A review of the performance of polymer parts printed on fused deposition modelling under cyclic loading

Abstract

Fused deposition modelling (FDM) is one of the most promising and widely used additive manufacturing (AM) technologies. FDM is commonly used to fabricate simple to complex 3D parts from polymeric materials. Different 3D-printed polymeric components manufactured using FDM technology exhibit various mechanical and load-bearing properties. They are utilized in various industries, particularly the medical industry, for load-bearing applications in bio-implants. Therefore, it is crucial to understand the mechanical characteristics, especially the fatigue behaviour, of these 3D-printed parts under cyclic loadings. This paper focuses on the dynamic behaviour of 3D-printed polymeric parts produced through the FDM process and under different loading modes. First, the FDM mechanism, the various polymeric materials used in FDM, and the effective FDM parameters are briefly introduced. Then, the paper comprehensively covers one of the most important mechanical characteristics of 3D-printed parts for load-bearing applications: their fatigue life under different printing conditions and cyclic loadings. The most influential factors on the fatigue behaviour of polymers include the type of polymeric material, surrounding environmental conditions, cyclic loading conditions, the type of testing specimen, and the FDM printing parameters (such as raster angle, infill density, nozzle diameter, and nozzle temperature). In addition to the anisotropic behaviour reported by various studies on 3D-printed parts using FDM, it has been concluded that the layered structure (with a large number of interfaces between the raster) and the presence of microholes are two factors that weaken the fatigue strength of 3D-printed structures compared to other fabrication processes. These conditions can be exacerbated by choosing inappropriate printing parameters, and often, the failure mechanism in 3D-printed parts fabricated with FDM is delamination.

Keywords

Additive manufacturing delamination and failure mechanism fatigue life fused deposition modelling printing parameters

Introduction

Different components of industrial machines, vehicles, and medical implants frequently undergo repeated or cyclic loadings. These loadings result in cyclic stresses that can cause microscopic damage to the components and materials. Even at stresses below the ultimate material strength, these damages can accumulate due to continuous cyclic loadings and eventually develop into cracks or other macroscopic damages, leading to component failure. Therefore, it is important to study the fatigue life of components, which refers to the number of loading stresses or cycles that an element can sustain before failure occurs. Fatigue failure is a gradual process that is not easily observable. It slowly weakens the material, making it unable to withstand even stresses below the ultimate stress threshold.

The term ‘fatigue’ was first used in a book by French scientist J.V. Poncelet, who focused on machines. Since then, fatigue failure of various engineering parts has been the subject of engineering investigations for over 150 years. Many individuals and industries have extensively discussed fatigue, particularly concerning metallic parts, in response to failures in components such as gears, bridge girders, shafts, railway axles, and medical implants.¹ Despite the extensive research on the fatigue life of metallic parts, there has been a lack of comprehensive study and investigation into the fatigue life of polymers and thermoplastics, as well as their ability to undergo multiple melting and cooling cycles.

Thermoplastics are a group of engineering polymers that find wide applications in various industries due to their exceptional properties.^2,3 These materials can be recycled multiple times without any alteration to their chemical properties.⁴ In addition to their recyclability, thermoplastics are known for their high strength, formability, chemical resistance, hydraulic resistance (the ability to withstand pressure caused by volume flow through hydraulic components such as pipes and valves), flame resistance, and durability.⁵

There are various methods of producing polymeric components, the most important being plastic injection, forming processes, machining, and moulding. However, with the invention of additive manufacturing (AM) methods, the use of thermoplastics has surpassed metals and ceramics. Recently, researchers and industrialists have taken notice of polymeric parts fabricated through AM technologies.^6,7 The advantages of AM techniques in producing complex geometries have led to their widespread use in industries such as engineering, construction, medicine, electronics, and aerospace.⁸ As a result, their applications have increased over time. Additionally, compared to traditional production methods, AM processes generate minimal waste material and do not require heavy peripheral equipment (which refers to non-essential heavy devices or equipment connected externally to a host computer to extend its capabilities).⁹ Therefore, the cost and time of production, particularly for creating unique and customized parts with complex geometries, have been significantly reduced with the invention of additive manufacturing methods.^10,11

Based on the printing process mechanism and the material used, AM techniques can be categorized into seven main categories. One of the most popular categories is material extrusion, with the fused deposition modelling (FDM) process being the most well-known method. FDM is widely used in AM due to its simple mechanism and relatively low cost for producing complex parts.^12,13 Figure 1 shows the schematic of the FDM process.

According to the figure, thermoplastic filaments are the consumable materials. These filaments are heated in a chamber and then extruded in a semi-liquid form through a nozzle onto the printing bed.^14–17 The final shape or part is manufactured layer by layer through the extrusion of the melted filament based on the computer-aided design (CAD) model.

Although the mechanism of this method is straightforward, achieving the desired mechanical and physical properties can be difficult and challenging due to various effective parameters, such as material type, process input parameters, and loading conditions. Furthermore, FDM 3D printing has recently been used in bio-applications, including structures like implants that are subjected to cyclic loadings. Therefore, it is necessary to study the effect of different parameters on the mechanical properties, especially the fatigue life of 3D-printed parts.¹⁸

Therefore, in this paper, a comprehensive study of fatigue life in polymeric parts 3D-printed with FDM is reviewed and discussed for the first time. This study takes into account the material, printing parameters, and loading modes. To achieve this, the fatigue mechanism of polymers is thoroughly examined, along with a detailed analysis of the FDM process, its challenges, and previous research. Finally, the fatigue behaviour of polymers printed with FDM is discussed.

