Abstract:This paper presents details of the mechanical properties related to the static and fatigue strength of carbon fiber reinforced polyetherketoneketone (CF/PEKK) thermoplastic induction-welded composite joints. To better understand the process parameters, the finite element modeling (FEM) of the heat distribution was analyzed based on the generator power, coil coupling distance, coil moving speed, frequency, compaction force, and coil geometry while maintaining the optimal coil speed. The temperature behavior cal… Show more
“…The ultrasonic scanning, namely NDT method, was used to evaluate the resin infiltration efficiency following injection as shown in Figure 6. The C-scan maps of laminate were expressed as the ratio of the amplitude of the received to the transmitted ultrasonic waves 55 The C-scan scale of colors are indicated with different amplitude levels (in dB). The transmitted ultrasonic wave may be attenuated when passing through the irregularities inside the composite laminates, such as voids, porosity, or delamination.…”
This study presented the details of multi-wall carbon nanotubes (MWCNTs)-modified resin injection repair aiming to enhance the mechanical properties, considering the flexural and compression behavior. The resin injection of epoxy resin dispersed with MWCNTs (0.1, 0.3, and 0.5 wt.%) as low viscosity resin that delaminated composite structure repair was conducted using a developed vacuum-based resin injection system at 80°C with constant injection pressure. The quasi-static indentation (QSI) method with a circular window was applied to create the barely visible impact damage (BVID) in the laminate specimen and thus obtain the delamination damage with reproducibility. The flexural strength and compression after impact (CAI) test were conducted on repaired carbon fiber reinforced laminates to assess the effect of the dispersion of the MWCNTs in the epoxy resin injection approach compared to neat epoxy resin. The mechanical test results exhibited that the recovery rate was better improved in the case of the modified resin infiltration approach in laminate composites dispersed with nanoparticles. It was attributed to their more enhanced strengthening mechanisms under effective interaction in mixed interface of fiber-matrix-MWCNTs, mainly attributing to bridge connection and stronger interfacial adhesion properties.
“…The ultrasonic scanning, namely NDT method, was used to evaluate the resin infiltration efficiency following injection as shown in Figure 6. The C-scan maps of laminate were expressed as the ratio of the amplitude of the received to the transmitted ultrasonic waves 55 The C-scan scale of colors are indicated with different amplitude levels (in dB). The transmitted ultrasonic wave may be attenuated when passing through the irregularities inside the composite laminates, such as voids, porosity, or delamination.…”
This study presented the details of multi-wall carbon nanotubes (MWCNTs)-modified resin injection repair aiming to enhance the mechanical properties, considering the flexural and compression behavior. The resin injection of epoxy resin dispersed with MWCNTs (0.1, 0.3, and 0.5 wt.%) as low viscosity resin that delaminated composite structure repair was conducted using a developed vacuum-based resin injection system at 80°C with constant injection pressure. The quasi-static indentation (QSI) method with a circular window was applied to create the barely visible impact damage (BVID) in the laminate specimen and thus obtain the delamination damage with reproducibility. The flexural strength and compression after impact (CAI) test were conducted on repaired carbon fiber reinforced laminates to assess the effect of the dispersion of the MWCNTs in the epoxy resin injection approach compared to neat epoxy resin. The mechanical test results exhibited that the recovery rate was better improved in the case of the modified resin infiltration approach in laminate composites dispersed with nanoparticles. It was attributed to their more enhanced strengthening mechanisms under effective interaction in mixed interface of fiber-matrix-MWCNTs, mainly attributing to bridge connection and stronger interfacial adhesion properties.
“…Figure 7 shows comparison between the S-N curves of the NE, SiC, and Al 2 O 3 -SAJs with t a of 0.17 mm and 0.25 mm. Because of the S-N curves of the FRP composites are continues to slope downwards even after 10 8 cycles, the fatigue limits (strengths) of the SAJs were determined at 10 7 cycles, according to JIS K 7118, by the power function model as 37 where N f is the fatigue life, a and b are the parameters of the power model.Figure 7.S-N curves of the NE and SiC-SAJs with different bondline thicknesses ( t a ).…”
In this study, fatigue results of the scarf adhesive joints (SAJs) were extensively analyzed regarding the effect of the adhesive materials (neat epoxy (NE), and SiC and Al2O3-nanocomposite), bond thickness (0.17 mm and 0.25 mm) on their dynamic properties, which include loss factor (tan δ), loss modulus ( E''), dissipated energy ( U d), potential energy ( U p), and storage modulus ( E'). Safe fatigue lives of the NE, SiC, and Al2O3-SAJs were estimated at different reliability levels. The experimental measurements revelated that reducing the adhesive layer thickness from 0.25 mm to 0.17 mm result in enhancing the tensile strength and stiffness of the SiC-SAJs by 9.6% and 4.4%, respectively, in return of 9.5% and 5.4% for the Al2O3-SAJ relative to the NE-SAJ. The strength and stiffness of the SiC-SAJs with 0.17 mm bond thickness are higher than those of the Al2O3-SAJ by 15.4% and 3.3%, respectively. The highest improvement of 22.0% in the fatigue strength was occurred for the SiC-SAJ with bond thickness of 0.17 mm in return of 4.8% for the Al2O3-SAJ. The U p was used for the first time (except author works) for monitoring and predicting the damage in the adhesive joints practically the change in the enclosed area of the hysteresis loop is too small to cause a large variation in the tan δ, E'', and U d. Damping factor of the NE-SAJs is marginally increased with the stress levels compared to the aggravated increase of both SiC and Al2O3-SAJs. Zhang model predicts well the potential energy and storage modulus specially at higher stress levels.
“…To date, implementation of electromagnetic SHM techniques for induction welded CFRP joints have not been found in literature according to the authors' effort. The only available studies on monitoring of thermoplastic welded components are focused on ultrasonic [48][49][50] and microwave 51 welded joints using mainly guide waves 48,49,51 and electrical resistance 50 SHM methods.…”
The health of thermoplastic induction welded joints was evaluated by monitoring the electromagnetic response to a time variant magnetic field through a local measurement of the attenuated and reflected field. For this purpose, a numerical model was developed to study how the joint interface affects this response in the presence and absence of a delamination and as a function of the electromagnetic characteristics of a susceptor. Using a single loop coil geometry as local magnetic field excitation and measurement, the frequency range at which the highest damage detection sensitivity occurs has been identified for different sizes of a delamination in the bond line. It has been found that the presence of a susceptor reduces the capability of damage detection for the considered values of electromagnetic properties. The obtained results are the starting point for further research activities aimed at developing an electromagnetically based sensitive layer for monitoring the health of thermoplastic joints, capable of detecting and quantifying joint damage and assessing residual fatigue life.
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