Composite Load Research Articles

Effect of Stress Ratio and Loading Inclination on the Fatigue Life of Carbon-Fiber-Reinforced Polymer Composites: Multiscale Analysis Approach

The integration of mesoscale modeling and macroscale experimentation has emerged as a promising approach for understanding and predicting the mechanical behavior and fatigue performance of fiber-reinforced polymer composites. In this work, the mean field homogenization technique is implemented to predict the fatigue performance of the carbon-fiber-reinforced polymer composites under cyclic loading conditions. To predict the number of fatigue cycles, Modified Gerber criteria are used with the stress-based Tsai–Hill failure indicator. Fatigue strength factor (α) and creep rupture strength factor (β) are experimentally evaluated and further implemented in a computational approach to predict fatigue life cycles of the composite. The effect of composite constituents, stress ratio, and loading direction are investigated in detail against the fatigue performance of the composite. Fatigue cycles are predicted at individual matrix and fiber levels at various stress ratios of 0.2, 0.4, 0.6, and 0.8 at different loading inclinations. The experimental results are compared with the mesoscale S–N curves.

Fracture evolution characteristics of strainburst under different gradient stress

AbstractStrainburst often occurs in the loading process of tangential stress concentration from surrounding rocks after excavation and unloading of deep rock mass. The concentrated tangential stress is relatively larger on the tunnel walls, which decreases towards the interior of surrounding rocks with a certain gradient. To explore the fracture evolution characteristics of surrounding rocks under different tangential gradient stresses and understand various phenomena in the strainburst process, a large‐scale true‐triaxial gradient and hydraulic‐pneumatic composite loading rockburst test device was adopted to carry out the strainburst tests under four different gradient stresses. Based on the macroscopic failure phenomena, distribution of rockburst debris, macro‐micro morphology of failure cross section, and monitored data of acoustic emission (AE), the fracture evolution of rockburst specimens was analyzed under different stress gradient loadings. The results indicate that the stress gradient has an obvious influence on the fracture characteristics, resulting in different rockburst phenomena. With the increase of stress gradient, the failure stress of rockburst decreases, while the dynamic failure characteristics of rockburst trends to be significant. The increase of stress gradient contributes to higher fragmentation degree of debris, more uniform distribution and better continuity. The total number of cracks in the model decreases with the rise of the stress gradient, and the proportion of shear failure increases, which is the main reason for the enhancement of the rockburst intensity.

The influence of saturation and loading angle on sandstone damage characteristics after freeze-thaw cycle

The strength deterioration and fracture tendency of freeze-thaw rock determine the construction and operation safety of rock engineering. This article conducted compression-shear composite load tests on sandstones with various saturations to examine the failure law of rocks in cold climates and the contributing elements of strength degradation. It was found that with an increase in saturation and loading angle, the compressive strength and elastic modulus dropped. The concept of freeze crack threshold and saturation threshold was proposed. The peak shear stress was negatively correlated with saturation and positively correlated with loading angle. The σ CI (crack initiation stress) and σ CD (crack damage stress) in the saturated state were only 39.91% and 45.18% of those in the dry state. Serious damage occurred at high saturations, which is consistent with the scanning electron microscopy results. The σ CI and σ CD under 30°loading angle are 49.72% and 42.91% of those under uniaxial, respectively. This is mainly due to the change of the failure mode from tensile-shear failure to combined tension-shear failure, and finally to single-shear failure. A strength prediction model was established based on sandstone damage characteristics. The research results have important reference value for rock engineering design in frigid climates and complex load environments.

Ductile fracture simulation on 10.9 HP bolts under composite loading at elevated temperatures

AbstractThe mechanical properties of the bolts deteriorate significantly at elevated temperatures; accurate prediction of the performance and fracture behaviour of steel bolted connections is essential for the fire safety assessment of steel structures and is a prerequisite for performance‐based fire safety design. Existing studies on the fracture mechanical properties of bolts at elevated temperatures are limited due to the difficulty and economics of testing. This paper presents the numerical analysis of combined loads on grade 10.9 high‐performance (HP) bolts. Based on the proven fracture analysis method, the fracture behaviour of HP bolts at high temperatures was investigated by fitting material parameters. Significant changes in the fracture shape of the bolts at high temperatures were found. The ultimate resistance, fracture deformation behaviour and strength reduction factors were analyzed. This study demonstrates the potential of using numerical analysis to reasonably predict the fracture behaviour of steel bolted joints at high temperatures and under complex loading conditions.

