materials
ArticleMechanical Properties Analysis of theAA2519-AA1050-Ti6Al4V Explosive Welded Laminate
Ireneusz Szachogluchowicz 1, * , Lucjan Sniezek 1 , Tomasz Slezak 1 , Janusz Kluczyński 1 ,Krzysztof Grzelak 1 , Janusz Torzewski 1 and Teresa Fras 2
1

2*

Institute of Robots & Machine Design, Faculty of Mechanical Engineering, Military University of Technology,
2 Gen. S. Kaliskiego St., 00-908 Warsaw 46, Poland; lucjan.sniezek@wat.edu.pl (L.S.);
tomasz.slezak@wat.edu.pl (T.S.); janusz.kluczynski@wat.edu.pl (J.K.); krzysztof.grzelak@wat.edu.pl (K.G.);
janusz.torzewski@wat.edu.pl (J.T.)
French-German Research Institute of Saint-Louis (ISL), 5 rue du Général Cassagnou,
68301 Saint-Louis, France; teresa.fras@isl.eu
Correspondence: ireneusz.szachogluchowicz@wat.edu.pl; Tel.: +48-261-837-208

Received: 20 August 2020; Accepted: 28 September 2020; Published: 30 September 2020


Abstract: Explosively welded layered materials made of (a) an AA2519 aluminum alloy (AlCuMgMn +ZrSc), (b) titanium alloy Ti6Al4V and (c) an intermediate layer composed of a thin aluminum alloyedAA1050 layer are considered herein. This study presents test results connected to measurement
science including microstructural observations of the material combined with the explosive method,
and a basic analysis of the strength properties based on microhardness and tensile tests. Owing to thejoint’s special manufacturing conditions, the laminate was subjected to deformation measurementswith the digital image correlation (DIC) method. The research was supplemented by the residual
stress measurements with the sin2ψ X-ray method based on the diffraction–reflection analysis thatwas verified by the bore trepanation method.
Keywords: deformation analysis; residual stresses measurement; AA2519; Ti6Al4V; explosive welding;layered laminate

1. Introduction
In this article, a layered composite was tested which will be used as a construction material withincreased ballistic resistance for spacecraft and military vehicles. In space technology, the 2519 alloy isused for protective panels against micrometeorites and for the construction of space station chambers [1].
The Ti6Al4V alloy is characterized by increased ballistic resistance and therefore it can be,
especially in combination with aluminum alloys with increased ballistic resistance, an alternative to,inter alia, homogeneous armor plates [2,3]. Due to its special functional properties, the Ti6Al4V alloy
has long been used in the production of aircraft components, including: jet engine rotor blades and wing
caissons, one of the largest elements in the construction of fighters and combat vehicles [4,5]. The Future
Combat System (FCS) program developed by the American army assumes that materials that can playa special role in the development of special structures for military purposes, including the constructionof combat vehicles, aircraft and satellite structures, include titanium alloy Ti6Al4V, alloys aluminumAA2519 and AA5083 and polymer composites [6–9]. It is anticipated that the use of the appropriatematerials, especially light alloys with different densities and mechanical properties, can provide anappropriate level of strength and ballistic resistance while reducing the weight compared to classic
passive shields. The layered structure is to increase the phenomenon of energy dissipation of thehitting projectile and thus increase the ballistic resistance of the material. Traditional joining techniques

Materials 2020, 13, 4348; doi:10.3390/ma13194348

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are not able to effectively join titanium and aluminum alloys, so it was decided to use the explosive
joining technique [10–13].
Combining these theoretically not weldable materials may be by explosive bonding. This process
over the years has not been resolved from the theoretical. There are many theories that describe
the process of merging, and so far, they have not explained specifically which of them is the mostappropriate approach [14–18]. Changing parameter combinations has an amazing effect on the typeand quality of the connection. This translates into the subsequent mechanical properties and structural
material. There is therefore a need to understand and analytically represent intervention input
components affecting the future connection type [19–21].
Layered materials are characterized by different mechanical properties than in monolithic parts.
This phenomenon was taken into account during our previous research of layered materials obtained
through different manufacturing technologies: additively manufactured using selective laser melting
technology [22–26], additively manufactured, double-material restraint joints using fused filament
fabrication technology [27] and explosively welded lightweight materials [28–30]. All the mentioned
manufacturing technologies are characterized by the layered structure of the materials obtained byjoining each layer of the material using high-energy sources. That kind of approach generates high-level
residual stresses which directly affect the mechanical properties of manufactured parts. The joint area
is characterized by different mechanical properties to the other part of the material. The mentioned
area is very small so to properly verify the residual stresses level, special X-ray technologies have to be
used [31].
The produced ballistic material was subjected to basic tests of its strength properties.
Metallographic specimens were cut out of the produced material and examined with a scanningmicroscope. The quality of the connection between the layers of the joined material was assessed.
The structure in the joining layers was checked for any separation or fragmentation of the structure.
In addition, the chemical composition of selected elements in critical connection points was checked.
Due to the innovative joining technique, the last monotonic tensile test of the base materials and the
produced laminate were examined. The work also investigates the deformation distribution using
the digital image correlation (DIC) method. This test was performed on each side of the laminate
produced. During the explosive bonding process, a pressure wave is generated, which imparts very
high velocity to the solids (plates made of joined materials). The collision of the joined materials
at such high velocities releases pressures of up to 2 × 104 MPa. Such pressure makes it possible toobtain physical states unattainable under static load conditions. The effect of their influence is thepresence of significant values of residual stresses, deviating from the primary stress distribution in the
joined materials. The type of residual stress has a decisive influence on the functional properties of thematerial and the level of ballistic resistance. For this reason, the residual stresses will be measured by
the X-ray method and the hole-drilling strain gauge method.
2. Materials
Composites characterized by the unique properties of their constituent materials often comprise astructural or layered nature. Explosive bonding is a practical-based technique that recognizes the factthat explosive welding is a special type of pressure bonding. Achievement of material connections is
possible by the massive impact generated between at least two elements in high-pressure conditions
caused by the explosive welding process. This type of technology allows the joining of different
types of metals, which cannot be bonded using all types of methods except from gluing or fromusing conventional mechanical joints. This technology makes the joining of materials which are
difficult-to-weld possible, even if these have extremely different properties. The main advantageof this technology is the higher breaking strength of the joints compared to the strengths of theconstituent materials of the composite [32]. An additional advantage of this technology refers to
the economic benefits that result from the reduction in consumption of expensive materials used asadhesives. All the physical phenomena observed during the explosive bonding process are extremelyMaterials 2020, 13, 4348

