Applied Composite Materials最新文献

In this study, the influence of four different process parameters on hot gas welding of CF/epoxy fiber composites functionalized with a PA6 thermoplastic film is investigated. Additional experiments are carried out on specimens adorned with triangular beads of coupling material that are printed onto the plates, ensuring extra material within the joining zone. This approach offers a great advantage for compensating geometric tolerances. The parameters considered are common process parameters for regular two-step processes: Heating element temperature (THE), heating time (HT), welding force (F) and welding time (HTF). The design of experiments (DoE) is planned according to the Taguchi method. An orthogonal array is used to set up the experimental plan. Three factor levels of each welding parameter are considered. The test series are carried out with two sample variants. In the second sample variant, additional thermoplastic material is placed in the joining zone. The strength of the welded joints is investigated by tensile shear tests according to DIN EN 1465. The results show that the welding force has the greatest influence on the welding strength. Heating times of 20 s were found to be optimal. Within the first sample variant, a saturation behavior of the welding force can be observed at 500 N. Higher heating element temperatures (500 °C) and welding forces (1165 N) are advantageous using additional material. High welding temperatures result in a negative effect on the interdiffusivity of the polymer chains.

Hybrid components consisting of continuous fiber reinforced thermoplastic (CFRT) and steel components exhibit promising potential in advanced lightweight construction. However, the joining operation presents a significant challenge due to the materials’ distinct physical and chemical properties. This paper studies a joining method in which dual pin arrays protruding from the surface of the metal component are inserted into the locally heated CFRT component to create a form-fitting joint. The primary objective is to scrutinize the influence of various CFRT materials on joint formation and quantify the resulting properties. The fiber type (glass and carbon) and fiber architecture (unidirectional and bidirectional reinforcement) are varied. All materials could successfully be joined via the direct pin pressing process, while depending on the CFRT material, distinct characteristic fiber morphologies could be identified. Bidirectionally reinforced carbon fiber reinforced samples showed the highest overall strength, while unidirectionally glass fiber reinforced samples showed the highest energy absorption and second highest ultimate strength.

This study aims to increase the ductility and the damage tolerance capability of composite structures with interlayer nonwoven reinforcement. The novelty of this study stems from its innovative approach: a comprehensive examination of the arrangement of warp and weft fibres, as well as the preform layer, coupled with both intra-layer and inter-layer hybridization, all while accounting for the incorporation of nonwoven reinforcement. The flexural, compressive, impact and post-impact compressive strengths of unreinforced and interlayer nonwoven reinforced glass/carbon/epoxy hybrid composites are carefully investigated and compared. The nonwoven reinforcement led to a reduction in flexural strength and modulus for composite structures, while enhancing their strain, thus imparting greater ductility to the structure. Both hybridization and interlayer nonwoven reinforcement increased the peak forces of composites while reducing deformations. The cracks occurring in the composite structure under load were arrested by the barrier created by the nonwoven surfaces used between the layers, which was considered an enhancement in the damage tolerance of composite structures.

Abstract

Composite panels made-up of multi-cellular 3D flat-knitted (M3DFK) fabrics were manufactured in this research and mechanically evaluated in order to analyze their bending functionality after being filled with polyurethane (PU) foam. Using an electronic flat knitting machine, two different groups of M3DFK fabrics varied in their cross-sectional shapes were initially prepared from glass/polyester yarns and then, being molded through vacuum injection method with epoxy resin. A three-point bending test was used to experimentally evaluate the mechanical performance of PU-foam filled composite panels. Also, the composites mechanical behaviors were theoretically investigated using the multi-scale modeling method. The results indicated that the reinforcement structural geometries and foam presence in the composite specimens have a significant impact on their bending properties. The empirical findings revealed that foam injection resulted in a 113.8% and 92.3% increase in energy absorption for double- and single-decker composite structures during the bending process, respectively. According to the results, foam-filled composite structures experience a significant increase in core shear and facing stresses. This increase amounts to 18.4% for the single-decker and 84.7% for the double-decker 3D structure. The results of the simulation method were used to understand the effect of composite structure as well as foam injection on the stress distribution and maximum stress applied during the bending process. Also, no delamination between foam and facing layers was observed.

This paper proposes an efficient optimization method for the stacking sequence of composite pressure vessels based on the joint application of finite element analysis (FEA), artificial neural network (ANN), and genetic algorithm (GA). The composite pressure vessel has many winding layers and varied angles, and the stacking sequence of the composite pressure vessel affects its performance. It is essential to carry out the optimal design of the stacking sequence. The experimental cost for optimal design of composite pressure vessels is high, and numerical simulation is time-consuming. ANN is used to predict the fiber direction stress of composite pressure vessels, which replaces FEA in the optimization process of GA effectively. In addition, the optimization efficiency of the optimization method proposed in this paper can be improved significantly when the neural network model is employed. The optimization results show that the peak stress in the fiber direction can be reduced by 37.3% with the design burst pressure. The burst pressure of the composite pressure vessel can be increased by 13.4% by optimizing the stacking sequence of composite pressure vessels while keeping the number of plies and the winding angle unchanged. The results imply that the work undertaken in this paper is of great significance for the improvement of the safety performance of composite pressure vessels.

