Material selection · Mechanical performance

Creep and stress relaxation in FDM parts

Use measured creep and retained-stress evidence to screen continuously loaded brackets, locating fixtures and fastened joints, with time, environment and control mode kept attached.

3D Printing Info · Published 2026-10-18 · Revised 2026-10-18

Editorial synthesis assisted by AI, based on the linked experimental research. No mechanical testing was performed for this article.

Decide whether position or retained force must stay stable

Engineering interpretation. A support carrying a steady force can gradually deflect: that is the creep question. A clip or interference fit held at a set deformation can lose force: that is the stress-relaxation question. Specify which change would make the part fail its function, then seek a test with the same loading condition. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details]

Engineering interpretation. The printed PLA experiments below demonstrate both responses near room temperature. They use different grades, specimen shapes, load controls and durations, so the results remain separate. For a fixture, use them to choose a relevant hold test and acceptance limit; they do not choose a universally creep-resistant polymer. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details]

Constant force and fixed deformation produce different evidence

In a constant-load creep test, record deformation over time. Compliance expresses strain per unit stress; creep modulus expresses the corresponding stress-to-strain ratio at a stated time. A lower creep modulus during the hold means greater deformation under that load. It is different from the initial tensile modulus in a quick pull test. Fischbach and Weinberg [details]

Engineering interpretation. In a fixed-strain relaxation test, hold deformation and record how much stress remains. For a spring clip, retained force may matter more than its initial stiffness. A bracket under a hanging weight calls for displacement measurements instead. A bolted joint combines the stiffness of the fastener, washers, contacts and printed member, so its behavior needs an assembly test. Liber-Kneć and Łagan / Materials [details] · Amza et al. / Polymers [details]

Two measured responses, under separate protocols

These independent experiments supply a long bending-creep endpoint and a shorter tensile-relaxation endpoint. The row conditions define each result. The second table compares the start and end of one hold in one cohort, rather than comparing polymer families. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details] · Liber-Kneć and Łagan / Materials [details]

Constant-load bending creep — one printed Ultrafuse PLA specimen

ISO 899-2, nominal 10 N held for 170 h at approximately 20 °C and 30–50% RH; specimen age 5 h when loaded. This is a flexural creep result, not tensile strength.

Exact grade & process	Orientation & specimen state	Flexural creep modulus at 170 h MPa	Test conditions & source
Ultrafuse PLAFFF · Independent experiment	Not reportedConditioning: Cooled in the printer for about 10 min to ambient; long-duration loading began at a specimen age of 5 hPost-processing: Not reported	1040 Fischbach and Weinberg [details]	ISO 899-2 flexural creep; revision unspecified; nominal geometry follows ISO 178Test temperature: Approximately 20 °CControl mode: constant loadLoad: 10 N nominal, held nearly constantStress: Not reportedDuration: 170 hHumidity: 30–50% RHSpecimen state: 5 h old at loading; no UV exposureStrain: Not reportedRaster to load axis: Not reportedSpecimen & processing details

The result is calculated from the measured load, specimen dimensions and time-dependent crosshead displacement. No replicate spread is available for this long-duration endpoint. The source reports continuing creep at the end of the hold. Fischbach and Weinberg [details] · Fischbach and Weinberg [details]

Fixed-strain tensile relaxation — ROSA PLA Starter initial cohort

Flat FDM specimens, 100% infill and 0°/90° raster; 2% strain held for one hour at 20 ± 1 °C and 40% RH. Values are mean ± standard deviation, n = 5.

Exact grade & process	Orientation & specimen state	Maximum stress at the imposed strain MPa	Residual stress after 1 h MPa	Test conditions & source
ROSA PLA Starter, white — PLA_100 initial cohortFDM · Independent experiment	Flat XY; 0°/90° raster relative to the specimen print layoutConditioning: Initial-state cohort, without the 30-day Ringer’s-solution incubation; prior moisture equilibration not specifiedPost-processing: Not reported	43.53 ± 1.54 Liber-Kneć and Łagan / Materials [details]	36.8 ± 3.33 Liber-Kneć and Łagan / Materials [details]	Author one-hour fixed-strain tensile-relaxation protocol; no relaxation standard specifiedTest temperature: 20 ± 1 °CControl mode: constant strainStrain: 2% tensile strainLoad: Not reportedStress: Variable response; measured maximum and one-hour residual stress in the tableDuration: 1 h (3600 s)Humidity: 40% RHSpecimen state: Initial-state PLA_100; 100% infillPrior moisture conditioning: Not reportedTime since printing: Not reportedStrain ramp rate: Not reportedSpecimen & processing details

