High Laser Scanning Research Articles

Deep learning revealed statistics of the MgO particles dissolution rate in a CaO–Al2O3–SiO2–MgO slag

Accelerated material development for refractory ceramics triggers possibilities in context to enhanced energy efficiency for industrial processes. Here, the gathering of comprehensive material data is essential. High temperature-confocal laser scanning microscopy (HT-CLSM) displays a highly suitable in-situ method to study the underlying dissolution kinetics in the slag over time. A major drawback concerns the efficient and accurate processing of the collected image data. Here, we introduce an attention encoder–decoder convolutional neural network enabling the fully automated evaluation of the particle dissolution rate with a precision of 99.1%. The presented approach provides accurate and efficient analysis capabilities with high statistical gain and is highly resilient to image quality changes. The prediction model allows an automated diameter evaluation of the MgO particles' dissolution in the silicate slag for different temperature settings and various HT-CLSM data sets. Moreover, it is not limited to HT-CLSM image data and can be applied to various domains.

Effect of high laser scanning speed on microstructure and mechanical properties of additively manufactured 316L

AbstractDue to its ease of processing, the stainless steel 316L is a widely used material for the laser powder bed fusion (PBF-LB/M) process. Compared to other additive manufacturing technologies PBF-LB/M has a lot of advantages such as design freedom and high resolution of details. However, PBF-LB/M also has some disadvantages, such as a reduced build-up rate. In general, 316L provides a wide range of parameter settings used for PBF-LB/M. In this study, the manufacturing limits were approached allowing a maximum build-up rate along with a high relative density > 99% without compromising the required mechanical properties. Microstructure analyses as well as tensile tests were performed to validate this approach. This article also provides insights on defects and relative density for scanning speed above 3000 mm/s. Furthermore, it was shown that the scanning speed has a major influence on the grain size and on the texture of the specimens. For the first time, the relative density, microstructure and mechanical properties of additively manufactured 316L were determined in relation to each other for high scanning speed. A set of parameters has been found that works best with a laser power of 285 W and a scanning speed of 1250 mm/s which results in a specimen relative density of 99.2%, a yield strength of 425 MPa, a tensile strength of 586 MPa and a build-up rate of 4.64 mm3/s. The findings can be further used to enhance the mechanical properties of PBF-LB/M 316L in terms of high build-up rates.

Fabrication and characterization of particle-stacking microporous nickel using laser powder bed fusion

Nickel (Ni) and nickel-based materials with specific pore configurations, particularly interconnected micropores as channels, have significant potential in new energy technologies. Laser 3D printing is a simple, rapid, and effective method for one-step formation; however, challenges remain in the fabrication of micropores (< 50 μm). This study successfully designed a particle-to-particle stacking microporous nickel structure using laser energy to regulate the melting and fusion behaviors of nickel particles. While laser power had a minimal effect on the pore size, it significantly impacted the porosity. The formation of interconnected pores depended on a large hatch distance and high laser scanning speed, while the latter also contributed to the creation of uniform micropores characterized by narrow sintered bands. The particle-stacking microporous nickel exhibited a homogeneous pore distribution, with pore sizes ranging from approximately 10 to 50 μm in both mean pore size and median pore size (D50), along with a high percentage size distribution in 1 – 10 μm. Furthermore, it displayed controllable porosities between 18.44% and 52.94%, along with remarkable resistance to deformation and superior compressive performance, featuring a high yield strength exceeding 50 MPa compared to the conventionally-processed porous nickels.

A high precision laser scanning system for measuring shape and volume of transtibial amputee residual limbs: Design and validation.

