Reliably simulating complex mechanical processes with Marc and Mentat

With its Product Innovation and Engineering business units, the Swiss company pinPlus AG focuses on the applications of structural-mechanical and thermomechanical simulations. For example, pinPlus develops and designs implants and instruments for the fields of orthopaedics, traumatology, and dentistry.

One challenge it encounters is giving medical products greater rigidity, while also reducing the weight of parts, systems, and components. The owner, graduate engineer Martin Züger and his team are evaluating how the design of these parts, systems, and components can be predicted as accurately as possible using simulations of nonlinear processes.

The specialists use modern materials, consider the latest standards in lightweight construction, and use topology and structural optimization to develop market-driven, safe products. Thanks to design-accompanying strength calculations and simulations, engineers at pinPlus identify vulnerable weak points early on and can eliminate them before prototypes are built. Development lead times and the number of prototypes required are reduced with numerical simulation, enabling faster time-tomarket at a lower cost.

The highly complex nonlinear material behaviour of elastomers

Elastomers are plastics with the special property of rubber elasticity. They play an important role in the medical and pharmaceutical industries and the work at pinPlus. For example, elastomers are used to manufacture tires, hoses, or seals. The decisive factors for the use of elastomers are their elasticity, sealing, and friction properties. Due to their elasticity, elastomers exhibit highly complex nonlinear material behaviour, which poses challenges in the development, manufacture, and analysis of these products.

In technical structures and systems, complex interactions occur between the various components. For example, elastomer components can fold in on themselves and buckle during installation. In addition, the material properties are influenced by the factors of temperature and time.

Application example in the pharmaceutical industry: behavioural analysis of the sealing of elastomer stoppers for medical syringes

A pharmaceutical company that contacted pinPlus suspected problems with the sealing behaviour of rubber stoppers on medical syringes. The company then conducted tests on its own and found that the elastomer plugs were damaged at the sealing points of the syringes. As a result, pinPlus helped determine whether these defects were affecting the sealing behaviour of the plugs by performing a finite element analysis (Figure 1).

Tightness represents an important quality criterion, especially in the medical sector. The syringes are stored filled, so the tightness must be ensured over the entire lifetime of the product, otherwize, the shelf life will be compromised. pinPlus performed a structural analysis of the stoppers using Hexagon’s simulation solution Marc. The solution is extremely useful for elastomer components: it is possible to use real material data to measure the viscoelasticity. “One of the key advantages of Marc is the ability to simulate processes such as heating or cooling to check tightness. This is essential for our customers,” emphasizes Martin Züger.

To find out whether the elastomer plugs adequately sealed the medical syringes, the geometry data of the pharmaceutical company was scanned with computer tomography. In this way, the construction geometry was recorded and fed back. A digital twin was then created from the reconstructed geometry (Figure 2), and the viscoelastic material data was then determined in an external laboratory using dynamic mechanical thermal analysis (DMTA).

With the simulation model of the damaged component, Martin Züger and his team were able to simulate timeand temperature-dependent sealing behaviour (Figure 3).

Conclusion

By creating nonlinear structural analyses with Marc and Mentat, the behaviour of materials can be predicted, and optimal development quality can be achieved in the shortest possible time. This leads to cost savings, as no costly prototypes must be built. “With Marc, the robustness of elastomers in terms of damage to the sealing surface can be investigated based on feedback geometry and measured viscoelastic material data,” concludes Martin Züger. “The digital twin corresponds to a single real part with concrete damage and not to an ideal CAD geometry as is usually the case. By simulating different representatively selected plugs, the robustness of the products could be thoroughly evaluated.”

Nonlinear Finite Element Analysis (FEA) with Marc and Mentat

Finite element analysis (FEA) is the most widely used numerical method for simulating and predicting the properties of solids and structures. For nonlinear structures such as elastomers, the FEA approach is needed to obtain reliable simulation results.

When creating nonlinear structural analyses, pinPlus uses Hexagon’s Marc, Mentat, MSC Apex, Digimat, MSC Patran, and MSC Nastran simulation solutions individually or in combination, depending on the problem. PinPlus chose the Marc solution in the late 1990s because its performance in the nonlinear domain was convincing. “Marc-Mentat has steadily gained in functionality and performance and has evolved in the right direction for us. The procurement of the remaining applications has always served to improve the services with Marc,” reports Martin Züger. The applications are also supplemented by in-house developments, depending on the problem, so that data flows through different applications to combine the functionality of the various applications.

The goal is to create a simulation that focuses on the reliability and innovativeness of the software used. Marc-Mentat is used to perform finite element analysis (FEA) of structures while respecting any nonlinearities. In combination with the Mentat pre- and post-processor, Marc can be used for advanced nonlinear structural analyses, contact calculations, complex material models, and multi-physical analyses.

Reliable simulation of the structural-mechanical properties of medical implants and instruments - in parallel with development and design - helps pinPlus to achieve optimum development quality in less time. The goal is always to create a reliable simulation of complex mechanical processes with a very good price-to-performance ratio for the customer.