Large Parts Research Articles

Tomographic eigenstrain reconstruction for full-field residual stress analysis in large scale additive manufacturing parts

Current experimental and numerical quantification methods are limited in their ability to full-field mapping of the unpredictable distribution of all residual stress and permanent plastic strain components in additive manufacturing parts with discontinuous processing properties. To address this limitation, a tomographic eigenstrain (inherent strain) reconstruction method, that merges eigenstrain reconstruction with diffraction strain tomography for mapping volumetric distribution of all components of eigenstrains and corresponding elastic deformations like residual stresses non-destructively using minimum amount of tomographic scans is presented through numerical experiments, and then applied to the analysis of a CM 247 LC superalloy additive manufacturing part using diffraction strain tomography data. The method reconstructs all eigenstrain and corresponding residual stress components, parallel to the build direction, aligned with the experimental data component accurately, demonstrating its potential in optimizing the performance and reliability of parts designed for high-tech industries such as aerospace. Subsequent validations using the X-ray diffraction sin2ψ and neutron diffraction strain scanning techniques confirm the method's reliability in reconstructing residual stress components parallel to the plane of powder bed that are different from the experimental data component. Furthermore, the novel findings of this study reveal a characteristic residual stress distribution pattern within additive manufacturing parts particularly those featuring rectangular shapes. Microstructural analysis also validates eigenstrain distribution in accordance with the findings on the characteristic distribution of residual stresses, highlighting the significance of this method in advancing materials research and development.

Hard anodizing of AK9ch high silicon aluminum alloy

This work is devoted to anodic oxidation at low temperatures in the sulfuric acid electrolyte of the foundry aluminum alloy AK9ch, with a high silicon content. Optimal anodizing conditions were chosen for obtaining coatings with a hardness of more than 300 HV and a thickness of about 40 microns. With an increase in the thickness of the coatings by increasing the current density or anodizing time, their hardness begins to decrease. The resulting hard coatings are planned to be used on large parts obtained by casting aluminum alloy AK9ch.

Detection of US and Kobe‐type Babesia microti in ticks collected from small mammals of the Republic of Korea

AbstractHuman babesiosis is an emerging tick‐borne zoonotic disease prevalent in large parts of the world. This study aimed to examine the status of Babesia microti infection in ticks collected from small mammals captured during the nationwide survey of the Republic of Korea (ROK), 2017. Ixodid ticks from small mammals of three species, Apodemus agrarius, Crocidura lasiura, and Tscherskia triton, were used for the molecular detection of B. microti. PCR analyses amplifying 18S ribosomal RNA (rRNA) of the genus Babesia showed 8.4% of the ticks to be positive. Nucleotide sequencing of the PCR products revealed two different genotypes of B. microti, the US and Kobe‐type. The US‐types of B. microti were detected in ticks from small mammals of almost all study sites, whereas detections of Kobe‐types were restricted to ticks from southern part of ROK. Phylogenetic analysis also indicated that each of the two types of B. microti clustered into two distinct clades. This is the first report on the presence of the US and Kobe‐type B. microti in ticks collected from small mammals trapped on a national scale in ROK.

The Role of Aerial Prospection for Monitoring and Preserving Cultural Heritage in Northeastern Africa

Anthropogenic and environmental processes present unique challenges for preserving cultural heritage in North Africa. Large parts of this region are characterised by unfavourable arid and semi-arid conditions and rapid changes to the landscapes caused by heightened regional development (e.g., urban expansion, road building, agricultural intensification, and socio-political conflicts). As a result, we are facing a fast-paced disappearance of heritage sites in regions that are still poorly understood. Following this, the utilisation of Earth observation data through aerial photographs and satellite imagery has emerged as an unmatched tool in the exploration of endangered archaeological heritage. Drawing on this context, this paper underscores the critical significance of incorporating digital research methods, such as remote sensing, GIS, or cartographic analysis, to ensure the evaluation and (digital) preservation of the historical sites along these vulnerable areas. Furthermore, our study seeks to provide new insights into data management and dissemination, fostering open research practices within North African archaeological research.

