PSI - Issue 68

P.N.B. Reis et al. / Procedia Structural Integrity 68 (2025) 1301–1304 P.N.B. Reis et al. / Structural Integrity Procedia 00 (2025) 000–000

1303

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In this case, acoustic emission is associated with the detection of acoustic burst signals called hits, whose amplitude exceeds a duly predefined limit. The CCNT feature (total number of positive threshold exceedances during a hit cascade) that showed the highest sensitivity was then related to the increase in temperature to determine the critical self-heating temperature. Therefore, the CCNT feature is recorded and the point (on the time scale) where the events begin with greater activity/intensity (beginning of a monotonic increase of AE activity) when related to the temperature curve, makes it possible to obtain the critical self-heating temperature. These values are presented in Table 1 so that they can be compared with those obtained using the curve-fitting approach described previously. The comparability of the results shown in Table 1 indicates that the critical self-heating temperature values obtained from the acoustic emission results are slightly higher than those obtained using the curve-fitting approach. Moreover, because the maximum error does not exceed 3.8%, it can be concluded that this is a methodology that can be used to calculate the critical self-heating temperature.

Fig. 1. CCNT features with the indication of the time signature for the beginning of a monotonic increase of AE activity versus the self-heating temperature history curve with the indication of a time signature and corresponding self-heating temperature.

Table 1. Estimation of critical self-heating temperature.

Critical self-heating temperature [ ° C]

Material

From curve-fitting approach

From AE results

[3F]

50.8 (3.2) 42.4 (1.7) 36.5 (2.2)

50.9 (3.4) 44.0 (2.7) 36.6 (2.4)

[1C + 2F + 1C] [1K + 2F + 1K]

4. Conclusions Hybrid composites become more and more popular in numerous industrial applications and evaluation of their mechanical performance is of key importance for their efficient and safe operation. One of the critical parameters from the point of view of their operation is fatigue resistance and character of degradation. In the case of PMCs, the self heating effect can appear during cyclic loading, significantly shortening their operational lifetime. Therefore, in this study, we focused on the investigation of this specific thermomechanical behaviour of hybrid composites. We adapted the concept of estimation of fatigue resistance based on the critical self-heating temperature, which can be considered as a material property characteristic for a specific material and determine the temperature at which the formation of a global cracking front forcing significant acceleration of a degradation and sudden structural failure. The results presented in this study demonstrated the influence of various types of fibers used for hybridization on the fatigue