Flexural Bending Research Articles

Bending Fatigue Properties of Ultra-High Toughness Cementitious Composite (UHTCC).

Ultra-High Toughness Cementitious Composite (UHTCC) represents a composite material meticulously engineered on the foundation of micromechanical principles. The multi-crack cracking and strain-hardening characteristics of UHTCC enable it to be applied to orthotropic steel decks to control the crack width. Different from most studies which only focus on hybrid fiber or fatigue characteristics, this paper studies the influence of hybrid fiber content on static mechanical properties, flexural toughness, and flexural fatigue characteristics of UHTCC under different stress levels. The compressive and flexural strength, bending toughness, and fatigue damage of UHTCC under different fiber ratios were compared, and the fatigue properties of hybrid fiber UHTCC were verified. The results reveal that hybrid fiber exerts a more pronounced effect on toughness, augmenting the maximum folding ratio by 23.7%. Single-doped steel fiber UHTCC exhibits a characteristic strain-softening phenomenon attributable to inadequate fiber content, whereas the bending toughness index of hybrid fiber UHTCC surpasses that of SF1.5P0 by 18.6%. Under low-stress conditions, UHTCC demonstrates a nearly threefold increase in bending fatigue life with a mere 1% steel fiber content, while the influence of polyvinyl alcohol (PVA) fiber on fatigue life is more significant: with an increase of only 1/5 volume content, the fatigue life increased by 29.8%, reaching a maximum increase of 43.2% at 1/4 volume content. Furthermore, the fatigue damage accumulation curve of UHTCC follows a three-stage inverted S-shaped trajectory. The inclusion of PVA fiber facilitates early initiation of stable cracking during the fatigue failure process, thereby advancing the entire strain stability development stage and mitigating external load forces through the proliferation of micro-cracks. Consequently, compared to SF1P0, the ε0 of SF1P5 experiences a significant increase, reaching 143.43%.

Numerical and experimental study of Yellow River sand in engineered cementitious composite

Engineered cementitious composites (ECCs) represent a significant advancement in concrete technology, addressing the issues and limitations of conventional concrete and environmental challenges related to sedimentation in rivers such as the Yellow River in China. This study investigates the integration of Yellow River sand (YRS) into ECC mix designs for sustainable development. YRS replacement rates (0, 25, 50, 75 and 100%) with quartz sand are systematically analysed through flexural, compressive, uniaxial tensile and four-point bending tests. In addition, scanning electron microscopy and mercury intrusion porosimetry tests are conducted to investigate the micro-mechanical properties. The results reveal that the optimal mechanical performance with 100% YRS substitution improves the compressive and flexural strengths to 26.4 and 11.5 MPa, respectively. These values are 6.20% lower than the those of the 0% substitution rate. Notably, a 100% replacement maintains an ultimate tensile strain of 3.71%, improving the crack width and spacing compared with those at 0%. The average crack width and spacing decrease by 4.87 and 11.2%, respectively, compared with those of 0% substitution. The four-point bending test results show the highest ductility at a 75% substitution rate. Furthermore, a finite-element method model of ECC beams with YRS is developed and validated under the same loading conditions as the experimental data. This study recommends an analytical method for predicting flexural strength compared with the experimental data, enhancing its suitability for sustainable engineering applications.

Optimizing toughness and cost-effectiveness in one-part geopolymers via fiber reinforcement: A comprehensive investigation of PVA, PE, and glass fibers

This study explores developing and characterizing a one-part geopolymer, an innovative and sustainable construction material. The effects of incorporating polyvinyl alcohol (PVA), polyethylene (PE), and glass fibers (GF) on the toughness of slag and fly ash-based one-part geopolymer mortars were investigated through compressive, three-point flexural, and four-point bending tests. The findings demonstrate that fiber incorporation reduces fluidity and compressive strength due to increased porosity, lower elastic modulus of fibers, and weak interfacial bonding. However, fibers significantly enhance damage resistance and toughness via crack bridging and load transfer mechanisms. Formulations with 2 % PVA fibers and combinations of 1 % PVA with 1 % PE fibers and 1 % PVA mixed with 0.5 % PE and 0.5 % GF demonstrate excellent toughness. Notably, the latter two fiber blends achieve 14 % and 10 % cost reductions, respectively, compared to using only PVA fibers, making them economically viable for large-scale applications. Scanning electron microscopy and X-ray diffraction provided insights into the toughening mechanisms, including crack bridging, fiber pull-out, and enhanced stress distribution within the geopolymer matrix. Digital image correlation techniques further elucidated the fibers' role in improving the post-cracking behavior and structural resilience under load.

