Systematic approach for reducing micro-crack formation in Inconel 713LC components fabricated by laser powder bed fusion

Purpose For high crack-susceptibility materials such as Inconel 713LC (IN713LC) nickel alloy, fabricating crack-free components using the laser powder bed fusion (LPBF) technique represents a significant challenge because of the complex interactions between the effects of the main processing parameters, namely, the laser power and scanning speed. Accordingly, this study aims to build up a methodology which combines simulation model and experimental approach to fabricate high-density (>99.9%) IN713LC components using LPBF process. Design/methodology/approach The present study commences by performing three-dimensional (3D) heat transfer finite element simulations to predict the LPBF outcome (e.g. melt pool depth, temperature and mushy zone extent) for 33 representative sample points chosen within the laser power and scanning speed design space. The simulation results are used to train a surrogate model to predict the LPBF result for any combination of the processing conditions within the design space. Then, experimental trials were performed to choose the proper hatching space and also to define the high crack susceptibility criterion. The process map is then filtered in accordance with five quality criteria, namely, avoiding the keyhole phenomenon, improving the adhesion between the melt pool and the substrate, ensuring single-scan-track stability, avoiding excessive melt pool evaporation and suppressing the formation of micro-cracks, to determine the region of the process map which improves the relative density of the IN713LC component and minimizes the micro-cracks. The optimal processing conditions are used to fabricate IN713LC specimens for tensile testing purposes. Findings The optimal processing conditions predicted by simulation model are used to fabricate IN713LC specimens for tensile testing purposes. Experimental results show that the tensile strength and elongation of 3D-printed IN713LC tensile bar is higher than those of tensile bar made by casting. The yield strength of 791 MPa, ultimate strength of 995 MPa, elongation of 12%, and relative density of 99.94% are achieved. Originality/value The present study proposed a systematic methodology to find the processing conditions that are able to minimize the formation of micro-crack and improve the density of the high crack susceptivity metal material in LPBF process.

Significance of Stable Crack Extension to Fatigue Crack Growth

A long-overlooked aspect of fatigue crack growth is the potential contribution to it, of stable crack extension (SCE). Reduction in specimen size and increase in magnitude of cyclic loading will induce increased contribution of SCE. SCE as a load interaction effect is manifest in disproportionately high crack extension due to periodic overloads. SCE can exceed by more than an order of magnitude estimates of crack growth from the da/dN versus DK relationship. Simple equations are proposed to account for SCE in fatigue crack growth. A numerical analysis is performed to characterize the significance of SCE to constant amplitude and variable amplitude fatigue crack growth.

Compressive Test Characteristics and Constitutive Relationship of Wet Polypropylene Macrofiber-Reinforced Shotcrete

Shotcrete is often subject to poor ductility and cracking problems, particularly under high stresses. In order to deal with these issues, the feasibility of adding polypropylene macrofibers to shotcrete was verified. To ascertain the supporting effect, dry shotcrete, wet shotcrete, and wet polypropylene macrofiber-reinforced shotcrete (WPMS) were used as samples. Furthermore, the mechanical response characteristics thereof in uniaxial compression tests were compared and analyzed by acoustic emission (AE) monitoring. The results showed that the three materials were brittle, but the ductility, residual strength, and bearing capacity of polypropylene macrofiber-reinforced shotcrete were significantly enhanced. The energy absorption value of plain shotcrete was higher in the cracking stage, while that of polypropylene macrofiber-reinforced shotcrete was greater in the postpeak stage, which showed that the polypropylene macrofiber-reinforced shotcrete had the characteristics of a high crack-initiation strength and toughness. Besides, the energy release from fiber shotcrete occurred after the peak stress rather than near the peak stress. The average energy absorbed by polypropylene macrofiber-reinforced shotcrete was significantly higher than that in dry shotcrete and wet shotcrete, which implied that polypropylene macrofiber-reinforced shotcrete could mitigate the brittle instability of a shotcrete layer. A constitutive model of damage statistics was established based on the test data. The comparison between the experimental data and the fitting results can reflect the characteristics of the total stress-strain curve of such shotcrete. The results provide a basis for the optimization of polypropylene macrofiber-reinforced shotcrete layers.

Automatic Detection of Cracks in Asphalt Pavement Using Deep Learning to Overcome Weaknesses in Images and GIS Visualization

The crack ratio is one of the indices used to quantitatively evaluate the soundness of asphalt pavement. However, since the inspection of pavement requires much labor and cost, automatic inspection of pavement damage by image analysis is required in order to reduce the burden of such work. In this study, a system was constructed that automatically detects and evaluates cracks from images of pavement using a convolutional neural network, a kind of deep learning. The most novel aspect of this study is that the accuracy was recursively improved through retraining the convolutional neural network (CNN) by collecting images which had previously been incorrectly analyzed. Then, study and implementation were conducted of a system for plotting the results in a GIS. In addition, an experiment was carried out applying this system to images actually taken from an MMS (mobile mapping system), and this confirmed that the system had high crack evaluation performance.

