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This study introduces an ultrasonic vibration assisted resin transfer molding (RTM) technique as an innovative approach to address the inherent challenges associated with traditional methods for producing CFRP laminates. It investigates the mechanism of void formation in CFRP composites under ultrasonic vibration using 3D X-ray microscopy. Numerical calculations and simulation analyses are also employed to validate the impact of ultrasonic vibration on mechanical properties of CFRP. The findings indicate that ultrasonic vibration results in CFRP laminates with more uniform thickness, leading to a substantial increase in fiber volume fraction up to ∼16 %. Concurrently, there are significant improvements in flexural strength (∼20 %) and fracture energy (∼90 %). Ultrasonic vibration also effectively reduces CFRP porosity by at least 25 %, resulting in a more consistent distribution of voids, primarily consisting of small circular voids. This porosity reduction is attributed to the cavitation effect and enhancing wettability, consequently improving the mechanical properties of CFRP. Moreover, simulations and numerical calculations demonstrate the significant occurrence of cavitation effect within the resin under specific process conditions. The intensity of cavitation is influenced by factors such as the initial bubble radius, acoustic pressure amplitude, and static pressure of the resin. The ultrasonic-assisted RTM process is proved as a promising method for producing CFRP laminates with superior properties. [ABSTRACT FROM AUTHOR]

High power fiber laser was proved to be feasible to cut carbon fiber reinforced plastic (CFRP) laminate with high efficiency, while the machined quality on mechanical performance was not fully understood. This paper studied the effect of high temperature up to 220°C on tensile strength degradation and strain distribution of unidirectional CFRP laminate with open hole machined with fiber laser. Differential scanning calorimetry (DSC) was firstly employed to determine the glass transition temperature (Tg) of polymer‐matrix composite. Digital image correlation technique was applied to evaluate whole‐field strain distribution and crack propagation/evolution of CFRP laminate featured with open hole under tensile loading. Results showed that the tensile strength of laser machined CFRP laminate degraded significantly during working in high temperature above 100°C. The value of strains distributed around center hole was highly related to the elevated temperature and applied load levels. Splitting was the prevalent failure mode of CFRP laminate under elevated temperature up to 180°C. Finally, semi‐empirical model was developed for evaluating tensile performance of laser machined CFRP laminate at elevated temperature based on regression analysis. [ABSTRACT FROM AUTHOR]

Fiber laser was feasible to cut carbon fiber reinforced plastic (CFRP) laminate with high efficiency and particularly meet short cycle time in large-volume vehicle production. Large differences in physical and thermal properties between fiber and resin, however, have been prohibiting the application of fiber laser cutting on CFRP composites. Joining of CFRP parts is mainly dependent on mechanical bolting/riveting, which depends critically on the quality of processed holes. In this study, CFRP laminates used for manufacturing new energy vehicles were employed to investigate the hole quality during fiber laser cutting in continuous wave and pulse modes. Statistical analysis was performed to optimize process parameters to minimize heat affected zone (HAZ) levels. Results indicated that thermal defects including matrix recessing/decomposition and protruding and uncut fibers were prevalent at hole entry and exit irrespective of processing parameters. Low level of laser power (800 W) and linear energy (50 J/mm) together with the pulse mode were preferred to minimize HAZ during fiber laser cutting of CFRP laminates, while the effect of a laser mode was negligible. Tensile strength of samples with open hole (6.0 mm diameter) cut by a fiber laser varied from 131 to 143 MPa, which depended to some extent on HAZ levels. Massive delamination, fiber breakage, and splitting bounds were the main damage/failure modes. [ABSTRACT FROM AUTHOR]

Experimental data is presented relating to hole quality and feasibility studies when using continuous wave (CW) fiber laser to cut CFRP laminates (6.0 mm diameter hole) with single- and multi-pass strategy. The effect of typical processing parameters including laser power and cutting speed on thermal defect was also investigated. The statistical significance of individual cutting parameters was determined using main effects plot together with ANOVA analysis. Three methods were proposed to characterize HAZ based on the feature of thermal defect. According to statistical analysis, both cutting speed and laser power were significant with respect to HAZ (recorded at hole exit). The minimal value of HAZ was recorded with laser power of 650 W and cutting speed of 1100 mm/min. Energy per unit length ( E l ) should be set above 40 J/mm to ensure cutting through CFRP laminates using fiber laser in high efficient machining process. Multi-pass strategy was investigated without setting pause/break time between each pass in order to increase cutting efficiency. Results showed limited improvement in terms of the level of HAZ even with cutting speed up to 10,000 mm/min, while machining time was significantly reduced to cut 6.0 mm diameter hole compared with single-pass strategy. For machining small holes with diameter down to 2.0 mm, high power fiber laser was not preferred due to severe thermal defect observed at hole entry and exit. [ABSTRACT FROM AUTHOR]

