Horizontal Building Research Articles

사회복지학 전공 대학생의 팀 기반 학습(TBL) 과정에 관한 질적 연구

This study is a qualitative study for the holistic understanding of the Team-Based Learning (TBL) process conducted in social welfare subjects. By examining the research participants' perceptions through their practical experiences with TBL, this study aims to derive suggestions necessary for the instructional design and implements of TBL conducted for their major subjects. The data collection conducted a team-by-team interview with 24 students who took the "Social Welfare Administration Theory" subject(2nd semester of 2022), at department of social welfare in J university. TBL was conducted 13 times in this class. In the data analysis, the raw data was analyzed using open coding and categorization based on abstract meaning units. As a result of the analysis, 8 categories and 18 subcategories were derived. The TBL process was in the initial, middle, and terminal stages. At the initial stage, themes such as ‘felt pressured with TBL’, ‘spontaneous and horizontal team building’, and ‘time management-based team learning activities in class’ were derived. At the middle stage, ‘discovering the value of applying knowledge’, ‘recovering relationships due to the covid-19’ and professor's ‘scaffolding that suggested directions’, ‘team interaction of adjustment and compromise’ were derived. At the terminal stage, the students were able to outcomes ‘learning results that would not have been possible on their own’. Based on this, we make the following suggestions. Firstly, it requires creating an spontaneous atmosphere, secondly, building up relationships among team members, and finally, needing appropriate scaffolding which providing a guide.

Effects of lift-up building design, building setback, and urban open space on pedestrian danger under the joint effect of floodwater and wind

Urban block layouts affect both the flow patterns of floodwater and wind in urban built environments and ultimately pedestrian danger within the urban building array. Computational fluid dynamics (CFD) is used to simulate both the floodwater inundation process and the wind-blowing process within three kinds of urban block configurations under a floodwater-wind joint effect, including the lift-up building design, horizontal and vertical building setbacks, and urban open space. The obtained floodwater velocity, depth, and wind speed at the pedestrian level are adopted to quantify the level of pedestrian danger by using the instability threshold formula of a human body. A laboratory flume experiment regarding the stability/instability of a dummy that represents a pedestrian in a quasi-natural state is performed to qualitatively validate the numerical simulation results. Compared to the cuboid or triangular pillar that supports the lift-up building structure, the circular pillar yields the minimum resistance against floodwater and increases the wind speed at the pedestrian level, consequently leading to a large danger zone area. Horizontal building setbacks decrease the pedestrian danger, but vertical building setbacks intricately affect it. The existence of open space within the block decreases pedestrian danger to some extent depending on the location and area of open space. The wind plays the dominant role in triggering pedestrian instability for both the lift-up building design and the horizontal setback case. For both the lift-up building design and the open space configuration, the walking and running speeds of pedestrians decrease much more than the conventional urban block. The results of this study could be referred to by administrators and stakeholders in the design and management of urban building arrays to mitigate pedestrian risk in the content of resilient city management.

Micromechanical characteristics of titanium alloy (Ti-6Al-4V) made by laser powder bed fusion using an in-situ SEM micropillar compression technique

While titanium alloy (Ti-6Al-4V) made by laser powder bed fusion (L–PBF) exhibits complex deformation behaviors, its important micromechanical properties in relation to loading directions are not fully understood. This research aims to investigate the micromechanical behaviors of printed L–PBF Ti-6Al-4V alloys under vertical (i.e., the loading direction perpendicular to printed layers) and horizontal (i.e., the loading direction parallel to printed layers) compressions using in-situ scanning electron microscopy (SEM) micropillar techniques. Ti-6Al-4V alloys were L-PBF-printed using a 45° rotate scanning strategy with vertical and horizontal build directions. The microstructures of the two alloys were analyzed using the SEM with energy-dispersive X-ray spectroscopy (EDS). The titanium alloy micropillars were produced using focused ion beam (FIB) milling in the SEM. In-situ SEM micropillar compressions were conducted using a flat diamond indenter. Vertical alloy had smaller cross-patterned finer α′ martensite than horizontal one. While both vertical and horizontal micropillars showed elastic-plastic behaviors, the former had significantly higher yield, fracture, and compression strength values, as well as resilience and toughness, than the latter, leading to the formation of favorable shear bands. Both micropillars exhibited ductile fractures but had distinct failure mechanisms. The ductile fracture in the vertical micropillars was due to strain hardening, large plastic deformation, and shear band formation, while the ductile fracture in the horizontal ones was attributed to compression-induced bending and plastic buckling. The micromechanical characteristics of L–PBF Ti-6Al-4V materials provides an important insight into the small-scale deformation and failure mechanisms of the alloys influenced by loading directions.

