Browsing by Author "Li, Wenhao"

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    3D-printed thermoplastic composite fasteners for single lap joint reinforcement
    (Elsevier, 2021-12-10) Li, Wenhao; Guo, Shijun; Giannopoulos, Ioannis K.; Lin, Minxiao; Xiong, Yi; Liu, Yiding; Shen, Zhengquan
    This study presents findings for the strength and failure mechanism of a 3D-printed Continuous Carbon Fibre reinforced Onyx (CCF/Onyx) Thermo-Plastic Composite Fastener (TPCF) and a single lap-joint (SLJ) made of fibre/polymer composite reinforced by the TPCF. The study was carried out by numerical analysis and experiment methods including test sample design, manufacturing process and mechanical test. The 3D-printed fasteners were manufactured and tested in shear mode for two types of joining arrangement: fastened and hybrid bonded/fastened joints. Firstly, experiment was carried out for the TPCF fastened SLJ and the results show that addition of CCF in the Onyx matrix and post heat-treatment process could significant enhance the TPCF strength. The results was then benchmarked against a SLJ with steel fastening. The shear failure load of the SLJ reinforced by heat-treated CCF/Onyx TPCF of 8mm diameter was 36% lower than a SLJ reinforced by a steel bolt of the same size. Numerical model for progressive damage simulation was also created based on the failure theory from Puck and Schürmann achieving good correlation with the experimental data. Secondly, the TPCF fasteners were manufactured with two types of heat-treated countersunk head and pan head forming and used to reinforce bonded SLJ. The test results show that the bonded SLJ reinforced by the TPCF fastener of countersunk head is of 11.7% higher strength and an increase in ultimate deformation by 9.1% compared to a bonded SLJ reinforced by steel fastener of 5mm diameter. From the numerical and experimental study, it was noted that this was attributed to countersunk configuration to reduce out-out-plane bending and provide better crack arresting for the joint bonding.
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    Composites joints reinforced by composite rivets
    (Asranet, Glasgow, 2018-05-08) Li, Wenhao; Guo, Shijun; Giannopoulos, Ioannis K.
    This paper presents an investigation into the mechanical behaviour of composite joints reinforced by using a novel composite rivet made of rolled laminates. Two typical joints have been modelled using three-dimensional solid finite element model in the study. The first type is a composites single lap joint bonded and reinforced by a composite rivet compared with the joint reinforced by a titanium bolt subjected to tensile load. The results are also compared with an adhesive bonded joint as reference. The second type of joint model is a wing box section with skin-rib joint reinforced by composite rivet subjected to a pulling load. A range of adhesive damage was modelled up to 50% (undamaged WBDM, WBDM I 16%, WBDM II 33% and WBDM III 50% respectively) of the bonding area. The results show that the rivets located in the regions where the adhesive bonding failed will carry higher stress and make more contribution to the structure integrity. Although the titanium rivets provide better mechanical performance to carry more load, composite rivets offer an alternative adequate reinforcement to delay the bonding failure and safeguard the structure.
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    Investigation of adhesive joining strategies for the application of a multi-material light rail vehicle
    (MDPI, 2021-11-18) Liu, Yiding; Carnegie, Craig; Ascroft, Helen; Li, Wenhao; Han, Xiao; Guo, Hua; Hughes, Darren J.
    To meet the high demand for lightweight energy-efficient and safe structures for transport applications, a current state-of-the-art light rail vehicle structure is under development that adopts a multi-material design strategy. This strategy creates the need for advanced multi-material joining technologies. The compatibility of the adhesive with a wide range of material types and the possibility of joining multi-material structures is also a key advantage to its success. In this paper, the feasibility of using either epoxy or polyurethane adhesive joining techniques applied to the multi-material vehicle structure is investigated. Importantly, consideration is given to the effect of variation in bond thickness for both families of structural adhesives. Multi-material adhesively bonded single lap joints with different adhesives of controlled bond thicknesses were manufactured and tested in order to experimentally assess the shear strength and stiffness. The torsional stiffness and natural frequency of the vehicle were modelled using a global two-dimensional finite element model (FEM) with different adhesive properties, and the obtained vehicle performances were further explained by the coupon-level experimental tests. The results showed that the vehicle using polyurethane adhesive with a target bond thickness of 1.0 mm allowed for optimal modal frequency and weight reduction.
