An easy way to evaluate elastic modulus, compressive yield strength, ultimate compressive strength, and compressive strain at break from engineering stress-strain curve obtained from a standard compression test . Enjoy watching!
In a compression test of metals, the curve at the start is not linear due to the initial non-uniform deformation and material behavior as the load is first applied. Primary reason for this could be contact imperfections. At the start of the test, the surfaces of the metal specimen and the compression platens may not be perfectly aligned or in full contact. As the load increases, the specimen "settles" into the test configuration, causing an initial non-linear response.
Hello, sir. When entering this data into computer material model im supposed to define "plastic strains" are those strains just the strains past the yield strenght from the lab test or plastic strains are somehow calculated from this diagram from compression test?
Hi, strains values from the compression test can be obtained by using a video extensometer. If video extensometers are not available then strain values can be measured from the displacement values as change in height of the sample divided by original height of the sample (before test). If you are entering these plastic strain values in FEA-based models for an approximate solutions then you can enter strain values obtained in the plastic region- means beyond or after the yield point.
Hi, simple question i have stress strain values and graphs, i want to calculate the compressive strength of my specimen. Which point or formula should i look for?
The highest point of the compressive or tensile stress-strain curve corresponds to ultimate strength of the material. You can use maximum formula in Excel , e.g., = max(select the column of stresses) and this would give you the maximum value of stress in that column which corresponds to ultimate strength of the material. I hope it helps! good luck.
The tensile strength gives the maximum stress the material can withstand before its permanent fracture. However, Young's modulus is calculated within the elastic region, not at the tensile strength point. Therefore, you have to use the stress and strain values from the elastic region, not at break or tensile strength, unless the stress-strain relationship is linear up to the breaking point.
The calculation of yield strength involves taking into account the elastic modulus value. The elastic modulus value in this example was recorded in GPa (Giga Pascals) so the values of YS in Pa units were multiplied with 10^9.
Hello Sir, I have one small query that during the adding of second curve why you plot the yield stress corresponding to previous strain instead of (0.002+strain) values?
The ASTM standard for compression testing of metals is ASTM E9 which was used to obtain stress-strain diagram in this example. Whereas, the ASTM standard for compression testing of viscoelastic materials is ASTM D575-91(2016). Simple answer is 'NO' because the stress-strain curve of a viscoelastic material doesn't exhibit distinct linear portions or yield points like those seen in elastic materials (e.g., metals). Instead, it displays a more complex behavior such as initial elastic response, creep behavior, stress relaxation, and strain hardening or softening, due to the combination of elastic and viscous responses over time.
Please, can you share any reference or book or research paper which gives totally idea about UTM and its different curves and which things we have to keep in mind during analysis. Thankyou
