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Carbon Fibre-Reinforced Polymers (CFRPs) in aerospace applications are expected to operate in moist environments where carbon fibres have high resistance to water absorption; however, polymers do not. To develop a truly optimised structure, it is important to understand this degradation process. This study aims to expand the understanding of the ro...
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... energy propagates through structures as a transient wave [35] and can be detected by piezoelectric sensors [36]. From these recorded waveforms, the parameters summarised in Figure 1 can be extracted [37]. Many researchers have attributed various AE parameters to the characteristics of composite materials in order to gain deeper insight into the damage mechanism [36,[38][39][40][41]. Kumosa et al. [41] reported that AE can be used to distinguish between different types of damage in glassfibre-reinforced polymers (GFRP). ...
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... peak detection time (PDT), hit definition time (HDT), hit lockout time (HLT), and max duration were 200 µs, 800 µs, 100 µs, and 100 ms, respectively. The progressive growth of damage was monitored by acquiring four parameters from the AE waveforms, which were sampled at 40 MHz, these parameters were absolute energy, amplitude, duration, and counts ( Figure 1). Both load and displacement were also recorded at a rate of 10 Hz and with each hit. ...
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... peak detection time (PDT), hit definition time (HDT), hit lockout time (HLT), and max duration were 200 µs, 800 µs, 100 µs, and 100 ms, respectively. The progressive growth of damage was monitored by acquiring four parameters from the AE waveforms, which were sampled at 40 MHz, these parameters were absolute energy, amplitude, duration, and counts ( Figure 1). Both load and displacement were also recorded at a rate of 10 Hz and with each hit. ...
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... the dry (control) specimen, crushing in the upper 0 • ply under the loading nose after 59 s is observed, as shown in Figure 10. The post-test microscopy images shown in Figure 11, confirms and shows that no further propagation of this damage occurred, and the applied load rose until the final failure of single delamination occurred (as expected [7,26]). ...
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... the dry (control) specimen, crushing in the upper 0 • ply under the loading nose after 59 s is observed, as shown in Figure 10. The post-test microscopy images shown in Figure 11, confirms and shows that no further propagation of this damage occurred, and the applied load rose until the final failure of single delamination occurred (as expected [7,26]). This shows that some damage has occurred prior to the final failure, which has led to the observed AE activity discussed above, but it is not significant enough to cause an observable drop in the load versus displacement/time curve. ...
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... three and nine days of water immersion, similar crushing of the upper 0 • ply under the loading nose is seen after 65 and 64 s, as shown in Figures 12 and 13, respectively. The post-test micrographs shown in Figure 14 for the three-day aged specimen and in Figure 15 for the nine-day aged specimen show that this damage propagated further in the sample compared to the dry specimen, resulting in crushing of the second 0 • ply. ...
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... three and nine days of water immersion, similar crushing of the upper 0 • ply under the loading nose is seen after 65 and 64 s, as shown in Figures 12 and 13, respectively. The post-test micrographs shown in Figure 14 for the three-day aged specimen and in Figure 15 for the nine-day aged specimen show that this damage propagated further in the sample compared to the dry specimen, resulting in crushing of the second 0 • ply. This local damage did not propagate any further and a final failure of a single delamination still occurred. ...
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... three and nine days of water immersion, similar crushing of the upper 0 • ply under the loading nose is seen after 65 and 64 s, as shown in Figures 12 and 13, respectively. The post-test micrographs shown in Figure 14 for the three-day aged specimen and in Figure 15 for the nine-day aged specimen show that this damage propagated further in the sample compared to the dry specimen, resulting in crushing of the second 0 • ply. This local damage did not propagate any further and a final failure of a single delamination still occurred. ...
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... longer exposure times (24 and 43 days), crushing is also seen directly under the loading nose at the upper 0 • ply after 60 s and 58 s after 24 and 43 days of immersion, as seen in Figures 16 and 17, respectively. There is some noticeably high AE activity at the point of crushing in the observed data ( Figures 6, 7 and 9), which is well correlated with the drop in the applied load prior to the final failure. ...
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... is some noticeably high AE activity at the point of crushing in the observed data ( Figures 6, 7 and 9), which is well correlated with the drop in the applied load prior to the final failure. The post-test micrographs shown in Figure 18 for the 24-day aged specimen and in Figure 19 for the 43-day aged specimen confirm the significant development of the crack propagation of this damage occurred at the upper 0 • ply, leading to the final failure of multiple transverse cracks and delaminations occurring throughout the thickness, but predominantly in the upper half of the specimens. In the cases of the dry, 3-day, and 9-day aged specimens, surface crushing does not appear to influence the final failure, which is by a single delamination at approximately the mid-plane. ...
