R Value Sheet Metal Forming

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 r value is the ratio of the true strain in the width direction to the true strain in the thickness direction when a sheet material is pulled in uniaxial tension beyond its elastic limit see figure 1. The r value of drawing quality steel is typically 1 and that of aluminum sheet 1 so the wrinkling problem is more severe in aluminum.

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For instance if you have a material with an r value of 12 attached to another material with an r value of 3 then both materials combined have an r value of 15.

R value sheet metal forming.

If a material has a higher r value it is easy to avoid plane strain deformation and the material formability is higher such as mild steel. In practice the value is usually measured at 20 elongation in a tensile test. The effect of the n value in deep drawing is ambiguous. Thus as the n value increases the material s resistance to necking increases and the material can be stretched farther before necking starts.

The r and n values are determined in the tensile test in order to characterize the forming properties. Less radial stretching is required with a high r value decreasing the chance of tearing failure. The r value is an index that the material can resist thinning deformation in thickness direction. The n value describes the hardening increase in strain during plastic deformation up to uniform elongation while the r value describes the vertical anisotropism.

Simply put it measures the resistance of a material to thinning or thickening when put tension or compression. In simple terms r values measure the effectiveness of insulation and a higher number represents more effective insulation. The constant n plays a crucial role in sheet metal forming. The plastic strain ratio r is considered a direct measure of sheet metal s drawability and is useful for evaluating materials intended for forming shapes by deep drawing see lead photo.

For sheet metals the r displaystyle r values are usually determined for three different directions of loading in plane 0 45 90 displaystyle 0 circ 45 circ 90 circ to the rolling direction and the normal r value is taken to be the average. R value is a very important material property to understand for materials that will be formed into various shapes in their end use. The larger the n value the more the material can elongate before necking. In construction the r value is the measurement of a material s capacity to resist heat flowfrom one side to the other.

R value also known as plastic strain ratio is a measurement of the drawability of a sheet metal. It is the ability to maintain thickness as the material is drawn.