Browsing by Author "Xu, Xiaodong"

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    An experimental investigation into fracture resistance of carbon fibre sheet moulding compound
    (Elsevier, 2025-06-26) Xu, Xiaodong; Kiat Lo, Darren Kong; Adi Satriya, Ilham Akbar; Zheng, Liyi
    Carbon Fibre Sheet Moulding Compound (CF-SMC) is an attractive material due to its good formability and green credentials. However, there is a lack of reliable fracture data, posing challenges when analysing CF-SMC materials which already have built-in randomness. Fracture Resistance curves (R-curves) and their variability have not been reported before for CF-SMC materials. This knowledge gap in the literature is addressed through Double Cantilever Beam (DCB) and first End Loaded Split (ELS) tests on CF-SMC. This work also explains the toughening mechanisms in CF-SMC materials during interlaminar fracture. Under Mode I, the toughening mechanism is fibre bridging while it is crack migration for Mode II. The new R-curve data provides new insights into the interlaminar fracture behaviour of CF-SMC materials and can be used as invaluable inputs for their failure analyses.
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    Critical comparison of potential machine learning methods for lightning thermal damage assessment of composite laminates
    (Taylor and Francis, 2024-10-21) Lee, Juhyeong; Millen, Scott L. J.; Xu, Xiaodong
    The present study assesses the potential of using machine learning (ML) methods to predict the extent of lightning thermal damage in fiber-reinforced composite laminates using three supervised machine learning (SML) algorithms: (1) linear regression (LR), (2) decision tree (DT)-based, and (3) MLP models. These models were based on the 10 most significant factors that influence the severity of lightning damage, including three current waveform parameters, four material configurations, and three orthogonal electrical conductivities of each composite. All models demonstrated good performance with coefficient of determination (R2) values between 0.84 ~ 0.96. The multilayer perceptron (MLP) regression model trained with the lightning matrix damage dataset showed the most promising results (R2 > 0.94). Additional hyperparameter optimization was performed to improve the prediction performance of the baseline MLP model. The hyperparameter optimization (Adam optimizer, tanh activation function, and three hidden layers with 234 neurons) slightly improved the performance of the baseline MLP model by ~0.02, but achieved faster convergence. This result suggests that the baseline MLP model trained with the lightning matrix damage dataset is sufficiently accurate and robust. This paper highlights that ML-informed regression models can serve as an efficient first pass-estimator of lightning matrix damage in composite laminates, potentially reducing the amount of extremely time-consuming and expensive laboratory-scale lightning tests or streamlining the development of complex lightning damage models for future design.
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    The effects of environmental conditions on the failure of double lap composite joints with different overlap lengths and adherend thicknesses
    (Elsevier, 2025-09-01) Paul, Aakash; Xu, Xiaodong; Shimizu, Takayuki; Wisnom, Michael R.
    This paper provides a comprehensive study of the effects of environmental conditions on the failure of Double Lap Joints (DLJ) with composite adherends of different overlap lengths and thicknesses. The environmental conditions tested are Room Temperature Dry (RTD), Hot Temperature Dry (HTD) and Hot Temperature Wet (HTW). The mechanical properties of both the adhesive and composite adherends were characterised at these environmental conditions, showing conflicting trends. A new way of presenting the data based on simple calculations of strength or fracture dominated failure allows all the data to be shown on a single plot, and satisfactorily explains the failure modes, failure loads and opposite trends observed for a total of 13 DLJ configurations tested at the three environmental conditions.
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    Hygrothermal effects on translaminar fracture toughness of quasi-isotropic laminates with different stacking sequences
    (Elsevier, 2023-12-14) Gong, Bowen; Ge, Yuzhong; Wang, Huan; Peng, Hua-Xin; Wisnom, Michael R.; Xu, Xiaodong
    Hygrothermal effects on the translaminar fracture toughness of the carbon/epoxy composite with two different stacking sequences at 120 °C were studied and the failure mechanisms are explained. The eccentrically loaded single-edge-notch tension (ESET) experiments showed that two different quasi-isotropic stacking sequences ([90/45/0/-45]4s and [45/90/-45/0]4s) have negligible difference in translaminar fracture toughness. It was found that the fracture toughness of conditioned specimens at hot temperature wet (HTW) condition increased by 75 % compared to that at room temperature dry (RTD). The average saturated damage height at HTW increased by 48 % compared with that at RTD according to ex situ X-ray computed tomography (CT) observation. The larger saturated damage height observed in the 0° plies of the HTW specimens results in the higher translaminar fracture toughness.
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    Influence of one-dimensional material flow on mechanical properties and fiber orientation distribution of thin-ply carbon fiber reinforced thermoplastics sheet molding compounds
    (Elsevier, 2024-11) Zhao, Zihao; Wan, Yi; Xu, Xiaodong; Takahashi, Jun
    The molding flow of carbon fiber reinforced thermoplastic sheet molding compounds (CFRTP-SMC) is complex and requires a comprehensive understanding of underlying processes. This study investigates the material behavior during compression molding processes, focusing on the influence of the ratio of initial material charge area over mold area (charge ratio) on mechanical properties. The results highlight the CFRTP-SMC material's excellent flowability and moldability and confirm that the mechanical properties and internal morphology change with charge ratios. In addition, a correlation between mechanical properties and internal morphology is established through quantitative analysis of fiber orientation distributions using X-ray computed tomography. This comprehensive investigation not only sheds light on the molding ‘behavior of CFRTP-SMCs, but also underscores the importance of material charge ratios in influencing the mechanical properties. This study also provides a case study for validating numerical process models.
