Experiment 6: Mechanical Properties of Materials

Question 1

is defined as the force exerted on a material perpendicular to its cross-sectional area.

Answer 1

Engineering stress

Question 2

is the change in length divided by the original length of the material

Answer 2

strain

Question 3

is defined as fully recoverable ___ resulting from an applied stress, is elastic if it develops instantaneously and remains as long as the stress is applied

Answer 3

strain

Question 4

• is used to characterize the mechanical behavior of the
• material being tested help engineers determine the constitutive relationship between stress and strain for a particular material
• affected by temperature

Answer 4

stress

Question 5

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

Answer 5

elasticity

Question 6

• is the slope of the elastic region of its stress-strain diagram
• is not necessarily linear, this the slope of the tangent at a particular stress-strain point is used as its value

Answer 6

The Young’s modulus

Question 7

have large elastic deformations

Answer 7

elastomers:
- natural rubber
- silicone

Question 8

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

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

The forces applied can be in the form of tensile force, compression force, torsion or shear force.

The act of applying the force is known as loading.

Answer 8

stress

Question 9

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

Answer 9

Compression
Tension
Shear
Torsion
Bending
Stretching

Question 10

= is the action of applying a force to a solid, liquid, or gas so that it takes up less space.
= is the application of balanced inward (“pushing”) forces to different points on amaterialor structure, that is, forces with no net sum or torque directed so as to reduce its size in one or more directions.

Answer 10

compression

Question 11

= 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

Answer 11

Tension

Question 12

is a deformation of amaterialsubstance in which parallel internal surfaces slide past one another.

Answer 12

Shear

Question 13

is a load that is applied to amaterialthroughtorque. Thetorquethat is applied creates a shear stress. If atorsionforce is large enough, it can cause amaterialto undergo atwistingmotion during elastic and plastic deformation.

Answer 13

Torsion

Question 14

= is a manufacturing process that produces a V-shape, U-shape, or channel shape along a straight axis in ductilematerials.

Answer 14

Bending

Question 15

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

Answer 15

Strain

Question 16

• The relationship between thestressandstrainthat a particular material displays is known as that particular material’s
• 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). (any form of deformation).
• These curves reveal many of the properties of a material (including data to establish theModulus of Elasticity.
• Curves representing the relationship between stress and strain in any form of deformation can be regarded as stress-strain curves.

Answer 16

stress-strain curve

Question 17

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

Answer 17

Deformation

Question 18

Types of deformation:

Answer 18

Elastic deformation.
True stress and strain.
Plastic deformation.
Fracture.

Question 19

• 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

Answer 19

Elastic deformation

Question 20

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

Answer 20

plastic deformation

Question 21

– represents the stress-strain relationship for elastic deformation.

Answer 21

Hooke’s Law

Question 22

• 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 occur.
• engineering calculations use a material’syield strengthfor determining its ability to resist a load. If the load is greater than the yield strength, the result will be unwanted deformation.

Answer 22

Yield strength point

Question 23

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.

Answer 23

Strain hardening

Question 24

it 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.

Answer 24

Ultimate Strength

Question 25

• 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.
• The stress is so high that it leads to the formation of a neck at the weakest point of the material.

Answer 25

Necking

Question 26

• will occur at the neck usually with a cup and cone shape formation at either end of the rod. This point is known as the fracture or rupture point and is denoted by D on the stress and strain graph.
• the maximum stress that is experienced in a crack point before it breaks down

Answer 26

fracture

Question 27

Why is the Strain-Stress Curve Important?

Answer 27

• The stress-strain curve provides design engineers with a long list of important parameters needed for application design for a mechanical properties like: strength, toughness, elasticity, yield point, strain energy, resilience, and elongation during load.
• It also helps in fabrication. Whether you are looking to perform extrusion, rolling,bendingor some other operation, the values stemming from this graph will help to determine the forces necessary to induce plastic deformation.

Question 28

• refers to a fractional change in size of a material in response to a change in temperature.
• For most materials, over small temperature ranges, these fractional changes are directly proportional to temperature change (ΔT) and have the same sign (i.e., materials usually expand when heated and contract when cooled), except for rubbers.

Answer 28

Thermal Expansion

Question 29

rubber ___ when it gets colder and ___ when it gets hotter

Answer 29

expand, contract

Question 30

• describes the tensile elasticity or the tendency of an object to deform along an axis when opposing forces are applied along that axis.
• ratio of tensile stress and tensile strain.

Answer 30

Young’s Modulus of the material (elastic modulus)

Question 31

High Young’s modulus value :

Answer 31

stiff material

Question 32

Low Young’s modulus value :

Answer 32

flexible material