General Purpose Interface (/INTER/TYPE7)

Interface TYPE7 is a general purpose interface and can simulate all types of impact between a set of nodes and a main surface. Contrary to interface TYPE3 and TYPE5, interface TYPE7 is non-oriented and secondary nodes can belong to the main surface. Therefore, this interface can simulate self-impact, especially buckling during a high speed crash.

Interface TYPE7 solves all problems and limitations encountered with interface TYPE3 and TYPE5. The search for the closest segment is done via a direct search algorithm; therefore, there are no search limitations and all possible contacts are found. The energy jumps induced by a node impacting from the shell edges are removed by the use of a cylindrical gap around the edges.

Finally, the main advantage of interface TYPE7 is that the stiffness is not constant and increases with penetration preventing the node from going through the shell mid-surface. This solves many bad contact treatments (common when using either interface TYPE3 or TYPE5).

The gap used in interface TYPE7 is rather different than those of the previous interfaces. The gap used is on both sides of the shell mid-surface, and a cylindrical gap is added around the edges (Figure 2). The gap used is on both sides of the shell mid-surface, and a cylindrical gap is added around the edges.

The cylindrical gap allows getting rid of energy jumps, node impacting from the edges follow the same path during the penetration and the depenetration. Moreover, such a gap keeps the reaction force smooth during sliding between segments.

Contrary to interface TYPE3 and TYPE5, a variable gap in space is available. Depending on option I_gap, variable gap is computed for each impact as the sum of the main element gap (g_m) and the secondary node gap (g_s).

If I_gap=1, variable gap is computed as:(1)

\max [G a p_{\min}, (g_{s} + g_{m})]

If I_gap=2, variable gap is computed as:(2)

\max {G a p_{\min}, \min [F s c a l e_{g a p} \cdot (g_{s} + g_{m}), G a p_{\max}]}

If I_gap=3, variable gap is computed as:(3)

\max {G a p_{\min}, \min [F s c a l e_{g a p} \cdot (g_{s} + g_{m}), % m e s h_s i z e \cdot (g_{s_l} + g_{m_l}), G a p_{\max}]}

Table 1. Variable Gap Computation
Element	Main Element Gap (g_m)	Secondary Node Gap (g_s)
SHELL	$g_{m} = \frac{t}{2}$ t: thickness of the main segment	$g_{s} = \frac{t}{2}$ t: largest thickness of shell elements connected to the secondary node
BRICK	$g_{m} = 0$	$g_{s} = 0$
TRUSS and BEAM	Non-applicable	$g_{s} = \frac{1}{2} \sqrt{S}$ S: cross section

If a minimum gap for impact activation (Gap_min) is also used, the computed variable gap cannot be smaller than the minimum value. It is also possible to apply a scale factor to the gap and define a maximum gap value.