Fused deposition modelling

FDM is an AM technology that utilizes a simple layer-by-layer fabrication mechanism. It is more affordable than other 3D printing methods, making it a popular choice among users. Consequently, research in this field is extensive. However, while there has been limited interest in studying the dynamic behaviour of FDM-printed parts, the static behaviour of various thermoplastics, particularly ABS and PLA, under different loading modes has been extensively investigated in numerous studies. Therefore, further research is needed to explore the fatigue life of 3D-printed FDM parts. It is crucial to consider the materials used for FDM and the process parameters that can potentially impact the properties of the resulting 3D-printed FDM structures.

Fused deposition modelling materials

The raw materials used for FDM 3D printing are primarily commercial filaments. The number of materials capable of being used in this process is expanding due to developments in the field of FDM and the attention of researchers.^19,20 However, only certain materials with specific properties can be printed using FDM. These properties include but are not limited to, strength and stiffness. The printability of a material is influenced by its inherent properties and the printing parameters. Printability refers to a material's ability to form a 3D structure with acceptable fidelity and integrity. In other words, it is the suitability of a material to be used as a substrate in 3D printing. Therefore, printability is one of the factors that determine the strict selection of materials. Among the different materials used in FDM, polylactic acid (PLA), also known as poly (lactic acid) or polylactide, is the most widely used printable plastic filament material in FDM 3D printing. This is due to its low melting point, high strength, low thermal expansion, and good layer adhesion. However, PLA exhibits poor heat resistance unless it is annealed.

Another commonly used thermoplastic polymer in FDM is acrylonitrile butadiene styrene (ABS). When extruded into a filament, ABS becomes a suitable material for 3D printers. It is cheap, strong, has high stability, and can be post-processed in various ways, such as sanding, painting, glueing, filling, and chemical smoothing. Polycarbonates (PCs)²¹ are a group of thermoplastic polymers that contain carbonate groups in their chemical structures. They are widely used in 3D FDM printing to create solid plastic products that are durable. However, printing with PCs can be challenging because they have a higher melting point compared to ABS and PLA. Nylon,²² on the other hand, is a highly durable material with an excellent strength-to-flexibility ratio. It can be used as an alternative to standard PLA or ABS in FDM printing. The use of nylons in additive manufacturing not only provides new mechanical possibilities but also helps to reduce the weight of parts and gas emissions. Poly (methyl methacrylate (PMMA)^23,24 (a transparent durable thermoplastic), polycaprolactone (PCL)^25,26 (a biodegradable polyester with a low melting point), polyethylene terephthalate (PETG)^27–29 (the most common thermoplastic polymer resin of the polyester family), and thermoplastic polyurethane (TPU)^30,31 (a class of polyurethane plastics with many properties, including elasticity, transparency, and resistance to oil, grease, and abrasion) are among the recently developed polymers to be printed via the FDM process.

In addition to the intrinsic properties, printability is also influenced by the printing parameters mentioned earlier.³² Therefore, the following section will focus on the FDM printing parameters.

Fused deposition modelling printing parameters

Various FDM printing parameters affect the printing process and the resulting properties of 3D-printed parts. These parameters include nozzle temperature and diameter, infill density, bed temperature, printing speed, raster angle, printing orientation, and layer thickness. Changing any of these parameters can directly or indirectly impact the properties of the 3D-printed product.

Table 1 provides a summary of previous research on 3D-printed parts using the FDM process with different process parameters. ABS and PLA were the most commonly used materials in these studies. The process parameters that were varied to observe their effects on the printed parts included nozzle temperature, infill density, printing speed, layer thickness, air gap, raster width, support style, orientation, raster angle, and number of contours. The properties of interest that were studied included tensile strength, compressive strength, yield strength, density, build time, elongation, fracture behaviour, porosity, absorbed energy, impact strength, flexural strength, modulus, toughness, and hardness.

Table 1.

A summary of previous research considering printing parameters, mechanical and physical properties.

