4 Mechanical Behavior of Materials Free Online FlashCards

How is engineering stress calculated?

Engineering stress is applied force divided by the specimen’s original cross-sectional area: $\sigma = \frac{F}{A_0}$.

How is axial strain calculated, and does it have units?

Axial strain is the change in length divided by initial length: $\varepsilon = \frac{L-L_0}{L_0}$. It has no units.

What makes deformation elastic?

Elastic deformation is recoverable: after the load is removed, the material returns approximately or completely to its original shape.

What is plastic deformation?

Plastic deformation is permanent. After unloading, a specimen that has deformed plastically retains residual strain.

What does Young’s modulus measure?

Young’s modulus $E$ is the slope of the linear elastic stress–strain curve and measures resistance to elastic deformation: $\sigma = E\varepsilon$.

What does yield strength indicate?

Yield strength marks the onset of significant permanent deformation. For materials without a sharp yield point, it is commonly reported using a specified offset method.

What is ultimate tensile strength?

Ultimate tensile strength is the maximum engineering stress reached during a tensile test.

Why does component stiffness depend on geometry as well as material?

Material stiffness is described by Young’s modulus, but component stiffness also depends on geometry. A longer or thinner rod stretches more than a shorter or thicker one of the same material under the same force.

What does ductility describe?

Ductility is the amount of plastic deformation a material can undergo before fracture. It is often measured by elongation or reduction in area after a tensile test.

What does hardness measure?

Hardness is resistance to localized deformation, commonly measured by pressing an indenter into a surface or by a scratch test.

What does toughness represent on a stress–strain curve?

Toughness describes the ability to absorb energy before breaking; it corresponds to the area beneath the stress–strain curve up to fracture.

What is creep?

Creep is the gradual increase in strain while stress is held approximately constant. It generally becomes more important as temperature or applied stress increases.