The Anisotropic Mechanical and Tribological Behaviors of Additively Manufactured (Material Extrusion) Implant-Grade Polyether Ether Ketone (PEEK)

In this study, we investigated the mechanical and tribological properties of the layer-by-layer structure of additively manufactured implant-grade Polyether Ether Ketone (PEEK) through the Material Extrusion (ME) process as a potential substitute for artificial joints. The effective elasticity modulus of the anisotropic 3D-printed PEEK was determined to be 2.505 GPa along the vertical and horizontal build orientations. The lubricated friction and wear performance were assessed using a pin-on-disk test under various loads, including 14, 30, 50, and 70 N, with a sliding speed of 50 mm/s over a total distance of 1 km at 37 °C. The contact parameters between the hemispherical steel pin and 3D-printed PEEK disks, involving contact pressures over the circle of contact, were observed to increase as the load increased. The results indicated that the wear coefficient exhibited a rise from 1.418 × 10−5 to 2.089 × 10−1 as the applied loads increased, signaling a shift from mild to severe wear regimes. Fetal Bovine Serum (FBS) as a lubricant exhibited a mixed mechanism, ascertained through the Stribeck curve, as well as a minimum fluid film thickness of 1.346 nm under an isoviscous–elastic regime, as calculated by the maximum load. Moreover, the mechanism governing wear during sliding, influenced by both normal axial and shear loads, primarily involved adhesion.

Lisbon Urban Climate: Statistical Analysis/Approach for Urban Heat Island Effect Based on a Pioneering Urban Meteorological Network

The urban heat island (UHI) effect is a widely recognized phenomenon consisting of heat accumulation by dense urban construction and human activities, resulting in higher temperatures across urban areas compared to their surroundings. This article aims to quantify the UHI effect on several areas throughout the city of Lisbon, Portugal, with the main goal of validating, evaluating, and reinforcing urban climate adaptation and resilience strategies proposed in the recent scientific literature. A set of nine quality-controlled weather stations from the “Lisboa Aberta” network that are compliant with the World Meteorological Organization (WMO) standards and installation requirements were used to characterize Lisbon’s UHI, in comparison to a reference weather station from the Instituto Português do Mar e da Atmosfera (IPMA), located at Lisbon Airport. By applying a principal component analysis (PCA) in an innovative way to 10 urban indexes, it is shown that the thermal inertia in Lisbon’s urban areas is positively correlated with the UHI intensity and urban density, regardless of the daily heating/cooling cycle. Furthermore, the results show that land use also has an impact on the UHI effect, with continuous, vertical building areas showing the greatest deviations in comparison to the reference, averaging +1.8 °C. Contrastingly, horizontal building areas reveal an average deviation of +1.3 °C, with sparse, discontinuously built areas representing an average UHI effect of +0.2 °C. Finally, through a climatope analysis, it is determined that, across Lisbon, high-density urban areas and ventilation corridors are responsible for inducing average UHI effects of +1.7 °C and +0.2 °C, respectively.

