Three-point Bending Research Articles

Shape Sensing of Resin Pipe with a Helical-winding Optical Fiber in Bending Test

In this study, we developed a shape-sensing technique for a pipe. An optical fiber was helically bonded on the outer surface of a resin pipe whose length, outer diameter and inner diameter are 3200 mm, 34 mm, and 26.6 mm, respectively. Firstly, four grooves were made on the surface along the pipe in a helical pattern with the same pitch of 360 mm. At the one pipe end, adjacent grooves were offset by 90 degrees and the offset was maintained along the pipe. The single-mode fiber was put into a groove and fixed by epoxy and then it was embedded into the adjacent groove. Consequently, the optical fiber was going back and forth twice along the pipe. At the pipe ends, there were stress-free fibers between the grooves. Shape sensing for the pipe is conducted as follows. 1. Strain distributions along the grooves are measured by a distributed fiber-optic strain sensing system. 2. The bending strain is extracted from the measured strain to calculate the curvature and bending angle. 3. The shape of the pipe is reconstructed based on the curvature and bending angle using the Frenet-Serret formulas. Three-point bending tests were conducted. In the tests, the pipe ends were clamped to be the fixed ends and a point load was applied to the pipe center. Strain distributions were measured by tunable wavelength coherent optical time domain reflectometry (TW-COTDR) or optical frequency domain reflectometry (OFDR). Then the pipe shape was reconstructed as described above. We compared the reconstructed shape with the deformation calculated by finite element analysis and the agreement was excellent. If we insert the developed pipe into a bedrock and reconstruct the pipe shape continuously, it is expected that we can detect cracks or damage in the bedrock. This approach is expected to make rock excavation constructions safer.

Dynamic flexural strength of Aluminosilicate glass with a perspective of impulsive and quasi-impulsive responses: An experimental–numerical coupled evaluation

The flexural strength of glass is a critical design parameter for applications encountering impact loadings. However, the micro defects, specimen geometry, loading rate, and load transformation from a quasi-dynamic to quasi-impulsive state may influence the measurement accuracy. Due to the stochastic and amorphous nature of the material, an accurate determination of the flexural strength remains a challenge. In this two-fold study, a coupled experimental–numerical strategy was devised to evaluate the dynamic flexural strength. In the first phase, three-point bending experiments were conducted on a novel “Electromagnetic Split Hopkinson Pressure Bar (ESHPB)”. The incident stress signal and fracture time were recorded from experimental data, while the flexural strength was indirectly computed from a numerical algorithm. A quantitative comparison of the flexural strength with those in existing literature established the accuracy of the proposed methodology. Results of the study indicate that the specimen response became independent of the support conditions under impulsive loading. That being said, the specimen behaved like it had an infinite span length, and the measured flexural strength remained the same whether the specimen was supported or not. Besides, the specimen also maintained contact at the interfaces of the incident bar and fixture supports for the entire loading duration. In the second part of this study, the computed flexural strength was used to calibrate the existing JH-2 model. Numerical prediction of the damage propagation corroborated with that obtained from reprography images, though qualitatively. This work presents a precise and robust methodology to determine the dynamic flexural strength of brittle ceramics like Aluminosilicate glass over traditional experimental procedures to facilitate its adoption.

The influence of sub-surface damage microstructure on ultra-thin die flexural strength

In the semiconductor industry, where miniaturization is a key driver, mechanical properties of ultra-thin dies are increasingly important research topics. Sub-surface damage (SSD) is a common issue in wafer thinning processes, but there is a lack of research on the relationship between SSD microstructure and ultra-thin die strength. In this study, the influence of SSD microstructure on flexural strength was investigated through three-point bending tests of ultra-thin dies prepared by distinct wafer-thinning methods, coupled with SSD microstructure characterization. Flexural strength was highest for dies dry polished with N pad, intermediate for dies dry polished with M pad, and lowest for dies with fine grinding. We researched SSD microstructure by high-resolution transmitted electron microscope (HRTEM), revealing that it comprises amorphous regions, micro-cracks, and high-density distortion areas. The SSD of the fine grinding samples was thick and intermittent, with observable micro-cracks. Comparatively, the SSD structure from M pad polishing was uniform but thicker, whereas SSD from N pad polishing was thinner but exhibited greater variability. SSD thickness not only influences the average value but also dictates the distribution of flexural strength. This research enhances the understanding of SSD microstructure's impact on ultra-thin die flexural strength, providing valuable insights for optimizing wafer thinning processes to enhance die reliability.

