Mechanical Principles of Stress and Strain

This set of vocabulary flashcards covers fundamental concepts of engineering mechanics including stress, strain, material properties, and design considerations based on lecture assessment notes.

Normal Strain

The ratio of change in length to original length ($\text{strain} = \frac{\text{elongation}}{\text{original length}}$), characterized as a dimensionless quantity.

Stress Concentration

A localized increase in stress caused by geometric discontinuities, such as sharp square corners, holes, or keyways, which may initiate structural failure.

Serviceability Problem

An engineering issue where excessive deformation impairs a structure's function, alignment, or user safety, even if structural failure or collapse has not occurred.

Modulus of Elasticity (Young's Modulus)

A measure of a material's stiffness defined as the ratio of stress to strain within the elastic range ($E = \frac{\text{Stress}}{\text{Strain}}$).

Poisson's Ratio

The material property that explains why a member's diameter becomes slightly smaller when it is stretched in tension.

Hooke's Law

The principle stating that within the elastic range, stress is proportional to strain.

Bearing Stress

Stress developed in the contact area between components (such as a pin or bolt), which can be reduced by increasing the projected contact area.

Static Equilibrium

The fundamental principle where internal resisting forces within a component exactly balance the externally applied loads.

Elastic Deformation

The behavior of a material that elongates under load but returns to its original dimensions once the load is removed.

Allowable Stress

The maximum stress permitted for a safe design, typically set below the material's failure strength to account for uncertainties.

Shear Stress

A type of internal stress that acts parallel to the surface, commonly developed in bolted lap joints subjected to sliding forces.

Normal Stress

The internal resistance that acts perpendicular to the cross-sectional area of a member, resulting from tensile or compressive axial loads.

Thermal Strain

Deformation resulting from temperature fluctuations, often addressed in design through expansion joints to prevent structural damage.

Fillet Radii

Generous curved transitions used between structural features (like a shaft and its shoulder) to reduce stress concentration.

Normal Stress (Conversion)

A stress value of $200\,\text{MPa}$ is equivalent to approximately $29.0\,\text{ksi}$; whereas a value of $145,000\,\text{psi}$ is approximately $1000\,\text{MPa}$.

Unit Consistency

An essential engineering practice to prevent unsafe designs and extreme inaccuracies by converting all quantities into one consistent system before calculation.