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Adhesive bonding is an effective technique for connecting fiber reinforced composites (FRPs) and plays a crucial role in determining load transfer capability and overall structural safety. However, long-term exposure to temperature and moisture can degrade adhesive joints, highlighting the significant importance of accurately predicting their durability when designing reliable adhesive structures. This study aims to address the industry's demand and academic interest by proposing a convenient and accurate prediction method to evaluate the durability of adhesive structures subject to complex stresses. Laboratory accelerated aging experiments were conducted on butt joints (experiencing pure normal stress) and shear joints (experiencing pure shear stress). Quasi-static tensile tests and adhesive FTIR tests were performed to establish a dataset of adhesive functional group absorbance and failure strength under single stress conditions. To compare and assess the predictive performance of different models for aging behaviors, Artificial Neural Network (ANN), Support Vector Regression (SVR) and Random Forest (RF) models were selected. The model hyperparameters were further optimized using the Genetic Algorithm (GA). The results demonstrated that the ANN model exhibited superior correlation and accuracy compared to the SVR, and RF. The characteristic importance analysis revealed that the hydrolysis and post-curing of adhesives were the primary factors affecting joint performance under hygrothermal environments. By incorporating environmental degradation factors and defining initial failure criteria, the CZM constitutive model was modified and a predictive method was established for assessing the hygrothermal aging behavior of CFRP/aluminum alloy bonding structures. This method effectively eliminates the effect the intricate aging process (e.g. aging time, aging conditions) and establishes a direct correlation between the molecular structure of adhesive and the macroscopic mechanical properties of the bonded joint, which serves as a valuable reference and guidance for the safety design of automotive composite material bonding structures throughout their entire lifespan. [ABSTRACT FROM AUTHOR]

The existing studies on the degradation mechanism of composite adhesive joints mostly focus on the aging of adhesives, but the aging effect of composites is often ignored. In this paper, the degradation mechanism of adhesive, CFRP, as well as shear joints (SJ) and butt joints (BJ) in thermal-humidity-cycles (T-H-C) for automobiles were investigated by chemical detection and mechanical testing. The aging effects of adhesives and composites are compared and analyzed by the variation in chemical and mechanical properties to reveal the degradation mechanism of composite adhesive joints. Experimental testing show that the adhesive and CFRP underwent hydrolysis and oxidative decomposition respectively, and there was a reduction in Tg (glass transition temperature) and thermal stability. The joint strength of composite adhesive joints fell by around 40% after 30d (days), and interfacial failure appeared. The variation in the composition of adhesive and CFRP, interfacial failure and thermal stress contributed to the degradation of composite adhesive joints. Degradation mechanism analysis shows that SJ under shear stress state were less affected by CFRP aging, while BJ under normal stress state were more affected by CFRP aging and the effect became more obvious with time growth. [ABSTRACT FROM AUTHOR]

With the increasing scale of the automotive industry, the mixed application of multiple materials and bonding technology have become indispensable means to achieve lightweighting. In this paper, accelerated aging experiment and tensile test were developed to study the effect of loading rate (1 mm/min–100 mm/min) on the failure of BFRP-Aluminum alloy single lap joint after hygrothermal aging (0 days–28 days). The aging mechanism of the adhesive and BFRP in the hygrothermal environment was also analyzed by Fourier transform infrared and differential scanning calorimetry. The test results showed that the joint failure strength varied with the hygrothermal aging time and loading rate, with the former showing a negative correlation and the latter a positive correlation. Combined with the joint failure surface, it was found that the joint strength decrease was mainly caused by the hydrolysis reaction of the adhesive and the interfacial failure of the joint. A regression model was developed to characterize the failure strength of the joints under different loading rates in the hygrothermal environment, and it was concluded that the aging time was more significant than the loading rate on the strength of the joints. [ABSTRACT FROM AUTHOR]

To systematically and comprehensively analyze the effects of different aging environments on the aging failure of aluminum alloy/CFRP (Carbon Fiber Reinforced Plastics) composite bonded shear and butt joints, seven typical aging environments of room temperature (23°C/20%RH, RT), high-temperature (80°C/20%RH, HT), low temperature (−40°C, LT), temperature cycles (−40 ~ 80°C/20%RH, TC), immersed in water at room temperature (IRT), high temperature and high humidity (80°C /95%RH, HTHH), and hygrothermal cycles (−40°C ~ 80°C /95%RH, HC) were selected to perform aging tests. The composition analysis revealed that the adhesive underwent the most significant post-curing in HT, followed by TC, while LT had almost no effect on the adhesive. It was also found that the degree of moisture absorption and hydrolysis of the adhesive in IRT, HTHH and HC decreased sequentially. A single temperature or humidity environment had small effect on the failure strength of bonded joints less than 20%, increasing temperature or humidity could further reduce the failure strength by about 30%, and periodically changing the temperature or humidity had the greatest effect on the failure strength by more than 40%. ANOVA (Analysis of Variance) shows that all the single factors of aging time, load type, or aging environment had significant effects on the failure strength, but the aging environment had the greatest effect. Multifactor coupling effects on the failure strength was not significant, except for the coupling effects of aging environment and aging time. [ABSTRACT FROM AUTHOR]

The energy absorbing property of corrugated tube subjected to axial crushing was researched through theoretical analysis. In view of the energy absorbing mechanism for axisymmetric deformation mode,a calculation formula for the mean crush load was put forward. It shows that the mean crush load is mainly influenced by the tube geometric parameters,material properties and loading rate. The theoretical analysis method was proved with the simulation results. Based on the theoretical analysis and numerical simulation effects of geometric parameters on the mean crush load were studied. Decreasing corrugation angle or increasing corrugation wavelength leads to accelerated increasing the mean crush load. Compared to the quasi-static crushing tests,the mean dynamic crush loads increase at about 80%. This work provides valuable theoretical guidance and design reference for the application of corrugated tube to structural crashworthiness field.

