Same E for true stress true strain?

In summary, true stress considers the changing cross-sectional area of a material during testing while engineering stress assumes a constant cross-sectional area. True strain is calculated using the natural logarithm of the ratio between the final length and original length of a material. It is important to use true stress and strain for more accurate measurements of a material's behavior. However, they cannot be directly measured and are instead calculated using engineering stress and strain. Some limitations of using true stress and strain include only being applicable to homogeneous materials and not accounting for plastic deformation. The calculation also involves taking the natural logarithm, which may introduce errors.
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kelvin490
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Before yield we know that stress/strain= E. Can we obtain the same E if we substitute true stress and true strain in the equation? Why
 
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For materials that approximately obey Hookes law in the elastic region prior to yield (steel being the classic example), the true E modulus is slightly higher, but insignificant. True stress versus engineering stress becomes significant after yield , especially when necking begins. Before yield, the reduced area of the cross section is a rather small percentage of the original.
 
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1. What is the difference between true stress and engineering stress?

True stress takes into account the actual cross-sectional area of a material at any given point, while engineering stress assumes a constant cross-sectional area throughout the test. This means that true stress values will be higher than engineering stress values in the later stages of deformation.

2. How is true strain calculated?

True strain is calculated by taking the natural logarithm of the ratio between the final length of a material and its original length.

3. Why is it important to use true stress and true strain instead of engineering stress and strain?

True stress and strain provide more accurate measurements of a material's behavior under stress and deformation, especially in the later stages of testing. This is important for understanding the material's true strength and properties.

4. Can true stress and true strain be directly measured in experiments?

No, true stress and true strain cannot be directly measured as they require knowledge of the actual cross-sectional area and length of the material, which can change during the test. They are instead calculated using engineering stress and strain values.

5. What are the limitations of using true stress and true strain?

One limitation is that true stress and strain can only be accurately calculated for homogeneous materials. They also do not account for any plastic deformation that may occur during testing. Additionally, the calculation involves taking the natural logarithm, which can introduce errors in the final values.

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