Structure Formation by 3D-Printing of Cellulose from Cellulose-NMMO-Water Solutions: Analysis of Extrusion, Regeneration, and Drying Stages.

Processing cellulose from 4-methyl morpholine n-oxide (NMMO)-water solutions is a completely circular route that produces biodegradable cellulose fibers or films while recovering reusable NMMO [Guo, Y.; Cai, J.; Sun, T.; Xing, L.; Cheng, C.; Chi, K.; Xu, J.; Li, T. The purification process and side reactions in the N-methylmorpholine-N-oxide (NMMO) recovery system. Cellulose 2021, 28(12), 7609-7617]. Despite proven success in two-dimensional applications, challenges in transitioning to three-dimensional objects arise from the critical changes that cellulose undergoes during deposition, regeneration, and postregeneration stages. While emphasizing the critical diffusion-driven precipitation during regeneration, this investigation explores the influence of extrusion temperature, printing alignment, regeneration, and drying processes on interfilament fusion, bonding, shape integrity, and mechanical properties. Three distinct drying processes: ambient, vacuum, and freeze-drying were investigated. Tensile and flexural bending tests provided insight into the delamination of dried specimens. Ambient and vacuum drying enhanced the properties of specimens, while freeze-drying resulted in a more stable shape. The findings contribute to advancing the understanding of 3D-printing cellulose from NMMO solutions, addressing crucial aspects of the extrusion, regeneration, and drying stages for enhanced applications in sustainable manufacturing.

Direct-write printed controllable concave surface for fabricating flexible metal electrode

Structured surface of flexible substrate could generate a positive impact on flexibility of metal electrode due to the surface free energy relaxation, which could make the flexibility of metal electrode meet the performance requirement of flexible electronics. However, the preparation of controllable structured surface of flexible substrate is still a tough and challenge process. In this research work, controllable concave surface of flexible substrate was prepared by direct-write print with a viscoelastic substrate. When the controllable concave surface of flexible substrate was evaporated with a nanoscale metal layer, various metal electrodes could be obtained with a controllable morphology of concave surface. The direct-write printed concave surface efficiently enhanced the flexibility of metal electrodes. When the prepared concave surface generated a continuous connected structure with a 0.1 mm printing space, an excellently enhanced flexibility of metal electrode was achieved with an internal bending flexibility of 93.72%, external bending flexibility of 93.67%, stretchability of 85% and number of stable cyclic bending times over 12,000. Meanwhile, the direct-write printed concave surface generated a reversed convex surface, which could be used for pressure sensing as a flexible pressure sensor. Therefore, this research work provides an efficient method for fabricating flexible electrode, which has important research and application value in the area of high-performance flexible electronics.

Experimental Design and Analysis of MWCNT, Nanoclay and ZnO Nanofillers on Bi-Directional-Chopped Stranded Glass Fibre Reinforced Epoxy Matrix on Mechanical Properties using L9 and L18 Taguchi’s Orthogonal Technique

Stealth, mechanical and thermal properties, resistance to fire by limiting oxygen and retarding flame can lead to save several human lifes travelling and working in civil, commercial as well as defence air transport and could even develop drone and aircraft meant to escape enemy countries radar tracing and monitoring range. GFRP play very important role in engineering application. The composite manufactured using nanofillers have found to posses better propeties in certain application. In the present work, MWCNTs, Nanoclay and ZnO have been used in GFRP. The developed material can be a promising replacement of composites being used for structural applications in the aerospace sector and space technology apart from the automotives to impart light weight, superior bending and tensile strength. Testing of GFRP infused nanofillers was conducted to obtain the ultimate tensile strength and flexural bending strength of the composite. Experimental design with three Nanofillers as parameters at three levels for optimization of output characteristics with superior properties for structural applications was done using Taguchi’s L9 and L18 orthogonal arrays. ANOVA Analysis was also performed for both L9 and L18 arrays. The effects of three nanofillers infused GFRP was investigated and their impact on tensile and flexural strength were evaluated.