Material	Input printing parameters	Output properties	Results	Reference
PLA	Nozzle temperature	Tensile strength	The highest tensile strength was reported to be 47.0212 MPa at infill density of 100%, temperature of 210°C, and speed of 124.778 mm/s	⁵⁰
	Infill density
	Printing speed
PLA	Nozzle temperature	Tensile strength	Increasing layer thickness leads to an improved strength of specimens and build time, while, increasing part weight. Infill percentage is the second major parameter influencing part characteristics.	⁵¹
	Infill density	Density		⁵¹
	Layer thickness	Build time	Increasing infill percentage at low extruder temperatures and increasing extruder temperature at low infill percentages end up producing more tough specimens
	Layer thickness	Elongation
PLA-Bronz	Nozzle temperature	Tensile strength	Higher layer thickness and increased infill percentage led to better mechanical properties.	⁵²
	Infill density	Density
	Layer thickness	Build time	The optimized printed Br-PLA specimen achieved with a layer thickness of 0.25 mm, 15.20 infill percentage, and 222.82°C extruder temperature could resist more than 1000 N
		Elongation
		Fracture mechanism
ABS	Air gap	Yield strength	Air gap and raster width as the most significant parameters in affecting the porosity and mechanical properties of the ABS scaffold structures.	⁵³
	Raster width	Compressive strength	The relationship between scaffolds' mechanical properties and porosity was determined to be logarithmic, with the best mechanical properties observed in scaffolds of low porosity
	Orientation	Porosity
ABS	Layer thickness	Build time	The optimum level of process parameters for build time was: Layer thickness-0.3302 mm, infill density-sparse low density, and support style-smart.	⁵⁴
	Infill density	Surface roughness	The optimum level of process parameter for surface roughness was: Layer thickness-0.254 mm, infill density-sparse low density, and support style-smart.
	Support style	Surface roughness	Layer thickness was highest influencer on surface roughness
ABS	Layer thickness	Build time	A decrease in the fill density and shell thickness, and an increase in the layer thickness and feed rate decreased the measurable properties	⁵⁵
	Printing speed	Consumables
	Infill density	Absorb energy
ABS	Orientation	Compressive strength	The sample with 80% infill gyroid pattern at 0.2 mm layer thickness and 90° build orientation provides the compressive strength close to solid part of ABS	⁵⁶
	Layer thickness	Consumables
	Infill density	Consumables
ABS	Layer thickness	Tensile strength	Infill density and layer thickness were most significant factor	⁵⁷
	Infill density
	Infill pattern
ABS	Layer thickness	Tensile strength	Zero air gap will improve the diffusion between the adjacent rasters and reduces the heat dissipation and total bonding area.	⁵⁸
	Orientation	Tensile strength
	Air gap	Impact strength	An increase in number of layers increases the number of heating and cooling cycles and induces residual stress, leading to distortion, interlayer cracking and part delamination or fabrication failure and decreased strength
	Raster angle	Impact strength
	Raster width	Flexural strength
ABS	Orientation	Tensile strength	A negative air gap significantly enhances the tensile strength.	⁵⁹
	Air gap		Smaller raster widths improve tensile strength.
	Raster angle		Zero part orientation leads to the maximum tensile strength.
	Raster width		Increasing raster angle also improves tensile strength
ABS	Layer thickness	Tensile strength	The optimum parameters for 3D printing using ABS are 80% infill percentage, 0.5 mm layer thickness, and 65° raster angle.	⁶⁰
	Layer thickness	Yield strength
	Raster angle	Elongation	The optimum ultimate tensile strength, elastic modulus, yield strength, fracture strain, and toughness (energy absorption) are 31.57 MPa, 774.50 MPa, 19.95 MPa, 0.094 mm/mm, and 2.28 Jm⁻³, respectively
	Infill density	Toughness
ABS-PC	Layer thickness	Toughness	The layer thickness, the air gap, and the number of contours have the largest impact on dynamic mechanical properties. The optimal parameters for maximum dynamic mechanical properties were found to be layer thickness of 0.3302 mm, air gap of 0.00 mm, raster angle of 0.0°, build orientation of 0.0°, road width of 0.4572 mm, and 10 contours	⁶¹
	Raster angle	Toughness
	Air gap	Storage modulus
	Orientation	Storage modulus
	Number of contours	Loss modulus
	Raster width	Loss modulus
Nylon	Printing speed	Tensile strength	Infill percentage of 100% resulted in the maximum hardness and strength.	⁶²
	Printing speed	Flexural strength
	Infill density	Impact strain	Fill density had the highest contribution factor
	Layer thickness	Hardness	Fill density had the highest contribution factor
Nylon	Air gap	Flexural strength	Zero air gap increased flexural strength	⁶³
	Raster angle
	Orientation
PEEK	Nozzle temperature	Tensile strength	The best properties were at 400°C with a printing speed of 30 mm/s, 0.15 mm layer thickness and raster orientation of [0°/15°/−15°]	⁶⁴
PEEK	Printing speed	Elongation		⁶⁴

However, it is evident from Table 1 that less attention has been given to investigating the fatigue life of components that are 3D-printed using the FDM process.

Fatigue life of parts fabricated using fused deposition modelling technology

Fatigue occurs when a structural element is subjected to cyclic stress and may result in failure at much lower stresses than the material's ultimate strength.³³ Traditionally, metals have always been used under cyclic loadings, but recent developments in polymeric materials and their fabrication methods have enabled their more comprehensive applications, especially in load-bearing situations.³⁴ Polymeric materials are now employed in various industries, including passenger aircraft, cars, and medical implants. Therefore, studying and understanding their fatigue behaviour is crucial in determining their long-term durability and reliability.³⁵ Consequently, more attention needs to be paid to the fatigue life of 3D-printed structures made from such polymers.

Fatigue mechanism for polymers

The theory behind fatigue failure in polymers revolves around the growth of inherent damages and defects until they reach a critical point. This process is greatly influenced by factors such as the type of polymeric material, surrounding environmental conditions, cyclic loading conditions, and the type of testing specimen.

For example, when subjected to high cyclic loadings, polymers experience thermal softening. This occurs because, at higher frequencies, polymers can melt and become softened. Figure 2 provides a visual representation of each influential factor on the fatigue life of polymers. Figure 3 illustrates cyclic loading, which involves repeatedly applying stress levels that fluctuate between a constant maximum and minimum, a concept known as “constant amplitude stressing.”

