The yield strength of an alloy is the stress at which it begins to deform plastically (permanently), and it is typically determined using a tensile test. The yield strength can be estimated from the tensile test by finding the intersection of the linear portion of the stress-strain curve (the elastic region) and the extrapolation of the linear portion to the strain axis (the yield point). This method is known as the 0.2% offset yield strength, as the strain at the yield point is typically around 0.2%.
If the stress-strain curve of the alloy exhibits a smooth curve without a distinct yield point, it is said to have a "ductile" behavior. In this case, the yield strength can be estimated using the 0.5% offset method, in which the yield strength is taken as the stress at a strain of 0.5%. This method is based on the idea that the alloy will have deformed plastically by 0.5% strain, even if it has not yet reached the yield point.
It is important to note that both of these methods involve some degree of estimation, and the actual yield strength of the alloy may differ slightly from the value obtained using these methods. The yield strength of an alloy can also be affected by various factors such as temperature, strain rate, and the presence of defects or impurities in the material.
Determining the yield strength of an alloy that exhibits a smooth stress-strain curve in a tensile test can be challenging, as the alloy may not exhibit a distinct yield point.
One common method for determining the yield strength, in this case, is to use the 0.2% offset method. This method defines the yield strength as the point on the stress-strain curve at which the stress is equal to 0.2% of the strain. This is the point where the material starts to show plastic deformation and it's not fully elastic anymore.
Another method used to determine the yield strength in case of a smooth curve is using the linear elastic-plastic region, this method defines the yield strength as the intersection point of the linear elastic region and the linear plastic region of the stress-strain curve.
A third method is to use the "elastic-plastic transition" method, where the yield strength is determined by extrapolating the tangent of the elastic-plastic transition point, this method will give the closest approximation to the true yield strength.
The easy way to find the yield stress of such material is by 0.2% offset technique. In this technique, the value of yield stress at a point when 0.2% strain is occurred has been taken.
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