Here's a String Quartet.

String Quartet in D Minor-1 Free Sheet Music by Robert C. Fox for Various Instruments | Noteflight

String Quartet In D Minor-2 Free Sheet Music by Robert C Fox for Various Instruments | Noteflight

String Quartet In D Minor-3 Free Sheet Music by Robert C Fox for Various Instruments | Noteflight

String Quartet In D Minor-4 Free Sheet Music by Robert C. Fox for Various Instruments | Noteflight

Wrote five, but this one is closest to a true string quartet.  2009.

Hi Churchcantor, or Robert, however you prefer 😁. It seems that this post went through in silence. Let's fix that.

I listened to the first movement. While I enjoy the repetition of some ryhtmic patterns, I think it's too contrasting in terms of material (or it appears so at first) and not very well-founded structurally. At the same time it sounds plain: not a single dynamic marking (maybe I missed some?), almost constant tutti except from some sections where all in a sudden virtuoso-fast passages appear and also a pizz. ending that does not convince me at all. But I just could be wrong, I listened to it twice and more often than not pieces require a bit more to be appreciated, specially if they're ones like you submitted. Some other times I just don't like them, though. It's perhaps harmonically daring or inconsistent in that regard too: a more in-depth analysis would reveal one or the other, or both, since practically everything is valid this days and I'm sure you could justify many of the things I may have heard as "wrong" or "weird" or "misplaced", etc. At the end of the day, almost all that matters is that you yourself feel that the work is decent enough. Several years have passed since 2009 so if you are not fully convinced now, maybe these points I brought here are worth noting (and maybe at this point, you know the majority):

• Even if you didn't change a note, a better balance of the dynamics of each instrument would greatly help.
• The sudden contrasting sections do not reinforce the stability/coherence of the movement, in my humble opinion they rather weaken it. M17 & M18 appearing in the middle of the syncopated section, so dense and all on a sudden, is one example of such a contrasting section. In my opinion, even if you want an abrupt transition, I think it could be stated better (again via dynamics, but also via articulation or even slight rhythm changes, there are many ways to accomplish this better) both in the "before" measures and in the "after" measures. 
• I can see the movement can be technically demanding at times too. Quadruple stops... Assuming these ones in the score are doable specifically, are you completely sure you need them to be quadruple? After all, it's not a solo, maybe you can distribute the voices in order to avoid these maybe problematic stops. 

I won't comment much on the score per se, since I am well aware of the poor layout results noteflight default usually delivers. Not to mention the default midi sounds it uses. Wish you could upload a better audio here, it would be neat... I'm myself not a fan of it, but perhaps porting your sheet music to Musescore 4 is not a bad idea.

It's 7 AM here and I really need to sleep, but I am eager to listen to the rest of your work...! Thank you for submitting it here and once again, I am sorry the post got a bit lost. Usually posts with material to be analysed are replied sooner or later...

Kind regards,
Daniel.