Multi-pass Approach Research Articles

A numerical and experimental analysis of CO2 laser micro-milling on PMMA sheet considering a multipass approach for microfluidic devices

Laser-assisted machining is an advanced manufacturing process that provides excellent cutting quality, flexibility, and precision. The current study used a CO2 laser to create microchannels in polymethyl methacrylate (PMMA) sheets using a series of laser passes by varyingparameters such as laser power (30–40 Watt), number of passes (1–4), and cutting speed (20–25 mm/s). A finite element analysis is performed using ABAQUS with subroutines such as Distributed Flux (DFLUX) and User Defined Field (USDFLD) to simulate and predict the upper and lower kerf width, kerf angle, and heat-affected zone (HAZ) during the process. Thermal analysis has been performed by considering the laser beam as body heat flux with a moving heat source. It has been observed that the HAZ tends to reduce with the increase of laser cutting speed. During the laser cutting process, the upper kerf width is found to increase with increasing laser power, as well as with increasing the number of passes at a given laser power and cutting speed. It is also predictedthat when laser cutting speed increases, the kerf width for a given laser power decreases. The experimental and simulation results are in good agreement and the results demonstrated thatthe average percentage error in HAZ, kerf angle,upper kerf, and lower kerf width was 3.21 %, 5.06 %, 7.60 %, and 22.2 %, respectively. The results of this study have significance for the advancement of precise and state-of-the-art manufacturing for application in microfluidic devices.

Coherent field sensing of nitrogen dioxide.

We introduce a portable dual-comb spectrometer operating in the visible spectral region for atmospheric monitoring of NO2, a pollution gas of major importance. Dual-comb spectroscopy, combining key advantages of fast, broadband and accurate measurements, has been established in the infrared as a method for the investigation of atmospheric gases with kilometer-scale absorption path lengths. With the presented dual-comb spectrometer centered at 517 nm, we make use of the strong absorption cross section of NO2 in this spectral region. In combination with a multi-pass approach through the atmosphere, we achieve an interaction path length of almost a kilometer while achieving both advanced spatial resolution (90 m) and a detection sensitivity of 5 ppb. The demonstrated temporal resolution of one minute outperforms the standard chemiluminescence-based NO2 detector that is commercially available and used in this experiment, by a factor of three.

How to improve surface integrity in discrete laser spot hardening of AISI 4140 when using a fiber laser with the Gaussian beam: A dynamic multi-pass approach based on time-domain energy modulation

Improving the surface quality of discrete laser spot hardening when using a fiber laser with the Gaussian beam has been a major concern in industry applications. A dynamic multi-pass approach based on time-domain energy modulation was proposed and successfully implemented using an innovative motion system. Surface quality characteristics, including geometrical dimensions, topography, residual stress state, microhardness, and metallographic structure, were evaluated to compare the effects of multi-pass. Additionally, the heat transfer in solid module was employed to simulate the temperature histories. The result shows the diameter of hardened zone keeps about 1000 μm with the increase of multi-pass. It indicates that there was no notable additional thermal effect observed as the number of passes in the temperature histories increased. Meanwhile, the maximum microhardness of the multi-pass processed samples increases by more than 5 % in cross-sectional direction. This increase can be attributed to the occurrence of multiple rapid re-austenitization processes, which lead to a significant refinement in grain sizes and a more uniform distribution. Therefore, this particular method can be recognized as an effective approach for improving surface quality, i.e., reducing remelting, regulating geometrical parameters, ameliorating the 3D topography of the hardened area, increasing the uniformity of the hardened layer, and reducing the tensile residual stress.

