Durability of viscoelastic fibre prestressing in a polymeric composite

Viscoelastic fibre prestressing (VFP) is a promising technique to counterbalance the potential thermal residual stresses within a polymeric composite, offering superior mechanical benefits for structural engineering applications. It has been demonstrated that the time required for desirable creep strain can be significantly reduced by implementing higher creep stresses, while its long-term reliability is still unknown. Here, we developed the prestress equivalence principle, and investigated the durability of viscoelastic fibre prestressing within a composite, in order to further enrich the prestress mechanisms. The effectiveness of the prestress equivalence principle was refined through Charpy impact testing of prestressed samples with various prestrain levels. The durability was investigated by subjecting samples to both natural aging (up to 0.5 years) and accelerated aging (by using the time-temperature superposition principle). It is found that the prestress equivalence principle offers flexibilities for viscoelastically prestressed polymeric matrix composite (VPPMC) technology; the impact benefits offered by VFP are still active after been accelerated aged to an equivalent of 20,000 years at 20˚C, inferring long-term reliability of VFP-generated fibre recovery within a polymeric composite. These findings demonstrated that both materials and energy con-sumptions could be conserved for advanced composites. Therefore, they promote further steps of VPPMC technology towards potential industrial application especially for impact protections

Lactobacillus rhamnosus GG powder supplementation alleviates intestinal injury in piglets challenged by porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) has become a challenging problem in pig industry worldwide, causing significant profit losses. Lactobacillus rhamnosus GG (LGG) has been regarded as a safe probiotic strain and has been shown to exert protective effects on the intestinal dysfunction caused by PEDV. This study evaluated the effect of LGG on the gut health of lactating piglets challenged with PEDV. Fifteen piglets at 7 days of age were equally assigned into 3 groups (5 piglets per group): 1) control group (basal diet); 2) PEDV group: (basal diet + PEDV challenged); 3) LGG + PEDV group (basal diet + 3×109 CFU/pig/day LGG + PEDV). The trial lasted 11 days including 3 days of adaptation. The treatment with LGG was from D4 to D10. PEDV challenge was carried out on D8. PEDV infection disrupted the cell structure, undermined the integrity of the intestinal tract, and induced oxidative stress, and intestinal damage of piglets. Supplementation of LGG improved intestinal morphology, enhanced intestinal antioxidant capacity, and alleviated jejunal mucosal inflammation and lipid metabolism disorders in PEDV-infected piglets, which may be regulated by LGG by altering the expression of TNF signaling pathway, PPAR signaling pathway, and fat digestion and absorption pathway

Extending Relevance Model for Relevance Feedback

Relevance feedback is the retrieval task where the system is given not only an information need, but also some relevance judgement information, usually from users ’ feedback for an initial result list by the system. With different amount of feedback information available, the optimal feedback strategy might be very different. In TREC Relevance Feedback task, the system is given different sets of feedback information from 1 relevant document to over 40 judgements with at least 3 relevant. Thus, in this work, we try to develop a feedback algorithm that works well on all levels of feedback by extending the relevance model for pseudo relevance feedback to include judged relevant documents when scoring feedback terms. Within these different levels of feedback, it is more difficult for the feedback algorithm to perform well when given minimal amount of feedback. Experiments show that our algorithm performs robustly in those difficult cases.

Indoor environmental quality and pollutant dispersion estimation inside a bus at the downtown areas of Dalian, China

Among most public transport modes, the frequent start-stop urban bus has the most complex micro-environment. Indoor environment quality, airflow patterns, etc. has not been fully understood yet inside buses. In addition, under COVID-19 pandemic, it had been proved aerosol transmission risk might be enhanced inside the buses. Usually, carbon dioxide (CO2) could be considered the index of ventilation effect in enclosed environment, airborne particles are viral carriers. Thus, accurate forecasting of the two abovementioned key pollutants become important. The study analysed the CO2 and airborne particle dispersion inside a bus at the downtown areas of Dalian, China by employing field measurement at spring and autumn, 2021. Temperature, relative humidity, CO2 and airborne particle concentrations were logged by sensors at sampling points respectively, passengers onboard were counted manually. Correlation analysis was conducted and two empirical models for evaluating CO2 and airborne particle were concluded based on the measurement data. From preliminary results, transient concentration of pollutant is almost linearly correlated with cumulative and instant numbers of passenger respectively, with Pearson correlation coefficient larger than 0.8336 for CO2 and 0.8424 for PM2.5. The purpose of the study is to reflect environmental quality inside the bus and provide inspiration into pollution control strategies in buses

Investigation into Micro-Hardness and Wear Resistance of 316L/SiC Composite Coating in Laser Cladding

In order to improve the performance of the cladding layer, this study used the Taguchi orthogonal design to investigate the influence of laser power, scanning speed, gas flow, and SiC powder ratio on the micro-hardness and wear volume of the cladding layer. The results indicate that the SiC powder ratio was the major factor that had the main impact on the micro-hardness and wear volume of the cladding layer. The contribution of SiC powder ratio on the micro-hardness and wear volume are 92.08% and 79.39%, respectively. Through signal to noise ratio conversion and combining grey relational analysis, the multiple objectives optimization was attained. With the target of maximizing the micro-hardness and minimizing the wear volume simultaneously, grey relational analysis was applied to obtain the optimal processing parameters set and predict the corresponding grey relational grade. The error rate was 5.3% between the prediction and experimental validation. This study provides the guidance for optimizing multiple goals at the same time using grey relational analysis about the coating properties deposited by laser cladding in actual industrial applications. It provided theoretical basis for the processing parameters optimization with targeting the micro-hardness and wear resistance

