N Value Sheet Metal Forming

Astm e517 standard test method for plastic strain ratio r for sheet metal determines the plastic strain ratio.

N value sheet metal forming.

Sheet metal forming involves forming and cutting operations performed on metal sheets strips and coils. It is the ability to maintain thickness as the material is drawn. The surface area to volume ratio of the starting metal is relatively high. If thickness is in mm.

The diagram attempts to provide a graphical description of material failure tests such as a punched dome test. The strain hardening exponent plays an important role in sheet metal forming. The larger the n value the more the material can elongate before necking. In order to determine whether a given region has failed a mechanical test is performed.

The r value the plastic strain ratio of sheet metal intended for deep drawing applications is a measure of the resistance to thinning or thickening when subjected to either tensile or compressive forces in the plane of the sheet i e. The effect of the n value in deep drawing is ambiguous. The n value describes the hardening increase in strain during plastic deformation up to uniform elongation while the r value describes the vertical anisotropism. The constant n plays a crucial role in sheet metal forming.

All you need are the sheet metal thickness and strain hardening exponent also known as the n value. Tools include punch die that are used to deform the sheets. A forming limit diagram also known as a forming limit curve is used in sheet metal forming for predicting forming behavior of sheet metal. Thus as the n value increases the material s resistance to necking increases and the material can be stretched farther before necking starts.

Of all the mechanical properties determined by a tensile test the plastic strain ratio is the most difficult and requires close attention to detail. The r and n values are determined in the tensile test in order to characterize the forming properties. The shape and placement of the forming limit curve for low carbon steels have been known for decades thanks to the pioneering work of dr. The forming limit increases due to increase the n value.

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