Superhydrophobic Highly Flexible Triple-Network Polyorganosiloxane-Based Aerogels for Thermal Insulation, Oil-Water Separation, and Strain/Pressure Sensing.

Polyvinylpolymethylsiloxane (PVPMS)/polydimethylsiloxane (PDMS) copolymer aerogels were synthesized via consecutive radical polymerization and cohydrolytic polycondensation of vinylmethyldimethoxysilane and dimethyldimethoxysilane, followed by supercritical drying or ambient pressure drying. The resultant PVPMS/PDMS copolymer aerogels exhibit a highly porous, tunable triple-network structure consisting of interlinked hydrocarbon polymers, PVPMS and PDMS. These aerogels display superhydrophobicity (151°), low density (109 mg cm-3), low thermal conductivity (29.8 mW m-1 K-1), and adjustable pore structure. The combination of good machinability, low thermal conductivity, excellent compressive elasticity and bending flexibility, and efficient organic solvent adsorption gives these aerogels broad application prospects in thermal insulation and oil-water separation. In addition, PVPMS/PDMS/carbon nanotube (CNT) composite aerogels were obtained by incorporating the conductive CNTs, followed by vacuum drying. The resultant PVPMS/PDMS/CNT composite aerogel exhibits high sensitivity with a broad pressure sensing range in strain and pressure sensing applications.

Contact detection in a rib-reinforced vacuum driven actuator with an embedded CSR bridge sensor

ABSTRACT Stable control and accurate sensing are necessary for the safe operation of soft robots, and flexible sensors that can follow the flexible movements of soft robots are needed. In this paper, flexible bending sensors are embedded in a rib-reinforced vacuum-driven actuator with no risk of rupture, considering the application of flexible sensors to human cooperative work and wearable devices. The bending sensor is a bridge circuit with conductive silicone rubber (CSR) for variable resistance. The CSR bridge sensor consists of four CSRs that capture deformation and a circuit with a conductive coating spray printed on a laminated sheet. The sensor value is the output voltage divided by the input voltage, and the effects of the drift and input voltage variations are canceled out. The bending sensor embedded in the silicone actuator has a linear relationship, and the rib-reinforced vacuum driven actuator provides angle PID control for continuously changing reference inputs by feeding back sensor estimated angle. Furthermore, contact detection was established by using the pressure estimated from the CSR bridge sensor and the pressure sensor error as the threshold. The algorithm provides reliable contact detection and force estimation with actuator response thresholds and anti-chattering.

Flexural behaviours of concrete-filled stainless-steel tubular beams under cold-region low temperatures

Applications of concrete-filled square (or circular) stainless-steel tubes keep increasing in cold-region coastal engineering structures. However, their behaviours under low-temperature bending have not been fully investigated, which brings obstacles to their engineering applications. To address this issue, this paper investigated flexural behaviours of concrete-filled square/circular stainless-steel tubular beams (CFSSSTBs/CFCSSTBs) at low temperatures through eight four-point bending tests. The main studied parameters were low temperatures (20∼−60 ℃) and cross-section type (circular or square shape). Test results showed that both CFSSSTBs and CFCSSTBs exhibited flexural failure and exhibited excellent ductility under low-temperature bending benefiting from the excellent ductility of stainless steel; bending resistances of CFSSSTBs and CFCSSTBs were improved by 5% and 22%, respectively. This study also developed finite element models (FEMs) for simulations on flexural behaviours of CFSSSTBs/CFCSSTBs at low temperatures. The FEMs considered both low-temperature material and geometric nonlinearities. Validations against eight tests proved the capacities of FEM simulations on low-temperature flexural behaviours of CFSSSTBs/CFCSSTBs. Finally, the code equations in Eurocode 4 and AISC 360 were used to predict the stiffness and ultimate bending resistances of CFSSSTBs/CFCSSTBs. Validations showed that the code equations underestimated the bending resistances of CFSSSTBs/CFCSSTBs. This study provided fundamental information on the flexural bending mechanism of CFSSSTBs/CFCSSTBs) at low temperatures.

