Understanding Stress-Strain Curves

The video explains the differences between engineering and true stress-strain curves, highlighting that engineering curves are approximations. True stress-strain curves account for changes in the specimen's dimensions during a tensile test. The video discusses why engineers often use engineering curves due to measurement difficulties and the focus on elastic deformation. It also covers the importance of true curves in cases of significant plastic deformation and provides methods to calculate true stress and strain using assumptions and integration.

What is the main difference between engineering and true stress-strain curves?

• True curves are always decreasing.

• True curves drop after necking.

• Engineering curves are always increasing.

• Engineering curves drop after necking.

What happens to the cross-sectional area during necking?

• It increases rapidly.

• It remains constant.

• It decreases rapidly.

• It becomes zero.

What is the ultimate tensile strength?

• The minimum value on the engineering curve.

• The average value on the true curve.

• The initial value on the true curve.

• The maximum value on the engineering curve.

Why do engineers often use engineering stress-strain curves?

• They are more accurate.

• They are used for large plastic deformations.

• They are easier to measure.

• They are always increasing.

Why is it difficult to measure true stress-strain curves?

• The force applied is unknown.

• The test piece is too large.

• The cross-sectional area is hard to measure instantaneously.

• The test piece is too small.

What is a key assumption made when calculating true stress?

• The volume of the test piece remains constant.

• The volume of the test piece changes.

• The material is compressible.

• The cross-sectional area is constant.

In which region is the assumption of constant volume valid?

• Elastic region only.

• Plastic region only.

• Both elastic and plastic regions.

• Neither elastic nor plastic regions.

What is the relationship between true stress and engineering stress?

• True stress is always less than engineering stress.

• True stress is calculated using the initial area.

• True stress is unrelated to engineering stress.

• True stress accounts for changing cross-sectional area.

What mathematical method is used to derive true strain?

• Multiplication

• Subtraction

• Integration

• Differentiation

What is another name for true strain?

• Quadratic strain

• Exponential strain

• Linear strain

• Logarithmic strain