Study of Backpressure on the Composition and Characteristics of the AA5083 Alloy During ECAPed

Equal Channel Angular Processing Process at room temperature along varying backpressure level and numbers of passes produced hefty billets of 25 mm×25 mm×100 mm industrial alloy AA5083 with an ultrafinegrained microstructure. Supersaturated solid iron in an aluminium matrix was treated in brittle cast AA5083 during Equal Channel Angular Processing with Sixteen passes and a 285 MPa backpressure. The Equal Channel Angular Processing alloy’s strength, ductility, and microhardness were all greatly improved. Increased backpressure improves ductility of Equal Channel Angular Processing alloys, the workability and delays the craking of intermetallic particles. Alloys treated by Equal Channel Angular Processing have improved workability due to backpressure. The AA5083 alloy’s strength and microhardness were greatly improved. When an initially coarse-grained alloy undergoes 3 passes of Equal Channel Angular Processing with a 220 MPa backpressure, its microhardness and room strength (185 HV, UTS = 327 MPa) are significantly higher than their typical values following conventional processing with cold rolling or hot pressing. In Equal Channel Angular Processing, a super saturated solution was generated with a peak soluble of 0.6 wt.% of iron allow the ageing of the usually non-hardenable metal. The cast alloy treated using the Multi-pass approach has positively impacted toughness, elasticity, and microhardness.

Benchmarking of different Multi-pass Shake-the-Box strategies

Within this study several advanced Multi-pass Shake-the-Box processing strategies are compared to the standard single-pass approach and are evaluated based on their reconstruction quality of two time-resolved experimental flow cases. The covered processing strategies are Forward-Backward tracking, Variable Time-step Shake-the-Box (VT-STB) and the Extended Initialization approach, which is proposed for the first time within this work. All multi-pass approaches improve the trajectory reconstruction results, when compared to the single-pass processing. From the considered multi-pass strategies the Forward-Backward tracking shows the most universal improvements and it is recommended to always combine it with the other approaches. The proposed superior reconstruction results of VT-STB for flows with a large dynamic velocity range can be confirmed within this study. For the Extended Initialization strategy it is found, that it enhances the reconstruction quality during the critical convergence phase but these improvements cannot be carried over completely along the complete time series. It is therefore recommended for high seeding density cases, where the calculation time for full Forward-Backward tracking schemes might be to expensive.

Advanced THz MIMO Sparse Imaging Scheme Using Multipass Synthetic Aperture Focusing and Low-Rank Matrix Completion Techniques

This article proposes an advanced THz multiple-input-multiple-output (MIMO) near-field sparse imaging scheme for target detection that uses single-pass synthetic aperture focusing and multipass interferometric synthetic aperture focusing techniques to improve imaging effectiveness and efficiency. It benefits from the MIMO of the linear sparse periodic array (SPA) and random undersampling sparse imaging to reduce sampling data and system cost. Both simulated and proof-of-concept experimental results have verified the scheme, revealing that the single-pass synthetic aperture imaging approach is sufficient to identify pure metallic targets with 3.87% of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> sampling data. The multipass interferometric synthetic aperture imaging approach is capable of improving image quality on the image signal-to-noise ratio (SNR) and contrast, which is ideal for detecting more challenging targets. The random sparse imaging with help of the low-rank matrix completion (LRMC) technique has shown the promising potential of achieving equivalent image quality when further reducing 43.75% data in the experiment of five-pass imaging on a complex target; this corresponds to 82.51% data reduction compared to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> sampling.

Herriott cell enhanced SMF-coupled multi-scalar combustion diagnostics in a rapid compression expansion machine by supercontinuum laser absorption spectroscopy

A novel supercontinuum laser absorption spectroscopy (SCLAS) approach combining a planar external Herriott multi-pass cell (HMPC) with fully single-mode fiber (SMF) coupling is presented for broadband multi-scalar combustion measurements in a rapid compression expansion machine (RCEM). For the HMPC, 1-dimensional refractive index gradients occurring in the RCEM combustion chamber are analyzed via ray-tracing with respect to axial and vertical beam steering. The impact of beam steering on the SCLAS signal is compared with the ray-tracing analysis and high-speed flame luminosity images. SCLAS based measurements are presented during compression, auto-ignition and combustion in the RCEM for n-heptane/methane mixtures at varied AFR (air-fuel ratio) and n-heptane/EGR (exhaust gas recirculation) mixtures at temperatures exceeding 1800 K and pressures up to 80 bar. Simultaneous temperature and mole fraction courses of H2O, CH4, and CO2 are inferred from NIR (near-infrared) broadband absorbance spectra detected by a Czerny Turner spectrometer (CTS) in a spectral range of 1374 nm to 1669 nm. The multi-pass approach with SMF coupling, which avoids multi-mode fiber induced noise, allows for high-speed multi-species SCLAS measurements with low standard deviations; for temperature this amounts to about 5 K and partially below at a temporal resolution of 25 µs.

