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W. Zhou et al.
18.3.2 Response Behavior of the AE Signal
Figure 18.3 shows the variation of the force-accumulated counts-amplitude over
time for the specimen. As the progressive loading progresses, the AE amplitude
and accumulated counts continue to increase, revealing a deeper degree of damage.
In general, changes in AE amplitude and accumulated counts are associated with
internal damage activity and damage behavior [24]. By the 1st loading, it can be found
that the AE signal do not appear until loading for 45 s (2.58 kN), and the amplitude
does not exceed 60 dB, and the AE accumulated counts value is low, indicating that
the sample has almost no serious damage in the linear elastic stage. Then, performing
the 2nd load, increasing the load to the maximum value, the characteristics of the
corresponding AE signal are obtained. In fact, during the 2nd load, we find that there
is no (or very little) AE signal before reaching the maximum of the first load. This
interesting phenomenon of stress memory-damage is called the Kaiser effect [25].
By definition, little or no AE signal is recorded before reach any previous maximum
stress level. Subsequently, when loading to 90 s (5.24 kN), the AE accumulated
counts of the specimen increased significantly, the amplitude signal became richer
and some AE signals greater than 60 dB appeared. The cause of this phenomenon may
be several damage modes, such as matrix cracking, fiber debonding and delamination,
occurring simultaneously [19]. Complex damage behavior is accompanied by rich
AE signals.
Fig. 18.3 Flexural load, amplitude and accumulated counts versus time of specimen
W. Zhou et al.
18.3.2 Response Behavior of the AE Signal
Figure 18.3 shows the variation of the force-accumulated counts-amplitude over
time for the specimen. As the progressive loading progresses, the AE amplitude
and accumulated counts continue to increase, revealing a deeper degree of damage.
In general, changes in AE amplitude and accumulated counts are associated with
internal damage activity and damage behavior [24]. By the 1st loading, it can be found
that the AE signal do not appear until loading for 45 s (2.58 kN), and the amplitude
does not exceed 60 dB, and the AE accumulated counts value is low, indicating that
the sample has almost no serious damage in the linear elastic stage. Then, performing
the 2nd load, increasing the load to the maximum value, the characteristics of the
corresponding AE signal are obtained. In fact, during the 2nd load, we find that there
is no (or very little) AE signal before reaching the maximum of the first load. This
interesting phenomenon of stress memory-damage is called the Kaiser effect [25].
By definition, little or no AE signal is recorded before reach any previous maximum
stress level. Subsequently, when loading to 90 s (5.24 kN), the AE accumulated
counts of the specimen increased significantly, the amplitude signal became richer
and some AE signals greater than 60 dB appeared. The cause of this phenomenon may
be several damage modes, such as matrix cracking, fiber debonding and delamination,
occurring simultaneously [19]. Complex damage behavior is accompanied by rich
AE signals.
Fig. 18.3 Flexural load, amplitude and accumulated counts versus time of specimen