Polymers are viscoelastic and heat-sensitive, making them prone to melting and thermal rupture under high loading frequencies and temperatures. Fatigue failure in polymers begins with the initiation of micro defects and crazing in areas with high-stress concentrations.³⁶ Crazing refers to the formation of a network of fine cracks on the surface of a material resulting from internal and external surface defects, voids, and poorly bonded matrix interfacial zones. Crazing significantly impacts mechanical stability and strength, leading to deformation. The application of cyclic loads leads to plastic deformation and the propagation of cracks in polymeric materials until they reach a critical size, causing sudden failure. To control and delay crack propagation and fatigue failure in polymers, reinforcements such as fibres and fillers can be used. The characteristics of these reinforcements depend on their type, length, fibre orientation, and bonding/debonding behaviour. Fibre debonding is one mechanism of fatigue failure in polymers, along with delamination, separation of fibre layers, and matrix cracking. The fatigue failure of polymers occurs in three stages, starting with fibre debonding and progressing to complete failure. In the first stage, fibres tend to debond from the matrix in weaker bond regions, misaligned fibre regions, or from defected surfaces (voids and pores). In the second stage, fibres become completely delaminated from the matrix. Finally, in the third stage, damage and cracks propagate until they reach a critical point, resulting in fatigue failure.³⁷

Fatigue test standard for polymeric structures

Various ASTM standards are available for fatigue tests based on the material type, such as metals and polymers. However, for polymers, tests are conducted under cyclic compression, tension, bending, torsion loadings, or a combination of these loadings, such as tension-tension, compression-tension/compression, and so on. Uniaxial loadings, such as tension to tension, tension to compression, compression to tension, or strain-controlled modes, are the most frequently used loading/unloading conditions for studying the fatigue behaviour of polymeric materials.³⁸ Table 2 summarizes the different types of fatigue test standards used for various kinds of polymeric materials. Other fatigue tests, such as biaxial, triaxial, multiaxial, bending, and torsional tests, can also be used, but they are less common for evaluating the fatigue of polymers compared to uniaxial tests.

Table 2.

Fatigue test standards for polymeric materials.

Test type	Standard	Material
Uniaxial fatigue (tension or compression)	ASTM D7791	Polymer
Tension fatigue	ASTM D3479	Polymer matrix composite
Uniaxial flexural fatigue (three- or four-point bending)	ASTM D7774	Polymers
Fatigue delamination growth	ASTM D6115	Polymer matrix composite
Statistical analyses of fatigue data	ASTM E739	Metals/polymers
Strain-controlled fatigue – uniaxial forces	ASTM E606	Homogeneous materials
Lamina/laminate dynamic properties	ASTM D4762	Polymer matrix composite
Bearing fatigue response	ASTM D6873	Polymer matrix composite
Open hole fatigue (tension-tension, compression-compression, or tension-compression cyclic loading)	ASTM D7615	Polymer matrix composite
Fatigue crack propagation – notched condition (tension-tension)	ISO 15850	Polymers
Axial tensile fatigue test/flexural bend test (tension-tension)	ISO 13003	Polymer matrix composite

Since the mentioned fatigue tests require multiple specimens and analysing the results is time-consuming, another method called the thermographic method (TM) was introduced by La Rosa and Risitano in 2000. This technique utilizes temperature variation to plot S-N curves (fatigue curves) and estimate the fatigue life of components, especially for polymers that are sensitive to heat.

Fatigue of the polymeric components fabricated using fused deposition modelling technology

Among the different methods of fabricating polymers, FDM, as a 3D printing method, can produce polymers with much better properties than other conventional manufacturing methods. However, additively manufactured polymers suffer from inevitable voids, defects, and imperfections that are severely dependent on FDM printing conditions and the type of polymeric material. Moreover, since FDM is an AM technology that adds polymer layer-by-layer based on the printing direction, the resultant polymeric structure is anisotropic, meaning it does not have the same strength in all directions. Figure 4 illustrates various FDM parameters, such as the filament, build parameters, part position, and surrounding environment, which can affect the fatigue behaviour of printed polymers.

Due to recent interest in using FDM-printed polymers in various load-bearing applications, efforts have been made to investigate the fatigue behaviour of these 3D-printed polymeric materials. PLA is considered one of the most commonly used polymers in different applications, including medical ones. Therefore, Afrose et al. conducted a study to examine the impact of FDM build direction on the fatigue characteristics of FDM-printed dog-bone-shaped PLA specimens. They used FDM to create test specimens in three build directions: X (0°), Y (90°), and Z (45°). These specimens were subjected to both uniaxial tension static and cyclic loading.

Among the different build orientations, the researchers observed that FDM-printed PLA specimens in the 45° build direction exhibited higher fatigue life and a better ability to store strain energy compared to the specimens in the other two directions. Interestingly, the results also showed that specimens with the highest fatigue life did not necessarily have the highest ultimate tensile strength. This was because the PLA polymers printed in the X direction had a higher tensile strength than those in the Y and 45° orientations, indicating the anisotropic behaviour of the printed parts (see Figure 5).³⁹ According to Figure 5(d), the 3D-printed PLA sample in the X direction had the lowest fatigue life, while the one in the 45° direction had the highest fatigue life. On the other hand, based on Figure 5(e), the sample in the X direction had the highest tensile strength, while the one in the Y direction had the lowest tensile strength. Therefore, it is evident that build orientation does not have the same effect on the properties of the printed parts using FDM technology.

The same results (anisotropic behaviour) were reported by Padzi et al. on the fatigue characteristics of 3D-printed ABS parts with the help of tensile strength and based on the raster angle.⁴⁰ They conducted tension-tension fatigue cycling tests according to ASTM standard D7791-12, with a stress ratio 0.01. Their results showed that both the tensile and fatigue performance of ABS components fabricated using FDM technology exhibited anisotropic behaviour. The specimens with a raster orientation of +45/−45° showed the longest fatigue life, while those with a raster orientation of 0° had the highest tensile strength.

