308
Y. Wang et al.
some extent, that phenomenon could be reflected on the graphs of the distribution of
absolute energy. The distance between energy peaks of initial loading and reloading
indicates that the two main cracks generated during each loading stages are not in
the same place. Even some of the specimens cannot be visualized from the surface
but still can be verified by the energy distribution, which would be helpful to the
damage location of new cracks. Since most of the energy is generated in the middlenotched area of each specimen, the range of X-axis of the graphs shown below has
been shortened to 60 mm for a more focused and clear representation. The middle
of specimen is signed by a grey dotted line and the distance from each energy peak
to the centre line has been labelled.
25.3.3 Evaluation of Self-healing Efficiency Based on AE
Felicity Effect
25.3.3.1 Kaiser Effect and Felicity Effect
Generally, the loading path history of the material has an important impact on the
AE characteristics during the repeated loading. The Kaiser effect was put forward by
the German scholar Kaiser in the first place [4]. It was discovered in a test of loading
metal materials. The Kaiser Effect is manifested and defined as the absence of AE
signals (or no obvious AE signals) at loads not exceeding the previous maximum
load level when material undergoes repetitive loading. In other words, material has
a memory for the historical load with respect to the presence of Acoustic Emission
phenomenon. Conversely, if the material gives off significant AE signals at a lower
load than the one previously reached in an increasing repeated loading, then this
phenomenon is defined as Felicity Effect.
During the two stages of loading of self-healing concrete beams, it can be observed
that all the specimens generated AE signals from the very beginning until they were
unloaded before the pause. Then those specimens which were healed during the pause
generated AE signals again before the unloading point (i.e., the maximum loading
level during initial loading stage) was exceeded. The presence of this phenomenon
is called “Felicity effect” and it can be manifested as the occurrence of “detectable
and effective AE activities” during repeated loading of the material before the load
level reaches the previous maximum applied load. The criteria used to determine the
“effective AE signal” are discussed in the next section.
Meanwhile, the Felicity effect can also be quantified using the Felicity Ratio (FR),
which is the ratio of load where considerable AE resumes during reloading, divided
by the previous maximum load applied as shown below:
FR(i) =
P AE (i + 1)
P MAX (i)
(1)
where
Y. Wang et al.
some extent, that phenomenon could be reflected on the graphs of the distribution of
absolute energy. The distance between energy peaks of initial loading and reloading
indicates that the two main cracks generated during each loading stages are not in
the same place. Even some of the specimens cannot be visualized from the surface
but still can be verified by the energy distribution, which would be helpful to the
damage location of new cracks. Since most of the energy is generated in the middlenotched area of each specimen, the range of X-axis of the graphs shown below has
been shortened to 60 mm for a more focused and clear representation. The middle
of specimen is signed by a grey dotted line and the distance from each energy peak
to the centre line has been labelled.
25.3.3 Evaluation of Self-healing Efficiency Based on AE
Felicity Effect
25.3.3.1 Kaiser Effect and Felicity Effect
Generally, the loading path history of the material has an important impact on the
AE characteristics during the repeated loading. The Kaiser effect was put forward by
the German scholar Kaiser in the first place [4]. It was discovered in a test of loading
metal materials. The Kaiser Effect is manifested and defined as the absence of AE
signals (or no obvious AE signals) at loads not exceeding the previous maximum
load level when material undergoes repetitive loading. In other words, material has
a memory for the historical load with respect to the presence of Acoustic Emission
phenomenon. Conversely, if the material gives off significant AE signals at a lower
load than the one previously reached in an increasing repeated loading, then this
phenomenon is defined as Felicity Effect.
During the two stages of loading of self-healing concrete beams, it can be observed
that all the specimens generated AE signals from the very beginning until they were
unloaded before the pause. Then those specimens which were healed during the pause
generated AE signals again before the unloading point (i.e., the maximum loading
level during initial loading stage) was exceeded. The presence of this phenomenon
is called “Felicity effect” and it can be manifested as the occurrence of “detectable
and effective AE activities” during repeated loading of the material before the load
level reaches the previous maximum applied load. The criteria used to determine the
“effective AE signal” are discussed in the next section.
Meanwhile, the Felicity effect can also be quantified using the Felicity Ratio (FR),
which is the ratio of load where considerable AE resumes during reloading, divided
by the previous maximum load applied as shown below:
FR(i) =
P AE (i + 1)
P MAX (i)
(1)
where