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      <title>CQUAD8</title>
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      <div class="title_refTopic" id="xps10_pagetitle">CQUAD8 </div>
      <hr noshade="true">
      <h4 class="refClassification">Curved Quadrilateral Shell Element Connection </h4>
      <p class="para_refTopic">Defines a curved quadrilateral shell or plane strain element with eight grid points. </p>
      <div class="title_refCategory">Format: </div>
      <div class="refCategoryContent">
         <table border="1" width="100%" align="center">
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               <col span="1" width="10.76*">
               <col span="1" width="10*">
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               <col span="1" width="9.22*">
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            <thead>
               <tr>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">1 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">2 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">3 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">4 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">5 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">6 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">7 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">8 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">9 </p>
                  </th>
                  <th align="center" colspan="1" rowspan="1">
                     <p class="para_th">10 </p>
                  </th>
               </tr>
            </thead>
            <tbody>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">CQUAD8 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">EID </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">PID </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G1 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G2 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G3 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G4 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G5 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G6 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G7 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">G8 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">T1 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">T2 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">T3 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">T4 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">THETA or MCID </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">ZOFFS </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">TFLAG </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" bgcolor="gray" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
               </tr>
            </tbody>
         </table><br></div>
      <div class="title_refCategory">Example: </div>
      <div class="refCategoryContent">
         <table border="1" width="100%" align="center">
            <colgroup span="1">
               <col span="1" width="11.12*">
               <col span="1" width="9.98*">
               <col span="1" width="9.98*">
               <col span="1" width="9.98*">
               <col span="1" width="9.98*">
               <col span="1" width="9.98*">
               <col span="1" width="9.98*">
               <col span="1" width="9.98*">
               <col span="1" width="9.98*">
               <col span="1" width="9*">
            </colgroup>
            <tbody>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">CQUAD8 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">207 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">3 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">31 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">33 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">73 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">71 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">32 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">51 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">&nbsp; </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">53 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">72 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">0.125 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">0.025 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">0.030 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">.025 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">30. </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">.03 </p>
                  </td>
                  <td align="center" colspan="1" rowspan="1">
                     <p class="para_td">&nbsp; </p>
                  </td>
               </tr>
            </tbody>
         </table><br></div>
      <div class="title_refCategory">Fields:</div>
      <div class="refCategoryContent">
         <table cellpadding="10" width="100%" align="center">
            <colgroup span="1">
               <col span="1" width="16*">
               <col span="1" width="84*">
            </colgroup>
            <thead>
               <tr>
                  <th align="left" colspan="1" rowspan="1">
                     <p class="para_th"><b class="uiTerm">Field </b></p>
                  </th>
                  <th align="left" colspan="1" rowspan="1">
                     <p class="para_th"><b class="uiTerm">Contents </b></p>
                  </th>
               </tr>
            </thead>
            <tbody>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">EID </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Element identification number.  (Integer &gt; 0) </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">PID </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Property identification number of a PSHELL, PCOMP, or PLPLANE entry.  (Integer &gt; 0) </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">G1, G2, G3, G4 </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Identification numbers of connected corner grid points.  Required data for all four grid points.  (Unique Integers &gt; 0) </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">G5, G6, G7, G8 </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Identification numbers of connected edge grid points.  Optional data for any or all four grid points.  (Integer &ge; 0 or blank) </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Ti </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Membrane thickness of element at grid points G1 through G4 if TFLAG=0 or blank. If TFLAG=1, membrane thickness becomes a product of Ti and the thickness on the PSHELL card. Ti is ignored for hyperelastic elements.  (Real &ge; 0.0 or blank, not all zero.  See Remark <a class="links" href="javascript:void(0)" onclick="top.openFile('QRG/14topic_17.html#ref82374a');return(false);">27-4</a> for the default.) 
                     </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">THETA </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Material property orientation angle in degrees. See <a class="links" href="javascript:void(0)" onclick="top.openFile('QRG/14topic_17.html#ref70201');return(false);">Figure 13-</a>.  THETA is ignored for hyperelastic elements.  (Real; Default = 0.0) 
                     </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">MCID </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Material coordinate system identification number.  The x-axis of the material coordinate system is determined by projecting the x-axis of the MCID coordinate system (defined by the CORDij entry or zero for the basic coordinate system) onto the surface of the element (see Remark <a class="links" href="javascript:void(0)" onclick="top.openFile('QRG/14topic_17.html#mcid_ref');return(false);">3</a>). MCID is ignored for hyperelastic elements.  (Integer &ge; 0;  If blank, then THETA = 0.0 is assumed.) 