Traditional carbon fiber reinforced carbon matrix composites are mostly two-dimensional laminated structures with low interlayer properties. Z-fiber reinforcement technology can improve the properties of composites in the thickness direction. However, the low axial modulus of Z-fiber results in insufficient stiffness, and its implanting in large-thickness preforms is susceptible to buckling due to heavy resistance. The existing Z-fiber implantation techniques are challenging to realize the Z-direction reinforcement of large-thickness and high-density preforms. Therefore, this paper proposes a method of using hollow tubes to guide Z-fiber implantation into preforms and puts forward an improved solution for the issue of buckling during the insertion of hollow tube into the preform. A cutting edge was designed for the hollow tube, and a metal rod was utilized to provide support. The enhanced hollow tube was named "Z-fiber guiding needle." A mechanical model of the Z-fiber guiding needle inserted into the preform was established to optimize needle parameters. Then Abaqus software was used to study the strength and stiffness of the needle, as well as analyze its stability. Finally, experimentally verifies the Z-fiber guiding needle. The final results show that the strength, stiffness, and stability of the designed Z-fiber guiding needle can meet the requirements of implantation. This proves the designed method is correct and feasible, and provides a theoretical basis for the design of ultra-long needles used to guide Z-fiber implants into large-thickness, high-density composite material preforms.

Graphical Abstract

The mechanical property of lap joints can be strongly modified by tufting technique. The influence of tufting density, tufting loop and tufting direction on the fracture strength of tufted lap joints (TLJ) are mainly investigated via shearing tests. The experimental results show that lap joint strength can be much improved when the tufting density is increased. Conversely, tufting loop and tufting direction seem to have no apparently effect on the lap joint strength. However, they help to increase the specific strength of the lap joints. In this study, the samples tufted in 0º or 90º direction with a tufting density of 4.17 pts/cm² and without tufting loops can achieve the highest specific strength. The current study revealed that the tufting technique can improve the lap joints strength within a certain range and tufting parameters need to be well designed to reduce the total material weights.

Bi-adhesive repair method is one of several repair technologies that use the adhesive bonding approach for patch-repaired composites. However, these repairs are subject to matrix-cracking and interface debonding damage. Furthermore, a change in the length ratio (the length of the rigid adhesive region divided by the length of the overall repaired region) also produces a change in the damage modes, which has a significant impact on the repair performance. Hence, this study aims to evaluate the effects of four different length ratios (0, 0.2, 0.5, 1) on the behavior of damage evolution in bi-adhesive repaired composites. The acoustic emission damage identification and micro-CT characterization are carried out based on the machine learning method. A simple prediction method is employed to distinguish damage modes in bi-adhesive repaired composites, achieving a prediction accuracy over 90%. The results demonstrated that the length ratio has a substantial effect on matrix-cracking, fiber-matrix debonding, and their interaction in bi-adhesive repaired composites. These acquired characteristics information of acoustic emission signals provide insights into the impact of length ratio on the progression of damage evolution. Additionally, the visualization of interior damage offers insights into the variations in failure characteristics within distinct bi-adhesive repaired composites, thereby supporting the conclusions gained from acoustic emission studies. This research effectively achieves the real-time monitoring of damage modes in bi-adhesive repaired composites, contributing to the comprehension of the relationship between length ratio and damage mechanism.

With the development of integrated circuits and the miniaturization/ integration of electronic devices, heat dissipation solutions have become an increasingly important issue. The thermal conductivity of polymer-based thermal management materials is typically influenced by the amount of incorporated fillers. However, an innovative solution to increase the thermal conductivity without increasing the total filler content is the improvement of the filler connectivity by using specific surface modifications. Surface modifications using thermal conductive submicron particles can reduce the interfiller distances, acting as thermal bridges between the particles. In this paper, copper submicron particles modified BN (BN@CuSMPs) have been prepared by in situ reduction and mixed with graphene oxide (GO). A three-dimensional BN@CuSMPs/rGO aerogel (CBGA) framework with "point-surface" connection has been prepared by using the self-assembly mode of GO. CBGA/EP composites were then prepared using epoxy resin (EP) as matrix and a vacuum assisted impregnation method. The thermal conductivity of CBGA/EP composites has been found to be 1.918 W m⁻¹ K⁻¹ using a filler content of 19.61%, which was 12.8% higher than that of BN/rGO/EP composites and 909.5% higher than that of pure EP. The thermal resistance of the composites was analyzed using the Foygel model. It was found that the introduction of CuSMPs effectively decreased the thermal resistance between the BN particles, forming a thermal conductive three dimensional network inside the polymer-based material system.

This study investigates the impact of ultrasonic welding amplitudes and time on the properties of carbon fiber reinforced polyaryletherketone (CF/PAEK) composite joints. To enhance the performance of CF/PAEK ultrasonic welded joints, a hybrid energy director (ED) was proposed, which was composed of the interfacial microgroove and resin film or metal mesh. This study investigated the effect of different types of ED on the forming quality, shear failure load, and fracture interface microstructure of single lap joints made of CF/PAEK. The results indicated that the hybrid ED with resin film offers a distinct effect on enhancing the strength of ultrasonic welded joints. The hybrid ED with resin film essentially improves the tensile properties of the joint, with the strength and toughness increased by 35.8% and 174.3%, respectively. This strengthening effect is primarily attributed to the added resin film providing adequate interfacial resin. Sufficient resin is filled into the interior of the microgroove, ultimately forming a mechanical anchoring structure to strengthen the joint strength.