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Evaluation of the creep strength of samples produced by fused deposition modeling

  • Peter Hausler EMAIL logo , Lukas Holzner , Matthias Ehrnsperger and Rudolf Bierl
Published/Copyright: November 21, 2024
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Open Engineering
From the journal Open Engineering Volume 14 Issue 1

Abstract

Data sheets for 3D printing materials typically include softening temperature, impact strength, tensile strength, and stiffness. However, creep strength, an important parameter for components used over an extended period, is usually not included. Nevertheless, this parameter is of significant importance for components that are used over an extended period of time. This study compares the long-term creep behavior of a selection of materials that are commonly used in fused deposition modeling 3D printing. The materials under investigation are acrylonitrile butadiene styrene, acrylonitrile styrene acrylate, polylactic acid, and polycarbonate. In addition, the influence of fiber reinforcements on these materials is also examined. A simple, reproducible test procedure is proposed for users to determine and compare creep resistance of materials. This enables developers to select materials suitable for their own requirements on creep resistance and allows 3D-printing users to compare different materials. Results suggest that fiber reinforcement generally improves creep stability in 3D-printing materials, with GreenTEC Pro Carbon and add:north PC Blend HT LCF showing the most promise in this study.

Keywords: 3D-printing; FDM; material property; creep strength; additive manufacturing

1 Introduction

Additive manufacturing, particularly 3D printing, has made significant progress in recent years and has become an important aspect of technology and science. Fused deposition modeling (FDM) has been widely established due to its cost efficiency and accessibility [1].

FDM 3D printing is rapidly growing in industry and research. The global additive manufacturing market is projected to grow from $15 billion in 2022 to $96 billion in 2032, with a 20% annual growth rate [2]. In Germany, 25% of companies with 250+ employees used 3D printing in 2022 [3]. The 3D-printing hype cycle [4] shows that the technology has moved past initial enthusiasm and is now used industrially.

The most used material is polylactic acid (PLA), which is rigid, easy to process, can be obtained from natural sources, and is biodegradable. Unfortunately, this type of polymer is not very stable at high temperatures and has a low impact strength. However, there are many other types of material that can fill this gap. There are also filaments whose properties have been improved by adding fillers [5,6].

Design engineers often require material parameters such as softening temperature, stiffness, elongation at break, and notched impact strength [7,8]. They can select the most suitable material for their own specific requirements by referring to the parameters specified in the material data sheets. However, certain applications create creep under constant load for 3D-print relevant polymers [9]. Creep is a time-dependent plastic deformation that occurs when a material is subjected to a constant load. This phenomenon can cause a material that initially resists pressure to buckle over a long period of time. Unfortunately, most material data sheets for FDM filaments do not include details on creep behavior, despite its significance for devices that are in constant use.

A 2022 survey identified “New materials and composites” as the top expected development (44%) [4], while 34% cited “Material types” as a hindrance to 3D-printing adoption [10]. Currently, plastics are predominantly used in FDM, but their low temperature resistance and pronounced creep behavior are significant drawbacks. Plastic creep under load has been studied extensively [11], with FDM thermoplastics being particularly susceptible [12]. Research has also explored how printing parameters affect component creep behavior [13].

The influence of temperature [14] and printing parameters [15] on the creep behavior of various materials has been the subject of previous research. Nevertheless, the test phases were conducted over a short timescale.

The open engineering scene project Voron exemplifies the importance of investigating long-term dimensional stability in FDM 3D-printing materials. The Voron open 3D printer uses acrylonitrile butadiene styrene (ABS) for its frame parts, but some users attempted to improve it with fiber-reinforced nylon-based filament. Despite its better stiffness, this material was not dimensionally stable and failed under stress over time, highlighting the need for further research on creep behavior and long-term stability in FDM materials [16,17].

Furthermore, filament manufacturers typically provide only one data sheet for each material class, which covers all materials of that class (e.g. all PLA or all ABS filaments). Nevertheless, studies conducted by 3D-printing experts, such as CNC Kitchen, have demonstrated that the color of the filament can significantly impact its stability [18]. As a result, it is important for users to have a simple method to determine filament data themselves. To enable users to conduct tests themselves, it is necessary to develop a simple procedure.

The aim is to provide both engineers and makers with a method that they can use to compare filament materials themselves. In addition, the easy-to-perform test should also enable the various experts to easily compare their results. A widely used system, the Prusa MK3, was chosen to print the materials. The test series compared materials with a relatively high temperature resistance, making them potentially suitable for use in the Voron Open-Source Printer Project.

As the flexural stiffness of some materials is specified in the data sheet and a correlation with creep resistance was assumed, this value was determined for all materials in accordance with ISO 178. The creep strength was then determined using the method proposed here. This involved analyzing the extent to which a sample bends under load over a longer period of time and the extent to which it deforms back again over a longer period of time.

2 Methods

2.1 Definition of the term creeping

Under operating conditions, plastic components may experience creep, which can negatively affect their dimensional stability, accuracy, and functionality. When a load is applied to a test specimen or component and held for a defined period, the specimen or component initially experiences a sudden increase in deformation. Depending on the duration of the load, a time-dependent deformation known as creep occurs. Figure 1 shows the creep behavior of a test specimen supported on both sides under bending load.

