Li Chang

This study presents a novel material design approach for wear‐resistant sandwich‐structured hybrid composites fabricated using dual‐nozzle fused deposition modeling (FDM). By co‐printing commercially available mono‐filaments, this approach prevents the compounding difficulties and enables the strategic placement of nanoparticles and micro‐fibers layers. Two hybrid architectures were produced by combining a nano‐copper polylactic acid (nano‐Cu PLA) phase with either a carbon flake (CF PLA) or short carbon fiber (SCF PLA) reinforced phase. The additive manufacturing process was optimized for flexural performance, followed by systematic tribological evaluation using pin‐on‐disc dry sliding tests under different normal pressures and sliding velocities. Micro‐Computed Tomography revealed an interconnected carbon‐filler network with a dispersed nanoparticle phase and a transition band that enhances mechanical interlocking. The hybrid composite filled with copper nanoparticles and SCF achieved a flexural strength of 97.30 MPa, outperforming its base components. At a contact pressure of 1 MPa and a sliding velocity of 0.2 m/s, the specific wear rate decreased to 3.4 × 10 ⁻⁷ mm ³ /Nm. Microscopic analysis suggests that copper nanoparticles released at the interface act as rolling agents for exposed fiber tips, and change the contact mode, leading to synergistic wear reduction. These findings provide insights for designing high‐performance tribological components via additive manufacturing.

The present research investigates the effects of re-entrant auxetic structure’s on friction-induced vibrational behaviour of three-dimensional (3D) printed polylactic acid (PLA) samples. A series of re-entrant auxetic specimens with different re-entrant angles were prepared for sliding wear tests. The results showed that with the increase in re-entrant angles, the negative Poisson ratio becomes greater. Accordingly, the specimen showed less vibration during the sliding wear process, with a lower average friction coefficient. As a result, the wear resistance of the specimens with embedded re-entrant structures was clearly improved. Microscopic images revealed that surface fatigue wear was effectively prevented with the re-entrant structures, thanks to their energy absorption and vibration insulation capacities. The findings demonstrated that 3D printing technology could provide a new route for the design and fabrication of high wear resistant engineering components by creating complex functional structures to control and optimize their dynamic behaviour and, thus tribological performance.

In the present study, post-heat treatment was applied to improve the mechanical and tribological performance of 3D-printed polymer components. Two polymers, i.e., polylactic acid (PLA) and polyether ether ketone (PEEK), were used as base materials. Re-entrant structures were incorporated into printed specimens to mitigate friction-induced vibrations (FIV). The results showed that the heat-treatment process effectively enhanced the mechanical properties of both materials by increasing their elastic modulus and yield strength. Specifically, the tensile and compressive strengths of heat-treated PLA increased from 44.14 MPa to 47.66 MPa and from 68 MPa to 82 MPa, respectively. A similar trend was observed for heat-treated PEEK, with tensile strength increasing from 75.53 MPa to 84.91 MPa and compressive strength from 106 MPa to 123 MPa. Furthermore, the increased stiffness enabled the re-entrant structures to more effectively reduce FIV during the sliding process of specimens. However, heat treatment produced contrasting effects on the wear performance of the two polymers. The specific wear rate of the heat-treated PLA sample with the re-entrant structure increased from 2.36 × 10⁻⁵ mm³/(N · m) to 4.5 × 10⁻⁴ mm³/(N · m), while it decreased for the PEEK sample from 3.18 × 10⁻⁶ mm³/(N · m) to 6.2 × 10⁻⁷ mm³/(N · m). Microscopic observations revealed that this difference was due to the variations in the brittleness of the treated materials, which influenced wear-debris formation and the development of the transfer film on the steel counterface. These findings demonstrate that post-heat treatment is an effective method for tailoring and optimizing the mechanical behavior of printed polymers while also emphasizing the necessity of systematically evaluating its influence on the tribological performance of printed engineering parts subjected to different sliding conditions.

