Progress in Additive Manufacturing最新文献

We present a finite element modelling approach for unidirectional Fused Filament Fabrication (FFF)-printed specimens under tensile loading. In this study, the focus is on the fracture behaviour, the goal is to simulate the mechanical behaviour of specimens with different strand orientations until final failure of the specimens. In particular, the aim is to represent experimentally observed failure modes for different print orientations and the typical dependence of the parts' strength on the print orientation. We investigate several modelling aspects like the choice of a suitable failure criterion, a suitable way to represent fracture in the finite element mesh or the necessary level of detail when modelling the characteristic edges of FFF-printed specimens. As a result, this work provides an approach to model FFF printed specimens in finite element simulations, which can represent the characteristic relation between mesostructural layout and macroscopic fracture behaviour.

The multiphase alloy Mo-9Si-8B (at.%) exhibits high oxidation, creep, and fracture resistance at high temperatures. With a melting point of about 2360 °C, it is a promising material for ultra-high temperature applications in turbine engines. However, Mo-9Si-8B (at.%) is difficult to process by traditional manufacturing methods due to its brittleness. Additive manufacturing offers a solution by enabling the production of complex near-net-shape bulk materials (e.g., turbine blades) in a single step. In this study, electron beam powder bed fusion (PBF-EB), which is characterized by extremely high local processing temperatures and associated high powder bed temperatures (i.e., above the brittle-to-ductile transition temperature of the material), was employed to process this Mo-Si-B alloy. The processing window was rapidly developed for the first time using novel strategies that combine high-throughput thermal modeling to predict the melt pool dimensions with in situ electron-optical imaging. High-density bulk Mo-9Si-8B (at.%) samples were successfully fabricated according to the established processing window, and the typical microstructure and phase composition of the as-built samples were analyzed. This novel approach significantly reduces the effort required to generate processing windows, making it highly viable for developing stable processing conditions for new materials in PBF-EB.

In recent years, four-dimensional (4D) fabrication has emerged as a powerful technology capable of revolutionizing the field of tissue engineering. This technology represents a shift in perspective from traditional tissue engineering approaches, which generally rely on static-or passive-structures (e.g., scaffolds, constructs) unable of adapting to changes in biological environments. In contrast, 4D fabrication offers the unprecedented possibility of fabricating complex designs with spatiotemporal control over structure and function in response to environment stimuli, thus mimicking biological processes. In this review, an overview of the state of the art of 4D fabrication technology for the obtainment of cellularized constructs is presented, with a focus on shape-changing soft materials. First, the approaches to obtain cellularized constructs are introduced, also describing conventional and non-conventional fabrication techniques with their relative advantages and limitations. Next, the main families of shape-changing soft materials, namely shape-memory polymers and shape-memory hydrogels are discussed and their use in 4D fabrication in the field of tissue engineering is described. Ultimately, current challenges and proposed solutions are outlined, and valuable insights into future research directions of 4D fabrication for tissue engineering are provided to disclose its full potential.

Residual stresses are recognized as a critical factor influencing the mechanical performance and structural integrity of additively manufactured parts, particularly in nickel-based superalloys. Although the contour method and strain tomography have been applied independently for residual stress evaluation of such materials, a direct comparison of their reconstructions in laser powder bed fusion fabricated specimens has not been reported. In this study, both techniques were employed on identically produced specimens of CM247LC superalloy, and a strong qualitative agreement in residual elastic strain distributions was observed. Using the contour method, tensile residual stresses up to +1300 MPa were identified near the specimen edges, while compressive stresses approaching - 600 MPa were found in the central regions. Strain tomography, based on synchrotron X-ray diffraction, was used to non-destructively reconstruct internal residual elastic strain fields, revealing consistent trends and capturing localized variations aligned with the contour method. Through this integrated approach, a complete validation of stress reconstruction was achieved, and new insights into the stress evolution of laser powder bed fusion manufactured CM247LC were provided. The findings demonstrate how the complementary strengths of these techniques can be leveraged for improved residual stress characterization in high-performance superalloy parts.

Heterogeneous temperature distributions in additively manufactured metallic parts, particularly in laser powder bed fusion (PBF-LB/M), pose a major challenge to achieving high-quality components due to thermal distortions, microstructural inconsistencies, and shifts in the process window. This study introduces a physics-aware feedforward approach for regulating dwell time that effectively mitigates distortion in 3D-printed cantilevers by reducing thermal variations along the build direction. A fast, 1D finite volume method thermal simulation is employed to estimate the temperature profile throughout the build. The interlayer dwell time is dynamically adjusted based on a predefined thermal difference threshold between layers to minimize residual stresses and part deformation. Experimental validation on a cantilever beam geometry confirms that the adaptive dwell time strategy significantly reduces distortion compared to a constant dwell time approach. The proposed method enhances thermal stability while maintaining processing times, offering an efficient solution for distortion control in PBF-LB/M. These findings contribute to advancing process optimization strategies by integrating physics-based thermal modeling with feedforward control.