Wide-Area Composite Load Parameter Identification Based on Multi-Residual Deep Neural Network.

Accurate and practical load modeling plays a critical role in the power system studies including stability, control, and protection. Recently, wide-area measurement systems (WAMSs) are utilized to model the static and dynamic behavior of the load consumption pattern in real-time, simultaneously. In this article, a WAMS-based load modeling method is established based on a multi-residual deep learning structure. To do so, a comprehensive and efficient load model founded on combination of impedance-current-power and induction motor (IM) is constructed at the first step. Then, a deep learning-based framework is developed to understand the time-varying and complex behavior of the composite load model (CLM). To do so, a residual convolutional neural network (ResCNN) is developed to capture the spatial features of the load at different location of the large-scale power system. Then, gated recurrent unit (GRU) is used to fully understand the temporal features from highly variant time-domain signals. It is essential to provide a balance between fast and slow variant parameters. Thus, the designed structure is implemented in a parallel manner to fulfill the balance and moreover, weighted fusion method is used to estimate the parameters, as well. Consequently, an error-based loss function is reformulated to improve the training process as well as robustness in the noisy conditions. The numerical experiments on IEEE 68-bus and Iranian 95-bus systems verify the effectiveness and robustness of the proposed load modeling approach. Furthermore, a comparative study with some relevant methods demonstrates the superiority of the proposed structure. The obtained results in the worst-case scenario show error lower than 0.055% considering noisy condition and at least 50% improvement comparing the several state-of-art methods.

Deformation and fracture mechanisms of Ti-55531 alloy with a bimodal microstructure under the pre-tension plus torsion composite loading

The deformation and fracture behavior of the Ti-55531 alloy with a bimodal microstructure (BM) under the pre-tension plus torsion composite loading were systematically investigated at room temperature. The results indicate that the pre-tension loading dramatically reduces the subsequent torsional strength of the alloy, while its torsional plasticity is almost not affected. A (101¯0) prismatic slip is initiated inside the primary equiaxed α (αp) phase during the pre-tension stage. Subsequently, several dislocation jogs form inside the αp particles due to the crossing of the (0002)[1¯ 2 1¯ 0] basal and (11¯01) [1¯ 2 1¯ 0] pyramidal slip systems during the torsion deformation stage, which may be a novel deformation mechanism of the Ti-55531 alloy. Moreover, the αp particles are cut by numerous parallel slip bands, resulting in ladder-like structures be formed at the αp/βtrans (β transformed microstructure) interface, which can promote microcrack initiation at the αp/βtrans interfaces. Furthermore, {101¯1}α deformation twins are only detected inside secondary α (αs) phase just during the subsequent torsion deformation stage. In the main bearing phase, the αp particles elongate along specific directions in different deformation regions due to a change in the maximum shear stress. Thus, the cross-section profile from the surface to the center of the specimens after the pre-tension plus torsion deformation can be divided into three regions: torsion, tension plus torsion, and tension deformation regions. These findings can provide a theoretical basis for understanding the deformation damage of aerospace components under complex loads and optimizing their structural design.

Novel Strategy for Engineering Ultra-Thin Proton Exchange Membranes for Advanced PEM Fuel Cells