Changes in limb volume and shape among transtibial amputees affects socket fit and comfort. The ability to accurately measure residual limb volume and shape and relate it to comfort could contribute to advances in socket design and overall care. This work designed and validated a novel 3D laser scanner that measures the volume and shape of residual limbs. The system was designed to provide accurate and repeatable scans, minimize scan duration, and account for limb motion during scans. The scanner was first validated using a cylindrical body with a known shape. Mean volumetric errors of 0.17% were found under static conditions, corresponding to a radial spatial resolution of 0.1 mm. Limb scans were also performed on a transtibial amputee and yielded a standard deviation of 8.1 ml (0.7%) across five scans, and a 46 ml (4%) change in limb volume when the socket was doffed after 15 minutes of standing.

Effect of Laser Irradiation and Tensile Stress on Microstructure and Magnetic Properties of Fe-Based Amorphous Alloys.

The effect of laser irradiation and tensile stress on the microstructure and soft magnetic properties of the FeSiBNbCu nanocrystalline alloy prepared using a continuous laser has been investigated. The experimental results indicate that a decreased laser scanning speed provides more thermal energy to induce nanocrystals and encourage grain growth. When the scanning speed is excessively high, the crystallization process will cease due to a lack of energy to drive diffusion phase transitions. Nevertheless, the introduction of tensile stress could significantly promote crystallization in FeSiBNbCu alloy samples irradiated at these high laser scanning speeds. This phenomenon can be attributed to the augmentation of compressive thermal stress at the interface between the laser-treated track and the untreated region. This heightened compressive stress promotes the diffusivity of atoms, and, as a result, the transformation from amorphous to crystalline states can be enhanced. As the applied tensile stress increases, both grain size and crystalline volume fraction exhibit a proportional augmentation. Consequently, these changes manifest in the soft magnetic properties. The crystalline volume fraction can reach 62%, and the coercivity is 2.9 A/m at the optimized scanning speed; these values correspond to 54% and 3.3 A/m under specific tensile stress loading.

In-situ X-ray computed tomography tensile tests and analysis of damage mechanism and mechanical properties in laser powder bed fused Invar 36 alloy

Laser powder bed fusion (LPBF) is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry. Whereas it inevitably introduces specific microstructures and pore defects, which will further influence the mechanical properties. Hence, aiming at exploring the LPBF process-related microstructures and pore defects, and especially their influences on the damage mechanism and mechanical properties, Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds. The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density, while lower scanning speeds result in elongated columnar grains with lower dislocation density. The pore defects analyzed by X-ray computed tomography (XCT) suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion (LOF) pores, and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity. Moreover, the in-situ XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism. Specifically, high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scanning direction. Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces, while metallurgical and keyhole pores have little impact on damage evolution. Eventually, the process-structure-property correlation is established. The presence of high volume fraction of lamellar LOF pores, resulting from high scanning speed, leads to inferior yield strength and ductility. Besides, specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds, slightly reducing yield strength while slightly enhancing ductility. This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.

Revealing thermal behavior, cracking behavior, phase and microstructure formation of a ternary equiatomic alloy additively manufactured using directed energy deposition

Additive manufacturing (AM) of multi-principal element alloys (MPEAs) has recently attracted considerable attention. However, few studies focus on the thermal behavior, cracking behavior, and microstructure tunability of AM-processed MPEAs, which can significantly affect the final performance of AM MPEA parts. In this study, a ternary equiatomic MPEA CrCoNi, with a single-phase face-centered-cubic (FCC) structure, was fabricated by the AM process via directed energy deposition (DED) at different laser scan speeds (10, 30, and 50 mm/s), and special focus was given to the thermal behavior, cracking behavior and microstructure formation. The increase in the laser scan speed from 10 to 50 mm/s causes a sharp increase in temperature gradients and cooling rates by five-fold and seventeen-fold, reaching up to 1148 K/mm and 57,778 K/s, respectively, as in-situ measured by a high-speed and high-resolution thermal pyrometer. Furthermore, the increased laser scan speed induces the severe cracking, which propagates along high angle grain boundaries and is classified as solidification cracking based on the observed protruding dendrites from the cracked plane. Although the Scheil-Gulliver solidification predicts a very narrow critical temperature range of 16 K which is indicative of a low solidification cracking susceptibility, the high temperature gradient and the resulting high thermal stress, as evidenced from the high density of dislocations and stacking faults, are believed to trigger the severe solidification cracking of the CrCoNi MPEA deposited at a high laser scan speed of 50 mm/s. With increasing the laser scan speed, the grain structure changes from elongated grains, which are roughly oriented along the build direction, to a more heterogenous grain structure with elongated grains converging towards the centerline and equiaxed grains arranged between the columns of elongated grains. Furthermore, with increasing the laser scan speed, the cellular structures are refined down to ∼ 2 µm due to the increased cooling rates. These findings not only contribute to better understanding the thermal behavior, cracking behavior, and microstructure formation of the AM-processed MPEAs, but also pave a road for further enhancing the mechanical properties of AM parts via tuning the thermal behavior and microstructures.