Effect of processing speed on wear and corrosion behavior of novel MoS2 and CeO2 reinforced hybrid aluminum matrix composites fabricated by friction stir processing

The extensive use of aluminum matrix composites as structural material urges it to possess good surface properties such as wear and corrosion resistance. To achieve that, mixture of MoS 2 and CeO 2 powder was reinforced in Al7075 alloy through friction stir processing with different processing speed and multi-pass approach. The microstructural image analysis by optical microscope and scanning electron microscope revealed reduction of matrix grain size and improvement of particle distribution for lower processing speed and multi-pass processing. The elemental analysis indicated well dispersion of reinforcement particles in matrix along with the presence of compounds of aluminum alloy. The microhardness and tensile strength were increased with reduction of processing speed and increase of number of pass. The friction coefficient and the wear loss were also low for composites produced with low processing speed and multi-pass. A combined abrasive and adhesive wear was observed in all the processed composites. With increase of processing speed and number of pass, the corrosion behavior of the composites in 3.5% NaCl solution deteriorated. The composite produced with 30 mm/min and 2 pass exhibited best particle distribution, microhardness and wear resistance. However, the composite fabricated with 30 mm/min and 1 pass yielded best corrosion resistance. • Novel hybrid aluminum matrix composites developed by friction stir processing • Microstructure of the fabricated composites analyzed • Microhardness distribution measured • Wear mechanism and friction coefficient variation analyzed and effect of processing speed on wear loss discussed • Corrosion behavior and effect of process parameters on corrosion parameters discussed

Nonlinear pulse compression to 22 fs at 15.6 µJ by an all-solid-state multipass approach.

We demonstrate nonlinear compression of pulses at 1.03 µm and repetition rate of 200 kHz generated by a ytterbium fiber laser using two cascaded all-solid-state multipass cells. The pulse duration has been compressed from 460 to 22 fs, corresponding to a compression factor of ∼21. The compressed pulse energy is 15.6 µJ, corresponding to an average power of 3.1 W, and the overall transmission of the two compression stages is 76%. The output beam quality factor is M2 ∼1.2 and the excess intensity noise introduced by nonlinear broadening is below 0.05%. These results show that nonlinear pulse compression down to ultrashort durations can be achieved with an all-solid-state approach, at pulse energies much higher than previously reported, while preserving the spatial characteristics of the laser.

Multi-pass approach to reduce cone-beam artifacts in a circular orbit cone-beam CT system.

We propose a multi-pass approach to reduce cone-beam artifacts in a circular orbit cone-beam computed tomography (CT) system. Employing a large 2D detector array reduces the scan time but produces cone-beam artifacts in the Feldkamp, Davis, and Kress (FDK) reconstruction because of insufficient sampling for exact reconstruction. While the two-pass algorithm proposed by Hsieh is effective at reducing cone-beam artifacts, the correction performance is degraded when the bone density is moderate and the cone angle is large. In this work, we treated the cone-beam artifacts generated from bone and soft tissue as if they were from less dense bone objects and corrected them iteratively. The proposed method was validated using a numerical Defrise phantom, XCAT phantom data, and experimental data from a pediatric phantom followed by image quality assessment for FDK, the two-pass algorithm, the proposed method, and the total variation minimization-based iterative reconstruction (TV-IR). The results show that the proposed method was superior to the two-pass algorithm in cone-beam artifact reduction and effectively reduced the overcorrection by the two-pass algorithm near bone regions. It can also be observed that the proposed method produced better correction performance with fewer iterations than the TV-IR algorithm. A qualitative evaluation with mean-squared error, structural similarity, and structural dissimilarity demonstrated the effectiveness of the proposed method.

