Nothing Special   »   [go: up one dir, main page]
Scribd Logo
Upload

Welcome to Scribd!

  • 151 views

    Lab 9 Fatigue Testing

    Uploaded by

    Tommy Miles
    The document describes how to conduct fatigue tests and interpret their results. It discusses two types of fatigue testing machines: 1) a rotary bending machine, which subjects specimens to dynamic stress through rotation, and 2) a servo-hydraulic testing system that can test components through stroke-controlled loading. Tests are performed by applying cyclic loads at different stress levels and recording the number of cycles until failure. The results are then plotted on an S-N curve and used to estimate the material's fatigue limit.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Lab 9 Fatigue Testing

    Uploaded by

    Tommy Miles
    151 views2 pages
    The document describes how to conduct fatigue tests and interpret their results. It discusses two types of fatigue testing machines: 1) a rotary bending machine, which subjects specimens to dynamic stress through rotation, and 2) a servo-hydraulic testing system that can test components through stroke-controlled loading. Tests are performed by applying cyclic loads at different stress levels and recording the number of cycles until failure. The results are then plotted on an S-N curve and used to estimate the material's fatigue limit.

    Original Description:

    materials engineering lab

    Copyright

    © © All Rights Reserved

    Available Formats

    PDF, TXT or read online from Scribd

    Did you find this document useful?

    Is this content inappropriate?

    The document describes how to conduct fatigue tests and interpret their results. It discusses two types of fatigue testing machines: 1) a rotary bending machine, which subjects specimens to dynamic stress through rotation, and 2) a servo-hydraulic testing system that can test components through stroke-controlled loading. Tests are performed by applying cyclic loads at different stress levels and recording the number of cycles until failure. The results are then plotted on an S-N curve and used to estimate the material's fatigue limit.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    151 views2 pages

    Lab 9 Fatigue Testing

    Uploaded by

    Tommy Miles
    The document describes how to conduct fatigue tests and interpret their results. It discusses two types of fatigue testing machines: 1) a rotary bending machine, which subjects specimens to dynamic stress through rotation, and 2) a servo-hydraulic testing system that can test components through stroke-controlled loading. Tests are performed by applying cyclic loads at different stress levels and recording the number of cycles until failure. The results are then plotted on an S-N curve and used to estimate the material's fatigue limit.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 2

    Lab 9 – Fatigue Testing

    Objective
    To demonstrate how fatigue tests are conducted and how to interpret results.

    Introduction
    Fatigue failure accounts for the majority of mechanical failure of metallic materials
    subjected to cyclic loads. Fatigue failures result from repeated applications of stress
    which is usually well below the static yield stress. Fatigue cycles are often completely
    reversed state of stress, i.e. tension and compression in a rotating beam but can also be
    tension-tension. In all cases the number of cycles to produce failure increases with the
    lowering of the stress leve1. There are different types of fatigue testing machines. The
    modern fatigue test frames are servo-controlled electro-hydraulic or electro-mechanical
    devices. Rotary bending fatigue testing machines are simple and low-cost practical
    machines which are used since 1850.

    Equipment
    • CJ Rotary bending fatigue testing machine
    • Dartec 100kN servo-hydraulic testing system.

    Determination of Fatigue Limit on the Rotary Bending Machine

    Figure 1: Rotary bending machine

    Each point on the surface of the rotating specimen will go through the points 1, 2, 3, etc.
    and will be subjected to a dynamic stress. The stress – time curve is a sinusoidal curve
    with the amplitude σ a.
    ▪ The load F can be adjusted by positioning the sliding piece with the weight G.
    ▪ The number of rotations is determined by a counter and the machine is stopped at
    failure.
    ▪ The "stress amplitude - number of cycles" curve can be determined by repeating the
    test at different stress levels.

    Fatigue Component Test on the Dartec Fatigue Tester


    Here a component test is demonstrated. The fatigue loading of a spring is done in
    stroke controlled mode and the number of cycles to failure is determined.

    MSE364/METE358 Materials/Metallurgical Laboratory II, Materials Engineering Department, KNUST, Kumasi Page 1
    Figure 2: Modern closed-loop servohydraulic testing system

    Results
    1) Plot all the available results on a S-N curve. Note the scatter.
    2) Estimate the fatigue limit for this steel.

    Post Lab Questions


    1) What is distinctive about the surface appearance of a fatigue fracture? What information
    can be obtained by observing the fracture surface?
    2) What are the stages in a fatigue fracture?
    3) Where do most fatigue cracks start? Why?
    4) What is mean stress and the R-ratio?
    5) What are fatigue properties? Why are fatigue properties important in engineering and
    how are they used?
    6) Why does improving surface finish improve fatigue properties?

    MSE364/METE358 Materials/Metallurgical Laboratory II, Materials Engineering Department, KNUST, Kumasi Page 2

    You might also like