Evolution of fracture process zone and variation of crack propagation velocity in sandstone

To solve the safe containment and recovery efficiencies of gas in rock masses, a study on fracture process zone (FPZ) and crack propagation is conducted. By using digital image correlation technology, the displacement of three-point bending specimens was measured. By analyzing the distributions of displacement at different loading stages, a specific region between the pre-crack tip and the loading point was divided into three zones: the intact zone, the crack propagation zone, and the FPZ. The length and the migration velocity of FPZ were determined, and the crack propagation velocity was also measured. The microstructures in FPZ were investigated through optical microscopy, x-ray diffraction analysis, and x-ray photoelectron spectroscopy. The results show that (1) FPZ length slightly varies during crack propagation and the FPZ is fully formed at the peak load; (2) the average value of the bond energy (446.7 eV) in the grains is greater than that (296.7 eV) in the matrix, thus the microdamage appears in the matrix around grain boundaries in FPZ; (3) the mean FPZ length varies from 4.09 to 8.42 mm for all tested specimens during crack propagation; (4) the propagation of the crack and the migration of FPZ proceed simultaneously in the loading process, and both velocities of crack propagation and FPZ migration are almost the same and with the same trend; (5) the peak velocity of crack propagation appears after the peak load, and the crack propagation progress was intermittent due to fracture energy accumulation, fracture energy release, and FPZ's shielding effect.

Experimental investigation on shear behavior of cracked reinforced concrete beams strengthened with carbon textile reinforced concrete

This study examines the strengthening effects of carbon textile-reinforced concrete (CTRC) on the shear behavior of pre-cracked reinforced concrete beams. Six reinforced concrete beams, each with an aspect ratio of 1.6, underwent three-point bending tests, comprising two control specimens and four strengthened specimens. Prior to the application of U-wrapped carbon textile reinforcement, all beams were subjected to pre-loading to induce shear cracking. The strengthening process involved utilizing either two or three layers of carbon textile. The findings reveal a significant enhancement in the shear capacity of the CTRC-strengthened beams compared to the control beams. Notably, the shear strength of the specimens reinforced with two layers of carbon textile increased by 34.7%, whereas those reinforced with three layers increased by 50.9% compared to the control specimens. Thus, carbon TRC effectively restored and elevated the shear capacity of damaged specimens to levels akin to those of control beams.

Comparative investigation of mechanical properties in banana fiber and ramie fiber composites enhanced by SiC nanoparticles

This research explores into analyzing the mechanical characteristics of banana fiber and ramie fiber composites bolstered with silicon carbide (SiC) nanoparticles. The integration of SiC nanoparticles aims to amplify the mechanical robustness and endurance of these natural fiber composites. Through water absorption assessments, we evaluated the composites’ resistance to moisture. In addition, we assessed the mechanical performance via hardness, impact, and three-point bending tests. The results indicate a significant enhancement in the mechanical attributes of both banana and ramie fiber composites due to SiC nanoparticle inclusion. The results reveal a notable enhancement in mechanical characteristics following the incorporation of SiC nanoparticles. Notably, composites containing 8% SiC nanoparticles demonstrated the highest hardness value of 102 HV and the lowest water absorption percentage of 1.5%. In addition, these composites exhibited a superior flexural strength (80 MPa) and modulus of elasticity (4.3 GPa), alongside a maximum impact energy absorption of 18 J. These findings underscore the beneficial influence of SiC nanoparticles on the mechanical properties of the composites, including increased strength, reduced water absorption, enhanced hardness, and improved impact resistance.