Traditional material-joining techniques are facing enormous challenges due to the wide use of new materials in engineering. Therefore, the application of bonding technique in engineering becomes more and more important. In order to facilitate designers evaluating the joint strength of bonding structure, a fast and simple strength evaluation method which can be easily used for adhesive joints under complex working conditions was proposed in this article. The normal and shear stresses of the adhesive interface were selected as the main research objects in the method considering the complex working conditions that many bonding structures may face in engineering. Butt joint, single lap joint, and several groups of scarf joint specimens with different adhesive angles were fabricated. Numerous repetitive tensile tests were conducted to obtain the adhesive failure stresses under different conditions. The adhesive failure stress envelope was fitted based on the experimental data, and the evaluation method of adhesive joint strength was developed in detail. Finally, verification experiments were designed. The results indicate that the evaluation method of adhesive joint strength based on the normal–shear stress of the adhesive interface is simple and effective in engineering application.

To investigate the influence of sealing treatment on the resistance of lap joints to hygrothermal environment, Al-CFRP single lap joints (SLJ) and Al-CFRP-Al double lap joints (DLJ) were selected as the research objects, and hygrothermal-cyclic aging test was carried out based on the vehicle service environment. The failure strength and failure mode of the joints before and after the sealing treatment and hygrothermal aging were analyzed. Fourier transform infrared (FTIR), thermogravimetric (TG), and scanning electron microscopy (SEM) analyses were used to explain the aging behavior of the adhesive and CFRP. The failure strength of the lap joints decreases with the aging time, but the rate of decline of the joints strength after the sealing treatment is considerably lower. The failure mode of the lap joints is cohesive failure before aging. At the beginning of the aging process, interface failure appears at the edge of the failure surface of the joints and gradually leads to the fiber tearing. Moreover, due to the diffusion mechanism of water molecules, the aging behavior at the edge and the center of the interface is different. When the joints is sealed, the aging behavior caused by aging time and aging path will be considerably weakened. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of cyclic hygrothermal aging on the mechanical behavior of the adhesive bonded aluminum joints. The adhesive joint specimens were immerged in the temperature/relative humidity set at 80 °C/95％ and −40 °C/30％ for cycle experiments for un–aged, 20, 40, and 60 cycles, respectively. Joint bonding angles were set to 0°, 15°, 30°, 45°, 60°, 75° and 90°. The stress modes of the adhesive joints were directly related to the bonding angles. It revealed that the hygrothermal aging significantly decreased the ultimate failure strength and stiffness of adhesive joints. The failure strength decreased with the increase of aging cycles. Besides, for the tensile–shear combined loading, the environmental degradation was much more obvious. The joint failure displacement values increased obviously after hygrothermal aging than that of un–aged. With the increase of aging cycles, the failure displacement of 75° and 90° joints increased more obviously than that of 0°, 15°, 30°, 45° and 60° joints. Moreover, Fourier Transform Infrared (FTIR), Energy Dispersive X-ray Spectrometer (EDS), Scanning electron microscope (SEM) and Differential scanning calorimetry (DSC) was used to analyze the characteristic of adhesive. [ABSTRACT FROM AUTHOR]

To predict the failure of adhesively bonded CFRP (Carbon Fiber Reinforced Plastics)-aluminum alloy joints applied to High Speed EMU (Electric Multiple Units) more accurately with consideration of temperature influence, a combined experimental-numerical approach is developed in this study. Bulk specimens and adhesive joints, including thick-adherend shear joints(TSJ), scarf joints(SJ) with scarf angle 30°(SJ30°), 45°(SJ45°), and 60°(SJ60°), as well as butt joints(BJ), were manufactured and tested at 23°C (room temperature, RT), 80°C (high temperature, HT) and −40°C (low temperature, LT). Quadratic stress criteria built at different temperatures were introduced in the cohesive zone mode (CZM) to conduct a simulation analysis. Test results suggest that the effects of HT on mechanical properties of adhesive are more obvious than the effects of LT. It is also found that TSJ show the greatest improvements in failure strengths at LT due to the occurrence of cohesive failure, while SJ and BJ tend to develop fiber tears due to the presence of normal stress. Stress distributions of adhesive layer are found to be symmetrical except for the normal stress of SJ. This simulation analysis shows that the prediction accuracy is related to quadratic stress criteria applied, and that the relative errors of prediction results are less than 7.5% for engineering applications. [ABSTRACT FROM AUTHOR]