Figure 1 (1) In the initial state, prior to the application of an externally applied load, the specimen does not exhibit any deformation; (2) upon the application of a load by the test apparatus, the specimen exhibits an initial deflection; (3) as a consequence of creep, the specimen exhibits additional deformation after a specified period, even in the absence of further load application; (4) upon the removal of the load from the specimen, a spontaneous re-deformation occurs, although it does not reach the original state; and (5) subsequently, the specimen reverts to its original state through a process of creep.
Figure 1

(1) In the initial state, prior to the application of an externally applied load, the specimen does not exhibit any deformation; (2) upon the application of a load by the test apparatus, the specimen exhibits an initial deflection; (3) as a consequence of creep, the specimen exhibits additional deformation after a specified period, even in the absence of further load application; (4) upon the removal of the load from the specimen, a spontaneous re-deformation occurs, although it does not reach the original state; and (5) subsequently, the specimen reverts to its original state through a process of creep.

When a weight is applied to this test specimen, it undergoes either purely linear–elastic deformation or a combination of linear–elastic and linear–viscoelastic deformation, depending on the load level. Creep is defined as the increase in deformation under a constant load, which results in a time-dependent deformation when the load is maintained for a period. Upon removal of the weight, a spontaneous reverse deformation occurs, leaving only the time-dependent deformation. Viscoelasticity is a time-dependent elasticity that is based on the delayed equilibrium adjustment of the macromolecules. It therefore takes a certain amount of time for the initial length to be restored through creep-back processes. This stress/strain behavior is typical for linear viscoelastic materials and is represented in a closed hysteresis curve. However, if the load is increased, non-linear viscoelastic behavior may occur, resulting in irreversible deformation. This is characterized by an open load hysteresis, which prevents the specimen from returning to its original state [19].

2.2 Printer setup

The samples are produced using a Prusa MK3S+ printer, which is widely used in the Open Source community. Due to the widespread use of the Prusa MK3 family, the results of these tests are comparable with many other users. The printer is equipped with a hardened 0.4 mm NozzleX nozzle to enable it to process fiber-filled filaments, which are abrasive.

Optimal 3D printer nozzle design requires balancing multiple factors. Key considerations include minimizing filament adhesion through smooth surfaces and materials with superior sliding properties, exemplified by nickel-plated copper nozzles. Efficient heat conduction from the heating block to the filament is crucial, with copper excelling in this aspect. Cost-effectiveness precludes specialized options like gemstone-insert nozzles. For non-abrasive materials, plated copper nozzles often present the ideal solution. However, abrasive materials necessitate more durable alternatives. The NozzleX nozzle, composed of a heat-resistant steel alloy with a smooth nickel coating and an additional polyphobic WS2 nanocoating, offers superior performance for abrasive materials at a maximum printing temperature of 300°C (Table 1).

Table 1

Comparison of different nozzle types, for the use of abrasive filaments like fiber-reinforced filaments, a wear resistant nozzle is required; it is important to note that some materials like stainless steel can lose their wear resistance at higher temperatures

Nozzle material Wear resistant Maximum temperature (°C) Heat conduction Non-stick properties
Brass No 300 Good Good
Stainless steel Moderate 500 Poor OK
Ruby-tipped Yes 400 Good Good
Plated copper Moderate 400 Excellent Excellent
NozzleX Yes 500 Good Excellent

The Prusa MK3’s heat-break design, utilizing a metal tube with polytetrafluoroethylene (PTFE) insert, poses potential risks at temperatures exceeding 240°C due to PTFE decomposition. To mitigate this, full-metal heat-breaks are necessary for high-temperature printing. Traditional titanium heat-breaks, while thermally resistant, often suffer from heat creep issues. Advanced bimetallic heat-breaks offer an optimal solution, combining materials strategically to balance thermal properties. These designs typically feature a titanium- or copper-threaded portion for the heat-block interface, a thin titanium tube for thermal isolation, and a copper thread at the cooler end for efficient heat dissipation. This configuration, exemplified by the BROZZL V6 bi-metal heat-break, provides superior performance and safety for high-temperature 3D-printing applications, effectively addressing the limitations of conventional designs.

The Prusa MK3S+ is enclosed within a chamber maintaining a constant ambient temperature of 29°C and a relative humidity of 10%.

2.3 Materials

Eight different filaments were compared within the test (Table 2). PLA was used as it is by far the most used filament. PLA is very easy to print and can be recycled; it is also very rigid and generally does not produce toxic fumes during printing. Unfortunately, PLA has a very low softening temperature – the exact value varies between manufacturers – but is around 55°C. Prusament PLA was used for these tests. ABS was tested as it is the recommended material for printing the VORON printer. The stiffness is slightly lower, but the softening temperature of the TitanX ABS from FormFutura used here is 97°C. FormFutura ApolloX acrylonitrile styrene acrylate (ASA) was used in the tests because it is easier to print than ABS and has better resistance to environmental influences. GreenTEC Pro from Extrudr, which is based on PLA, was chosen as it has a higher stiffness than PLA and a softening temperature of 160°C. These four materials are without fiber reinforcement.