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dynamic. It is thus impossible to analyze and compare phenomena that result from the displacement
to joined
which itis not pertinent
to carryouttimecomparisons
theisphysicalphenomena
with moreclassicalofmaterial
sheets within
shortperiods. ofThisthe mainreason according
to whichitweldingtechnologies.
Structuralchangesofjoinedmaterials
areusually
limitedonlytotheis not pertinent to carry out comparisons of the physical phenomena with more classical welding
connection zonethat spansseveralmicrometers.
of changes
in thematerial’s
chemicaltechnologies.
Structuralchangesof joinedmaterialsThe
are lack
usually
limited only
to theconnection
zone
composition
is justified
by the fact
retainthe uniquepropertiesof their constituent
thatspans several
micrometers.
The thatlack compositesof changes in
the material’s
chemicalcomposition
is justified
materials
bythe fact[33].
that composites retain the unique properties of their constituent materials [33].
of thethe explosive
explosive welding
welding technology
technology from base
The layered composite produced with the use ofmaterials, i.e.,
aluminumalloy
AA2519(AlCuMgMn
+
ZrSc)
and
titaniumalloy
Ti6Al4Vwiththe usei.e., aluminum alloy AA2519 (AlCuMgMn + ZrSc) and titanium alloy
Ti6Al4V
with
the
of an
intermediate
layerlayerof AA1050
alloyalloy
withwitha thickness
in theof 0.6–0.8
mm, mm,wasuse
ofadditionalan additional
intermediateof AA1050
a thickness
inrangethe rangeof 0.6–0.8
tested.
The Thetechnologicaltreatment
includedsurfacepreparation
andwastested.
technologicaltreatment
includedsurfacepreparationbased
basedononsurfacesurface rolling
rolling andgrinding. Manufactured laminates are shown in Figure 1a. The cross-section of the laminate
laminate showsshows
the connection
connection zone
zone ofof thethe Ti6Al4V
Ti6Al4V andand AA2519
AA2519 alloys
alloys with
with thethe
the AA1050
AA1050 alloy
alloy interlayerinterlayer (Figure(Figure 1b).
1b).
On thethe AA2519–AA1050
AA2519–AA1050 borderborder junction,
junction, characteristic
characteristic wavy
wavy andand flatflat surfaces
surfaces were
were observed
observed inin thetheOncombined
Ti6Al4V–AA1050
construct.
combined Ti6Al4V–AA1050 construct.

(a)

(b)

Figure 1.
(b)(b)
metallographic
cross-sectionof
1. Laminate
Laminate AA2519-AA1050-Ti6Al4V:
AA2519-AA1050-Ti6Al4V:(a)(a)sheets
sheetsproduced,
produced,
metallographic
cross-section
thecomposite.
of thecomposite.

The
in in
terms
of wavy
structures
withwithsimilardensities
andThe characteristics
characteristicsofofmaterialmaterialcombinations
combinations
terms
of wavy
structures
similardensities
masseswere determinedbased onthe appropriate
selection selectionof the joining
parameters.
The connection
and masses
were determinedbased
on the appropriateof thejoining parameters.
The
qualityofaflat
borderbetween
AA1050and
Ti6Al4V
canbedemonstratedbytheintermetallic
connection quality of a flat border between AA1050 and Ti6Al4V can be demonstrated by theprecipitations
formed in the additional
For moreaccurateFor
microstructural
analyses,
the JEOL
intermetallic precipitations
formed insublayer.
the additional
sublayer.
more accurate
microstructural
JSM-6610
microscope(Jeol LTD,Tokyo, Japan)
used.
Samplepreparations
analyses, scanning
the JEOL electron
JSM-6610
scanning electron
microscope(Jeol wasLTD,Tokyo,
Japan)
was used.
in
the
form
of
metallographic
samples
wererequiredtoobtainhigh-quality
surfaces.
classical
Sample preparations in the form of metallographic samples were required to obtain The
high-quality
methodsamplepreparation
polishing) could
not provide
a propersurfacesurfaces.ofTheclassical
method(mechanicalof sample preparation(mechanicalpolishing)could
not quality
providefora
alllaminatecomponents.
Mechanicalion
polishing
was
used
only
at
the
initialpreparatory
stage.
proper surface quality for all laminate components. Mechanical ion polishing was used only attheIon
polishingisdedicatedtosamplemetallographic
testing
preparation.
The
ion-polishingprocess
initial preparatory stage. Ion polishing is dedicated to sample metallographic testing preparation.
involved
the removal
of atomic
layersthefromthe material
surfacewithan theargon
ion beam.
The withsurface
The ion-polishingprocess
involved
removalof atomic
layersfrommaterial
surfaceanpreparationofsamplesformetallographic
tests
was
performedwiththeHitachi
IM4000
Ion
Millingargon ion beam. The surface preparation of samples for metallographic tests was performed with the
SystemLTD,
Tokyo,
Japan)(Hitachiwith a protectivemask
thatwithallowedthe generationof allowedsmoothHitachi (Hitachi
IM4000 Ion
Milling
SystemLTD, Tokyo,
Japan)
a protective
mask that
surfaces.
This technology
dedicatedto multicomponent
materialtopolishingwith constituent
the generationof smooth was
surfaces.
This technology
was dedicatedmulticomponent
materialmaterials
withdifferent
hardnessvalues.
polishing with constituent materials with different hardness values.
A
manufactured at
the Non-Ferrous
Non-Ferrous Metals
Metals Institute
Institute inin Gliwice,Gliwice,
A specially
specially modified
modified AA2519
AA2519 alloy
alloy manufactured
at thePoland,wasused
toproducethecomposite.
Owing
to
the
increased
fatiguedurability
anddiminished
Poland, was used to produce the composite. Owing to the increased fatigue durability andtendency
fortendency
fragmentation
during theduring
dynamic
impact ofimpact
missiles,the AA2519
alloy wasdiminished
for fragmentation
the dynamicof missiles,
the AA2519
alloyusedwasin
the inconstructionof combat
vehicles,vehicles,
devices devices
with increased
ballistic resistanceand in elements
usedthe constructionof combat
with increased
ballistic resistanceand indedicated
to aerospace
applications.
In the spaceindustry,
are usedelements dedicatedto aerospace
applications.
In thespace AA2519
industry,alloys
AA2519alloysfor
areprotective
used forpanel
construction
for devices covering
againstmicrometeorites[34]. The AA2519
alloyAA2519
modification
protective
panel construction
for devices
covering
against micrometeorites[34]. Thealloy
developedby theInstitute ofconsisted of additionalalloyingof
elements,
includingZr
modification
developed
byNon-Ferrous
the InstituteMetalsof Non-Ferrous
Metals consisted
additionalalloying
andSc,
inconcentrations
in
the
range
of
0.2–0.3%.
The
improvementoftheprocess
allowsforelements, including Zr and Sc, in concentrations in the range of 0.2–0.3%. The improvement of theprocess allows for precipitation strengthening and an increase in the secondary recrystallization
resistance of the structure. The mentioned modifications could obtain stable mechanical properties
in high-temperature conditions as a result of the homogeneous phase dispersion of Al3Zr. The

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precipitation strengthening and an increase in the secondary recrystallization resistance of the structure.
The mentioned modifications could obtain stable mechanical properties in high-temperature conditions
as a result of the homogeneous phase dispersion of Al3 Zr. The strength properties of AA2519 alloy
were obtained on the basis of our own research. The chemical composition of the material was givenby the manufacturer. The data are presented in Table 1.
Table 1. Strength properties and chemical composition of the AA2519 alloy.
Strength Properties
R0.2 [MPa]312

