Search Results (52)

In this in vitro study, we compare the discoloration potential of three premixed calcium silicate cements, specifically EndoCem MTA Premixed, Bio-C Repair, and NeoPUTTY, when applied with or without two surface pretreatments (Nd-YAG laser irradiation or dentin-bonding agents). One hundred extracted human maxillary incisors were allocated into ten groups (n = 10), including the untreated control group. A standard access cavity was prepared in all teeth except the control group. Groups were formed according to the type of premixed calcium silicate cement used and the surface pretreatment applied to the internal surfaces of the cavities. Color measurements were taken with a VITA Easyshade Advance 5.0 spectrophotometer and converted to ΔE values using the CIEDE2000 formula at baseline (T0) and 7 (T1), 30 (T2), 90 (T3), and 180 (T4) days. Data were analyzed using the Shapiro–Wilk test to assess normality, followed by the Friedman and Kruskal–Wallis tests for within- and between-group comparisons, respectively (α = 0.05). No statistically or clinically significant differences in ${∆\mathrm{E}}_{00}$ were detected among materials, surface treatments, or timepoints (p > 0.05). All mean ${∆\mathrm{E}}_{00}$ values remained below the perceptibility threshold (3.5). Within the limitations of this 180-day in vitro model, the tested materials showed favorable short-term color stability, and neither the Nd-YAG laser nor the dentin-bonding agents altered the outcomes. Long-term in vivo studies are required to recommend their clinical use in aesthetically critical areas. Full article

Many countries around the world are in a race against time to decarbonise their energy systems. One of the avenues being explored in detail is Offshore Renewable Energy (ORE), with technologies such as wind, wave, and tidal. All of these technologies are in their infancy within the marine environment and required heavy Research and Development (R&D) to make them commercially viable. With so much demand for these industries, the supply chain is heavily constrained. A solution that has shown great potential to alleviate the pressure on the supply chain is the use of Wire Arc Additive Manufacturing (WAAM) for the use of onsite repair or manufacture for components. This is due to its ability to produce large-scale parts, with low emissions and at a lower cost than other Additive Manufacturing (AM) processes. The opportunity to use this technology could result in shorter downtimes and lead to a reduction in the Levelised Cost of Energy (LCOE). However, knowing that offshore structures are subject to cyclic loading conditions during their operational lifespan, fatigue properties of new materials and manufacturing processes must be well documented and studied to avoid any catastrophic failures. An issue often seen with WAAM is the presence of residual stresses. This study looks at fatigue cracking on Compact Tension C(T) specimens that have undergone laser shock peening and rolling, surface treatment processes that form compressive residual stresses at the surface of the material. In this study, the influence of fatigue overloading on the residual stress distribution in surface-treated WAAM specimens is evaluated and the effectiveness of the post-processing techniques on the subsequent fatigue behaviour is explored. Full article

Ti and Ti alloys are being widely used as bone tissue repair materials. Progress on mechanical properties and bio-functionality is required for their applications due to the large difference in elastic modulus between bone and Ti implants and the fact that the Ti materials themselves are biologically inert. In this work, a low-modulus, β-phase Ti-15Mo alloy based on a triply periodical minimal surfaces (TPMS) structure was fabricated using a Powder Bed Fusion-Laser Beam (PBF-LB) under optimized printing parameters into implant samples with controllable porous structures. The selection of TPMS, lattice unit cell size, and relative density was based on a combination of mechanical properties and cytocompatibility. Surface modifications were used to further impart antibacterial, antioxidant, and osteogenesis properties to the implants. Broad-spectrum antibacterial Ag, antioxidant tannic acid (TA), and highly stable fluorinated hydroxyapatite ((F)HA) were applied as an advanced coating on a microporous TiO₂ surface modification layer formed by micro-arc oxidation. Ultimately, porous Ti-15Mo implant samples with a biofunctional coating were obtained with Young’s modulus 15–50 GPa, a yield strength of approximately 100 MPa, and good cytocompatibility, hemocompatibility, and bactericidal effects. This study provides a systematic scheme for the preparation and surface modification of β Ti alloy implants for subsequent studies. Full article