Table 2

Overview of the materials used in the test and material properties according to the data sheet

No. Filament name Manufacturer Material Fiber-reinforced HDT/VST (°C) Tensile modulus (MPa) Elongation at break (%)
1 ApolloX FormFutura ASA No 98 (VST) 2,020 15
2 TitanX FormFutura ABS No 97 (VST) 2,030 34
3 Prusament PLA Prusa Polymers PLA No 55 (HDT) 2,300 2.9
4 GreenTEC Pro Extrudr PLA + copolyester No 115 (HDT) 4,300 2.8
160 (VST)
5 CarbonX ABS + CF 3DXTech ABS Yes 76 (HDT) 5,210 2
6 CarbonX ASA + CF 3DXTech ASA Yes 97 (HDT) 5,355 3
7 GreenTEC Pro Carbon Extrudr PLA + copolyester Yes 115 (HDT) 7,120 3
166 (VST)
8 Polycarbonate (PC) blend HT LCF Add:north PC + additive Yes 185 (HDT) 9,800 2.9

The materials are sorted according to their tensile modulus. It is important to note that there are several methods for determining the softening temperature. The heat deflection temperature (HDT) and the Vicat softening temperature (VST) are two such methods that are used to measure the softening temperature of plastics. In the case of HDT, at a three-point bending test, a constant heating rate is applied to samples until a certain deflection is reached. In contrast, VST measures the temperature at which a loaded indenter penetrates the sample to a certain deep.

To show the influence of fiber reinforcement on the material behavior, ABS, ASA, and GreenTEC Pro have been tested with and without fibers. The following materials are used as fiber-reinforced filaments: CarbonX ASA + CF and CarbonX ABS + CF both from 3DXTech as well as GreenTEC Pro Carbon from Extrudr. Additionally, PC Blend HT LCF, a fiber-reinforced, polycarbonate-based mixture of polymers from add:north, is tested, as this material has a particularly high temperature resistance of 185°C.

2.4 Printer settings

All samples were printed with an extrusion width of 0.6 mm and a layer height of 0.16 mm. The samples were printed with 6 perimeters and 7 top/bottom layers. The infill structure is cubic with a filling degree of 50%. It should be noted that varying the printing parameters, such as extrusion width, layer height, number of perimeters, top and bottom layers, infill structure, infill level, printing temperature, and print head travel speed, can have a non-negligible influence on the stability of the components. However, this was not investigated in this study and can be taken into account in future material comparisons. The printing temperature of the various materials was selected as shown in Table 3.

Table 3

Printing temperature of the materials used in the tests, sorted by temperature

No. Print temperature
3 220°C Prusament PLA
6 235°C ASA + CF
4 235°C GreenTEC Pro
7 255°C GreenTEC Pro Carbon
5 260°C ABS + CF
1 260°C ApolloX ASA
2 265°C TitanX ABS
8 290°C PC Blend HT LCF

2.5 Test procedure

The samples for the ISO178 test are printed flat on the print bed, with a base area of 10 mm × 120 mm. Since the support distance for the creep test was only 65 mm, these samples had a length of only 100 mm. Subsequently, 24 layers, each with a height of 0.16 mm, were printed on top of the base layer. This results in a sample height of 4 mm. During the load tests, the 3D-printed samples are loaded perpendicular to the printed layers (Figure 2). The dimensions of the samples employed in the creep test were aligned with those utilized in the ISO-178 test, with the objective of enhancing the comparability of the outcomes derived from both test methodologies.

Figure 2 Illustration of the load direction of the 3D-printed specimens.
Figure 2

Illustration of the load direction of the 3D-printed specimens.

2.5.1 Flexural stiffness according to ISO 178

The sample size is selected according to ISO 178 [20] and has a cross section of 4 mm × 10 mm. The bending tests according to ISO 178 are carried out with a universal testing machine Inspekt Table 50 kN from Hegewald & Peschke.

The flexural strength and flexural modulus are measured as they are not included in all data sheets. We hypothesize that there is a correlation between flexural modulus and creep strength. Typically, filament manufacturers publish material data based on 100% filled components. The test rods are also occasionally injection-molded. Injection molding may impact all materials, but it is particularly noteworthy in fiber-reinforced materials, as the orientation of the fibers may be more aligned in printed materials, thereby increasing the anisotropy. In our case, the test specimens are filled to only 50%. This approach is selected to attain values that are more representative of real-world applications, since in 3D printing, hollow components are usually printed in order to reduce printing times.

2.5.2 Creep strength

The determination of creep behavior is regulated by the DIN EN ISO 899-2 standard [21]. As manufacturers usually do not provide values according to this standard, users must determine creep resistance themselves. Testing according to the standard is not feasible for most users; hence, a simpler and more convenient method is proposed in the following.

The measurement setup (Figure 3) comprises two support surfaces connected by a frame. The sample is positioned in the center between the two support surfaces. The measuring device for determining the deflection [22] is placed next to the sample. For calibration, a zero adjustment is carried out with the ruler of the measuring device. The sample is then loaded with weight (Figure 3 right side) and left in place for 1 week, during which the deflection is measured daily. The load levels of 5 kg were previously determined in preliminary tests, with the objective of inducing a measurable deformation during the test period. A spring steel scale (KS-Tools 300.0101) was used to determine the deflection. The scale has tolerance class 2 in accordance with Directive 2014/32/EU [23].

Figure 3 Measuring stand for determining the permanent creep behavior. The sample body and the measuring device are located centrally on the measuring stand with two firmly connected support surfaces at a distance of 65 mm.
Figure 3

Measuring stand for determining the permanent creep behavior. The sample body and the measuring device are located centrally on the measuring stand with two firmly connected support surfaces at a distance of 65 mm.

To evaluate the durability of deformation, the dropping deflection of the unloaded samples was measured. The measuring stand used for the deflection allows direct reading of the sample’s deformation. The ruler used has a scale division of 500 µm.

