n 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">mean_stress</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">        returns the mean stress</span>
<span class="sd">        &quot;&quot;&quot;</span>
        <span class="k">return</span> <span class="mf">1.</span><span class="o">/</span><span class=