The high-temperature durability performance plays a crucial role in the applications of single-crystal (SX) superalloys repaired by laser-directed energy deposition (L-DED). A specialized heat treatment process for L-DED-repaired SX superalloys was developed in this study. The effect of the newly customized heat treatment on the microstructure and high-temperature mechanical properties of DD32 SX superalloy repaired by L-DED was investigated. Results indicate that the repaired area of the newly customized heat treatment specimen still maintained a SX structure, the average size of the γ′ phase was 236 nm, and the volume fraction was 69%. Obviously recrystallized grains were formed in the repair area of the standard heat treatment specimens, and carbide precipitated along the grain boundary. The size of the γ′ phase was about 535 nm. The high-temperature durable life of the newly custom heat treatment specimen was about 19.09 h at 1000 °C/280 MPa, the fracture mode was microporous aggregation fracture, and the fracture location was in the repair area. The durable life of the standard heat treatment specimen was about 8.70 h, the fracture mode was cleavage fracture, and the fracture location was in the matrix area. The crack source of both specimens was interdendrite carbide. Full article

The number of easily destroyed parts with high value is increasing in industry, and green remanufacture engineering is now mainstream in this new and expanding industrial field. Equal–additive–subtractive manufacturing, as a new technology that combines strengthening technology, additive manufacturing, and machining technology has great potential for development in the area of remanufacturing. Aiming at the damage characteristics of a plunger rod, this paper carries out a study about the repair technology by equal–additive–subtractive manufacturing of laser-directed energy deposition and shot peening. It was found that the microstructure of the materials repaired by equal–additive–subtractive technology is finer and the tensile strength can reach 100.4% of the base material. The surface residual stress of cladding materials changes from tensile stress to compressive stress, which reduces forming defects. Equal–additive–subtractive manufacturing has great significance in expanding the application of hybrid manufacturing and promoting green remanufacturing of parts with high value. Full article

Hyperboloid cooling towers are counted among the largest cast-in-place industrial structures. They are an essential element of cooling systems used in many power plants in service today. Their main structural component, a reinforced-concrete shell in the form of a one-sheet hyperboloid with bidirectional curvature continuity, makes them stand out against other towers and poses very high construction and service requirements. The safe service and adequate durability of the hyperboloid structure are guaranteed by the proper geometric parameters of the reinforced-concrete shell and monitoring of their condition over time. This article presents an original concept for employing terrestrial laser scanning to conduct an end-to-end assessment of the geometric condition of a hyperboloid cooling tower as required by industry standards. The novelty of the proposed solution lies in the use of measurements of the interior of the structure to determine the actual thickness of the hyperboloid shell, which is generally disregarded in geometric measurements of such objects. The proposal involves several strategies and procedures for a reliable verification of the structure’s verticality, the detection of signs of ovalisation of the shell, the estimation of the parameters of the structure’s theoretical model, and the analysis of the distribution of the thickness and geometric imperfections of the reinforced-concrete shell. The idea behind the method for determining the actual thickness of the shell (including its variation due to repairs and reinforcement operations), which is generally disregarded when measuring the geometry of such structures, is to estimate the distance between point clouds of the internal and external surfaces of the structure using the M3C2 algorithm principle. As a particularly dangerous geometric anomaly of hyperboloid cooling towers, shell ovalisation is detected with an innovative analysis of the bimodality of the frequency distribution of radial deviations in horizontal cross-sections. The concept of a complete assessment of the geometry of a hyperboloid cooling tower was devised and validated using three measurement series of a structure that has been continuously in service for fifty years. The results are consistent with data found in design and service documents. We identified a permanent tilt of the structure’s axis to the northeast and geometric imperfections of the hyperboloid shell from −0.125 m to +0.136 m. The results also demonstrated no advancing deformation of the hyperboloid shell over a two-year research period, which is vital for its further use. Full article