In order to facilitate a more precise measurement of the deflection, the sample is removed from the measuring stand and fixed to a test plate on one side. The black granite test plate from Wabeco (article number: 11,396) is ground and lapped in accordance with DIN 876/1. The height of the sample is measured on the side of the sample that is bent upward. The deflection is quantified using a vertical ripper from Metrica (G 15566). The measurements are taken immediately after the sample is removed, as well as 1, 10, 60 min, and 1 day later.

2.6 Calculation of the flexural modulus

Flexural modulus, also referred to as bending modulus or modulus of elasticity in bending, is a measure of a material’s stiffness in response to applied bending stress. It quantifies the material’s resistance to deformation when subjected to bending forces. A higher flexural modulus indicates greater stiffness and resistance to bending deformation, while a lower flexural modulus implies greater flexibility and ease of bending. To calculate the bending modulus, flexural stress and the bending strain are needed.

The flexural modulus, as defined by the ISO 178 standard, is determined by measuring the deflection of a sample at a specified point [24]. The deflection si is dependent on the geometry of the sample:

(1) s i = ε f i L 2 6 h ,

where ε fi is the bending strain, L is the support distance in the test apparatus in millimeters, and h is the thickness of the test specimen in millimeters.

The ISO standard specifies the values for the bending strain at which the deflection is determined. ε f1 and ε f2 are used to calculate s 1 and s 2, respectively:

(2) ε f 1 = 5 × 10 − 4 ,

and

(3) ε f 2 = 25 × 10 − 4 .

Flexural stress is the internal resistance a material exhibits when subjected to bending forces. It arises from the distribution of tension and compression along the cross-section of a specimen as it bends. The flexural modulus is calculated as follows:

(4) σ f = 3 F L 2 b h 2 ,

where F is the applied force in newton, L is the support distance in millimeters, b is the width of the test specimen in millimeters, and h is the height of the test specimen in millimeters.

The flexural stress is plotted against the flexural strain, as shown in Figure 4. The maximum flexural stress that a specimen can withstand during the bending test is called σ fM. It is calculated at the maximum applied force.

Figure 4 Stress–strain diagram of all tested materials. The individual graphs consist of averaged values of four measurements per material.
Figure 4

Stress–strain diagram of all tested materials. The individual graphs consist of averaged values of four measurements per material.

With the given bending strain and the calculated flexural modulus, the flexural modulus can be calculated as follows:

(5) E f = σ f 2 − σ f 1 ε f 2 − ε f 1 .

2.7 Calculation of the flexural creep modulus

The flexural creep modulus E t is a material property that describes how a material deforms over time when subjected to a constant bending stress [21]. It quantifies the material’s resistance to deformation under sustained bending loads. This modulus is measured by applying a constant bending stress to a specimen over an extended period and monitoring the resulting deformation:

(6) E t = L 3 F 4 b h 3 s t ,

where L is the initial distance, in millimeters, between the test specimen supports; F is the applied force, in newtons; b is the width, in millimeters, of the test specimen; h is the height, in millimeters, of the test specimen; and s t is the deflection, in millimeters, at mid-span at time t.

3 Results and discussions

3.1 Three-point bending test

Table 4 shows the results of the bending test according to ISO 178. The results in the table are organized according to increasing bending stiffness. If the results are compared with the tensile modulus of the data sheets in Table 1, the materials have a nearly similar sequence. The comparison indicates that the tensile modulus could serve as an indicator for the range in which the flexural modulus is located.

Table 4

Measured material properties: (sorted by flexural modulus, ascending)

No. Flexural modulus [MPa] Flexural strength [MPa] Maximum force [N]
1 ApolloX ASA 1822.1 50.2 82.3
2 TitanX ABS 2261.0 61.3 100.6
3 Prusament PLA 3554.9 99.6 163.4
5 CarbonX CF-ABS 3713.2 67.1 110.1
6 CarbonX CF-ASA 4083.3 78.8 129.3
4 GreenTEC Pro 4640.4 81.2 133.3
8 PC-HT-LCF 5777.2 137.9 137.0
7 GreenTEC Pro Carbon 6209.7 83.52 226.3

The variations of the flexural modulus between the materials are significant. The modulus of the strongest material is over three times higher than that of the weakest material. This difference is even more notable when comparing the non-mechanical properties of the materials. The GreenTEC Pro, which is particularly rigid, is made from renewable raw materials, is biodegradable, and has food approval. In contrast, printing ASA and ABS requires an extraction system for the printer’s build chamber due to the harmful gases released when the plastic is heated.

Figure 4 shows the curves of the three-point flexural test, which was conducted according to ISO 178. The bending stress is plotted against the bending strain. For materials such as ABS and ASA, which are tougher, the samples do not fracture but instead, they bend until they slip through the test device. However, the toughness of both materials is reduced by the presence of fiber reinforcement to such an extent that they fracture when reinforced with carbon fiber.

The measurements indicate that fiber reinforcement results in increased stiffness and reduced flexural strain in all tested materials (Table 5). The findings are consistent with those reported in the existing literature [25,26]. This effect is particularly pronounced in the ductile materials ABS and ASA. However, the PLA-based GreenTEC Pro, which is very stiff, experienced a smaller benefit from the fiber reinforcement.

