Design of Foss Cuvette-system

3D Mechanical contact and elastic-plastic analysis

Challenge and Ambition

FOSS uses a diamond-based sealing between a cuvette and a retainer ring in a liquid analysis instrument. The system should be designed so that:

  1. The sealing remains closed during thermal cycling, where differences in thermal expansion of the components can result in leakage.
  2. The stress state in the diamond sealing does not induce fracture.

To achieve this the cuvette-holder geometry and material can be changed.

Solution 

To accurately capture the behavior at the diamond to cuvette-holder interface, a FEA analysis in COMSOL Multiphysics is carried out, observing the following:

  1. The diamond to cuvette-holder interface can change status (go in- and out of contact) during a thermal cycle – thus the analysis must include a contact formulation.
  2. The cuvette-holder will yield locally in the contact region, and this will in turn affect contact pressure, thus the analysis must account for plastic yielding.
  3. The cuvette-holder can undergo deformation leading to ovalization, thus a 3d analysis accounting for the full structure is needed.
  4. The analysis is carried out for several candidates for cuvette-holder material, and the geometry is parameterized, and a combination that fulfills the requirements is chosen.

The simulation work saved a large number of expensive prototypes otherwise needed to find the optimal design. It also promoted an in-depth understanding of the system used for later design modifications.

Customer: FOSS Analytics

Industry: Food tech

Discipline: Structural Mechanical