Mechanical properties of an improved flexible auxetic metamaterial and its application in self-expanding vascular stents

Auxetic metamaterials have shown great significance in the field of cardiovascular stents, but improving their applicability remains an issue. Here, we develop a type of improved auxetic metamaterial called the Re-entrant-Arrow-Snake (RAS) structure by adding arrow-shaped and snake-shaped structures to the Re-entrant (RE) structure. We first systematically study its in-plane elastic properties and compression behaviors. It is observed that the RAS structure exhibits improved vertical stiffness, horizontal flexibility, and clear auxetic effect in the vertical direction. The influence of the additional structures on the deformation pattern and the stability is also discussed by the in-plane compression analysis. Furthermore, we propose a new self-expanding (SE) vascular stent named RAS-SE based on the RAS structure. Numerical analysis demonstrates that the RAS-SE stent possesses enhanced dual-plateau radial force, negative foreshortening behavior, and improved bending flexibility, indicating better deployment performance and support in clinical applications. Biomechanical studies also show that axial deformation caused by the auxetic effect of the RAS-SE stent only slightly increases stress damage to plaque without affecting stress damage of the intima. This study further expands the application of metamaterials in SE vascular stents, and the proposed RAS structure shows high applicability on the SE stent, thus warranting further attention.

The effect of Al2O3 content on the microstructure and properties of Al/Al2O3 functionally graded material

This study aims to survey effect of Al2O3 content on the microstructure and also the physical and mechanical properties of Al/Al2O3 which functionally graded material (FGM) that are manufactured by the powder metallurgy technique. For this purpose, five-layer Al/Al2O3 green part samples with Al:Al2O3 different weight ratios were fabricated by cold pressed under 620 MPa. After compaction, the samples were sintered for 1 h in a nitrogen atmosphere at a temperature range between 600 °C and 640 °C. An optical microscope and a field emission scanning electron microscope (FESEM) were used to evaluate the Microstructural characterization. The Archimedes density, Vickers hardness and flexural strength of sintered samples were measured. The highest relative density of 95 % was achieved at a sintering temperature of 640 °C on lower Al:Al2O3 weight ration variation on Al/Al2O3 FGM sample. The hardness values gradually changed in cross section of different FGM samples from 31 HV to 65 HV which depend on the sequence of Al2O3 content in different layers. However, the highest flexural bending strength of 70 MPa was obtained at the sample on Al/Al2O3 FGM included the compositions of 35, 25, 15, 5, 0 wt% Al2O3. By decreasing Al2O3 content along Al/Al2O3 FGM, the changing semi-brittle or brittle to ductile failure mechanism was observed. In some fabricated FGM samples observed a few cracks in the interfacial region between layers with high Al2O3 content.

Experimental validation of auxetic stent designs: three-point bending of 3D printed Titanium prototypes.

Numerical simulations have demonstrated the superior bending flexibility of auxetic stents compared to conventional stent designs for endovascular procedures. However, conventional stent manufacturing techniques struggle to produce complex auxetic stent designs, fueling the adoption of additive manufacturing techniques. In this study, we employed DMLS additive manufacturing to create Titanium Ti64 alloy stent prototypes based on auxetic stent designs investigated in a previous study. These prototypes were then subjected to experimental three-point bending tests. The experimental results were replicated using a finite element model, which showed remarkable accuracy in predicting the bending flexibility of four auxetic stents and two conventional stents. Although this validation study demonstrates the promising potential of DMLS and other additive manufacturing methods for fabricating auxetic stents, further optimization of current stent design limitations and the incorporation of post-processing techniques are essential to enhance the reliability of these additive manufacturing processes.