Table 5

Improvement of the material properties by adding fiber reinforcements

Material Flexural strain Flexural modulus
Pure (%) Fiber (%) Improve (%) Pure Fiber Improve (%)
ABS 12.5 4 68 2261.0 3713.2 64.22
ASA 12.2 4.5 36.11 1822.1 4083.3 124.1
GreenTEC Pro 2.3 1.9 17.39 4640.4 6209.7 33.82

3.2 Long-term creep test

3.2.1 Deflection

Plastics typically experience an initial deflection followed by a slow creeping deformation. However, the three-point bending test does not adequately capture the latter due to its short duration. Therefore, the specimen’s deformation was assessed over a 7 day period. Table 6 presents the deflection of the specimens over time. The deflection at time zero corresponds to the initial deflection. After 1 hour, the deflection was measured again, as a greater change was expected at the beginning of the test. Subsequently, the deflection was determined every 24 h. Three samples could not be observed over the entire period. On average, the ASA specimens deformed after around 100 h to such an extent that they slipped through the test device. The GreenTEC Pro (GTP) and GreenTEC Pro Carbon samples spontaneously broke on average after 69 and 114 h, respectively.

Table 6

Deflection in mm versus time in hours, for each tested material

No. Time (h) deflection (mm) 0 1 24 48 72 96 120 144 168
1 ASA 4.0 5.0 7.5 9.5 11.0 14.5 — — —
2 ABS 3.0 3.0 3.1 3.8 4.0 4.0 4.0 4.0 4.0
3 PLA 2.1 2.1 2.1 2.1 2.2 2.2 2.2 2.5 3.0
5 ABS + CF 1.8 2.0 2.2 2.2 2.2 2.2 2.5 2.5 2.5
6 ASA + CF 1.5 2.0 2.1 2.2 2.2 2.2 2.2 2.2 2.2
4 GTP 1.1 1.3 1.7 2.0 — — — — —
8 PC HT LCF 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
7 GTP-Carbon 0.6 0.7 0.7 0.7 0.7 0.7 — — —

Sorted according to the last measured deflection in the decreasing order.

The ASA material exhibited significant deflection, ultimately slipping through the two support points. In contrast, the two GreenTEC Pro samples were very rigid and exhibited minimal bending, but eventually fractured spontaneously. Regarding the fiber-reinforced materials, it is noticeable that after an initial deflection phase, the test specimen exhibits minimal further yield. The only exception is the carbon fiber-reinforced ABS, which shows some change even after several days. Notably, PC HT LCF and GreenTEC Pro Carbon exhibit exceptional behavior, as they exhibit almost no deformation. The creep modulus (Figure 5) of the materials was calculated using the values measured in Table 6.

Figure 5 Creep modulus is a measure of the current stiffness, which is plotted over the test period of 168 h. As most materials exhibit significantly greater deformation in the initial phase than in the final phase, the time scale is plotted logarithmically.
Figure 5

Creep modulus is a measure of the current stiffness, which is plotted over the test period of 168 h. As most materials exhibit significantly greater deformation in the initial phase than in the final phase, the time scale is plotted logarithmically.

GTP and PC are both very stiff base materials. As can be seen in Table 6 and Figure 5, the two fiber-reinforced variants of these materials only show an initial deflection before no further creep occurs. In the case of the soft base material ASA, the fiber reinforcement also results in no further deformation occurring after 2 days under load. In contrast to the previously mentioned materials, the fiber reinforcement in ABS does not appear to cause the material to stabilize permanently. However, it is also conceivable that stabilization occurs at a later point in time. It should also be noted that GTP, which is actually stiffer, exhibits constant drift, while PLA barely creeps over 5 days. The reason for the sharp drop in PLA after 5 days is unclear. It is conceivable that this is a similar effect to that which leads to fracture in GTP and GTP Carbon. As expected, the softest material in the test, ASA, shows the most pronounced creep behavior and slips through the holder after around 4 days due to the large deflection.

3.2.2 Reverse deformation

The remaining deflection is an indication of whether the deformation of the sample under load is elastic or plastic. Figure 6 illustrates the specimens’ re-deformation after unloading. At the beginning of the test (time = 0 s), the samples were still under load.

Figure 6 Deflection of the samples was measured at different time intervals after unloading. The samples were unloaded at time zero, and the deflection was measured after 1, 10, 60, and 1,440 min.
Figure 6

Deflection of the samples was measured at different time intervals after unloading. The samples were unloaded at time zero, and the deflection was measured after 1, 10, 60, and 1,440 min.

The PC HT LCF sample did not show any permanent deformation after unloading the load. The graphs for ASA + CF and ABS indicate that there will be only minimal or no permanent deformation. It is unclear whether the deformation of PLA samples will revert. A longer testing period is required to determine this. The ABS + CF samples have likely undergone permanent deformation and will not return to their original shape. The ASA specimen, which slipped through the holder due to its severe deformation, initially showed a certain amount of re-deformation, but was hardly able to regenerate, compared to the severe deformation. No conclusions can be drawn regarding the GreenTEC-based materials from this test, as they broke into two pieces.

The comparison between the flexural modulus obtained from the three-point bending test (bold in Table 7) and the maximum deflection from the long-term creep test (italics in Table 7) indicates a correlation among the materials.