Additive friction stir deposition (AFSD) is an emerging solid-state non-fusion additive manufacturing (AM) technology, which produces parts with wrought-like material properties, high deposition rates, and low residual stresses. However, impact of process interruption on defect formation and mechanical properties has not yet been well addressed in the literature. In this study, Al6061 aluminium structure with two final heights and deposition interruption is successfully manufactured via AFSD and characterised. Defect analysis conducted via optical microscopy, electron microscopy, and X-ray computed tomography reveals > 99% relative density with minimal defects in centre of the parts. However, tunnel defects at interface between substrate and deposit as well as kissing bonds are present. Edge of deposit contains tunnel defects due to preference for greater material deposition on advancing side of rotating tool. Virtual machining highlights the ability to remove defects via post-processing, avoiding mechanical performance impact of stress concentrating pores. Electron backscatter diffraction revealed regions with localised shear bands that contain 1-5 µm equivalent circular diameter grains. Kissing bonds are exhibited in areas separated by large grain size difference. Meanwhile, Vickers hardness testing reveals hardness variation with deposit height. This work advances the understanding of complex microstructure development, material flow, and mechanical behaviour of AFSD Al6061 alloy.

Supplementary information: The online version contains supplementary material available at 10.1007/s40964-024-00904-6.

In polymer laser powder bed fusion (PBF-LB-P) techniques, such as laser sintering, the time between scanning a given point in one layer and the same x-y point in the next layer is known as the 'inter-layer delay time'. Multiple parts are normally fabricated in a PBF-LB-P build for efficiency; however, this leads to variation in the inter-layer delay time for individual parts; in this study, we present a specific investigation using a commercially available thermoplastic polyurethane (TPU). Multiple part layouts were used and the resulting parts were subject to tensile testing and fracture surface analysis. The results demonstrate that an increase in inter-layer delay time can lead to a significant reduction in mechanical properties. Fabricating specimens in groups of 5 led to a 10% reduction in ultimate tensile strength, 30% reduction in extension at break, and 15 $\%$ reduction in Young's modulus compared to specimens fabricated individually. Fractography suggests this is due to decreased inter-layer bonding and an increase in defects. This has significant implications for the production of multiple parts in a build where consistent mechanical properties are critical. Based on our understanding of this detrimental effect, we put forward a novel build packing approach for PBF-LB-P, based on scanning area equivalence rather than the conventional time minimisation, to mitigate against it.

The application of fused filament fabrication (FFF) in vacuum changes the heat transfer of the process. This work investigates the influence of the working ambient pressure conditions in FFF-based 3D printing of polyetheretherketone (PEEK) specimens, and its impact on the resulting part strength. Layer adhesion drastically improves with decreasing pressure, maximum layer adhesion is reached for ambient pressure below ${10}^{-3}$ mbar. We show that simple and low-cost vacuum equipment is sufficient to achieve such pressure conditions, making this process interesting for the general processing of high-temperature polymers using FFF.

Cellular ceramic structures were fabricated via 3D printing of thermoplastic polyurethane (TPU) followed by impregnation with polysilazane, and pyrolysis. The 3D printing was performed using fused filament fabrication (FFF), while the ceramic was obtained through the polymer derived ceramic (PDC) process starting from a commercially available polysilazane, Durazane 1800. We investigated the role of ester- and ether-based TPUs with two different Shore hardness (90A vs 80A) on the impregnation of polysilazane. Regardless of the TPU type and Shore hardness, impregnation of the TPU 3D structure was successful and resulted in dense, non-hollow ceramic struts after pyrolysis. All polyester- and polyether-based TPUs showed a similar mass and volume increase after impregnation with high deviation. The mass loss during pyrolysis was also very similar for all the TPUs. The behavior of these TPUs was then compared with one commercial TPU filament (Ninjaflex with a Shore hardness of 85A). While the Ninjaflex 3D-printed structures showed a greater increase in mass and volume after impregnation, the pyrolysis outcome was almost identical to that of the samples fabricated with both ester- and ether-based TPUs, resulting in dense, non-hollow ceramic struts.

Supplementary information: The online version contains supplementary material available at 10.1007/s40964-025-01243-w.

Articular cartilage in synovial joints such as the knee has limited capability to regenerate independently, and most clinical options for focal cartilage repair merely delay total joint replacement. Tissue engineering presents a repair strategy in which an injectable cell-laden scaffold material is used to reconstruct the joint in situ through mechanical stabilisation and cell-mediated regeneration. In this study, we designed and 3D-printed millimetre-scale micro-patterned PEGDA biomaterial microscaffolds which self-assemble through tessellation at a scale relevant for applications in osteochondral cartilage reconstruction. Using simulated chondral lesions in an in vitro model, a series of scaffold designs and viscous delivery solutions were assessed. Hexagonal microscaffolds (750 μm x 300 μm) demonstrated the best coverage of a model cartilage lesion (at 73.3%) when injected with a 1% methyl cellulose solution. When chondrocytes were introduced to the biomaterial via a collagen hydrogel, they successfully engrafted with the printed microscaffolds and survived for at least 14 days in vitro, showing the feasibility of reconstructing stratified cartilaginous tissue using this strategy. Our study demonstrates a promising application of this 4D-printed injectable technique for future clinical applications in osteochondral tissue engineering.

Supplementary information: The online version contains supplementary material available at 10.1007/s40964-022-00360-0.