A study on the effect of the geometric properties and surface defects on silicon chip flexibility for wearable electronics

A study on the effect of the geometric properties and surface defects on silicon chip flexibility for wearable electronics

Low-energy avionic piezoelectric deicing system

Piezoelectric actuators are widely used in several applications and are becoming increasingly attractive in aircraft and industrial contexts, mainly when efficiency and economical energy conversion are required. One of these applications is the avionic piezoelectric deicing system. Piezoelectric actuators are considered as a potential solution for developing a low-energy ice protection system for aircraft. This type of system applies vibration to the structure by activating its own resonant frequencies to generate sufficient stress to break the ice and cause it to delaminate from the substrate. The deicing mechanism depends strongly on the chosen excitation mode, whether it is flexural (bending) mode, extension (stretching) mode, or a combination in between, hence affecting the efficiency and effectiveness of the deicing process. In this contribution, a proof of concept of a deicing system utilizing lightweight piezoelectric actuators with minimal power requirement is proposed. Deicing was demonstrated with a power input density of 0.074 W cm−2 and a surface ratio of 0.07 piezoelectric actuators per cm2. First, a numerical method for positioning piezoelectric actuators and choosing the proper resonance mode was validated to assist in the system’s design. Then, the numerical method was used to implement piezoelectric deicing on a more representative structure of an aircraft wing or nacelle. Finally, a converter topology adapted for deicing application was proposed.

Influence of Stitch Angle on the Flexural Response of Composite Structures

Utilizing lightweight composites in aerospace vehicles plays a pivotal role in sustainability by improving fuel efficiency and mitigating emissions. However, due to their low interlaminar strength, delaminations and microcracking degrade their strength and stiffness properties. Through-thickness stitching improves the interlaminar strength, thus increasing the delamination tolerance of composite structures. Therefore, in this study, the influence of repeated periodic stitching patterns, stitched at three different angles (0, 45, and 90°) w.r.t. the transverse direction, on the flexural properties of stitched composites is investigated. The strain distributions of these specimens were obtained using a single continuous optical fiber bonded to the tensile surface of the specimens. The results show that stitching at a 45° angle produced lower strains and higher flexural strength and bending modulus when compared to the stitched and unstitched laminates. An increase of 32.3 and 47.4% in the flexural strength and bending modulus were obtained, respectively, with reference to the unstitched laminates. The failure morphology of specimens was also analyzed using optical microscopy and revealed that the stitch seams arrested delaminations. However, due to the 45° angle, the damage progressed along a longer distance, thus resulting in an increased ultimate failure load.

Experimental study on flexural behavior and bending capacity prediction of Q550E steel beams within corroded shear span

An experimental study is carried out to investigate the degradation behavior of Q550E HPS steel beams with corroded shear span. At first, tensile tests of 15 pieces of steel are undertaken to obtain the degradation law of mechanical property parameters. Four steel beams with different corrosion damage levels in shear span are designed by electrochemical accelerated corrosion. The flexural loading tests of corroded steel beams are conducted, and the mechanical response of local corrosion to steel beams behavior is discussed. The necessity of lateral bracing is discussed theoretically. Considering the constitutive model affected by corrosion and the role of stiffeners, a predictive model of bending bearing capacity is proposed. The results show that the increasing corrosion damage will cause the failure position to move from mid-span to shear span, and the failure mode will shift from mid-span compressive flange buckling to bending-shear buckling, and finally appear web buckling. Corrosion damage level higher than 10% will lead to insufficient strain development. The proposed model can predict the flexural capacity and deflection well. Compared with the test results, the bearing capacity and deflection of corroded HPS beams are predicted by the nonlinear iterative method with high accuracy.