Producing Sustainable Nanostructures in Ti-6Al-4V Alloys for Improved Surface Integrity and Increased Functional Life in Aerospace Applications by Cryogenic Burnishing

Finishing processes such as shot peening, polishing and burnishing have a major influence on the functional performance of manufactured components. In this study, cryogenic burnishing is investigated as a low-force technique for imparting nanostructured grains and hardness increase in the processed surface layers of Ti-6Al-4V alloy. Using a multi-pass approach, deflection of the workpiece can be significantly reduced, allowing for processing of thin walled aerospace components such as turbine blades. Looking forward, the ability to design and manufacture nanostructured components at industrial scales is envisioned to enable the creation of new products with engineered surface layers for improved functional performance.

Learning deep similarity metric for 3D MR-TRUS image registration.

The fusion of transrectal ultrasound (TRUS) and magnetic resonance (MR) images for guiding targeted prostate biopsy has significantly improved the biopsy yield of aggressive cancers. A key component of MR-TRUS fusion is image registration. However, it is very challenging to obtain a robust automatic MR-TRUS registration due to the large appearance difference between the two imaging modalities. The work presented in this paper aims to tackle this problem by addressing two challenges: (i) the definition of a suitable similarity metric and (ii) the determination of a suitable optimization strategy. This work proposes the use of a deep convolutional neural network to learn a similarity metric for MR-TRUS registration. We also use a composite optimization strategy that explores the solution space in order to search for a suitable initialization for the second-order optimization of the learned metric. Further, a multi-pass approach is used in order to smooth the metric for optimization. The learned similarity metric outperforms the classical mutual information and also the state-of-the-art MIND feature-based methods. The results indicate that the overall registration framework has a large capture range. The proposed deep similarity metric-based approach obtained a mean TRE of 3.86mm (with an initial TRE of 16mm) for this challenging problem. A similarity metric that is learned using a deep neural network can be used to assess the quality of any given image registration and can be used in conjunction with the aforementioned optimization framework to perform automatic registration that is robust to poor initialization.

Measuring the velocity fields of granular flows – Employment of a multi-pass two-dimensional particle image velocimetry (2D-PIV) approach

Measuring velocity fields plays a crucial role in investigating the dynamics of granular flows, which can improve the modeling of hazardous geophysical flows (e.g. avalanches and debris flows) and the control of powder flows in industrial applications. Non-invasive optical methods are invaluable tools for estimating this physical quantity at the laboratory scale. Despite the recent improvements of particle image velocimetry (PIV) algorithms, the employment of PIV to granular flows is still a non-trivial application, where there are several specific aspects to be carefully addressed. Here, we address the main challenges of granular PIV applications and systematically test the open-source window deformation multi-pass code, PIVlab [Thielicke and Stamhuis, J. Open Res. Soft., 2014], for dry granular flows in rotating drum and chute flow experiments. Three granular media (glass spheres, Ottawa sand and acetalic resin beads) with different optical properties are used as a broad test bench for validating the PIV approach. As well, comparisons between the estimations by PIVlab and those obtained by the commercial code, IDT ProVision-XS, are reported, where the advantages of the multi-pass approach are highlighted. This extensive experimental investigation allowed the evaluation of the accuracy of PIVlab in granular flow applications and also helped to assess the reliability of measurements of second-order statistics, such as the granular temperature. Finally, a guideline for setting a reliable PIV arrangement is suggested.