Evaluation of flexural strength and microhardness in Vaccinium macrocarpon (cranberry)-added self-cure polymethyl methacrylate dental resin: An in vitro study.

Occurrence of denture stomatitis and prosthesis breakage are common problems faced by elderly people wearing removable dentures. To overcome this, several attempts are made to improve the denture material by addition of antimicrobials without compromising original properties. The aim of the study was to evaluate flexural strength and microhardness of self-cured polymethyl methacrylate (PMMA) denture base resin after addition of Vaccinium macrocarpon (commonly called as cranberry), extract as antimicrobial, at varying proportions. Experimental in vitro study. Frozen cranberry fruits were subjected to extraction process in the presence of aqueous solvents. Lyophilized extract was added in proportions of 0, 0.5, 1.0, 1.5, and 2.0 dry wt/wt % into polymer of self-cure PMMA denture base resin. Based on cranberry inclusion, the study comprised one control (0%) and four test groups (0.5%-2%) with total of 100 samples. A three-point bending test for flexural strength was done for fifty study samples (n = 10). Surface of fractured samples was analyzed using a scanning electron microscope (SEM). Microhardness was determined using Vickers hardness test. One-way statistical ANOVA test was done to find the difference between groups, followed by Tukey's post hoc test for multiple pairwise comparison. Flexural strength ranged from 66.80 to 69.28 MPa, and a statistically insignificant difference was observed between groups (P > 0.05). SEM evaluation showed uniformly dispersed strands of cranberry extract in PMMA matrix. With higher concentration, less voids were seen. Vickers microhardness value significantly decreased from 15.96 in the control group to 14.57 with 2% cranberry addition (P < 0.05). Incorporation of cranberry extract into self-cure PMMA denture base resin, up to 2 dry wt %, did not decline the flexural strength. However, there was a significant decrease in Vickers microhardness values when compared against the control group (0% cranberry inclusion).

Experimental investigation on shear behavior of cracked reinforced concrete beams strengthened with carbon textile reinforced concrete

This study examines the strengthening effects of carbon textile-reinforced concrete (CTRC) on the shear behavior of pre-cracked reinforced concrete beams. Six reinforced concrete beams, each with an aspect ratio of 1.6, underwent three-point bending tests, comprising two control specimens and four strengthened specimens. Prior to the application of U-wrapped carbon textile reinforcement, all beams were subjected to pre-loading to induce shear cracking. The strengthening process involved utilizing either two or three layers of carbon textile. The findings reveal a significant enhancement in the shear capacity of the CTRC-strengthened beams compared to the control beams. Notably, the shear strength of the specimens reinforced with two layers of carbon textile increased by 34.7%, whereas those reinforced with three layers increased by 50.9% compared to the control specimens. Thus, carbon TRC effectively restored and elevated the shear capacity of damaged specimens to levels akin to those of control beams.

TYPES OF TREATMENT AND FAILURE MODE OF CEMENTITIOUS MORTARS REINFORCED WITH SUGARCANE BAGASSE

The entire scientific community now agrees that sustainable development depends on environmentally friendly and renewable materials. Thus, all government policies are taking numerous steps to encourage research in this direction. The aim of the present work is to study the fracture mechanism of Sugarcane Bagasse (SCB) mortars as a function of the different treatments applied to the bagasse.To achieve this, two different types are applied toSCB. These were treatment in a sodium hydroxide solution and heat treatment at 200°C. Mortars reinforced with these different types of bagasse were then produced. The volume fractions of SCB used were 0%, 3% and 6%, giving M0 for reference mortar, MBr3 and MBr6 for mortars with untreated SCB reinforcement, MBt3 and MBt6 for mortars with heat-treated SCB reinforcement, MBc3 and MBc6 for mortars with sodium hydroxide-treated SCB reinforcement. Three-point bending tests at 28 days of age were carried out on specimens of dimensions 4×4×16cm3 obtained from the different formulations, to determine the flexural strengths. The fracture surfaces of the specimens were analyzed to understand the fracture mechanism as a function of the type of treatment applied to the SCB.The results of the studies show that all the formulations containing SCB have a flexural strength greater than that of the control mortar, with the highest strength found in the MBt6 mortar. Analysis of the fracture surfaces shows that mortars containing untreated and heat-treated SCB exhibit failure by ravelling. However, mortars containing SCB treated with sodium hydroxide break by fiber rupture.