                     </p>
                  </td>
               </tr>
            </tbody>
         </table><br><table width="100%" align="center">
            <colgroup span="1">
               <col span="1" width="16.85*">
               <col span="1" width="83.15*">
            </colgroup>
            <tbody>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">ZOFFS </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Offset from the surface of grid points to the element reference plane.  See Remark <a class="links" href="javascript:void(0)" onclick="top.openFile('QRG/14topic_17.html#ref27418a');return(false);">27-6</a> ZOFFS is ignored for hyperelastic elements.  (Real) 
                     </p>
                  </td>
               </tr>
               <tr>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">TFLAG </p>
                  </td>
                  <td align="left" colspan="1" rowspan="1" valign="top">
                     <p class="para_td">Integer Flag which specifies how Ti is used to define membrane thickness of element. (0, 1, or blank) </p>
                  </td>
               </tr>
            </tbody>
         </table><br></div>
      <div class="title_refCategory">Remarks: </div>
      <div class="refCategoryContent">
         <ol type="1" start="1">
            <li>
               <p class="para_item">Element identification numbers should be unique with respect to all other element IDs of any kind. </p>
            </li>
            <li>
               <p class="para_item">Grid points G1 to G8 must be numbered as shown in <a class="links" href="javascript:void(0)" onclick="top.openFile('QRG/14topic_17.html#ref70201');return(false);">Figure 13-</a>. 
               </p>
            </li>
            <li><a name="mcid_ref"></a><p class="para_item">The orientation of the material property coordinate system is defined locally at each interior integration point by THETA, which is the angle between x<sub class="subscript">material</sub> and the line of constant xi. THETA is calculated by projecting the x-axis of the MCID coordinate system onto the surface of the element. Since the shape of a CQUAD8 can vary from one integration point to the next, the direction of xi can also vary, causing the resulting material coordinate definition to vary. When using orthotropic or anisotropic materials which depend on consistent material coordinate directions, it is recommended to use the QUAD4 element.
               </p>
            </li>
            <li><a name="ref82374a"></a><p class="para_item">T1, T2, T3 and T4 are optional. If they are not supplied, they will be set equal to the value of T on the PSHELL entry.</p>
            </li>
            <li>
               <p class="para_item">It is recommended that the midside grid points be located within the middle third of the edge.  If the edge point is located at the quarter point, the program may fail with a divide-by-zero error, or the calculated stresses will be meaningless.</p>
            </li>
            <li><a name="ref27418a"></a><p class="para_item">Elements may be offset from the connection points by means of the ZOFFS field.  Other data, such as material matrices and stress fiber locations, are given relative to the reference plane. A positive value of ZOFFS implies that the element reference plane is offset a distance of ZOFFS along the positive z-axis of the element coordinate system. If the ZOFFS field is used, then both the MID1 and MID2 fields must be specified on the PSHELL entry referenced by PID.</p>
               <p class="para_item">The specification of offset vectors gives erroneous results in solution sequences with linear buckling analysis, SOLs 5, 16, 105 and 200.</p>
            </li>
            <li>
               <p class="para_item">If all midside grid points are deleted, then the element will be excessively stiff and the transverse shear forces incorrect.  A User Warning Message is printed, and a CQUAD4 element is recommended instead. If the element is hyperelastic, then it is processed identically to the hyperelastic CQUAD4 element.</p>
            </li>
            <li>
               <p class="para_item">For a description of the element coordinate system, see <a class="links" href="javascript:void(0)" onclick="top.popUpPage('QRG/linkInter_target_not_resolved.html#element:ref55634:-aux,-home','linkInter','menubar=yes,status=yes,resizable=yes,toolbar=yes,scrollbars=yes,location=no,directories=no');return(false);">&ldquo;Plate and Shell Elements&rdquo; </a>in the <em>NX Nastran Element Library</em>.  Stresses and strains are output in the local coordinate system identified by <em>x<sub class="subscript">l</sub></em> and <em>y<sub class="subscript">l</sub></em> in <a class="links" href="javascript:void(0)" onclick="top.openFile('QRG/14topic_17.html#ref70201');return(false);">Figure 13-</a>.  However, for hyperelastic elements, the stress and strain are output in the coordinate system identified by the CID field on the PLPLANE entry. 