Influence of High Laser Scanning Speed on Macro-form, Microstructure, and Tensile Properties of Austenitic Stainless Steel Made by Oscillating Laser-PTA Additive Manufacturing

Influence of High Laser Scanning Speed on Macro-form, Microstructure, and Tensile Properties of Austenitic Stainless Steel Made by Oscillating Laser-PTA Additive Manufacturing

Microstructure, mechanical properties, and corrosion performance of additively manufactured CoCrFeMnNi high-entropy alloy before and after heat treatment

Equiatomic CoCrFeMnNi, one of the well-known high-entropy alloys, possesses attractive mechanical properties for many potential applications. In this research, the effects of heat treatment on additively manufactured CoCrFeMnNi materials were studied. A pilot experiment was conducted to select two selective laser melting (SLM) conditions of different laser scanning speeds based on the density and porosity of obtained materials. Thereafter, microstructure, tensile properties, impact fracture, microhardness, and corrosion resistance were investigated for the materials obtained under the two selected SLM conditions, with and without heat treatment. It was discovered that while the texture with a strong &lt;100&gt; alignment was observed in both as-built and heat treated materials, the texture of heat treated materials was stronger. Also, heat treatment drastically improved the ductility of as-built CoCrFeMnNi by 23 – 59% for the selected SLM conditions, while the ultimate tensile strength showed only negligible change. The increase of ductility was believed to result from the release of residual strain and the increase of average grain size after heat treatment. Moreover, heat treatment was able to bring noticeable improvement in energy absorption for the as-built CoCrFeMnNi, reflected by 11 – 16% more energy absorption. Besides, all studied materials showed signs of ductile fracture, but more signs of brittle fracture, such as cleavage facets, were found in the as-built materials as compared with the heat-treated materials. In addition, higher laser scan speed was found to cause moderate reduction in corrosion resistance. Effect of heat treatment was also negative and mild for lower scanning speed case. However, the highest reduction in corrosion resistance was observed after heat treatment of the high laser scanning speed case.

Multi-sensor airborne lidar requires intercalibration for consistent estimation of light attenuation and plant area density

Leaf area is a key structural characteristic of forest canopies because of the role of leaves in controlling many biological and physical processes occurring at the biosphere-atmosphere transition. High pulse density Airborne Laser Scanning (ALS) holds promise to provide spatially resolved and accurate estimates of plant area density (PAD) in forested landscapes, a key step in understanding forest functioning: phenology, carbon uptake, transpiration, radiative balance etc. Inconsistencies between different ALS sensors is a barrier to generating globally harmonised PAD estimates. The basic assumption on which PAD estimation is based is that light attenuation is proportional to vegetation area density. This study shows that the recorded extinction strongly depends on target detectability which is influenced by laser characteristics (power, sensitivity, wavelength). Three different airborne laser scanners were flown over a wet tropical forest at the Paracou research station in French Guiana. Different sensors, flight heights and transmitted power levels were compared. Light attenuation was retrieved with an open source ray-tracing code (http://amapvox.org). Direct comparison revealed marked differences (up-to 25% difference in profile-averaged light attenuation rate and 50% difference at particular heights) that could only be explained by differences in scanner characteristics. We show how bias which may occur under various acquisition conditions can generally be mitigated by a sensor intercalibration. Alignment of light weight lidar attenuation profiles to ALS reference attenuation profiles is not always satisfactory and we discuss what are the likely sources of discrepancies. Neglecting the dependency of apparent light attenuation on scanner properties may lead to biases in estimated vegetation density commensurate to those affecting light attenuation estimates. Applying intercalibration procedures supports estimation of plant area density independent of acquisition characteristics.