Rm [MPa]
335

Chemical Composition [wt %]
A [%]
6.5

Si
0.06

Fe
0.08

Cu
5.77

Mg
0.18

Zn
0.01

Ti
0.04

V
0.12

Zr
0.2

Sc
0.36

Al
rest

Advantageous mechanical properties, good weldability, high corrosion resistance and a melting
point temperature of 1955 K indicate that titanium alloys can be extensively used in the aerospace,
space and military industries. The Ti6Al4V alloy is also characterized by increased ballistic resistancethat makes it an alternative material to those used for homogeneous armor plate productions [35].
The specific properties of the Ti6Al4V alloy allow its use in the production of aircraft components,
including jet engine rotor blades and wing caissons [36]. The strength properties of Ti6Al4V alloy wereobtained on the basis of our own research. The chemical composition of the material was given by the
manufacturer. The data are presented in Table 2.
Table 2. Strength properties and chemical composition of the Ti6Al4V alloy.
Strength Properties
R0.2 [MPa]950

Rm [MPa]
1020

Chemical Composition [wt %]
A [%]
14

O
<0.20

V
3.5

Al
5.5

Fe
<0.30

H
C
<0.0015 <0.08

N
<0.05

Ti
rest

The explosive bonding of AA2519 and Ti6Al4V alloys was achieved with the use of an AA1050
aluminum alloy interlayer. The strength properties of AA1050 alloy were obtained on the basis of ourown research. The chemical composition of the material was given by the manufacturer. The data arepresented in Table 3.
Table 3. Strength properties and chemical composition of the AA1050 alloy.
Strength Properties
R0.2 [MPa]78

Rm [MPa]
168

Chemical Composition [wt %]
A [%]
2.9

Fe
0.4%

Si
0.25<

Zn
0.07<

Mg
0.18

Ti
0.05<

Mn
0.05<

Cu
0.05<

Al
rest

Owing to its high plasticity, the AA1050 alloy has very good adhesive properties which improve
the strength properties of the connection zone.
The microstructure of the AA2519-AA1050-Ti6Al4V joint was considered. Particular attention
was paid to areas near the junction zone, such as the area near Ti6Al4V with the AA1050 alloys andthat near the AA2919 and AA1050 alloys. The surface of the Ti6Al4V alloy, shown in Figure 2 has aproper structure for this type of material and does not show visible deformations or damages. In thecase of the AA1050 aluminum alloy, grain deformations in the form of elongated shapes are visible.
This phenomenon is connected to the process of the high pressure generated during the explosive
joining process and the location of the material next to the hard deformable titanium alloy. The useof the same material interfaced with the AA2519 aluminum alloy in the connection area retains a
regular grain structure. The AA2519 aluminum alloy structure yields fine, copper-rich precipitations,which are visible as bright areas in Figure 2. The presence of copper in the AA2519 aluminum alloy
improves the bonding capacity of the explosive.

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Figure 2. Metallographic cross-sections obtained with scanning electron microscopy of the manufactured
Figure 2. Metallographic cross-sections obtained with scanning electron microscopy of thelaminate AA2519-AA1050-Ti6Al4V.
manufactured laminate AA2519-AA1050-Ti6Al4V.

A more detailed analysis of the AA1050 aluminum joining zone and the AA2519 alloy showed
In the case of the border of the titanium alloy Ti6Al4V with the 1050 aluminum alloy, anthat during the explosive bonding, a precipitation sublayer with an increased copper concentration inintermediate layer was observed with a thickness of approximately 8–15 µm (Figure 3a). In this layer,
phaseFigureΘ was formed owing to cross-sections
the increased obtainedpressure andtemperature
growth. Thiszone
with short-term
the presence2.ofMetallographic
numerous precipitates of various
sizes
andscanning
irregularelectron
shapes microscopy
was found. ofTo theidentify
is a natural
obstacleto the AA2519-AA1050-Ti6Al4V.
dislocation movement that strengthens the entire alloy. In addition to the
manufactured
laminatethe chemical composition of materials in the diffusion layer, an energy-dispersive spectrometry (EDS)
increasing distance from the joining zone, grain growth was also observed [37,38].
analysis was performed (Figure 3b).
In thethetheborderof theoftitanium
alloy Ti6Al4V
with the 1050
an intermediate
thecasecaseof ofborderthe titanium
alloy Ti6Al4V
withaluminumthe 1050 alloy,
aluminumalloy, anlayer was observed
witha thickness
8–15 µm (Figure
this layer,
thethispresence
intermediate
layer wasobserved
withofaapproximately
thickness of approximately
8–153a).
µmIn(Figure3a). In
layer,
of numerous
precipitatesvarious sizes
and irregularshapeswas found.
identify
thepresence ofnumerousof
precipitatesof various
sizes andirregular
shapesTo
wasfound.theTochemical
identify
compositionmaterials in
diffusionlayer,
an energy-dispersive
spectrometryspectrometry(EDS) analysis
wasthechemical ofcomposition
ofthematerials
in thediffusionlayer, an energy-dispersive(EDS)
analysiswasperformed
performed(Figure3b). (Figure 3b).

(a)

(b)

Figure 3. Micro-area of the AA1050-AA2519 material connection zone: (a) microstructure, (b)chemical composition measurement locations.

The results of the additional
chemical composition measurements (the(a)(b)spectral points in Figure3b) indicated the presence of Ti–Al compounds in the intermediate layer. The relative chemicalthetheAA1050-AA2519
material
connection
zone: (a)microstructure,(b) chemical
Figure 3.3. Micro-area
Micro-areaof of
AA1050-AA2519
materialzone:
compositionsofthese elements
inthe selected spectra
areconnection
listed in Table
4.(a) microstructure, (b)composition
measurement
locations.locations.
chemicalcomposition
measurement

The results of the additional chemical composition measurements (the spectral points in Figure3b) indicated the presence of Ti–Al compounds in the intermediate layer. The relative chemicalcompositions of these elements in the selected spectra are listed in Table 4.

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The results of the additional chemical composition measurements (the spectral points in Figure 3b)
indicatedthe13,
presenceof Ti–Al
compounds in the intermediate layer. The relative chemical compositions
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x FOR PEER
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Table 4. Results of chemical composition measurements in the connection zone of the Ti6Al4V and
Table
4. aluminum
Results of chemical
AA1050alloys. composition measurements in the connection zone of the Ti6Al4V andAA1050 aluminum alloys.

Measurement Point Name
Measurement Point Name

Spectrum 9
Spectrum
Spectrum9 10
Spectrum10 11Spectrum
Spectrum
11 12Spectrum
Spectrum 12

Chemical Composition [%]ChemicalTi Composition
Al[%]
Ti
Al
92.8
7.2
69.6
30.4
92.8
7.2
69.6
30.4
83.1
16.9
83.10
16.9
100
0

100

Boronski et al. [39] and Milosavljevi M et al. [40] proved that the observed intermediate layer
was formed
resultaluminumdeposition
theproved
titaniumdue tointermediate
the high temperature
Boronskiaseta al.
[39]ofand
Milosavljevi
M et al.on[40]
thatsubstrate
the observed
layer wasand pressure.
formedas a result of aluminum deposition on the titanium substrate due to the high temperatureand pressure.
3. Testing Basic Strength Properties
3. Testing Basic Strength Properties
Microhardness measurements were carried out with a Struers DURA SCAN 70 metallographic
Microhardness
were carried
witha Struers
DURA
SCANin70accordance
metallographic
microhardness testermeasurements(Struers Inc, Cleveland,OH,outUSA)
withthe Vickers
methodwithmicrohardness
tester(Struers
Inc,
Cleveland,
OH,
USA)
with
the
Vickers
methodaccordance
the methodology included in the standard PN-EN ISO 6507-1:2007. The obtained inresultsof thewiththe methodology
included
standard PN-EN ISO 6507-1:2007.
The connection
obtained results
microhardness
measurementof inthetheAA2519-AA1050-Ti6Al4V
alloys in the
area,
of
the
microhardness
measurementoftheAA2519-AA1050-Ti6Al4V
alloysintheconnection
area,
including the microhardness of constituent materials before the connection, are presented in Figure
includingthe microhardness of constituent materials before the connection, are presented in Figure 4.
4.