Investigation of Micro-Hardness, Wear Resistance, and Defects of 316L Stainless Steel and TiC Composite Coating Fabricated by Laser Engineered Net Shaping

The influence of processing parameters in laser engineered net shaping (LENS) on the properties of 316L stainless steel and titanium carbide (TiC) composite coating was studied. The key processing parameters were laser power, scanning speed, TiC powder ratio, and powder feed rate. Mathematical models were developed to investigate the micro-hardness, wear volume, and defect area of the coating. The accuracy of the models was examined by analysis of variance and experimental validation. Results showed that micro-hardness was positively correlated with TiC powder ratio. Increasing TiC powder ratio could reduce the wear volume. In addition, the wear volume displayed an increase then decrease with increasing laser power and decreasing scanning speed. Both scanning speed and TiC powder ratio showed a recognizable impact on the defect area. Reducing the scanning speed and TiC powder ratio can effectively reduce the defect area. The targets for the processing parameters optimization were set to maximize micro-hardness, minimize wear volume, and defect area. The difference between the model prediction value and experimental validation result for micro-hardness, wear volume, and defect area were 0.46%, 4.54%, and 8.82%, respectively. These results provide guidance for the LENS processing parameters optimization in controlling and predicting of 316L/TiC composite coating properties

A bistable helical structure based on composite tape-springs

Conventional twistable structures use discrete parts articulated around a number of linkages. These allow only a limited degree of twisting angle, are low in storage ratio, heavy and complex in morphing mechanisms. Double-helix structures are commonly applied to induce twistable shape-changing capability for deployable structures, these being capable of large axial deformations where prestressed thin-shell composite flanges or strips are employed; however, their structural stabilities are susceptible to thermal effects, and suffer from non-zero Gaussian curvature deformation induced by prestressing of the precured flat strips. Here, we propose a novel bistable helical structure, where zero Gaussian curvature deformation applies, and shows more stable and reliable morphing mechanics for a twistable structure to be engineered. This is achieved by exploiting bistable composite tape-spring (CTS) structures, where two CTS samples are pin-joined through spokes to formulate a helical structure. It is capable of large axial morphing, and stable in both the fully extended and twisted configurations, with adjustable storage ratio. A theoretical model was established to predict its bistability and a bespoke axial displacement rig was developed to investigate its non-linear morphing mechanisms in order to reveal the underlying fundamentals. These will facilitate torsional structural design for aerospace deployable structures

Durability of Viscoelastic Fibre Prestressing in a Polymeric Composite

Viscoelastic fibre prestressing (VFP) is a promising technique to counterbalance the potential thermal residual stress within a polymeric composite, offering superior mechanical benefits for structural engineering applications. It has been demonstrated that the time required for a desirable creep strain can be significantly reduced by implementing higher creep stress, while its long-term stability is still unknown. Here, we developed the prestress equivalence principle and investigated the durability of viscoelastic fibre prestressing within a composite in order to further enrich the prestress mechanisms. The effectiveness of the prestress equivalence principle was refined through Charpy impact testing of prestressed samples with various pre-strain levels. The durability was investigated by subjecting samples to both natural aging (up to 0.5 years) and accelerated aging (by using the time-temperature superposition principle). It is found that the prestress equivalence principle offers flexibility for viscoelastically prestressed polymeric matrix composite (VPPMC) technology; the impact benefits offered by VFP are still active after being accelerated aged to an equivalent of 20,000 years at 20 °C, inferring long-term reliability of VFP-generated fibre recovery within a polymeric composite. These findings demonstrated that both materials and energy consumption could be conserved for advanced composites. Therefore, they promote further steps of VPPMC technology toward potential industrial applications, especially for impact protection

Elastic Fibre Prestressing Mechanics within a Polymeric Matrix Composite

The elastic fibre prestressing (EFP) technique has been developed to balance the thermal residual stress generated during curing of a polymeric composite. The continuous fibre reinforcements are prestressed and then impregnated into a polymeric matrix, where the prestress load is only removed after the resin is fully cured in order to produce an elastically prestressed polymeric matrix composite (EPPMC). Although the EFP is active in improving the static mechanical performance of a composite, its mechanics on dynamic mechanical performance and viscoelasticity of a composite is still limited. Here, we established a theoretical model in order to decouple the EFP principle, aiming to better analyse the underlying mechanics. A bespoke fibre prestressing rig was then developed to apply tension on a unidirectional carbon-fibre-reinforced epoxy prepreg to produce EPPMC samples with various EFP levels. The effects of EFP were then investigated by carrying out both static and dynamic mechanical testing, as well as the viscoelastic creep performance. It was found that there is an optimal level of EFP in order to maximise the prestress benefits, whilst the EFP is detrimental to the fibre/matrix interface. The EFP mechanisms are then proposed based on these observations to reveal the in-plane stress evolutions within a polymeric composite