Detecting individual dead trees using airborne laser scanning

The global crises – climate change and biodiversity loss – have created a need for precise and wide-scale information of forests. Airborne laser scanning (ALS) provides a means for collecting such information, as it enables mapping large areas efficiently with a resolution sufficient for object-level information extraction. Deadwood is an important component of the forest environment, as it stores carbon and provides a habitat for a wide variety of species. Mapping deadwood provides information about the valuable areas regarding biodiversity, which can be used in, e.g., conservation and restoration planning. The aim of this thesis was to develop automated methodology for detecting individual fallen and standing dead trees from ALS data. Studies I and II presented a line detection based method for detecting fallen trees and evaluated its performance on a moderate-density ALS dataset (point density approx. 15 points/m2) and a high point density unmanned aerial vehicle borne laser scanning (ULS) dataset (point density approx. 285 points/m2). In addition, the studies inspected the dataset, methodology, and forest structure related factors affecting the performance of the method. The studies found that the length and diameter of fallen trees significantly impact their detection probability, and that the majority of large fallen trees can be identified from ALS data automatically. Furthermore, study I found that the amount and type of undergrowth and ground vegetation, as well as the size of surrounding living trees determine how accurately fallen trees can be mapped from ALS data. Moreover, study II found that increasing the point density of the laser scanning dataset does not automatically improve the performance of fallen tree detection, unless the methodology is adjusted to consider the increase in noise and detail in the point cloud. Study III inspected the feasibility of high-density discrete return ULS data for mapping individual standing dead trees. The individual tree detection method developed in the study was based on a three-step process consisting of individual tree segmentation, feature extraction, and machine learning based classification. The study found that, while some of the large standing dead trees could be identified from the ULS dataset, basing detection on discrete return data and the geometrical properties of trees did not suffice for acquiring applicable deadwood information. Thus, spectral information acquired with multispectral laser scanners or aerial imaging, or full-waveform laser scanning is necessary for detecting individual standing dead trees with a sufficient accuracy. The findings of this thesis contribute to the existing deadwood detection methodology and improve the understanding of factors to take into account when utilizing ALS for detecting dead trees at a single-tree-level. Although remotely sensed deadwood mapping is still far from a resolved topic, these contributions are a step towards operationalizing remotely sensed biodiversity monitoring.

Study on Process Parameters of Low-power Semiconductor Laser Stripping PTFE Insulating Layer of Aviation Wire

Faced with the increasingly high-quality requirements for the insulation layer stripping at the end of aviation wires, laser wire stripping technology is becoming more and more popular due to its good processing quality and production efficiency. Traditional laser wire strippers generally have problems of bulky size and high control cost and are not suitable for the decentralized processing of large wire harness products. This work explores the feasibility of using a low-power semiconductor laser to strip the PTFE insulating layer of aviation wires. The influence of the parameter changes of each processing factor on the cut morphology of the insulating layer was studied separately. It was found that higher laser power removed more insulating layers per unit of time, but reduced the cutting quality. High laser scanning speed can obtain good insulation cutting quality, but too large or too small scanning speed will reduce the stripping efficiency. Simultaneous improvements in insulation cutting quality and efficiency depend on the right mix of power and scanning speed.

Characterization of pig skin microbiome and appraisal as an in vivo subcutaneous injection model.