Lateral load behavior of shear connections between steel storage racks and the spine bracing with posts

High-rise steel storage racks are cold-formed thin-walled steel frames, which achieve their lateral strength and stiffness by the use of a spine bracing system in the down-aisle direction commonly located at a short horizontal distance away from the main rack frames. The shear connections between the main rack frame and the spine bracing system play a dominant role in the effectiveness of the spine bracing system. This paper experimentally investigates the behavior of the shear connections used in industrial practice between a steel storage rack and the spine bracing system with posts using four groups of three nominally identical connection specimens. By employing a digital image correlation (DIC) system, the tests generate comprehensive data and establish the real-time deformation fields of individual components of such shear connections. Based on the component-based approach, a linear-elastic analytical model is developed for the type of shear connections under consideration. The proposed analytical model explicitly captures the behavior of the individual connection components, including the three-dimensional flexural bending of endplates, as well as the distortions of the open sections of the upright and the bracing post. Based on the proposed model, this paper quantifies the contribution of each component towards the total deformation of the shear connections. The investigation establishes that the cross-sectional distortion of the bracing post and the out-of-plane bending of the upright web are the most flexible components of such shear connections. Recommendations associated with the shear connections under consideration are proposed for the rack designers and manufacturers.

Velocity profile in steady flow with submerged flexible vegetation based on multi-factor-dependent drag coefficient

Flexible submerged vegetation plays a pivotal role in ecosystem. Understanding the complex impact of flexible vegetation bending on flow drag is crucial. The wide variability in drag coefficients within flexible vegetation poses challenges in accurately predicting flow drag. In this paper, the developed prediction model of velocity profile based on multi-factor-dependent drag coefficient is derived based on Euler-Bernoulli beam assumption, dual-layer averaged velocity model and the relationship between the averaged inclination angle of bent vegetation and Cauchy number. This model makes it possible to calculate the drag coefficients and velocity profiles at the same time, instead of using an assumed constant drag coefficient, and the application of this prediction model is highly favorable with experimental data. Meanwhile, new function of the depth-averaged drag coefficient applicable to submerged and emergent vegetation are presented, describing its relationship with the deformation angle of canopy, Reynolds number, submergence and water depth. The result shows that the drag coefficients for the same vegetation are smaller at higher submergence and Reynolds number. The findings of this study may provide valuable insights into the variability of drag coefficients and the flow structure with submerged flexible vegetation, and being applicable for the restoration and management of freshwater ecosystems.

Composite Delta Beam for Slim Floor Construction

Abstract: The structural behaviour of the composite Flush Beam for slim floor as a whole has been investigated. The deformation behaviour of the structural members Steel beams with trapezoidal cross-sections and specially punched webs were developed as composite beams in slim floors. The estimation of the flexural stiffness and bending capacity of composite slim beams is rather complicated, because the influence of many factors should be taken into account. These factors include variable section dimensions, Profile of the beam, stiffness of the beam and interaction between steel and concrete. In this paper, analytical investigations have been conducted to investigate the deflection behaviour of Flush beam specimens under monotonic loading. A design procedure is developed for composite slim floor Flush beams based on cross-sectional analysis and the flexural properties of the slim floor beams are evaluated. From the analytical investigation it was found that the deflection of delta beam is 48% less than the conventional I-beam More over the stiffness of the Delta beam is 49.8% higher than the I-beam

Modified plastic damage model for steel fiber reinforced concrete

AbstractSteel fiber reinforced concrete (SFRC) structures have been widely adopted and attracted great research attention due to their excellent performance in resisting tension and flexure bending. However, the existing analytical and numerical analyses of SFRC structures rely mainly on the experimental data of material tests, thereby being suitable for a case‐by‐case basis. This is due to the lack of a general and reliable constitutive material model for SFRC, which analytically considers the fiber‐dependent parameters such as fiber geometry, fiber stiffness, and interface properties of fibers and concrete matrix. This study presents an approach to modify the concrete plastic damage model to represent the SFRC material constitutive relations for simulating the structural behavior of SFRC. In this approach, the general procedure to integrate the bridging effect of fibers through the pull‐out mechanism into the constitutive relation of SFRC was proposed. The comparison between the numerical and experimental results was conducted to verify the reliability of the proposed model. The results demonstrated the proposed model could well represent the material performance of SFRC and the numerical simulations could capture reasonably the effect of the volume fraction, geometry, and properties of fibers on the structural response of SFRC.