Public acceptance in direct potable water reuse: a call for incorporating responsible research and innovation

ABSTRACT As global issues such as climate change and diminishing resources become increasingly pressing, water recycling has moved into the focus. However, the successful implementation of Direct Potable Water Reuse (DPR) projects hinges on securing public acceptance, which remains challenging. This paper aims to flesh out possible reasons for the lingering public rejection of DPR. We will do so by conducting a literature review on how public acceptance is understood and what approaches are proposed to enhance it. These approaches are analyzed using Responsible Research and Innovation principles and the `opening up', `closing down' and `leaving ajar' approaches. Our research identifies an overreliance on the controversial information deficit model, closing down large parts of public engagement. We advocate for becoming more inclusive through the `leaving ajar' approach. Particularly, attention should be paid to reflexivity and responsiveness to public concerns to ensure meaningful public engagement.

Sensitivity of air quality model responses to emission changes: comparison of results based on four EU inventories through FAIRMODE benchmarking methodology

Abstract. Despite the application of an increasingly strict EU air quality legislation, air quality remains problematic in large parts of Europe. To support the abatement of these remaining problems, a better understanding of the potential impacts of emission abatement measures on air quality is required, and air chemistry transport models (CTMs) are the main instrument to perform emission reduction scenarios. In this study, we study the robustness of the model responses to emission reductions when emission input is changed. We investigate how inconsistencies in emissions impact the modelling responses in the case of emission reduction scenarios. Based on EMEP simulations over Europe fed by four emission inventories – EDGAR 5.0, EMEP-GNFR, CAMS 2.2.1 and CAMS version 4.2 (including condensables) – we reduce anthropogenic emissions in six cities (Brussels, Madrid, Rome, Bucharest, Berlin and Stockholm) and two regions (Po Valley in Italy and Malopolska in Poland) and study the variability in the concentration reductions obtained with these four emission inventories. Our study reveals that the impact of reducing aerosol precursors on PM10 concentrations result in different potentials and potencies, differences that are mainly explained by differences in emission quantities, differences in their spatial distributions as well as in their sector allocation. In general, the variability among models is larger for concentration changes (potentials) than for absolute concentrations. Similar total precursor emissions can, however, hide large variations in sectorial allocation that can lead to large impacts on potency given their different vertical distribution. Primary particulate matter (PPM) appears to be the precursor leading to the major differences in terms of potentials. From an emission inventory viewpoint, this work indicates that the most efficient actions to improve the robustness of the modelling responses to emission changes would be to better assess the sectorial share and total quantities of PPM emissions. From a modelling point of view, NOx responses are the more challenging and require caution because of their non-linearity. For O3, we find that the relationship between emission reduction and O3 concentration change shows the largest non-linearity for NOx (concentration increase) and a quasi-linear behaviour for volatile organic compounds (concentration decrease). We also emphasise the importance of accurate ratios of emitted precursors since these lead to changes in chemical regimes, directly affecting the responses of O3 or PM10 concentrations to emission reductions.

Identifying umbrella and indicator species to support multispecies population connectivity in a Himalayan biodiversity hotspot

