fatigue testing and analysis theory and practice pdf

Fatigue Testing And Analysis Theory And Practice Pdf

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Haynes ManualsThe Haynes Author : Yung-Li Lee, Jwo Pan, Richard Hathaway, Mark Barkey Description:This book is a summary of experimental and analytical techniques that are essential to students and practicing engineers for conducting mechanical component design and testing for durability.

More specifically, it covers the most comprehensive methods to capture the component load, to characterize the scatter of product fatigue resistance and loading, to perform the fatigue damage assessment of a product, and to develop an accelerated life test plan for reliability target demonstration. This book is most useful for test and design engineers in the ground vehicle industry. Fatigue Testing andAnalysis introduces the methods to account for variability of loads and statistical fatigue properties that are useful for further probabilistic fatigue analysis. The text incorporates and demonstrates approaches that account for randomness of loading and materials, and covers the applications and demonstrations of both linear and double-linear damage rules.

Fatigue Testing and Analysis: Theory and Practice(PDF)

Fatigue Testing and Analysis: Theory and Practice presents the latest, proven techniques for fatigue data acquisition, data analysis, and test planning and practice. More specifically, it covers the most comprehensive methods to capture the component load, to characterize the scatter of product fatigue resistance and loading, to perform the fatigue damage assessment of a product, and to develop an accelerated life test plan for reliability target demonstration.

This book is most useful for test and design engineers in the ground vehicle industry. The text incorporates and demonstrates approaches that account for randomness of loading and materials, and covers the applications and demonstrations of both linear and double-linear damage rules. The reader will benefit from summaries of load transducer designs and data acquisition techniques, applications of both linear and non-linear damage rules and methods, and techniques to determine the statistical fatigue properties for the nominal stress-life and the local strain-life methods.

This chapter addresses the sensors, sensing methods, measurement systems, data acquisition, and data interpretation used in the experimental work that leads to fatigue life prediction. A large portion of the chapter is focused on the strain gage as a transducer. Accurate measurement of strain, from which the stress can be determined, is one of the most significant predictors of fatigue life. Prediction of fatigue life often requires the experimental measurement of localized loads, the frequency of the load occurrence, the statistical variability of the load, and the number of cycles a part will experience at any given load.

A variety of methods may be used to predict the fatigue life by applying either a linear or weighted response to the measured parameters. Experimental measurements are made to determine the minimum and maximum values of the load over a time period adequate to establish the repetition rate. If the part is of complex shape, such that the strain levels cannot be easily or accurately predicted from the loads, strain gages will need to be applied to the component in critical areas.

Measurements for temperature, number of temperature cycles per unit time, and rate of temperature rise may be included. Fatigue life prediction is based on knowledge of both the number of cycles the part will experience at any given stress level during that life cycle and other influential environmental and use factors. Section 1. One of the most commonly accepted methods of measuring strain is the resistive strain gage.

Modern strain gages are resistive devices that experimentally evaluate the load or the strain an object experiences. In any resistance transducer, the resistance R measured in ohms is material and geometry dependent.

Resistance increases with length and decreases with cross-sectional area for a material of constant resistivity. In Figure 1.

If the wire experiences a mechanical load P along its length, as shown in Figure 1. The resistance change that occurs in a wire under mechanical load makes it possible to use a wire to measure small dimensional changes that occur because of a change in component loading. It is possible, with proper bonding of a wire to a structure, to accurately measure the change in length that occurs in the bonded length of the wire.

This is the underlying principle of the strain gage. In a strain gage, as shown in Figure 1. In a strain gage, the change in resistance occurs when the conductor is stretched or compressed.

The resistance strain gage is convenient because the change in resistance that occurs is directly proportional to the change in length per unit length that the transducer undergoes.

Two fundamental types of strain gages are available, the wire gage and the etched foil gage, as shown in Figure 1. Both gages have similar basic designs; however, the etched foil gage introduces some additional flexibility in the gage design process, providing additional control, such as temperature compensation. The etched foil gage can typically be produced at lower cost. The product of gage width and length defines the active gage area, as shown in Figure 1.

The active gage area characterizes the measurement surface and the power dissipation of the gage. The backing length and width define the required mounting space. The gage backing material is designed such that high transfer efficiency is obtained between the test material and the gage, allowing the gage to accurately indicate the component loading conditions.