Experimental Study on Fracture Toughness of Shale Based on Three-Point Bending Semi-Circular Disk Samples

A large number of construction practice projects have found that there are many joints and microcracks in rock, concrete, and other structures, which cause the complexity of rock mechanical properties and are the main cause of geological or engineering disasters such as earthquakes, landslides, and rock bursts. To establish a rock fracture toughness evaluation method and understand the distribution range of fracture toughness of Longmaxi Formation shale, this study prepared three-point bending semi-circular disk shale samples of Longmaxi Formation with different crack inclination angles. The dimensionless fracture parameters of the samples, including the dimensionless stress intensity factors of type I, type II, and T-stress, were calibrated using the finite element method. Then, the peak load of the samples was tested using quasi-static loading, and the load–displacement curve characteristics of Longmaxi Formation shale and the variation in fracture toughness with crack inclination angle were analyzed. The study concluded that the specimens exhibited significant brittle failure characteristics and that the stress intensity factor is not the sole parameter controlling crack propagation in rock materials. With an increase in crack inclination angle, the prefabricated crack propagation gradually transitions from being dominated by type I fracture to type II fracture, and the T-stress changes from negative to positive, gradually increasing its influence on the fracture. An excessively large relative crack length increases the error in fracture toughness test results. Therefore, this paper suggests that the relative crack length a/R should be between 0.2 and 0.6. The fracture load distribution range of shale samples with different crack angles is 3.27 kN to 10.92 kN. As the crack inclination angle increases, the maximum load that the semi-circular disk shale samples can bear gradually increases. The pure type I fracture toughness of Longmaxi Formation shale is 1.13–1.38 MPa·m1/2, the pure type II fracture toughness is 0.55–0.62 MPa·m1/2, and the T-stress variation range of shale samples with different inclination angles is −0.49–9.48 MPa.

Experimental investigation of prestressed beam made from ultra-high performance fibre reinforced concrete

The paper presents experimental results prestressed beam made of high-strength fiber reinforced concrete. The I-shaped beam with a height of 0.2 m and a length of 2.8 m was tested in a four-point scheme until the bending load capacity was achieved. The element was prestressed with one tendon Y1860S7 with a diameter of 12.5. The fiber reinforced concrete was made with KrampeHarex DM12.5/0.175 fibers. Concrete was tested in compression (fc ≈ 110 MPa) and in tension, checking the resistance in both the splitting test (fct,sp ≈ 17.5 MPa) and the three-point bending test (fct,fl ≈ 11.9 MPa). After fabrication and prestressing of the beam, changes in strains on the element's surface were observed for 19 days, after which destructive test was conducted. During the test deflections and deformations of the element were recorded. The failure was as a result of bending and followed yielding of the prestressing strand and the subsequent formation of one localised crack. The calculation of the load carrying capacity in the light of the SIA 2052 standard, assuming the elasto-plastic material model of the fibre reinforced concrete, showed good agreement with the experimental results

Experimentally calibrated viscoelastic phase-field fracture method of thermoplastic resins