Pig skin is commonly used in the medical industry as an injection model due to its compelling physiological affinity to human skin. However, the pig neck skin microflora remains largely uncharacterized, which may have undesirable implications for the translatability of results to humans. This study aimed to characterize pig neck skin microbiome with direct comparison with human skin microflora at emblematic injection sites to appraise its suitability as an injection model. Ten minipigs were sampled with tape strips and swabs and analysed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and 16S/ITS high throughput sequencing and confocal laser scanning microscopy. Results were directly compared with previous investigations of human injection sites. Pig skin was dominated by phyla 94.8% Firmicutes, 3% Proteobacteria, and 2.2% Actinobacteria. Staphylococcus spp. prevailed (44.4%) at the genus level with S. capitis and S. chromogenes present in all samples. Pig skin revealed populations in the 104 colony-forming units (CFU)/cm2 range with 3% identified as Gram-negative and increased alpha diversity (compared with 102 CFU/cm2 and 10% in humans). While notable taxonomical differences on species levels were seen, pig skin encompassed 97.1% of genera found in human samples. The increased population and variation found support the pig neck as an imperfect but fidelitous subcutaneous injection model that can adequately challenge devices from a microbial standpoint.

Directed energy deposition additive manufacturing of CoCrFeMnNi high-entropy alloy towards densification, grain structure control and improved tensile properties

Additive manufacturing (AM) of high-entropy alloys (HEAs), such as CoCrFeMnNi, is of high interest owing to their potential applications for extreme conditions (e.g., cryogenic environment). However, a major drawback of additively manufactured (AMed) metallic components is their poor and anisotropic mechanical properties, which primarily originate from the presence of metallurgical defects and coarse columnar grains. This study herein aims to (i) manipulate directed energy deposition (DED) AM parameters towards densification and (ii) suppress the formation of coarse columnar grains in DED AMed CoCrFeMnNi HEA. First, the effects of laser powers and laser scan speeds on the formation of various metallurgical defects in the DED AMed CoCrFeMnNi samples were investigated. Contrary to the laser powder bed fusion (L-PBF) AMed CoCrFeMnNi HEAs which were reported to form lack-of-fusion defects in the regime of low laser powers and high laser scan speeds, the lack-of-fusion defects in DED AMed CoCrFeMnNi HEAs tend to form in the regime of high laser powers and low laser scan speeds. This abnormal observation was rationalized by recourse to the resultant large layer thickness and hence insufficient melting. Cracking was observed in the regime of high laser scan speeds, and these cracks were classified into solidification cracks based on the observation of the intruding cellular/dendritic features on the cracked surface. High angle grain boundaries were found to be more sensitive to solidification cracking and the inherent mechanisms were discussed. Through such a high throughput library of samples, a printability map and near-full density were achieved for DED AMed CoCrFeMnNi HEAs. Second, for the grain structure control, contrary to the previous works that tried to manipulate the solidification conditions or introduce the secondary heterogenous particles, the current paper employed ultrasonic-assisted DED AM processing of CoCrFeMnNi HEA. Despite the measured lowered cooling rate, the coarse columnar grains were replaced by finer equiaxed grains in the presence of ultrasound, i.e., the average grain size decreases from 140 to 44 μm. The formation of fine equiaxed grains were rationalized by the combined effects of the ultrasonic-facilitated dendrite fragmentation as heterogenous nucleation sites and the enhanced liquid supercooling in the columnar front. As a direct result, the tensile yield strength of the ultrasonic-assisted DED AMed CoCrFeMnNi HEA increases by ∼ 17%, with no obvious tensile ductility drop. The strength increase was well explained by the grain refinement effect based on the classic Hall-Petch relationship. These findings provide opportunities to additively manufacture high-performance and complex-geometry HEAs components for critical applications.

High speed two-photon laser scanning stereomicroscopy for three-dimension tracking multiple particles simultaneously in three-dimension.