Figure 4. Microhardness distribution in the AA2519-AA1050-Ti6Al4V laminate.
Figure 4. Microhardness distribution in the AA2519-AA1050-Ti6Al4V laminate.

The gray graphs indicate the transition layer in the form of AA1050 aluminum. The microhardness
Thegraphsindicate
the transition
layer in theof aluminum
AA1050 aluminum.
The
tests inthegraylaminate
indicate
an increasein the microhardnessof theform
AA2519alloy comparedmicrohardness
tests
in
the
laminate
indicateanincreaseinthemicrohardnessoftheAA2519with the base alloy. This change is the effect of the dislocation strengthening phenomenon that results
aluminumcomparedwithbase alloy. This change is the effect of the dislocation
owing
to thealloy
crumplecaused by
the theexplosion.
strengthening
phenomenon
that
resultsowing
to thecrumplecausedby materials
the explosion.
Tensile tests of the AA2519-AA1050-Ti6Al4V
laminateandits basein the presence ofTensiletestsof thelaminate
and its basematerials
theofuniaxial,
quasi
staticandAA2519-AA1050-Ti6Al4V
crosshead-controlled tensile
testing conditions
werecarriedinout
in presenceaccordance
uniaxial,
quasi
staticandcrosshead-controlledtensiletesting
conditions
werecarriedoutinwith PN-EN ISO 6892-1:2010 with an Instron 8802 hydraulic pulsator (Worldwide Headquarters,
accordance
with
PN-EN
ISO
6892-1:2010
withanInstron8802
hydraulicpulsator(Worldwide
Norwood, MA, USA). Deformation measurements were carried out with an Instron 2630-112
Headquarters,(Worldwide
Norwood, MA,
United States).
Deformation
measurements
werecarried out
withanextensometer
Headquarters,
Norwood,
MA, USA)with a 50 mm
measuringbasein theInstron2630-112
extensometer(Worldwide
Headquarters,
Norwood,
MA,
USA)
with
a
50
mm
presence of axial stretching conditions. Monotonic tensile tests were carried out on samples made ofmeasuringbase inlaminate
the presence
of 5)
axial
conditions.
tests
were carriedthemanufactured(Figureandstretchingon samples
produced Monotonic
with the usetensile
of basematerials
beforeout on samples made of the manufactured laminate (Figure 5) and on samples produced with the useof base materials before and after heat treatment. All samples subjected to tensile testing had the same
geometry. Six samples were made of each material.

Materials 2020, 13, 4348

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made
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Figurelaminate.
Figure 5.
5. Samples
made ofof thethe AA2519-AA1050-Ti6Al4V
AA2519-AA1050-Ti6Al4V
Samples subjectedsubjected to
to aa static
static tensile
tensile test
test madeAA2519-AA1050-Ti6Al4V laminate.
laminate.

The
AA2519-AA1050-Ti6Al4V
In thethe
The tensile
tensile test
test chart
chart ofof AA2519-AA1050-Ti6Al4V
AA2519-AA1050-Ti6Al4V isis shown
shown inin thethe Figure
Figure 6.
6. InInthe casecase ofof thethetitaniumalloy,
themaximumtensilestrength
R
m
=
910
MPa
This
value
exceededthethemaximumtensilestrengthR=
wasreached.
mtitanium alloy, the maximum tensile strength Rm = 910 MPa was reached. This value exceeded the
maximum
strengthoftheAA2519
alloy
(R
>2.5
times. The
The relative
relative elongation
maximum tensile
tensile strength
strengthof
ofthe
theAA2519
AA2519alloy
alloy(R(Rmmm == 358
358 MPa)MPa) byby >2.5>2.5 times.
times.
The
relativeelongation
titaniumalloy
Ti6Al4V
approximately
11.2%,
while
that
for
the
aluminumalloy
AA2519A
forthealuminumalloy
AA2519isA forfor thethe titanium
titaniumalloy
alloyTi6Al4V
Ti6Al4Visis
isapproximately
approximately11.2%,
11.2%,while
whilethat
that
for
the
aluminumalloy
AA2519isapproximately
6.8%.
The
tensilestrengthRmoftheelements
producedbythemethodapproximately
6.8%.
The
tensilestrengthRoftheelements
producedbythemethodof
explosive
mm of the elements produced by the method of explosive
is approximately 6.8%. The tensile strength R
welding
was
657
MPa,
and
the
conventionalyieldstrength
R
was
436
MPa,
with
aa totalelongation
welding
R0.2
was
with
a totalelongation
A
welding was
was657657MPa,MPa,andandthetheconventional
conventionalyield
yieldstrength
strength
R0.2
0.2
was436436MPa,
MPa,
with
total
elongation
A
6.5%.
of
6.5%.
A of
of
6.5%.

FigureMonotonic tensile
tensile test
test chart
chart forFigure 6.
6. Monotonic
for dog-boned
dog-boned samples
samples mademade ofof thethe basebase material.
material.

of themanufactured
composite
Them
The tensile
tensile strength
strength R
Rm
m of
of
the manufactured
manufactured composite
composite inin whichwhich thethe constituent
constituent materials
materials arearecharacterized
by
the
solid
material
structurecanbecomparedwiththetheoreticalcomposite
strengthcharacterized by the solid material structure can be compared
compared with thethe theoreticaltheoretical composite
composite strength
calculated
calculated based
based onon thethe “mixtures“mixtures law”.
law”.
For
the
testedAA2519-AA1050-Ti6Al4V
material,
themixtureslaw
canbe
expressedas
For the tested AA2519-AA1050-Ti6Al4V material,material, thethe mixtures
mixtureslaw
lawcancanbe
beexpressed
expressedas
as