Table 7

Comparison of flexural modulus and bending strain form three-point bending test with the remaining deformation and the highest deflection from creep test

Flexural modulus [MPA] Bending strain [%] Highest deflection [mm] Remaining deflection [mm]
ApolloX ASA 1822.1 12.3 14.5 (failure) Deformation
TitanX ABS 2261.0 12.8 4.0 0.25
Prusament PLA 3554.9 4.1 3.0 1.5
CarbonX CF-ABS 3713.2 3.7 2.5 1.0
CarbonX CF-ASA 4083.3 4.6 2.2 0.5
GreenTEC Pro 4640.4 2.4 2.0 (failure) Brittle fracture
PC-HT-LCF 5777.2 3.5 1.0 0.0
GreenTEC Pro Carbon 6209.7 1.8 0.7 (failure) Brittle fracture

The samples were sorted according to the flexural modulus.

Assuming that the two broken materials, GreenTEC Pro and GreenTEC Pro Carbon, would have largely re-deformed, the remaining deformation of the samples could eventually be estimated from the flexural modulus. The ABS material is an exception due to its high elasticity, which causes significant deformation under load. However, it is also capable of re-deforming to a large extent. The test results suggest that a longer relaxation period should be selected for softer materials.

To investigate the suitability of GreenTEC Pro Carbon for technical applications, samples measuring 6 mm × 10 mm were printed instead of 4 mm × 10 mm. These samples were loaded with the same load, as in the previous test series, and with one and a half the load (7,500 g) in a second test. A constant deflection was measured while the samples were loaded, but no residual deformation was measurable after unloading.

4 Conclusion

A simple test method for analyzing the creep resistance of 3D-printing materials has been developed. This method allows to differentiate between plastic and elastic deformation. It enables users to test their materials themselves and compare them with other users. If a creep test cannot be conducted, the flexural modulus can serve as an indicator of creep strength. However, the flexural modulus cannot determine whether the creep deformation will be plastic or elastic. Therefore, it is recommended that the long-term creep test suggested here is performed, as it is easy to reproduce.

It was shown that fiber reinforcements have a positive effect on stiffness in all tested materials. However, it is also shown that fiber reinforcement usually, but not always, has a positive effect on creep resistance. Further investigations are necessary to clarify why ABS does not benefit from fiber reinforcement in terms of creep resistance. Additionally, it is important to investigate the effect of other printing parameters such as line width, line height, and printing temperature on stability.

The measurement data presented here show that FDM materials can be used to construct components that do not deform significantly or permanently under load, even over an extended period of time.

It is our conviction that the establishment of a publicly accessible material database would prove to be of considerable benefit to both users and manufacturers. Such a database would facilitate the contribution and sharing of material data by users, while also enabling material developers to access and benefit from this information. The website https://www.cpubenchmark.net/ illustrates a process whereby users assess the performance of a component in accordance with their own conditions and subsequently share the results with the wider community.

The objective of our study was to evaluate the performance of materials under laboratory-environmental conditions. However, it is also important to assess the behavior of these materials under diverse environmental conditions, such as varying temperature and humidity levels. A more comprehensive understanding of the practical applications of these materials could be achieved by investigating their creep resistance across a range of environmental factors.

With regard to fiber-reinforced composite materials, future research may benefit from exploring the influence of slower printing speeds, broader nozzle cones, and different printing temperatures. This could facilitate better interlayer bonding of the fibers, potentially enhancing the overall creep resistance of the printed parts.

  1. Funding information: The work was funded by the Bavarian State Ministry of Economic Affairs, Regional Development and Energy (StMWi) via the “Elektronische Systeme” program under the funding code DIE0191/01.

  2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results, and approved the final version of the manuscript. PH: conceptualization, methodology, visualization, validation and writing – original draft. LH: data acquisition, methodology, conceptualization and visualization. ME: critical revision, resources and writing – reviewing and editing. RB: guidance, resources, and validation.

  3. Conflict of interest: The authors state no conflict of interest.

  4. Data availability statement: Most datasets generated and analyzed in this study are comprised in this submitted article. The other datasets are available on reasonable request.

References

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Received: 2024-05-16
Revised: 2024-07-30
Accepted: 2024-08-23
Published Online: 2024-11-21

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/eng-2024-0084
Keywords for this article
3D-printing; FDM; material property; creep strength; additive manufacturing
Creative Commons
BY 4.0