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    An innovative tactile sensor roller for composites inspection
    (IEEE, 2024-06-05) Lu, Zhenyu; Li, Xiaolong; Li, Tunwu; Xu, Xiaodong; Yang, Chenguang
    A vision-based tactile sensor roller prototype has been designed and developed to detect defects on composite prepreg and dry fabric surfaces. The tactile sensor features an innovative design comprising a transparent acrylic tube encased in a gel elastomer. The outer tube serves as a protective and flexible layer, while the inner structure includes a connecting shaft equipped with a camera, force, and speed sensors. This configuration allows for detailed capture of tactile information, integrating visual and pressure data for comprehensive sensory feedback. The connecting shafts are fitted with wheels and handles at both ends, enabling human manipulation and control. Typical defects such as wrinkles, gaps, overlaps and foreign objects and debris (FOD) can be detected by this prototype. In this study, we assessed the performance of the tactile sensor roller by rolling it across areas affected by human-made composite prepreg and dry fabric defects that include wrinkles and foreign objects. With the comparison of the tactile image results, we have demonstrated that the tactile sensor roller can identify flaws with a precision of 0.125mm. It can efficiently examine a 35cm by 18cm section of woven fabric without compromising the integrity of the 3D data gathered. This innovative tactile sensor is set to enhance the automation of the hand layup process. It enables real-time quality control, substantially reducing the need for extensive manual inspections. This leads to a significant cut in inspection costs, making the manufacturing process both more efficient and cost-effective.
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    Observation of damage initiation for trans-laminar fracture using in situ fast synchrotron x-ray radiography and ex situ x-ray computed tomography
    (Springer, 2024-02-21) Xu, Xiaodong; Leung, Nathanael; Jargalsaikhan, Urangua; Bongaers, Evi; Sui, Tan
    Trans-laminar fracture is an important topic for engineering composites. In this study, trans-laminar fracture initiation in quasi-isotropic carbon/epoxy laminates made of non-crimp fabrics was examined using in situ fast synchrotron X-ray radiography and ex situ X-ray computed tomography. The maximum split lengths were measured by in situ radiography and were compared with the predicted values in a detailed FE model using cohesive elements. Ex situ computed tomography scans were also conducted to confirm that no fibre breakage occurs before the final load drop in the experiments. In situ and ex situ observations are complementary for the understanding of damage initiation.
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    On residual tensile strength after lightning strikes
    (Elsevier, 2025-07-01) Xu, Xiaodong; Millen, Scott L. J.; Mitchard, Daniel; Wisnom, Michael R.
    The study of post lightning strike residual strength is still relatively underdeveloped in the literature. Different approaches including in-plane compression or flexural testing have been used, but in-plane tensile loading post-strike has not been studied in detail. Although previous attempts have been made to determine the residual strength using Compression-After-Lightning (CAL) tests on composite laminates, these have been limited and not readily applicable under tensile loads. Therefore, this work completes Tension-After-Lightning (TAL) testing at 75 kA on composite laminates, a more realistic peak current than previously reported for TAL tests, to assess the knock-down in strength post-strike. The measured average TAL failure stress was 716 MPa, a reduction of 23 % from the baseline tensile failure stress of 929 MPa in the literature. This confirms a similar knock-down factor reported at lower peak currents (e.g. 50 kA), but the new TAL specimen geometry ensures that the lightning damage is contained within both the lightning and TAL specimen widths. In addition, a new Finite Element (FE) based virtual test was conducted, considering 0° ply splitting, and validated with the TAL tests herein. The TAL simulation predicted the residual tensile failure stress well, within 6 % of the measured value.
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    A stochastic modelling framework for predicting flexural properties of ultra-thin randomly oriented strands
    (Taylor and Francis, 2025-01) Xu, Xiaodong; Jesus, André; Wan, Yi; Takahashi, Jun
    A stochastic modelling framework is developed to predict the flexural properties of high-strength sheet moulding compounds made of randomly oriented ultra-thin carbon fibre-reinforced thermoplastic prepreg tapes. The model enables reliable designs using ultra-thin randomly oriented strands with less testing, leading to potential applications in automotive primary structures. The stochastic model is based on a Monte Carlo simulation. The flexural modulus is predicted using classical laminate theory, while the flexural strength is predicted by following a Weibull distribution. Fibre discontinuities are considered through stress concentrations introduced by tape overlaps. The results are validated against new 3-point bending and previously reported 4-point bending experimental results. A scaling effect on strength and scatter is predicted, and its implications for structural applications are also discussed.
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    Towards a virtual test framework to predict residual compressive strength after lightning strikes
    (Elsevier, 2023-08-06) Millen, Scott L. J.; Xu, Xiaodong; Mukhopadhyay, Supratik; Wisnom, M. R.; Murphy, A.
    A novel integrated modelling framework is proposed as a set of coupled virtual tests to predict the residual compressive strength of carbon/epoxy composites after a lightning strike. Sequentially-coupled thermal-electric and thermo-mechanical models were combined with Compression After Lightning Strike (CAL) analyses, considering both thermal and mechanical lightning strike damage. The predicted lightning damage was validated using experimental images and X-ray Computed Tomography. Delamination and ply degradation information were mapped to a compression model, with a maximum stress criterion, using python scripts. Experimental data, in which artificial lightning strike and compression testing were performed, was used to assess the predictive capabilities of the framework, considering three lightning strike peak current amplitudes (25, 50, and 75 kA). The framework herein achieved a residual strength prediction within 6% of the experimental values for all peak currents. The relationship between individual lightning damage morphologies (thermal, mechanical and delamination damage) and CAL strength has been numerically established.