×× V
w
mo×
mm
(1)
R
mk
Rmw
mw
w+
+RR
R
×V
V
RR
mm×
×V
V×mmVm
(1)
Rmk R
=mk
R==mwR
×V
Vooo+++R
(1)
wV+
momo×
mm
where
where RRmk
mk is
is thethe composite
composite tensile
tensile strength,
strength, R
Rmw
mw is
is thethe tensile
tensile strength
strength ofof thethe basebase material,material, V
Vww isis thethewhereR
composite
tensile strength,
Rmw is the tensile
strengthof thebase material,
VwRmois
mk is thetensilestrength
ratio
of
the
reinforcement
cross-sectional
area
to
the
matrixcross-sectionalarea,
tensile strength ratio of the reinforcement cross-sectional area to the matrix cross-sectional area, Rmothetensilestrength
ratio
of
the
reinforcement
cross-sectional
area
to
the
matrixcross-sectionalarea,
isis thethe warp
warp tensile
tensile strength,
strength, V
Voo isis aa ratio
ratio ofof thethe matrix
matrix cross-sectionalcross-sectional area
area toto thethe strengthening
strengthening crosscrossR
warpRtensile
strength,Vo isa ratio ofandthe V
matrixcross-sectional
area to the strengthening
mo is thearea,
sectionalmm
istheinterlayer
resistance
m
is
the
ratio
of
the
cross-sectionalareaofsectional area, Rmm is the interlayer resistance and Vm is the ratio of the cross-sectional area of thetheinterlayerinterlayer toto thethe cross-sectionalcross-sectional area
area ofof reinforcement.
reinforcement.
The
The theoreticaltheoretical tensile
tensile strength
strength was
was determined
determined onon thethe basis
basis ofof thethe mixtures
mixtures law
law for
for R
Rmk
mk =
= 604
604
MPa.
The
obtained
test
results
carriedout
ontheproducedlaminates
indicatethatthetensilestrength
MPa. The obtained test results carried out on the produced laminates indicate that the tensile strengthofof thethe AA2519-AA1050-Ti6Al4V
AA2519-AA1050-Ti6Al4V laminate
laminate isis R
Rmm == 657
657 MPa
MPa (Figure(Figure 7).
7). Explosive
Explosive bonding
bonding increased
increased its
its
strength
by
>8%.
The
observed
increase
in
the
R
m
value
was
influencedbythestrengtheningofthestrength by >8%. The observed increase in the Rm value was influenced by the strengthening of theMaterials 2020, 13, 4348

8 of 16cross-sectional area, Rmm is the interlayer resistance and Vm is the ratio of the cross-sectional area of theinterlayer to the cross-sectional area of reinforcement.
The theoretical tensile strength was determined on the basis of the mixtures law for Rmk = 604 MPa.
The obtained test results carried out on the produced laminates indicate that the tensile strength oftheAA2519-AA1050-Ti6Al4V
laminate is Rm = 657 MPa (Figure 7). Explosive bonding increased
Materials
2020, 13, x FOR PEER REVIEW
8 ofits
16
strength by >8%. The observed increase in the Rm value was influenced by the strengthening of theconstituent material caused
caused by the crushingcrushing during
during thethe evolution
evolution ofof the explosive
explosive bonding
bonding process.
process.
Another factor
factor thatthatincreases
increasestensile
tensilestrength
strengthisisthe
theformation
formation
3Tiintermetallic
phasematerials
Anotherofof
AlAl
intermetallic
phasematerials
in
3 Ti
in theintermediate
layer[41,42].
Owing
to thediffusivenatureof Al-Ti
the Al-Ti
formation
processtheintermediate
layer[41,42].
Owing
to thediffusivenatureof thejointjoint
formation
processandandthermo-mechanicalthe thermo-mechanicalprocesses,
elements
are segregatedin a narrow
very narrowarea
the transition
theprocesses,
elements
are segregatedin a very
area oftheoftransition
zone.
zone.results
This resultsin achange
local change
in mechanicalproperties.
These infactors
in conjunction
theThisin a local
in mechanicalproperties.
These factors
conjunction
with thewith
layeredlayered structureof the produced
have a significant
impacton thedifferentofstructureof the produced
compositecomposite
can have acansignificant
impact on the
different
valuesof thevalues
material
the material deformation.
ofsurface
the laminate
surfaceprocess
deformation
process ina monotonic
deformation.
Verification ofVerification
the laminate
deformation
in a monotonic
tensiletest wastensile test
was carried
withthe useof thedigital image
correlation(DIC) method.
Deformation
carriedout withthe use outof thedigitalimage
correlation(DIC) method.
Deformation
observations
were
observations
were
out from
three sidesof thethe aluminum
laminate, namely
the aluminum
carriedout from
thecarried
three sidesof thethelaminate,
namelyalloy, titanium
alloy andalloy,sidetitaniumsurfaces.
alloy andside
samplesurfaces.
Thein
tests
results
sampleThe
tests
resultsare shown
Figure7. are shown in Figure 7.

Figure 7. Deformation distribution using the digital image correlation (DIC) method for selected
Figure 7. Deformation distribution using the digital image correlation (DIC) method for selected
points of the monotonic tensile test of a flat-layered AA2519-AA1050-Ti6Al4V composite sample: 1:
points of the monotonic tensile test of a flat-layered AA2519-AA1050-Ti6Al4V composite sample: 1:
conventional yield point R0.2 , 2: tensile strength for εp = 2%, 3: maximum tensile strength Rm and 4:
conventional yield point R0.2, 2: tensile strength for εp = 2%, 3: maximum tensile strength Rm and 4:
crack sample.
crack sample.

Obtained test results for points 1 and 2 (in Figure 7) yield homogeneous strain distributions on all
test resultsfor points areas
1 andwere
2 (in only
Figure7) yieldafter
homogeneous
strain distributions
onsides.Obtained
Visible material
deformation
observed
the yield strength
was exceeded.
allsides.
Visiblematerial
deformation
areas
were
only
observed
after
the
yield
strengthwas
It should be noted that the images of deformation fluctuations on the side of the sample did not yieldexceeded.
It should
notedthat the imagesof deformation
fluctuations
on theof thestrength
samplebanding
effects.
Thisbemay
be attributed
to the layered
arrangementof materials
withsidedifferent
did not yield
effects.
may
be attributed
the layered
arrangement
ofobserved
materialsatwith
properties.
Atbandingpoint 3 inFigureThis
7, theconcentrationof tomaximum
deformations
wasthedifferent
strengthproperties.
At
point
3
in
Figure7,
theconcentrationofmaximum
deformations
wascrack initiation site. The location of the maximum deformations and the continuous nature of theirobservedindicate
at the cracksite. The within
location
ofentirethe maximum
andthethetest.
continuous
growthjoint initiation
plain consistency
therange of deformations
the load during
Samplenatureoftheirgrowthindicate
joint
plain
consistency
withintheentire
range
of
the
load
during thecracks were present in the zones of maximal deformation.
test. Sample cracks were present in the zones of maximal deformation.

4. Residual Stress Measurements
4.1. X-ray Stress Measurements
X-ray stress tests were carried out in cooperation with the Institute of Metallurgy and Materials
Engineering of the Polish Academy of Sciences in Krakow. The tests were conducted on a Bruker D8
Discover X-ray diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) with a Euler wheel (Bruker
AXS GmbH, Karlsruhe, Germany) and a sample positioning table (Figure 8).

