Subsequent Passes Research Articles

Thinking Green on 3D Printing: Sustainable Polymer Compositions of Post-Consumer Polypropylene and Tire Rubber Crumbs Intended for Industrial Applications

Year by year, more and more plastic is used worldwide. A large part of post-consumer waste is still stored in landfills instead of being reused. The solution to this problem may be recycled materials (recyclates) or biodegradable materials. The method of 3D printing, regarded as a clean processing technology, can significantly contribute to addressing global plastic pollution by utilizing post-consumer recycled polymers to create new components and parts. Therefore, this study focuses on the assessment of various properties and characteristics of 3D-printed compositions based on post-consumer polypropylene (PP) and rubber crumbs, recycled from packages foils and car tires, respectively. Moreover, within this study, we compared the mechanical performance of the injection molding material with the one obtained from 3D printing. A characterization was made considering the thermal and mechanical properties as well as the “print quality” through the microscopic and tomographic analysis of subsequent print passes, the number of free spaces, and imperfections in the polymer melt. Samples obtained using the FDM and injection methods exhibited comparable melting temperatures, while the samples obtained by injection molding exhibited slightly better mechanical performance, higher hardness, and impact strength.

Influence of multiple friction stir welding passes on the microstructure and mechanical properties of AA2024 age-hardened aluminum alloy

Friction stir welding (FSW) is a promising joining process for age-hardened aluminum alloys. However, when the process is used for welding age-hardened aluminum alloys, the hardness and joint efficiency are poor mainly because the strengthening precipitates become incoherent and/or get dissolved during the welding process. In this novel work, efforts have been made to enable the reprecipitation of the strengthening precipitates using multi-pass FSW. After producing FSW welds on AA2024 alloy, the welds have been processed by the same tool and at the same parameters several times to facilitate the reprecipitation of strengthening precipitates. As the precipitation kinetics of age-hardened aluminum alloys are temperature-dependent, a thermal imaging camera was utilized to record the temperature history during welding and subsequent cooling of the welded plates. The metallurgical examination of welded samples was carried out using optical microscopy, Scanning Electron Microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and microhardness test. It was observed that grain refinement occurs continuously due to dynamic recrystallization and severe plastic deformation up to the third FSW pass, after which there is no significant change in grain size. Generally, the microhardness value was higher in the stir zone than the heat-affected zone (HAZ), and the hardness in the stir zone increased after 4 passes of FSW. SEM images show clusters of incoherent precipitates, fragmentation, precipitate dispersion, dissolution, and reprecipitation of precipitates during each subsequent pass. The identification of the precipitates was carried out using EDS and XRD analysis.

Effect of ultrasonic assisted-ECAP processing on the microstructure, mechanical properties, and fluoride-induced corrosion performance of pure titanium

The influence of the ultrasonic assisted equal channel angular pressing (UA-ECAP) process on the microstructural characteristics, mechanical properties, and fluoride-induced corrosion behavior of grade 2 commercially pure titanium (CP-Ti) is investigated. The UA-ECAP process, particularly in the first pass, induces the formation of twins and slip bands. Continued slip band activity leads to non-equilibrium structures and ultrafine grains in subsequent passes. Mechanical properties analyses show hardness progression from 147 HV (annealed state) to 233 HV (3-pass UA-ECAPed) and yield strength increase from 465 MPa to 765 MPa with elongation reduction from 24.6 % to 16.6 %. Fluoride-induced corrosion of various samples in 1 wt% HF solution is investigated through electrochemical and immersion tests. After 28 days of immersion, the 3-pass UA-ECAPed sample exhibits a corrosion rate around half that of the annealed one and lower than other UA-ECAPed samples. Microscopic observations of corroded samples reveal the 3-pass UA-ECAPed sample's film is denser and more uniform, as compared with the other samples. Glow discharge optical emission spectroscopy (GDOES) confirms the corrosion films on all samples consist of an outer region rich in oxygen/fluorine and an inner region rich in oxygen; however, the film exists on the 3-pass UA-ECAPed sample exhibits over twice thicker than other samples and with higher contribution of oxygen in it as well. A proposed physical model is provided to explain the 3-pass ECAP sample's enhanced corrosion resistance.