Articles in the same Issue

  1. Regular Articles
  2. Methodology of automated quality management
  3. Influence of vibratory conveyor design parameters on the trough motion and the self-synchronization of inertial vibrators
  4. Application of finite element method in industrial design, example of an electric motorcycle design project
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  73. The optimal allocation of thyristor-controlled series compensators for enhancement HVAC transmission lines Iraqi super grid by using seeker optimization algorithm
  74. Numerical and experimental study of the impact on aerodynamic characteristics of the NACA0012 airfoil
  75. Effect of nano-TiO2 on physical and rheological properties of asphalt cement
  76. Performance evolution of novel palm leaf powder used for enhancing hot mix asphalt
  77. Performance analysis, evaluation, and improvement of selected unsignalized intersection using SIDRA software – Case study
  78. Flexural behavior of RC beams externally reinforced with CFRP composites using various strategies
  79. Influence of fiber types on the properties of the artificial cold-bonded lightweight aggregates
  80. Experimental investigation of RC beams strengthened with externally bonded BFRP composites
  81. Generalized RKM methods for solving fifth-order quasi-linear fractional partial differential equation
  82. An experimental and numerical study investigating sediment transport position in the bed of sewer pipes in Karbala
  83. Role of individual component failure in the performance of a 1-out-of-3 cold standby system: A Markov model approach
  84. Implementation for the cases (5, 4) and (5, 4)/(2, 0)
  85. Center group actions and related concepts
  86. Experimental investigation of the effect of horizontal construction joints on the behavior of deep beams
  87. Deletion of a vertex in even sum domination
  88. Deep learning techniques in concrete powder mix designing
  89. Effect of loading type in concrete deep beam with strut reinforcement
  90. Studying the effect of using CFRP warping on strength of husk rice concrete columns
  91. Parametric analysis of the influence of climatic factors on the formation of traditional buildings in the city of Al Najaf
  92. Suitability location for landfill using a fuzzy-GIS model: A case study in Hillah, Iraq
  93. Hybrid approach for cost estimation of sustainable building projects using artificial neural networks
  94. Assessment of indirect tensile stress and tensile–strength ratio and creep compliance in HMA mixes with micro-silica and PMB
  95. Density functional theory to study stopping power of proton in water, lung, bladder, and intestine
  96. A review of single flow, flow boiling, and coating microchannel studies
  97. Effect of GFRP bar length on the flexural behavior of hybrid concrete beams strengthened with NSM bars
  98. Exploring the impact of parameters on flow boiling heat transfer in microchannels and coated microtubes: A comprehensive review
  99. Crumb rubber modification for enhanced rutting resistance in asphalt mixtures
  100. Special Issue: AESMT-6
  101. Design of a new sorting colors system based on PLC, TIA portal, and factory I/O programs
  102. Forecasting empirical formula for suspended sediment load prediction at upstream of Al-Kufa barrage, Kufa City, Iraq
  103. Optimization and characterization of sustainable geopolymer mortars based on palygorskite clay, water glass, and sodium hydroxide
  104. Sediment transport modelling upstream of Al Kufa Barrage
  105. Study of energy loss, range, and stopping time for proton in germanium and copper materials
  106. Effect of internal and external recycle ratios on the nutrient removal efficiency of anaerobic/anoxic/oxic (VIP) wastewater treatment plant
  107. Enhancing structural behaviour of polypropylene fibre concrete columns longitudinally reinforced with fibreglass bars
  108. Sustainable road paving: Enhancing concrete paver blocks with zeolite-enhanced cement
  109. Evaluation of the operational performance of Karbala waste water treatment plant under variable flow using GPS-X model
  110. Design and simulation of photonic crystal fiber for highly sensitive chemical sensing applications
  111. Optimization and design of a new column sequencing for crude oil distillation at Basrah refinery
  112. Inductive 3D numerical modelling of the tibia bone using MRI to examine von Mises stress and overall deformation
  113. An image encryption method based on modified elliptic curve Diffie-Hellman key exchange protocol and Hill Cipher
  114. Experimental investigation of generating superheated steam using a parabolic dish with a cylindrical cavity receiver: A case study
  115. Effect of surface roughness on the interface behavior of clayey soils
  116. Investigated of the optical properties for SiO2 by using Lorentz model
  117. Measurements of induced vibrations due to steel pipe pile driving in Al-Fao soil: Effect of partial end closure
  118. Experimental and numerical studies of ballistic resistance of hybrid sandwich composite body armor
  119. Evaluation of clay layer presence on shallow foundation settlement in dry sand under an earthquake
  120. Optimal design of mechanical performances of asphalt mixtures comprising nano-clay additives
  121. Advancing seismic performance: Isolators, TMDs, and multi-level strategies in reinforced concrete buildings
  122. Predicted evaporation in Basrah using artificial neural networks
  123. Energy management system for a small town to enhance quality of life
  124. Numerical study on entropy minimization in pipes with helical airfoil and CuO nanoparticle integration
  125. Equations and methodologies of inlet drainage system discharge coefficients: A review
  126. Thermal buckling analysis for hybrid and composite laminated plate by using new displacement function
  127. Investigation into the mechanical and thermal properties of lightweight mortar using commercial beads or recycled expanded polystyrene
  128. Experimental and theoretical analysis of single-jet column and concrete column using double-jet grouting technique applied at Al-Rashdia site
  129. The impact of incorporating waste materials on the mechanical and physical characteristics of tile adhesive materials
  130. Seismic resilience: Innovations in structural engineering for earthquake-prone areas
  131. Automatic human identification using fingerprint images based on Gabor filter and SIFT features fusion
  132. Performance of GRKM-method for solving classes of ordinary and partial differential equations of sixth-orders
  133. Visible light-boosted photodegradation activity of Ag–AgVO3/Zn0.5Mn0.5Fe2O4 supported heterojunctions for effective degradation of organic contaminates
  134. Production of sustainable concrete with treated cement kiln dust and iron slag waste aggregate
  135. Key effects on the structural behavior of fiber-reinforced lightweight concrete-ribbed slabs: A review
  136. A comparative analysis of the energy dissipation efficiency of various piano key weir types
  137. Special Issue: Transport 2022 - Part II
