mechanical.ppt

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Chapter 6 - 1 Chapter 5: Mechanical Properties Introduction : Materials in service are subjected to forces or loads . It’s necessary to know the characteristics (properties) and the composition of the material In this chapter we study the behavior of the material when it's subjected to force or load. Important mechanical properties : strength, hardness, ductility and stiffness…. Load types : tension, compression and shear.
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Chapter 6 - 2 Concepts of Stress and strain Mechanical behavior may be analyzed by a simple stress-strain test (conducted for metals at room T). A load is applied uniformly over a cross section or surface of a member. Three principal ways in which a load may be applied: tension, compression shear.
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Chapter 6 - 3 Tension Tests : One of the most common mechanical stress-strain tests is performed in tension. Shape before deformation Shape after deformation Tensile load produces an elongation Tension test:
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Chapter 6 - 4 Tension test: standard tensile specimen Normally: cross section is circular Rectangular specimens are also used During testing: deformation is confined to the narrow center region.
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Chapter 6 - 5 During testing: deformation is confined to the narrow center region Tension test: standard tensile specimen How we can perform this tension test ?
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Chapter 6 - 6 Tension test • Typical tensile test machine Adapted from Fig. 6.3, Callister 7e. (Fig. 6.3 is taken from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials , Vol. III, Mechanical Behavior , p. 2, John Wiley and Sons, New York, 1965.) specimen ensometer Specimen is mounted by its ends into the holding grips Specimen is elongated at a constant rate Applied load and resulting elongations are measured by a load cell and an extensometer . A stress strain test takes several minutes to perform The test specimen is permanently deformed and usually fractured
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Chapter 6 - 7
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Chapter 6 - 8 Tension test • Typical tensile test machine Adapted from Fig. 6.3, Callister 7e. (Fig. 6.3 is taken from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials , Vol. III, Mechanical Behavior , p. 2, John Wiley and Sons, New York, 1965.) specimen tensometer The specimen is elongated by the moving crosshead Load cell measure the magnitude of the applied load Extensometer measure the elongation
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Chapter 6 - 9 The result is recorded on a chart as load or force versus elongation Load-deformation charcteristics are dependent on the specimen size Ex: it will require twice the load to produce the same elongation if the cross-sectional area of the specimen is doubled. specimen extensometer
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Chapter 6 - 10 Tension Test : Engineering Stress Engineering stress (applied force) , is defined by the relationship: = F A o F : Is the load applied perpendicular to the specimen cross section (in units of newtons (N)).
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  • Winter '15
  • Amir Alimohammad
  • Deformation, Tensile strength

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