A new experimental methodology for investigating the impact of subsequent welding passes on the properties of the austenitic stainless clad steel plates welded joint: part I – a substrate case study

In this study, the influence of the applying repeated thermal cycling during welding on the microstructural transformations and mechanical properties in Austenitic Stainless Clad-Steel Plates (ASCSP) has been investigated, particularly in the substrate. For this purpose, a novel methodology was used, by filling the entire groove length and gradually shortening the subsequent passes. Afterwards, microstructural characterization of different zones in the welded joint was conducted using optical microscope. Results showed a decrease in acicular ferrite (AF) in the Weld Metal Substrate (WM-S) from the root pass (10 kJ/cm) to the second pass (13.5 kJ/cm). This decrease continued until a total disappearance by the third pass due to a heat input of 17.8 kJ/cm. Vickers micro-hardness test was used to investigate the effect of the subsequent passes on the mechanical properties of the joint. Micro-hardness examination confirms the metallurgical results. It was revealed that micro-hardness variations are influenced by AF percentage and pro-eutectoid ferrite levels.

Scaled performance on the Vascular Qualifying Examination does not correlate with Vascular Certifying Examination first attempt pass in a national cohort of residents and fellows

BackgroundSpecialty board certification is an important indicator of surgeon competence and necessary for residency and fellowship programs to maintain accreditation by the Accreditation Council for Graduate Medical Education. Thus, identification of trainees at risk of board certification failure is important for both vascular surgery graduates and their parent program. We sought to examine the correlation of Vascular Qualifying Examination (VQE) performance on first-time pass achievement of the Vascular Certifying Examination (VCE). MethodsWe used American Board of Surgery data to examine predictive associations of a national longitudinal cohort of all vascular surgery integrated residents (VIRs) and vascular surgery fellows (VSFs) who completed the VQE and VCE from 2016 through 2021. Descriptive statistics were used to examine trends. We used χ2 tests to examine proportional group differences. Predictive associations between VQE scaled score performance and first-time pass achievement on subsequent VCE attempts were examined using logistic regression. ResultsVQE scaled score performance and VCE pass rates were obtained for all VIRs and VSFs (n = 579; 175 residents and 404 fellows) from 151 programs (48 residency and 103 fellowship) during the study period. First-attempt pass rate for the VQE was 96% in the study cohort, and first-attempt pass rate for the VCE was 94%. There were no significant differences in pass-fail rates in VQE and VCE for VIR and VSF candidates (P = .210 and P = .116, respectively). Trainee scaled score performance on the VQE was not predictive of subsequent first-attempt pass achievement on VCE (odds ratio, 1.00; 95% confidence interval, 1.00-1.01; P = .077). Stratified subgroup analyses by VIR and VSF cohorts also showed no significant predictive first-attempt VCE pass achievement (P = .190 and P = .094, respectively). ConclusionsIn this national cohort of vascular trainees taking the VQE and VCE, VQE performance was not predictive of subsequent VCE first-time pass achievement. This finding highlights the necessity to identify other measures of trainee competence to indicate the preparedness of trainees for board certification examinations. Furthermore, this may be reflective of the ability to assess distinctive competencies between the two examinations, with the VQE focused on medical knowledge and the VCE on clinical judgment and interpersonal communication skills, thus broadening assessment of the Accreditation Council for Graduate Medical Education core competencies to ensure certification of vascular surgeons possessing both the knowledge and judgment necessary to maintain high-quality standards within our specialty.

