Bending Loading Tests Research Articles

Revealing grain refinement and hydrogen trapping mechanism for anti-hydrogen susceptibility of Nb-alloyed 34MnB5 press hardened steel

Hydrogen embrittlement (HE) extant a substantial concern to press-hardened steel (PHS) owing to superior strength. The high strength to light-weight automobile structures necessitates the advancement of superior HE resistance PHS. This study investigated the HE susceptibility of Nb-microalloyed PHS by slow strain rate tensile testing, u-shaped constant bending load test, and thermal desorption spectroscopy. Nb enhances microstructure and HE resistance by introducing retained austenite, refining prior austenite grains (21.14–13.73 μm), forming low-angle grain boundaries, and nano-scale precipitates. Nb-alloyed steel exhibits no-cracking over 300 h under high pre-bending stress and decreases elongation loss up to 48% in hydrogen environment as compared to Nb-free steel. Diffusible H-content in 0.12 wt% Nb-steel reduces to 14.9% of that in Nb-free steel owing to enhanced hydrogen traps, the Fcc/Bcc matrix, and carbide precipitation. The multi-phase microstructure with nano-scale NbC precipitation impeded the localized H-dispersion, enhancing the HE resistance in PHS despite its high strength.

Flexural behavior of assembled FRP-steel Pre-Tightened Teeth Connection (PTTC): Experimental study and failure mechanism

This study focused on understanding the flexural failure behavior of a newly-developed assembled FRP-Steel Pre-Tightened Teeth Connection (PTTC) used for rapid connection of pultruded Fiber Reinforced Polymer (FRP) tubular beams. Four-point bending loading tests were conducted on a specific type of assembled joint that incorporated the FRP-Steel PTTC and threaded connections. The results indicated that each component demonstrated a typical flexural behavior with a desired load-bearing capacity. The assembled FRP-steel PTTC exhibited a gradual occurrence of various failure modes, which significantly differed from those observed under uniaxial compressive or tensile loadings that typically exhibit a more singular failure mode. The initial failure is identified as the local transverse shear failure occurring at the upper junction interface of the composites between the FRP segments and the external steel sleeves. It is thus crucial to carefully assess the stress concentration effects during the design process of FRP-steel PTTC and its assembled joints. Corresponding numerical analysis was performed and compared to experimental results, which demonstrated good agreement in relation to deformation, initial failure modes, and bearing capacity. The comparison results indicated that the developed numerical model is capable of predicting the flexural behavior prior to the initiation of the failure process of the assembled composite joints.

Osteological profiling of femoral diaphysis and neck in aquatic, semiaquatic, and terrestrial carnivores and rodents: effects of body size and locomotor habits

The increased limb bone density documented previously for aquatic tetrapods has been proposed to be an adaptation to overcome buoyancy during swimming and diving. It can be achieved by increasing the amount of bone deposition or by reducing the amount of bone resorption, leading to cortical thickening, loss of medullary cavity, and compaction of trabecular bone. The present study examined the effects of locomotor habit, body size, and phylogeny on the densitometric, cross-sectional, and biomechanical traits of femoral diaphysis and neck in terrestrial, semiaquatic, and aquatic carnivores, and in terrestrial and semiaquatic rodents (12 species) by using peripheral quantitative computed tomography, three-point bending, and femoral neck loading tests. Groupwise differences were analyzed with the univariate generalized linear model and the multivariate linear discriminant analysis supplemented with hierarchical clustering. While none of the individual features could separate the lifestyles or species adequately, the combinations of multiple features produced very good or excellent classifications and clusterings. In the phocid seals, the aquatic niche allowed for lower femoral bone mineral densities than expected based on the body mass alone. The semiaquatic mammals mostly had high bone mineral densities compared to the terrestrial species, which could be considered an adaptation to overcome buoyancy during swimming and shallow diving. Generally, it seems that different osteological properties at the levels of mineral density and biomechanics could be compatible with the adaptation to aquatic, semiaquatic, or terrestrial niches.

