24 Experiment Research on Tensile Process …
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It can be seen from the amplitude-time of the preset round notch sample, as shown
in Fig. 24.11c. The acoustic emission signal appears in the elastic stage, the amplitude
is 36.1, 36.5, 37.5 dB; An acoustic emission signal appears in the yield stage, the
amplitude is 37.3 dB; In the plastic deformation stage, the acoustic emission signal
that does not reach the specified threshold appears; At the break point, two acoustic
emission signals appear and the maximum amplitude appears, the amplitudes are
72.7 dB and 40.7 dB, respectively.
It can be seen from the amplitude-time of the preset V-shaped notch sample, as
shown in Fig. 24.12c.The acoustic emission signal appears in the elastic stage with
amplitudes of 45.6 and 48.2 dB; The acoustic emission signal appears in the yield
stage with amplitude 35.5 dB; In the plastic deformation stage, the acoustic emission
signal that does not reach the specified threshold appears; At the breaking point,
three acoustic emission signals appear and the maximum amplitude appears, the
amplitudes are 100 dB, 45.8 dB and 48.5 dB, respectively.
From the energy-time correlation diagram, it can be seen that two kinds of acoustic
emission signals appeared in the samples without pre-defects during the tensile
process. When the duration was greater than 200 µs, a signal with low energy and
long duration time appeared. Combining the graphs of tensile force and time, the
signal appears when there are many acoustic emission signals during the plastic
deformation stage at a tensile time of 1400 s, that is, the acoustic emission signals
are the signals generated by the plastic deformation of the sample.
24.4 Analysis and Discussion
24.4.1 Discussion of Tensile Characteristics Analysis
The tensile process of HDPE material is divided into four stages: elastic deformation
stage, yield stage, plastic deformation and fracture stage.
In the elastic deformation stage, the deformation is completely reversible, and
the deformation occurs when the force is applied, and the deformation is completely
restored after the force is released. From a microscopic point of view, the balance
force between the molecules in the HDPE material is destroyed. In order to achieve a
new balance, the position between the molecules is adjusted. After the external force
is removed, the molecules returns to the original balance position.
In the yield stage, the HDPE material has thin necks during the process of forcing,
and the narrow necks gradually expand. From the molecular mechanism, the movement of the HDPE material macromolecular segments (amorphous regions) begins
to increase, and the stress is concentrated inside the grains;
In the plastic deformation stage, all the samples are drawn into thin necks, the
strain hardening of the material and the softening caused by the geometric shape
reach a balance, at this time, the force no longer increases, and tiny voids begin to
appear in the center of the weakest section of the sample, expanding into small cracks,
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It can be seen from the amplitude-time of the preset round notch sample, as shown
in Fig. 24.11c. The acoustic emission signal appears in the elastic stage, the amplitude
is 36.1, 36.5, 37.5 dB; An acoustic emission signal appears in the yield stage, the
amplitude is 37.3 dB; In the plastic deformation stage, the acoustic emission signal
that does not reach the specified threshold appears; At the break point, two acoustic
emission signals appear and the maximum amplitude appears, the amplitudes are
72.7 dB and 40.7 dB, respectively.
It can be seen from the amplitude-time of the preset V-shaped notch sample, as
shown in Fig. 24.12c.The acoustic emission signal appears in the elastic stage with
amplitudes of 45.6 and 48.2 dB; The acoustic emission signal appears in the yield
stage with amplitude 35.5 dB; In the plastic deformation stage, the acoustic emission
signal that does not reach the specified threshold appears; At the breaking point,
three acoustic emission signals appear and the maximum amplitude appears, the
amplitudes are 100 dB, 45.8 dB and 48.5 dB, respectively.
From the energy-time correlation diagram, it can be seen that two kinds of acoustic
emission signals appeared in the samples without pre-defects during the tensile
process. When the duration was greater than 200 µs, a signal with low energy and
long duration time appeared. Combining the graphs of tensile force and time, the
signal appears when there are many acoustic emission signals during the plastic
deformation stage at a tensile time of 1400 s, that is, the acoustic emission signals
are the signals generated by the plastic deformation of the sample.
24.4 Analysis and Discussion
24.4.1 Discussion of Tensile Characteristics Analysis
The tensile process of HDPE material is divided into four stages: elastic deformation
stage, yield stage, plastic deformation and fracture stage.
In the elastic deformation stage, the deformation is completely reversible, and
the deformation occurs when the force is applied, and the deformation is completely
restored after the force is released. From a microscopic point of view, the balance
force between the molecules in the HDPE material is destroyed. In order to achieve a
new balance, the position between the molecules is adjusted. After the external force
is removed, the molecules returns to the original balance position.
In the yield stage, the HDPE material has thin necks during the process of forcing,
and the narrow necks gradually expand. From the molecular mechanism, the movement of the HDPE material macromolecular segments (amorphous regions) begins
to increase, and the stress is concentrated inside the grains;
In the plastic deformation stage, all the samples are drawn into thin necks, the
strain hardening of the material and the softening caused by the geometric shape
reach a balance, at this time, the force no longer increases, and tiny voids begin to
appear in the center of the weakest section of the sample, expanding into small cracks,