In the past few years, there has been considerable emphasis on investigating fracture behavior in composite materials using the phase-field fracture (PFF) method. However, accurately characterizing the viscoelasticity of the matrix necessitates employing the viscoelastic PFF method, and there remains an ongoing debate regarding the precise determination of the viscous driving force introduced in this methodology. This study aims to propose a feasible calibration method for quantifying the viscous driving force. To achieve this goal, benchmark experiments utilizing Polyetheretherketone (PEEK), a typical thermoplastic resin, are carried out by designing uniaxial tension tests, three-point bending tests, as well as compression tests at various strain rates. Through employing the viscoelastic PFF method, we discuss the effect of strain rate and viscous driving force on mechanical response. Our findings reveal a non-linear relationship between the influence of viscous driving force and strain rate with an initial increase followed by a subsequent decrease. By combining simulation results with experimental data analysis, the viscous driving force value is determined. The results demonstrate that our proposed approach is reliable for quantifying the viscous driving force in the viscoelastic PFF method, laying a foundation for investigating the mechanical response of composite materials.

Damage characterization of high- and low-temperature performance of porous asphalt mixtures under multi-field coupling

Porous asphalt (PA) have attracted considerable interest due to their functional advantages such as significant water permeability and noise attenuation properties. Nevertheless, its vulnerability to damage significantly hinders its widespread application. Therefore, this paper aims to investigate the damage characteristics of PA's high- and low-temperature performance under the coupled effects of moisture and temperature. Firstly, Hamburg Wheel-Tracking Test (HWTT) and three-point bending tests were conducted on PA under different coupling conditions. Subsequently, its damage characteristics were analyzed using the three-stage permanent deformation model, logistic model, and two-way analysis of variance (ANOVA) method. The findings indicate that under dry conditions, PA-13 exhibits a linear decrease in rutting resistance within the temperature range of 40–60 °C, followed by a significant decrease at 70 °C. During immersion in water, PA-13 undergoes a second and third-stage rutting evolution process, with an accelerated creep rate observed at 70°C. High temperatures exacerbate the viscoelastic damage of PA-13, while multi-field coupling promotes the simultaneous occurrence of viscoelastic damage and stripping damage. Furthemore, the results of the two-way ANOVA indicate that moisture has a more significant impact on high-temperature performance damage. In addition, in a dry environment, the low-temperature crack resistance of PA-13 deteriorates with decreasing temperature, but there is little difference at −20 °C and −30 °C. This is attributed to PA-13 exhibiting flexible cracking at 0 °C and −10 °C, while undergoing brittle cracking at −20 °C and −30 °C. Additionally, the coupled effect of temperature and moisture reduces the damage tolerance of PA-13 and accelerates its cracking process. The results of the two-way ANOVA indicate that both low temperature and treatment methods have a statistically significant impact on low-temperature performance, with treatment methods having a higher degree of influence. The findings of this paper contribute to an in-depth understanding of the damage mechanism of PA-13.

Effects of Testing Methods and Sample Configuration on the Flexural Properties of Extruded Polystyrene.

Extruded polystyrene (XPS) is frequently used in the construction of many different structures. Therefore, it is necessary to appropriately characterize its mechanical properties to ensure the safety of said structures. Among the available characterization tests, static bending tests are simple and easy to perform; owing to these characteristics, they should be performed more frequently than other tests. In static bending tests on XPS, there are several challenges owing to the high flexibility of XPS, and the chosen testing method and sample configuration affect the accuracy of characterization. For cellular plastics, including XPS, three-point bending (TPB) test methods are standardized by the International Organization for Standardization (ISO) and Japanese Industrial Standards (JIS) as in ISO 1209-2:2007 and JIS K 7221-2:2006, respectively, where the sample configurations are determined. Therefore, TPB tests of cellular plastics have been conventionally performed based on these standardized methods to characterize the bending properties. In contrast, investigations on the effects of testing methods and sample configurations have often been neglected due to the existence of these standardized methods. However, to characterize the bending properties of XPS accurately, the effects of the testing method and sample configuration must be examined in detail. In this study, three bending properties (Young's modulus, proportional limit stress, and bending strength) of samples cut from an XPS panel were determined using three-point bending (TPB), four-point bending (FPB), and compression bending (CB) tests with varying sample span/depth ratios from 5 to 50 at intervals of 5, and statistical analyses were performed to determine the relevance of the tests. The effect of sample configuration on Young's modulus could be reduced when the span/depth ratio range was 25-50, 25-50, and 15-50 in the TPB, FPB, and CB tests, respectively, whereas that on the proportional limit stress was reduced in the span/depth ratio range of 5-50, 20-50, and 15-50 in the TPB, FPB, and CB tests, respectively. Additionally, the effect on the bending strength was reduced when the span/depth ratio range was 5-50, 20-50, and 5-50 in the TPB, FPB, and CB tests, respectively. Therefore, these results suggest that the TPB and CB tests were more feasible than the FPB test when the span/depth ratio was determined as being 25-50 and 15-50, respectively. However, clear differences were observed in the sample bending properties determined in these tests. In light of these findings, further studies should be conducted to elucidate these differences.