Practicability and environmental impact assessment of synthetic fibre reinforced polymer (SFRP) stirrups in reinforced concrete beams

In this study, the objective is to explore the practicability of incorporating synthetic fibre reinforced polymer (SFRP) stirrups into reinforced concrete beams. This investigation revolves around evaluating their effectiveness from two key perspectives: their structural performance and environmental impact. To accomplish this, four set of specimens were prepared, each integrating SFRP stirrups, and testing them under a rigorous three-point bending load test. The structural performance analysis entails a comprehensive examination on the critical design factors such as: the load-deflection relationship and the contribution these SFRP stirrups to improve the ductility performance, flexural stiffness, deformability factor, flexural toughness and energy absorption capacity. The findings of this study indicate that the SFRP stirrups exhibit commendable shear capacity, meeting the necessary requirements, and simultaneously demonstrate satisfactory ductility. It is determined, that the optimal design for these SFRP stirrups involves utilizing narrow and thin stirrups placed at relatively larger intervals. Furthermore, this research delves into assessing the environmental impact of incorporating SFRP stirrups. This assessment enables us to comprehensively evaluate the environmental implications of the entire life cycle of these stirrups in structural beam. Moreover, the analysis reveals that, SFRP stirrups yields lower environmental impacts compared to their steel counterparts, they still provide valuable insights into the overall sustainability considerations within the context of reinforced concrete structures.

Bending performance and failure modes of sinusoidal corrugated sandwich panels fabricated using stereolithography technology: Effects of geometric parameters

The sinusoidal wave corrugated sandwich panel is an exceptional component with outstanding performance, making it highly suitable for both military and civilian applications. Its strength, rigidity, lightweight nature, low density, simple structure, cost-effectiveness, high load-carrying efficiency, remarkable load-bearing capacity, as well as excellent sound insulation and thermal insulation properties, have positioned the sinusoidal wave corrugated sandwich panel as an ideal choice for energy absorption devices. To evaluate the bending performance of the sinusoidal wave corrugated sandwich panel, this study fabricated single-layer and double-layer sinusoidal wave core sandwich panels using the light-curing molding process described in this research. The research analyzed the impact of various geometric parameters, including skin thickness, core layer thickness, core height, and corrugation wavelength, on the bending performance and failure modes of the single-layer sinusoidal wave core sandwich panels through three-point bending loading tests. The failure modes of the sinusoidal wave corrugated sandwich panel were validated using finite element simulation. Additionally, the study examined the bending performance of the sandwich panels with double-layer sinusoidal wave cores and investigated the influence of wavelength distribution in the upper and lower core layers on the force–displacement curve and energy absorption capacity of the double-layer sinusoidal wave core sandwich panel. These findings provide valuable theoretical support for the design of lightweight and high-strength sandwich panels.

Evaluation of ultimate bearing capacity of large-scale perforated beams with variable cross-section: Experimental verification and numerical simulation

In order to meet the requirements of outfitting layout and light weight, circular or elliptical holes need to be opened on the web of the hull beam. Excessive opening will lead to stress concentration and reduce the bearing capacity of the beam. For the super-standard openings, the general strengthening method cannot guarantee the ultimate bearing capacity of the beam, and locally increasing the web to form a variable cross-section beam can compensate for the lost bearing capacity. In the present paper, the three-point bending load tests of variable cross-section opening beams and equal cross-section beams are carried out. Combined with the results of nonlinear finite element analysis, the ultimate bearing capacity and failure mode of transverse bending are compared, and it is verified that the ultimate bearing capacity of beams with variable cross-section openings is better than that of beams with equal cross-section. By changing the cross-section size and optimizing the transition form, the variable cross-section perforated beam is further improved and optimized to enhance the ultimate strength.