In contrast, the effect of build orientation on the fatigue life of Ultem 9085 differed from that of PLA and ABS. Fischer and Schoppner studied the fatigue life of Ultem 9085 components fabricated and printed via FDM. They found that parts built in the X direction had a higher fatigue life compared to the Y and Z directions.

ULTEM 9085 filament is a high-performance thermoplastic with superior physical and mechanical properties manufactured using FDM technology. It is one of the most robust FDM materials, and its high-strength-to-weight ratio makes it suitable for high-strength/low-weight applications. Fischer and Schoppner prepared their samples in the X, Y, and Z directions according to ASTM D638 standards and conducted the tests at room temperature. Their results showed that the test specimens in the X and Y directions developed cracks in the shoulder area before complete failure. For example, in the case of samples in the X direction, these cracks mainly occurred in the first or second stages of cross-section enlargement and propagated until the specimen failed (Figure 6). Figure 7 also shows the S-N curves obtained from their study data.⁴¹

It is clear from Figure 7 that samples fabricated in the X direction had higher fatigue life.

Such anisotropic behaviour in the mechanical properties of 3D-printed polymeric materials fabricated using FDM technology has also been observed in other studies, including the work by Ziemian et al.⁴² In their study, they examined the tensile and fatigue behaviour of ABS components fabricated using FDM technology. Tensile and fatigue tests were conducted on dog-bone-shaped specimens prepared according to the ASTM D638-03 standard, with the FDM ABS components printed in four different raster orientations (54). Figure 8 illustrates the four raster orientations and the corresponding samples used in their study for the tensile and fatigue tests. Notably, Figure 8(B) clearly demonstrates that the fatigue life of the parts printed at different raster angles varies.

He and Khan⁴³ investigated the effect of FDM printing parameters on the fatigue life of ABS parts printed using FDM under dynamic thermo-mechanical loads. They tested different building orientations (0°, ±45°, and 90°), nozzle sizes (0.4, 0.6, and 0.8 mm), and three-layer thicknesses (0.05, 0.1, and 0.15 mm) to observe their impact on the fatigue behaviour of the parts and determine the optimal conditions. The experimental study was conducted at temperatures ranging from 50 to 70°C. According to their results, the samples fabricated with a 0° building orientation, 0.8 mm nozzle size, and 0.15 mm layer thickness exhibited a higher fatigue life. They also reported that increasing nozzle size and layer thickness improved fatigue performance.

Gomez-Gras et al. also conducted a study on the fatigue characteristics of FDM-printed PLA parts. They examined the effect of four printing parameters: infill pattern and density, velocity, nozzle diameter, and layer height on the fatigue behaviour of cylindrical-shaped specimens. According to their findings, infill density had the most significant influence on the fatigue performance of FDM-printed PLA. Nozzle diameter and layer height ranked second and third in terms of impact. However, the printing velocity had either no effect or a negligible one. Figure 9 displays various images of the broken areas of the specimens after the fatigue tests, captured using a MOTIC SMC binocular loupe equipped with a MOTICAM three digital camera. The researchers observed that cracks consistently initiated near the first or last printed layer in all cases (Figure 9(A)). This suggests that fibres act as concentration zones at the curved areas where cracks start and propagate.⁴⁴ Another study on the fatigue behaviour evaluation of 3D-printed PLA parts using the FDM process was done by Dadashi and his colleague Azadi. They examined the impact of nozzle diameters, extruder temperature, and print speed on the fatigue life of the printed PLA parts. They found that reducing the nozzle diameter and printing temperature enhanced the fatigue life.⁴⁵ This same finding was also reported by Yankin et al.,⁴⁶ who studied the fatigue characteristics of ABS and Nylon components printed using FDM. Their results showed that Nylon had better fatigue characteristics compared to ABS under the same printing conditions. Additionally, reducing the nozzle diameter for both materials increased the fatigue life.⁴⁶

The raster angle or orientation is a geometrical parameter that affects the mechanical properties and failure mechanism in the FDM process. In recent years, selecting optimal parameters and considering the effect of anisotropy has become a fundamental challenge in printed parts. Kiendl's research demonstrated that by changing the pattern and direction of printing for PLA material, it is possible to control the mechanical properties and determine the failure mechanism.⁴⁷ They found that the anisotropy, or difference in mechanical properties in different directions, is much less for the 90° alternating infill angle compared to the unidirectional infill angle. Additionally, by decreasing the raster angle relative to the loading direction, more favourable mechanical properties can be achieved.

The failure mechanism during fatigue can be divided into two general categories: tearing of rasters and delamination. Delamination can occur within a single layer, between rasters, or between two rasters in different layers. Due to the layered structure of FDM-printed parts, the delamination mechanism is typically more dominant in fatigue tests, particularly in bending loading modes. As mentioned, failure in cyclic loading occurs during the stages of microcrack formation, growth, and joining. Cracks tend to form earlier in vulnerable and weaker areas, such as layered structures, composites, and welded joints. The interface is often the initial site for the failure mechanism to initiate.⁴⁸ In fact, weak adhesion between layers or structures in these particular arrangements acts as a weak point and stress concentration compared to a continuous structure. In printed parts, samples are made by placing a raster with a diameter and width of less than 0.5 mm, which creates numerous interfaces for each part. A layered structure with many vulnerable points at the interface is ideal for printing parts, but it heavily relies on printing conditions and parameters that are not accessible with FDM. According to the FDM mechanism, the molten thermoplastic cools rapidly after the address layer, causing the raster to shrink and lose continuity. These factors result in microholes and voids at the raster interfaces. Moreover, the holes can become larger and more noticeable under the influence of printing parameters. For instance, high temperature, high speed, and a large nozzle diameter increase the feeding rate, leading to a reduction in microhole density. In summary, in the FDM process, the layered structure (with a large number of interfaces between rasters) and the presence of microholes are two factors that weaken fatigue strength. These conditions can be worsened by selecting inappropriate printing parameters, often resulting in delamination as the failure mechanism in 3D-printed parts with FDM.