Development of Dielectric Material Enabling Low Insertion Loss of Organic Substrates at Various Operational Temperatures

With IP traffic increasing by 10-fold over the last decade, together with limitation and cost increase due to shrinking semiconductor nodes have led to requiring technological breakthrough in the packaging of semiconductor devices especially those used in high performance computing (HPC).This increase in IP traffic has led to requirement for higher data speed transmission in these devices, and consequently packaging technologies that enable those solutions such as 2.5D packaging utilizing silicon interposers. Furthermore, in recent years, increasing number of dies are placed in a single package for these devices thereby making the size of silicon interposers larger. Thus, the design of organic substrates used in these devices, are also becoming ever complex often with multiple layers with long trace lengths for routing increased number of IOs and allowing for power and signal control management. In order to facilitate the high speed data transmission requirement with longer trace lengths, stable low insertion loss design of organic substrates are becoming significantly important even when devices are exposed at elevated humidity or higher temperatures due to surrounding environment or from dies heating. Additionally, as silicon interposers are increasing in size, preventing stress build-up, which can cause cracking between the interposer and the organic substrate, is also becoming paramount. These requirements have led to innovative materials to be developed to enable organic substrates to have these properties. In this paper, we present a new dielectric build-up material for use in advanced organic substrates, by combining newly developed original resin with existing formulation technology that meet these criteria of enabling lower insertion loss with design that reduces deterioration even at elevated humidity and temperature, and furthermore having high crack resistance during temperature cycle testing.

Compressive Test Characteristics and Constitutive Relation of Wet Polypropylene Macrofibers Shotcrete

Shotcrete is often subject to poor ductility and cracking problems, particularly under high stresses. To address these issues, we investigated the feasibility of adding polypropylene macrofibres to shotcrete. To evaluate the supporting effect, we used dry shotcrete, wet shotcrete, and wet polypropylene macrofibre shotcrete as samples. We compared and analysed the mechanical response characteristics thereof in uniaxial compression tests by acoustic emission monitoring. The results showed that the three materials were brittle, but the ductility, residual strength, and bearing capacity of polypropylene macrofibre shotcrete were significantly enhanced. The energy absorption value of plain shotcrete was higher in the cracking stage, while that of polypropylene macrofibre shotcrete was higher in the post-peak stage, which indicated that the polypropylene macrofibre shotcrete had the characteristics of a high crack-initiation strength and toughness. Besides, the energy release from fibre shotcrete occurred after the peak stress rather than near the peak stress. The average energy absorbed by polypropylene macrofibre shotcrete was significantly higher than that in dry shotcrete and wet shotcrete, which suggested that polypropylene macrofibre shotcrete could mitigate the brittle instability of a shotcrete layer. Based on the test data, a constitutive model of damage statistics was established. The comparison between the experimental data and the fitting results could reflect the characteristics of the total stress-strain curve of such shotcrete. The results provide a basis for the optimisation of polypropylene macrofibre shotcrete layers.

Fine-Grained Polymer-Cement Basalt Fibrous Concrete for 3D Printing

The construction concrete printing requires new approaches at reinforcement performing. Only successful integration of the existing reinforcement systems will provide for the opportunity to design concrete structures and make objects with the help of additive technologies. The paper dwells upon the issues of possibilities and the efficiency of disperse reinforcement with basalt fibers. It presents a composition of a composite material for 3D printing of a type of fine-grained fibrous concretes with the required technological properties: a necessary plasticity and a high plastic strength for printing large-dimensioned items and structures without timbering by means of extrusion with a high material adhesion between the layers and controlled setting periods. The author studied a possibility to reclaim basalt fiber production wastes as a high-disperse fibrous filler for the reinforcement of polymer-modified concretes. The article provides the dependence of plastic strength on the fiber content in concrete. The authors consider the influence of components and the mechanism of modifying disperse particles of basalt fibrous concrete at obtaining the material for 3D printing. The obtained polymer-modified basal fibrous concrete has a good impact resistance, low water absorption and high crack resistance.

Experimental investigation on strength properties of concrete using polypropylene pellets

The handmade tiles are manufactured in Athangudi, Sivagangai district. We observed that these tiles are reducing foot pain and appearing aesthetic look. But one disadvantage was that these Athangudi tiles were getting easily cracked. We studied that these tiles are getting cracks. Due to its lesser resistance. It shows some cracks on surface of tiles after setting and hardening process. In this project, we gave solution to rectify the problem for this purpose we adding the zirconium di oxide to cement paste at the time of manufacturing process. Because the zirconium di oxide possess high crack resistance property in these tiles. The field test (water penetration test), abrasion test, water absorption test and acid resistance test were conducted on Athangudi tiles with zirconium di oxide and without zirconium di oxide. Then the test result was compared between normal tiles and zirconium di oxide used tiles. Hence we conclude that zirconium di oxide used tiles are somewhat better than normal Athangudi tiles from the above result. We will conduct more tests and come with the conclusion that zirconium di oxide used tiles having better cracking resistance in future.