Characterisation and Application of Bio-Inspired Hybrid Composite Sensors for Detecting Barely Visible Damage under Out-of-Plane Loadings.

Traditional inspection methods often fall short in detecting defects or damage in fibre-reinforced polymer (FRP) composite structures, which can compromise their performance and safety over time. A prime example is barely visible impact damage (BVID) caused by out-of-plane loadings such as indentation and low-velocity impact that can considerably reduce the residual strength. Therefore, developing advanced visual inspection techniques is essential for early detection of defects, enabling proactive maintenance and extending the lifespan of composite structures. This study explores the viability of using novel bio-inspired hybrid composite sensors for detecting BVID in laminated FRP composite structures. Drawing inspiration from the colour-changing mechanisms found in nature, hybrid composite sensors composed of thin-ply glass and carbon layers are designed and attached to the surface of laminated FRP composites exposed to transverse loading. A comprehensive experimental characterisation, including quasi-static indentation and low-velocity impact tests alongside non-destructive evaluations such as ultrasonic C-scan and visual inspection, is conducted to assess the sensors' efficacy in detecting BVID. Moreover, a comparison between the two transverse loading types, static indentation and low-velocity impact, is presented. The results suggest that integrating sensors into composite structures has a minimal effect on mechanical properties such as structural stiffness and energy absorption, while substantially improving damage visibility. Additionally, the influence of fibre orientation of the sensing layer on sensor performance is evaluated, and correlations between internal and surface damage are demonstrated.

Acoustic Emission-Based Analysis of Damage Mechanisms in Filament Wound Fiber Reinforced Composite Tubes.

This study investigates the mechanical behavior and damage mechanisms of thin-walled glass/epoxy filament wound tubes under quasi-static lateral loads. The novelty is that the tubes are reinforced in critical areas using strip composite patches to provide a topology-optimized tube, and their damage mechanisms and mechanical performance are compared to that of un-reinforced (reference) tubes. To detect the types of damage mechanisms and their progression, the Acoustic Emission (AE) method is employed, accompanied by data clustering analysis. The loading conditions are simulated using the finite element method, and the results are validated through experimental testing. The findings confirm that the inclusion of reinforcing patches improves the stress distribution, leading to enhanced load carrying capacity, stiffness, and energy absorption. Compared to the reference tubes, the reinforced tubes exhibit a remarkable increase of 23.25% in the load carrying capacity, 33.46% in the tube's stiffness, and 23.67% in energy absorption. The analysis of the AE results reveals that both the reference and reinforced tubes experience damage mechanisms such as matrix cracking, fiber-matrix debonding, delamination, and fiber fracture. However, after matrix cracking, delamination becomes dominant in the reinforced tubes, while fiber failure prevails in the reference tubes. Moreover, by combining the AE energy and mechanical energy using the Sentry function, it is observed that the reinforced tubes exhibit a lower rate of damage propagation, indicating superior resistance to damage propagation compared to the reference tubes.

Multivariable Signal Processing for Characterization of Failure Modes in Thin-Ply Hybrid Laminates Using Acoustic Emission Sensors.

The aim of this study was to find the correlation between failure modes and acoustic emission (AE) events in a comprehensive range of thin-ply pseudo-ductile hybrid composite laminates when loaded under uniaxial tension. The investigated hybrid laminates were Unidirectional (UD), Quasi-Isotropic (QI) and open-hole QI configurations composed of S-glass and several thin carbon prepregs. The laminates exhibited stress-strain responses that follow the elastic-yielding-hardening pattern commonly observed in ductile metals. The laminates experienced different sizes of gradual failure modes of carbon ply fragmentation and dispersed delamination. To analyze the correlation between these failure modes and AE signals, a multivariable clustering method was employed using Gaussian mixture model. The clustering results and visual observations were used to determine two AE clusters, corresponding to fragmentation and delamination modes, with high amplitude, energy, and duration signals linked to fragmentation. In contrast to the common belief, there was no correlation between the high frequency signals and the carbon fibre fragmentation. The multivariable AE analysis was able to identify fibre fracture and delamination and their sequence. However, the quantitative assessment of these failure modes was influenced by the nature of failure that depends on various factors, such as stacking sequence, material properties, energy release rate, and geometry.

Enhancing flexibility and strength-to-weight ratio of polymeric stents: A new variable-thickness design approach.