Conclusion

The present review paper summarizes the fundamental principles of fatigue life evaluation and provides more information on the fatigue life of 3D-printed polymers using the fused deposition modelling (FDM) method. FDM is an additive manufacturing technique that fabricates parts layer by layer. Although FDM has advantages over other conventional fabrication methods for polymers, further research is needed on the mechanical properties, particularly the fatigue life, of components printed using this method. With the increasing use of polymeric materials in industrial and medical applications, it is important to investigate their ability to withstand cyclic loadings or their fatigue life. This paper focuses on evaluating the fatigue life of polymers printed via FDM and provides information on fatigue test standards and the polymers that have been studied. Among the different polymers, ABS and PLA components fabricated using FDM technology are the most widely used and studied in terms of their fatigue life and the impact of printing parameters on their fatigue behaviour. The FDM printing parameters have a significant effect on the fatigue life of the resulting polymeric components, with building orientation and raster angle having a greater impact than other parameters. However, there is still a need for a more comprehensive investigation into the effect of FDM printing parameters on the quality and properties of printed parts.

Furthermore, since polymeric materials are considered viscoelastic, their fatigue life is reduced in high-temperature environments. Therefore, more attention should be given to FDM and the fatigue test process conducted at various temperatures. Defect formation is another common issue during FDM, leading to cracks and stress concentrations that affect the fatigue behaviour of the printed part. Therefore, optimizing FDM printing parameters to enhance mechanical properties, microstructure, and fatigue life while reducing defects is highly important. The layered structure, with a large number of interfaces between the raster, and the presence of microholes are two factors that weaken fatigue strength. These conditions can be worsened by choosing inappropriate.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Shaanxi Province Department of Science and Thechnology (2022KXJ-163), the Initial Scientific Research Fund for Special Zone Talents (XJ19T01).

Ethical statement

ORCID iD

Shaoguo Zhang"> https://orcid.org/0000-0003-4026-3924

References

Dowling

. Mechanical behavior of materials: engineering methods for deformation, fracture, and fatigue. Indianapolis, Indiana: Pearson Education Limited, 2013, pp. 936.

Xie

Yang

, et al. A review of thermoplastic polymer foams for functional applications. J Mater Sci 2021; 56: 11579–11604. DOI: 10.1007/s10853-021-06034-6.

Chen

Huang

, et al. Preparation and characterization of coaxial electrospun thermoplastic polyurethane/collagen compound nanofibers for tissue engineering applications. Colloids Surf B Biointerfaces 2010; 79: 315–325. DOI: 10.1016/j.colsurfb.2010.03.043.

Rahmatabadi

Aberoumand

Soltanmohammadi

, et al. Toughening PVC with biocompatible PCL softeners for supreme mechanical properties, morphology, shape memory effects, and FFF printability. Macromol Mater Eng 2023; 308: 2300114.

Mallick

. Thermoplastics and thermoplastic–matrix composites for lightweight automotive structures. Mater Des Manuf Light Veh 2021: 187–228.

Chen

Wang

, et al. Recent progress on 3D-printed polylactic acid and its applications in bone repair. Adv Eng Mater 2020; 22: 1901065.

Akhoundi

Behravesh

Bagheri Saed

. Improving mechanical properties of continuous fiber-reinforced thermoplastic composites produced by FDM 3D printer. J Reinf Plast 2018; 38: 99–116. DOI: 10.1177/0731684418807300.

Soleyman

Aberoumand

Rahmatabadi

, et al. Assessment of controllable shape transformation, potential applications, and tensile shape memory properties of 3D printed PETG. J Mater Res Technol 2022; 18: 4201–4215.

Rahmatabadi

Soltanmohammadi

Aberoumand

, et al. Development of pure poly vinyl chloride (PVC) with Excellent 3D printability and macro- and Micro-structural properties. Macromol Mater Eng 2023; 308: 2200568.

10.

Das

Chatham

Fallon

, et al. Current understanding and challenges in high temperature additive manufacturing of engineering thermoplastic polymers. Addit Manuf 2020; 34: 101218. DOI: 10.1016/j.addma.2020.101218.

11.

Rahmatabadi

Aberoumand

Soltanmohammadi

, et al. A new strategy for achieving shape memory effects in 4D printed two-layer composite structures. Polym 2022; 14: 5446.

12.

Popescu

Zapciu

Amza

, et al. FDM process parameters influence over the mechanical properties of polymer specimens: a review. Polym Test 2018; 69: 157–166.

13.

Rahmatabadi

Aberoumand

Soltanmohammadi

, et al. 4D printing-encapsulated polycaprolactone–thermoplastic polyurethane with high shape memory performances. Adv Eng Mater 2023; 25: 2201309.