Materials 2020, 13, 4348

9 of 16

4. Residual Stress Measurements
4.1. X-ray Stress Measurements
X-ray stress tests were carried out in cooperation with the Institute of Metallurgy and Materials
Engineering of the Polish Academy of Sciences in Krakow. The tests were conducted on a Bruker
D8 Discover X-ray diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) with a Euler wheel(Bruker
AXS13,
GmbH,
Karlsruhe,
Materials 2020,
x FOR PEER
REVIEWGermany) and a sample positioning table (Figure 8).
9 of 16(a)(b)

Figure 8.
with
a Euler
wheel(a), (a),andandlocationsof areasof self-stress
8. Bruker
BrukerD8
D8Discover
Discoverdiffractometer
diffractometerwitha Eulerwheel
locationsof areasof selfmeasurements
based basedon the on
X-ray(b). (b).
stress measurements
the method
X-ray method

X-ray
were carried
carried out
out onon thethe surface
surface ofof thethe cross-sections
cross-sections ofof thethe sample.
sample.
X-ray stressstress measurements
measurements were
Measurements
were
made
locallyatvariouspoints(separatedby1
mm
distances)ontheMeasurements were made locally at various points (separated by 1 mm distances) on the surface
surface2 in accordance with Figure 9. During the tests, standard residual stress measurements(area(area of
of 25
25 mm
mm2)) inaccordance with Figure 9. During the tests, standard residual stress measurements
weremethodusing
a scintillation
detector
in a inparallelbeambeamsystemwithwere mademadeaccording
accordingtotothe
thesin2ψ
sin2ψ
methodusing
a scintillation
detectora parallelsystemawith
Soller0.34
collimator.
The
Texture-aided
ResidualStressInvestigation
Systemsoftwarepackagea Soller 0.34 collimator. The Texture-aided Residual Stress Investigation System software(TARSIuS)
was developedby ProfessorbyBonarski
andBonarski
Mr. Kania
fromInstituteof theMetallurgy
package (TARSIuS)
was developed
Professor
andMr.theKania
from
InstituteandofMaterials
ScienceofthePolishAcademyof
Sciences.
The
softwareregulatestheanalysisprocessoftheMetallurgy and Materials Science of the Polish Academy of Sciences. The software regulates thetestedsamples,the samples,
applicationof directthe
controlof the diffractometer
duringanalysisprocessincludingof the tested
includingapplicationof direct controlof themeasurements,
diffractometerorthe automatic
processing
ofautomaticpartially acquired
results
and the acquired
visualizationof theresults in theduringmeasurements,or theprocessingof partiallyresults
andfinal
the visualization
formofstressmaps.
The
identified
residualstressesinthetestedsamplesarecompressive
andsamples
tensile.
of the final results in the form of stress maps. The identified residual stresses in the tested
Tofacilitate
theinterpretationofthestressvalues,two-dimensionalmaps
arepresented
separatelyinare compressive and tensile. To facilitate the interpretation of the stress values, two-dimensionalthegraphical
form ofseparately
the testedincomposites’
measurements(Figurecomposites’
9). Measurements
for the AA2519
maps
are presented
the graphicalform of the tested
measurements(Figure
alloy
are
shown
in
Figure
9a–c,
and
for
the
Ti6Al4V
alloy
inFigure9d–f.
9). Measurements for the AA2519 alloy are shown in Figure 9a–c, and for the Ti6Al4V alloy in Figure
9d–f.In the composite formed after explosive welding, the topographies of the main stresses in thetitanium and aluminum layers are characterized by their laminar natures that are determined by theinteraction of both composite component layers. The titanium layer is characterized by considerablyincreased stress values (up to −800 MPa) compared with the aluminum layer (up to −100 MPa).
The closer the titanium layer is to the intermediate layer, the more profound is the increase in thecompressive stress. Near the AA1050 alloy layer, compressive stresses are transformed into tensile
owing to the shear forces that increase the effect generated by the crystal lattice mismatches in the
two joined materials. The intermediate results obtained for one of the directional stress measurementsin this alloy are illustrated in Figure 10. The recorded peaks differ significantly in intensity, and theobtained dhkl relations are neither linear nor elliptical.

Materials 2020, 13, 4348
Materials 2020, 13,(a)x FOR PEER REVIEW

(b)

(d)
(a)

(b)

(e)

(c)

10 of 16

10 of 16(f)(c)

Figure 9. Distribution of residual stress in a sample made of the AA2519-AA1050-Ti6Al4V laminate
after explosive joining: AA2519 stresses in vertical direction (a), AA2519 stresses in the horizontal
direction (b), AA2519 principal stresses (c), Ti6Al4V stresses in vertical direction (d), Ti6Al4V stresses
in the horizontal direction (e), Ti6Al4V principal stresses (f),In the composite formed after explosive welding, the topographies of the main stresses in thetitanium and aluminum layers are characterized by their laminar natures that are determined by theinteraction of both composite component layers. The titanium layer is characterized by considerablyincreased stress values (up to −800 MPa) compared with the aluminum layer (up to −100 MPa). The
closer the titanium layer is to the intermediate layer, the more profound is the increase in thecompressive stress.
into tensile(d) Near the AA1050 alloy layer,(e)compressive stresses are transformed(f)owing to the shear forces that increase the effect generated by the crystal lattice mismatches in the
Figure
9. Distributionofofresidual
residualstressstressininaasample
sample mademade ofthe AA2519-AA1050-Ti6Al4V
laminate
Figure
9. Distribution
theAA2519-AA1050-Ti6Al4V
laminate
two joinedmaterials.
The intermediate
results
obtained
forofoneofthe directional stress measurements
after
explosive
joining:AA2519
AA2519stresses
stresses inin verticalvertical direction
direction (a),AA2519stresses
ininthehorizontal
after
explosive
joining:(a),AA2519stressesthehorizontal
in this alloy are illustrated in Figure 10. The recorded peaks differ significantly in intensity, and the
direction
AA2519principal stresses(c),(c), Ti6Al4V stresses
stresses instresses
direction(b),(b),AA2519in verticalverticaldirection
direction(d),(d),Ti6Al4V
Ti6Al4V
stressesobtained
dhkl relations
areprincipal
neither stresses
linear nor Ti6Al4V
elliptical.
in thehorizontal
direction(e),Ti6Al4V
Ti6Al4Vprincipal
principalstresses
stresses (f),(f),
in thehorizontal
direction(e),

In the composite formed after explosive welding, the topographies of the main stresses in thetitanium and aluminum layers are characterized by their laminar natures that are determined by theinteraction of both composite component layers. The titanium layer is characterized by considerablyincreased stress values (up to −800 MPa) compared with the aluminum layer (up to −100 MPa). The
closer the titanium layer is to the intermediate layer, the more profound is the increase in thecompressive stress. Near the AA1050 alloy layer, compressive stresses are transformed into tensile
owing to the shear forces that increase the effect generated by the crystal lattice mismatches in the
two joined materials. The intermediate results obtained for one of the directional stress measurementsin this alloy are illustrated in Figure 10. The recorded peaks differ significantly in intensity, and theobtained dhkl relations are neither linear nor elliptical.

FigureDistribution ofof intermediate
intermediate results
results of
Figure 10.
10. Distributionof oneone measuring
measuring direction
direction forfor AA2519
AA2519 alloy.
alloy.