In depositing multiple layers on the surface of failed metal parts, the overlap rate is a critical factor in determining the surface smoothness and uniformity of the coating thickness. Therefore, special attention must be given to the spacing between adjacent melt tracks when planning laser paths on complex metal parts. A strategy for selecting the overlap rate for multi-track cladding is proposed, based on the key parameters of surface curvature, mass conservation, and the profile of single-track coatings. A multi-track overlap model is developed, expressing the relationship between coating morphology and the overlap rate. The optimal spacing value is determined to achieve the goal of high-quality coating remanufacturing. To verify the effectiveness of this method, nickel-based powder was used for laser forming on the surface of metal gears. The results showed that the surface of the cladding layer was smooth and flat, further demonstrating that this model helps improve the repair quality and overall performance of curved metal parts. Thus, it provides valuable guidance for the remanufacturing of failed metal parts. Full article

Biomaterials and biopharmaceuticals for correcting large bone defects are a potential area of translational science. A new bioproduct, purified from snake venom and fibrinogen from buffalo blood, aroused interest in the repair of venous ulcers. Expanding potential uses, it has also been used to form biocomplexes in combination with bone grafts, associated with physical therapies or used alone. The aim of this preclinical study was to evaluate low-level laser photobiomodulation (PBM) in critical defects in the calvaria of rats filled with nanohydroxyapatite (NH) associated with the heterologous fibrin biopolymer (HFB). Sixty animals were used, divided into six groups (n = 10 each): G1 (NH); G2 (HFB); G3 (NH + HFB); G4 (NH + PBM); G5 (HFB + PBM); G6 (NH + HFB + PBM). PBM simultaneously used red (R) and infrared (IR) light emission, applied intraoperatively and twice a week, until the end of the experiment at 42 days. Microtomography, bone formation can be seen initially at the margins of the defect, more evident in G5. Microscopically, bone formation demonstrated immature and disorganized trabeculation at 14 days, with remnants of grafting materials. At 42 days, the percentage of new bone formed was higher in all groups, especially in G5 (HFB, 45.4 ± 3.82), with collagen fibers at a higher degree of maturation and yellowish-green color in the birefringence analysis with Picrosirius-red. Therefore, it is concluded that the HFB + PBM combination showed greater effectiveness in the repair process and presents potential for future clinical studies. Full article

Laser-based direct energy deposition (DED-LB/M) has been a promising option for the surface repair of structural aluminum alloys due to the advantages it offers, including a small heat-affected zone, high forming accuracy, and adjustable deposition materials. However, the unequal powder particle size during powder-based DED-LB/M can cause unstable flow and an uneven material flow rate per unit of time, resulting in defects such as pores, uneven deposition layers, and cracks. This paper presents a multiscale, multiphysics numerical model to investigate the underlying mechanism during the powder-based DED-LB/M surface repair process. First, the worn surfaces of aluminum alloy components with different flaw shapes and sizes were characterized and modeled. The fluid flow of the molten pool during material deposition on the worn surfaces was then investigated using a model that coupled the mesoscale discrete element method (DEM) and the finite volume method (FVM). The effect of flaw size and powder supply quantity on the evolution of the molten pool temperature, morphology, and dynamics was evaluated. The rapid heat transfer and variation in thermal stress during the multilayer DED-LB/M process were further illustrated using a macroscale thermomechanical model. The maximum stress was observed and compared with the yield stress of the adopted material, and no relative sliding was observed between deposited layers and substrate components. Full article