An experimental and numerical effort on the vibration behavior of additively manufactured recycled polyethylene terephthalate glycol components

AbstractThe importance of recycling engineering components and thus obtaining low‐cost production solutions has become prominent in today's world. In this study, the mechanical and dynamic behaviors of three‐dimensional‐printed recycled polyethylene terephthalate glycol (RePET‐G) beams were investigated numerically and experimentally for the first time in the literature. Initially, the governing equations of the beams were determined according to the Bernoulli–Euler beam theory, and these equations were numerically solved using the differential quadrature method and ANSYS program. Subsequently, to validate the accuracy of the numerical models, the obtained natural frequencies were compared with experimental results. It was observed that the numerical results showed good agreement with the experimental results. Finally, the effects of beam length, infill rate, and building direction on the natural frequencies of RePET‐G beams were investigated. The outcomes showed that as the beam length changed, natural frequencies were significantly affected. Increasing the infill rate, especially for beams with vertical building direction, from 20% to 100% led to a slight decrease in the natural frequency values of the structure. Moreover, it was found that for beams with an infill rate of 100%, the natural frequency values obtained in the horizontal building direction were higher than those obtained in the vertical building direction.Highlights Printable recycled filaments have great potential for vibration applications. Sample length affects the first natural frequency value of RePETG parts. Differential quadrature and ANSYS methods can be utilized for the vibration. For the 3D‐printed samples, rising infill rate causes a natural frequency drop.

On the Mechanical Behavior of LP-DED C103 Thin-Wall Structures

Laser Powder Directed Energy Deposition (LP-DED) can produce thin-wall features on the order of 1 mm. These features are essential for large structures operating in extreme environments such as regeneratively cooled nozzles and heat exchangers, which often make use of refractory metals. In this work, the mechanical behavior of LP-DED C103 was investigated via quasi-static tensile testing and low cycle fatigue (LCF) testing. The effects of vacuum stress relief (SR) and hot isostatic pressing (HIP) heat treatments were investigated for specimens in the vertical and horizontal build orientations during tensile testing. The AB and SR properties were lower than literature values for wrought and laser powder bed fusion (L-PBF) bulk components but higher than electron beam powder bed fusion (EB-PBF). The application of a HIP cycle improved strength by 7% and ductility by 27% past the initial as-built condition. Fracture images reveal that interlayer stress concentration sites are responsible for fracture in specimens in the vertical orientation. Meanwhile, fracture in the horizontal specimens mainly propagates at a slanted angle typical of plane stress conditions. The LCF results show cycles to failure ranging from 100 cycles to 8000 cycles for max strain levels of 2% and 0.5%, respectively. Fractography on the fatigue specimens reveals an increasing propagation zone as max strain levels are increased. The impact of these findings and future work are discussed in detail.

Tensile Properties and Fracture Analysis of Duplex (2205) and Super Duplex (2507) Stainless Steels, Produced via Laser Powder Bed Fusion Additive Manufacturing

Additive manufacturing of duplex (DSS) and super duplex stainless steel (SDSS) has been successfully demonstrated using laser powder bed fusion (LPBF) in recent years. Owing to the high cooling rates, as-built LPBF-processed DSS and SDSS exhibit close to 100% ferritic microstructures and require heat treatment at 1000–1300 °C to obtain the desired duplex microstructure. In this work, the mechanical properties of DSS and SDSS processed via LPBF were investigated in three building directions (vertical, horizontal, diagonal) and three processing conditions (as-built, stress-relieved, annealed, and quenched) using uniaxial tensile testing. As-built samples exhibited tensile and yield strength greater than 1000 MPa accompanied by less than 20% elongation at break. In comparison, the water-quenched samples and samples annealed at 1100 °C exhibited elongation at break greater than 34% with yield and tensile strength values less than 950 MPa. Stress relief annealing at 300 °C had a negligible impact on the mechanical properties. Austenite formation upon high-temperature annealing restored the reduced ductility of the as-built samples. The as-built and stress-relieved SDSS showed the highest yield and tensile strength values in the horizontal build direction, reaching up to ≈1400 and ≈1500 MPa (for SDSS), respectively, as compared to the vertical and diagonal directions. Fractographic investigation after tensile testing revealed predominantly a quasi-ductile failure mechanism, showing fine size dimple formation and cleavage facets in the as-built state and a fully ductile fracture in the annealed and quenched conditions. The findings in this study demonstrate the mechanical anisotropy of DSS and SDSS along three different build orientations, 0°, 45°, 90°, and three post-processing conditions.