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... is some noticeably high AE activity at the point of crushing in the observed data ( Figures 6, 7 and 9), which is well correlated with the drop in the applied load prior to the final failure. The post-test micrographs shown in Figure 18 for the 24-day aged specimen and in Figure 19 for the 43-day aged specimen confirm the significant development of the crack propagation of this damage occurred at the upper 0 • ply, leading to the final failure of multiple transverse cracks and delaminations occurring throughout the thickness, but predominantly in the upper half of the specimens. In the cases of the dry, 3-day, and 9-day aged specimens, surface crushing does not appear to influence the final failure, which is by a single delamination at approximately the mid-plane. ...
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... repeats every two plies at the 90/0 interface until approximately the mid-plane of the specimen. The thickness of the material between the delaminations, shown in Figures 16 and 17, is ≈0.4 mm, which corresponds to two-ply thicknesses. Further evidence of this behaviour is seen in the optical microscope images (Figures 18 and 19). ...
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... thickness of the material between the delaminations, shown in Figures 16 and 17, is ≈0.4 mm, which corresponds to two-ply thicknesses. Further evidence of this behaviour is seen in the optical microscope images (Figures 18 and 19). Evidence of kink bands, commonly associated with in-plane compressive failure, can also be seen in these images. ...
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... the dry (control) specimen, crushing in the upper 0° ply under the loading nose after 59 s is observed, as shown in Figure 10. The post-test microscopy images shown in Figure 11, confirms and shows that no further propagation of this damage occurred, and the applied load rose until the final failure of single delamination occurred (as expected [7,26]). ...
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... the dry (control) specimen, crushing in the upper 0° ply under the loading nose after 59 s is observed, as shown in Figure 10. The post-test microscopy images shown in Figure 11, confirms and shows that no further propagation of this damage occurred, and the applied load rose until the final failure of single delamination occurred (as expected [7,26]). This shows that some damage has occurred prior to the final failure, which has led to the observed AE activity discussed above, but it is not significant enough to cause an observable drop in the load versus displacement/time curve. ...
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... shows that some damage has occurred prior to the final failure, which has led to the observed AE activity discussed above, but it is not significant enough to cause an observable drop in the load versus displacement/time curve. After three and nine days of water immersion, similar crushing of the upper 0° ply under the loading nose is seen after 65 and 64 s, as shown in Figures 12 and 13, respectively. The post-test micrographs shown in Figure 14 for the three-day aged specimen and in Figure 15 for the nine-day aged specimen show that this damage propagated further in the sample compared to the dry specimen, resulting in crushing of the second 0° ply. ...
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... three and nine days of water immersion, similar crushing of the upper 0° ply under the loading nose is seen after 65 and 64 s, as shown in Figures 12 and 13, respectively. The post-test micrographs shown in Figure 14 for the three-day aged specimen and in Figure 15 for the nine-day aged specimen show that this damage propagated further in the sample compared to the dry specimen, resulting in crushing of the second 0° ply. This local damage did not propagate any further and a final failure of a single delamination still occurred. ...
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... three and nine days of water immersion, similar crushing of the upper 0° ply under the loading nose is seen after 65 and 64 s, as shown in Figures 12 and 13, respectively. The post-test micrographs shown in Figure 14 for the three-day aged specimen and in Figure 15 for the nine-day aged specimen show that this damage propagated further in the sample compared to the dry specimen, resulting in crushing of the second 0° ply. This local damage did not propagate any further and a final failure of a single delamination still occurred. ...
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... longer exposure times (24 and 43 days), crushing is also seen directly under the loading nose at the upper 0° ply after 60 s and 58 s after 24 and 43 days of immersion, as seen in Figures 16 and 17, respectively. There is some noticeably high AE activity at the point of crushing in the observed data (Figures 6, 7, and 9), which is well correlated with the drop in the applied load prior to the final failure. ...
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... is some noticeably high AE activity at the point of crushing in the observed data (Figures 6, 7, and 9), which is well correlated with the drop in the applied load prior to the final failure. The post-test micrographs shown in Figure 18 for the 24-day aged specimen and in Figure 19 for the 43-day aged specimen confirm the significant development of the crack propagation of this damage occurred at the upper 0° ply, leading to the final failure of multiple transverse cracks and delaminations occurring throughout the thickness, but predominantly in the upper half of the specimens. The damage observed for a 3-day water-immersed specimen prior to final fracture. ...