The energy needs of the modern world currently relies heavily on fossil fuels and energy conversion technologies that emit greenhouse gases (GHGs). These GHGs have been shown to have a detrimental impact on global climate. Climate change has created a vital shift in the way society thinks about energy conversion and storage. Today we are seeing huge increase in the demand for utilization of renewable energy sources (solar, wind, and etc.) as well as in their integration with zero-carbon emission energy conversion and storage devices such as fuel cells, water electrolyzers, and batteries. The renewable energy sources are intermittent by nature since the wind does not always blow and the sun does not always shine. This creates a need for a way to store excess green energy that would otherwise be wasted when the demand does not meet the production. Development of advanced Proton Exchange Membrane (PEM) water electrolyzers and fuel cells that can be integrated with renewable energy sources to convert the excess electricity to hydrogen, is the most efficient approach for sustainable energy storage and utilization. Development of such sustainable energy systems is of primary importance for implementation and widespread application of the green energy technologies in our everyday life and elimination of the GHG emissions. Low temperature Polymer Electrolyte Membrane Fuel Cells (PEMFC) are the most promising type of fuel cells for application in the transportation sector. Currently, the commercialization of these devices is hindered by their high cost and limited durability. Further research is needed to increase their efficiency, power output, catalyst utilization, and durability. Fabrication of thinner proton conductive membranes, is one of the strategies that are of particular research interest. Successful development of thinner PFSA membranes will result in reduction of the ohmic resistance of the MEAs, cost reduction, and will improve their performance. Fabrication of thinner PEM membrane is a challenging task that requires innovative engineering approaches that will allow to fabricate ultra-thin, pinhole free membranes with the desired mechanical stability and hydrogen crossover suppression properties. This work aims on development of novel approaches for engineering ultra-thin PEM membranes with thicknesses below 10µm, and to perform a systematic study of the membrane thickness impact on the MEAs cost, activity, and durability performance. In addition, the effect of various reinforcement materials on the membrane properties have been studied, and their optimal concentrations and position in the volume of the membrane has been investigated. All PEM membranes of interest have been fabricated with a state-of-the-art ultrasonic spray deposition method, designed, and developed at UConn. This methodology allows for precise control of the thickness and composition of the thin membranes, as well as of the thickness, composition, and precious metal loading in the catalysts layers. The newly designed MEAs have been tested at real fuel cell operating conditions, and the results will be presented and discussed in detail at the 243rd ECS meeting in Boston, MA.

Micromechanics based analytical model for composites subjected to combined torsion-compression loading

A micromechanics based analytical model under combined loading for unidirectional composites has been developed. The peak compressive load predicted from the combined loading analytical model is compared with the experimental results of carbon epoxy pultruded rod having a volume fraction 60%. The specimens were subjected to torsional load under rotational control and longitudinal compressive load using displacement control. The model captures the compressive strength of the composite subjected to remotely applied shear stress. It is observed that the peak compressive strength of the composite decreases linearly with an increase in shear stress. The analytical modeling results are in good agreement with the experiment data. The analytical model and the experimental results are used to find the effect of shear stress on longitudinal compressive loading. The peak compressive strength caused in the presence of applied shear stress and compressive load and the effect of shear on the compressive strength are predicted using a 2D analytical model in this study. The model results are confirmed using experimental data from combined loading.

Inactivation of E. coli and S. aureus by novel binary clay/semiconductor photocatalytic macrocomposites under UVA and sunlight irradiation

The disinfection efficiency of several novel photocatalytic macrocomposites made of Ecuadorian clay mixed with two semiconductor materials (TiO2, ZnO) has been evaluated with Staphylococcus aureus and Escherichia coli as target bacteria. They have been tested under two irradiation sources (UVA lamp and sunlight) in different configurations. Two different semiconductor/clay ratios (60/40 and 80/20) were tested at 10–20 g·L–1 (with UVA) and 20–40 g·L–1 (with sunlight) composite loadings. With the presence of the photocatalyst, a four- to five-fold increase in the inactivation rate by UVA was observed with respect to single UVA inactivation, while the performance with sunlight reaches up to six-fold. The particular effect of nature, ratio and loading on the inactivation kinetics depends on the specific bacterial species tested. In this case, the inactivation of S. aureus was faster in comparison with E. coli, probably due to the interaction between bacteria and the catalytic material and the associated ζ-potential. In general, the 80% ZnO composites at maximum loading show the highest efficiency, comparable to that of nanosized semiconductors. The ability of these composites to maintain a high disinfection efficiency after three uses, together with their low cost and ease of recovery, make these composites an attractive option for wider use in water disinfection facilities.