The PLA_100 row is the initial-state group, without the study’s separate immersion treatment. The residual result is the finite one-hour endpoint. It is neither an ultimate strength nor a bolt-preload measurement. Liber-Kneć and Łagan / Materials [details] · Liber-Kneć and Łagan / Materials [details]

For a loaded fixture, measure drift at the working surface

Fischbach and Weinberg’s Ultrafuse PLA beam continued to creep through the end of its week-long bending hold, even though the test was well below the grade’s reported glass transition. The final creep modulus came from one specimen. Its unknown raster-to-load-axis definition and crosshead-based strain measurement matter when deciding how closely the experiment represents a proposed part. Fischbach and Weinberg [details] · Fischbach and Weinberg [details]

Engineering interpretation. For a locating fixture or overhung bracket, define the allowed movement where the part locates or supports the work. Test its actual section, lever arm and build orientation under a representative sustained load. A room-temperature coupon endpoint cannot determine the drift of a warmer bracket, or establish a general reduction factor for its static strength. Fischbach and Weinberg [details]

For a constrained feature, measure force after the hold

The ROSA PLA Starter result shows that holding deformation does not hold stress constant. Its maximum and one-hour residual values describe the same 2% strain protocol. The paper’s infinity subscript labels a one-hour endpoint; it does not demonstrate that relaxation has ended for all later times. Liber-Kneć and Łagan / Materials [details] · Liber-Kneć and Łagan / Materials [details]

Engineering interpretation. For a clip, spring feature or interference fit, set the installed deformation and measure the remaining force through the required holding period and environmental range. The 2% tensile strain in this experiment is a test condition, not an allowable strain for a differently shaped clip. Include installation damage and repeat assembly if the part is reused. Liber-Kneć and Łagan / Materials [details]

Removal torque is useful joint evidence with a limited meaning

Amza and colleagues tested washer-loaded M6 assemblies in printed Fillamentum PLA Extrafill and PrimaSelect PETG. After seven days, the screws required less torque to remove than the original tightening torque. That observation can motivate a joint-retention test, but the experiment did not directly measure bolt preload or a fixed-strain retained stress. Amza et al. / Polymers [details]

Engineering interpretation. For a clamped fixture, specify the minimum retained clamping force or the permitted slip, then measure that quantity on the assembled joint. Record tightening procedure, washer geometry, contact area and operating cycles. A metal compression limiter or a spring element is a candidate design change to evaluate in that test; a removal-torque percentage alone cannot qualify it. Amza et al. / Polymers [details]

Keep specimen age, moisture and measurement method attached

The creep beam was loaded five hours after printing. Its laboratory humidity varied over the reported range, and the authors calculated strain from crosshead travel. The relaxation study reports five specimens per case and standard deviation, but does not specify prior moisture equilibration, time since printing or the relaxation strain ramp rate. Expand the records for the exact printing and test details. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details]

Engineering interpretation. These studies do not establish a common-condition comparison for PETG, ASA, PC, nylon or their fiber composites. A supplier’s molded-compound creep curve also needs its grade, process, loading direction and environment checked before it can inform a printed component. Request printed-grade evidence or conduct a representative test when those conditions are missing. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details]

Ultrafuse PLA · Not reported

Material identity: BASF 3D Printing Solutions · PLA · filler: Not reported
Process: FFF
Source orientation: Not reported
Specimen geometry: Nominal 100 × 10 × 5 mm beam, support span 80 mm; individual width and height measured before testing
Test method: ISO 899-2 flexural creep; revision unspecified; nominal geometry follows ISO 178
Test rate: Not reported
Test temperature: Approximately 20 °C
Specimen conditioning: Cooled in the printer for about 10 min to ambient; long-duration loading began at a specimen age of 5 h
Printer: Not reported
Post-processing: Not reported
Sample count: 1
Meaning of ±: Not reported
Source locator: §3.1 and Table 1 (fabrication), §3.2/Eqs. 9–10 (measurement), §3.3 (170 h protocol), §4.2/Figure 11 (single-specimen endpoint).
Layer height: 0.2 mm
Infill: 100%; line pattern reported as 45°–90°
Perimeters: 1
Nozzle temperature: 215 °C
Bed temperature: 30 °C
Chamber temperature: Not reported
Slicer: Not reported
Infill print speed: 60 mm/s (reported general print speed)
Top bottom solid layers: Not reported
Specimen cooling: Cooling fan always on
Extrusion multiplier: 102%
Control mode: constant load
Load: 10 N nominal, held nearly constant
Stress: Not reported
Duration: 170 h
Humidity: 30–50% RH
Specimen state: 5 h old at loading; no UV exposure
Strain: Not reported
Raster to load axis: Not reported

