PUBLICATIONS

Porous-based bone implants with the integration of Triply Periodic Minimal Surface, TPMS, porous architectures are designed to support the growth and proliferation of bone tissue, bone marrow, and capillaries. This disclosure intends to reduce the adverse effect of conventional implants such as bone resorption over time, which is called the “stress shielding effect”. The “stress shielding effect” is caused by the mismatch between the implant and natural bone stiffness.

Orthognathic surgery, a crucial procedure for correcting jaw deformities, relies on precise jawbone segmentation to ensure effective virtual surgical planning and optimal patient outcomes. This study presents the development of a deep learning-based 3D segmentation model that incorporates customized preprocessing techniques to effectively segment the jawbone from 3D CBCT reconstruction images, an essential component of virtual orthognathic surgery planning. A dataset of 100 CBCT images was retrospectively collected from Dental University Hospital to facilitate this development. A U-Net Transformer architecture was employed to create the automatic deep learning-based 3D segmentation model. The preprocessing approach utilizes CBCT-specific characteristics as normalization parameters, effectively reducing variability in relative Hounsfield Unit (HU) values associated with these images.

Numerical modeling and experimental studies are developed to reveal the thermal, mechanical and material phenomena in the Direct Metal Laser Sintering (DMLS) processes of the Ti-6Al-4V products. Numerical models along with physical criteria and analytical equations are used to establish the processing window to show the interplay between the processing parameters and suggests the desirable operating regions. Samples are made to confirm the numerical predictions and show that the favorable part’s characteristics could be obtained if the undesirable work regions are avoided. Energy deposition density, in many occasions, is found to be a very useful factor enabling the simultaneous consideration of multiple parameters to determine the process response.

In this paper the heat transfer and residual stress evolution in the direct metal laser sintering process of the additive manufacturing of titanium alloy products are studied. A numerical model is developed in a COMSOL multiphysics environment considering the temperature-dependent material properties of TiAl6V4. The thermo-mechanical coupled simulation is performed. 3-D simulation is used to study single-layer laser sintering. A 2-D model is used to study the multi-layer effects of additive manufacturing.

The finite-element (FE) model and the Rosenthal equation are used to study the thermal and microstructural phenomena in the laser powder-bed fusion of Inconel 718. A primary aim is to comprehend the advantages and disadvantages of the Rosenthal equation (which provides an analytical alternative to FE analysis), and to investigate the influence of underlying assumptions on estimated results. Various physical characteristics are compared among the FE model, Rosenthal equation, and experiments.

The selective laser sintering (SLS) process or the additive manufacturing (AM) enables the construction of a three-dimensional object through melting and solidification of metal powder. The primary advantage of AM over the conventional process is providing the manufacturing flexibility, especially for highly complicated products. The quality of AM products depends upon various processing parameters such as laser power, laser scanning velocity, laser scanning pattern, layer thickness, and hatch spacing. The improper selection of these parameters would lead to parts with defects, severe distortion, and even cracking. I herein perform the numerical and experimental analysis to investigate the interplay between processing parameters and the defect generation.

A product-scale part was additively manufactured from Inconel 718 by laser powder-bed fusion. The thermal and microstructural behavior was experimentally examined to reveal physical characteristics while a high fidelity numerical model was developed to predict characteristics throughout the part volume.

Defects in selective laser melting parts are among major reasons that hinder the wider adoption of a laser powder bed–based manufacturing. Experiments and numerical modeling are often proceeded to gain a better understanding of defect generation.

An excessive residual stress is one of the primary challenges for additive manufacturing of metal products. It often leads to part’s distortion, powder recoating blade failure, and cracking. The present study investigated the influence of process parameters on residual stress formation. A mesoscale model was developed to examine thermal and mechanical responses in a single layer.

A transient three-dimensional thermomechanical model was developed to examine the evolution of thermal and mechanical fields in the laser powder bed fusion of Ti-6Al-4V alloy, particularly with respect to the development of plastic strain. A primary focus was to evaluate the influence of material constitutive models on predicted mechanical behaviors. Johnson-Cook (JC) constitutive material models were chosen to account for the contribution of strain, strain rate, and temperature on material responses.

