influence of additional force impulse at the monotonic load on the

INFLUENCE OF ADDITIONAL FORCE IMPULSE AT THE MONOTONIC
LOAD ON THE DEFORMATION OF 2024-T3 ALUMINUM ALLOY
VOLODYMYR HUTSAYLYUK
Military University of Technology, Warsaw, [email protected]
LUCJAN ŚNIEŻEK
Military University of Technology, Warsaw, [email protected]
JANUSZ TORZEWSKI
Military University of Technology, Warsaw, [email protected]
MYKOLA CHAUSOV
National University of Life and Environmental Sciences of Ukraine, Kyiv, [email protected]
VALENTIN BEREZIN
National University of Life and Environmental Sciences of Ukraine, Kyiv, [email protected]
Abstract: The paper presents results of experimental studies the impact of additional force impulse at the monotonic
tension on the tensile strain of 2024-T3 aluminium alloy. The loading was carried out in the inelastic range.
Microfracture analysis of surfaces and fractures were used for establishing the nature and mechanisms of destruction
of the examined elements.
Keywords: additional force impulse, dynamic non-equilibrium processes, 2024-T3 aluminium alloy, dissipative
structure, banded structure.
Immediate destruction of the sample occurs when the
material is not able to absorb the external energy,
although the overall load is below the permissible level.
Authors of papers [5,6] involve changes in the structure of
the material on dynamic unbalanced processes with
significant fluctuations in supply of energy to the sample
material at high speeds of deformation, resulting in a
sample material is still in an activated state. Energy
dissipation occurs in the local weak zones.
1. INTRODUCTION
In real service conditions of engineering structures and its
components are exposed to various external loads.
Usually, in most calculation methods of metal structures,
is assumed to determine strength of the structure
including the predominant load. However, this approach
does not fully use even in the case of summation of the
actions of one type of load. In particular, it refers to the
impact additional force impulse at strength of the material
during the monotonic tension.
Previously performed a study on changes of mechanical
properties of the material identified during monotonic
tension [6,7] allow for quantification of the impact of
dynamic unbalanced processes occurring during the
implementation an additional force impulse.
We can observe initiation non-equilibrium dynamic
processes leading to adaptation of the material for a new
conditional equilibrium depending on the value of the
additional force impulse and the conditions of its
implementation. Internal equilibrium is possible only by
absorbing the outside total energy by the material. It lead
to a formation of a new ordered structure (material state),
so-called dissipative structure. From the energy point of
view the best situation is to create the dissipative structure
in a specified volume of material. The newly formed
structure (material state) causes changes in the
mechanical properties of the material compared to its
initial state [1-4].
Still unclear is the physical nature of this phenomenon.
There is a lack of fractographic research aimed at
determining mechanisms of structural changes at the
micro level during the implementation of a given type of
load. In the present work the authors attempted to clarify
the mechanism of structural changes on the basis of
fractographic analysis.
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The test stand was equipped with a computerized
measuring system to record and store the results of
measurements at a frequency of up to 2400 measurements
per second. Additional force impulse was executed in the
elastic and inelastic range stress-strain diagram.
2.1. Material and test procedure
The material used in tests was 2024-T3 Alclad aluminium
alloy as supplied. According to the manufacturer its
chemical composition and mechanical properties are
given in Table 1.
Detailed methods and test conditions are presented in the
work [9].
Table 1 Chemical composition and mechanical
properties 2024-T3 aluminium alloy
Chemical composition [%]
Si
Fe
Cu
Mn Mg
Cr
Zn
Ti
0,05 0,13 4,7 0,70 1,5 0,01< 0,02 0,04
Mechanical properties in the rolling direction
Rm, MPa
R0.2, MPa
A%
459 - 466
339 - 345
21,5 - 24,7
Microfractographic analysis was performed using
scanning electron microscope (SEM) Philips XL30/LaB6.
More details concerning the effect additional force
impulse and monotonic tensile stress on fatigue fracture
above elastic stress
were obtained from SEM
micrographs.
3. DISCUSSION AND RESULTS
The specimens were cut in the rolling direction of sheets
with a thickness of 3 mm and its size was plotted in
Picture 1.
Implementation of the pulse load during monotonic
tensile tests (indicated by the dashed line in Picture 3)
causes the disorder of the straightness of the load
segment, change of the line angle and local spikes
(vibration) stress and strain of the material.