Study on Microstructure and Properties of Cold Metal Transfer and Pulse Hybrid Welded Super Duplex Stainless Steel

The investigation focuses on the microstructure, impact toughness, and pitting corrosion resistance of cold metal transfer and pulse hybrid welded joints of unified numbering system (UNS) S32750 duplex stainless steel. The results show that the filler pass exhibits the highest austenite ratio (47.9%), whereas the heat‐affected zone (HAZ) shows the lowest (32.3%). Notably, secondary austenite (γ2) is present in both the backing pass and HAZ, but conspicuously absent in the filler pass, indicating that reheating from subsequent weld pass is a prerequisite for the precipitation of γ2. Additionally, chromium nitride (Cr2N) also precipitates in the HAZ and backing pass. Comparative analysis with the weld metal (WM) and base metal (BM) indicates that the HAZ displays lower impact toughness, primarily attributing to imbalanced phase ratio, coarse ferrite grains and the brittle Cr2N. Owing to the lower austenite content and Cr2N precipitation in the backing pass, its toughness (122.6 J cm−2) is found to be inferior to that of the filler pass (130.1 J cm−2). Furthermore, the HAZ with a lower critical pitting temperature compared to the WM (79.1 °C) and BM (87 °C), and exhibits the worst pitting corrosion resistance due to the abundant precipitation of secondary phases and excessive ferrite with low pitting resistance equivalent number.

Effect of Sequential Burr Passes on Minimally Invasive Akin and First Metatarsal Dorsiflexion Osteotomies

Introduction/Purpose: Minimally invasive surgical (MIS) techniques for are exponentially increasing as a surgical option for treating midfoot and forefoot conditions. However, performing percutaneous osteotomies using the burr prevents direct visualization to estimate the correct measurements for the resection. This study aimed to evaluate the impact of each burr pass on the degree of correction, gap size, and alignment in MIS Akin and first metatarsal dorsiflexion osteotomies (DFO). It is hoped that this will improve the surgeon's ability to correct the desired amount of deformity and assist in surgical planning. Methods: Minimally invasive Akin and first metatarsal DFO were performed on ten cadaveric specimens using a 2 mm Shannon burr. The lateral (for Akin) and plantar (for 1st DFO) cortices were left intact. A total of 5 passes with the Shannon burr were performed during each osteotomy. The osteotomy gap was manually closed after each pass and held closed while completing the subsequent passes. Fluoroscopy images were obtained before and after each of the five passes, on which two independent reviewers performed measurements and inter-observer reliability was evaluated with ICC analysis. Measurements included the metatarsal dorsiflexion angle (MDA) and dorsal cortical length (MDCL). Likewise, the phalangeal measurements included the first phalangeal medial cortical length (PCML) and proximal to distal phalangeal articular angle (PDPAA) (Figure 1). Results: The average decrease in PCML with each burr pass was as follows: 1.53 mm at the 1st pass, 1.33 mm at the 2nd pass, 1.27 mm at the 3rd pass, 1.23 mm at the 4th pass, and 1.13 mm at the 5th pass. The MDCL sequentially decreased by 1.80 mm, 1.59 mm, 1.35 mm, 0.75 mm, and 0.60 mm. The MDA consistently decreased, and the PDPAA incrementally became more valgus oriented following each consecutive burr pass. Interobserver reliability analysis demonstrated good agreement for all parameters. Conclusion: The results revealed the length and alignment changes trends in the forefoot and midfoot osteotomies with each burr pass. On average, a first metatarsal dorsal wedge resection of 4.7 mm and first phalangeal medial wedge resection of 2.9 mm was achieved after 3 and 2 burr passes, respectively. The first burr pass provided a correction of 76% of the burr diameter, while it decreased to 66%, 63%, 61%, and 56% of the burr diameter with each subsequent pass. This data may aid surgeons determine the optimal number of burr passes required for the amount of resection needed. Overview of the radiographic measurements. A) first metatarsal dorsiflexion angle (MDA), B) first metatarsal dorsal cortical length (MDCL), C) first phalangeal medial cortical length (PCML) and D) proximal to distal phalangeal articular angle (PDPAA). The diameter of the sphere © The Author(s) 2024(Dsphere) was calculated automatically by the MATLAB script for calibration purposes.