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    Nonlinear aeroelastic behavior of an airfoil with free-play in transonic flow
    (Elsevier, 2019-12-16) He, Shun; Guo, Shijun; Li, Wenhao; Yang, Daqing; Gu, Yingsong; Yang, Zhichun
    An investigation has been made into the nonlinear aeroelastic behavior of an airfoil system with free-play nonlinear stiffness in transonic flow. Computational Fluid Dynamics (CFD) and Reduced Order Model (ROM) based on Euler and Navier-Stokes equations are implemented to calculate unsteady aerodynamic forces. Results show that the nonlinear aeroelastic system experiences various bifurcations with increasing Mach number. Regular subcritical bifurcations are observed in low Mach number region. Subsequently, complex Limit Cycle Oscillations (LCOs) and even non-periodic motions appear at specific airspeed regions. When the Mach number is increased above the freeze Mach number, regular subcritical bifurcations occur again. Comparisons with inviscid solutions are used to identify and elaborate the effect of viscosity with the help of aeroelastic analysis techniques, including root locus, Single Degree of Freedom (SDOF) flutter and aerodynamic influence coefficient (AIC). For low Mach numbers in the transonic regime, the viscosity has little effect on the linear flutter characteristic because of limited influence on AIC, but a remarkable impact on the nonlinear dynamic behavior due to the sensitivity of the nonlinear structure. As the Mach number increases, the viscosity becomes significantly important due to the existence of shock-boundary layer interaction. It affects the unstable mechanism of linear flutter, impacts the aerodynamic center and hence the snap-through phenomenon, influences the AIC and consequently the nonlinear aeroelastic response. When the Mach number is increased further, the shock wave dominates the air flow and the viscosity is of minor importance.
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    Numerical analysis and experiment of sandwich T-joint structure reinforced by composite fasteners
    (Elsevier, 2020-07-29) Guo, Shijun; Li, Wenhao
    This study presents an investigation into the failure mechanism and strength improvement of a sandwich composite T-joint bonded and reinforced by fasteners made of thermoplastic composite. The T-joint subjected to pulling load was analysed by numerical simulation and experiment methods. Cohesive zone model (CZM) and Hashin damage model were used in the FE analysis to simulate the crack propagation and composite fastener damage. According to the results, the composite joint reinforcement is mainly attributed to the resistance of composite fasteners to shear failure of the bonded interface. Following the interface delamination and crack propagation in mode II failure, fracture of the composite fasteners occurred in transverse shear mode. The results show nearly 19% increase of bonding strength for the T-joint reinforced by composite fasteners of 5 mm diameter compared to the T-joint without fasteners. After the interface delamination, pull-out failure of fasteners was also observed and correlated to the numerical model considering material property reduction due to the sparse fibre tows in the fastener head forming and T-joint assembly. The investigation was extended to a parametric study of diameter and fibre orientation of the composite fasteners. The results show that the T-joint reinforced by composite fasteners of 6.28 mm diameter and lay-up can achieve the same strength and 44% weight saving compared to a titanium fastener opponent of 5 mm diameter.
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    Strength enhancement of bonded composite laminate joints reinforced by composite pins
    (Elsevier, 2020-01-10) Li, Wenhao; Guo, Shijun; Giannopoulos, Ioannis K.; He, Shun; Liu, Yiding
    This paper presents an experimental and numerical investigation in the static strength enhancement of composite laminate Single Lap bonded Joints (SLJ), reinforced by pins made of Uni-Directional (UD) fibre reinforced plastic composite materials. Bonded lap joint specimens were experimentally tested in tension to obtain the failure loads and failure modes. The specimens were subsequently benchmarked against the hybrid version of the joint resulted from the introduction of composite Pins. The Pin reinforcement enhanced the hybrid single lap joint strength by an average of 19.1% increase. Numerical models generated were used for correlation with the experimental results. Numerical and experimental results observation indicated that increased strength of the hybrid bonded/Pinned joint was partly attributed to the load sharing between the adhesive and the Pin past the adhesive failure initiation as well as to the enhanced out-of-plane bending stiffness after the Pin introduction on the lap joint. Numerical investigations were performed as well with hybrid SLJ reinforced by composite pins versus designs employing metallic Pins. The simulations showed that for the investigated lap joint design parameters, the hybrid metallic pin joint failed at a higher failure load. Nevertheless, the hybrid joint utilizing the composite Pin could benefit from the enhanced corrosion resistance properties. In the case of applying a larger composite Pin diameter and/or rearranging the fibre orientation in the Pin, the hybrid SLJs could potentially achieve higher strength characteristics before the adhesive bond ultimate failure in relation to the steel Pin, as well as resulting to additional weight saving up to 46.9%.
