13 research outputs found
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Study of Spatter Formation and Effect of Anti-Spatter Liquid in Laser Powder Bed Fusion Processed Ti-6Al-4V Samples
Spatter deposition has been found to have serious effects on mechanical properties of the metal
parts printed using laser powder bed fusion technique. The spatter powder formation can cause
unfavorable changes in phases and impurity content and may result in the formation of defects in
the as-fabricated parts. This study is the first of its kind focusing on mitigation of spatter formation
through a novel technique of spraying nonflammable welding liquid during the LPBF process.
Identifying the spatter particle size distribution and dampening its formation have been the focus
of this study. Characterization of the powder spatter behaviors for Ti-6Al-4V have been made
through image processing and microstructure characterization. The findings of this study will help
in improving the mechanical properties and reducing the post-processing procedures required for
the parts processed by LPBF. This study is believed to bring a new perspective in production
planning and print quality optimization to obtain an enhanced performance from laser powder bed
fusion technique.Mechanical Engineerin
MAPS: Scaling Privacy Compliance Analysis to a Million Apps
The app economy is largely reliant on data collection as its primary revenue model. To comply with legal requirements, app developers are often obligated to notify users of their privacy practices in privacy policies. However, prior research has suggested that many developers are not accurately disclosing their apps’ privacy practices. Evaluating discrepancies between apps’ code and privacy policies enables the identification of potential compliance issues. In this study, we introduce the Mobile App Privacy System (MAPS) for conducting an extensive privacy census of Android apps. We designed a pipeline for retrieving and analyzing large app populations based on code analysis and machine learning techniques. In its first application, we conduct a privacy evaluation for a set of 1,035,853 Android apps from the Google Play Store. We find broad evidence of potential non-compliance. Many apps do not have a privacy policy to begin with. Policies that do exist are often silent on the practices performed by apps. For example, 12.1% of apps have at least one location-related potential compliance issue. We hope that our extensive analysis will motivate app stores, government regulators, and app developers to more effectively review apps for potential compliance issues
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Microstructural and Mechanical Characterization of Laser Powder Bed Fusion of IN718 Overhangs
Inconel 178 (IN718), a nickel-chromium-based superalloy known for its superior properties is used
in aerospace, oil, and gas industries. Due to its high hardness, IN718 is difficult to be machined.
Therefore, fabrication of IN718 components with complex geometries is a big challenge when
conventional manufacturing techniques are used. Laser powder bed fusion (LPBF) technique can
be used to fabricate IN718 parts with high precision. During fabrication of overhang structures,
supports are typically employed, which significantly increases the use of resources such as material
consumption and postprocessing. The focus of this study is to determine the angle at which an
overhang structure can be fabricated without employing supports. To this aim, the angled-overhang samples with varied angles (30°-90°) were manufactured with no support. The effect of
overhang state on the microstructural and mechanical properties of the LPBF-processed IN718
samples was analyzed. According to the microstructural analysis, the deepest melt pools in the
overhang sample seemed to be at a hanging angle of 45°. Moreover, the overhang sample
fabricated at 45° had the greatest Vickers hardness value of 382.90 HV. This study urges a
reconsideration of the common approach of selecting supports for overhang samples in the LPBF
process when a higher quality of the as-fabricated parts is desired.Mechanical Engineerin
MAPS: Scaling Privacy Compliance Analysis to a Million Apps
The app economy is largely reliant on data collection as its primary revenue model. To comply with legal requirements, app developers are often obligated to notify users of their privacy practices in privacy policies. However, prior research has suggested that many developers are not accurately disclosing their apps’ privacy practices. Evaluating discrepancies between apps’ code and privacy policies enables the identification of potential compliance issues. In this study, we introduce the Mobile App Privacy System (MAPS) for conducting an extensive privacy census of Android apps. We designed a pipeline for retrieving and analyzing large app populations based on code analysis and machine learning techniques. In its first application, we conduct a privacy evaluation for a set of 1,035,853 Android apps from the Google Play Store. We find broad evidence of potential non-compliance. Many apps do not have a privacy policy to begin with. Policies that do exist are often silent on the practices performed by apps. For example, 12.1% of apps have at least one location-related potential compliance issue. We hope that our extensive analysis will motivate app stores, government regulators, and app developers to more effectively review apps for potential compliance issues
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Investigation of the Properties of Reinforced IN718 Structures Fabricated using Laser Powder Bed Fusion
Inconel 718 (IN718) superalloy, known for its high strength and corrosion resistant behavior, is
