Jin Zhou

This study develops an impact-acoustic framework for classifying predefined surface-damage states on steam-turbine blades, identifying one of three damage regions, and estimating class-dependent severity parameters. Impact signals were recorded for 5 s at 22,050 Hz under controlled impact and microphone angles. After event screening, each signal was converted into a 13-coefficient W-MFCC map that combines continuous-wavelet time-frequency localization, Mel-scale subband mapping, and cepstral compression. A hybrid ResNet-50-Transformer-PANet-CMTL network was designed to extract hierarchical local features, model long-range dependencies, fuse multi-scale information, and produce conditional multi-task outputs. The dataset contained 1,200 training samples and 300 validation samples covering crack, crack-erosion, and crack-abrasion conditions in Areas 1-3. On the reported validation split, W-MFCC correctly classified 296 of 300 samples (98.67 %), compared with 89.33 % for MFCC and 87.33 % for wavelet input, and its loss curves showed more stable convergence. The full multi-scale configuration also exhibited smoother training behavior than the ResNet-50 + Transformer baseline. These findings demonstrate the feasibility of combining W-MFCC representation learning with multi-scale conditional prediction for controlled turbine-blade condition assessment.

Tangential interfacial slip behavior of unidirectional (UD) uncured thermosetting prepregs is a critical state-dependent phenomenon in Automated Fiber Placement (AFP). Tangential slip at prepreg-prepreg (P/P) and prepreg-tool (P/T) interfaces directly affects tow steering capability, initiation and propagation of defects (such as wrinkles and tow deviation), which further affects the microstructure, stress distribution, strength, and for aerospace applications the aerodynamic performance of the part. However, there remains significant room for improvement in characterizing multi-variable tangential slip, especially for studying and understanding transient yield-like and orientation-dependent behaviors. The present study experimentally investigates and models these behaviors of the P/P and P/T interface at different interfacial ply angles, compaction pressures and temperatures. A device capable of measuring the interlaminar slip characteristics of prepregs at any interfacial angle was designed, and experimentally tested, with data analysis and microstructural analysis subsequently conducted on T800/AC531 aerospace prepregs. Based on the slip mechanism characteristics, a phenomenological two-channel model was developed to characterize the evolution of the slip force as slippage progressed. Following calibration, the model demonstrates high-fidelity agreement with experimental data. By incorporating multiple experimental factors such as temperature, pressure, and orientation, the model accurately replicated the slip history (for P/P contact and for P/T contact), providing a reliable mathematical model for AFP process simulation and optimization.

Lightweight composite energy-absorbing structures are increasingly required in aerospace vehicles, where in-service low-velocity impacts may compromise their residual crashworthiness and damage tolerance. This study investigates the damage behaviour and residual crashworthiness of lotus stem-inspired multi-cell composite tubes containing transverse impact damage using a combined experimental and numerical approach. An efficient residual-performance prediction framework is developed by employing an impact damage-mapping technique, which enables the accurate transfer of intralaminar damage, interlaminar delamination, and permanent deformation between different analysis models. To further elucidate the energy-absorption mechanisms during impact and subsequent axial crushing, energy absorption and dissipation calculations are integrated into a VUMAT subroutine. The finite element model demonstrates a high level of predictive accuracy for both the transverse impact response and the post-impact compressive behaviour. Using this framework, the effects of circumferential and height impact locations on residual performance are systematically examined. The results show that transverse impact loading markedly affects the energy-absorption characteristics of composite tubes, while the multi-cell configuration reduces the degradation caused by prior impact damage. The residual energy-absorption capacity of the circular tube decreases by approximately 61 %, whereas the multi-cell tube exhibits a more moderate reduction of approximately 23 %. During the impact phase, interlaminar damage dominates energy dissipation, whereas during axial crushing intralaminar failure represents the primary energy-absorbing mechanism. Although circumferential impact locations produce different local responses, their effect on global residual performance is limited; in contrast, impact height has a significant influence on the remaining load-bearing capacity and ensuing failure modes. The proposed framework provides a methodological basis for the damage-tolerant design of lightweight aerospace composite energy-absorbing structures.

This study explores the mechanical performance and failure mechanisms of composite bolted joints under static pull‐through loading by integrating experimental tests and numerical analyses. Three configurations, including the asymmetrical composite joint (ABJ), symmetrical composite joint (SBJ), and shim‐reinforced symmetrical composite joint (RSBJ), are designed and examined via a custom‐designed fixture. The out‐of‐plane bearing strength and damage characteristics of these joints are comparatively analyzed. Test results demonstrate that the stiffness and ultimate bearing load of ABJ are notably inferior to those of SBJ, with respective reductions of 22.27% and 35.62% in these two key parameters. A three‐dimensional numerical model was established via ABAQUS/Explicit 2024 and validated with high accuracy for predicting both the mechanical response and failure modes of joints with all configurations. The intralaminar and interlaminar damage mechanisms were further explored through numerical analyses, indicating that matrix damage and delamination serve as the primary failure modes of the tested joints. The bolt stress distribution patterns across different joint configurations are predicted and analyzed. The findings demonstrate that the symmetrical composite lap joint enhances stress distribution uniformity in the bolt under out‐of‐plane pull‐through loading, and the addition of shims leads to stress concentration near the bolt head, increasing the risk of joint failure.