Experimental analysis of failure behaviour of PA12 specimens manufactured by SLS as a function of wall thickness and build direction

PurposeThis paper aims to investigate and explain the dual fracture behaviour of PA12 specimens sintered by selective laser sintering (SLS) as a function of wall thickness and build direction with a powder mixture 30:70. To achieve this objective, research related to chemical, thermal and structural behaviours as a function of the input variables was carried out to describe and explain why ductile-fragile behaviour occurs during fractures under uniaxial tension manufactured via a methodology of material analysis and manufacturing processes.Design/methodology/approachThe factorial design 32 relates the fracture of PA12 tensile specimens to the horizontal, transverse and vertical build directions at 2.0, 2.5 and 3.0 mm thicknesses, respectively. Fractographic images revealed the fracture surfaces and their dual ductile-fragile behaviour related to the specimens’ measured crystalline, thermal, surface and chemical properties.FindingsThe study showed that thermal property variables differ depending on the input variables. The wall thickness variable affected this morphology the most, showing the highest percentage of the ductile area, followed by the transverse and vertical directions. It was determined that the failure in the vertical direction is due to crystalline gradients associated with the layer-by-layer construction process. The pore density may be closely related to generating ductile and brittle areas.Originality/valueIn this paper, fracture characterisation is performed based on the mechanical, chemical, structural, thermal and morphological properties of PA12 manufactured by SLS. In addition, a heatmap of porosities in cross-sections is constructed using a machine learning model (k-means) related to dual fracture behaviour. This research revealed significant differences in the fracture type according to the build direction. In addition, thin-section fractography provides a more detailed explanation of the fragile behaviour of the vertical direction associated with crystalline changes due to the direction of the sintering layers.

Seismic Analysis of Horizontal and Vertical Irregular RC Multi Storey Building With Effect of Opening in Shear Wall

At present days building a structure with all the regular configurations is not feasible in most of the cases due to the irregular plot dimensions, aesthetic visual and functional requirements in the urban cities. The structure with more irregular configuration either horizontally or vertically are more vulnerable to earthquake which leads to collapses of structure, property loss and casualties. The shear walls are commonly used as a vertical element. Shear walls may have one or more openings for functional reasons such as windows, ventilation and other types of openings in shear wall. Frequently the shear wall is provided with openings thus necessary to study effect of irregular building. The present study was carried out the opening in shear wall with different shape of RC multi-Storey building and Study different building model with Combination of Horizontal & Vertical irregularities. The models were created using the ETABS software with Full Shear walls, Shear walls with a 25% opening. The location of the Shear wall was optimal. Prepared models of G+9 story and Analyze the model by Response Spectrum Analysis and Compare the Result with different buildings layout with parameters like storey Displacement, Storey Shear, Storey Drift, Storey Stiffness, Base shear, Torsion, Time Period and Mode Shape

Microstructure evolution in AM produced superalloy thin struts at low plastic strain

This paper discusses the microstructures and textures that develop in thin struts fabricated in Inconel 718 using laser melting powder bed fusion. Thin struts 1 mm wide were fabricated in the vertical (ZX) and horizontal build (XY) orientations with respect to the build plate. Three distinct regions of well-defined grain structures with centerline symmetry from the outer border to the center of the inner volume were present, which was attributed to the laser scan strategy, consisting of a fill hatch, inner and outer border scan on each 30 μm layer. Using ex situ micro-tensile testing and enhanced Back-Scattered Electrons (BSE) and Electron Back Scattered Diffraction (EBSD), the microstructure evolution to a plastic strain near 1%, in both the ZX and XY build direction was studied in the initial undeformed and final deformed states. For the ZX build direction, grain rotation as well as grain boundary migration was observed and was more significant than in the samples fabricated in XY. This paper discusses the evolution of the microstructure offering valuable insights into the relationship between microstructure and mechanical properties in complex AM produced microstructures.

