The present study provides a comparative investigation and discussion on the influence of laminate thickness uncertainty on reliability of laminated composite. Laminate thickness uncertainty in three different scenarios is considered: component level thickness uncertainty, fiber-dominated ply level thickness uncertainty and matrix-dominated ply level thickness uncertainty. Monte-Carlo and Markov-chain Monte-Carlo methods are employed to calculate failure probabilities of symmetric and balanced laminate panels bearing uniaxial and multiaxial loads. It is shown that conventional considerations on laminate thickness uncertainty in the component level could underestimate or overestimate the composite failure probability. Ply level thickness uncertainty primarily caused by fiber or matrix quantity may also result in very different failure probabilities. This study highlights the importance of a thorough analysis and classification of the laminate thickness uncertainty in the ply level in order to achieve confident reliability evaluation of composite structures.

In this letter, compact ultra-wideband filters are designed by employing a novel ridged half-mode folded substrate-integrated waveguide (RHMFSIW) and double-ridged half-mode SIW (DRHMSIW). The RHMFSIW is proposed by loading the half-mode folded substrate integrated waveguide with a ridge, where the ridge introduces additional capacitance hence leading to a lower cutoff frequency and a smaller size. Compact ultra-wideband filters are designed and fabricated based on the RHMFSIW. Another novel DRHMSIW is developed to implement the tight coupling required in the ultra-wideband filters. To improve the out-of-band rejection while keeping a small size, mixed coupling is employed in the ultra-wideband filter to generate transmission zeros. The proposed filters demonstrate the advantage of high selectivity, low loss, compact size, and easy integration with other electronic systems.

The reliability evaluation of fibre reinforced plastic composite structures are currently receiving more attention in industry. However, possible statistical correlation between ply mechanical properties has not been comprehensively concerned. The present study conducts an investigation on the effect of statistical correlation between ply mechanical properties on reliability of fibre reinforced plastic composite structures. The statistics of the ply mechanical properties are derived based on micro-mechanical model, and significant statistical correlation between ply mechanical properties is observed. Then, the failure probability of laminate plates is calculated in cases considering and not considering the statistical correlation, using the Monte Carlo and Markov Chain Monte Carlo methods, respectively. The results highlight the importance of accounting for the statistical correlation between ply mechanical properties to achieve accurate failure probability of laminate plates. Furthermore, it is found that for the multi-layer laminate plate, the statistical correlation between the ply stiffness (including the Poisson’s ratio) significantly affects the laminate reliability while the effect of statistical correlation between the ply strength is minimal.

Recent prediction on the heavy statistical correlation between the mechanical properties of fiber reinforced composite (FRP) raises new concerns on the accurate reliability evaluation of composite structures, but such statistical correlation still lacks experimental verification. In this work, an experimental methodology is proposed to determine the statistical correlation between mechanical properties of unidirectional FRP composite. A rectangular shaped carbon fiber reinforced plastic (CFRP) specimen with a circular hole is loaded by tension, and 3D digital image correlation (DIC) is employed to characterize the heterogeneous strain field around the hole. Virtual field method (VFM) is used to derive E₁₁, E₂₂, ν₁₂, and G₁₂ of specimens. Specimen configuration considering fiber angle and hole diameter is optimized to achieve accurate determination of correlation coefficients. Experimental results on the linear correlation coefficients between E₁₁, E₂₂, ν₁₂, and G₁₂ agree well with previous theoretical predictions.

Neuromuscular Electrical Stimulation (NMES) is commonly used in motor rehabilitation for stroke patients. It has been verified that NMES can improve muscle strength and activate the brain, but the studies on how NMES affects the corticomuscular connection are limited. Some studies found an increased corticomuscular coherence (CMC) after a long-term NMES. However, it is still unknown about CMC during NMES, as relatively pure EMG is very difficult to obtain with the contamination of NMES current pulses. In order to approach the condition during NMES, we designed an experiment with short-term NMES and immediately captured data within 100 s. The repetition of wrist flexion was used to realize static muscle contractions for CMC calculation and dynamic contractions for event-related desynchronization (ERD). The result of 13 healthy participants showed that maximal values (p = 0.0020) and areas (p = 0.0098) of CMC and beta ERD were significantly increased immediately after NMES. It was concluded that a short-term NMES can still reinforce corticomuscular functional connection and brain activation related to motor task. This study verified the immediate strengthen of corticomuscular changes after NMES, which was expected to be the basis of long-term neural plasticity induced by NMES.

Composite structure often shows undesirably significant uncertainty in its mechanical properties, which may consequently result into large stochastic variation of its natural frequency. This study provides stochastic natural frequency analysis of typical composite structures based on micro-scale (constituent-scale) and meso-scale (ply-scale) uncertainty. Uncertainty propagation across micro-scale and meso-scale is investigated. Response surface method (RSM) based on finite element modeling is employed to obtain approximate natural frequency of structures with complex shape or boundary conditions, and mean value and standard deviation of natural frequency of composite plate and cylindrical shell are derived. Differences in natural frequency statistics of composite plates and cylindrical shells derived by considering uncertainty at different scales are quantified and discussed. Significant statistical correlation between ply elastic properties and ply density is observed, and the statistical correlation is demonstrated to lay great influence on the statistics of structure natural frequency.