Stress and Strain

• What can opposite forces do to an object?

  Deform the object
• What are tensile forces?

  Forces that stretch an object
• What two properties do tensile forces lead to?

  Tensile stress and tensile strain
• How is tensile stress defined?

  Force per unit cross-sectional area
• What is the symbol for tensile stress?

  σ (sigma)

  
• What are the units of tensile stress?

  Pascals (Pa)

  
• What is ultimate tensile stress?

  Maximum force per original area before breaking
• What does tensile strain measure?

  Extension per unit length
• Why is strain considered a dimensionless unit?

  It is a ratio of lengths
• How would you express strain as a percentage?

  Strain = (extension/original length) × 100
• What is the tensile stress of a wire with a force of 50 N and cross-sectional area of $1.2566 \times 10^{-6} \text{ m}^2$?


  $397.899 \times 10^{6} \text{ Pa}$
• What is the tensile strain of a wire that extends from 4.50 m to 4.53 m?

  $6.7 \times 10^{-3}$
• What do stress-strain curves describe about materials?

  • Properties like brittleness and ductility
  • Stress and strain behavior
  • Elastic and plastic behavior

  
• What is yield stress?

  Force per unit area for plastic extension
• What does the area under the Hooke's Law region represent?

  Elastic strain energy stored per unit volume
• What is the breaking point in a stress-strain graph?

  Maximum stress before material fractures

  
• What happens in the elastic region of a stress-strain graph?

  Material returns to original shape after force removal
• What occurs in the plastic region of a stress-strain graph?

  Material deforms permanently and does not return
• What is the breaking stress for copper wire?

  190 MPa

  
• At what stress does plastic deformation begin for copper wire?

  130 MPa
• What is the acceptable range for the stress at which plastic deformation begins?

  120 MPa - 135 MPa