03 Mechanical Behavior: Stress, Strain, and Deformation Free Online FlashCards

How is engineering stress calculated?

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

How is engineering strain calculated?

Engineering strain is the change in gauge length divided by its original length: $\varepsilon = \frac{L-L_0}{L_0} = \frac{\Delta L}{L_0}$.

What characterizes elastic deformation?

Elastic deformation is recoverable: when the load is removed, the material returns approximately to its original dimensions.

What happens to a material after plastic deformation?

Plastic deformation is permanent. After unloading, the material may recover some elastic strain but retains permanent strain.

What relationship does Hooke’s law describe?

In the initial linear-elastic region, Hooke’s law relates stress and strain: $\sigma = E\varepsilon$.

What does Young’s modulus indicate?

Young’s modulus $E$ is the slope of the linear portion of a tensile stress–strain curve. A larger modulus means less elastic strain for a given stress, not necessarily greater strength.

What marks the proportional limit?

The proportional limit is where the linear relationship between stress and strain ends. A material may remain elastic beyond it, but stress is no longer proportional to strain.

How does the 0.2% offset method estimate yield strength?

When a material has no clear yield point, the 0.2% offset method uses a line parallel to the initial elastic slope, starting at strain $0.002$. Its intersection with the curve defines the offset yield strength.

What is ultimate tensile strength?

Ultimate tensile strength (UTS) is the maximum engineering stress on the tensile stress–strain curve. In a ductile specimen, necking generally begins around this maximum.

Why can engineering stress fall after necking begins?

After necking begins, engineering stress may fall because it divides force by the original area, even while the local section continues deforming.

What does the area under a stress–strain curve represent?

The area under the stress–strain curve up to a given strain represents work per unit original volume. The area up to fracture is related to toughness, or energy absorption before breaking.

How do ductile and brittle fracture behavior differ?

A ductile material undergoes substantial plastic strain before fracture; a brittle material fractures with little plastic deformation.