Influence of Layer-Thickness Proportions and Their Strength and Elastic Properties on Stress Redistribution during Three-Point Bending of TiB/Ti-Based Two-Layer Ceramics Composites

A mathematical model was developed to determine the order of failure of layers in a two-layer ceramics composite and to determine the conditions for achieving the maximum limit load under three-point loading. The model was set in the space of three “bilayer parameters”: the ratio of the thickness of the lower layer to the whole thickness of the beam, the ratio of Young’s moduli of the lower layer to the upper layer, and the ratio of flexural strengths of the materials of the lower layer to the upper layer. The adequacy of the model obtained was confirmed by experimental results on the three-point bending of the experimental specimens. The experimental samples were two-layer composites consisting of a cermet layer TiB/Ti and a layer of α-Ti. The samples were obtained by free self-propagating high-temperature synthesis (SHS) compression and with varying their thickness. The results obtained make it possible to predict in advance which layer, based on the specific bilayer parameters, will trigger the brittle fracture mechanism as well as to set the maximum destructive load of bilayer composites.

Buckling of Laminated Composite Cylnidrical Panels Ijnder Transverse Load

The bubHing of laminated composite cylindrical shell panels subjected to transverse load is investigated. The geometrical non-linear analysis is carried out using thefinite element method based o,n a higher-order shear deformation theory. An eight nodded degenerated isoparametric shell element with nine degrees of freedom at each node is considered. The geometric non-linear behaviour and the collapse pressures ere presented for symmetrically and antisymmetrically laminated cross-ply and angle-ply cylindrical shell panels subiected to uniform normal pressure.

Online correction of the transient voltage security region boundary based on load parameter variations in power systems

The transient voltage security region (TVSR) is an essential part of the dynamic safety region of a power system, which represents the safe operating region of the transient voltage where there is no loss in stability. The power system load significantly affects the transient voltage stability. However, the load model in the existing power systems, which considers the security region of the dynamic process, is too simple to comprehensively characterize the load characteristics of the dynamic process. Furthermore, it neglects the influence of the load model parameters on the dynamic process security region. In this study, a composite load model with distributed photovoltaic power is used as the research object. The main load parameters affecting the voltage stability and the generator nodes that are sensitive to the load parameters are calculated using the trajectory sensitivity method. The TVSR of the system is constructed based on the load and generator’s active powers. The correlations between different load-leading parameter combination scenarios and TVSR boundary points are mined using the CatBoost learning framework. Thus, the TVSR boundary can be promptly corrected online based on the changes in the load parameters, and the system security boundary can be described more accurately. The proposed method is verified using the IEEE39 and IEEE118 node systems. It is observed that the proposed method can correct the TVSR boundary online with high precision corresponding to real-time changes in the load model parameters. This provides a more accurate TVSR boundary for the power system operation scheduler, which helps in guiding it to control the system more accurately.

Interfacial interaction of controlled poly(ether-imide) (PEI) - titanium dioxide-based nanocomposites

The nanocomposites were produced using a melt-blending process and poly (ether imide) (PEI) reinforced with bioactive titanium dioxide (TiO2) nanoparticles. Fourier Transformed Infrared Spectroscopy (FTIR), Microstructural analysis, Differential Scanning Calorimetric (DSC) of the generated interfacial interaction materials is exploited. The prominent peaks in FTIR measurement are found to be sensitive to TiO2 content. The peaks shift towards higher wavelength as a consequence of TiO2 addition. Polymer matrix and filler in the FTIR spectrum have a significant hydrogen bonding coupling. The uniform dispersion of TiO2 nanoparticles within the polymer was studied without surface treatment or polymer functionalization. It has been observed that with increasing TiO2 concentration, the matrix's crystallisation rate was altered from promotion to retardation, while its crystalline structure remained unaffected. TiO2 addition gradually lowers the glass transition temperature (Tg) of poly (ether imide) composite. The polymer matrix was concurrently made stiffer, stronger, and tougher by the nanoparticles, and the best characteristics were attained at 5.0 wt% of TiO2. Even though the nanocomposites had improved thermal stability and glass transition temperatures, they also showed less water absorption. The analyses are utilised to determine the type of nanoparticle and the consistency of the composite material's loading.