Novel strategy for automated quality enhancement of up-facing inclined surfaces by incremental dual laser powder bed fusion

The low quality of up-facing inclined surfaces, combined with a lack of in-situ treatments, is a crucial challenge in Laser Powder Bed Fusion of metals. A recently proposed strategy, so-called Incremental Dual Laser Powder Bed Fusion (IDLPBF), aims to enhance the quality of up-facing inclined surfaces of metal parts directly during building. This is achieved through automatically alternating between laser remelting and building in height steps of 1.5 mm. Laser remelting involves selectively removing powder that is covering the inclined surface through nanosecond pulsed laser-induced shock waves and subsequently remelting the uncovered surface using a continuous wave laser. Treated surfaces are hence composed of laser remolten zones separated by elevated ridges in the overlap region, referred to as stitching zones. These stitching zones can compromise the geometrical accuracy and, consequently, pose a serious risk to fatigue performance. This work focuses on the enhancement of stitching zones and resulting quality of inclined surfaces through IDLPBF of a novel tool steel (M789). The paper covers the effect of various scan strategies for laser remelting on the stitching zone size. By optimizing the orientation of consecutive remelting passes and the position of the remelting fields, the stitching zone width could be reduced from 830 µm to 70 µm. Moreover, the optimized IDLPBF process was successfully applied to a large range of surface inclinations with respect to the horizontal build plate (5°-60°). For the first time, a significant quality improvement for 60° inclined surfaces was achieved, reducing the stress concentration factor by 35 %. The significantly reduced maximum stress concentrations were largely observed at stitching zones, in contrast to multiple high stress concentration sites randomly scattered across as-built surfaces. As a proof of concept, 60 mm high demonstrator parts including typically inaccessible surfaces located in the shadow zone were fully automated manufactured by IDLPBF.

Microstructure Study on Very High Cycle Fatigue of an Additively Manufactured Aluminium Alloy via Advanced Characterization Methods

The engineering application of additively manufactured (AM) metallic materials is quite limited by their fatigue behaviors, which are very inconsistent with that of conventionally wrought or cast ones. Here, based on advanced material characterization techniques, such as focused ion beam (FIB), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the microstructures underneath fracture surfaces were thoroughly investigated in an AM aluminum (AlSi10Mg) alloy with horizontal and vertical building orientation enduring very high cycle fatigue (VHCF) loading under the stress ratios R = −1, 0, and 0.5. Two VHCF failure specimens A and B were representatively selected to further examine SEM and TEM sample preparation via FIB milling. Specimen A was horizontally printed and failed at R = −1; specimen B was vertically printed and failed at R = 0. TEM samples A1 and B1 were lifted from locations near the crack initiation sites on the fracture surfaces of specimens A and B; The locations of TEM samples A2 and B2 kept away from the crack origin sites but still within the “fish-eye” region of crack steady growth. TEM observations show that there was no characteristic microstructure induced by VHCF in different oriented specimens and under various R values.

Ecosystem pipelines: Collective action in entrepreneurial ecosystems

Entrepreneurial ecosystems comprise a range of different actors, structures and processes that support entrepreneurs in starting and growing their ventures. They are governed through collective action, which helps ecosystem actors achieve common goals that otherwise would be beyond the scope of their individual abilities. However, we have a limited understanding of the key mechanisms through which they organise their interactions. This article explores how ecosystem actors engage in collective action based on a case study of the Scottish entrepreneurial ecosystem. The main contribution is the introduction of a novel ecosystem governance mechanism coined ‘ecosystem pipelines’, which are logical pathways between ecosystem actors through which entrepreneurs can access support and resources as they progress their ventures. This article highlights that entrepreneurial ecosystems are purpose-driven networks based on horizontal relationship building among actors – as opposed to top-down or bottom-up organising – in pursuit of a common purpose to promote entrepreneurship.

