Mechanics of Materials Chapters 1-5 Exam Review

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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


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