Comparison of the pore distribution and sizes for different entrapping times, illustrating the common crack patterns of the specimens. The computed tomography (CT) porosity of the specimens at different layering times, where the parameters are detailed in Table 2: (a) specimen T5, (b) specimen T10, (c) specimen T15, and (d) specimen T20.
david 3d scanner 3.4 crack
Download Zip: https://phimohosjons.blogspot.com/?bu=2vCMX9
david scanner, david scanner software, david scanner forum, david scanner turntable, david scanner download, david scanner hp, david scanner sls 3, david scanner software download, david scanner calibration, david scanner sls 2
Several studies have focused on the influence of scanning strategies during the processing of different materials. Thijs et al. [8] found a relation between the crystallographic texture of AlSi10Mg alloy and a applied scanning strategy as a consequence of directional solidification due to the moving heat source, while Read et al. [11] found the island size to have the least influence on porosity formation in comparison to laser speed and laser power when processing AlSi10Mg alloy using the island scanning strategy. In addition, Lu et al. [21] studied the mechanical properties and residual stress induced in the Inconel 718 alloy while using a different size of island scanning strategy. They found that the 5 5 mm island size is promising for lowering the residual stress. They observed the cracks on the border of the islands, thus the enlargement of island size (lowering the number of borders) produced material with lower porosity and higher elongation. On the contrary, the smaller island produced material with slightly higher UTS and lower residual stress. Carter et al. [22] also investigated the island scanning strategy. They found the influence on the grain structure of nickel superalloy CM247LC by the localization of cracks in the border zones of the islands. They estimated that the higher crack occurrence is present at the high-angle grain boundaries. Popovich et al. [23] showed that the different process parameters together with the scanning strategy strongly affects grain orientation and the resulting mechanical properties of Inconel 718, thus functionally graded materials can be produced with this approach.
This paper builds mainly on the findings of the initial study of high power processing of EN AW 2618 proposed in two articles, Koutny et al. [24] and Koukal et al. [25]. In these studies, a SLM 280HL machine from SLM Solutions with a maximum laser power of 400 W was used. Experiments comprised of single-track welds and volume samples (cubes 5 5 5 mm), all with a layer thickness of 50 µm. A wide range of processing parameters (laser power, laser speed, and hatch distance) was studied. For cube tests, a relative density above 99% was achieved with LP 200 W, LS 200 mm/s and a hatch distance (HD) of 110 µm. These results correspond with the other studies of Al-Cu alloy mentioned above. However, low surface roughness was observed with parameters LP 400 W and LS 1400 mm/s. In all of the above mentioned articles focused on aluminum alloy EN AW 2618 [17,18,20], the authors describe the presence of a large number of cracks in the samples.
As expected, the microstructure of SLM-processed material is different (Figure 16a,b). On the samples there is a visible lack of fusion porosity, cracks and gas porosity. At higher magnification (Figure 16c,d) individual weld tracks can be observed. Alongside these tracks intermediary particles can be found. In comparison with the extruded state they are very fine. In this area the initiation of solidification cracks (also known as hot cracking) occurs.
The results showed some differences in the microstructure of extruded and SLM state material, however hardness measurements for both states are almost identical (100 HV 0.3 for SLM, and 104 HV 0.3 for extruded state). This suggests that the main reason for the different tensile properties is the defects observed in the SLM state. Most of these defects are solidification cracks which were present in samples for all evaluated scanning strategies.
Some laser applications employ electro-mechanical or electro-optical scanner units to allow a raster-scan capability to the beam. In this way, the beam can be scanned over a large area (such as in a laser print maker) or over a small area (such as a laser UPC label reader) in a repeated geometry.
For example, the ocular exposure for a Helium Neon laser (beam size 1mm) scanner with 20 degrees scan angle located at a distance of 30 cm from the eye (r = 30 cm) which scans at a rate of 50 Hz will be: (assume d(p) = 7mm):
NOTE: Class IIA is a special designation that is based upon a 1000 second exposure and applies only to lasers that are "not intended for viewing" such as a supermarket laser scanner. The upper power limit of Class IIA is 4.0 ?W. These are products whose emission does not exceed the Class I limit for an emission duration of 1000 seconds.
