Measuring modeling validating testing where we stand

When I first started in a development department, measuring parts was done with simple tools like calipers, micrometers, dynamometers… new equipment started to appear resorting to 3D measurements automatic measurements with a computer with a ball pointer. Drawings were not measurement friendly making it difficult to measure according to new technologies. Today’s approach take seriously GDT and combining it with CT scans (3D scanner) a new approach is starting to grow resorting to model based definitions. Since all the information necessary for measurement is in a model when a CT scan is performed one can imideatly discover part variation and perform analysis on the intended planes with no miss communication.

A glimpse into the future of metrology

The mystery of the train seat uncovered

Will the train seat withstand 120Kg? was I seeing things? Maybe the weight was more since the person had a backpack. But the load was extreme.

Seat deformation
Seat deformation

I calculated 5 mm deformation on the cushion. Could I have seen it? Well maybe. Stresses were far away from the plasticity limit, however the structure feels loaded.

From my analysis the structure could take even more load and wobble even more. Maybe the squeaking sound over exaggerated my notion of wobbling.

Undeformed to undeformed seat
Undeformed to deformed seat comparison

The light blue image is the deformed state, we can see the deformation direction, which moves in a expected direction.

Close up of seat
Close up of seat

In this close up we can see a slight displacement. But very small.

So my conclusions:

The heavy train traveller was safe, the seat could stand a few extra Kg’s of weight with some more camping equipment.

The design seems fairly robust, however it actually wobbles.

Train seat analysing

Finally I got time to mesh and solve my imaginary problem. I will not dive into meshing since it is a chapter on its own. I used a tetrahedron mesh as standard as it gets. The work flow is simple; get a CAD model, get material data, mesh it, add supports and loads and finally get some results, either by stresses or displacements.

Train seat mesh & Result
Train seat mesh & Result

My results for a small load of 1.2Kg shows that the T tube element will suffer most when we sit on it. I would say that if it breaks it will be there. Ok this case is more then evident since the only thing holding my weight is this connection.

But will it wobble with 120Kg weight?