Due to various factors such as aging, natural environment erosion, and man-made destruction, architectural heritage has formed various diseases and cracks, especially in pathology cracks, which are the most typical masonry–timber architectural heritages, directly affecting the structural stability of masonry–timber buildings. This paper uses artificial intelligence and architecture and other multi-disciplinary research methods, taking James Jackson Gymnasium, a famous masonry–timber architectural heritage in Wuhan, as an example, using 3D laser scanning technology to obtain disease details and crack data of architectural heritage, using a Mask R-CNN model to detect crack area, using an FCN model to identify and calculate single cracks, and finally summarizing the type, location, and characteristics of cracks, analyzing the causes of cracks, and then putting forward corresponding hierarchical restoration strategies. The research results build a set of detection and repair systems of masonry–timber architectural heritage pathology cracks, which provide a set of accurate and objective pathology cracks data for architectural heritage protection and repair, and provide a reference for architectural heritage repair. Full article

Biomaterials are used extensively in graft procedures to correct bone defects, interacting with the body without causing adverse reactions. The aim of this pre-clinical study was to analyze the effects of photobiomodulation therapy (PBM) with the use of a low-level laser in the repair process of bone defects filled with inorganic matrix (IM) associated with heterologous fibrin biopolymer (FB). A circular osteotomy of 4 mm in the left tibia was performed in 30 Wistar male adult rats who were randomly divided into three groups: G1 = IM + PBM, G2 = IM + FB and G3 = IM + FB + PBM. PBM was applied at the time of the experimental surgery and three times a week, on alternate days, until euthanasia, with 830 nm wavelength, in two points of the operated site. Five animals from each group were euthanized 14 and 42 days after surgery. In the histomorphometric analysis, the percentage of neoformed bone tissue in G3 (28.4% ± 2.3%) was higher in relation to G1 (24.1% ± 2.91%) and G2 (22.2% ± 3.11%) at 14 days and at 42 days, the percentage in G3 (35.1% ± 2.55%) was also higher in relation to G1 (30.1% ± 2.9%) and G2 (31.8% ± 3.12%). In the analysis of the birefringence of collagen fibers, G3 showed a predominance of birefringence between greenish-yellow in the neoformed bone tissue after 42 days, differing from the other groups with a greater presence of red-orange fibers. Immunohistochemically, in all experimental groups, it was possible to observe immunostaining for osteocalcin (OCN) near the bone surface of the margins of the surgical defect and tartrate-resistant acid phosphatase (TRAP) bordering the newly formed bone tissue. Therefore, laser photobiomodulation therapy contributed to improving the bone repair process in tibial defects filled with bovine biomaterial associated with fibrin biopolymer derived from snake venom. Full article

A number of studies have recently demonstrated the effectiveness of CO₂ laser irradiation for the repair and regeneration of scar tissue from injuries or surgical wounds. However, such studies of the oral mucosa are highly limited. Previous studies using CO₂ laser irradiation have indicated that two factors contribute to esthetic healing, namely, artificial scabs, which are a coagulated and carbonized blood layer formed on the wound surface, and photobiomodulation therapy (PBMT) for suppressing wound scarring and promoting wound healing. This review outlines basic research and clinical studies of esthetic healing with the use of a CO₂ laser for both artificial scab formation by high-intensity laser therapy and PBMT in the treatment of injuries and surgical wounds with small parenchymal defects in oral soft tissues. The results showed that the wound surface was covered by an artificial scab, enabling the accumulation of blood and the perfusion necessary for tissue regeneration and repair. Subsequent PBMT also downregulated the expression of transformation growth factor-b1, which is involved in tissue scarring, and decreased the appearance of myofibroblasts. Taken together, artificial scabs and PBMT using CO₂ lasers contribute to the suppression of scarring in the tissue repair process, leading to favorable esthetic and functional outcomes of wound healing. Full article