This behavior of the material at a complex load is likely
to result of breach material balance by the additional force
impulse and leading to the initiation of dynamic nonequilibrium processes. These processes are aimed at
restoring a stable state of the structure of the new external
load conditions.
Picture 1. Geometry of specimen
Research of the effect of additional force impulse was
performed using a hydraulic machine ZD-100Pu equipped
with a mechanical system to achieve additional force
impulse impulse, as described in [8]. A general view of
the test stand shown in Picture 2.
Picture 3. Stress-strain diagram of 2024-T3 aluminum
alloy after the implementation of the additional impulse
and monotonic loading on the overall deformation
ε=13,8%.
The material is forced to adapt its structure to the new energy
state through the creation of new forms with altered
mechanical properties as a result of absorption of external
energy. Newly formed "dissipative structure" causes global
changes in mechanical properties of the material. This
phenomenon is evident in the second part of diagram the
destruction of the specimen. In the first stage of the
additional force impulse was finalized forming" dissipation
structure" in the material . Evidenced by the nearly smooth
section of the final part of the stress-strain diagram (step I in
Picture 3). Also in this case an additional force impulse was
registered only as a small "fault" on the graph illustrating the
change in local stress and strain.
Picture 2. Stand to carry out additional force impulse; test
specimen (1), brittle specimens (2), torque rods (3), and
mounting flanges (4).
Destructive testing of specimens under monotonic loading
were provided on Instron 8802 testing machine.The
dynamic strain extensometer with a base measuring 12.5
mm was used to measure deformation. During the test
was recorded the values of deformation and load.
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continuity of clad layer Pic.6. Evidenced by the
stratifications observed at grain boundaries (Pic. 7).
Registered change the course of the graph is mainly the
effect of inertia of the measuring apparatus cooperating
with the testing machine. Much more interesting is the
second part of the diagram. For monotonic loading the
specimen, causing deformation of ε = 13.8% exhaust the
supply of material plasticity. Re-load resulted in almost
immediate destruction of the specimen. Behaves quite
differently specimen after additional pulse power. Apart
from that observed at room temperature, a significant
increase in plasticity of the test element, the stresses in the
cross section does not exceed the calculated value for an
element subjected to normal tension. On this basis we can
suppose that in this specimen reached levels equal to the
total strain ε = 13.8% is the optimum level for the
implementation of structural changes of the material.
The effect of structural changes were investigated after
the load tests were performed on scanning electron
microscope. There were analyses section of the material
in the initial state, clad surfaces of the specimen at
baseline and after loads and fracture surfaces after the
failure.
Picture 5. Example of clad layer surface of 2024-T3
aluminum alloy sheet in the initial state.
Picture 4. Example of intersection 2024-T3 aluminum
alloy sheet in the initial state (after etching)
The cross-sectional specimens can be clearly divided into
two zones: clad layer and base material. Clad layer with a
thickness of about 100 microns is quite homogeneous
with minor inclusions evenly located throughout the
width of the layer. Base materials have a granular
structure. As a result of plastic forming operations and
heat to give the structure characteristic of deformation
after rolling, composed of elongated grains of irregular
shape. Noticeable is the uniform distribution of small
inclusions in the entire volume of the native material.
The whole structure has a clear directionality Pic.5.
Significant structural changes were observed in the clad
layer on the surface of the samples after the impact of
additional force impulse Pic.6. On the fracture surface
were clearly revealed the basic shapes of grains of
material, delamination and cracks at grain boundaries.
Within the grains are visible stripes displacement
crystallographic surfaces on the Pictures 6-7. Additional
force impulse results in a deeper damage in breach of the
Picture 6. Examples of clad surface layer plated of 2024T3 aluminum alloy: a - the additional force impulse, b after monotonic loading.
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of microstructures surface clad layer was observed at
higher magnification (Pic. 9). In the case of additional
impulse force on the clad layer Pic.9 were revealed the
grain boundaries.
Picture 7. Specimen images showing the shapes of grains
on the surface of the specimen clad layer 2024-T3
aluminum alloy: a - the additional force impulse, b - after
monotonic loading.
Changes on the surface were much smoother In the case
of monotonic loading (Pic. 6b) than additional force
impulse. Observed shapes of grains were similar to the
previous case, the load is shown by the slip lines oriented
along the crystallographic planes (Pic. 7b). The identified
phenomenon does not cause too deep platter damage or
delimitation of grain boundaries.