Fine-Needle Aspiration Biopsy for Molecular Genomic Classification: Evaluation of Transscleral vs Transvitreal Biopsy

Purpose: To evaluate the transvitreal and transscleral fine-needle aspiration biopsy (FNAB) approach for molecular classification with gene-expression profiling (GEP) of uveal melanoma. Methods: Institutional review board–approved single-surgeon retrospective analysis of a consecutive case series of all patients undergoing FNAB using a 25-gauge-needle multipass approach for GEP analysis of uveal melanoma between 2012 and 2016. All FNAB specimens were processed for uveal melanoma diagnostic testing using a standard processing approach, and all testing was completed at a single laboratory (Castle Biosciences, Inc.). Results: Three hundred fifty-three eyes (353 patients) were included. Transvitreal biopsies were performed in 216 eyes (216/353, 61.2%), whereas transscleral biopsies were performed in 137 eyes (137/353, 38.8%). Twenty biopsies exhibited multiple gene failure (20/353, 5.6%). Excessive fluid biopsy volume was the primary association with reported multiple gene failure, occurring in 10 of 20 eyes (50%). FNAB performed via the transvitreal approach was significantly more likely to have an excessive volume report compared with transscleral biopsy (18/216, 8.3% vs 1/137, 0.7%; P &lt; .001). Conclusions: FNAB performed via a transscleral or transvitreal multipass approach utilizing a 25-gauge needle achieves molecular classification in 95% of all patients undergoing treatment for presumed uveal melanoma independent of tumor size. Complications related to FNAB using these techniques are rare and may be associated with the presentation of the uveal melanoma.

Influence of drawing practices on the mechanical, texture and work hardening characteristics of Co-Cr-Ni-Mo wires

This study investigates the influence of cold wire drawing practices namely Full Die Drawing (FDD) and Half Die Drawing (HDD) on the microstructure, mechanical and work hardening characteristics on Co-35Ni-20Cr-10Mo material. The wires were subjected to different reductions using a multipass drawing approach and the resulting microstructures were characterized by EBSD and FESEM. It was found that wires drawn with FDD practice showed a higher Yield strength (σYS,) Ultimate Tensile strength (σUTS), higher work hardening rate, and different regimes of work hardening curves when compared to the wires drawn with HDD practice, for the same amount of Cold Work (CW). It was observed that FDD wires had a smaller grain size, homogenous texture and higher amount twins and dislocations in the microstructure, whereas the HDD wires exhibited coarser grains, non-uniform texture and a lower amount of lattice defects.

Analysis of the Multipass Approach for Collection and Processing of Mobile Laser Scan Data

AbstractThe standard method in surveying practice for adjusting mobile terrestrial laser scan (MTLS) data to correct for global navigation satellite system (GNSS) positioning errors consists of pla...

Controlling grain size via dynamic recrystallization in an advanced polycrystalline nickel base superalloy

Controlling grain size in polycrystalline nickel base superalloy is of paramount importance in optimizing hot-working process and achieving the desirable mechanical properties. Typically, a uniform and fine grain size is required throughout forging process to realize the superplastic deformation. Unfortunately, the forging processing window is very narrow and needs to be synergistically controlled by deformation temperature, strain rate, as well as strain amount, and the failure would lead to the non-uniform grain size, abnormal grain growth and even cracking. During superplastic deformation, dynamic recrystallization (DRX) is the governing mechanism to be adopted to maintain the required grain size. Previous literature have extensively documented the separated effect of deformation parameters using monotonic-pass compression test. Herein, we perform the multi-pass compression experiments to investigate the flow stress behavior and grain size evolution. By conducting multi-pass tests over a range of deformation parameters, it was demonstrated that the flow stress and grain size response differed from that in single-pass tests. The multi-pass compression tests unambiguously uncover the roles of DRX and static recrystallization (SRX) in regulating grain size and affecting flow stress. The experimental results further show, comparing to the monotonic-pass compression, the multi-pass approach can provide versatile routes to attain the desirable grain size distribution by means of utilizing DRX and SRX principles.

