Materials-strain

• What does strain measure in materials?

  Deformation when pulled or pushed
• How is strain calculated?

  Change in length divided by original length
• What does $\Delta L$ represent?


  Change in length of a material
• What does $\Delta L$ stand for in the strain formula?


  Change in length of the material
• If a wire's original length is 10 cm and it extends to 12 cm, what is $\Delta L$?


  $2 cm$
• Why is knowing the original length important in material science?

  It helps calculate deformation effects
• What does strain ($\epsilon$) represent in materials?


  Relative change in length
• How do the symbols in the strain formula interact to describe material deformation?

  Strain relates change in length to original length
• How does expressing strain as a percentage help in material comparison?

  It allows for straightforward comparison of elongation
• If the original length of a material is 200 cm and it changes to 202 cm, what is $\Delta L$?


  $2 \text{ cm}$
• What is elastic deformation in materials?

  • Temporary change in shape
  • Material returns to original shape after stress
  • Example: Stretching a rubber band
• What is the relationship between engineering stress and strain shown in the image?

  • The image shows the engineering stress-strain relationship for a material
  • It has two curves: the engineering stress and strain relationship, and the true stress and strain relationship
  • The engineering stress and strain relationship is linear in the elastic region and then shows a plastic region with a yield strength
  • The true stress and strain relationship shows a higher ultimate strength compared to the engineering relationship
• What does the symbol $L$ represent in the strain formula?


  Original length of the material
• What does a strain of 0.2 indicate about the wire?

  The wire has been stretched by 20%
• What symbols represent change in length and original length in strain calculations?

  $\Delta L$ and $L$
• What is the change in length for a steel bar that expands from 100 cm to 103 cm?

  $3 \text{ cm}$
• How does the strain formula relate to stretching a rubber band?

  • $\Delta L$ shows the extension of the rubber band
  • $L$ is the rubber band's original length
  • $\epsilon$ indicates the overall amount of stretch
• What does the formula $\epsilon =$$\frac{\Delta L}{L}$ represent?


  Strain as change in length over original length
• What does $L$ represent in material science?


  Original length of a material
• How do you calculate strain if $\Delta L =$$5 \text{ cm}$ and $L =$$50 \text{ cm}$?


  $\epsilon =$$\frac{5}{50} =$$0.1$
• If a material's original length is $L =$$10 \text{ cm}$ and its new length is $15 \text{ cm}$, what is $\Delta L$?


  $5 \text{ cm}$
• What is the yield strength of the material shown in the image?

  Yield Strength
• What happens to a rubber band when it stretches from 10 cm to 15 cm?

  It experiences a change in length of 5 cm
• What does a positive $\Delta L$ indicate about a material?


  The material has stretched or grown
• What is the strain formula?

  $\epsilon =$$\frac{\Delta L}{L}$
• How is $\Delta L$ calculated?


  By subtracting original length from new length
• What happens to a rubber band when it is stretched?

  It undergoes elastic deformation
• How does the original length affect material deformation?

  It helps determine stretching or compressing
• If a steel bar's original length is $L =$$20 \text{ cm}$, what does this indicate?


  It is the length before deformation
• What is the original length of a steel bar that elongates from 20 cm to 21 cm?

  20 cm
• What does the symbol $\epsilon$ represent in the strain formula?


  Strain, measuring material deformation
• What are the steps to substitute values into the strain formula?

  1. Identify $\Delta L$ and $L$.
  2. Substitute these values into the formula.
  3. Calculate the strain $\epsilon$.
• Why are the concepts of elastic, plastic, and failure regions important?

  • Essential for structural integrity
  • Crucial for materials selection
• What are the important regions illustrated in the strain and stress image?

  Elastic, plastic, and failure regions
• What are the two types of deformation materials undergo when stress is applied?

  • Elastic deformation: Returns to original shape
  • Plastic deformation: Permanently changes shape
• Why is strain often expressed as a percentage?

  To easily compare deformation of different materials
• What is the key difference between the elastic region and plastic region shown in the stress-strain curves?

  In the elastic region, the material deforms reversibly, while in the plastic region, the deformation is permanent
• If you wanted to determine the maximum stress the material can withstand before failure, which point on the stress-strain curve would you look at?

  Ultimate Strength
• If a rubber band has $\epsilon =$$0.01$, what percentage has it been stretched?


  1%
• How does the true stress-strain relationship differ from the engineering stress-strain relationship in the image?

  • The true stress-strain relationship shows a higher ultimate strength compared to the engineering relationship
  • This is because the true stress accounts for the reduction in cross-sectional area during deformation, while engineering stress does not
  • The true stress-strain curve also shows a more gradual transition from the elastic to plastic regions