               </p>
            </li>
            <li>
               <p class="para_item">For hyperelastic elements the plot codes are specified under the CQUADFD element name in <a class="links" href="javascript:void(0)" onclick="top.openFile('QRG/09ref75809_1.html');return(false);">&ldquo;Item Codes&rdquo;</a>. 
               </p>
            </li>
         </ol>
      </div>
      <div class="title_refCategory">Remarks related to SOL 601: </div>
      <div class="refCategoryContent">
         <ol type="1" start="1">
            <li>
               <p class="para_item">Only elements with 4 or 8 grid points are allowed, i.e., either G5 to G8 are all specified or none are specified. </p>
            </li>
            <li>
               <p class="para_item">ZOFFS is ignored. </p>
            </li>
            <li>
               <p class="para_item">8-node elements may be converted to 9-node elements (with 1 additional node at the centroid of the element) by specifying ELCV=1 in the NXSTRAT entry. As a plane strain element, the 9-node element is more effective in the analysis of incompressible media and inelastic materials, e.g., rubber-like materials, elasto-plastic materials, and materials with Poisson&rsquo;s ratio close to 0.5. As a shell element, the 9-node element is also more effective than the 8-node shell, e.g., support of large strain. </p><a name="ref70201"></a><div class="figure">
                  <p align="center"><img align="bottom" src="graphics/bulkc2-fig14.gif"></p>
               </div>
               <div class="title_figure">Figure. CQUAD8 Element Geometry and Coordinate Systems </div>
               <p class="para_item">where </p>
               <table cellpadding="15" width="100%" align="center">
                  <colgroup span="1">
                     <col span="1" width="82.84*">
                  </colgroup>
                  <tbody>
                     <tr>
                        <td align="left" colspan="1" rowspan="1" valign="top">
                           <p class="para_td"><img align="bottom" src="graphics/bulkc2-ufig01.gif" border="0"> is tangent to &eta; at Gi 
                           </p>
                        </td>
                     </tr>
                     <tr>
                        <td align="left" colspan="1" rowspan="1" valign="top">
                           <p class="para_td"><img align="bottom" src="graphics/bulkc2-ufig02.gif" border="0"> is tangent to &xi; at Gi 
                           </p>
                        </td>
                     </tr>
                     <tr>
                        <td align="left" colspan="1" rowspan="1" valign="top">
                           <p class="para_td"><img align="bottom" src="graphics/bulkc2-ufig03.gif" border="0"> is formed by bisection of <img align="bottom" src="graphics/bulkc2-ufig01.gif" border="0"> and <img align="bottom" src="graphics/bulkc2-ufig02.gif" border="0"></p>
                        </td>
                     </tr>
                     <tr>
                        <td align="left" colspan="1" rowspan="1" valign="top">
                           <p class="para_td"><img align="bottom" src="graphics/bulkc2-ufig04.gif" border="0"> and <img align="bottom" src="graphics/bulkc2-ufig03.gif" border="0"> are perpendicular 
                           </p>
                        </td>
                     </tr>
                     <tr>
                        <td align="left" colspan="1" rowspan="1" valign="top">
                           <p class="para_td"><em>y<sub class="subscript">l</sub></em> is formed by bisection of <img align="bottom" src="graphics/bulkc2-ufig03.gif" border="0"> and <img align="bottom" src="graphics/bulkc2-ufig04.gif" border="0"></p>
                        </td>
                     </tr>
                     <tr>
                        <td align="left" colspan="1" rowspan="1" valign="top">
                           <p class="para_td"><em>x<sub class="subscript">l</sub></em> is perpendicular to <em>y<sub class="subscript">l</sub></em></p>
                        </td>
                     </tr>
                  </tbody>
               </table><br></li>
         </ol>
      </div>
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