This paper presents a new design strategy to improve the flexibility and strength-to-weight ratio of polymeric stents. The proposed design introduces a variable-thickness (VT) stent that outperforms conventional polymeric stents with constant thickness (CT). While polymeric stents offer benefits like flexibility and bioabsorption, their mechanical strength is lower compared to metal stents. To address this limitation, thicker polymer stents are used, compromising flexibility and clinical performance. Leveraging advancements in 3D printing, a new design approach is introduced in this study and is manufactured by the Liquid Crystal Display (LCD) 3D printing method and PLA resin. The mechanical performance of CT and VT stents is compared using the Finite Element Method (FEM), validated by experimental tests. Results demonstrate that the VT stent offers significant improvements compared to a CT stent in bending stiffness (over 20%), reduced plastic strain distribution of expansion (over 26%), and increased radial strength (over 10%). This research showcases the potential of the VT stent design to enhance clinical outcomes and patient care.

Shape-Adaptive Metastructures with Variable Bandgap Regions by 4D Printing.

This article shows how four-dimensional (4D) printing technology can engineer adaptive metastructures that exploit resonating self-bending elements to filter vibrational and acoustic noises and change filtering ranges. Fused deposition modeling (FDM) is implemented to fabricate temperature-responsive shape-memory polymer (SMP) elements with self-bending features. Experiments are conducted to reveal how the speed of the 4D printer head can affect functionally graded prestrain regime, shape recovery and self-bending characteristics of the active elements. A 3D constitutive model, along with an in-house finite element (FE) method, is developed to replicate the shape recovery and self-bending of SMP beams 4D-printed at different speeds. Furthermore, a simple approach of prestrain modeling is introduced into the commercial FE software package to simulate material tailoring and self-bending mechanism. The accuracy of the straightforward FE approach is validated against experimental observations and computational results from the in-house FE MATLAB-based code. Two periodic architected temperature-sensitive metastructures with adaptive dynamical characteristics are proposed to use bandgap engineering to forbid specific frequencies from propagating through the material. The developed computational tool is finally implemented to numerically examine how bandgap size and frequency range can be controlled and broadened. It is found out that the size and frequency range of the bandgaps are linked to changes in the geometry of self-bending elements printed at different speeds. This research is likely to advance the state-of-the-art 4D printing and unlock potentials in the design of functional metastructures for a broad range of applications in acoustic and structural engineering, including sound wave filters and waveguides.

Comparison between the Outcomes of Intracoronary and Intravenous Administration of Eptifibatide during Primary Percutaneous Coronary Intervention in Patients with Acute ST-Elevation Myocardial Infarction.

AIM: To compare the outcomes of intracoronary (IC) and intravenous (IV) administration of eptifibatide during primary percutaneous coronary intervention (PPCI) in patients with ST-elevation myocardial infarction (STEMI). METHODS: In this prospective double-blind randomized clinical trial, 76 patients with STEMI selected for PPCI were randomly assigned in two groups to receive either IC or IV bolus of eptifibatide. The primary end point was coronary perfusion assessment by thrombolysis in myocardial infarction (TIMI) flow grade (TFG), TIMI perfusion grade (TPG), and corrected TIMI frame count (cTFC). Secondary end points were left ventricular ejection fraction (LVEF) restoration, ST-segment elevation resolution, and in-hospital major cardiovascular adverse events (MACEs) (including recurrent MI, need for target vessel revascularization (TVR), stroke, and death resulting from any cause) until discharge. RESULTS: Assessment revealed significantly better TFG (95% CI: 1.01-10.26, OR=3.224, P=0.042), more TFG 3 (65.79% vs. 86.11% in IV and IC groups, respectively), better TPG (P=0.024), more achieved TPG 3 and TPG 2＋3 (TPG 3: 44.74% vs. 72.22% and TPG 2＋3: 78.95% vs. 94.44% in the IV and IC groups, respectively) with better cTFC in the IC group (37.33±15.84 vs. 32.53± 20.71 in the IV and IC groups, respectively; P=0.034). LVEF was better restored in the IC group (6.21±8.61% vs. 14.72±5.34% in the IV and IC groups, respectively; P＜0.001) and the ST-segment elevation resolution was better achieved in the IC administration (95% CI: -22.55 to -6.23, P=0.001). There were no recurrent MI, stroke, or need for TVR among patients during the in-hospital stay. CONCLUSIONS: IC administration of eptifibatide during PPCI in patients with STEMI in comparison with IV administration of eptifibatide is associated with significantly better coronary reperfusion and improved clinical outcomes (IRCT2012090510751N1).