Hi everybody,
i know Tangent modulus is defined as the slope of a line tangent to the stress-strain curve at a point of interest. it is mostly used to describe the stiffness of a material in the plastic range, and it is denoted by Et.
if i know for copper it is about 800 MPa . i read in an article that Tangent Modulus of Brass equal to 0.59 . So , Whats the meaning of it ??!!
Many Thanks
I would like to add the following: While Young's modulus is applicable to elastic deformation, tangent modulus is applicable to plastic deformation. In both cases the modulus is the ratio of the stress to strain, but the tangent modulus varies with the (true) strain and therefore should be specified at a particular true strain. As seen in Wiki, Ramberg-Osgood relation brings the two moduli together by considering that the in a plastically deformed material, the total strain is the sum of the elastic plastic strain. Using symbols, Epsilon = (sigma/E) + K times(sigma/E)^n. Here epsilon represents total strain, sigma is the true stress, E is the Young's modulus, K and n are material constants.
I would like to add the following. Tangent modulus is the slope of true stress-true strain curve in the plastic region (beyond the elastic region). The equation for the plastic part of this stress-strain curve is sigma = K times (epsilon)^n where sigma is the true stress, epsilon is the true strain, K and n are material constants. Since the plastic part in brass is a parabolic curve (and not a straight line as in elastic part) the slope is not constant and is applicable only to the chosen strain. In your case my feeling is that the tangent modulus is specified at a true strain of 0.59. If you can get hold of the applicable stress -strain curve, You can evaluate the slope of this curve to determine the tangent modulus. It is not uncommon for cold rolled brass to have a true strain of 0.59.
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