Fracture properties of basalt-fiber-reinforced bridge concrete under dynamic fatigue loading

Basalt fibers with different lengths and contents were incorporated into concrete to improve the expansion and extension of microfractures in bridge deck concrete. A fracture performance test of basalt-fiber-reinforced bridge concrete (BFRBC) was conducted using a three-point bending loading test. A fatigue test was performed using a self-designed loading device, and load stress levels of 0.5 and 0.7 were used to investigate the deterioration trend of the fracture toughness of the BFRBC under dynamic fatigue loading. The inhibition effect of basalt fiber on concrete cracks under fatigue loading was investigated. The crack resistance mechanism of basalt fiber on concrete under fatigue loading was revealed by scanning electron microscopy using Image-Pro Plus and MATLAB software to extract relevant crack parameters. The results of the fracture performance of BFRBC showed that basalt fiber with an appropriate length and content can greatly improve the fracture performance of concrete, and 12-mm basalt fiber was adopted in concrete with a content of 0.08%. At a stress level of 0.7 after 200,000 fatigue load cycles, the deterioration of concrete without fiber content was the most significant, and the initial fracture toughness and unstable fracture toughness decreased by 22.67% and 29.28%, respectively. In addition, the crack area density, average crack width, and maximum crack length of the BFRBC decreased by 46.69%, 21.94%, and 21.35%, respectively, because of the incorporation of basalt fiber. BFRBC disperses and transmits cracks through the bridging action of fibers in its internal stresses, delaying the generation and propagation of cracks and, thus, improving the crack resistance of concrete.

An innovative method for improving the cyclic performance of concrete beams retrofitted with prefabricated basalt-textile-reinforced ultra-high performance concrete

Retrofitting reinforced concrete structures (RC) with textile reinforced concrete is an alternative material. In this paper, the primary objective is to develop a novel type of strengthening method for RC structures by utilizing prefabricated textile-reinforced concrete composites. This study examined the flexural behavior of RC beams retrofitted with prefabricated basalt textile reinforced concrete (BTRC) panels. An experimental study was conducted on five retrofitted reinforced concrete beams to demonstrate the effectiveness of this strengthening method. A cyclic four-point bending load test was performed to determine the flexural behavior of BTRC retrofitted reinforced concrete beams. Polymer concrete is used to join the BTRC composite panel, which is constructed from layers of ultra-high performance fiber reinforced concrete (UHPFRC) and basalt textile. A comparison is made between the results obtained using cast-in-situ strengthening and those obtained using textile layers. Based on the results, prefabricated BTRC strengthening method was more effective than cast-in-place strengthening in improving the loading carrying capacity of reinforced RC beams. Compared to cast-in-situ retrofitting, the flexural strength was improved by 56%. In addition, the proposed method for connecting prefabricated BTRC composites to RC beams resulted in the tensile rupture of BTRC layers. As a result, BTRC composites can improve the flexural performance of reinforced concrete beams due to their maximum capacity. This method is an effective and affordable method, and the retrofitting technique was successful. The advantages of this method may outweigh the disadvantages of other methods.

STUDY ON ASSURANCE DESIGN METHOD OF CONNECTIONS AT THE BOTTOM OF COLUMNS IN WOODEN WALL STRUCTURE (PART 3): VALIDATION OF THE CALCULATION METHOD OF DESIGN STRESS OF CONNECTION

The purpose of this series of studies is to propose an assurance design method of connection in wooden wall structure calculated on allowable stress design and to verify its validity. In this paper, tensile, bending and combined load tests for the connection were conducted focusing on transition of uplifting condition, tensile load acting on each fastener and so on. From the test result, the point of deformation that column uplifting vanishes and each fastener’s tensile load could be appropriately predicted by the proposed calculation method. Furthermore, an already-known verification formula for combined stress was applied into the test results.

A mixed stress-strain driven computational homogenization of spiral strands

Spiral strands subjected to tensile force and bending loading display a nonlinear dissipative behavior due to frictional interactions between their elementary wires. This study aims to provide an efficient method, based on a computational homogenization procedure, to accurately characterize the nonlinear response of such strands. By using 1D beam elements in both micro- and macro-scale, homogenization is performed along the axial direction of a representative volume element (RVE), leading to expressing a boundary value problem on RVE, driven in a mixed manner by either strains or resulting forces or moments. The boundary value problem on the RVE is solved using an in–house implicit finite element solver for finite strain, considering all frictional contact interactions. A method is proposed to predict the bending moment’s evolution for any curvature variation from the simulation results of only one bending loading test on the RVE. The nonlinear behavior of the strand in the micro-scale identified through this offline technique can then be used in the macro-model to simulate various bending loading tests under constant tensile load. Results obtained with the multiscale model are compared to those provided by direct numerical simulation to demonstrate the validity of the proposed approach.