ROSA PLA Starter, white — PLA_100 initial cohort · Flat XY; 0°/90° raster relative to the specimen print layout

Material identity: ROSA PLAST Sp. z o.o. · PLA · filler: Not reported
Process: FDM
Source orientation: Flat XY; 0°/90° raster relative to the specimen print layout
Specimen geometry: Dumbbell specimen with reduced grip width and length; source states ISO 527-2 cross-sectional dimensions and gauge length; §2.2.1 reports a 60 mm test gauge
Test method: Author one-hour fixed-strain tensile-relaxation protocol; no relaxation standard specified
Test rate: Not reported
Test temperature: 20 ± 1 °C
Specimen conditioning: Initial-state cohort, without the 30-day Ringer’s-solution incubation; prior moisture equilibration not specified
Printer: MarketBot SKETCH (source spelling)
Post-processing: Not reported
Sample count: 5
Meaning of ±: Mean ± standard deviation; five specimens for each case (§2.2.4)
Source locator: PDF pp. 4–7, §2.1/Table 1 and §§2.2.1, 2.2.4; p. 13 §3.3; p. 14 Table 5, PLA_100 row.
Layer height: 0.2 mm
Infill: 100%; Diamond Fill Fast; 0°/90° raster
Perimeters: 2
Nozzle temperature: 220 °C
Bed temperature: 50 °C
Chamber temperature: Not reported
Slicer: UltiMaker Cura Cloud V5.2 (reported name)
Infill print speed: 50 mm/s non-monolithic layers; 35 mm/s monolithic layers
Top bottom solid layers: Two bottom/top layers reported; outer thickness 0.72 mm and inner thickness 0.36 mm, in the source wording
Specimen cooling: Not reported
Extrusion multiplier: Not reported
Control mode: constant strain
Strain: 2% tensile strain
Load: Not reported
Stress: Variable response; measured maximum and one-hour residual stress in the table
Duration: 1 h (3600 s)
Humidity: 40% RH
Specimen state: Initial-state PLA_100; 100% infill
Prior moisture conditioning: Not reported
Time since printing: Not reported
Strain ramp rate: Not reported

A hold test that resolves the design decision

Engineering interpretation. Select the observable first: displacement for a loaded support, retained force for a constrained feature, or clamping force and slip for an assembled joint. Set the acceptable limit and holding period from the component’s function. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details] · Amza et al. / Polymers [details]

Engineering interpretation. Print repeated specimens or components in the intended grade, build orientation, wall/infill layout and thermal history. Record time since printing and moisture conditioning. Include the service temperature and humidity range rather than relying on a Tg or HDT entry. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details]
Engineering interpretation. Log force and displacement from loading through the hold. Verify that the intended force or strain remains controlled. After unloading, measure recovery and any residual set that affects fit or reuse. For a joint, retain the actual fastener and contact stack. Fischbach and Weinberg [details] · Amza et al. / Polymers [details]
Engineering interpretation. If the requirement extends beyond the measured duration, obtain longer tests or validate an acceleration/modeling method against independent holds. Check whether deformation, force loss or failure mode changes with load and environment. The published one-hour and week-long results cannot establish years of service. Fischbach and Weinberg [details] · Liber-Kneć and Łagan / Materials [details]

Sources and evidence records

These records distinguish supplier tests, independent experiments and engineering interpretation. “Not reported” identifies a source gap; it is not an assumed test condition.

Accelerated Aging Effect on Mechanical Properties of Common 3D-Printing Polymers
Amza et al. / Polymers · Independent experiment · document date: 2021-11-26 · version: Polymers 13(23), 4132; DOI 10.3390/polym13234132 · accessed 2026-10-18
Catalin Gheorghe Amza, Aurelian Zapciu, Florin Baciu, Mihai Ion Vasile, Adrian Ionut Nicoara
FFF specimens: opaque blue Fillamentum PLA Extrafill and transparent natural PrimaSelect PETG; Creality Ender-3, Cura 4.5, 100% grid ±45° infill, 0.2 mm layers, two contours. PLA nozzle/bed: 205/45 °C; PETG: 235/65 °C. Unaged controls are discussed separately from UV-B-aged groups; ASTM D638-14 Type I dimensions, 1 mm/min, 23 °C / 50% RH, five specimens per tensile group. Ultimate strength is distinct from the supplier yield property.
Effect of physical aging on the flexural creep in 3D printed thermoplastic
Fischbach and Weinberg · Independent experiment · document date: 2023-08-16 · version: arXiv:2302.11240v2 · accessed 2026-10-18
Marcel Fischbach, Kerstin Weinberg
Author manuscript, printed BASF Ultrafuse PLA; 100% infill, 0.2 mm layers, 215 °C nozzle, 30 °C bed; ISO 899-2 bending creep. The long-duration test uses one specimen under a 10 N nominal force for 170 h near 20 °C. No family-wide lifetime or reduction factor is inferred. The long-duration specimen had an initial age of five hours; the authors report laboratory relative humidity of 30–50%.
Effect of Mass Reduction of 3D-Printed PLA on Load Transfer Capacity—A Circular Economy Perspective
Liber-Kneć and Łagan / Materials · Independent experiment · document date: 2025-07-10 · version: Materials 18(14), 3262; DOI 10.3390/ma18143262 · accessed 2026-10-18
Aneta Liber-Kneć, Sylwia Łagan
FDM ROSA PLA Starter specimens, white, flat XY, 0°/90° raster. This article uses only the initial-state PLA_100 relaxation cohort: 100% infill, a 2% tensile strain held for one hour, 20 ± 1 °C and 40% humidity. Table 5 reports maximum and one-hour residual stress; §2.2.4 defines the reported ± as standard deviation for five specimens. The hydrated cohorts, mass-normalized results and tensile-strength tables are outside this comparison. Residual stress at one hour is not an infinite-time equilibrium value.