Modeling and Programming of a Spiral Winding Cycle Using a Robotic Arm

This article is devoted to solving the problem of manufacturing products from carbon fiber composite materials, which are obtained as a result of layer-by-layer laying of carbon fiber with impregnation of their binder components. This paper presents a description of the process of spiral winding of products on a cylindrical mandrel and the mathematical model, which takes into account the coefficient of friction and the necessary reverse zones in which the tape will not slip. The model is implemented as a Python program and is capable of simulating and visualizing the step-by-step winding of a carbon tape on a cylindrical surface. It is possible to optimize the friction coefficient to ensure the tightest winding of subsequent passes. The program takes into account reverse zones, which are calculated taking into account the friction coefficient of the cylindrical mandrel. Based on the simulated winding process, a control program for the robotic arm is generated. The performance of the proposed model and its implementation was tested on a test bench with a robot.

Mathematical analysis and process optimization of wire and arc additive manufactured Ti6Al4V ELI alloy with in-situ rolling

The combination of wire and arc additive manufacturing (WAAM) and rolling offer the advantages of high efficiency, low cost, and fine grain, making it a viable option for the rapid production of aerospace thin-wall forgings using titanium alloy. However, the interplay between various factors such as temperature gradient, deformation force, and prior pass morphology directly influence the morphology and grain evolution before and after subsequent pass deformations, which lead to insufficient overall morphological accuracy and grain refinement uniformity. Building upon theoretical analysis, numerical simulation, and experimental verification, this study focuses on investigating the metal flow behavior and grain evolution mechanism during WAAM with in-situ rolling single-pass multi-layers. By establishing correlations between morphology, microstructure, temperature, stress-strain and deformation characteristics, the process optimization strategies of large width-height ratio, shallow melting depth and fixed width spread were proposed. These findings can provide theoretical support for the deformation machine design and the high-precision, uniformly fine grains additive manufacturing of thin-walled titanium alloy forgings.

Abstract WP206: Single Center Experience Using the 3-Max Catheter in Medium and Distal Vessel Occlusion

Introduction: Stroke thrombectomy for medium and distal vessel occlusion is a topic of great interest with several clinical trials underway. We describe a single center experience with the Penumbra 3 max aspiration catheter in stroke thrombectomy. In our study, we compare the use of the 3 max as a de novo first pass catheter to its use as a rescue aspiration catheter following attempted thrombectomy with other devices. Methods: From January 2017 to January 2023, 84 patients underwent mechanical thrombectomy with use of a Penumbra 3 Max aspiration catheter at our comprehensive stroke center. Of these patients, 26 had 3 Max used as a first pass catheter (de novo) and 58 had it used on subsequent passes (rescue). We retrospectively reviewed these patient charts for demographic variables, and clinical and radiographic outcomes. We compared the effectiveness of the 3 Max catheter in achieving recanalization on first pass when used de novo, to the successful recanalization of a vessel when the 3 Max was used as a rescue device (“rescue rate”). Results: There were no significant differences in baseline demographic variables including age, gender, presenting NIHSS, and vascular risk factors between the de novo and rescue groups. There was no significant difference in location of occlusion and IV or IA thrombolytic use between the groups. The rescue rate was higher than the first pass effect [67.2% vs. 38.5%, X 2 (1, N =84) = 6.1, p<.05]. Rates of successful thrombectomy, defined as TICI2c or better, were similar between the de novo and rescue groups (44.4% vs. 40.4%, p=0.722). The de novo group had higher rates of favorable outcome at 90 days (mRS 0-2), but this did not reach statistical significance (44% vs. 28.1%, p=0.158). Hemorrhage and mortality rates between the two groups were low and not statistically significant when compared to each other. Conclusion: Medium and distal vessel occlusion carry high rates of morbidity and deserve consideration of endovascular therapy. The Penumbra 3 Max catheter has a higher rescue recanalization rate than first pass recanalization rate. It appears to be a safe and effective device when used in mechanical thrombectomy.

