David 3d Scanner 3.4 Crack

Comparison of the pore distribution and sizes for different entrapping time=
s, illustrating the common crack patterns of the specimens. The computed to=
mography (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
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Several studies have focused on the influence of scanning strategies during=
 the processing of different materials. Thijs et al. [8] found a relation b=
etween the crystallographic texture of AlSi10Mg alloy and a applied scannin=
g 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 leas=
t influence on porosity formation in comparison to laser speed and laser po=
wer when processing AlSi10Mg alloy using the island scanning strategy. In a=
ddition, Lu et al. [21] studied the mechanical properties and residual stre=
ss 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 th=
e islands, thus the enlargement of island size (lowering the number of bord=
ers) produced material with lower porosity and higher elongation. On the co=
ntrary, the smaller island produced material with slightly higher UTS and l=
ower residual stress. Carter et al. [22] also investigated the island scann=
ing strategy. They found the influence on the grain structure of nickel sup=
eralloy CM247LC by the localization of cracks in the border zones of the is=
lands. They estimated that the higher crack occurrence is present at the hi=
gh-angle grain boundaries. Popovich et al. [23] showed that the different p=
rocess parameters together with the scanning strategy strongly affects grai=
n 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 Solution=
s with a maximum laser power of 400 W was used. Experiments comprised of si=
ngle-track welds and volume samples (cubes 5  5  5 mm), all with a layer th=
ickness of 50 =C2=B5m. A wide range of processing parameters (laser power, =
laser speed, and hatch distance) was studied. For cube tests, a relative de=
nsity above 99% was achieved with LP 200 W, LS 200 mm/s and a hatch distanc=
e (HD) of 110 =C2=B5m. These results correspond with the other studies of A=
l-Cu alloy mentioned above. However, low surface roughness was observed wit=
h parameters LP 400 W and LS 1400 mm/s. In all of the above mentioned artic=
les focused on aluminum alloy EN AW 2618 [17,18,20], the authors describe t=
he presence of a large number of cracks in the samples.

As expected, the microstructure of SLM-processed material is different (Fig=
ure 16a,b). On the samples there is a visible lack of fusion porosity, crac=
ks 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 S=
LM 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 su=
ggests that the main reason for the different tensile properties is the def=
ects observed in the SLM state. Most of these defects are solidification cr=
acks which were present in samples for all evaluated scanning strategies.

Some laser applications employ electro-mechanical or electro-optical scanne=
r units to allow a raster-scan capability to the beam. In this way, the bea=
m 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) sc=
anner with 20 degrees scan angle located at a distance of 30 cm from the ey=
e (r =3D 30 cm) which scans at a rate of 50 Hz will be: (assume d(p) =3D 7m=
m):

NOTE: Class IIA is a special designation that is based upon a 1000 second e=
xposure 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 int=
ense Q-switched pulsed laser exposures. In some instances, the shattering o=
ccurred after one-quarter to one-half hour had elapsed following the exposu=
re. 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 a=
ssessment of various structures and infrastructure, which involves inspecti=
on, monitoring, and maintenance to support economics, quality of life and s=
ustainability in civil engineering. Currently, research has been conducted =
in order to develop non-destructive techniques for SHM to extend the lifesp=
an of monitored structures. This paper will review and summarize the recent=
 advancements in non-destructive testing techniques, namely, sweep frequenc=
y approach, ground penetrating radar, infrared technique, fiber optics sens=
ors, camera-based methods, laser scanner techniques, acoustic emission and =
ultrasonic techniques. Although some of the techniques are widely and succe=
ssfully utilized in civil engineering, there are still challenges that rese=
archers 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 investi=
gating and applying artificial intelligence, namely machine learning algori=
thms to address the challenges. In addition, researchers have combined mult=
iple techniques in order to improve accuracy and acquire additional paramet=
ers to enhance the measurement processes. This study mainly focuses on the =
scope and recent advancements of the Non-destructive Testing (NDT) applicat=
ion for SHM of concrete, masonry, timber and steel structures.Keywords: con=
crete structures; non-destructive testing; sensors; steel structures; struc=
tural engineering; structural health monitoring (SHM)

The purpose of this paper is to investigate the effect of remelting each la=
yer on the homogeneity of nickel-titanium (NiTi) parts fabricated from elem=
ental nickel and titanium powders using laser powder bed fusion (LPBF). In =
addition, the influence of manufacturing parameters and different melting s=
trategies, including multiple cycles of remelting, on printability and macr=
o defects, such as pore and crack formation, have been investigated.

Fischer et al. (2016), Simonelli et al. (2018) and Vrancken et al. (2014) e=
xplored LPBF powder mix fabrication of different alloys where only basic LP=
BF parameters were adjusted during the manufacturing process. This resulted=
 in the high inhomogeneity of fabricated materials when no remelting or las=
er focus variation was used. Therefore, given what has previously been stud=
ied 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 th=
e homogeneity of NiTi parts fabricated from elemental nickel and titanium p=
owders 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 macro=
scopic defects, such as pores and cracks, were investigated. Currently, the=
re are two major limitations to using as-cast NiTi, machining difficulties =
and its high price. One major benefit of AM technologies is the reduction o=
r elimination of the need for machining. Prealloyed NiTi powder used for AM=
 is also expensive. Production Ni-Ti components using premixed Ni and Ti el=
emental powders, instead of prealloyed powders, would reduce the material c=
osts of fabrication by nearly three times. Consequently, the price of the f=
inal 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 specimen=
s using light microscopy (Zeiss AxioScope Light Microscope). The relative d=
ensity 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 fabricate=
d with different energy densities and melting strategies. The presence of p=
ores and cracks in the microstructure of the fabricated parts was observed.=
 The size and distribution of pores, as well as cracks, depend on the manuf=
acturing parameters. The porosity decreases with increasing energy density =
and with the remelting applied for most parts. Li et al. (2019) and Griffit=
hs et al. (2018) reported that remelting provided good metallurgical bondin=
g 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 result=
s in their works, where remelting was applied. It was reported that due to =
good metallurgical fusion provided by remelting, the pores were successfull=
y reduced. Moreover, the number of pores and their average size were minimi=
zed.
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