Experiment 6: Mechanical Properties of Materials Flashcards
is defined as the force exerted on a material perpendicular to its cross-sectional area.
Engineering stress
is the change in length divided by the original length of the material
strain
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
strain
- 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
stress
ability of the material to return to its original shape upon the removal of an applied force
elasticity
- 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
The Young’s modulus
have large elastic deformations
elastomers:
- natural rubber
- silicone
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.
stress
There are five different ways in which these forces/load may be applied on a metal part.
Compression
Tension
Shear
Torsion
Bending
Stretching
= 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.
compression
= 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
Tension
is a deformation of amaterialsubstance in which parallel internal surfaces slide past one another.
Shear
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.
Torsion
= is a manufacturing process that produces a V-shape, U-shape, or channel shape along a straight axis in ductilematerials.
Bending
Strain - the change in dimensions, or deformation elongation, ΔL as a result of a tensile or compressive stress normalized to the length L.
Strain
- 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.
stress-strain curve
the action or process of changing in shape or distorting, especially through the application of pressure.
Deformation
Types of deformation:
Elastic deformation.
True stress and strain.
Plastic deformation.
Fracture.
- 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
Elastic deformation
When the stress is removed, the material does not return to its previous dimension but there is a permanent, irreversible deformation.
plastic deformation
– represents the stress-strain relationship for elastic deformation.
Hooke’s Law
- 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.
Yield strength point
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.
Strain hardening
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.
Ultimate Strength
- 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.
Necking
- 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
fracture
Why is the Strain-Stress Curve Important?
- 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.
- 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.
Thermal Expansion
rubber ___ when it gets colder and ___ when it gets hotter
expand, contract
- 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.
Young’s Modulus of the material (elastic modulus)
High Young’s modulus value :
stiff material
Low Young’s modulus value :
flexible material