Successful conservation hinges on the reliable prediction and prioritisation of population core habitats and dispersal corridors. However, reliance on single-species connectivity has produced mixed results and, in most cases, failed to protect other species under the appealing but often unfulfilled guise of umbrella protection. The main objectives of this study were: (1) to identify core habitats and dispersal corridors for population connectivity of 15 terrestrial mammal species across Bhutan, (2) to identify indicator species of wildlife connectivity, (3) to prioritise core areas and dispersal corridors for the focal umbrella and indicator species, (4) to develop composite multispecies connectivity maps and evaluate the effectiveness of the existing protected area network. We used kernel density (KD) to identify core habitat areas and factorial least-cost path (LCP) to map dispersal corridors. We used correlation and cluster analyses to identify umbrella and indicator species, and quantitative ranking to prioritise core areas and corridors for these focal species. Finally, we produced maps of multispecies core areas and corridors, and identified gaps in the existing protected area network (PAN). We found that ungulates were generally more effective than carnivores in serving as umbrella species for core habitat protection, with Asian elephant (Elephas maximus) emerging as the most effective umbrella for core habitats and muntjac (Muntiacus muntjac) for dispersal corridors. We identified six focal connectivity indicator species in Bhutan: tiger (Panthera tigris), dhole (Cuon alpinus), clouded leopard (Neofelis nebulosa), Asiatic black bear (Ursus thibetanus), Asian elephant, and sambar deer (Rusa unicolor). Most indicator species’ core areas and dispersal corridors outside the PAN were in southern Bhutan, indicating opportunities for increased multispecies connectivity through expanding protected area network in this region. A total of 40% of multispecies core areas and 24% of dispersal corridors were under PAN, with large parts of Bhutan offering suitable core areas and corridors for multispecies conservation. Core areas and corridors of the 15 considered species only partially overlapped, stressing the importance of multi-species consideration in designating wildlife corridors.

A finite element model with multi-flow fields for the quenching process of mill liner component made of bainite and martensite: simulation and experimental validation

Controlling the type and location of microstructure transformation through heat treatment processes is the key to improving the property of workpieces, especially they are large-sized and highly thick irregular. Such as mill liner, the worst wear in mining machinery, of which microstructure inhomogeneity is key to developing cost-efficient mining process. In order for advanced high strength steel (AHSS) to be used in mining machinery, its microstructure uniformity must be optimized, usually by adjusting the process parameters of the heat treatment process to optimize the microstructure distribution uniformity. However, the research on the simulation of large-sized and highly thick irregular heat treatment process is limited. Previous studies usually controlled the heat transfer process by using the heat transfer coefficient as the boundary condition, but only applied to small size and simple structure of the workpiece. As the heat transfer coefficient is a process quantity, its size depends on the thermal property parameters of the fluid on both sides of the wall, the flow rate, the shape of the solid surface, the thermal property number of the material and other factors, which is not suitable for large-sized and highly thick irregular. Therefore, for the large-sized and highly thick irregular heat treatment simulation process, the equivalent heat transfer coefficient of flow field was introduced as the boundary condition, and the temperature field, microstructure field and stress field were coupled to improve the accuracy of the numerical model. The accuracy of the finite element model is verified by comparing the temperature simulation error of less than 10% through temperature measurement experiments of the quenched workpiece. The evolution process of heat transfer in large-sized and highly thick irregular water bath quenching is obtained through the finite element model data. The difference in the flow rate of the wall fluid is the fundamental reason for the difference in cooling effect, and the wetting process of the wall is the secondary reason. At the same time, the corresponding microstructure and surface hardness distribution of different cooling regions are obtained, which can provide more accurate guidance for the optimization of heat treatment process of large size and thick special-shaped parts.

Estimating Surface EMG Activity of Human Upper Arm Muscles Using InterCriteria Analysis

Electromyography (EMG) is a widely used method for estimating muscle activity and could help in understanding how muscles interact with each other and affect human movement control. To detect muscle interactions during elbow flexion and extension, a recently developed InterCriteria Analysis (ICrA) based on the mathematical formalisms of index matrices and intuitionistic fuzzy sets is applied. ICrA has had numerous implementations in different fields, including biomedicine and quality of life; however, this is the first time the approach has been used for establishing muscle interactions. Six human upper arm large surface muscles or parts of muscles responsible for flexion and extension in shoulder and elbow joints were selected. Surface EMG signals were recorded from four one-joint (pars clavicularis and pars spinata of m. deltoideus [DELcla and DELspi, respectively], m. brachialis [BRA], and m. anconeus [ANC]) and two two-joint (m. biceps brachii [BIC] and m. triceps brachii-caput longum [TRI]) muscles. The outcomes from ten healthy subjects performing flexion and extension movements in the sagittal plane at four speeds with and without additional load are implemented in this study. When ICrA was applied to examine the two different movements, the BIC–BRA muscle interaction was distinguished during flexion. On the other hand, when the ten subjects were observed, four interacting muscle pairs, namely DELcla-DELspi, BIC-TRI, BIC-BRA, and TRI-BRA, were detected. The results obtained after the ICrA application confirmed the expectations that the investigated muscles contribute differently to the human upper arm movements when the flexion and extension velocities are changed, or a load is added.