Abstract WMP89: Reperfusion Pattern as a Predictor of Final Infarct Growth in Patients With Anterior Large Vessel Occlusion Ischemic Stroke

Aim: The first pass effect (FPE) and complete sudden recanalization (cSR) have been identified as an indicator of favorable clinical outcome. We aimed to compare final infarct volume (FIV) according to different reperfusion pattern. Methods: We included consecutive patients admitted with an anterior LVO stroke (intracranial internal carotid artery, MCA-M1) who underwent endovascular treatment between January 2018 and April 2022. Patients with partial or no-reperfusion (eTICI 0-2b) were excluded. Final complete reperfusion (TICI 2c-3) was categorized as achieved at first pass (FPE) or in subsequent passes as sudden (cSR: from TICI 0-1 to TICI 2c-3 in a single pass) or progressive (PR: interim partial recanalization). FIV was quantified using an automatic segmentation tool (Methinks AI) on 24-hour NCCT. Aggregated infarct distribution heatmaps were generated to compare FIV distribution. Results: Of 316 consecutive patients, complete reperfusion was achieved in 202 patients (63.9%). Reperfusion patterns were as follows: FPE (109/202, 54.0%), cSR (28/202, 13.9%) and PR (65/202, 32.1%). The mean FIV was 28.1mL (95%CI 19.1-37.1), 49.5mL (95%CI 18.8-80.2) and 58.4mL (95% CI 37.6-79.2) in FPE patients, cSR and PR patients, respectively (p=0.014). After adjusting for confounders, FPE and cSR patterns were independently associated with a reduced FIV (FPE: -61.7%, 95%CI -77.2% to -35.8%, p<0.001; cSR: -39.7%, 95%CI -63.8% to 0.6%, p=0.05). The rate of excellent clinical outcome (mRS 90d 0-1) was higher in FPE (36.1%) and cSR (35.7%) groups compared to the PR group (20.3%, p=0.081). Conclusion: Improved clinical outcomes in patients with FPE and cSR patterns seem to be influenced by reduced infarct volume in a stepwise manner (FIV FPE<cSR<PR). PR may reflect clot fragmentation and embolization, contributing to infarct growth and worse outcomes. Reperfusion patterns should be explored for selecting target populations for adjunctive neuroprotective therapies during EVT.

Tailoring microstructure and mechanical properties of 17-4PH steel fabricated by wire-arc directed energy deposition via a combination of intrinsic and post-processing heat treatments

This paper examines the effect of intrinsic heat treatment, i.e., multiple transient heating from subsequent passes, and post-processing heat treatment on the microstructure and mechanical properties of 17–4PH stainless steel fabricated by wire-arc directed energy deposition. By carefully controlling the interpass temperature to remain below the martensite start (Ms) temperature, intrinsic heat treatment effectively triggers the formation of Cu-rich clusters and the reversion of austenite. This approach results in a concurrent enhancement in the ultimate tensile strength, increasing from 1036 MPa to 1128 MPa, and elongation, increasing from 13.2% to 18.5%, for the as-built part. During post-processing heat treatment, the microstructural response to direct aging treatment hinges on the initial microstructure induced by intrinsic heat treatment. Notably, direct aging treatment significantly enhances the hardness and ultimate tensile strength of the as-built part created at an interpass temperature surpassing the Ms temperature. Conversely, its influence on the mechanical properties of the as-built component, fabricated at an interpass temperature lower than the Ms temperature, remains minimal. Additionally, the application of a solution treatment effectively eradicates the inherent microstructural characteristics, regardless of the initial fabrication conditions. Nonetheless, the grain size of the solution-treated specimen is markedly influenced by the as-built microstructure. Ultimately, a judicious amalgamation of intrinsic and post-processing heat treatments yields an exceptional combination of properties, including high hardness (465 HV), ultimate tensile strength (1437 MPa), and elongation (14.5%). These results underscore the significance of a comprehensive consideration of intrinsic and post-processing heat treatments to tailor the microstructure and mechanical properties of 17–4PH steel fabricated by wire-arc directed energy deposition.