In some tests, glass filter plates have cracked and shattered following intense Q-switched pulsed laser exposures. In some instances, the shattering occurred after one-quarter to one-half hour had elapsed following the exposure. Also, at least one glass filter type has been shown to photobleach when exposed to the short pulses of a Q-switched laser.
Abstract:Structural health monitoring (SHM) is an important aspect of the assessment of various structures and infrastructure, which involves inspection, monitoring, and maintenance to support economics, quality of life and sustainability in civil engineering. Currently, research has been conducted in order to develop non-destructive techniques for SHM to extend the lifespan of monitored structures. This paper will review and summarize the recent advancements in non-destructive testing techniques, namely, sweep frequency approach, ground penetrating radar, infrared technique, fiber optics sensors, camera-based methods, laser scanner techniques, acoustic emission and ultrasonic techniques. Although some of the techniques are widely and successfully utilized in civil engineering, there are still challenges that researchers are addressing. One of the common challenges within the techniques is interpretation, analysis and automation of obtained data, which requires highly skilled and specialized experts. Therefore, researchers are investigating and applying artificial intelligence, namely machine learning algorithms to address the challenges. In addition, researchers have combined multiple techniques in order to improve accuracy and acquire additional parameters to enhance the measurement processes. This study mainly focuses on the scope and recent advancements of the Non-destructive Testing (NDT) application for SHM of concrete, masonry, timber and steel structures.Keywords: concrete structures; non-destructive testing; sensors; steel structures; structural engineering; structural health monitoring (SHM)
The purpose of this paper is to investigate the effect of remelting each layer on the homogeneity of nickel-titanium (NiTi) parts fabricated from elemental nickel and titanium powders using laser powder bed fusion (LPBF). In addition, the influence of manufacturing parameters and different melting strategies, including multiple cycles of remelting, on printability and macro defects, such as pore and crack formation, have been investigated.
Fischer et al. (2016), Simonelli et al. (2018) and Vrancken et al. (2014) explored LPBF powder mix fabrication of different alloys where only basic LPBF parameters were adjusted during the manufacturing process. This resulted in the high inhomogeneity of fabricated materials when no remelting or laser focus variation was used. Therefore, given what has previously been studied in regard to LPBF of Ni and Ti elemental powders, the objective of the current study is to investigate the effect of remelting of each layer on the homogeneity of NiTi parts fabricated from elemental nickel and titanium powders via LPBF. In addition, the influence of manufacturing parameters (i.e. laser parameters and scanning strategy) and different melting strategies, including multiple remelting, on printability and the occurrence of macroscopic defects, such as pores and cracks, were investigated. Currently, there are two major limitations to using as-cast NiTi, machining difficulties and its high price. One major benefit of AM technologies is the reduction or elimination of the need for machining. Prealloyed NiTi powder used for AM is also expensive. Production Ni-Ti components using premixed Ni and Ti elemental powders, instead of prealloyed powders, would reduce the material costs of fabrication by nearly three times. Consequently, the price of the final part would be significantly reduced, thereby providing the possibility of wider application of this material in many industrial fields.
After fabrication, parts were removed from the substrate and hot mounted in resin. All parts were mechanically ground and polished for further tests. Pore and crack density were studied on metallographically prepared specimens using light microscopy (Zeiss AxioScope Light Microscope). The relative density of the parts was calculated on the basis of microscopic images using MicroMeter software (Wejrzanowski et al., 2008, 2010).
Figure 5 shows optical micrographs of a polished surface of parts fabricated with different energy densities and melting strategies. The presence of pores and cracks in the microstructure of the fabricated parts was observed. The size and distribution of pores, as well as cracks, depend on the manufacturing parameters. The porosity decreases with increasing energy density and with the remelting applied for most parts. Li et al. (2019) and Griffiths et al. (2018) reported that remelting provided good metallurgical bonding between adjacent melt pools and the formation of shallower melt pools. As a result, the density and surface quality was improved. Chen et al. (2018), Griffiths et al. (2018) and Xiong et al. (2020) discovered similar results in their works, where remelting was applied. It was reported that due to good metallurgical fusion provided by remelting, the pores were successfully reduced. Moreover, the number of pores and their average size were minimized. 2ff7e9595c
Comments