Heat flow of the Mozambique channel: New data and predicted surface heat flow map

The Mozambique Channel, a complex domain composed of passive margins and oceanic crust affected by younger strike-slip and volcanic activity, is still poorly studied for surface heat flow. We present 33 new marine-type heat flow estimations acquired offshore in 2014–2015 during the MOZ cruises, completed with 4 new heat flow values derived from reappraised old well sites (PAMELA project). Offshore heat flow is generally low to normal and does not display strong variations. As poor data coverage persists in large parts of the area, we performed a heat flow prediction mapping using the similarity method. Based on an extrapolation of old and new data guided by 14 geological and geophysical proxies, we obtain on a 0.1° × 0.1° grid a predicted heat flow and its uncertainty from the statistics of all values at global grid points with similar proxies. We succeeded to obtain good predictability on 70% of pixels and an RMS error <2.3 mW/m2. The proxies selected for the prediction include a map of genetic domains, sediment thickness, topography and bathymetry, crustal ages, Curie point depth, Free air anomaly, distances to volcanoes, tectonic structures and continent-ocean boundaries. The new Mozambique heat flow map shows a predominantly low offshore heat flow of around 50 mW/m2, associated with the Jurassic and early Cretaceous age of the oceanic crust. Several heat flow anomalies standoff to this background heat flow with two main orientations: low heat flow anomalies with a N–S orientation and high anomalies with a mostly NE-SW orientation, which are linked mainly to tectonic structures.

Relative importance of the mechanisms triggering the Eurasian ice sheet deglaciation in the GRISLI2.0 ice sheet model

Abstract. The last deglaciation (21 to 8 ka) of the Eurasian ice sheet (EIS) is thought to have been responsible for a sea level rise of about 20 m. While many studies have examined the timing and rate of the EIS retreat during this period, many questions remain about the key processes that triggered the EIS deglaciation 21 kyr ago. Due to its large marine-based parts in the Barents–Kara (BKIS) and British Isles sectors, the BKIS is often considered to be a potential analogue of the current West Antarctic ice sheet (WAIS). Identifying the mechanisms that drove the EIS evolution might provide a better understanding of the processes at play in the West Antarctic destabilization. To investigate the relative impact of key drivers on the EIS destabilization, we used the three-dimensional ice sheet model GRISLI (GRenoble Ice Shelf and Land Ice) (version 2.0) forced by climatic fields from five Paleoclimate Modelling Intercomparison Project phases 3 and 4 (PMIP3, PMIP4) Last Glacial Maximum (LGM) simulations. In this study, we performed sensitivity experiments to test the response of the simulated Eurasian ice sheets to surface climate, oceanic temperatures (and thus basal melting under floating ice tongues), and sea level perturbations. Our results highlight that the EIS retreat simulated with the GRISLI model is primarily triggered by atmospheric warming. Increased atmospheric temperatures further amplify the sensitivity of the ice sheets to sub-shelf melting. These results contradict those of previous modelling studies mentioning the central role of basal melting on the deglaciation of the marine-based Barents–Kara ice sheet. However, we argue that the differences with previous works are mainly related to differences in the methodology followed to generate the initial LGM ice sheet. Due to the strong sensitivity of EIS to the atmospheric forcing highlighted with the GRISLI model and the limited extent of the confined ice shelves during the LGM, we conclude by questioning the analogy between EIS and the current WAIS. However, because of the expected rise in atmospheric temperatures, the risk of hydrofracturing is increasing and could ultimately put the WAIS in a configuration similar to the past Eurasian ice sheet.