14.

Gurrala

Regalla

. Part strength evolution with bonding between filaments in fused deposition modelling. Virtual Phys Prototyp 2014; 9: 141–149. DOI: 10.1080/174527592014913400.

15.

Abdul Haq

Wahab

Wahid

. Fused deposition modeling of PCL/HA/MMT biocompatible polymer nano-composites. Adv Struct Mater 2016; 61: 23–32.

16.

Kačergis

Mitkus

Sinapius

. Influence of fused deposition modeling process parameters on the transformation of 4D printed morphing structures. Smart Mater Struct 2019; 28. DOI: 10.1088/1361-665X/ab3d18.

17.

Fernandez-Vicente

Calle

Ferrandiz

, et al. Effect of Infill parameters on tensile mechanical behavior in desktop 3D printing. 3D Print Addit Manuf 2016; 3: 183–192.

18.

Niu

Zhu

, et al. Defect tolerant fatigue assessment of AM materials: size effect and probabilistic prospects. Int J Fatig 2022; 160: 106884.

19.

Rahmatabadi

Ghasemi

Baniassadi

, et al. 4D printing of PLA-TPU blends: effect of PLA concentration, loading mode, and programming temperature on the shape memory effect. J Mater Sci 2023; 58: 7227–7243.

20.

Aberoumand

Soltanmohammadi

Rahmatabadi

, et al. 4D printing of polyvinyl chloride (PVC): a detailed analysis of microstructure, programming, and shape memory performance. Macromol Mater Eng 2023; 308: 2200677.

21.

Masood

Mau

Song

. Tensile properties of processed FDM polycarbonate material. In: Materials science forum. Aedermannsdorf, Switzerland: Trans Tech Publications, 2010, pp. 2556–2559.

22.

Moradi

Aminzadeh

Rahmatabadi

, et al. Statistical and experimental analysis of process parameters of 3D Nylon printed parts by fused deposition modeling: response surface modeling and optimization. J Mater Eng Perform 2021; 30: 5441–5454.

23.

Kotz

Mader

Dellen

, et al. Fused deposition modeling of microfluidic chips in polymethylmethacrylate. Micromachines 2020; 11: 873. DOI: 10.3390/mi11090873.

24.

Bressan

Adamo

Quero

, et al. A simple procedure to produce FDM-based 3D-printed microfluidic devices with an integrated PMMA optical window. Anal Methods 2019; 11: 1014–1020. DOI: 10.1039/c8ay02092b.

25.

Mohd Pu’ad

NAS

Abdul Haq

Mohd Noh

, et al. Review on the fabrication of fused deposition modelling (FDM) composite filament for biomedical applications. Mater Today Proc 2020; 29: 228–232.

26.

Haryńska

Kucinska-Lipka

Sulowska

, et al. Medical-grade PCL based polyurethane system for FDM 3D printing-characterization and fabrication. Materials 2019; 16. DOI: 10.3390/ma12060887.

27.

Dolzyk

Jung

. Tensile and fatigue analysis of 3D-printed polyethylene terephthalate glycol. J Fail Anal Prev 2019; 19: 511–518.

28.

Soleyman

Aberoumand

Soltanmohammadi

, et al. 4D printing of PET-G via FDM including tailormade excess third shape. Manuf Lett 2022; 33: 1–4.

29.

Soleyman

Rahmatabadi

Soltanmohammadi

, et al. Shape memory performance of PETG 4D printed parts under compression in cold, warm, and hot programming. Smart Mater Struct 2022; 31: 085002.

30.

Wang

Yang

Lin

, et al. Research of TPU materials for 3D printing aiming at non-pneumatic tires by FDM Method. Polym 2020; 12: 2492.

31.

Xiao

Gao

. The manufacture of 3D printing of medical grade TPU. Prog Addit Manuf 2017; 2: 117–123.

32.

Yaman

Ekşi

Karabeyoğlu

, et al. Effect of build orientation on tribological and flexural properties of FDM-printed composite PLA parts. J Reinforc Plast Compos. 2023. DOI: 10.1177/07316844231157790/ASSET/IMAGES/LARGE/10.1177_07316844231157790-IMG01JPEG.

33.

Zhu

Luo

, et al. Size effect in fatigue modelling of defective materials: Application of the calibrated weakest-link theory. Int J Fatig 2022; 165: 107213.

34.

Liao

Zhu

Keshtegar

, et al. Probabilistic framework for fatigue life assessment of notched components under size effects. Int J Mech Sci 2020; 181: 105685.

35.

Xin

. Durability and reliability in diesel engine system design. Diesel Engine Syst Des 2013: 113–202.

36.

Dudescu

Racz

Popa

. Effect of infill pattern on fatigue characteristics of 3D printed polymers. Mater Today Proc 2023; 78: 263–269.

37.

Shanmugam

Das

Babu

, et al. Fatigue behaviour of FDM-3D printed polymers, polymeric composites and architected cellular materials. Int J Fatig 2021; 143: 106007.

38.

Bermudo Gamboa

Martín-Béjar

Javier Trujillo Vilches

, et al. Fatigue behavior analysis in reinforced PLA parts manufactured by FDM: Key Engineering Materials, 2023. https://riuma.uma.es/xmlui/handle/10630/27269 (accessed 8 September 2023).

39.

Afrose

Masood

Iovenitti

, et al. Effects of part build orientations on fatigue behaviour of FDM-processed PLA material. Prog Addit Manuf 2016; 1: 21–28.