Investigation of the Mechanical Characteristics of Metal 3D Printing at Different Build Orientation and Directions

Abstract In this paper, metal 3D printing technology was used to investigate the effects of build orientation angles and direction on the mechanical characteristics of 316L stainless steel produced by the Bound Metal Deposition (BMD) process. Several orientation angles (0 deg, 45 deg, and 90 deg) of the test specimens were made for both horizontal and vertical build directions. The tensile testing apparatus was used on metal 3D-printed samples to determine their mechanical characteristics, such as Young's modulus, elongation at break, and ultimate strength. Brinell hardness tester was also used to compare the hardness of 3D-printed samples to the original native material. In addition, the porosity and microstructure of the printed samples were analyzed in this study. The findings of this investigation revealed how, in comparison to the original material, the mechanical properties of the metal 3D-printed material rely on the raster orientation and build type. The experimental results demonstrate that the 3D-printed parts using the BMD process have comparable ultimate tensile strength and elongation at break compared to the original material for 0 deg orientation and horizontal build direction. The elongation at break was found to depend strongly on the build direction for 45 deg and 90 deg printing orientation. Further, Young's modulus was found to be much lower than the original material using the BMD process.

Multiple values of beekeeping (with A. mellifera) as an element of diversified, agroecological coffee farms in Chiapas, Mexico

Abstract Honeybees (Apis mellifera) and native bee species have ecological, economic, social, and cultural importance to smallholder coffee farmers. While the ecological contributions of bees to the sustainability of coffee systems are well documented, particularly in relation to the coffee crop, fewer studies have examined socio-economic dimensions of beekeeping for honey as an agroecological diversification strategy for coffee producers. Yet, understanding the multiple values of different diversification strategies is important as many coffee farmers in different parts of the world are finding it increasingly difficult to make a living on coffee alone and are adopting alternative strategies, such as on-farm diversification. In this Participatory Action Research (PAR) study, we examined the opportunities, limitations, and trade-offs of beekeeping (with A. mellifera) as an agroecological diversification option for smallholder coffee farmers in Chiapas, Mexico. We applied a mixed-methods approach, which consisted of monthly surveys with 25 beekeepers of Campesinos Ecológicos de la Sierra Madre de Chiapas (CESMACH)/Apicultores Miel Real del Triunfo (ART) producer cooperatives for 12 months and five focus groups between 2018 and 2019. We found that beekeeping is less labor-intensive than coffee, and there are opportunities to integrate beekeeping into the annual farming cycle of coffee and maize production without causing competing labor demands or additional time pressures. We also found that beekeeping could generate economic gains for peasant families; however, profitability hinged on various factors, such as the price for honey, yield per hive, and the number of beehives. Our results further show that beekeeping yielded multiple non-monetary benefits by contributing to the nutrition and health of farmer families and their communities, serving as a vehicle for horizontal learning and relationship building, and contributing to the emotional well-being of beekeepers. Finally, producers who hoped to gain economically from beekeeping were generally interested in growing their apiaries but expressed concerns about limited technical knowledge and the impacts of climate change. Given the multiple social, economic, and ecological benefits of beekeeping, it has great promise as a part of agroecological food and farming systems. We argue that efforts to promote beekeeping as a diversification strategy should take a holistic approach, underscoring the potential of apiculture to enhance the well-being and resilience of beekeeping families and strengthen food sovereignty and local economies (including solidarity economies) in peasant communities. These findings can be useful in supporting beekeepers and their organizations in strategic planning for enhancing the long-term sustainability of beekeeping.

Prototype Development for Solar Energy Tracking Based on Arduino in QUEST Campus Larkana

The utilization of solar energy has become increasingly popular due to its renewable and sustainable nature. However, one of the primary challenges in solar energy harvesting is the optimization of the amount of energy that can be captured from the sun. The implementation of solar trackers is an effective solution that enables the automatic adjustment of the solar panel's position to face the sun throughout the day. In this project, an Arduino-based solar tracker prototype was designed and implemented to optimize the solar energy harvesting process. The system employs Light-Dependent Resistors (LDRs) to detect sunlight intensity and a servo motor to adjust the position of the solar panel accordingly. The system was programmed using the Arduino programming language and was tested using a small-scale solar panel. The increasing demand for cost-effective and easy-to-install renewable energy systems has led to a growing interest in photovoltaic solar energy for residential use. To optimize energy production, a two-axis photovoltaic solar tracker that orients the solar panel toward the maximum solar radiation is proposed in this study. The use of Free Computer Aided Design (CAD) 0.15 for the prototype's design, combined with Arduino technology, provides an affordable solution for mounting the solar tracker on flat roofs and other horizontal building elements. The performance of the solar tracker was evaluated under various testing conditions, showcasing an enhanced level of accuracy and energy production when compared to traditional fixed systems. The prototype's successful demonstration represents a significant advancement in the field, providing a practical solution for small-scale and residential solar energy applications. This research prototype was developed and installed on the roof of the Electrical department of QUEST, Campus Larkana, and validated through simulation results.

