STRESSES, STRAINS, STRESS INTENSITY

1.1 Fundamental Definitions Static Stresses TOTAL STRESS on a section mn through a loaded body is the resultant force S exerted by one part of the body on the other part in order to maintain in equilibrium the external loads acting on the part. Thus, in Figs. 1, 2, and 3 the total stress on section mn due to the external load P is S. The units in which it is expressed are those of load, that is, pounds, tons, etc. UNIT STRESS, more commonly called stress , is the total stress per unit of area at section mn. In general it varies from point to point over the section. Its value at any point of a section is the total stress on an elementary part of the area, including the point divided by the elementary total stress on an elementary part of the area, including the point divided by the elementary area. If in Figs. 1, 2, and 3 the loaded bodies are one unit thick and four units wide, then when the total stress S is uniformly distributed over the area, P/A P/4. Unit stresses are expressed in pounds per square inch, tons per square foot, etc. TENSILE STRESS OR TENSION is the internal total stress S exerted by the material fibers to resist the action of an external force P (Fig. 1), tending to separate the material into two parts along the line mn. For equilibrium conditions to exist, the tensile stress at any cross section will be equal and opposite in direction to the external force P. If the internal total stress S is distributed uniformly over the area, the stress can be considered as unit tensile stress S/A. COMPRESSIVE STRESS OR COMPRESSION is the internal total stress S exerted by the fibers to resist the action of an external force P (Fig. 2) tending to decrease the length of the material. For equilibrium conditions to exist, the compressive stress at any cross section will be equal and opposite in direction to the external force P. If the internal total stress S is distributed uniformly over the area, the unit compressive stress S/A. SHEAR STRESS is the internal total stress S exerted by the material fibers along the plane mn (Fig. 3) to resist the action of the external forces, tending to slide the adjacent parts in opposite directions. For equilibrium conditions to exist, the shear stress at any cross section will be equal and opposite in direction to the external force P. If the internal total stress S is uniformly distributed over the area, the unit shear stress S/A.
Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz, 2006 by John Wiley & Sons, Inc.

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Volumes of revolution - Ruled surfaces

Volumes of revolution for objects the shape of which is symmetrical about a central axis. The wheel is a simple example of this type of 3D object. The input is a half outline, or a cross-section through the object, which is rotated about the axis by the modeller, to produce a 3D illustration.

Ruled surfaces is a simple form of modelling, where any two sections or profiles can be joined at all points by straight lines. An airfoil, or a turbine blade is a typical example where this method can be applied. Examples of various methods of CAD modelling are shown in Fig. 3.5.





  • Manual of Engineering Drawing
    Second edition
    Colin H Simmons
    I.Eng, FIED, Mem ASME.
    Engineering Standards Consultant
    Member of BS. & ISO Committees dealing with
    Technical Product Documentation specifications
    Formerly Standards Engineer, Lucas CAV.
    Dennis E Maguire
    CEng. MIMechE, Mem ASME, R.Eng.Des, MIED
    Design Consultant
    Formerly Senior Lecturer, Mechanical and
    Production Engineering Department, Southall College
    of Technology
    City & Guilds International Chief Examiner in
    Engineering Drawing

    for STEP BY STEP GUIDE unigraphics simple tutorial please visit.........
    www.unigraphicsimpletutorial.blogspot.com

    ---or---




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    Meshed surfaces

    X, Y and Z co-ordinates are either calculated, transferred from 2D drawing views, or measured to provide basic modelling input. The modeller will then generate a 3D meshed surface joining up all the specified points. In order to build up a welldefined surface, the modeller interpolates between points defined in the user input in order to develop a fine enough mesh to show a smooth change in cross-section.
    This method can be used to produce the freeform shapes used in, for example, styling household appliances.




  • Manual of Engineering Drawing
    Second edition
    Colin H Simmons
    I.Eng, FIED, Mem ASME.
    Engineering Standards Consultant
    Member of BS. & ISO Committees dealing with
    Technical Product Documentation specifications
    Formerly Standards Engineer, Lucas CAV.
    Dennis E Maguire
    CEng. MIMechE, Mem ASME, R.Eng.Des, MIED
    Design Consultant
    Formerly Senior Lecturer, Mechanical and
    Production Engineering Department, Southall College
    of Technology
    City & Guilds International Chief Examiner in
    Engineering Drawing


    for STEP BY STEP GUIDE solidwork simple tutorial please visit.........
    www.solidworksimpletutorial.blogspot.com

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    Geometric modellers

    Geometric modellers build models from geometric solids, which have the attribute that mathematical formulae exactly define any point in 3D space occupied by these solids. Shapes include planes, cylinders, spheres, cones, toroids, etc. These shapes are combined using Boolean operations to produce the component.
    The Boolean operations produce a 3D model by a combination of the following methods:
    (a) resulting from the union of any two 3D objects or shapes;
    (b) resulting from the difference between any two 3D objects or shapes;
    (c) resulting from the volume that is common to any two 3D objects or shapes.

    This approach is very successful for modelling machined components but cannot handle anything that might be described as having a freeform shape.





  • Manual of
    Engineering Drawing
    Second edition
    Colin H Simmons
    I.Eng, FIED, Mem ASME.
    Engineering Standards Consultant
    Member of BS. & ISO Committees dealing with
    Technical Product Documentation specifications
    Formerly Standards Engineer, Lucas CAV.
    Dennis E Maguire
    CEng. MIMechE, Mem ASME, R.Eng.Des, MIED
    Design Consultant
    Formerly Senior Lecturer, Mechanical and
    Production Engineering Department, Southall College
    of Technology
    City & Guilds International Chief Examiner in
    Engineering Drawing



    for STEP BY STEP GUIDE unigraphics simple tutorial please visit.........
    www.unigraphicsimpletutorial.blogspot.com

    ---or---





  • Read More......