The effect of surface treatments on the adhesive bond in all-ceramic dental crowns using four-point bending and dynamic loading tests

The aim of this study was to determine the effect of sandblasting, grinding and plasma treatment on the adhesive bond strength between framework ceramic (Y-TZP) and veneering ceramic (feldspar ceramic). Therefore, four-point bending specimens (n = 180) were cut from densely sintered 3Y-TZP blanks. Subsequently, 80 of these samples received surface treatment by sandblasting and 80 samples by grinding. A reference group (20 samples) was not processed. Half of the specimens that received a surface treatment were additionally exposed to an oxygen plasma treatment. After processing, all specimens were manually veneered with feldspar ceramic and examined with a four-point bending test to evaluate the strain energy release rate G. The surface treatment parameters that achieved the highest and lowest G were transferred to real geometries of a posterior crown (n = 45). The crowns’ ceramic framework was sandblasted and veneered by hand. The all-ceramic crowns were tested in a dynamic loading test and Wöhler curves were evaluated. Four-point bending samples blasted at an angle of 90° at 6 bar and a working distance of 1.5 cm without plasma treatment achieved the highest energy release rate. Samples blasted at an angle of 90° at 2 bar and a working distance of 1 cm with plasma treatment achieved the lowest energy release rate. Overall, plasma treatment did not improve bond strength. In the dynamic loading test, the group blasted with 2 bar showed the best results.

Impedance-based damage assessment of steel-ECC composite deck using piezoelectric transducers

The excellent crack and fatigue resistance of Engineering Cementitious Composites (ECC) materials makes it promising to be used in orthotropic bridge deck system. However, overloading and fatigue load might cause structural damage and, consequently, structural performance degradation. In this work, the piezoelectric lead-zirconate-titanate (PZT) transducers are used to identify the structural damage of the steel-ECC composite deck by implementing both experimental test and numerical simulation. Two steel-ECC composite deck are prepared and four-point bending loading tests are performed on the two specimens to introduce several damage scenarios by gradually increasing the load. The impedance output signals of the piezoelectric sensors are measured under different damage scenarios, and the damage index are extracted to identify the structural damage. A finite element model of the steel-ECC composite deck is established, and the impedance signals with different damage scenarios are calculated and used to assess the structural damages. According to the experimental test and numerical simulation, the impedance-based technology performs to be an effective way to identify the structural damage of the steel-ECC composite deck.

Study on Flexural Behavior of Self-Compacting Concrete Beams with Recycled Aggregates

Currently, numerous studies have focused on the differences in the properties of self-compacting concrete with recycled aggregate (RASCC) and normal concrete (NC), while less attention has been paid to the application of RASCC in reinforced concrete structures. In this paper, four-point bending loading tests were performed on seven RASCC beams and four NC beams, considering the parameter of reinforcement ratio, and the flexural properties were analyzed and compared. The results showed that the failure form, moment–deflection curves, and flexural capacity of the RASCC beams were similar to those of the NC beams. However, the cracking moment and the crack width of the RASCC beams were significantly smaller than that of the NC beams. With an increase in the longitudinal reinforcement ratio, the cracking resistance and flexural capacity of the RASCC beams increased significantly. The cracking moment and flexural capacity could be calculated using the method of the Chinese code GB50010-2010. However, compared with the test values, the predicted deflection was slightly less safe, while the maximum crack width calculation was slightly more conservative. Therefore, the current code formula was revised according to the test results.

