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      <title>R&ndash;value and area preserve</title>
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      <div class="title_topic4" id="xps10_pagetitle">R&ndash;value and area preserve</div>
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               <p class="para_td"> <a class="links" href="javascript:void(0)" onclick="top.openFile('sheetmetaldes/smfea_inset_flng.html');return(false);">General Flange Overview</a></p>
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               <p class="para_td"> Options</p>
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               <p class="para_td"> <a class="links" href="javascript:void(0)" onclick="top.openFile('sheetmetaldes/build_multi_parts.html');return(false);">Related Topics</a></p>
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      </table><br><p class="para_topic">You can specify an r&ndash;value (average strain ratio or normal anisotropy) or turn <b class="uiTerm">Area Preserve</b> on, which is equivalent to specifying an infinite r&ndash;value. The r&ndash;value is a property of the material being formed and will affect how the general flange is mapped to other states. Higher r&ndash;values represent higher resistance to thinning when the material is stretched or resistant to thickening when the material compresses. The default value of 1.0 corresponds to a homogeneous material.
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      <p class="para_topic">If you have <b class="uiTerm">Preferences&rarr;Sheet Metal&rarr;Use Feature Standards</b> turned on, the <img align="bottom" src="graphics/image336.gif" border="0"> button on each box will give you a list of standard acceptable values.
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      <div class="title_division">Distortion</div>
      <p class="para_division">When the general flange is unformed or formed to a different state and distortion is involved, this distortion always follows uniaxial stretch or compression. The general flange will always conform to the bend string along one edge. Other than this, you may specify constraints to the distortion in the <b class="uiTerm">Sequence Editor</b> (in the Sheet Metal Features and Forming/Flattening module). You may specify one of the following distortion algorithms:
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            <p class="para_item"><b class="uiTerm">Along Sections</b> &ndash; In the <b class="uiTerm">Along Section</b> algorithm, the flow of material is constrained to be along sections normal to the spine. Uniaxial distortion is followed in determining the length of material along each section.
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            <p class="para_item"><b class="uiTerm">Bi&ndash;directional</b> &ndash; With the <b class="uiTerm">Bi&ndash;directional</b> algorithm, material flow across sections may occur. The system considers the material to be unconstrained except at the bend edge and at any constraints that may be imposed in the <b class="uiTerm">Sequence Editor</b>.
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      <p class="para_division">The following figure shows how the two distortion algorithms affect an unformed general flange.</p>
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      <div class="title_figure">Distortion algorithms</div>
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