Material Properties and Strengths (Filaments)

[geert_2 557]

What about taking "flow rate" during printing into account too? Underextrusion still is a common issue, but it greatly affects strength as it hurts layer bonding and line-width. A good material printed with incorrect flow rate might perform worse than a lesser material with good flow. For example you could take your test bar, and print that as 100% filled at flow rates of 50%, 70%, 80%, 90%, 95%, 100%, 105%, 110%, 120%? This can be done by making one gcode file, and then manually adding the flow rate commands into it. I think this gcode is "M221 Sxxx", where "M221" is the command for flow rate, and "Sxxx" is the desired flow rate in percent, for example: M221 S105 for a 105% flow. I think the Ultimaker testers have done research on this, but I have no idea how systematically it was done?

 

Further, if you want to use parts outside, bio-degradability is an important aspect too. PLA should be bio-degradable, although a PLA sift sitting in my laboratory sink did not seem to degrade in a year time, in wet dirty conditions.

 

Other aspects are UV-resistance and temperature-resistance: PLA will warp in the sun, guaranteed, so you can't use it in a car. Don't ask how I know. :) And most plastics get brittle and crumble after long UV-exposure. You could try this with a strong UV-lamp such as those used for desinfecting aquariums and medical equipment., or for erasing EPROMS.

 

In my experience PLA gets harder and stiffer over time. So snap-fit lockings that worked well originally, will break after a year when activating them, because you keep pushing until the snap-fit mechanism locks in place, or breaks. However, small parts such as key chains and ID-card holders out of PLA survive longer in my pockets than identical parts in PET and NGEN, which break sooner. Just because the PLA is harder. I haven't tried nylon yet.

 

And then there is indeed the mechanical creep over time that gr5 mentioned above. PLA has this, but some light-cured plastics used in some 3D-printing systems have this even far worse, for example the models I had made on a Stratasys Objet v260 jet printer. Most plastics have it to some degree.

 

And then there is paintability, glue-ability (I don't know if that is a good word?), and machinability: these could be required too.

 

All these other aspects might be of great importance too when chosing a material to print, it's not just theoretical strength alone.

 

[FalmouthLouis 3]

GR5 - many thanks for all that. Have now got to get down to a talk aimed at artists in St Ives. They are interested in a much different set of issues, such as filaments with tactile qualities. Am just going to experiment with prints in Bronze and SteelFill. Should be fun. I'll get back to tensile issues early next week.

[FalmouthLouis 3]

Geert_2: thanks. When thinking about the marine environment, I have been aware of the importance of things like UV sensitivity. The trouble is that my colleague can only get limited access to the testing facilities, so we've had to zero in on a single issue - tensile strength. If we get decent results from this round of tests, we could see if there was funding for a next generation set of tests. Incidentally, I like your point about under and over extrusion.

[Hadlool 0]

regarding PLA ..could any one explain the importance of flexural mechanical properties and what is the effect of aging on it

[kmanstudios 1,120]

7 minutes ago, Hadlool said:

regarding PLA ..could any one explain the importance of flexural mechanical properties and what is the effect of aging on it

It gets more brittle with age.