Mechanics of Materials Chapters 1-5 Exam Review
Strain gage
A device used for measuring strain. A strain gage typically consists of a fine wire embedded in a polymer matrix. The strain gage is bonded to the test specimen and deforms as the specimen deforms. As the wire in the strain gage deforms, its resistance changes. The resistance change is directly proportional to the strain.
Shear force
A force that tends to cut
Stress-strain diagram
A graphic representation of the relationship between unit stress values and the corresponding unit strains for a specific material
Stress trajectory
A line that is parallel to the maximum normal stress everywhere else
Impact
A load suddenly applied to a structure
Elasticity
A material's ability to recover its initial shape after undergoing a force
Allowable Stress Design (ASD)
A method that focuses on loads that exist at normal or typical conditions
Residual strain/Permanent set/Plastic deformation
A portion of the strain that remains in the material permanently
Strain
A quantity used to provide a measure of intensity of deformation
Work hardening
Also known as strain hardening or cold working, this is the process of toughening a metal through plastic deformation.
Extensometer
An instrument to measure change in length of a tensile specimen, thus allowing calculation of strain.
Bearing stress
Compressive normal stresses that occur on the surface of contact between two separate interacting members
Live loads
Consist of the magnitude, duration, and location of the load varying throughout the lifetime of the structure
Dead loads
Consists of the weight of various structural members and the weight of objects that are permanently attached to a structure
Plastic behavior
Does not return to original shape resulting in permanent deformation
Poisson's Ratio
For elastic deformation, the negative ratio of lateral and axial strains that result from an applied axial stress.
Tension forces
Forces that tend to elongate a member
Compression forces
Forces that tend to shorten a member
Signage for compressive normal stress
Negative
Stress concentrations
Occurs where loads are applied, and they also occur in the vicinity of holes, grooves, notches, fillets, and other changes in shape that interrupt the smooth flow of stress through a solid body
Yielding
Past the elastic limit, relatively large deformations will occur for small or almost negligible increases in stress
Signage for tensile normal stress
Positive
Shear strain
Provides a measure of angular distortion (change in the angle between two lines that are orthogonal in the undeformed state)
Normal stress
Provides a measure of the elongation or contraction of an arbitrary line segment in a body after deformation
Ductility
The amount of strain that the material can withstand before fracturing
Deformation
The change in any dimension associated with these load or temperature induced displacements
Saint-Venant's Principle
The difference between the effects of two different but statically equivalent loads becomes very small at sufficiently large distances from load
Loads
The forces that act on a structure
Strain hardening
The increase in hardness and strength of a ductile metal as it is plastically deformed
Gage length
The initial distance between the knife-edges
Shear stress
The intensity of an internal force which acts on a surface that is parallel to the internal force
Stress
The intensity of internal force
Elastic limit
The largest stress that a material can withstand without any measurable permanent strain remaining after complete release of the stress
Hooke's Law
The law stating that the stress of a solid is directly proportional to the strain applied to it.
Displacement
The movement of a point with respect to some reference system of axes
Young's Modulus of Elasticity
The ratio of normal stress to the longitudinal strain produced in a body. (Also referred to as elastic modulus)
Stress-concentration factor (K)
The ratio of the maximum stress to the nominal stress on the section
Force-Temperature-Deformation Relationship
The relationship between internal force and axial deformation that includes the effects of temperature change
Force-deformation relationship
The relationship between the deformation of an axial member and its internal force
Stiffness
The resistance of an elastic body to deflection by an applied force.
Rigid-body displacement
The size and shape of the body are not changed by this type of displacement
Inelastic strain
The strain between points A and B (the moment when the plot begins to curve)
Elastic strain
The strain between the origin and the proportional limit
Yield point
The stress at which there is an appreciable increase ion strain with no increase in stress
Normal stress
The stress that acts on a surface that is perpendicular to the direction of the internal force (F)
Proportional limit
The strss at which the stress-strain plot is no longer linear
Method of sections
The technique of cutting an object to expose the internal forces acting on a plane surface
Elastic behavior
This reversible behavior often shows a linear relation between stress and strain. To minimize deformation, select a material with a large elastic modulus (E or G).
Perfectly plastic
When a material yields without an increase in stress
Single shear
When only one cross section of a pin/bolt transmits a load between the axial member and the support
Centric loading
When the maximum normal and shear stresses in an axial member that is subjected to an uniaxial tension or compression force applied through the centroid of the member
Cross section
a cutting along the longitudinal axis of a structure
Axial force
a load that is directed along the longitudinal axis of the member
Uniaxial
movement in one plane
factor of safety (FS)
the balance between destabilizing forces (shear stress) and stabilizing forces (shear strength) on a slope
Ultimate strength
the maximum amount of stress a material can withstand without breaking
Tension test
to determine strength, ductility, toughness, elastic modulus, and strain hardening
