Stress-Strain diagram for Brittle Materials

In Stress-strain diagram for ductile materials  it is clearly shows the Proportional Limit, elastic limit, yield point, ultimate tensile stress and Rupture stress at the breaking points. In Stress-strain diagram for ductile materials yield points are well-defined but stress-strain diagram for Brittle Materials, yield points are poorly defined which is shown in the following figure.

For the determination of the yield strength in brittle materials, following the general practice, one has to draw a straight line parallel to the elastic portion of the stress-strain curve at a predetermined strain ordinate value (say 0.1%). The point at which this line intersects the stress vs. strain curve is the yield point at off-set and called the yield strength at 0.1% or 0.2% of set strain.