Untitled Document

TENSILE TESTING

Stress-Strain Curve:

Click on Image to run the animation-1

click here to run Load-Elongation Vs Stress-Stain animation

Initial Modulus or Initial Young’s Modulus (within Hook’s region)

When an external free is applied it is balanced by internal force developed in the molecular structure of the material

Secant modulus:

Slope of the straight line drawn between zero and a specific point (D), i.e. known strain or stress.

a) OA - Elongation is due to stretching of primary or secondary bonds, totally recoverable, elastic zone.

b) By further increasing the stress, the curve bends sharply at ‘C’, where larger strain at smaller stress - ‘Yield point’, OC' - Yield strain,OC" - Yieldstress.

After this a plastic flow occurs, breaking of some secondary bonds. Rearrangement of molecules.

c) This rearrangement puts the material in a better position to withstand further stress.

d) The nature of curve varies, depending on the molecular structure of fibre or yarn structure.

e) Work of rupture: Measure of toughness of material. It is the energy of work required to break in specimen. Area under the load- Elongation curve (Area of shaded position) (gm. Centimeters)

click here to run the Work of rupture animation

For comparison purpose
	= g. cm / Den.cm

Because it is proportional to cross section and length. The effective unit will be, g/den or g/tex.

Nature of stress – Strain curve of yarn can also be changed by changing the spinning parameters, e.g. spindle speed, traveler weight, T.M., etc.
TM3 > TM2 > TM1

f) Work factor: If the curve follow Hook’s law up to breaking point, then;

click here to run the Work factor animation

This is work factor.

	Work factor > (1/2)
	Work factor < (1/2)

It describes the nature of curve numerically

g) Elastic recovery: It is the property of a material by which it tends to recover its original size and shape after deformation.

AB – original length

CD – elastic extension

BD – total extension

click here to run the Elastic recovery animation

BC – permanent set.

Elastic recovery = (CD/BD)

For perfectly elastic material, BD = CD
So, Elastic recovery = 1.0

For perfectly plastic materials, CD = 0
Elastic recovery = 0

Effect: Bagging or dimensional stability of garment.

h) Time dependent effect:

Click on Image to run the animation

qqqqqqqqqqqqqqqqqqqqqqTime dependent extension or creep