Nominal gage resistance is most commonly either or ohms. Higher-resistance gages are available if the application requires either a higher excitation voltage or the material to which it is attached has low heat conductivity. Increasing the gage resistance R allows increased excitation levels V with an equivalent power dissipation P requirement as shown in Equation 1. Testing in high electrical noise environments necessitates the need for higher excitation voltages V.

With analog-to-digital A—D conversion for processing in computers, a commonly used excitation voltage is 10 volts. At 10 volts of excitation, each gage of the bridge would have a voltage drop of approximately 5 V. The power to be dissipated in a ohm gage is thereby approximately 71mW and that in a ohm gage is approximately mW:. At a volt excitation with the ohm gage, the power to be dissipated in each arm goes up to mW. High excitation voltage leads to higher signal-to-noise ratios and increases the power dissipation requirement.

Excessively high excitation voltages, especially on smaller grid sizes, can lead to drift due to grid heating. The gage averages the strain field over the length L of the grid. If the gage is mounted on a nonuniform stress field the average strain to which the active gage area is exposed is proportional to the resistance change.

If a strain field is known to be nonuniform, proper location of the smallest gage is frequently the best option as shown in Figure 1.

Gage material from which the grid is made is usually constantan. The material used depends on the application, the material to which it is bonded, and the control required.

If the gage material is perfectly matched to the mechanical characteristics of the material to which it is bonded, the gage can have pseudo temperature compensation with the gage dimensional changes offsetting the temperature-related component changes.

The gage itself will be temperature compensated if the gage material selected has a thermal coefficient of resistivity of zero over the temperature range anticipated. If the gage has both mechanical and thermal compensation, the SYSTEM will not produce apparent strain as a result of ambient temperature variations in the testing environment. Selection of the proper gage material that has minimal temperature-dependant resistivity and some temperature-dependent mechanical characteristics can result in a gage SYSTEM with minimum sensitivity to temperature changes in the test environment.

Strain gage manufacturers broadly group their foil gages based on their application to either aluminum or steel, which then provides acceptable temperature compensation for ambient temperature variations.

The gage proportionality factor, commonly called the gage factor GF , which makes the two equations of 1. Most common strain gages have a nominal gage factor of 2, although special gages are available with higher gage factors.

The change in the resistivity, called piezoresistance, occurs at a molecular level and is dependent on gage material. In fatigue life prediction, cyclic loads may only be a fraction of the loads required to cause yielding. The measured output from the instrumentation will depend on the gage resistance change, which is proportional to the strain.

If the loads are relatively low, Equation 1. A ohm gage is to be used in measuring the strain magnitude of an automotive component under load.

The strain gage has a gage factor of 2. If the component is subjected to a strain field of microstrain, what is the change in resistance in the gage? If a high gage factor ohm strain gage is used instead of the ohm gage, what is the gage factor if the change in resistance is 0.

By using Equation 1. Strain gages may be purchased in a variety of arrangements to make application easier, measurement more precise, and the information gained more comprehensive. This arrangement is popular if the direction of loading is unknown or varies. With principle strains and principle angles known, principle stresses can be obtained from stress—strain relationships. Linear stress—strain relationships are given in Equations 1.

In high-strain environments, these linear equations may not hold true. The linear stress—strain relationships in a three-dimensional state of stress are shown in Equations 1.

The relationship between shear strains and shear stresses are given in Equation 1. Shear strains and shear stresses are related through the shear modulus G :. Equations 1.

Principle stresses for the three-element rectangular rosette can also be obtained directly from the measured strains, as shown in Equations 1. The change in resistance that occurs in a typical strain gage is quite small, as indicated in Example 1. Because resistance change is not easily measured, voltage change as a result of resistance change is always preferred. A Wheatstone bridge is used to provide the voltage output due to a resistance change at the gage.

The strain gage bridge is simply a Wheatstone bridge with the added requirement that either gages of equal resistance or precision resistors be in each arm of the bridge, as shown in Figure 1. The bridge circuit can be viewed as a voltage divider circuit, as shown in Figure 1. As a voltage divider, each leg of the circuit is exposed to the same excitation voltage Eex.

