><span class="n">deviator_stress</span><span class="o">.</span><span class="n">principal_invariants</span><span class="o">*</span><span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">])</span>

    <span class="nd">@property</span>
    <span class="k">def</span> <span class="nf">von_mises</span><s