Reproduction of reliable curves based on the obtained measurement data using the Reuss
methodology. In these cases, reliable interpretation of stress measurements was not possible owing to
the grain growth and/or the presence of precipitations.
4.2. Residual Stresses Based on the Hole-Drilling Strain Gauge Method
Nondestructive methods used to measure stress are subject to increased uncertainties. It isadvisable to carry out measurement verification using experimental methods. One of the mostcommonly used methods for this type of experiment is bore trepanation using standard strain
gauges. This method is often referred to as the “semidestructive technique” because the hole does
not usually cause significant damage to the structural integrity of the test object (usually holes have a4.2. Residual Stresses Based on the Hole-Drilling Strain Gauge Method
Nondestructive methods used to measure stress are subject to increased uncertainties. It isadvisable to carry out measurement verification using experimental methods. One of the mostcommonlyused methods for this type of experiment is bore trepanation using standard strain gauges.
Materials 2020, 13, 4348
11 of 16This method is often referred to as the “semidestructive technique” because the hole does not usuallycause significant damage to the structural integrity of the test object (usually holes have a diameter
0.8 mmand aofdepth
4.8 mm).
Removing
materialusing
a drillallowsmeasurementsofof
ofdiameter
0.8 mmofanda depth
4.8 ofmm).
Removing
materialusing
a drillallowsmeasurements
deformation
changescausedbytherelaxationofresidualstress.
In
thisresearchstudy,
hole-cutting
deformation changes caused by the relaxation of residual stress. In this research study, aahole-cutting
devicewas
wasusedusedtotoperformperformhole
holetrepanation
trepanationbased
basedononthe
theprocessprocessdescribed
describedininthe
theRS-200
RS-200Milling
MillingdeviceGuide-VPGMicro-Measurements.This
Thismeasurement
measurementsystemsystem(Figure(Figure11)11)waswasadapted
adaptedtotoallow
allowthethe
Guide-VPGMicro-Measurements.
precisedrilling
of
holes
at
the
markedpointsofthegeometricrosetteat
specific
depthswithsimultaneous
precise drilling of holes at the marked points of the geometric rosette at specific depths withmeasurementmeasurementof its diameter.
simultaneousof its diameter.

FigureFigure11.
11.StandStandforforresidual
residualstressstressmeasurements:
measurements:Esam
EsamTraveler
TravelerPlus
Plusstrainstraingauge
gaugebridge
bridgewith
withaapower
powersupply
supply(1),(1),RS-200
RS-200device
device(2)(2)andandtested
testedmaterialmaterial(3).
(3).

Residualstressstressmeasurements
measurementswere
werecarried
carriedout
outon
onthe
theproduced
producedlaminate
laminatefrom
fromthethetitanium
titaniumandandResidualaluminum alloy
alloy sides.
thethesurfacebeforethe installationof theofstrainaluminumsides. The
Thepreparation
preparationofof
surfacebeforethe installation
the gauge
strain rosettes
gauge
was carried
based
onbasedthe guidelines
containedcontainedin the Instruction
Bulletin B-129-8
Surface
Preparation
rosettes
was out
carriedout
on the guidelines
in the Instruction
Bulletin
B-129-8
Surfacefor Strain Gauge
Bonding,which
included
theincluded
degreasing
the aluminumtitaniumand
surfaces
andPreparationfor Strain
Gauge
Bonding,which
the ofdegreasingof theandaluminumtitanium
grinding.
The
preparedThesurfaces
weresurfaces
strippedwereof oxideswith of
Conditioner
A,Conditioner
and were thensurfacesandgrinding.
prepared
strippedoxides with
A,neutralized
and werewith neutralized
Neutralizer 5A,
which
allowed theof strainthe
gauges.
The measurement
methodology
then
with
Neutralizer
5A,application
which allowed
applicationof strain gauges.
The
has been developed
for the ASTM
Standard
Test Methods
837. ItStandard
included Test
the attachment
at least
measurement
methodology
has beendeveloped
for the EASTM
Methods Eof837.
Itthree strain
with cableinstallations
on eachtype withof testedsurface.
The EA-13-062RE-120
includedthegauges
attachment
of at least
three strain
gaugescable
installations
on each type ofrosettes
testedwere used
the aluminum alloy,
while
theused
EA-05-062RE-120
rosettes
wereused
the titanium
surface.
TheforEA-13-062RE-120
rosettes
were
for the aluminumalloy,
while
thefor
EA-05-062REalloy.
The next
step
was
drill
holes (witha diameter
1.6wasmmto
anda maximumof 2.0 mm)
120
rosettes
wereusedfortothetitaniumalloy.
The next of
step
drill
holes (withdeptha diameterof 1.6indesignatedmeasurement
at 0.1mm increments.
Voltage locations
signals fromstrainwere
mm
and a maximum
depthlocationsof 2.0 mm)
in designatedmeasurement
at 0.1mm gauges
increments.
amplified
by
means
of
the
Esam
Traveler
Plus-type1032-S
StrainGauge
Bridge.
ResidualstressesandVoltage signals from strain gauges were amplified by means of the Esam Traveler Plus-type 1032-S
their angularorientations
werestresses
determinedon thebasis ofmeasured werestraindeterminedvalues. Figure
12 shows
StrainGauge Bridge.
Residual
and their
angularorientations
on thebasis
emplacementof values.
strain gaugesof theproduced
for thegauges
needs ofonconducting
ofthemeasured
strainFigureon12plates
showsthelaminate
emplacementof strain
plates of tests
theusing theproducedhole trepanation
method.
laminate
for the needsof conducting tests using the hole trepanation method.
The resulting output signal registered in the respective depths of the bore was then converted tostrain values in accordance with Equation (2).
ε=

4·UWY
× 106 [µε]N × U0 × K × A(2)

where UWY is the output voltage [V], U0 is the input voltage [V], N is the bridge layout factor for thequarter bridge N = 1, K is the strain gauge constant and A is the output signal amplification.
As a result of the measurements and calculations, the characteristics of the relative deformation
changes as a function of the depth of the hole were obtained. To determine the values of the mainstresses and their direction, the following dependencies were used:
ε + ε2
1
σmax = 1
−
4×A
4×B

q

(ε3 − ε1 )2 + (ε3 + ε1 − 2ε2 )2 [MPa](3)Materials 2020, 13, 4348

12 of 16

σmin =q1
ε1 + ε2(ε3 − ε1 )2 + (ε3 + ε1 − 2ε2 )2 [MPa]
+
4×A
4×B
1
ε − 2ε2 + ε2[MPa]
α = arctg 12ε2 − ε1(4)(5)

where σmax and σmin are the principal stresses, ε1 , ε2 and ε3 are the strains measured on strain gauges 1,
2 and 3 and A and B are the coefficients that depend on the material properties, measuring rosettes
and hole geometry, while α is the angle between strain gauge 1 and the direction of the nearest
Materials 2020,
13, x FOR PEER REVIEW
12 of 16
residualstress.

(a)(b)

Figureof measuring
measuringrosettes
rosetteson
ona asection
section
AA2519-Ti6Al4V
laminate
plate
Figure12.
12.Emplacement
Emplacement ofofofthetheAA2519-Ti6Al4V
laminate
plate
in in
the
initialstate:
onthe
aluminum
alloy
side
(a),
on
the
titanium
alloy
side
(b).
the initial state: on the aluminum alloy side (a), on the titanium alloy side (b).