Read individual measurement and claim records

fischbach ultrafuse pla 170h creep modulus: Flexural stress divided by time-dependent flexural strain at the end of the 170 h constant-load test; authors calculate strain from crosshead displacement and specimen geometry.: 1040 MPa. Author-reported final calculated modulus from one printed specimen; the specimen was still creeping at the end of the hold. No curve digitization or lifetime extrapolation is used.
§4.2, final paragraph after Figure 11; protocol §3.3 and strain/stress definitions §3.2, Eqs. 9–10. Fischbach and Weinberg [details]
liber knec pla100 relaxation maximum stress: Maximum tensile stress associated with applying the 2% strain before the one-hour relaxation hold; Table 5 labels this σmax. It is not ultimate tensile strength.: 43.53 ± 1.54 MPa. Reported mean ± standard deviation for five specimens in the initial-state, 100%-infill cohort.
PDF p. 14, Table 5, PLA_100 row, σmax [MPa] column; test §2.2.1 and statistics §2.2.4. Liber-Kneć and Łagan / Materials [details]
liber knec pla100 relaxation one hour stress: Residual tensile stress after the one-hour hold at 2% strain. The source symbol σ∞ denotes this measured finite-duration endpoint here, not a demonstrated infinite-time limit.: 36.8 ± 3.33 MPa. Reported mean ± standard deviation for five specimens; the retained stress applies to the stated strain, environment, infill and specimen state.
PDF p. 14, Table 5, PLA_100 row, σ∞ [MPa] column; one-hour endpoint defined in §2.2.1 on p. 6. Liber-Kneć and Łagan / Materials [details]
creep below tg: One printed Ultrafuse PLA specimen continued to creep under the long room-temperature bending hold below its glass transition. This evidence calls for a sustained-load check but does not supply a general lifetime prediction.
§3.1/Table 1 (material and process), §3.3 (test protocol), §4.2/Figure 11 and §5 (long-duration observations). Fischbach and Weinberg [details]
fischbach creep control and measurement: The bending experiment maintains nominal force and measures increasing deformation. Compliance is strain divided by stress; flexural creep modulus is its reciprocal. Crosshead-derived strain and initial contact/load resolution affect the measurements; the authors discuss corrections and recommend improved force or direct strain measurement.
§2.1 (creep compliance), §3.2/Eqs. 9–10 (load and calculated strain), §3.3 (long hold), §5 final paragraphs (measurement limitations). Fischbach and Weinberg [details]
liber knec fixed strain protocol: The study holds tensile strain at 2% for one hour and records declining stress. All mechanical tests use 20 ± 1 °C and 40% humidity. The initial PLA_100 cohort is separate from the specimens incubated in Ringer’s solution. The reported finite-time residual stress does not establish long-term clamp-force retention.
PDF pp. 5–7, §§2.2.1 and 2.2.4; p. 13 §3.3 and Figure 13; p. 14 Table 5. Liber-Kneć and Łagan / Materials [details]
amza bolted joint removal torque: M6 assemblies with washers in printed Fillamentum PLA Extrafill and PrimaSelect PETG were initially tightened to 5.07 N·m. All tested assemblies required lower removal torque after seven days at 23 °C and 50% RH. The reported load is estimated from tightening torque and a screw coefficient; direct preload or retained stress was not measured. Removal torque is a joint-level proxy, not a fixed-strain relaxation curve.
§2/Table 1 (exact grades and print settings); §2/Figure 2b (joint); §3.4/Table 4 and Figure 7c (seven-day torque observations). Amza et al. / Polymers [details]