Sensitivity of sustainable urban drainage systems to precipitation events and malfunctions

Abstract In recent years, sustainable urban drainage systems (SUDSs) have become increasingly popular, sometimes taking over large parts of conventional stormwater management. SUDSs are usually designed using simple design procedures based on statistical rainfall data, without long-term simulations or real rainfall events. In addition, there is little experience of how SUDS respond to potential failures and malfunctions, often caused by ageing infrastructure and lack of asset management. Based on these two factors influencing the hydrological performance of SUDS, this study investigates the sensitivity of seven different SUDSs to rainfall events and malfunctions. The study was conducted using the SWMM 5.2 modeling software and the low impact development (LID) module was implemented for a period of 60 years. The SUDS are studied as individual infrastructure and as part of a small urban catchment. The results show that only the green roofs and rainwater cisterns have a statistically significant correlation between the length and return period of rain events and runoff values, with higher correlations for longer rain events. In contrast, the failures and malfunctions investigated can have a significant impact on the hydrological performance of SUDS. In particular, the design return period of SUDS was occasionally significantly exceeded for the strong malfunction scenarios studied.

Prejudicial findings regarding suitability for intended purpose during pre-purchase examinations in a mixed horse population-A retrospective observational study in the United Kingdom.

Pre-purchase examinations (PPEs) are performed for prospective purchasers of horses to identify prejudicial findings that could make animals unsuitable for an intended use. Although this examination process is often standardised, PPEs remain, in large parts, a subjective procedure. In the United Kingdom, PPEs generally consist of either a two stage (two stage vetting [2SV], i.e., general physical examination at rest and basic trot in-hand) or a five stage-examination (five stage vetting [5SV], i.e., general physical exam at rest and after exercise, lameness evaluation including strenuous exercise with re-evaluation after a period of recovery). To identify the proportion of PPEs with prejudicial findings in a mixed horse population in the United Kingdom and to determine those findings. Retrospective observational study. PPE certificates from three first opinion equine practices were reviewed. Data collected included practice identity, examination format (i.e., 2SV or 5SV), PPE outcome, radiographs obtained (yes/no), purchase price, animal signalment, intended use and prejudicial PPE findings, if indicated. Prejudicial findings were grouped in 10 subcategories. Descriptive statistics were obtained for all parameters. Non-normally distributed numeric data between groups were compared using Wilcoxon rank-sum test. Categorical data were compared between groups using Pearson's chi-squared test or Fisher's exact test. Overall, 133 pre-purchase examination certificates were analysed. Seventy-six horses (57.1%) had prejudicial findings: Sixty-one (68.5%) horses undergoing 5SV and 15 (34.1%) of horses undergoing 2SV. Most horses had lameness as the primary prejudicial finding. Horses with a higher purchase price were more likely to undergo 5SV, undergo pre-purchase radiography, and were more likely to have prejudicial findings identified. Data were obtained retrospectively from PPE certificates from a single mixed horse population and different results may have been obtained by analysing a larger number of animals or PPEs of horses intended for different uses, from different geographical regions or undergoing a different PPE format. The level of competition in the intended discipline for horses was not recorded. Analysed data were limited to the information recorded on the PPE certificates, and the original radiographs, ultrasonography images and other additional diagnostic data were not reviewed. Lameness was the most common prejudicial PPE finding. More expensive horses were more likely to undergo a 5SV, have pre-purchase radiographs obtained and have prejudicial findings identified. These results may help inform prospective studies examining the merits of 5SV versus 2SV formats and the value of inclusion of additional diagnostic imaging in PPEs in the general horse population.