Modeling the Evolution of Casting Defect Closure in Ingots through Radial Shear Rolling Processing

This paper investigates the behavior of transverse defects under significant total strain in conditions of complex vortex metal flow implemented through the radial shear rolling (RSR) method. The aim of this study is to assess the applicability of RSR processing for the in-depth transformation of small ingots of special steel into bars, particularly for the manufacturing of structural elements in specialized construction projects such as nuclear power plants. Although a substantial total strain is anticipated to enhance the steel structure and contribute to defect closure, the question of the development or closure of potential casting defects remains unclear. To address this issue, model tests were conducted to simulate the implementation of RSR processing. Defect behavior data under very complex vortex metal flow and high strain conditions were obtained for the first time and have scientific merit. A small steel ingot with a 32 mm diameter, containing a simulated artificial defect in the form of a transverse through-hole with a 5 mm diameter, was employed. During rolling, the workpiece diameter was progressively reduced by 2 mm with each subsequent pass, reaching a final diameter of 20 mm. Additionally, to provide a more detailed visualization of the defect evolution process, the same defect was modeled in an aluminum bar over six passes, and changes in defect volume and shape were analyzed after each pass. A highly detailed 3D visualization of the actual defect evolution was achieved based on cross-sections from experimental workpieces. These data corresponded to the total strain levels obtained by finite element method (FEM) simulation. Notably, a consistent similarity was observed between the test results for both metals, revealing a reduction in defect volume of up to 67.7%. The deformational welding of defects in the outer sections, encompassing one-third of the rod’s radius, occurred in the initial passes. However, defects in the axial zone of the rods remained unclosed, lengthening and gradually decreasing proportionally to the elongation of the rod, akin to conventional rolling. Consequently, the radial shear rolling (RSR) method is unsuitable for ingots with substantial discontinuities in the axial zone post-casting. Nevertheless, the method ensures the total welding of defects located in the outer zones of the ingots, even with minor applied deformations and a slight decrease in the diameter of the deformed ingot. Such data were obtained for the first time and should contribute to future investigations in this field.

Effects of friction stir processing and nano-hydroxyapatite on the microstructure, hardness, degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications

Nowadays, magnesium alloys are emerging in biomedical implants for their similar properties to natural bones. However, the rapid degradation of magnesium alloys in biological media hinders successful implantation. Refinement of microstructure, as well as reinforcement particles can significantly improve the degradation rate. In this work, multi-pass friction stir processing (FSP) was proposed to synthesize WE43/nano-hydroxyapatite (nHA) surface composite, the microstructure, reinforced particle distribution, micro-hardness, corrosion behavior and in-vitro bioactivity were studied. The subsequent FSP passes of WE43 alloy and WE43/nHA composite refined the grain size which was reduced by 94.29% and 95.92% (2.63 and 1.88 µm, respectively) compared to base metal after three passes. This resulted in increasing the microhardness by 120% (90.86 HV0.1) and 135% (105.59 HV0.1) for the WE43 and WE43-nHA, respectively. It is found that increasing FSP passes improved the uniform distribution of nHA particles within the composite matrix which led to improved corrosion resistance and less degradation rate. The corrosion rate of the FSPed WE43/nHA composite after three passes was reduced by 38.2% (4.13 mm/year) and the degradation rate was reduced by 69.7% (2.87 mm/y). This is attributed to secondary phase (Mg24Y5 and Mg41Nd5) particle fragmentation and redistribution, as well as a homogeneous distribution of nHA. Additionally, the growing Ca-P and Mg(OH)2 layer formed on the surface represented a protective layer that reduced the degradation rate. The wettability test revealed a relatively hydrophilic surface with water contact angle of 49.1 ± 2.2° compared to 71.2 ± 2.1° for base metal. Also, biomineralization test showed that apatite layer grew after immersion 7d in simulated body fluid with atomic ratio of Ca/P 1.60 approaching the stoichiometric ratio (1.67) indicating superior bioactivity of FSPed WE43/nHA composite after three passes. These results raise that the grain refinement by FSP and introduction of nHA particles significantly improved the degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications.