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    Structure health monitoring of a composite wing based on flight load and strain data using deep learning method
    (Elsevier, 2022-01-29) Lin, Minxiao; Guo, Shijun; He, Shun; Li, Wenhao; Yang, Daqing
    An investigation was made into a method for Structural Health Monitoring (SHM) of a composite wing using Convolutional Neural Network (CNN) model. In this method, various aerodynamic loads of an aircraft during flight and corresponding strain data were used for CNN model training. The proposed method was demonstrated by numerical simulation using vortex lattice method for aerodynamic loads of an A350-type aircraft in over a thousand flight conditions and a Finite Element (FE) model as a digital twin of the full-scale composite wing. To represent the measurement of 324 sensors mounted in the 18 skin-rib joints of the inboard wing, strain data from the 18x18 elements of the FE model in the sensor locations were calculated corresponding to the flight loadings. The strain data from the original structure FE model were employed to train a CNN model that was classified as healthy samples. Damaged elements were then introduced in random locations to produce data samples corresponding to the same set of flight loads for the CNN model training. In the subsequent damage detection process using the trained CNN model, confusion matrix, uncertainty and sensitivity analysis were evaluated. The study results show that robust damage detection results can be obtained with 99% accuracy without noise and 97% accuracy with 2% Gaussian noise. In the damage localization process, threshold value was set at 1.5, 2 or 2.5, and 83% overall accuracy was achieved using the CNN model when the threshold value was 1.5. The study demonstrated that the proposed method is efficient, accurate and robust.
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    Structure health monitoring of composites joint reinforced by acoustic emission based smart composite fasteners
    (Elsevier, 2022-06-16) Li, Wenhao; Guo, Shijun; Liu, Yiding; Shen, Zhengquan; Xiong, Yi; Gao, Fei; Hughes, Darren J.; Lin, Jing
    This paper proposed an Acoustic Emission (AE) based Smart Composite Fastener (SCF) concept for health monitoring of bonded/bolted composite single lap joints. The SCF was made of 3D-printed continuous carbon fibre reinforced thermoplastic materials with an embedded piezoelectric sensor. The SCF detected signals were found to be successfully associated with AE damage sources during the loading period. It was discovered that the adhesive crack/delamination AE sources resulted in burst-type signals with identifiable onset and end, whereas AE sources of frictional sliding between the SCF and fastener holes resulted in continuous-type signals producing broad frequency content. Furthermore, the amplitudes of the burst-type signal measured from the network of SCFs were successfully correlated with the locations of the damages. In the direction away from the damage, the amplitudes of the burst-type voltages measured from the SCF showed a decreasing trend, with 10195mv, 9,995mv, and 7,426mv respectively. Generally, the research in this paper explores the correlation between the voltage signal from a damaged AE source and the SCF, providing the feasibility of using a novel SCF for health monitoring in composite joint structures.
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    Transonic flutter characteristic of an airfoil with morphing devices
    (Sage, 2020-08-30) He, Shun; Guo, Shijun; Li, Wenhao
    An investigation into transonic flutter characteristic of an airfoil conceived with the morphing leading and trailing edges has been carried out. Computational fluid dynamics (CFD) is used to calculate the unsteady aerodynamic force in transonic flow. An aerodynamic reduced order model (ROM) based on autoregressive model with exogenous input (ARX) is used in the numerical simulation. The flutter solution is determined by eigenvalue analysis at specific Mach number. The approach is validated by comparing the transonic flutter characteristics of the Isogai wing with relevant literatures before applied to a morphing airfoil. The study reveals that by employing the morphing trailing edge, the shock wave forms and shifts to the trailing edge at a lower Mach number, and aerodynamic force stabilization happens earlier. Meanwhile, the minimum flutter speed increases and transonic dip occurs at a lower Mach number. It is also noted that leading edge morphing has negligible effect on the appearance of the shock wave and transonic flutter. The mechanism of improving the transonic flutter characteristics by morphing technology is discussed by correlating shock wave location on airfoil surface, unsteady aerodynamics with flutter solution