Strain uncertainties from two digital volume correlation approaches in prophylactically augmented vertebrae: Local analysis on bone and cement-bone microstructures

Combination of micro-focus computed tomography (micro-CT) in conjunction with in situ mechanical testing and digital volume correlation (DVC) can be used to access the internal deformation of materials and structures. DVC has been exploited over the past decade to measure complex deformation fields within biological tissues and bone-biomaterial systems. However, before adopting it in a clinically-relevant context (i.e. bone augmentation in vertebroplasty), the research community should focus on understanding the reliability of such method in different orthopaedic applications involving the use of biomaterials. The aim of this study was to evaluate systematic and random errors affecting the strain computed with two different DVC approaches (a global one, “ShIRT-FE”, and a local one, “DaVis-DC”) in different microstructures within augmented vertebrae, such as trabecular bone, cortical bone and cement-bone interdigitation. The results showed that systematic error was insensitive to the size of the computation sub-volume used for the DVC correlation. Conversely, the random error (which was generally the largest component of error) was lower for a 48-voxel (1872micrometer) sub-volume (64–221 microstrain for ShIRT-FE, 88–274 microstrain for DaVis-DC), than for a 16-voxel (624micrometer) sub-volume (359–1203 microstrain for ShIRT-FE, 960–1771 microstrain for DaVis-DC) for the trabecular and cement regions. Overall, the local random error did not appear to be influenced by either bone microarchitecture or presence of biomaterial. For the 48-voxel sub-volume the global approach was less sensitive to the gradients in grey-values at the cortical surface (random error below 200 microstrain), while the local approach showed errors up to 770 microstrain. Mean absolute error (MAER) and standard deviation of error (SDER) were also calculated and substantially improved when compared to recent literature for the cement-bone interface. The multipass approach for DaVis-DC further reduced the random error for the largest volume of interest. The random error did not follow any recognizable pattern with the six strain components and only ShiRT-FE seemed to produce lower random errors in the normal strains. In conclusion this study has provided, for the first time, a preliminary indication of the reliability and limitations for the application of DVC in estimating the micromechanics of bone and cement-bone interface in augmented vertebrae.

MULTI-PASS APPROACH FOR MOBILE TERRESTRIAL LASER SCANNING

Abstract. Mobile Terrestrial Laser Scanning (MTLS) has been utilised for an increasing number of corridor surveys. Current MTLS surveys require that many targets be placed along the corridor to monitor the MTLS trajectory’s accuracy. These targets enable surveyors to directly evaluate the magnitude of GNSS errors at regular intervals and can also be used to adjust the trajectory to the survey control. However, this “Multi-Target” approach (MTA) is an onerous task that can significantly reduce efficiency. It also is inconvenient to the travelling public, as lanes are often blocked and traffic slowed to permit surveyors to work safely along the road corridor. This paper introduces a “Multi-Pass” approach (MPA), which minimises the number of targets required for monitoring the GNSS-controlled trajectory while still maintaining strict engineering accuracies. MPA uses the power of multiple, independent MTLS passes with different GNSS constellations to generate a “Control Polyline” from the point cloud for the corridor. The Control Polyline can be considered as a statistically valid survey measurement and be incorporated in a network adjustment to strengthen a control network by identifying outliers. Results from a test survey at the MTLS course maintained by the Oregon Department of Transportation illustrate the effectiveness of this approach.

Numerical modelling of multi-pass solar dryer filled with granite pebbles for thermal storage enhancement

In this paper, a theoretical modelling of a cheap solar thermal dryer for small and medium scale farmers with multi-pass approach has been investigated. Comsol Multiphysics modelling tool was employed using numerical technique. The rock particles were used to enhance the thermal storage of the drying system. The local weather data were used during the simulation while parameters and coefficients were sourced from literature. An improvement on efficiency of up to 7% was recorded with error of 10-5 when compared with the reported double pass solar collector. A fair distribution of hot air within the cabinets was also achieved. Though the modelling tool used was robust but the characterization of the system materials need to be done to improve the system accuracy and better prediction.