An efficient method for estimating energy losses in distribution's feeder

This paper explains a simple and efficient methodology for calculating monthly energy losses (EL) using the load loss factor technique and a representative composite load profile. One of the important benefits of the proposed work is a simpler, more efficient and less rigorous method to estimate the system-wide energy loss of an extensive distribution network with reasonable accuracy. The sum of all EL provided by each feeder section is used to calculate the total feeder EL. A base case feeder with a typical cable type and power factor is used to generate regression equations, a peak power loss function to estimate the EL. A case study is then used to show the models and techniques that have been established. The result indicates a high level of agreement with the time-series load flow simulations (smaller than 10% deviations). With this model, an approach to estimate the EL of all radial feeders of various configurations and characteristics could be extended and implemented. The spreadsheet approach is ideal for completing a quick energy audit of existing distribution feeder EL and determining the sensitivity of distribution network efficiency to changes in feeder sections and load characteristics.

An efficient method for estimating energy losses in distribution's feeder

This paper explains a simple and efficient methodology for calculating monthly energy losses (EL) using the load loss factor technique and a representative composite load profile. One of the important benefits of the proposed work is a simpler, more efficient and less rigorous method to estimate the system-wide energy loss of an extensive distribution network with reasonable accuracy. The sum of all EL provided by each feeder section is used to calculate the total feeder EL. A base case feeder with a typical cable type and power factor is used to generate regression equations, a peak power loss function to estimate the EL. A case study is then used to show the models and techniques that have been established. The result indicates a high level of agreement with the time-series load flow simulations (smaller than 10% deviations). With this model, an approach to estimate the EL of all radial feeders of various configurations and characteristics could be extended and implemented. The spreadsheet approach is ideal for completing a quick energy audit of existing distribution feeder EL and determining the sensitivity of distribution network efficiency to changes in feeder sections and load characteristics.

Temperature-directed fluorescent switchable nanoparticles based on P3OT–PNIPAM nanogel composite

Poly(N-isopropylacrylamide) (PNIPAM) is a unique stimuli-responsive material that exhibits a lower critical solution temperature (LCST). Owing to this characteristic temperature-dependent behavior, PNIPAM has found extensive utilization as an active material in various applications, including sensors, drug delivery, and cellular imaging. Herein, we demonstrate temperature-directed fluorescent switchable nanoparticles based on poly(3-octylthiophene-2,5-diyl) (P3OT) nanoaggregate-embedded PNIPAM nanogel composites (POPNs) featuring different crosslinker contents. The amount of P3OT loading in the nanogel composites can be gradually controlled by varying the crosslinking density of the PNIPAM matrix; this may be attributable to the efficient entrapment of P3OT nanoaggregates in case of a dense polymeric network with the increase in crosslinking density. POPNs exhibit dramatic temperature-dependent fluorescence enhancement (by a factor of 2.11). This is based on the environmental changes affecting fluorescent P3OT chains at temperatures below and above the LCST of the PNIPAM matrix. Based on this temperature-directed fluorescent switching capability, POPN could find potential applications in various fields, including biomedical imaging and sensors.

The Effect of Laminated Layers on the Flutter Speed of Composite Wing

The paper presents an investigation to the flutter speed of composite wing for different ply orientation. Structurally the composite wing was idealized as a composite beam load carrying structure. Theodorsen’s expression was used to get the 2- dimension unsteady lifting force and pitching moment in the limit of incompressible flow and subsonic speed which were integrated over the wing span. A free vibration analysis was first carried out to get the natural frequencies and mode shapes .The velocity-damping (V-g) method was used to calculate the flutter speed and the flutter frequency. A wing of unmanned aerial vehicle was manufactured from woven glass and polyester resin where the flutter speed was calculated experimentally by the wind tunnel test .The flutter speed was calculated analytically for different ply orientation, it is found that the increasing in torsion rigidity leads to increase in the flutter speed, the fiber combination with high torsion rigidity and relatively low coupling rigidity give higher flutter speed.