The current that flows through each leg of the circuit is the excitation voltage divided by the sum of the resistances in the leg, as shown in Equation 1. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel. Carousel Previous. Carousel Next.

What is Scribd? Find your next favorite book Become a member today and read free for 30 days Start your free 30 days. Create a List. Download to App. Length: pages. Description Fatigue Testing and Analysis: Theory and Practice presents the latest, proven techniques for fatigue data acquisition, data analysis, and test planning and practice.

Covers the useful techniques for component load measurement and data acquisition, fatigue properties determination, fatigue analysis, and accelerated life test criteria development, and, most importantly, test plans for reliability demonstrations Written from a practical point of view, based on the authors' industrial and academic experience in automotive engineering design Extensive practical examples are used to illustrate the main concepts in all chapters.

Home Books Mechanical Engineering. About the author YL. Related authors. Related to Fatigue Testing and Analysis.

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Rated 4. Notice: This is the eBook of the printed book and may not include any media, website access codes, or print supplements that may come packaged with the bound book. Description Reviews 5 Fatigue Testing and Analysis: Theory and Practice presents the latest, proven techniques for fatigue data acquisition, data analysis, and test planning and practice. More specifically, it covers the most comprehensive methods to capture the component load, to characterize the scatter of product fatigue resistance and loading, to perform the fatigue damage assessment of a product, and to develop an accelerated life test plan for reliability target demonstration. This book is most useful for test and design engineers in the ground vehicle industry. The text incorporates and demonstrates approaches that account for randomness of loading and materials, and covers the applications and demonstrations of both linear and double-linear damage rules.

Fatigue Testing and Analysis: Theory and Practice presents the latest, proven techniques for fatigue data acquisition, data analysis, and test planning and practice. More specifically, it covers the most comprehensive methods to capture the component load, to characterize the scatter of product fatigue resistance and loading, to perform the fatigue damage assessment of a product, and to develop an accelerated life test plan for reliability target demonstration. This book is most useful for test and design engineers in the ground vehicle industry. The text incorporates and demonstrates approaches that account for randomness of loading and materials, and covers the applications and demonstrations of both linear and double-linear damage rules. The reader will benefit from summaries of load transducer designs and data acquisition techniques, applications of both linear and non-linear damage rules and methods, and techniques to determine the statistical fatigue properties for the nominal stress-life and the local strain-life methods. Transducers and data acquisitions; Fatigue damage theories; Cycle counting techniques; Stress-based fatigue analysis and design; Strain-based fatigue analysis and design; Fracture mechanics and fatigue crack propagation; Fatigue of spot welds; Development of accelerated life test criteria; Reliability demonstration testing; Fatigue analysis in the frequency domain.


Fatigue Testing and Analysis. Theory and Practice [1ed.], 0-​ admin | February 1, | Technology | No Comments.


Fatigue Testing and Analysis. Theory and Practice [1ed.]9780750677196, 0-7506-7719-8

By design, a material is selected to meet or exceed service loads that are anticipated in fatigue testing applications. Cyclic fatigue tests produce repeated loading and unloading in tension, compression, bending, torsion or combinations of these stresses. Fatigue tests are commonly loaded in tension — tension, compression — compression and tension into compression and reverse.

Haynes ManualsThe Haynes Author : Yung-Li Lee, Jwo Pan, Richard Hathaway, Mark Barkey Description:This book is a summary of experimental and analytical techniques that are essential to students and practicing engineers for conducting mechanical component design and testing for durability. There is a serious need for engineers to have an overview on the entire methodology of durability testing and reliability to bridge the gap between fundamental fatigue research and its durability applications. Covers the useful techniques for component load measurement and data acquisition, fatigue properties determination, fatigue analysis, and accelerated life test criteria development, and, most importantly, test plans for reliability demonstrations.

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Fatigue Testing and Analysis: Theory and Practice

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1 Comments

  1. Daisi M.

    Price includes VAT/GST. DRM-free (Mobi, PDF, EPub) Fatigue Testing and Analysis: Theory and Practice presents the latest, proven techniques for fatigue data acquisition, data analysis, and test planning and practice. More specifically, it.

    07.04.2021 at 05:18 Reply

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