Influence of laser shock peening on Residual stress and microhardness of AA2219 friction stir weld

This work focuses on the effect of Laser Shock Peening (LSP) on residual stress (RS) and microhardness of AA2219 T87 Friction Stir Weld (FSW). FSW plate was laser peened, covering all the regions of the weld and RS measurement was carried out before and after peening. RS distribution across the weld is non-uniform, and the profile is M shaped with tensile RS near to weld center and compressive RS away from the center. The maximum tensile RS is + 123.5 MPa and + 96.7 MPa on the top and bottom surfaces, respectively. LSP has reversed the tensile RS to compressive with a single pass of peening, and the subsequent passes increased the compressive RS further. Peak tensile RS changes to compressive RS of −20 MPa, −130.2 MPa, and −195.5 MPa with single, three and six passes of peening, respectively, on the top surface. It is due to plastic deformation and strain-hardening effect induced on the surface during LSP. An increase in hardness due to LSP on the surface and subsurface levels is noticed, and increased number of passes affected higher depth.

Effect of sequential burr passes on osteotomy magnitude and calcaneal morphology in minimally invasive Zadek osteotomy

PurposeThis study aimed to evaluate the impact of each burr pass on degree of correction, gap size and calcaneal morphology in MIS Zadek osteotomy. MethodsMIS Zadek osteotomy was performed on ten cadaveric specimens using a 3.1 mm Shannon burr. After each burr pass, the osteotomy gap was manually closed, and the subsequent burr passes were carried out with the foot held in dorsiflexion, which was repeated five times. Lateral X-rays were taken before and after each burr pass. Two independent reviewers measured the dorsal calcaneal length after each burr passage, as well as changes in several calcaneal parameters including X/Y ratio, Fowler Philip angle, and Böhler angle. ResultsThe average decrease in dorsal calcaneal cortical length with each burr pass was as follows: 2.6 ± 0.9 mm at the 1st pass, 2.4 ± 1 mm at the 2nd pass, 2 ± 1 mm at the 3rd pass, 1.6 ± 1 mm at the 4th pass, and 1.4 ± 0.7 mm at the 5th pass. The Fowler Philip and Böhler angles consistently decreased while the X/Y ratio consistently increased following each consecutive burr pass. Interobserver reliability analysis demonstrated good agreement for all parameters. ConclusionThe results revealed the trends of length and anatomical changes in the calcaneus with each burr pass. On average, a dorsal wedge resection of 10 mm was achieved after 5 burr passes. This data can aid surgeons in determining the optimal number of burr passes required for a particular amount of resection, ensuring the attainment of the desired patient-specific surgical outcome.

Demonstration of orbit determination for LEO objects using the Murchison Widefield Array

The rapidly increasing number of satellites in Earth’s orbit motivates the development of Space Domain Awareness (SDA) capabilities using wide field-of-view sensor systems that can perform simultaneous detections. This work demonstrates preliminary orbit determination capability for Low Earth Orbit objects using the 36°×36° field-of-view of the Murchison Widefield Array (MWA) at commercial Frequency Modulated (FM) frequencies (transmitters in 88-108 MHz range). Non-coherent passive radar techniques with the MWA produce spatially smeared detections, due to time averaging in the MWA’s standard signal processing chain. The work develops methods to extract time-stamped measurements of a satellite’s angular coordinates from these data. The developed method was tested on observations of 32 satellite passes and the extracted measurements were used to perform orbit determination for the targets using a least-squares fitting approach. The target satellites span a range in altitude and Radar Cross Section, providing examples of both high and low signal-to-noise detections. The estimated orbital elements for the satellites are validated against the publicly available Two Line Element (TLE) updates provided by the Space Surveillance Network (SSN) and the preliminary estimates are found to be in close agreement. The work also tests for re-acquisition for one target using the orbital elements and finds the trajectory predicted by the method to coincide within 0.2° cross-track and 0.3° in-track for a subsequent pass, reduced to approximately 0.1° cross-track (less than one kilometre) if two passes are used to predict the subsequent pass (using simple two-body propagation). The median uncertainty in the angular position for objects in LEO (range less than 1000 km) is found to be 860 m in the cross-track direction and 780 m in the in-track direction, which are comparable to the typical uncertainty of ∼1000 m in the publicly available TLE information. The techniques, therefore, demonstrate the MWA to be capable of being a valuable contributor to the global SDA community. Based on the understanding of the MWA SDA system, this paper also briefly describes methods to mitigate the impact of FM-reflecting LEO satellites on radio astronomy observations, and how maintaining a catalog of FM-reflecting LEO objects is in the best interests of both SDA and radio astronomy.