40.

Padzi

Bazin

Muhamad

WMW

. Fatigue Characteristics of 3D Printed Acrylonitrile Butadiene Styrene (ABS). IOP Conf Ser Mater Sci Eng 2017; 269: 012060.

41.

Fischer

Schöppner

. Fatigue behavior of FDM parts manufactured with ultem 9085. JOM (J Occup Med) 2017; 69: 563–568.

42.

Ziemian

Okwara

Ziemian

. Tensile and fatigue behavior of layered acrylonitrile butadiene styrene. Rapid Prototyp J 2015; 21: 270–278.

43.

Khan

. Effects of printing parameters on the fatigue behaviour of 3D-printed ABS under dynamic thermo-mechanical loads. Polym 2021; 13: 2362.

44.

Gomez-Gras

Jerez-Mesa

Travieso-Rodriguez

, et al. Fatigue performance of fused filament fabrication PLA specimens. Mater Des 2018; 140: 278–285.

45.

Azadi

Dadashi

Dezianian

, et al. High-cycle bending fatigue properties of additive-manufactured ABS and PLA polymers fabricated by fused deposition modeling 3D-printing. Forces Mech 2021; 3: 100016.

46.

Yankin

Serik

Danenova

, et al. Optimization of fatigue performance of FDM ABS and nylon printed parts. Micromachines 2023; 14: 304. DOI: 10.3390/MI14020304.

47.

Kiendl

Gao

. Controlling toughness and strength of FDM 3D-printed PLA components through the raster layup. Compos B Eng 2020; 180: 107562.

48.

Papon

Haque

. Tensile properties, void contents, dispersion and fracture behaviour of 3D printed carbon nanofiber reinforced composites. J Reinf Plast Compos 2018; 37: 381–395. DOI: 10.1177/0731684417750477.

49.

Solomon

Sevvel

Gunasekaran

. A review on the various processing parameters in FDM. Mater Today Proc 2021; 37: 509–514. DOI: 10.1016/j.matpr.2020.05.484.

50.

Deshwal

Kumar

Chhabra

. Exercising hybrid statistical tools GA-RSM, GA-ANN and GA-ANFIS to optimize FDM process parameters for tensile strength improvement. CIRP J Manuf Sci Technol 2020; 31: 189–199. DOI: 10.1016/j.cirpj.2020.05.009.

51.

Moradi

Meiabadi

Kaplan

. 3D Printed parts with honeycomb internal pattern by fused deposition modelling; experimental characterization and production optimization. Met Mater Int 2019; 25: 1312–1325.

52.

Moradi

Karami Moghadam

Shamsborhan

, et al. The synergic effects of FDM 3D printing parameters on mechanical behaviors of bronze poly lactic acid composites. J Compos Sci 2020; 4: 17.

53.

Chin Ang

Fai Leong

Kai Chua

, et al. Investigation of the mechanical properties and porosity relationships in fused deposition modelling-fabricated porous structures. Rapid Prototyp J 2006; 12: 100–105.

54.

Wankhede

Jagetiya

Joshi

, et al. Materials today: proceedings experimental investigation of FDM process parameters using Taguchi analysis. Mater Today Proc 2020; 27: 2117–2120.

55.

Al-Ghamdi

. Sustainable FDM additive manufacturing of ABS components with emphasis on energy minimized and time efficient lightweight construction. Int J Light Mater Manuf 2019; 2: 338–345.

56.

Dev

Srivastava

. Experimental investigation and optimization of FDM process parameters for material and mechanical strength. Mater Today Proc 2020; 26: 1995–1999.

57.

Srinivasan

Pridhar

Ramprasath

, et al. Prediction of tensile strength in FDM printed ABS parts using response surface methodology (RSM). In: Materials today: proceedings. Amsterdam, Netherlands: Elsevier Ltd, pp. 1827–1832.

58.

Sood

Ohdar

Mahapatra

. Parametric appraisal of mechanical property of fused deposition modelling processed parts. Mater Des 2010; 31: 287–295.

59.

Rayegani

Onwubolu

. Fused deposition modelling (fdm) process parameter prediction and optimization using group method for data handling (gmdh) and differential evolution (de). Int J Adv Manuf Technol 2014; 73: 509–519.

60.

Samykano

Selvamani

Kadirgama

, et al. Mechanical property of FDM printed ABS: influence of printing parameters. Int J Adv Manuf Technol 2019; 102: 2779–2796.

61.

Mohamed

Masood

Bhowmik

, et al. Effect of process parameters on dynamic mechanical performance of FDM PC/ABS printed parts through design of experiment. J Mater Eng Perform 2016; 25: 2922–2935.

62.

Ramesh

Panneerselvam

. Mechanical investigation and optimization of parameter selection for Nylon material processed by FDM. Mater Today Proc. 2021; 46: 9303–9307. DOI: 10.1016/j.matpr.2020.02.697.

63.

Kamoona

Masood

Mohamed

. Experimental investigation on flexural properties of FDM processed Nylon 12 parts using RSM. In: IOP conference series: materials science and engineering. Bristol, England: IOP Pub, 2018. DOI: 10.1088/1757-899X/377/1/012137.

64.

El Magri

El Mabrouk

Vaudreuil

, et al. Optimization of printing parameters for improvement of mechanical and thermal performances of 3D printed poly(ether ether ketone) parts. J Appl Polym Sci 2020; 137: 1–14.