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Subsection 6.1.2: Relative Boundary Conditions Up Chapter 6: Multi-Step Analysis Chapter 7: Parameter Optimization

## 6.2 An Example

The following example illustrates the use of the multi-step feature of FEBio. This problem defines two steps. In the first step, a single element is stretched using a prescribed boundary condition. In the second step, the boundary condition is removed and the analysis type is switched from quasi-static to a dynamic analysis. Note the presence of the global fixed boundary constraints, which will remain enforced during both steps:
---
<febio_spec version="3.0">
<Module type="solid"/>
<Material>
<material id="1" name="Material 1" type="neo-Hookean">
<density>1.0</density>
<E>1</E>
<v>0.45</v>
</material>
</Material>
<Mesh>
<Nodes>
<node id="1">-2.0,-0.5, 0.0</node>
<node id="2">-2.0,-0.5, 1.0</node>
<node id="3">-2.0, 0.5, 0.0</node>
<node id="4">-2.0, 0.5, 1.0</node>
<node id="5"> 2.0,-0.5, 0.0</node>
<node id="6"> 2.0,-0.5, 1.0</node>
<node id="7"> 2.0, 0.5, 0.0</node>
<node id="8"> 2.0, 0.5, 1.0</node>
</Nodes>
<Elements type="hex8" name="Part1">
<elem id="1">1,5,7,3,2,6,8,4</elem>
</Elements>
<NodeSet name="set1">
<node id="1"/>
<node id="2"/>
<node id="3"/>
<node id="4"/>
</NodeSet>
<NodeSet name="set2">
<node id="1"/>
<node id="2"/>
<node id="5"/>
<node id="6"/>
</NodeSet>
<NodeSet name="set3">
<node id="1"/>
<node id="3"/>
<node id="5"/>
<node id="7"/>
</NodeSet>
<NodeSet name="set4">
<node id="5"/>
<node id="6"/>
<node id="7"/>
<node id="8"/>
</NodeSet>
</Mesh>
<MeshDomains>
<SolidDomain name="Part1" mat="Material 1"/>
</MeshDomains>
<Boundary>
<bc type="fix" node_set="set1">
<dofs>x,y,z</dofs>
</bc>
</Boundary>
<points>
<point>0,0</point>
<point>1,0.1</point>
</points>
<Step>
<step id="1">
<Control>
<time_steps>10</time_steps>
<step_size>0.1</step_size>
</Control>
<Boundary>
<bc type="prescribe" node_set="set4">
<dof>x</dof>
<scale lc="1">1.0</scale>
</bc>
</Boundary>
</step>
<step id="2">
<Control>
<time_steps>50</time_steps>
<step_size>0.5</step_size>
<analysis>DYNAMIC</analysis>
</Control>
</step>
</Step>
</febio_spec>

Subsection 6.1.2: Relative Boundary Conditions Up Chapter 6: Multi-Step Analysis Chapter 7: Parameter Optimization