Outdoor materials for printed latches
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How sun, heat, creep, UV and moisture limit what a printed latch can hold for months.
Temperature
Black enclosure in direct sun reached 67.6 C inside (grey 51.4 C), informal hobby test: https://community.element14.com/challenges-projects/design-challenges/experimenting-with-extreme-environments/b/blog/posts/exploring-hidden-extremes-of-sheltered-environment---extra-blog-4--greenhouse-in-the-box . Design for 60-70 C surface.
HEAT LIMITS (HDT at 1.8 MPa unless stated). ASA: Tg 97.8 C, HDT 100.2 C (Polymaker https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf ); Bambu ASA HDT 92 C (snippet). PETG: HDT 68 C (Prusament https://cdn.shopify.com/s/files/1/1745/6181/files/PETG_TechSheet_ENG.pdf ), Polymaker PETG Tg 81 C, HDT 75 C. PETG-CF: Tg 68 C, HDT 68 C (74 C at 0.45 MPa) https://cdn.shopify.com/s/files/1/0380/5149/files/Bambu_PETG-CF_Technical_Data_Sheet.pdf , so carbon fibre does not fix PETG heat. PC (PolyMax): Tg 113 C, HDT 99-114 C. PA6-CF: HDT 173 C dry but Tg 74 C. PAHT-CF (PA12-type): HDT 170 C. Loaded oven test (CNC Kitchen): PLA fails ~65 C, PETG softens 80 C / fails ~85 C, ASA softens 110 / fails 120 C, PC Blend 110 / 125 C: https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament . A PETG latch at 60-70 C sits at or above its HDT: avoid for sustained load.
CREEP (data are thin). Dogan 2022, 3 h tests on milled specimens: ABS ruptured in ~3 min at 60 C and 20 MPa; PLA broke at 60 C even at 10 MPa; PC never ruptured and crept least; nylon crept most without rupture: https://ojs30.sv-jme.eu/index.php/sv-jme/article/download/191/118/2454 . No ASA or PETG creep data beyond 3 h at 60 C exists in anything I found. Bolt-preload tests: M4 at 0.8 Nm, 1 week, room temp: ASA and PLA needed about one re-tighten, PA6 almost daily (https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested ); bolted PETG joints lost 11.5 % preload in 7 days vs 3 % PLA (https://filamentspecs.com/creep-resistance-3d-printed-parts/ ). Fibre grades rank PAHT-CF > PC > PLA for creep (https://link.springer.com/10.1007/s11665-024-09144-9 ). My working rule (own judgement; researchers disagreed: 5-8, 5-9 and <=3-5 MPa): sustained in-plane stress for ASA at 60-70 C of 3-5 MPa cautious, up to 5-8 MPa optimistic; bearing under steel pins/washers ~8-10 MPa; across layers ~2 MPa. Put preload in steel (spring, screw, insert).
Anisotropy
Hook tests (CNC Kitchen, same link): ASA lying 57 kg vs standing 17 kg (29 %), PETG 55 vs 25 kg (46 %), PLA 73 vs 40 kg; ASA in a 30 C chamber 20 kg (+20 %). PC Blend lying 74-77 kg vs standing 22-35 kg (https://www.cnckitchen.com/blog/prusament-pc-blend-review ). Datasheets claim ASA Z/XY tensile of 73-84 % (Polymaker 32/43.8 MPa; Bambu 31/37 MPa) but Z elongation only 1.65 %; hooks are far worse, so design to 29 %. Rule: lever, link, hook and bearing loads in the XY plane, pin axes along Z, 4+ perimeters, 0.2 mm layers or finer on a 0.4 mm nozzle.
UV and weather
ASA -0.7 % yield and -3 % break stress after 1000 h QUV; unstabilised PC -34 % yield, dE 33 (strong yellowing); TPU 92A -15 %; nylon 12CF stable: https://stratasys.com/siteassets/abm-pages/aerospace/wp_fdm_uv-aging_a4_0123a.pdf . PETG UV results range +9 % (mild lamp, 100 h) to -36 % (UV-B), vendor/forum report yellowing and embrittlement at 6-12 months (https://pmc.ncbi.nlm.nih.gov/articles/PMC10146359/ , https://qidi3d.com/ja/blogs/print-lab/asa-petg-sprinkler-brackets-outdoor ). Field: original moulded pool-controller latches broke after ~10 years in sun (https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236 ). Avoid unstabilised PP (months). Cold: injection-moulded ASA 3 kJ/m2 notched Charpy at -30 C, so no sharp internal corners; PC stays tough (snippet).
Moisture and nylon
PA6-CF takes up 3.33 % water, XY strength -22 % and modulus -24 % after conditioning (https://cdn.shopify.com/s/files/1/0548/7299/7945/files/PolyMide_PA6_CF_TDS_V5.2.pdf ); PAHT-CF 0.88 %. Avoid PA6-CF outdoors; PAHT-CF acceptable but still creeps.
What changes with other materials
ASA is the default. PC (UV-stabilised grade only) gives the best heat and creep margin and probably raises sustained limits ~1.3-1.5x (own judgement, unmeasured). PETG and PETG-CF are marginal at 60-70 C. PA-CF mainly adds stiffness and heat margin, but moisture and nylon creep offset it.
Hardware and interfaces
Use A2/A4 stainless pins, screws and springs; zinc-plated steel 12-72 h salt spray, yellow zinc 96-120 h (https://www.albanycountyfasteners.com/media/48/29/31/1764608481/fastener-materials-and-coatings-guide.pdf ); music wire rusts and tops out ~121 C, 302/304 stainless spring ~288 C but 25-30 % weaker (https://www.leespring.com/music-wire-versus-stainless-steel ). M3 heat-set insert in PETG pulls out at 119 kg (~1.17 kN), torque-out 3 Nm; direct screw 118 kg but strips at 1 Nm; side-pocket nut 86 kg, bottom-pocket nut 166 kg (https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment ); room-temperature peak values, not hot or sustained. Class 8.8 proof loads M3 2.92, M4 5.10, M5 8.23 kN (https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads ), so the printed boss always limits.