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... is some noticeably high AE activity at the point of crushing in the observed data (Figures 6, 7, and 9), which is well correlated with the drop in the applied load prior to the final failure. The post-test micrographs shown in Figure 18 for the 24-day aged specimen and in Figure 19 for the 43-day aged specimen confirm the significant development of the crack propagation of this damage occurred at the upper 0° ply, leading to the final failure of multiple transverse cracks and delaminations occurring throughout the thickness, but predominantly in the upper half of the specimens. The damage observed for a 3-day water-immersed specimen prior to final fracture. ...
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... final fracture is also seen. Sensors 2021, 21, x FOR PEER REVIEW 17 of 23 Figure 13. The damage observed for a 9-day water-immersed specimen prior to final fracture. ...
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... repeats every two plies at the 90/0 interface until approximately the mid-plane of the specimen. The thickness of the material between the delaminations, shown in Figures 16 and 17, is ≈0.4 mm, which corresponds to two-ply thicknesses. Further evidence of this behaviour is seen in the optical microscope images (Figures 18 and 19). ...
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... thickness of the material between the delaminations, shown in Figures 16 and 17, is ≈0.4 mm, which corresponds to two-ply thicknesses. Further evidence of this behaviour is seen in the optical microscope images (Figures 18 and 19). Evidence of kink bands, commonly associated with in-plane compressive failure, can also be seen in these images. ...
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Carbon Fibre Reinforced Polymer (CFRP) is used in top industries like aerospace, automotive or medicine. Abrasive water jet (AWJ) technology has demonstrated its capacity in machining CFRP parts with a high dimensional accuracy due to its low mechanical loading, reduced machining temperature, high productivity, reduced tooling, and environmental fr...
Citations
... Initial weight-the weight of the dry sample [38]. ...
Natural fibre-reinforced materials are gaining potentiality for their advantages such as environmental friendly nature, light weight and abundant local availability. The fibres obtained from plant sources which are not suitable for converting into textiles or apparels may be fabricated by some other means for the fullest utilization of the eco-friendly materials to save the environment. This study focuses on the effect of the kapok fibre reinforcements and their orientation when reinforced in a composite using polylactic acid as matrix. The flexural strength and hardness of the composite material prepared from fibre-reinforced sample with bidirectional lay showed an increase to 54.51% and 1.51% respectively over the neat polylactic acid sample. In addition, among the fibre-reinforced biocomposites, the bidirectional laid fibre-reinforced material showed better tensile strength of 4.951 N/mm² and elongation of 2.01% though these were lesser than the neat polymer sample. The roughness was more in the sample unidirectional lay which was with 4.390 microns than the sample with bidirectional lay. The properties of the Kapok fibres can be enhanced by giving physical, chemical or biological treatment when used as reinforcement in the polylactic acid matrix for composite manufacturing. Hence, this study may be a rudimentary approach for preparing lightweight composite materials where these properties are essential.
... It is of interest to note that specimens that were not thermally aged (i.e., were maintained at room temperature, 23 • C) prior to immersion in deionized water for 72 weeks showed a decrease of 25.3%. While the thermally aged specimens at all temperatures of aging showed a threestage deterioration trend, the non-thermally aged specimens showed a gradual, but continuous, decrease with minor variation in levels from the beginning, as has been seen previously for SBS strength decrease due to hydrothermal exposure [87][88][89]. While fibers add to the strength and stiffness of the in-plane properties, the out-of-plane characteristics are often the limiting factor for laminate composites because they are dependent on the matrix. ...
... Botelho et al. [91] reported decreases of about 28% in interlaminar shear strength of unidirectional carbon/epoxy prepreg-based composites after conditioning at 80 °C and 90% RH until moisture equilibrium was attained. Almudaihesh et al. [87] reported a reduction of 24.5% after immersion of prepreg-based, autoclave-cured carbon/epoxy in water at 90 °C for 43 days. In comparison, in the current study, a decrease of 12.5% in SBS strength was recorded after a similar period of immersion of 8 weeks after thermal aging for 8 h at 93 °C, indicating that the sequential exposure may have lower deteriorative effects than the simultaneous exposure to temperature and moisture (such as through elevated temperatures of immersion). ...
... In comparison, in the current study, a decrease of 12.5% in SBS strength was recorded after a similar period of immersion of 8 weeks after thermal aging for 8 h at 93 °C, indicating that the sequential exposure may have lower deteriorative effects than the simultaneous exposure to temperature and moisture (such as through elevated temperatures of immersion). It is noted that an equivalent level of reduction to the 24.5% reported [87] is only attained between 48 and 72 weeks of immersion in the current case, with 31.5% reduction being attained after the full period of 72 weeks of immersion. ...
