Wenjun Huang’s scientific contributions

Polymer-based composites are widely used in aerospace, automotive, construction and wind energy fields due to their high specific strength and stiffness, corrosion resistance, and customizable properties [...]

Scarf repair is a common repair method for composite laminate structures. Poor workmanship may cause bonding defects in the repair area. In this paper, the tensile properties of scarf-repaired composite laminates with three types of adhesive pore defects were studied by finite element method, and the effects of defect type, area and location were discussed. The results indicate that adhesive pores lead to local stress concentrations, significantly reducing the damage initiation load of the adhesive and laminate, but have limited influence on the initial stiffness and ultimate load of the structure. Pore defects alter the adhesive damage propagation mode but do not change the ultimate failure mode of the structure. Larger defect areas (porosity) result in lower structural tensile performance, and defects located in high-stress regions cause earlier damage initiation. ‌Different types of adhesive defects exhibit varying effects on structural tensile performance.‌.

Compressive performances of composite structures can be significantly decreased due to the lightning strike damage, so the structures with lightning frighten must be considered lightning protection design. In this study, compressive experiments after lightning strikes were conducted on non‐protected, 12‐layer interlaminar carbon nanotube film (CNF) protected, and traditional surface silver coating (TSSC)‐protected composite laminates. A numerical analysis procedure was established, incorporating a lightning strike ablation damage simulation (LSADS) module and compressive residual strength calculation (CRSC) module. The procedure's effectiveness was verified by the experiment results. Based on this procedure, the compressive performances and the possible failure mechanism of laminates after lightning strikes were analyzed. The results show that the laminates with TSSC protection and 12‐layer interlaminar CNF protection can increase compressive residual strength compared with non‐protected laminates. The predominant compressive damages of the laminates after lightning strikes are fiber‐matrix shear damage and fiber fracture damage. Optimized one‐layer interlaminar CNF protection with a thickness of 0.36 mm can increase the laminate compressive strength but decrease the structural weight. This study offers a reference and basis for the lightning strike protection design of composite structures. Highlights CNF in lightning strike protection of composite structures. Compressive failure mechanism of composite laminates after lightning strikes. A numerical procedure to evaluate lightning damage and compressive performances. Design of interlaminar CNF protection.

Tensile experiments were conducted with single-bolted and multi-bolted countersunk composite-metal joints. The finite element models with Hashin criteria and modified Camanho degradation law were developed to predict the bearing load and to simulate the failure behavior. The models were validated with the experimental results, including load-displacement curves and composite damage profiles. Based on the verified models, bolt load distributions of multi-bolted joints were calculated and analyzed before and after damage occurs. Results show that composite damages can change the bolt load distributions to a certain extent, which needs to be considered during the structure design. To adjust the bolt load distribution, the effects of joint variables, including bolt-hole clearance, bolt spacing, countersunk height ratio, and bolt stiffness combination, have been studied. It is found that the increase of the pin clearance around the largest bearing bolt would decrease its corresponding bearing load. The countersunk height ratio affects the bolt load distribution difference that a greater ratio leads to a less difference. The bolt spacing and bolt stiffness can also be used to reduce the bolt load distribution difference with elaborately designed combinations.

A 3D progressive model with better convergence property is established to capture the mechanical properties and damage mechanism of a composite bolted π-joint under bending load and shown to closely match experimental results. This model is then used to investigate the effect of internal laminate stacking sequence and surface layers thickness on the bending performance of the joint. It was found that the stacking sequence and the surface layers thickness have a significant effect on the matrix crack and delamination distributions in the joint, respectively. Local surface layer thickness can be designed to control the delamination damage around the bolt hole. Finally, volume fraction of 0° layer in the internal laminate and surface layer thickness are used to improve the joint bending performances by proper design.

A kind of interlaminar film with carbon nanotubes inserted into polyether ketone with cardo was used for lightning strike protection of composite laminates. The distribution of the interlaminar film was investigated by experimental and numerical methods. Artificial lightning strike tests were conducted for 12-film carbon nanotube and traditional surface silver coating protected specimens. Then corresponding finite element models (FEMs) were established to analyze the lightning strike effect and validated by the experimental results. Based on the FEMs, the number, distribution and thickness of interlaminar film were investigated in order to obtain equivalent protection effect with the traditional surface silver coating. The results show that only the first two layers were damaged for the surface silver coating protected specimen, while 5 layers were ablated for the 12-film protected specimen. Lightning strike damage area of the laminate protected with 5-film carbon nanotube is almost the same as that of the laminate protected with 12-film carbon nanotube. Compared with traditional surface silver coating protection, one film protection with thickness of 360 μm can make the laminate to obtain equivalent damage depth, 54.8% smaller damage area and 58% less additional weight. And reparability of the laminate is better than that of the laminate protected with 5 interlaminar films.

Hybrid bonded/bolted (HBB) joint has been widely used in engineering practice because it can overcome the potential weakness of pure bonded and pure bolted joints. However, studies on HBB joint are still at the initial stage. In this paper, tensile properties of a composite-metal single-lap HBB joint was investigated experimentally. And a detailed finite element model (FEM) was established to simulate the tensile behavior of the joint. The model was verified by the experimental results. Then the damage propagation and load transfer mechanism were explored based on the FEM. The results show that the HBB joint can provide multi-load transmission paths and resist damage propagation in the adhesive. The HBB joint has higher strength and energy absorption capacity than the pure bonded joint. And the HBB joint has greater initial damage load and tensile stiffness than pure bolted joint. Adhesive fillets can obviously improve the tensile performances of the HBB joint. Lateral stiffness of the joint boundary and testing machine show obvious effects on tensile performances of single-lap hybrid joints.

In this paper, two analytic methods are presented to predict the geometry of resin pockets formed around rigid fiber inclusions at the interlayer of unidirectional prepregs. The bending strain energy is calculated on fiber scale in one method, while it is calculated on layer scale in the other method. For the fiber scale method, several fibers in thickness direction are tied together to account for the bending stiffness increase caused by the interaction between fibers. And for the layer scale method, a single ply is divided into several sublayers to account for the bending stiffness decrease caused by the sliding between adjacent fibers. Both analytic methods can provide the closed-form solution for the resin pocket width, and the analytic results agree well with experimental results. The physical consistency of two methods is proved. It is found that the resin pocket size depends mainly on ply angles of the plies close to the inclusion, and the stacking sequence has some effect.