A comparative study of solute trapping in Fe-(33–45 at%) Cu alloys manufactured by laser directed energy deposition

The high cooling rates in laser directed energy deposition (DED-LB) of alloys lead to substantial amounts of solute trapping as solute atoms cannot diffuse away from the solid/liquid interface before it advances. In some concentrated alloys, this results in supersaturated solid phases that form nanoscale hierarchical microstructures when the solute atoms precipitate out during reheating from subsequent laser passes. We choose the Iron-Copper (Fe-Cu) binary alloy as model system as it is chemically homogeneous in the liquid phase and has negligible solid solubility at room temperature. Two alloys with nominal compositions in atomic (at.) %, Fe67Cu33 and Fe55Cu45, were manufactured using DED-LB. Scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS) were used to characterize the nanostructures and heterogeneous chemical compositions. A non-equilibrium solute partitioning model was used to compute the supersaturated chemistries of the constituent phases and validated with experimentally measured compositions. The measured phase compositions of the two alloys were very similar, at roughly 12 at% Cu and 4 at% Fe in the α(bcc)-Fe and ε(fcc)-Cu phases respectively, despite having different processing parameters and mechanical behavior. This indicates that the total thermal history, that depends on both the processing parameters and laser scan pattern, plays a stronger role on the final microstructure evolution than just the initial quantity of trapped solute. Additionally, we find that current non-equilibrium solute partitioning models applied on the continuum scale fall short of predicting accurate quantitative phase compositions in concentrated alloys, although the qualitative trends are captured correctly.

Qualitative analysis of potential pore healing phenomenon in L-PBF using operando high speed X-ray imaging

A major source of flaws and defects in Laser Powder Bed Fusion stems from the creation of pores during the build process. In-process mechanisms that produce pores, such as keyholing and lack of fusion, and secondary processes that can reduce porosity, such as hot isostatic pressing, have been extensively studied. Many of these works also suggest that if pores are detectable then it could be possible to develop a schema to “heal” the defects in-situ. However, the effects of a subsequent laser pass on pores generated in prior layers have not been fully studied due to the experimental difficulties. It is therefore important to understand if these interaction mechanisms have the potential to “heal” and enable control methods that select laser parameters to target areas of suspected porosity. This paper identifies and qualitatively analyzes pore healing mechanisms in L-PBF using high speed X-ray imaging. Several key phenomena affecting keyhole and melt pool interactions with existing pores are identified in the X-ray images and the effects of these phenomena are discussed. Finally, several areas for future work are presented, including the need for robust quantitative analysis of these phenomena.

Increasing the efficiency of the forming process by the DRECE method

The DRECE method is a progressive method for forming sheet metal strips using the principle of severe plastic deformation (SPD). The DRECE method is characterized by extruding the sheet metal strip with a forming device which creates a forming angle of 108 ° in the deformation zone. During the practical verification of the DRECE method, it was found that the materials formed by the method show a significant increase in mechanical properties after the first pass through the forming equipment while maintaining sufficient ductility of the materials. With each subsequent pass of the material through the forming device, the mechanical properties increase. For the subsequent industrial use of the DRECE method, the key technological parameter of the forming equipment is the feed speed of the sheet metal strip. At present, the forming device makes it possible to regulate the feed speed of the sheet metal strip in the range of 10 - 100 mm / s. The device allows continuous sensing and recording of torque, extrusion force and feed rate of the sheet metal strip during the forming process. These facts are very important for the subsequent use of the method in industrial practice.