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Monday, 15 October 2012

STRESS-STRAIN DIAGRAM FOR MILD STEEL


The stress-strain diagram for a ductile material like mild
 steel is shown in Fig. 1.13. The curve starts from the origin , showing thereby that there is no initial stress of strain in the specimen. Upto point A, Hooke s law is obeyed and stress is
proportional to strain.Therefore, OA is a straight line. Point A is called the limit of proportionality. Upto point B, the material remains elastic, i.e. on removal of the
load, no permanent set is formed. AB is not a straight line. Point B iscalled the elastic limit point. Beyond point B, the material goes to the plastic stage until the upper yield point C is reached. At this point the cross-sectional area of the material starts decreasing and the stress decreases to a lower value to point D, called the lower yield point. Between DE, the specimen elongates by a considerable amount without any increase in stress. From point E onwards, the strain hardening phenomena becomes predominant and the strength of the material increases thereby requiring more stress for deformation, unitl point F is reached. Point F is called the ultimete point and the corresponding stress is called the ultimate strength. At point F, necking of the material begins and the cross-sectional area decreases at a rapid rate. The apparent stress deceases but the actual or true stress goes on increasing until the specimen breaks at point C, called the point of fracture. The fracture of ductile material is of the cup and cone type.The phenomena of yielding and necking is not exhibited by brittle materials. The ulimate strenght is calculated at 0.2 per cent of maximum strain.

14 comments:

  1. This comment has been removed by the author.

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  3. thank for sharing... helped me when i was in need... :D :)

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  4. there is a little confusion
    1- plastic stage start after point B till fracture point and you wrote the material goes to the plastic stage until the upper yield point C is reached.
    2-when the area of cross section decreases the stress should increase while at point D stress decreased
    3- what happened between DE why such phenomenon occurs

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    1. this is correct there is no legal point in your doubt

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    2. Owing to large reduction in area produced by the necking process the actual stress at fracture is often greater than the above value. Since the designers are interested in maximum loads which can be carried by the complete cross section, hence the stress at fracture is seldom of any practical value.

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  5. I have a doubt that it brakes at which point c or g.

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  6. why there is two yielding points in the curve


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  7. While testing on a UTM, can we recognize curve is sloping downwards between point 'C', 'D' & 'E'. How can we get a point on the downside?

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    1 explain stress strain diagram for mild steel under compressive loading.
    2 explain stress strain diagram for odinary concrete under compressive loading.
    3 compare stress strain diagram for for following under tensile loading.

    a) mild steel
    b)wrought iron
    c)high carbon steel
    d) pure iron
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