This paper presents results of specific cases of sequential exposure of wet layup ambient cured carbon/epoxy composites to thermal aging and immersion in deionized water. Thermal aging is conducted at temperatures between 66 °C and 260 °C for periods of time up to 72 h whereas immersion is up to 72 weeks. Effects are characterized in terms of moisture kinetics using a two-stage diffusion model, and through short beam shear (SBS) strength. The response is characterized by a competition between the mechanisms of postcure, which results in increased polymerization and increases in SBS strength and glass transition temperature; and thermally induced microcracking and polymer degradation as well as moisture-induced plasticization and hydrolysis accompanied by fiber-matrix debonding, which results in deterioration. Thermal aging by itself is not seen to negatively impact SBS strength until the highest temperatures of exposure are considered in the investigation. However, the subsequent immersion in deionized water is seen to have a greater deteriorative effect with the period of post-thermal aging immersion being the dominant deteriorative factor.
The thermal aging behavior of glass fiber reinforced composites has attracted much attention because of its application in elevated temperatures environments. In this study, to improve the thermal aging resistance performance of composites, multilayer graphene was embedded in glass fiber reinforced composites and the damage evolution behaviors of the composites after thermal aging treatments were investigated. The mapping relationship between damage modes and acoustic emission parameters is established by principal component analysis and k‐means clustering methods, then the acoustic emission data were trained by K‐Nearest Neighbor algorithms to obtain a damage modes identification model with positive predictive values above 90%. The results showed that more matrix cracking signals are captured (or matrix cracking accumulation acoustic emission (AE) energy is abruptly raised) at the early stage of loading after 32 days of thermal aging. With the addition of multilayer graphene, the fiber/matrix debonding accumulation AE energy is significantly less than the matrix cracking accumulation AE energy, which is more obvious after thermal aging. Damage initiation and extension obtained by the acoustic emission events help to find the correlation between aging time and interior interface damage mechanism.
Fibre-reinforced composites have shown a growing interest in pressure-resistant materials for deep-sea use due to their excellent properties. This paper presents the influence of the moisture absorption on the mechanical properties and damage mechanisms of three-dimensional six-directional (3D6D) braided composites under hydrostatic pressure. The bisphenol A epoxy resin, bisphenol F epoxy resin, and hydrogenated bisphenol A epoxy resin, are chosen. SEM and X-ray Micro-CT are employed to investigate the moisture absorption, tensile and compressive damage before and after subjecting to the hydrostatic pressure. Results show that the bisphenol F carbon/epoxy composite has the lowest porosity at 0.082% among the three composite materials. The average moisture absorption was the lowest at 0.3755%. Furthermore, moisture is mainly transported along micro cracks in the matrix and the fiber-matrix interface under hydrostatic pressure. After the composites absorb moisture, the average tensile strength retention rates of bisphenol A carbon/epoxy composite, bisphenol F carbon/epoxy composite, and hydrogenated bisphenol A carbon/epoxy composites drop to 88.282%, 76.34%, and 66.43%, respectively. Moreover, their average compressive strength retention rates drop to 53.15%, 74.26%, and 83.45%, respectively. The tensile and compressive strengths of the 3D6D braided composites decreased significantly after moisture absorption, mainly due to fiber-matrix debonding and matrix cracking.
The use of CFRP composites is significantly increasing in the aerospace, automotive, and marine industries, particularly in safety critical primary structures. This work presents a newly developed experimental approach to investigate the directional diffusion of water in CFRP composites with the use of Fick's law. The approach is used to study the effect of fiber architecture on directional diffusion rates, with a particular focus on the role of fiber waviness in the diffusion process. A comparison of water diffusion is made in three different fiber architectures: Unidirectional (UD), plain weave, and twill weave. The specimens were fully immersed in 90°C purified water until their maximum moisture saturation was achieved, with some specimens being selectively exposed from the edges only to obtain the directional diffusion coefficients. The water penetration process into the CFRP structure initiate from the micro‐cracks and defects. The experimental work of this study shows sharp mass increases within the first stage followed by an equilibrium stage where saturation is present. The interfacial region is found to be a critical parameter where detachment of the interfacial fiber/matrix bonding is observed further demonstrating the potential effect of different fiber architecture in this region. UD fiber architecture showed ~20% higher diffusion coefficient in the Dx,y direction compared with plain and twill woven architectures. The weave patterns in 2D woven fiber architectures are therefore believed to play a key role on the moisture ingress mechanism and subsequently contributed in slowing down the capillary process in the interfacial region. This has implications for materials development and selection for CFRP composites used in moist environments.