In this paper, we will describe a video rate two-photon laser scanning stereomicroscopy for imaging-based three-dimensional particle tracking. Using a resonant galvanometer, we have now achieved 30 volumes per second (frame size 512 × 512) in volumetric imaging. Owing to the pulse multiplexing and demultiplexing techniques, the system does not suffer the speed loss for taking two parallax views of a volume. The switching time between left and right views is reduced to several nanoseconds. The extremely fast view switching and high volumetric imaging speed allow us to track fast transport processes of nanoparticles in deep light-scattering media. For instance, in 1%-intralipid solution and fibrillar scaffolds, the tracking penetration depth can be around 400 μm.

Cross-Comparison of Individual Tree Detection Methods Using Low and High Pulse Density Airborne Laser Scanning Data

Numerous individual tree detection (ITD) methods have been developed for use with airborne laser scanning (ALS) data to provide tree-scale forest inventories across large spatial extents. Despite the growing number of methods, relatively few have been comparatively assessed using a single benchmark forest inventory validation dataset, limiting their operational application. In this study, we assessed seven ITD methods, representing three common approaches (point-cloud-based, raster-based, hybrid), across coniferous forest stands with diverse structure and composition to understand how ITD and height measurement accuracy vary with method, input parameters and data, and stand density. There was little variability in accuracy between the ITD methods where the average F-score and standard deviation (±SD) were 0.47 ± 0.03 using a lower pulse density ALS dataset with an average of 8 pulses per square meter (ppm2) and 0.50 ± 0.02 using a higher pulse density ALS dataset with an average of 22 ppm2. Using higher ALS pulse density data produced higher ITD accuracies (F-score increase of 10–13%) in some of the methods versus more modest gains in other methods (F-score increase of 1–3%). Omission errors were strongly related with stand density and largely consisted of suppressed trees underneath the dominant canopy. Simple canopy height model (CHM)-based methods that utilized fixed-size local maximum filters had the lowest omission errors for trees across all canopy positions. ITD accuracy had large intra-method variation depending on input parameters; however, the highest accuracies were obtained when parameters such as search window size and spacing thresholds were equal to or less than the average crown diameter of trees in the study area. All ITD methods produced height measurements for the detected trees that had low RMSE (&lt;1.1 m) and bias (&lt;0.5 m). Overall, the results from this study may help guide end-users with ITD method application and highlight future ITD method improvements.

Advancing dosimetry for Dating Environmental Materials: Development of an ultra-sensitive beta dosimeter system and potential for beta autoradiography

Beta Dose Rate heterogeneity is a recognized source of uncertainty when applying luminescence dating to heterogeneous samples, such as coarse crystalline rocks and clast-rich sediments. Simulations have shown that a combination of a heterogeneous distribution of minerals and radioactive elements can lead to complex dose distributions, overdispersion and potentially to bias in equivalent dose determinations. However setting realistic conditions for such simulations remains difficult, and there are at present only a few experimental validation cases for such simulated systems. Project ADDEM is investigating means of linking Monte Carlo simulations of dose rate to specific minerals with direct observations using high sensitivity phosphor plates and laser scanning imaging systems in combination with phase mapping. To overcome some of the limitations of autoradiographic imaging of low level beta dose distributions work has been undertaken using Landauer alumina OSL phosphor screens in combination with a laser scanning system developed at the Scottish Universities Environmental Research Centre (SUERC). Preliminary excitation spectra, emission band characterization and time resolved measurements were undertaken, confirming the potential to recording low doses using asynchronous stimulation at 635 nm coupled with blue band detection. Taking advantage of the slow decay of the luminescence signal the scanning equipment has been configured for pulsed stimulation and asynchronous detection to maximise signal to background ratios. Exploratory work was calibrated using a 60Co facility capable of calibrating doses in the μGy to mGy range. A series of powdered granulite/basalt mixtures of known mean activity and dose rate (Dr) have also been used to calibrate the phosphor screens. To reduce background levels during autoradiographic signal accumulation rock slices are being exposed in the Zeplin shield of the STFC Boulby Underground Laboratory, in an environment which is essentially free from cosmic ray muon background.Simulations have been conducted providing preliminary deconvolution parameters in order to either reconstruct the beta dose rate (β Dr) distribution received by the grains in the sample, or retrieve the radioactive element distributions in the minerals of the sample, providing the data required for representative simulations of β Dr.This paper outlines the spectroscopy and sensitivity verification of the autoradiography system, confirming its prospects for measuring spatially resolved β Dr distributions with single pixel lower detection limit of 130 μGy and spatial resolution of 150 μm. Prospects are outlined.