Strongly bonded CFx@S composite assisting the long-cycle stability of Li-S battery

Lithium‑sulfur battery (LSB) has drawn extensive concentration for its high energy density. Nevertheless, the “shuttle effect” of polysulfides leads to inferior sulfur utilization and short service life. Herein, CFx@S composites with a strongly bonded interface of S and CFx have been prepared by a simple solvent evaporation method. The research shows that CFx in the composites will be preferentially discharged to form F-doped carbon (F@C) conductive network and LiF, which improve the electronic and ionic conductivities of electrodes, separately. Numerous polar sites on F@C cooperate with the polar LiF to adsorb polysulfides effectively and then inhibit the “shuttle effect”. The robust F@C conductive network and the SEI film enhanced by LiF can work together to relieve the volumetric dilatation of S in the charge/discharge cycles. Profiting by the above-mentioned merits, even the as-prepared 10-CFx@S composite loads a sulfur content as high as 87.6 %, it manifests an excellent rate capability and stable cycling performance. Under a high current of 1600 mAh g−1, 10-CFx@S delivered a high capacity of 573 mAh g−1 in the initial discharge, and it remained as 334 mAh g−1 after 800 cycles with an average capacity decay of 0.052 % per cycle. This research supplies an easy and feasible approach to promote the performances of LSB.

Application of high‐performance DIC for a comprehensive evaluation of biaxial fatigue crack growth experiments

AbstractPrecise determination of the remaining service life of technical components requires sufficient knowledge of fatigue crack growth behaviour and the growth rate of defects. Cracks in real components often experience multiaxial far field stresses due to their complex geometry and composite loadings acting on it. Digital image correlation (DIC) is well established for crack length and displacement measurements, but it usually requires sample preparation with speckle paint and interferes with mechanical extensometers. To overcome these limitations, we use a novel 2D DIC system combining a graphics processing unit (GPU) with a CoaXPress 2.0 camera, acquiring up to 3 GB/s of image data. It enables real‐time evaluation of both integral strain like an extensometer and full‐field DIC on images selected automatically in real‐time. This combination enables the use of one single sensor for strain‐controlled testing and fatigue crack growth characterisation. The full‐field displacement is compared to a finite‐element model (FEM) simulating the actual crack contour measured by the DIC system. The results show that high‐performance DIC has the potential to simultaneously simplify crack‐growth experiments and provide comprehensive fracture mechanical information.

A comparative study on the inhibitory effects imposed on earthworms by brewery and rice mill wastewater

Of late, vermifiltration (VF) technology has gained major attention from researchers as a sustainable wastewater treatment alternative in which the treatment of wastewater has been driven by earthworms (EWs). Apart from parametric effects, the composition, biodegradability/complexity, hydraulic and organic loading rates (HLR/OLR), and the concentration of organics present in wastewater exhibit inhibitory effects on EWs, declining the treatment efficiency of vermifilters (VFs), which have not been adequately explored. Hence, the present study dealt with the assessment of such inhibitory effects on the survival, growth, and reproduction of EWs using four kinds of wastewater. Results indicated that EWs sustained the flow of rice mill, real brewery, synthetic brewery, and the mixture of real brewery and domestic wastewater for 5–11, 11–21, 20–40, and 23–45 d, respectively, before reaching 50% mortality, at the HLR of 8–4 m3/m2-d. For each wastewater, the lowest HLR (4 m3/m2-d) yielded the highest growth of EWs. The mixture of real brewery and domestic wastewater provided the most favorable conditions for the reproduction of EWs, ensuring the highest number of cocoons (8–12 nos./EW) and juveniles (11–26 nos./EW) produced per EW, followed by synthetic brewery (cocoon: 3–9 nos./EW; juvenile: 5–18 nos./EW), real brewery (cocoon: 2–7 nos./EW; juvenile: 2–12 nos./EW), and rice mill wastewater (cocoon: 1–5 nos./EW; juvenile: 2–8 nos./EW), with the HLR varying inversely with the reproduction rate of EWs. Hence, the mixture of real brewery and domestic wastewater portrayed the least biological inhibition on EWs, whereas rice mill wastewater had the highest. Outcomes of the present study revealed that the VF technology is best suited for remediating the mixture of real brewery and domestic sewage, can substantially remediate synthetic brewery wastewater, and may treat real brewery and rice mill wastewater after an appropriate pretreatment. The premixing of real brewery wastewater with rapidly biodegradable and low-strength domestic sewage at a specific volumetric ratio improved the treatability of the former using the VF technology attributed to the enhanced biodegradability and reduced organic strength of the wastewater mix.