widely used in the aerospace and automotive industries. Laser power bed fusion (LPBF), one of
the commonly used techniques of additive manufacturing, enables the fabrication of structures
with a variety of local properties. Using the same material, components with spatially varying
properties can be fabricated through applying different processing parameters. In this study, IN718
composite structures were fabricated using four types of rod reinforcements with different
geometry. A different set of process parameters was used to fabricated reinforcing rods compared
to that of the main part. The bonding quality at the interface between the main part and
reinforcements was determined by defect analysis on the microstructure results. Also, Vickers
hardness test was performed at the interface in order to examine the mechanical properties of the
samples. It was found out that a similar level of densification and hardness value, slightly less than
the plain sample, can be achieved using helical and arc reinforcing rods. By contrast, significantly
lower density and hardness were observed for the sample reinforced by square rods compared to
the plain sample.Mechanical Engineerin
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Impact of Porosity Type on Microstructure and Mechanical Properties in Selectively Laser Melted IN718 Lattice Structures
Laser Powder Bed Fusion (LPBF), one of the most employed additive manufacturing techniques
for metals, has opened new dimensions in realizing strong and weight reducing structures. In this
study, Inconel 718 (IN718) unit cell designs, were fabricated through the LPBF technique and
analyzed. Among the plethora of lattice structures in existence, BCC, BCC-Z, FCC, FCC-Z,
Gyroid, Diamond and Schwarz structures have been selected to focus on. A relationship between
the mechanical properties including yield strength, failure stress and strain, and hardness with each
type of unit cell was established. Also, the effect of the possible defects on the hardness value was
examined using microstructural analysis on samples. Scanning Electron Microscopy (SEM)
analysis was also performed to examine the possible defects and its effect on the hardness of the
as-built part. The SEM images of the grain structures indicated higher levels of isotropy in Gyroid,
and Diamond samples compared to the rest of the samples which relates to the load bearing
capacities of each unit cell structure. A similar trend was observed in terms of the uniformity of
meltpool which can be linked with the consistency in yield characteristics. Further, Diamond and
BCC-Z structures displayed high values of hardness in comparison with rest of the samples.Mechanical Engineerin
MAPS: Scaling Privacy Compliance Analysis to a Million Apps
The app economy is largely reliant on data collection as its primary revenue model. To comply with legal requirements, app developers are often obligated to notify users of their privacy practices in privacy policies. However, prior research has suggested that many developers are not accurately disclosing their apps’ privacy practices. Evaluating discrepancies between apps’ code and privacy policies enables the identification of potential compliance issues. In this study, we introduce the Mobile App Privacy System (MAPS) for conducting an extensive privacy census of Android apps. We designed a pipeline for retrieving and analyzing large app populations based on code analysis and machine learning techniques. In its first application, we conduct a privacy evaluation for a set of 1,035,853 Android apps from the Google Play Store. We find broad evidence of potential non-compliance. Many apps do not have a privacy policy to begin with. Policies that do exist are often silent on the practices performed by apps. For example, 12.1% of apps have at least one location-related potential compliance issue. We hope that our extensive analysis will motivate app stores, government regulators, and app developers to more effectively review apps for potential compliance issues
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Investigating the Effect of Heat Transfer on the Homogenity in Microstructure and Properties of Inconel 718 Alloy Fabricated by Laser Powder Bed Fusion Technique
Laser Powder Bed Fusion (LPBF) of metallic components is associated with microstructure and
inhomogeneity of properties in the fabricated components. In a recent work by the authors, a novel
technique of considering a border surrounding the main part during the LPBF fabrication is
proposed to address the issue of inconsistency in microstructure across the cross section of LPBF-fabricated parts. This study, on the other hand, aims to investigate the effect of such border on the
microstructure homogeneity along the build direction of LPBF-fabricated parts. For this purpose, a
cubic sample surrounded by a cubic border was fabricated to control the rate of heat transfer and
then improve the microstructure across the cross section. Also, a sample with identical dimensions
and the same process parameters was printed without border as a reference to be compared. To
investigate the variation of the properties along the build direction, microstructure and hardness
results were compared between areas near and away the substrate for both samples. For the area
away from the substrate, in both samples, a deeper pool, less surface porosity, and higher Vickers
hardness was observed compared to the area near the substrate. It was found out that, regardless of
the focused area, the sample fabricated with border possesses deeper pools, higher level of density
as well as higher hardness value. However, in term of homogeneity along the build direction, no
significant improvement was observed for the sample fabricated with the cubic border.Mechanical Engineerin