Exp. 10; MECHANICAL PROPERTIES OF MATERIALS

THE STRESS – STRAIN CURVE OF A DOOR SPRING

Engineering stress  

is defined as the force, F, exerted on a material perpendicular to its cross – sectional area, A. ​

Strain

is the change in length divided by the original length of a material, L0. Elastic if it develops instantaneously and remains as long as the stress is applied.

Engineering strain

defined as fully recoverable strain resulting from an applied stress.

Stress-strain curve

is used to characterize the ==mechanical behavior== of the material being tested.

Stress-strain curve

It is most often plotted using engineering stress and strain measures due to the ease of measuring reference length and cross – sectional area.

Stress-strain curve

can help engineers determine the constitutive relationship between stress and strain for a particular material.

Constitutive relationship

can help determine the stress exerted on a material given strain and vice-versa. This relationship is quite complex and can be affected by many factors including temperature. ​

Elasticity

is its ability to return to its original shape upon the removal of an applied force.

The Young’s modulus

___________ is the slope of the elastic region of its stress – strain diagram.

Stress–strain line

____________ is not necessarily linear, thus the slope of the tangent at a particular stress – strain point is used as the value of Young’s modulus.​

Elastomers

_________ have large elastic deformations. Examples include natural rubber and silicone. ​

Stress

_______ - is the applied force or system of forces that tends to deform a body.​

Stress

_______ - is the ratio of the applied force to the cross-sectional area of the material it is applied to.​

loading

The act of applying the force is known as *_______.*

compression, tension, shear, torsion, bending

There are five different ways in which these forces/load may be applied on a metal part:

Compression

________ is the action of applying a force to a solid, liquid, or gas so that it takes up less space.​

Compression

__________   is the application of balanced inward ("pushing") forces to different points ​on a material or structure, that is, forces with no net sum or torque directed so as to​

Tension

_________ is a quantity associated with stretching or tensile forces. It is responsible for the elongation of the material along the axis of the applied load also called ==*tensile stress​*==

Shear

__________-    is a deformation of a material substance in which parallel internal surfaces slide past one another. ​

Torsion

_______  is a load that is a applied to a material through torque. The torque that is applied creates a shear stress. If a torsion force is large enough, it can cause a material to undergo a twisting motion during elastic and plastic deformation.​

Bending

_______ is a manufacturing process that produces a V-shape, U-shape, or channel shape along a straight axis in ductile materials

Strain

_______ - the change in dimensions, or deformation elongation, ΔL as a result of a tensile or compressive stress normalized to the length L.​

Stress-strain behavior

It is unique for each material and is found by recording the amount of deformation (strain) at distinct intervals of a variety of loadings (stress). ​

stress–strain curve

____________ refers to the relationship between axial normal stress and axial normal strain of materials measured in a tension test.​

Deformation

___________ ​- the action or process of changing in shape or distorting, especially through the application of pressure.​

elastic, true stress and strain, plastic, fracture

Types of deformation;

Elastic deformation

When the stress is removed, the material returns to the dimension it had before the load was applied.

Valid for small strains (except the case of rubbers).

Deformation is reversible, non-permanent

Plastic deformation

When the stress is removed, the material does not return to its previous dimension but there is a permanent, irreversible deformation.​

Yield strength point

_________ ​- is where the deformation of the material is first observed. If the load of the material is removed from the testing machine beyond this point, it will not return to its original length, plastic deformation occurs.​

Strain hardening

___________ - is said to occur when the number of dislocations in the material becomes too high and they start to obstruct each other’s movement. The material constantly rearranges itself and tends to harden.​

Ultimate Strength

____________​ - is defined as the maximum stress that a material can withstand when a force is applied. When the materials are pushed beyond UTS they experience the cracking.​

Necking

___________ - ​ when the deformation continues to occur with increasing stress. In due time, a narrowing of cross-section will be observed at a point on the rod. ​

provides design engineers with a long list of important parameters needed for application design for a mechanical properties during load.

*Why is the Strain-Stress Curve Important?​*

thermal expansion, young’s modulus of the material

*Effects of Temperature to Elasticity:*

stiff

High Young’s modulus value: _____ material​

flexible

Low Young’s modulus value:______ material​