structural.de works since January 2018 at FEA based and methodically sound design methods for such parts. In litarature and research, not many results are published yet. Serios filament manufacturers like Ultimaker, Polymaker or Formfutura do issue data sheets with tensile strength values, but all those values are tested in XY plane, means in printing layer directions. Data tested perpenducular to the layer planes, i.e in Z-direction, are not available. Only few companies, e.g. Stratasys and Polymaker, have published its strength values for Z-direction as well.

It is widely known, that the tensile strenght in Z-direction perpendicular to the printing layer plane is often much less than the one in XY-direction. 3d-printed parts in FFF / FDM plastic technology show a very clear orthotropic behaviour. The problem is, that many functional parts have stresses in many directions, and it is only in few situations possible to turn the part so that major stresses run in the plane of the 3d printing process. So, we must live with the fact that major stresses will most likely occur also in Z direction, even if we try to optimize and even if we do the design stress check in FEA with different stress limits according to the direction.So, the limit stress in Z-direction will finally determine the usability of a material for load-bearing functional parts. 

Our present design method results for the plastics in a quite low usable stress level, due to the required safety factors for plastic and the limits of the material. The distance of the usable stresses to the breaking stresses is quite high. Therefore, we expect only a very low influence of creeping and aging for our purposes, as long as the ambient temperature is significantly lower than the vicat temperature of the plastic. To back this theses, we started middle term loading tests with typical stress levels of 5 MPa for periods of one to three month, the typical load duration times for fairground and event structures.


Metall

A very interesting alternative to plastic is the idea of 3d printed parts used as models for metal casting. Even with common cast aluminum alloys, the usable tensile stresses raise up to 10 times the value of the plastic part. And - for aluminum, the Eurocode 9 (DIN EN 1999) gives the engineer an officialy acknowledged code of practice for all the design work, also for large load bearing structures. All the known problems with plastics like aging, temperature and UV light exposition and  creeping are simultaneously vanished. For this reason, structural.de tests a handy technology chain in cooperation with a local foundry.  The disadvantage: The shape restrictions of both 3d printing and  sand casting add up quite a lot.

So, direct 3d printing in metall would be a dream. And now, it comes true also for small budgets! Since summer 2019, BASF Ultrafuse 316L metall filament is available! This filament contains about 20% POM plastic an 80% stainless steel powder (1.4404 - AISI 316L). You can print this in almost every common 3d printer, which is able to reach 100°C bed temperature and has a hardened steel nozzle. We had good success with our CreatBot F160, a 0,4 Microswiss hardened steel nozzle, 235° nozzle temp, 100°C bed temp, BuildTak printbed and Adimide adhesive. The green part  is then sent to  debinding and sintering at a service partners factory. The result: sintered stainless steel metal parts!  BASF writes a yield strenght for the sintered parts of 230 N/mm² in its data sheets.

Hardware

A second test device allowing tension forces up to 20 kN will help to verify the theory at test part which are similiar in shape and size to the real structural part and for metal parts