  138. Variability in road surface temperature in urban road network – A case study making use of mobile measurements
  139. Special Issue: BCEE5-2023
  140. Evaluation of reclaimed asphalt mixtures rejuvenated with waste engine oil to resist rutting deformation
  141. Assessment of potential resistance to moisture damage and fatigue cracks of asphalt mixture modified with ground granulated blast furnace slag
  142. Investigating seismic response in adjacent structures: A study on the impact of buildings’ orientation and distance considering soil–structure interaction
  143. Improvement of porosity of mortar using polyethylene glycol pre-polymer-impregnated mortar
  144. Three-dimensional analysis of steel beam-column bolted connections
  145. Assessment of agricultural drought in Iraq employing Landsat and MODIS imagery
  146. Performance evaluation of grouted porous asphalt concrete
  147. Optimization of local modified metakaolin-based geopolymer concrete by Taguchi method
  148. Effect of waste tire products on some characteristics of roller-compacted concrete
  149. Studying the lateral displacement of retaining wall supporting sandy soil under dynamic loads
  150. Seismic performance evaluation of concrete buttress dram (Dynamic linear analysis)
  151. Behavior of soil reinforced with micropiles
  152. Possibility of production high strength lightweight concrete containing organic waste aggregate and recycled steel fibers
  153. An investigation of self-sensing and mechanical properties of smart engineered cementitious composites reinforced with functional materials
  154. Forecasting changes in precipitation and temperatures of a regional watershed in Northern Iraq using LARS-WG model
  155. Experimental investigation of dynamic soil properties for modeling energy-absorbing layers
  156. Numerical investigation of the effect of longitudinal steel reinforcement ratio on the ductility of concrete beams
  157. An experimental study on the tensile properties of reinforced asphalt pavement
  158. Self-sensing behavior of hot asphalt mixture with steel fiber-based additive
  159. Behavior of ultra-high-performance concrete deep beams reinforced by basalt fibers
  160. Optimizing asphalt binder performance with various PET types
  161. Investigation of the hydraulic characteristics and homogeneity of the microstructure of the air voids in the sustainable rigid pavement
  162. Enhanced biogas production from municipal solid waste via digestion with cow manure: A case study
  163. Special Issue: AESMT-7 - Part I
  164. Preparation and investigation of cobalt nanoparticles by laser ablation: Structure, linear, and nonlinear optical properties
  165. Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior
  166. The effect of urban environment on large-scale path loss model’s main parameters for mmWave 5G mobile network in Iraq
  167. Formatting a questionnaire for the quality control of river bank roads
  168. Vibration suppression of smart composite beam using model predictive controller
  169. Machine learning-based compressive strength estimation in nanomaterial-modified lightweight concrete
  170. In-depth analysis of critical factors affecting Iraqi construction projects performance
  171. Behavior of container berth structure under the influence of environmental and operational loads
  172. Energy absorption and impact response of ballistic resistance laminate
  173. Effect of water-absorbent polymer balls in internal curing on punching shear behavior of bubble slabs
  174. Effect of surface roughness on interface shear strength parameters of sandy soils
  175. Evaluating the interaction for embedded H-steel section in normal concrete under monotonic and repeated loads
  176. Estimation of the settlement of pile head using ANN and multivariate linear regression based on the results of load transfer method
  177. Enhancing communication: Deep learning for Arabic sign language translation
  178. A review of recent studies of both heat pipe and evaporative cooling in passive heat recovery
  179. Effect of nano-silica on the mechanical properties of LWC
  180. An experimental study of some mechanical properties and absorption for polymer-modified cement mortar modified with superplasticizer
  181. Digital beamforming enhancement with LSTM-based deep learning for millimeter wave transmission
  182. Developing an efficient planning process for heritage buildings maintenance in Iraq
  183. Design and optimization of two-stage controller for three-phase multi-converter/multi-machine electric vehicle
  184. Evaluation of microstructure and mechanical properties of Al1050/Al2O3/Gr composite processed by forming operation ECAP
  185. Calculations of mass stopping power and range of protons in organic compounds (CH3OH, CH2O, and CO2) at energy range of 0.01–1,000 MeV
  186. Investigation of in vitro behavior of composite coating hydroxyapatite-nano silver on 316L stainless steel substrate by electrophoretic technic for biomedical tools
  187. A review: Enhancing tribological properties of journal bearings composite materials
  188. Improvements in the randomness and security of digital currency using the photon sponge hash function through Maiorana–McFarland S-box replacement
  189. Design a new scheme for image security using a deep learning technique of hierarchical parameters
  190. Special Issue: ICES 2023
  191. Comparative geotechnical analysis for ultimate bearing capacity of precast concrete piles using cone resistance measurements
  192. Visualizing sustainable rainwater harvesting: A case study of Karbala Province
  193. Geogrid reinforcement for improving bearing capacity and stability of square foundations
  194. Evaluation of the effluent concentrations of Karbala wastewater treatment plant using reliability analysis
  195. Adsorbent made with inexpensive, local resources
  196. Effect of drain pipes on seepage and slope stability through a zoned earth dam
  197. Sediment accumulation in an 8 inch sewer pipe for a sample of various particles obtained from the streets of Karbala city, Iraq
  198. Special Issue: IETAS 2024 - Part I
  199. Analyzing the impact of transfer learning on explanation accuracy in deep learning-based ECG recognition systems
  200. Effect of scale factor on the dynamic response of frame foundations
  201. Improving multi-object detection and tracking with deep learning, DeepSORT, and frame cancellation techniques
  202. The impact of using prestressed CFRP bars on the development of flexural strength
  203. Assessment of surface hardness and impact strength of denture base resins reinforced with silver–titanium dioxide and silver–zirconium dioxide nanoparticles: In vitro study
  204. A data augmentation approach to enhance breast cancer detection using generative adversarial and artificial neural networks
  205. Modification of the 5D Lorenz chaotic map with fuzzy numbers for video encryption in cloud computing
  206. Special Issue: 51st KKBN - Part I
  207. Evaluation of static bending caused damage of glass-fiber composite structure using terahertz inspection
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