Seismic Retrofitting Method Using CFRP Sheets for H-Section Steel Beam with Variable Cross Section

Severe damage to steel bridge piers and steel rigid-frame piers starting from regions of abrupt change in cross section has been widely reported. Therefore, finding a simple and effective seismic retrofitting method for steel structural members with variable cross sections to improve their plastic deformation performance is currently an urgent concern. The objective of this study was to establish an effective seismic retrofitting method for H-section steel beams with abruptly variable cross sections using a carbon fiber–reinforced plastic (CFRP) sheet because of its outstanding properties such as light weight, high strength, and superior durability. Bending and bending-shear cyclic loading tests were conducted with two parameters, including the type of CFRP sheets, and whether or not polyurea putty was inserted between the CFRP sheet and steel beam. The test results indicate that the proposed retrofitting method using intermediate-modulus CFRP and polyurea putty increases the load-carrying capacity, ductility, energy dissipation capacity, and bending stiffness of H-section steel beams significantly without any failure. Further, by implementing finite-element (FE) analyses considering the actual cyclic plasticity properties of steel, anisotropic performance of the CFRP sheets, and nonlinear bond-slip properties of the polyurea putty layer, the cyclic loading test results were reproduced accurately. Moreover, in the cases in which the polyurea putty was applied, parametric FE analysis of the CFRP bonding method with and without creating a stepped length at the top of each CFRP sheet showed that the retrofitting method without the stepped length was similar in effectiveness to the method with the stepped length.

Low-cycle fatigue life and duration-of-load effect for hybrid CLT fabricated from lumber and OSB

Given the nature of cross-laminated timber (CLT), with an orthogonal arrangement and rolling shear characteristics of transverse layers, it has a more complex duration-of-load (DOL) effect than other engineered wood products, such as glued-laminated timber. Developing hybrid CLT (HCLT) with structural composite lumber, which can improve the mechanical properties and material sources of CLT, is gaining increasing interest. Construction oriented strand board (COSB) and spruce-pine-fir (SPF) dimension lumber were used to fabricate HCLT specimens for this study. The regular SPF CLT and HCLT specimens having different lay-ups and numbers of layers were subjected to low-cycle fatigue bending and shear loading tests. The Foschi and Yao damage accumulation model was calibrated using the test results. The DOL factors for the CLT and HCLT specimens were calculated using the stress ratio evaluation method. Results showed that the primary failure modes for the fatigue test specimens were the same as those observed in previous short-term ramp loading tests, and a good fit was observed between the model's predictions and the test data. The DOL factor corresponding to a load duration of 50 years, for a three-layer shear CLT specimen, was determined to be 0.53, which was lower than that recommended in CSA O86-19. The fatigue life and long-term performance of CLT were improved by using COSB panels as CLT layers. The HCLT specimens that used COSB only as the transverse layer showed advantages in fatigue life, long-term performance, and practical applications.

Development of a new evaluation method for orthodontic forces generated in individual patients.

Numerous experimental studies have examined how much orthodontic force is needed to move teeth more smoothly; however, no reports have examined this clinically in individual, living subjects. We aimed to develop a method for quantifying the force exerted on individual teeth by an orthodontic wire to measure how loads placed on crowded teeth change dynamically over time. Accordingly, we fabricated a series of dental casts of patients undergoing orthodontic treatment (using optical impressions and a three-dimensional printer), fitted these models with nickel-titanium wire, and subjected them to bending load tests. During leveling, nickel-titanium wire is generally considered to exert a weak force due to its low elastic modulus, with a weak orthodontic force applied over a long period of time due to its superelasticity; however, we found that the actual energy exerted by nickel-titanium wire is also largely affected by other factors (e.g., amount of crowding).