The present study investigated the sensitivity of material constitutive models on thermomechanical responses in laser powder bed fusion additive manufacturing of Ti-6Al-4V. Uniform scan strategies with scan lengths of 0.5, 1, and 2 mm were applied so that wide ranges of thermal histories could be generated.

Residual stress has been among the primary problems in the laser powder bed fusion (LPBF) additive manufacturing. Nevertheless, complex physics and multi-scale nature of the problem make an accurate prediction of residual stress at the part level a great challenge. Thus, the present study developed the finite element framework to predict the part scale residual stress development in the LPBF of Inconel 718. Two-scale models were used coherently.

Various manufacturing defects are known to have significant impact on the mechanical properties of lattice structures. Therefore, defects-embedded FE models are essential for accurate mechanical prediction. However, previous studies often focused on the investigation of complete lattice structure models.

A computational model was developed to predict solid-state phase transformation kinetics within mechanical parts during metal additive manufacturing processes. This model is a modified version of the Johnson-Mehl-Avrami model for non-isothermal phase transformations that can be applied to various material systems undergoing solid-state phase transformations.

Al-12Si alloy processed through additive manufacturing exhibits a complex hierarchical structure. At the mesoscale, its melt pool boundaries constitute a network of weak interfaces that provides preferred pathways for crack kinking, leading to both marked anisotropy and apparent enhancement in the fracture energy.

Thanks to manufacturing flexibility provided by the laser powder bed fusion process (L-PBF), functional metal components could be designed and built with topological and complex structures. However, microstructures and mechanical properties of L-PBF parts are known to exhibit strong size-dependency. Therefore, the understanding of process-structure-property relationships from bulk samples may not fully translate to samples with small features.

A multi-laser powder bed fusion additive manufacturing can shorten manufacturing time and enable greater possibilities of process optimization. Nonetheless, previous studies showed that the process-dependent characteristics from the single laser may not fully translate to the multi-laser system. Therefore, the present work utilized a three-dimensional thermomechanical model to study the influence of process conditions on the physical behaviors of the dual-laser system of Ti-6Al-4V.

The laser powder bed fusion (L-PBF) process is a powder-based additive manufacturing process that can manufacture complex metallic components. However, when the metallic components are fabricated with the L-PBF process, they frequently encounter the residual stress and distortion that occurs due to the cyclic of rapid heating and cooling.

The mechanical reliability of alloys produced by Laser-Powder Bed Fusion (LPBF) is a key concern limiting their practical insertion into structural applications. While it is generally accepted that the presence of process induced defects such as lack-of-fusion porosity influences strain to failure, it is unclear what aspects of the defect distribution affect mechanical properties.

This research investigates the formation of metal-matrix composites (MMCs) using Inconel 718 (IN718) and TiC through single-track experiments with different energy inputs and TiC contents up to 5%. The study examines melt pool morphologies, defect formation, and microstructural analysis. Analytical predictions were used for melt pool size and defect anticipation.

This study investigates the post-yielding and failure mechanisms of additively manufactured Triply Periodic Minimal Surface (TPMS) lattice structures, including Primitive, Gyroid, Diamond, and Neovius. Experimental compression tests were conducted on Ti–6Al–4V samples made using the laser powder bed fusion process. In addition, numerical simulations were performed incorporating the modified Mohr-Coulomb damage criterion to analyze mechanical responses, deformation patterns, and local stress states.

This study focuses on enhancing the surface characteristics of Ti–6Al–4V alloy fabricated through laser powder bed fusion (LPBF), a prominent additive manufacturing technique. The primary objective is to assess the impact of post-processing surface treatments on the surface roughness, microstructure, and mechanical properties of LPBF Ti–6Al–4V. As-built specimens with fully dense structures underwent sandblasting (SB), chemical etching (CE), and a combination of sandblasting and chemical etching (SB + CE).