Extended finite element analysis for the 2nd and 3rd metatarsals stress fracture during push-off

Metatarsal stress fractures (MSF), particularly the 2nd and 3rd MSF, are common injuries among athletes. Although there are several practices to reduce foot and ankle injuries, there is no injury prevention program specifically designed to minimize MSF. This is mainly due to the lack of information about the loadings/postures that cause MSF. Therefore, this study aimed to investigate dangerous loadings/postures potentially causing MSF during push-off (PO). The analysis was conducted with Finite Element Modelling (FEM), calibrated with the three-point bending test, and validated with peak plantar pressure (PPP) and fracture force measurement. Extended Finite Element Method was used for MSF simulation such that ten different foot and ankle configurations were designed, with five for each of the 2nd and 3rd MSF under pure vertical loadings. A more complex loading, ankle eversion/inversion during PO, was also examined for the MSF. The average error percentage for the calibration of the model with the three-point bending test was 3.05%. The average error percentages for the validation of the model with PPP and fracture force measurements were 18% and 30%, respectively. The outcomes of pure vertical loadings indicated the higher potential for the 2nd and 3rd MSF at 30% PO and 70% PO, respectively. The results of ankle eversion/inversion loadings represented that the most dangerous posture for MSF was 30° ankle eversion for the 3rd metatarsal at 70% PO. These results provide a guide, including what postures to avoid for the 2nd and 3rd MSF among people who are at high risk of MSF.

Analytical and numerical analysis of composite sandwich structures with additively manufactured lattice cores

In this study, an analytical and numerical analysis of a hybrid sandwich structure with a lattice core produced by additive manufacturing with composite facesheets is carried out. This paper aims to analytically calculate the mechanical behavior of the hybrid sandwich structure under three-point bending and to verify the results by the finite element method. The analytical method used in this article for the analysis of the composite sandwich structure is the First-Order Shear Deformation Theory (FSDT). The numerical analysis of the hybrid sandwich structure was performed in ANSYS. In the analyses, homogenized models of lattice structures, which had been previously validated, were employed to reduce the number of elements and thereby save time during the solution process. As a result of the study, an extensive investigation into the deformation, shear, and normal stress values of sandwich structures with lattice cores of varying aspect ratios has been carried out. The findings suggest a potential for optimization in lightweight structures, which could lead to innovative advancements in design and manufacturing processes within the aerospace and automotive sectors.

