If the design requirements include brief dynamic events, such as drop tests, crash tests, ballistic impact, or blast wave propagation, explicit analysis is often the most practical method. This method focusses on a specific subset of dynamic analysis, and is becoming much more sought after in recent years. Femtec’s explicit calculations can provide a higher accuracy than more traditional quasi-static approaches. This increased accuracy can drive your design to becoming a better product.

Advantages of explicit analysis

  • The analysis cost of an explicit analysis (in terms of required computation power) increases only linearly with the model size. This is less than the norm, which makes explicit analysis an attractive option for large and intricate designs.
  • The explicit method is often more efficient at analysing extremely short-term discontinuous events.
  • Stress wave propagation (like blast waves) can be done more efficiently using the explicit method.

The choice to use the explicit method is not a trivial one

When choosing a method for a dynamic problem, considerations must be made with respect to the length of time in which the response can occur, compared to the stability limit of the explicit method. Also consider the size of the problem and the restrictions of explicit analysis with respect to useable element types. In some cases there is an obvious choice, but in many practical problems this choice depends on specific case-dependent details. Femtec’s experience can provides a useful guide in those cases.

Drop test simulation

As stated above, short severe loads are the forte of the explicit method. A drop test is a prime example. Femtec has experience in these simulations for the high-tech packaging industry, where damage to the payload must be avoided at all cost. Using highly elastic designs, the force on the payload can be calculated using conventional methods. But where room is at a premium, more compact methods of absorbing impact are needed. This can be achieved by targeted plastic deformation, which absorbs a lot of energy in compact structures. In analysing this behaviour, explicit calculations can play an important role.

Explicit software

The explicit method is one of the ways a dynamic analysis can be performed. Even though it used to be a rather specialist method, nowadays almost all of the bigger players in the finite element software business have incorporated it in their suites. FEMAP and NX simulation include it through their deep integration with NX/NASTRAN, which in turn incorporated Adina. Ansys, both classic APDL and Workbench, has incorporated the previously stand-alone LS DYNA, and ABAQUS uses one of the best renowned explicit solvers. For each of these software suites, Femtec can provide engineers experienced with that particular software.

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