Picture 8. A SEM micrographs illustrating cross-section
clad layer of 2024-T3 aluminum alloy specimen: a - the
additional force impulse, b - after monotonic loading.
Less severe monotonic loading confirms the presence of
inclusions on the surface pic.6b which admittedly may be
already damaged themselves but also are embedded in the
native material pic.7b.
On the surface grains are visible cracks and numerous
elliptical depression in the crumbled inclusions. In the
case of monotonic loading fracture area clad layer is
almost smooth (Pic.9b). In this case there was not the
presence of microcracks or grain boundaries. Visible on
the fracture surface minor imperfections are intact and
bigger one were entirely detached from the substrate and
remaining in the second part of the specimen Pic.9b.
The observed changes in the clad layer occur not only on
the surface but in the depth of this layer Pic.8-9.
In the analysis of the entire surface (Picture 8) for the load
of two types of cross section clad layer are similar. There
appears to be a noticeable shift along the crystallographic
planes of bands visible in the fatigue striations no
significant overall damage to the homogeneity of the
layer. The nature of the load does not cause any specific
changes are joining layers of material clad layer home. In
Pic. 8a and 8b zone looks almost identical. More details
It should be emphasized that the additional load pulse to
drive change in brittle layer clad layer manifested by
extrusion and intrusion. This layer plasticity was obtained
through the possibility of displacement of grains as a
result of destruction inclusions, creation of voids and
refinement of structure by a system of microcracks.
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snatching the grains group.
Picture 9. A SEM micrographs illustrating fracture clad
layer of 2024-T3 aluminum alloy specimen: a - the
additional force impulse, b - after monotonic loading.
Figure 10. Fracture surface of the base material of 2024T3 aluminum alloy observed with the use of the SEM: a the additional force impulse, b - after monotonic loading.
As mentioned earlier, the fracture surface of the base
material of 2024-T3 aluminum alloy for different load
cases have varied morphology (Pic. 8). With additional
force impulse clearly formed band of ridges (acclivity)
with fluent passing in the cavity. The monotonic load on a
much larger and deeper cavities of irregular shape and
size of several grains (Pic.8b). These elevations in most
individual joining the band formed micro areas the size of
some grains.
Another feature of the construction of fracture test
specimens is the presence of distortion of voids at
inclusions. When you load monotonic fracture surfaces
are characterized by a much less developed morphology
(Pic. 10b) and the void are more smooth edges. Fracture
was observed on the surface only a few inclusions.
It is interesting that a more detailed analysis of the band
structure revealed a fundamental change in a more
developed structure resulting from the impact of
additional force impulse (Pic. 11) formed as a result of the
destruction of the inclusions and local processes inside the
grains.
Regardless of the type of load, in both cases was observed
on the construction honeycomb structure (Pic. 10).
Introduction of an additional force impulse causes the
modification of the structure as a result of processes
similar to those found in the layer clad layer . The
difference is the scale of the observed changes. In
addition to the displacement of the grains also move
whole groups of grains. The result is a first forming a
reinforcement structure (Pic. 10), which acts as a support
structure for the base material. Forming this type of
structure in the form of "ridge" is at the edge area after
Honeycomb structure with spalling of large inclusions
and cavities are characteristic of local plastic deformation
and secondary microcracks on smooth surfaces of voids at
inclusions is shown in Pic.11b. The backs of the most
smooth surfaces on which only mark the future cell –
voids.
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The analysis of fracture surfaces under SEM in Picture 11
indicates the presence of the monotonic load carrying out
obtained results allow the following conclusions:
The complex load with single additional force pulse
involving in the investigated elements in aluminum alloy
2024-Т3 are formed plasticity zones of varying scope in
material, which are revealed during monotonic loading.
Observed after the implementation of the additional load
pulse increase up to 40% initial strength of alloy 2024-Т3
is dependent on the extent and location of the initial
deformation of the load pulse.
As a result of fractographic study was found that
additional force impulse cause additional realizations of
complex mechanisms of failure. The failure is carried out
simultaneously in at least three areas: the destruction of
the inclusions, deformation processes and the destruction
of individual or local groups grains.
The research also proved that implementation of force
impulse in a very short period of time results in an overall
increase in plasticity of the material by modifying the
slice structure during monotonic loading on the more
complex structure.
ACKNOWLEDGMENTS
Publication prepared within the project N N501 056 740.
The project was funded by the National Science Centre
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impulse on deformation aluminium alloy sheets. The
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