Effect of Reinforcement with Short Carbon Fibers on the Friction and Wear Resistance of Additively Manufactured PA12

Abstract

Reinforcing thermoplastic materials for additive manufacturing with either short, long, and continuous fibers or micro/nanoparticles is a sound means to enhance the mechanical/tribological properties of functional 3D printed objects. However, despite the fact that reinforced thermoplastics are being used extensively in modern applications, little data are found in open literature regarding the effect of such reinforcements on the friction and wear characteristics of additively manufactured objects. Therefore, this article presents a comparative study that aims to investigate the friction and wear behavior of carbon fiber-reinforced polyamide 12 (CF-PA12) as compared to pure polyamide 12 (PA12). The test specimens were prepared by selective laser sintering (SLS) at five different build orientations and examined using a pin-on-disc tribometer in dry sliding mode. The coefficient of friction (COF), interface temperature, friction-induced noise, and specific wear rate were measured. Scanning electron microscopy (SEM) was used to inspect the tribo-surfaces. The results revealed that both the COF and contact temperature of CF-PA12 are orientation-independent and are lower than those of pure PA12. Also, it was found that, compared with pure PA12, CF-PA12 has 25% smaller COF and 15–40% higher wear resistance. Further, the SEM of tribo-surfaces showed that adhesive wear dominates the surface of pure PA12, while both adhesive and abrasive wear patterns coexist in CF-PA12. Moreover, fiber crushing and thinning were observed, and this, under some circumstances, can result in a considerable increase in frictional noise.

Dry Friction and Wear Behavior of Laser-Sintered Graphite/Carbon Fiber/Polyamide 12 Composite

“…Another importa from Figure 5 is that the Z-oriented specimen has the lowest friction noise leve severe fluctuations. Since the COF of the Z-oriented specimen is still near the lo amongst all orientations throughout the test duration, this behavior may be at the interaction between carbon fibers and disc surface [20]; however, this explan not rule out the prominent effect of interfacial adhesion as the real area of contac with increasing sliding time. To emphasize the role of interfacial adhesion, Figu clear marks of strong tearing of the PA12 matrix, manifested by the appearance tongues unfirmly attached to the surface.…”

“…The measurements were conducted to evaluate the coefficient of friction (COF), approximate contact temperature, friction-induced noise, specific wear rate, and to investigate the dominant wear pattern along each build orientation. To evaluate the COF at the composite/disc interface, the friction force was measured by means of a double-bending beam force sensor along with an NI-9237 module and an NI-compactDAQ controller [7,20]. A Labview code was developed to manage the sensor signal, in which a moving average function was used to return the average value of the COF every 0.5 s.…”

“…At the initial stages of the running-in process, carbon fibers contribute to supporting the normal load; however, as rubbing continues, the PA12 layer that encapsulates the fibers and graphite particles is continuously removed, rendering the fibers and graphite particles susceptible to direct contact with the disc surface. Consequently, thinning of carbon fibers occurs and more PA12 spots get into contact with the disc surface, resulting in a corresponding increase in adhesive resistance [20], hence the COF of the Z-oriented specimen increases accordingly. The gradual increase of the COF for Z-oriented specimens at the running-in stage, shown in Figure 3b, is attributed to the corresponding gradual increase in real contact area.…”

“…Accordingly, the abrasive wear resistance of carbon fiber-reinforced polymers (CFRPs) is unsatisfactory. Moreover, in dry sliding conditions, it was reported that fiber crushing results in fiber thinning followed by fiber pull-out of the matrix, which in turn results in unstable frictional properties [20,21]. Therefore, reinforcement with short carbon fibers can efficiently promote the mechanical rather than the tribological properties of thermoplastic polymers.…”

Controlling Shear Rate for Designable Thermal Conductivity in Direct Ink Printing of Polydimethylsiloxane/Boron Nitride Composites

“…Three-dimensional printing emerged as an enticing manufacturing technology capable of generating a 3D object layer-upon-layer directly from CAD data, regardless of the complexity of the parts to be built. Benefiting from the layer-wise advantages, a variety of functional materials have been fabricated, such as loading-bearing devices [ 20 , 21 ], sensors [ 22 ], electronic devices [ 23 , 24 ], and soft actuators [ 25 ]. Controlling the condensed structure of materials by shear field, usually derived from extrusion-type 3D printing such as fused deposition modeling (FDM) and direct ink writing (DIW), is acknowledged as one of the important ways to prepare high-performance or multifunctional materials.…”