Frictional contact between biological tissues is of critical importance in biomechanics and clinical treatment strategies, which is particularly relevant to diarthrodial joints, where articular cartilage surfaces undergo reciprocal contact loading for thousands of cycles per day. Taking the temporomandibular joint (TMJ) as an example, mandibular resection and reconstruction significantly alters the masticatory system and impacts its biomechanical conditions. Clinical evidence indicates that pain is more frequent in the contralateral TMJ after this kind of surgery. However, there has been limited analysis of TMJ biomechanics following reconstructive surgery to date. Therefore, our study aimed to investigate the effects of masticatory muscle loss on stress distribution in the TMJs, determine an optimum loading region to mitigate excessive stress in the contralateral TMJ, and explore how the frictional change influences the biomechanics of the TMJ. The results demonstrate that the loss of masticatory muscles on the ipsilateral side due to resection can increase contact pressure in the contralateral TMJ and that incisor and ipsilateral dental implant occlusal loading generates the most desired stress patterns in the contralateral TMJ. This study reveals that the excessive contact pressure could increase the real contact area in the joint and further cause a transition from fluid film lubrication to solid contact, leading to increased friction and wear. This work sheds some light on asymmetric anatomy and frictional condition changes arising from surgery, which contribute to stress concentration in the contralateral TMJ and may be associated with degenerative changes. These findings hold significant clinical implications for selecting an optimal and patient-specific occlusal loading to mitigate excessive contact pressure and potential damage in the articular joint.

The advancement of 3D printing technology has changed material design and fabrication across various industries. Among its many applications, the development of high-wear-resistance polymer composites, particularly using Fused Deposition Modelling (FDM), has received increasing interest from both academic and industrial sectors. This paper provides an overview of recent advances in this field, focusing on the selection of key printing parameters (such as layer thickness, print speed, infill density, and printing temperature) and material compatibility optimisation to enhance print quality and tribological performance. The effects of various tribo-fillers, such as fibres and nanoparticles, on the tribological properties of the printed polymer composites were studied. Generally, in the case of nano-sized particles, the wear rate can be reduced by approximately 3 to 5 times when the nanoparticle content is below 5 vol.%. However, when the nanoparticle concentration exceeds 10 vol.%, wear resistance may deteriorate due to the formation of agglomerates, which disrupts the uniform dispersion of reinforcements and weakens the composite structure. Similarly, in short fibre-reinforced polymer composites, a fibre content of 10–30 vol.% has been observed to result in a 3 to 10 times reduction in wear rate. Special attention is given to the synergistic effects of combining micro- and nano-sized fillers. These advancements introduce novel strategies for designing wear-resistant polymer composites without requiring filament fabrication, making 3D printing more accessible for tribological applications. In the last part of the review, the impact of emerging AI technologies on the field is also reviewed and discussed. By identifying key research gaps and future directions, this review aims to drive further innovation in the development of durable, high-performance materials for wide industry applications in aerospace, biomedical, and industrial engineering.

The present work studied the water absorption behavior of polymeric composite materials fabricated using 3D printing technology, as well as its effect on their tribological properties. Polyamide-6 was selected as the base matrix material. Short and continuous carbon fibers are used as the reinforced material. The results showed that the moisture absorption would impair the mechanical properties of polymer matrix and interface bonding between the fiber and the matrix. As a result, the tensile strength of the fiber reinforced polymer composites (FRPCs) decreases with water absorption. Nevertheless, the effects of moisture absorption on the wear properties of FRPCs are more complicated, which are depending on the fiber length and sliding conditions. With the short fiber reinforcements, moisture absorption deteriorated the wear resistance under all the testing conditions. With the increase of moisture level, more severe fiber damage/removal was observed, associated with the higher wear loss. With a relative high volume fracture of continuous carbon fiber (∼35 vol%), however, the wear resistance of the FRPC increased with moisture level, especially under a relatively low load. Based on microscopic observations, it was proposed that water inside FRPC specimens is able to provide the lubricating and cleaning effects, which contribute to a lower friction and smooth worn surfaces. The work provides new insights into designing and selecting printed polymer materials, subjected to different loading conditions.

Fused deposition modelling (FDM) printed short carbon fibre reinforced nylon (SCFRN) composites were fabricated. The friction and wear behaviour of printed materials were systematically investigated under both dry sliding and water lubricated conditions. The results showed that with short fibre enhancements, the printed SCFRN achieved a lower friction coefficient and higher wear resistance than nylon under all tested conditions. Further, under water lubricated conditions, the printed SCFRN exhibited a low, stable friction coefficient due to the cooling and lubricating effects of water. However, the specific wear rate of the printed specimens could be higher than that obtained under dry sliding conditions, especially when the load was relatively low. The square textured surface was designed and created in the printing process to improve materials’ tribological performance. It was found that with the textured surface, the wear resistance of the printed SCFRN was improved under dry sliding conditions, which could be explained by the debris collection or cleaning effect of surface texture. However, such a cleaning effect was less noticeable under lubricated conditions, as the liquid could clean the surface effectively. On the other hand, surface textures could increase the surface area exposed to water, causing surface softening due to the higher water absorption rate. As a result, the samples having surface textures showed higher wear rates under lubricated conditions. The work has provided new insights into designing wear resistant polymer materials using three-dimensional (3D) printing technologies, subjected to different sliding conditions.