Due to the rapid advancement in processing efficiency, high-speed laser cladding has demonstrated significant potential in the repair and protection of various substrates. In this study, we established a comprehensive evaluation model for the coating quality of Fe-Cr-Ni-based alloy with high-speed laser cladding using the analytic hierarchy process and fuzzy comprehensive evaluation method (AHP-FCE). The weights obtained through the analytic hierarchy process for forming quality, microstructure, and surface performance are as follows: W_B1 = 0.1365, W_B2 = 0.2385, and W_B3 = 0.625, respectively. During the fuzzy comprehensive evaluation step, an evaluation level was graded while quantifying the level range through membership function judgment. By combining subjective and objective evaluations, qualitative issues were transformed into quantitative assessment methods. Through comprehensive evaluation analysis, it was concluded that the scanning speed of high-speed laser cladding had a greater impact on coating thickness compared to powder feeding speed while significantly enhancing microstructure densification. The overlap rate exerted the most influence on dilution rate homogenization of near-surface dendrites. Simultaneously, the optimal preparation technology was determined: laser power 660 W, scanning speed 14,400 mm/min, overlap rate/min. This study transforms multi-objective quality evaluation of high-speed laser cladding coatings into a single objective problem by realizing comprehensive quality quantification and providing a new method for quantitative evaluation and visualization of coating quality. Full article

With the development of laser surface modification techniques like direct laser metal deposition (DLMD), titanium alloy (TI6Al4V) may now have its entire base metal microstructure preserved while having its surface modified to have better characteristics. Numerous surface issues in the aerospace industry can be resolved using this method without changing the titanium alloy’s primary microstructure. As a result, titanium alloy is now more widely used in sectors outside of aerospace and automotive. This is made possible by fabricating metal composite coatings on titanium alloys using the same DLMD method. Any component can be repaired using this method, thereby extending the component’s life. The experimental process was carried out utilizing a 3000 W Ytterbium Laser System at the National Laser Centre of the CSIR in South Africa. Through the use of a laser system, AlCuTi/Ti6Al4V was created. The characterization of the materials for grinding and polishing was performed according to standard methods. There is a substantial correlation between the reinforcement feed rate, scan speed, and laser power components. Due to the significant role that aluminum reinforcement played and the presence of aluminum in the base metal structure, Ti-Al structures were also created. The reaction and solidification of the copper and aluminum reinforcements in the melt pool produced the dendritic phases visible in the microstructures. Compared to the base alloy, the microhardness’s highest value of 1117.2 HV_1.0 is equivalent to a 69.1% enhancement in the hardness of the composite coatings. The enhanced hardness property is linked to the dendritic phases formed in the microstructures as a result of optimized process parameters. Tensile strengths of laser-clad ternary coatings also improved by 23%, 46.2%, 13.1%, 70%, 34.3%, and 51.7% when compared to titanium alloy substrates. The yield strengths of laser-clad ternary coatings improved by 19%, 46.7%, 12.9%, 69.3%, 34.7%, and 52.1% when compared to the titanium alloy substrate. Full article

Directed energy deposition is a typical laser remanufacturing technology, which can effectively repair failed parts and extend their service life, and has been widely used in aerospace, metallurgy, energy and other high-end equipment key parts remanufacturing. However, the repair quality and performance of the repaired parts have been limited by the morphological and quality control problems of the process because of the formation mechanism and process of the deposition. The main reason is that the coupling of multiple process parameters makes the deposited layer morphology and surface properties difficult to be accurately predicted, which makes it difficult to regulate the process. Thus, the deposited layer forming mechanism and morphological properties of directed energy deposition were systematically analyzed, the height and width of multilayer deposition layers were taken as prediction targets, and a PSO-BP-based model for predicting the morphology of directed energy deposited layers was settled. The weights and thresholds of Back Propagation (BP) neural networks were optimized using a Particle Swarm Optimization (PSO) algorithm, the predicted values of deposited layer morphology for different process parameters were obtained, and the problem of low accuracy of deposited layer morphology prediction due to slow convergence and poor uniformity of the solution set of traditional optimization models was addressed. Remanufacturing experiments were conducted, and the experimental results showed that the deposited layer morphology prediction model proposed in this paper has a high prediction accuracy, with an average prediction error of 1.329% for the layer height and 0.442% for the layer width. The research of the paper provided an effective way to control the morphology and properties of the directed energy deposition process. A valuable contribution is made to the field of laser remanufacturing technology, and significant implications are held for various industries such as aerospace, metallurgy, and energy. Full article