The effect of high-intensity gamma radiation on PETG and ASA polymer-based fused deposition modelled 3D printed parts

There is growing interest in the application of 3D printing for demanding environments subject to gamma radiation in areas such as the nuclear industry and space exploration. In this work, the effect of gamma radiation on fused deposition modelled 3D printed parts composed of polyethylene terephthalate glycol (PETG) and acrylic styrene acrylonitrile (ASA) polymers was studied. Dose levels of up to 2.25 MGy were applied to the printed components, doses equivalent to over 1 year operating near spent nuclear fuel cells. Infrared spectroscopy showed the evidence of cross-linking by the formation of peaks corresponding to –OH and C–H bonds. Tensile and hardness testing was used to assess changes in mechanical properties and showed a reduction in ultimate tensile stress and maximum strain in parts made from both polymers, but with PETG retaining greater strength and ductility than ASA, especially at intermediate gamma exposure. Young’s modulus and hardness showed either modest increases or a fairly flat response with exposure. Mechanical properties were heavily dependent on the build structure, with horizontal build samples pulled parallel to the filament direction being several times stronger than vertical build samples pulled normal to the layers. Non-irradiated samples pulled parallel to the filament direction were indicative of ductile failure, with rough surfaces, distinct infill and wall regions and evidence of thinning occurring after fracture, but irradiated fracture surfaces were flatter, smoother and without local thinning, suggesting gamma radiation-induced embrittlement in the material. For samples pulled perpendicular to the filament direction, all fractures occurred between layers, creating flat fracture surfaces with no evidence of necking and indicative of brittle failure regardless of whether the samples were irradiated.

Fatigue strength improvement of additively manufactured 316L stainless steel with high porosity through preloading

This work investigates the influence of a single tensile preload, applied prior to fatigue testing, on the fatigue strength of 316L stainless steel parts manufactured using laser-based powder bed fusion (PBF-LB) with a porosity of up to 4 %. The specimens were produced in both the horizontal and vertical build directions and were optionally preloaded to 85 % and 110 % of the yield strength before conducting the fatigue tests. The results indicate a clear tendency of improved fatigue life and fatigue limit with increasing overload in both cases. The fatigue limits increased by 25.8 % and 24.6 % for the horizontally and vertically built specimens, respectively. Extensive modelling and experiments confirmed that there was no significant alteration in the shape and size of the porosity before and after preloading. Therefore, the observed enhancement in fatigue performance was primarily attributed to the imposed local compressive residual stresses around the defects.

An investigation of the contribution of vibration duration on subjective response to horizontal building vibration

As an evaluation method for evaluating the habitability to building vibration, the ISO 2031 series of international standards defines the VDV for transient vibration, in which the vibration duration is considered by time integration. The evaluation method for non-stationary-like vibrations in the guidelines for the evaluation of habitability to building vibration of the Architectural Institute of Japan (AIJ) also specifies a method to consider the effect of vibration duration on the evaluation. In this paper, laboratory experiments using an electrodynamic shaker were conducted to investigate the relationship between the subjective response regarding occupant habitability and the horizontal vibration of buildings caused by external vibration sources such as road traffic and railways. Binomial logistic regression analysis was used to quantify the effects of acceleration magnitude and vibration duration on the exposure-response relationship. The comparison of models with different proportions of occurrence (cutoff values) of subjective responses showed different effects of acceleration magnitude and vibration duration.