Evaluation of UAS LiDAR data for tree segmentation and diameter estimation in boreal forests using trunk- and crown-based methods

Very high point density laser scanning data from unmanned aerial systems (UAS) can be used to segment the trunks of individual trees. Such segmentation (e.g., individual trunk segmentation (ITS)) is useful, for example, in the estimation of diameter at breast height (DBH), which in turn is needed for the estimation of other tree and stand attributes, such as stem volume and diameter of the basal area median tree (DGM). In this paper, we assess the estimation of DBH directly from UAS LiDAR data in open and closed canopy conditions that represent the range of operational conditions encountered in boreal forests in Finland. We also compare trunk-based DBH estimates to corresponding estimates from individual tree crown segmentation (ITC) and fuse the results from the trunk- and crown-based estimates. The results showed that trunk segmentation performed slightly better than ITC in open canopy areas, whereas ITC performed better in closed canopy areas. The DBH prediction error was smaller for ITS (3.0 cm) than ITC (3.9 cm) when considering the trees that were recognized by both methods. We also conclude that a hybrid method, where both segmented tree trunks and tree crowns are fused, considerably increases the number of correctly segmented trees but does not decrease the prediction error associated with DGM compared to using either ITC or ITS individually.

Effect of non-lamellar α precipitate morphology on the mechanical properties of Ti5553 parts made by laser powder-bed fusion at high laser scan speeds

The influence of α precipitate morphology on the mechanical properties of additively manufactured Ti-5Al-5V-5Mo-3Cr (Ti-5553) is evaluated. Initially, Archimedes density measurements on cylindrical Ti-5553 samples printed using laser powder-bed fusion process were employed to determine the influence of parameters on the conduction melting band. The lowest and the highest volumetric energy densities (VEDs) identified in the conduction band were then selected for further characterization. X-ray Computed Tomography (XCT) was used to validate the expected high relative densities, the nature and distribution of defects in the samples printed at the two selected VEDs. Uniaxial tensile and impact tests were carried out on the samples printed at the two selected process parameter sets. The as-printed samples reached a notable fracture strain of 30 ± 5%. However, the impact-tested samples exhibited poor impact toughness. The results were compared and correlated with observed microstructural features. Electron backscatter diffraction, X-ray diffraction, and optical microscopy (OM) revealed the presence of non-lamellar α particles along the columnar grains in the building direction. The combination of outstanding ductility coupled with poor impact toughness was attributed to the presence of intragranular non-lamellar α particles. Fractured surfaces examined under scanning electron microscopy indicate a bi-modal fracture mode. Microhardness profiles and the corresponding OM images confirmed a grain size difference at the core-contour interface, which was attributed as a major contributing factor for the bi-modal fracture mode.

Ultrathin flexible terahertz metamaterial bandstop filter based on laser-induced graphene

An ultrathin, flexible metamaterial filter operated at terahertz (THz) frequencies based on one-step C O 2 laser-induced graphene (LIG) is proposed. The effects of laser machining parameters on conductivity and THz transmittance of the LIG are investigated, and a bandstop filter is fabricated from an ∼ 50 µ m polyimide film using the LIG method with relatively high laser power and scanning speed. At a blocking central frequency of 0.67 THz, the planar filter transmission is ∼ 40 % with only small variations for different bending angles. The simple, low-cost LIG method enables fabrication of THz metamaterial devices with great potential for THz imaging, sensing, and detection.