Nickel based alloy was fabricated by a laser powder bed fusion using the blue laser with the wavelength of 450 nm and maximum output power of 200 W, and the effect of volumetric energy density (VED), on the porosity was evaluated for fabricated samples. A fabricated sample using the blue diode laser, recorded a porosity of 0.012% at the VED of 33 J/mm3, indicating that it can be fabricated more efficiently than the sample fabricated using the near-infrared fiber laser. Furthermore, it was revealed that when the surface roughness of the fabricated sample reached 37.5 μm, large voids were generated, indicating a high likelihood of void formation at a surface roughness of approximately 40 μm or more during the layer-by-layer fabrication of nickel-based alloys using the blue diode laser in powder bed fusion.

A laser powder bed fusion (LPBF) process enables the production of intricate geometries for specialized applications demanding high precision in various industries such as medical, aerospace, and automotive. However, substantial thermal gradients in the LPBF process often led to residual stress, resulting in noticeable distortion and potential part failure of fabricated parts. Therefore, the present work investigates distortion prediction and geometry compensation for additively manufactured Ti-6Al-4V components employing a modified inherent strain method. Unlike previous studies, both relaxed distortions from substrate removal and as-built distortion are considered, incorporating specimens with varying geometrical features such as height and thickness.

The Ti6Al4V ELI alloy produced via laser powder bed fusion (L-PBF) has attracted interest for use in dental applications. However, surface finishing is an important property that can be managed by various methods. The purpose of this study was to investigate the effects of electropolishing (EP) on the surface roughness and corrosion resistance of L-PBF Ti6Al4V ELI alloy.

Laser power is referred to as one of the critical process parameters governing the volumetric energy density in the Laser Powder Bed Fusion (L-PBF) process. The purpose of the study is to systematically investigate the influence of laser energy density on the void morphology, microstructure, and mechanical properties of the L-PBF printed parts which were fabricated with laser power ranging from 75 to 175 W. Comprehensive analysis of void defect was conducted by employing Archimedes’ method, optical microscope (OM), and X-ray microcomputed tomography (Micro-CT).

Triply Periodic Minimal Surface (TPMS) scaffolds have recently received considerable attention because of their potentials to be used as internal structures of additively manufactured bone implants. Advantages of TPMS-based implant were from their implicit natures, allowing for precise geometric modification. As a result, many physical characteristics such as surface-to-volume ratio, pore size, elastic properties, and fluid behaviors became controllable parameters.

A laser powder bed fusion additive manufacturing has enabled the fabrication of triply periodic minimal surface (TPMS). These structures are widely acknowledged for their suitability in bone implant applications. Nevertheless, although it is essential for TPMS-based implants to exhibit graded features to mimic those of natural bones for desirable functionality, the effect of graded features on mechanical properties, flow behavior, and geometrical morphologies requires further clarification.

In the field of medical engineering, Triply Periodic Minimal Surfaces (TPMS) structures have been studied widely owing to their physical attributes similar to those of human bones. Computational Fluid Dynamics (CFD) is often used to reveal the interaction between structural architectures and flow fields. Nevertheless, a comprehensive study on the effect of manufacturing defects and non-Newtonian behavior on the fluid responses in TPMS scaffolds is still lacking.

Triple periodic minimal surface lattices have been introduced to dental and medical devices. Numerous designs of these porous structures have been proposed, but the impact of the surface properties of the different topographic lattices are not fully understood.

The present study investigated the influence of pore size of strut-based Diamond and surface-based Gyroid structures for their suitability as medical implants. Samples were made additively from laser powder bed fusion process with a relative density of 0.3 and pore sizes ranging from 300 to 1300 μm. They were subsequently examined for their manufacturability and mechanical properties.

Sacral chordoma, an invasive tumor, necessitates surgical removal of the tumor and the affected region of the sacrum, disrupting the spinopelvic connection. Conventional reconstruction methods, relying on rod and screw systems, often face challenges such as rod failure, sub-optimal stability, and limited osseointegration.

This case report highlights an innovative approach for enophthalmos correction using a patient-specific, modular orbital plate with a customized surgical guide. A 17-year-old patient presented with significant right eye enophthalmos and dystopia seven months after a motorcycle accident. Computer thermographic imaging revealed a fracture in the orbital floor and medial wall without extraocular muscle entrapment.