An elastoplastic damage ice material model based on modified Tsai-Wu yield criterion: Experiment, theory and numerical application

Ice, as a novel green and sustainable building material, has attracted more and more attention in building engineering. Appropriate ice material models are crucial for the performance analysis of the increasing ice structures. There is still challenging in modelling ice responses due to the complexity of ice. This study aims to present a nonlinear elastoplastic damage model for ice material. First, a triaxial compression test of artificial ice is conducted. Based on the test results, the modified Tsai-Wu failure criterion with better performance in the tensile zone and physical meaning for hydraulic strength is established. Then, combining plasticity theory with damage mechanics, an elastoplastic damage constitutive law considering the difference between tensile and compressive properties is proposed. The piecewise damage model and the Weibull exponential damage model are employed for compression and tension damage, respectively. Moreover, the numerical iterative algorithm is developed and a user-defined material subroutine (UMAT) is embedded in the finite element software ABAQUS to simulate the mechanical properties of ice. Furthermore, the constitutive model is verified by comparing the FEM results with the results of uniaxial compression, triaxial compression, and three-point bending tests. The results show that the constitutive model can well describe the stress-strain nonlinear behavior and capture the basic failure mode of ice materials. Finally, considering temperature affecting on the failure surface, a temperature dependent ice material model is developed. The current study would help in the design, operation and maintenance of ice structures.

EVALUATION OF WOOD DAMAGE AND FRACTURE BEHAVIOR BASED ON ENERGY ENTROPY OF ACOUSTIC EMISSION SIGNALS

In order to assess the damage and fracture behavior of wood under continuous loading, an energy entropy and b-value associated with the acoustic emission (AE) signal were defined to quantitatively describe the release of strain energy during loading. Firstly, the acoustic emission signals of the wood in the three-point bending test were collected. This paper presents the concept of energy entropy according to the definition of information entropy. In order to further evaluate the strain energy intensity released by the damage behavior of the wood specimen, the acoustic emission b-value was defined. Finally, by jointly analysing the dynamics of these two parameters, the test process can be divided into three phases. The results show that even in the elastic phase, micro-destructive behavior occur inside the wood specimen; in the plastic phase, the wood specimen is not only subjected to macroscopic damage, but also often accompanied by fine cracks inside.

Residual strength assessment of a heat straightened ASTM A 7 Steel I-section member exposed to a fire event

Heat straightening is an efficient and cost-effective method of repairing steel members that have experienced impact or fire-induced deformations. Postfire investigations have shown that fire exposure can cause considerable loss of residual mechanical properties. Beyond the fire event itself, additional heat applied to the member during the straightening process can, potentially, even further modify the mechanical properties of steels. This study aims to evaluate residual mechanical behavior at zones of maximum heat-induced distortion representative of both the fire event and the heat-straightening repair of a fire-damaged steel I-section. The study further aims to independently observe heating patterns, working temperatures, and external jacking forces during heat straightening. The fire-damaged member was restrained in three-point bending with fork boundary conditions simulating service conditions for a discretely braced bridge stringer. Results revealed that the cumulative effect of both the fire and the repair caused measurable differences in mechanical properties compared with an undamaged portion of the member, but mean properties still exceeded ASTM International’s ASTM A 7 product and the AASHTO nonfracture-critical toughness requirements. Supplemental metallographic analyses revealed no measurable alteration in metallurgical phase composition or grain size of the steel, indicating that heat straightening would have been a viable repair solution to keep the member in service.

Self-driven intelligent curved hinge based on shape-morphing composites

The space deployable structures based on shape memory polymer composites (SMPCs) possessed excellent self-deployable performance, which effectively avoided the impact and electromagnetic pulse (EMP) caused by the explosion of pyrotechnic devices. In this work, two types of self-driven curved hinges with different angles of 80° and 115° (Type 80 and Type 115) were designed based on SMPCs. The thermomechanical properties and time–temperature-dependent viscoelastic behaviors of SMPCs were systematically investigated. The three-point bending performance and cyclic shape memory performance of the developed hinges were also characterized. In addition, the deployment performances of Type 80 driven 350 g object under different heating powers were investigated in the environment of ± 70 °C and 103 Pa atmospheric pressure. A staircase-like heating strategy was proposed to achieve precise and controllable deployment under this environment. The developed self-driven curved hinges were expected to have tremendous application potential on the flap actuators and optical payload rotating platforms of the satellites.