Principal Preferred Orientation Evaluation of Steel Materials Using Time-of-Flight Neutron Diffraction

Comprehensive information on in situ microstructural and crystallographic changes during the preparation/manufacturing processes of various materials is highly necessary to precisely control the microstructural morphology and the preferred orientation (or texture) characteristics for achieving an excellent strength–ductility–toughness balance in advanced engineering materials. In this study, in situ isothermal annealing experiments with cold-rolled 17Ni-0.2C (mass%) martensitic steel sheets were carried out by using the TAKUMI and ENGIN-X time-of-flight neutron diffractometers. The inverse pole figures based on full-profile refinement were extracted to roughly evaluate the preferred orientation features along three principal sample directions of the investigated steel sheets, using the General Structure Analysis System (GSAS) software with built-in generalized spherical harmonic functions. The consistent rolling direction (RD) inverse pole figures from TAKUMI and ENGIN-X confirmed that the time-of-flight neutron diffraction has high repeatability and statistical reliability, revealing that the principal preferred orientation evaluation of steel materials can be realized through 90° TD ➜ ND (transverse direction ➜ normal direction) rotation of the investigated specimen on the sample stage during two neutron diffraction experiments. Moreover, these RD, TD, and ND inverse pole figures before and after the in situ experiments were compared with the corresponding inverse pole figures recalculated from the MUSASI-L complete pole figure measurement and the HIPPO in situ microstructure evaluation, respectively. The similar orientation distribution characteristics suggested that the principal preferred orientation evaluation method can be applied to the in situ microstructural evolution of bulk orthorhombic materials and spatially resolved principal preferred orientation mappings of large engineering structure parts.

Machining-induced residual stress and deformation during Mg–Li alloy thin-walled rib-web parts milling

The deformation of thin-walled parts based on the lightweight Mg–Li alloy materials caused by machining-induced stress is an important factor hindering the further development of lightweight in the aerospace field. Prediction of the machining-induced residual stress is the key to understand the deformation and derive low-stress machining scheme. In this study, the equivalent cutting deformation loads were applied to substitute the strongly coupled thermal-mechanical behavior between the tool and part to realize the prediction of the machining-induced stress and deformation of thin-walled rib-web part under different milling conditions. The local regular and complex rib-web parts share a same deformation mode, both behave as in-plane bending deformation of the machined surface. The low-stress milling scheme of up milling combined with cryogenic cooling obtained based on the local regular four rid-web thin-walled part was applicable to the prediction of the complex Mg-Li alloy disk rib-web part. Compared with the initial scheme, the maximum stress and deformation displacement based on the low-stress scheme were reduced from 80 to 36 MPa and from 0.04060 to 0.00814 mm, respectively. Finally, the effectiveness of low-stress milling scheme were verified based on the milling and measurement experiments of the complex thin-walled disk rib-web part. These results indicate the effectiveness of the modeling method for thin-walled rib-web parts and prove the results obtained based on the local model can be extended and applied to large complex parts with the same structural type.

Touching the cold in the Little Ice Age

Climate change urges us to reconsider the very cold. Its natural manifestations – ice and snow – are today shrinking elements, and the gravity of melting glaciers and thawing polar regions is indeed deeply worrying for the planet as a whole. In this article questions will be raised concerning how cold was understood and imagined during the Little Ice Age, when the freezing cold was a regular part of the everyday life in large parts of Europe. The very cold became an object of enquiry for natural philosophers in unprecedented ways. The article focuses on Robert Boyle’s New Experiments and Observations touching Cold, or an Experimental History of Cold, begun (London, 1665) and Margaret Cavendish’s Observations upon Experimental Philosophy (London, 1666) and explores early modern English imaginaries of the polar regions, and how they join in the scientific debate on how to understand the cold.

Thermomechanical characterization of brazed SiC assemblies for receivers of CSP plants

In order to increase the performance of solar tower power plants, it is necessary to improve the receivers in order to reach higher temperatures or a longer life span. Silicon carbide is a promising material for this purpose, but large parts cannot be made in one piece: a joining process is required. BraSiC® brazing alloys have been developed to produce silicon carbide assemblies that can withstand temperatures of about 1000°C, but their thermomechanical behavior is poorly understood. The understanding of the failure mechanisms as well as the knowledge of the limits of use of these materials is essential to be able to produce reliable receivers. In this article, two types of BraSiC® braze have been studied: CEA 0 and CEA 1, using the IMPACT test bench, specifically developed to characterize materials under concentrated solar flux. The results show that the CEA 1 braze is more resistant to thermomechanical stresses. Two damage mechanisms of the brazed joints were also identified using acoustic emission.