• Different repairs were designed to strengthen steel structures using CFRP. • Effects of repair method/configuration on strain distribution were investigated. • Damage evolution process was analyzed in comparison with strain distribution. • Hybrid repairs exhibited initial adhesive failure and final rivet shearing. • Various failure modes were characterized for different repair method/configuration. Mechanical behavior and fracture characteristics of adhesively bonded and hybrid bonded-riveted repairs with stepped single-side and double-side configurations were investigated. Digital image correlation (DIC) technique was used to systematically investigate the effects of repair configuration and repair method on full-field strain distribution and damage evolution process of CFRP-repaired steel structures under static loading. The strain distribution and evolution in the repairs were quantified to figure out failure process and fracture characteristics in details. The failure process of hybrid repairs displayed two stages including initial adhesive failure and final rivet shearing, and the behavior of rivets could prevent catastrophic failure of CFRP-repaired steel structures. Progressive failure process of different repairs indicated that crack initiated and propagated on the edge of repaired region between CFRP laminates and substrates, which was in good agreement with the findings from strain distribution. Mixed failure modes including adhesive failure, thin-layer cohesive failure, light-fiber-tear failure, stock-break/delamination and rivet shearing were identified for specific repairs. [ABSTRACT FROM AUTHOR]

• High power fiber laser was feasible to cut CFRP laminate with high efficiency. • The effect of cutting parameters on thermal defects were analyzed. • Two methods were proposed to characterize/quantify HAZ. • Full-field strain distribution was analyzed with DIC technique. • Numerical simulation of strain distribution was in line with DIC analysis. High power fiber laser cutting of CFRP composites has been proven to be feasible with high efficiency, while there are still several challenges due to different carbon fiber-epoxy resin properties and sensitivity to thermal heat. This paper studied the influence of processing parameters on machined hole quality and quasi-static tensile behavior of unidirectional CFRP laminate with open hole (6.0 mm in diameter) following fiber laser cutting process. Hole surface morphology was analyzed using optical microscope and scanning electron microscopy. The area of heat affected zone and defect factor were quantified to understand the effect of machining parameters on thermal defect. It was found that both cutting speed and laser power were statistically significant with respect to HAZ recorded at hole entry, while cutting speed was the only significant factor for HAZ observed at hole exit. The full-field strain distribution during tensile loading was characterized using 3D digital image correlation (DIC) technique. Surprisingly, laser processing parameters showed limited effect on surface strain distribution (ε xx , ε xy , ε yy) during tensile loading. Some highly localized strain zones were observed on the tangent of transverse edge of the hole, corresponding to final failure mode of splitting due to inevitably slight shear force during tensile loading and weak interface strength between carbon fiber and epoxy resin. Numerical simulation results of strain distribution were in good agreement with the DIC analysis. [ABSTRACT FROM AUTHOR]

Abstract Mechanical performance together with progressive failure process and failure modes of riveted, adhesively bonded and hybrid joints connecting CFRP and aluminum alloy with various overlap length were investigated. Experimental results showed that hybrid joints presented superior performance in terms of peak load and energy absorption, which increased by up to ~380%, 434% and ~19%, 56% respectively compared with solely riveted and bonded joints. Typical failure evolution photographs were taken with high speed camera for analyzing progressive failure process. Final failure modes of hybrid joints included rivet shear fracture, CFRP compressive deformation, adhesive failure, cohesive failure and light-fiber-tear failure. Highlights • Hybrid joint exhibited two different stages in progressive failure process to prevent catastrophic failure. • Hybrid joints showed superior mechanical performance in terms of peak load and energy absorption. • Failure evolution photographs were recorded with high speed camera for detailed progressive failure analysis. • Various failure modes were analyzed regarding to three different joining methods. [ABSTRACT FROM AUTHOR]