Effect of the Reinforced Plastic Clamp Fitting on the Bending Strength of the Spruce T-Type Loose Tenon Joints

This article presents the bending strength and flexural properties of the glued T-type spruce loose tenon construction joints with and without reinforced plastic clamp fitting. Construction joints are designed according to Eurocode 5. The samples are made from European spruce (Picea abies Karst.) C24 class construction material with relative wood moisture 18% and relative wood density 410 kg/m3. Samples are assembled with water/high temperature resistant polyurethane adhesive and polyvinyl acetate dispersion adhesive. The total number of samples is 48. The sample width is 95mm and thickness is 45mm. Samples were subjected to moisture, weight controls and 48h stored in the climate chamber before practical bending load test. T-type loose tenon joint construction samples with reinforced plastic clamp fittings glued with polyurethane adhesive under bending load are 2.6% stronger and 13.8% less flexural then without reinforced plastic clamp fittings. T-type loose tenon joint construction samples with reinforced plastic clamp fittings glued with polyvinyl acetate dispersion adhesive under bending load are 9.7% weaker and 20% less flexural then without reinforced plastic clamp fittings. The accuracy of the developed bending strength, deformability and elasticity modulus of the examined construction joints was verified positively by experimental studies.

Influence of GFRP Vertical Stirrups Using NSM Technique on Shear Behavior of Reinforced Concrete Beams with Recycled Coarse Aggregate

Shear strengthening with GFRP rods is the focus of this paper on concrete beams that contain aggregate replacement ratios of thermstone and bonza (pumice materials), obtained from the rubble of demolished buildings. A total of nine beams (2400×160×300mm dimensions) were loaded under a four-point bending load test. The parameters examined in this research were the replacement ratio of lightweight coarse aggregate (20% and 30% volumetric ratio), type of lightweight aggregate replaced by (thermstone or bonza) and strengthened in shear by GFRP rods using NSM technique. The characterization of the tested beams includes ultimate load, failure mode, load-deflection curve, load strain curves of stirrups, bottom longitudinal rebars, GFRP rods at the shear zone of concrete. The results showed that the use of GFRP rods to strengthen concrete beams was effective. As the failure mode was transformed from a shear failure in the reference beam that was cast using normal concrete to a concrete compression failure in the beams which was occurred when using suitable and sufficient amount of strengthening by GFRP rods for selected used lightweight aggregate replacement ratios.

Experimental investigation on mechanical performance of carbon fiber reinforced polymer wire after exposure to elevated temperature

The current study experimentally investigated the influence of elevated-temperature exposure on the mechanical performance of carbon fiber reinforced polymer (CFRP) wires through conducting the axial tensile, three-point bending and transverse load tests. The results show that the CFRP wires under axial tensile load exhibited a brittle fracture after exposure to 30 and 100 °C, and the wires after 200 °C exposure were pulled out from the anchorage. The axial tensile and three-point bending performance of the wires were adversely affected by the elevated temperature; and with the increase of the exposed temperature, the maximum contact force, maximum wire tension, maximum wire tension increment, deflection at fracture and the energy dissipation capacity of the preloaded CFRP wires in the transverse load tests declined. Based on the experimental results, reduction functions were established to quantify the degradation in tensile properties of the CFRP wires after elevated-temperature exposure, and the formulas used for predicting the post-elevated temperature transverse failure responses of the preloaded CFRP wires were proposed. Furthermore, through verification by the test results, the previously established failure criteria are demonstrated to be applicable to assess the failure state of a CFRP wire after evaluated-temperature exposure when subjected to combined tension and bending.

Rotating bending load tests of wheels. Methodological errors

Introduction (problem statement and relevance). Wheels are components that ensure the safety of vehicles. One of the main ways to test the fatigue strength of wheels is a rotating bending load test. The methodology of these tests, regulated by international and national regulatory documents, allows an indirect method for measuring the normalized force effect on the wheels, in which there are always risks of methodological errors.The purpose of the study was to identify potential sources of methodological errors when testing wheels in the bending-rotating mode.Methodology and research methods. Analytical research methods from the field of practical vibration theory were used in the article, considering the critical state of rotating shafts and rotors. Scientific novelty and results. The sources of potential methodological errors and their relationship with the design characteristics of the bench equipment and the wheel itself were determined.Practical significance. Practical recommendations have been given on the change and control of the stand components design characteristics aimed at minimizing errors. The high-speed test modes were determined, in which the error of the test effect on the wheel did not go beyond the normative limits.