Theobtained
selectedmeasuringare illustrated
theboreformof thenstrainconvertedchange courses
Theresults
resultingoutputfor
signalregisteredin thepoints
respective
depths ofinthe
was
to
as
a
function
of
the
hole
depth.
Figure13shows
theresultsfortheAA2519-AA1050-Ti6Al4V
laminate.
strain values
accordancewith Equation (2).
Materials
2020, 13,in
x FOR
PEER REVIEW
13 of 16
=

4∙
×

×

×

× 10

(2)

where UWY is the output voltage [V], U0 is the input voltage [V], N is the bridge layout factor for thequarter bridge N = 1, K is the strain gauge constant and A is the output signal amplification.
As a result of the measurements and calculations, the characteristics of the relative deformation
changes as a function of the depth of the hole were obtained. To determine the values of the mainstresses and their direction, the following dependencies were used:
+
4
×
(a)
=

−

1
4×

−

+

+

−2

(3)
(b)

1
+
Graphs ofof strainstrain changes
changesdependingon thethe hole
hole depth
depth onon the AA2519
AA2519 side
side (a) and on the
Figure 13. Graphs
depending
on
(4)
=
+
−
+
+ −2
4
×
4
×
Ti6Al4V alloy side (b) of the AA2519-AA1050-Ti6Al4V
AA2519-AA1050-Ti6Al4V laminate.
laminate.
1residual stress− 2 + determined at all the measurement points
The minimum
minimum values
values ofof principal
principal= residualThe
stress σσminmin determined at all the measurement(5)points2−in thethe case
MPa), while
while thetheincase ofof thethe AA2519
AA2519 alloy
alloy differ
differ fromfrom each
each other
other (in(in thethe range
range ofof −121−121 toto −104−104 MPa),maximum
valuesof areσdifferences
are in theMPa.
The observed
differenceswhere σmaxvaluesand σmintheprincipal stresses,
ε1,range
ε2 andofε3−88
are tothe−31strainsmeasuredon strain
gauges inmaximumof
σmax
max differences are in the range of −88 to −31 MPa. The observed differences in
1,
2
and
3
and
A
and
B
are
the
coefficientsthatdependonthematerial
properties,
measuringrosettesthevalues
of
σ
and
σ
are
associatedwithstressvaluechangesasafunctionof
distancefrom thethemaxare associated with stress value changes as a function of distance fromthe values of σmin
min and σmaxandholegeometry,
while
α
is
the
angle
betweenstrain
gauge
1
and
the
directionofthenearestmaterial surface.
stressvectorshowedthatthethedirectionof thematerial
surface. The
The orientation
orientationanalysis
analysisofofthe
theprincipal
principal
stressvectorshowedthat
directionofresidual stress.
minimum
stressσwasalmostperpendicularwithrespecttothelongeredge
oftheplate,
while
the
min
the minimum stress σmin was almost perpendicular with respect to the longer edge of the plate, while
The results
obtained σforselectedmeasuringare illustrated
in theform
changealloy
maximum
stressdirectionparallelto this points
edge. The
residual stress
level
in of
thestrainaluminummaxσwasthemaximum
stressdirection
max was parallel to this edge. The residual stress level in the aluminumcoursesasafunction
of
the
hole
depth.
Figure13shows
theresultsfortheAA2519-AA1050-Ti6Al4V
was verya homogeneous
distribution(invariant
as a functionof depth).
No tensile
alloy
wasclosevery toclose
to a homogeneous
distribution(invariant
as a functionof depth).
Nostresses
tensilelaminate.
wererecorded.
The
stressvaluesdetermined
at
all
the
measuredpointsinthe
Ti6Al4V
alloy
were
in
stresses were recorded. The stress values determined at all the measured points in the Ti6Al4V
alloy
the
followingranges:σ=−349–−184
MPa
and
σ
=
−111–−140
MPa.
Theobtained
test
resultsaremax and σmax = −111–−140 MPa. The obtained test
were in the following min
ranges: σmin = −349–−184 MPa
associatedwithchangesinstressvaluesasafunctionof themeasurement
The analysis
theresults are associated with changes in stress values asa functionof the depth.
measurement
depth.ofTheanalysis of the residual stress orientation vector showed that the direction of the external load that
affected the tested laminate was perpendicular to the longer edge of the plate. This caused higher
compressive stresses that were similar to those observed during the measurements of the internal
stress in the aluminum alloy AA2519.

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residual stress orientation vector showed that the direction of the external load that affected the tested
laminate was perpendicular to the longer edge of the plate. This caused higher compressive stresses
that were similar to those observed during the measurements of the internal stress in the aluminumalloy AA2519.
5. Conclusions
Explosive bonding enables the combination of hard bond materials, such as titanium andaluminum alloys. The combination of the proposed method generated an interlayer between the basematerials in the microstructure. As a result of the short-term effects of the high pressure in the layer
between the Ti6Al4V and AA1050 alloys, Al3 Ti precipitates were formed. This interlayer significantly
changed the functional properties of the material. It was used to form ballistic panels in spaceships.
Recognition of the stress values will allow for improving the numerical design in the phenomena ofballistic resistance [43]. In addition, the explosive joining process increased the tensile strength byapproximately 8% compared with the strength that resulted from the law of mixtures. Measurements ofinternal stress by both X-ray and bore trepanation methods showed an increase in the internal stressnear the joining zones. Long-range testers should consider the heat treatment of the laminate to relax
natural stress.
It should be noted that the stress values obtained in the titanium alloy may be subject to increased
uncertainty. This is owing to the fact that titanium cannot be easily cut. Titanium tends to cause
increased temperatures in the vicinity of the hole surface owing to the increased friction between the
drill and the low-thermal conductivity titanium surface. The described difficulties caused an increasein the cutting resistance and interfered with the recorded output signal that manifested in the formof changes in voltage pulses toward negative values, i.e., caused tensile stresses. These assumptions
confirmed that there was a significant increase in the cutting resistance that caused either a decreasein the rotational speed of the tool, or stopped the drill completely, followed by an abrupt increase in
the output voltage. It should be stated that certain stress values in the titanium alloy may be altered,however, the degree of this disturbance is impossible to determine.
Author Contributions: Conceptualization, L.S., K.G., J.T.; methodology, J.T., I.S., M.W., T.F.; software, J.K.,
M.W., T.F.; validation, J.K., J.T., J.L., formal analysis, L.S., J.T., T.S.; investigation, J.T., I.S., M.W.; resources, K.G.;
data curation, J.K., J.L.; writing—original draft preparation, J.K., T.S., T.F.; writing—review and editing, L.S., J.T.;
visualization, J.K., J.L.; supervision, L.S., T.S., T.F.; project administration, L.S., K.G., T.F.; funding acquisition, K.G.
All authors have read and agreed to the published version of the manuscript.
Funding: The programme is co-financed by the National Research and Development Center [Project
PBS2/A5/35/2013]. The research was also partially supported by the university research grant No. 22-758.
Acknowledgments: The authors want to thank the Institute of Metallurgy and Materials Engineering of the Polish
Academy of Sciences in Krakow for performing the X-ray stress tests. The authors express their gratitude to
B. Plonka from the Institute of Non-Ferrous Metals in Skawina who produced the alloy AA2519. The authors
would like to thank the Explomet company for making the laminate joined with the explosive method.
Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of thestudy; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to
publish the results.

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