Extremely warm European summers preceded by sub-decadal North Atlantic ocean heat accumulation

Abstract. The internal variability of European summer temperatures has been linked to various mechanisms on seasonal to sub- and multi-decadal timescales. We find that sub-decadal timescales dominate summer temperature variability over large parts of the continent and determine mechanisms controlling extremely warm summers on sub-decadal timescales. We show that the sub-decadal warm phases of bandpass-filtered European summer temperatures, hereinafter referred to as extremely warm European summers, are related to a strengthening of the North Atlantic Ocean subtropical gyre, an increase in meridional heat transport, and an accumulation of ocean heat content in the North Atlantic several years prior to the extreme summer. This ocean warming affects the ocean–atmosphere heat fluxes, leading to a weakening and northward displacement of the jet stream and increased probability of occurrence of high-pressure systems over Scandinavia. Thus, our findings link the occurrence of extremely warm European summers to the accumulation of heat in the North Atlantic Ocean and provide the potential to improve the predictability of extremely warm summers several years ahead, which is of great societal interest.

Adaptive powder nozzle setup for enhanced efficiency in laser metal deposition

Laser metal deposition (LMD) is a blown powder process used for the additive manufacturing of large and/or complex parts. The laser spot size is determined by the fiber optic cable and the imaging ratio of the process optics. Spot sizes typically used in LMD can range from 200 μm to several millimeters, whereby zoom optics can be employed to change the laser spot focus within seconds during the process. However, industrial powder nozzles are still static in terms of powder spot size. Changing the powder spot size in line with the laser spot size could ensure the favorable dual outcome of time savings when printing large volumes while also generating fine near-net-shape features. To help overcome the current limitations in the LMD process, this work examines an adaptive powder nozzle setup. In this discrete coaxial layout of three single lateral powder injectors, the individual powder injectors can be adjusted closer to or further from the process to, respectively, dilate or shrink the powder stream focus. Different inner diameters of powder injectors are hereby examined. The resulting powder propagation behavior is characterized for different setups of the single powder nozzles. Single beads are welded with different nozzle setups for fine and coarse powder spots, while the laser spot size is changed accordingly using zoom optics. The laser power is a closed-loop controlled by a two-color pyrometer to achieve comparative process temperatures. The single beads are evaluated with regard to their geometry. High-speed imaging provides supplementary information on weld bead generation.

Optimization of Fixture Number in Large Thin-Walled Parts Assembly Based on IPSO

There are lots of researches on fixture layout optimization for large thin-walled parts. Current researches focus on the positioning problem, i.e., optimizing the positions of a constant number of fixtures. However, how to determine the number of fixtures is ignored. In most cases, the number of fixtures located on large thin-walled parts is determined based on engineering experience, which leads to huge fixture number and extra waste. Therefore, this paper constructs an optimization model to minimize the number of fixtures. The constraints are set in the optimization model to ensure that the part deformation is within the surface profile tolerance. In addition, the assembly gap between two parts is also controlled. To conduct the optimization, this paper develops an improved particle swarm optimization (IPSO) algorithm by integrating the shrinkage factor and adaptive inertia weight. In the algorithm, particles are encoded according to the fixture position. Each dimension of the particle is assigned to a sub-region by constraining the optional position range of each fixture to improve the optimization efficiency. Finally, a case study on ship curved panel assembly is provided to prove that our method can optimize the number of fixtures while meeting the assembly quality requirements. This research proposes a method to optimize the number of fixtures, which can reduce the number of fixtures and achieve deformation control at the same time.