can we conclude based on its results ? and what are the steps used in this experiment?

Answer 1

WORKING

The supply to the machine is turned OFF and the spring load is reduced to zero. Then the bolts in the clamping
mechanism are loosened and the specimen is loaded in to it. The bolts are then tightened to ensure that the
specimen does not loosen during the operation of the machine. The required load is set on the spring load by
adjusting the nut below the spring load mechanism and the supply is turned ON. The digital counter is reset to
zero and the machine is turned ON. After a certain period of time the specimen will fail and the digital counter
will stop, then the machine is turned OFF. And the failed specimen is removed and a new specimen is loaded and
the test is repeated for different values of spring load.

IT GIVES US

The machine enables the evaluation of the stress life
fatigue characteristics of the material analyzed by plotting a graph of bending stress against number of cycles
from which the fatigue limit/fatigue strength of the material analyzed can be determined.

CONCLUSION BASED ON RESULTS

The benefit of the present design is the simplicity of its modeling and ease of understanding. The rotating
specimen can be modeled as a simply supported beam.The study and test conducted so far shows that fatigue failure
cannot be predicted accurately since material failure under fatigue are affected not by just reversal loading alone
but also the number of revolution (cycle per minute) and fluctuating stress and other factors such as temperature,
atmospheric condition, both internal and external defect on material subjected under fatigue stress. Such defect
includes notch, inclusion, stress concentration and non-homogeneity.

STEPS USED IN EXPERIMENT

1. Prepare specimen with applicable procedures.
        Cut to size.
        Polish if necessary.
        Put specimen ID on each piece of specimen for identification. If the specimen is tested to failure, put ID's on each part of specimen.
        Have all measurements (width, thickness, notch length, Yield stress, Young's Modulus, etc., hand for inputting into MATE when prompted after starting test.

2. Decide on ranges for loads, extensometer, and stroke and install appropriate cartridges into controllers.
        Calculate the approximate loads,strains, S compliances that will occur during the test.
        Install load cartridges that will provide the largest Voltage in the system while still remaining in the applicable test ranges. For example, for a load range of 1750 Ibs on the 20 Kip load cell, choose the +2000 Ibs cartridge; or if load range is 0 to 7600 Ibs., chose +10 Kip cartridge to maximize system voltage.
        Insert appropriate strain transducer, i.e. strain gage, clip gage, or extensometer, and matching range cartridges
        Leave Displacement cartridge at 100%, unless using displacement control for test.

3. Install appropriate grips into test machine.
        Adjust cross-head if necessary, making sure to re-tighten the Allen screws to 140 ft-lbs on the cross-heads.
        If using hydraulic grips, calculate the gripping force using the equations on the grip control.

4. Install any other necessary equipment to be used during the test.
        Get appropriate equipment ready for use in testing, i.e. microscopes, lights, cameras, or environmental chambers.

5. If necessary, warm-up test machine.
        It is necessary to warm-up the hydraulic oil after periods of non-use. Ideally, the machine should be warmed up before any testing is performed; however, it is especially necessary after periods of non-use over several days.
        See appropriate section of warming up of machine.

1. Prepare specimen with applicable procedures.
        Cut to size.
        Polish if necessary.
        Put specimen ID on each piece of specimen for identification. If the specimen is tested to failure, put ID's on each part of specimen.
        Have all measurements (width, thickness, notch length, Yield stress, Young's Modulus, etc., hand for inputting into MATE when prompted after starting test.

2. Decide on ranges for loads, extensometer, and stroke and install appropriate cartridges into controllers.
        Calculate the approximate loads,strains, S compliances that will occur during the test.
        Install load cartridges that will provide the largest Voltage in the system while still remaining in the applicable test ranges. For example, for a load range of 1750 Ibs on the 20 Kip load cell, choose the +2000 Ibs cartridge; or if load range is 0 to 7600 Ibs., chose +10 Kip cartridge to maximize system voltage.
        Insert appropriate strain transducer, i.e. strain gage, clip gage, or extensometer, and matching range cartridges
        Leave Displacement cartridge at 100%, unless using displacement control for test.

3. Install appropriate grips into test machine.
        Adjust cross-head if necessary, making sure to re-tighten the Allen screws to 140 ft-lbs on the cross-heads.
        If using hydraulic grips, calculate the gripping force using the equations on the grip control.

4. Install any other necessary equipment to be used during the test.
        Get appropriate equipment ready for use in testing, i.e. microscopes, lights, cameras, or environmental chambers.

5. If necessary, warm-up test machine.
        It is necessary to warm-up the hydraulic oil after periods of non-use. Ideally, the machine should be warmed up before any testing is performed; however, it is especially necessary after periods of non-use over several days.
        See appropriate section of warming up of machine.