Low Compressive Stress Research Articles

Giant Elastocaloric Effect and Improved Cyclic Stability in a Directionally Solidified (Ni50Mn31Ti19)99B1 Alloy.

Superelastic shape memory alloys with an integration of large elastocaloric response and good cyclability are crucially demanded for the advancement of solid-state elastocaloric cooling technology. In this study, we demonstrate a giant elastocaloric effect with improved cyclic stability in a <001>A textured polycrystalline (Ni50Mn31Ti19)99B1 alloy developed through directional solidification. It is shown that large adiabatic temperature variation (|ΔTad|) values more than 15 K are obtained across the temperature range from 283 K to 373 K. In particular, a giant ΔTad up to -27.2 K is achieved by unloading from a relatively low compressive stress of 412 MPa at 303 K. Moreover, persistent |ΔTad| values exceeding 8.5 K are sustained for over 12,000 cycles, exhibiting a very low attenuation behavior with a rate of 7.5 × 10-5 K per cycle. The enhanced elastocaloric properties observed in the present alloy are ascribed to the microstructure texturing as well as the introduction of a secondary phase due to boron alloying.

Evaluation of basalt fibers and nanoclays to enhance extrudability and buildability of 3D-printing mortars

A study of the rheological and fresh mechanical properties of fly ash-cement 3D printing (3DP) mortars with six types of nanoclays (NC) as rheology modifiers, two sepiolites, three attapulgites and one bentonite, and reinforced with short basalt fibers (BF) was carried out. Fresh mortar properties were evaluated with a flow table test (FTT), cylindrical slump test (CST) and cone-penetration test (CPT) on samples left at rest and stirred before testing. Squeeze test (SQT) was carried out on samples cast-in-the-mold and 3D printed to compare the effects of 3DP on the fresh mechanical behavior. Extrudability was assessed with an electrical barrel extrusion device. NC and BF enhanced mortar cohesion by preventing water drainage and improving material extrudability. NC increased shear yield stress (τ0) over time on samples left at rest, enhancing reversible thixotropy. Besides, NC required larger amounts of superplasticizer, increasing open time windows. Among NC, Sepiolite in powder form showed the best fresh mechanical performance on 3DP samples. BF enhanced extrudability due to the bridging effect but also shows mechanical synergies with some NC. 3DP samples showed lower compressive yield stress and Young modulus evolution over time (σ˙ and Ė) than cast-in-the-mold samples, due to their layered structure.

Experimental and numerical investigations of bending mechanical properties and fracture characteristics of cemented tailings-waste rock backfill under three-point bending

The bending mechanical properties and fracture characteristics of cemented tailings-waste rock backfill (CT-WRB) have a significant impact on efficient mine production. In this study, the effects of waste rock content (WRC) and waste rock size (WRS) on the bending mechanical properties and macroscopic failure characteristics of CT-WRB were investigated through experiments. Concurrently, PFC3D numerical simulation software was used to establish a three-point bending numerical model of CT-WRB with actual waste rock shapes to explore the crack evolution law and microscopic damage characteristics. Results showed that adding appropriate waste rock improved the initial stiffness, flexural strength, and modulus of the backfill, with optimal WRC and WRS at 40 % and 4–6 mm, respectively. Simulations indicated that under load, the displacement field of CT-WRB formed a vortex, with tensile stress in the middle and lower parts and compressive stress in an upper arch. Cracks started at the bottom and extended upward, leading to failure. Compared to OCTB (without waste rock incorporation), CT-WRB had more total cracks and tension-shear composite failure of internal particles. Waste rock altered stress distribution and crack paths, resulting in curved, bifurcated, and discontinuous main cracks. These findings provide a reference for efficiently recycling tailings, waste rock and ensuring safe mine production.

Residual stress tests and predictive model of friction stir welded normal-strength aluminium alloy H-shaped sections

To address the challenges of difficult extrusion for super-large cross-section aluminium alloy members, pairs of T-shaped sections were proposed to be longitudinally friction stir welded (FSW) to form the H-shaped sections widely used in structural engineering. It was significantly different from the previous member forming method that one web plate and two flange plates were welded at the flange-web junctions. To understand the novel FSW-induced residual stress distributions and magnitudes in the H-shaped sections, six specimens made of 6061-T6 and 6013-T6 normal-strength aluminium alloys, including various width-to-thickness ratio and plate thickness, were tested using the sectioning method, leading to over 4000 original readings of compressive and tensile residual stresses. The analysis results showed that great tensile residual stresses were clearly concentrated within the web weld, and then rapidly descended to lower compressive stresses near the weld region, followed by approximately linear regression to zero state from the weld edge to the flange-web junction, while the flange data points were relatively scattered. The compressive and tensile residual stresses in each flange and web plate were observed to be slightly associated with the width-to-thickness ratio and plate thickness. A simplified multi-linear residual stress distribution model, including the magnitudes and ranges of constant and linear variation curves, was proposed for the FSW aluminium alloy H-shaped sections, and good accuracy and consistency were observed between the test and predicted results.

Strain-rate effect on mechanical properties of rock-like specimens with narrow crack under uniaxial compression

Uniaxial compression tests were carried out on rock-like specimens containing prefabricated narrow crack under various strain rates. Experimental observations and numerical results show that narrow crack will close or partially close or expand under low compressive stress. Due to the unidirectional loading of loading device, the deformation degree of crack tip near the loading end was different with that of crack tip near the bearing end. With the increase of strain rate, the cracking modes can be divided into 3 categories, near vertical splitting failure affected by horizontal crack (α = 0°), anti-N-wing crack (15°≤α ≤ 60°) and wing crack (60°<α ≤ 90°). Both of the initiation angle θ1 of crack tip near the loading end and θ2 of crack tip near the bearing end decreased with the increase of α and strain rate. Specially, when α = 90°, both θ1 and θ2 rose with the increase of strain rate. Moreover, the value of θ2 was greater than that of θ1 under the same α value because of the different deformation characteristics at two tips. Besides, the mechanical properties of fissured rock including peak compressive stress, residual compressive stress, strain at peak stress, elastic modulus and post-peak softening modulus were significantly influenced by the strain rate and inclination angles.

Nanomechanical and Structural Characteristics of Nanodiamond Composite Films Dependent on Target-Substrate Distance

AbstractThis study explores the optimization of target-substrate distance (TSD) in coaxial arc plasma deposition technique for depositing nanodiamond composite (NDC) films on unheated WC–Co substrates, with a focus on enhancing properties relevant to cutting tool applications. TSD significantly impacted film growth and adhesion, while hardness and Young’s modulus remained stable within the 10–50 mm TSD range. Increased TSD led to reduced deposition rates and film thickness, but improved quality by eliminating macroparticles and reducing surface roughness. Notably, the NDC film deposited at 10 mm TSD exhibited exceptional adhesion resistance, a thickness of 11.45 μm, low compressive internal stress (2.8 GPa), and a surface roughness (Sa) of 280 nm, coupled with an impressive hardness of 49.12 GPa. This film also achieved a favorable deposition rate of 1.05 nm/s. In comparison, the film deposited at 15 mm TSD displayed a maximum hardness of 51.3 GPa, lower Sa of 179 nm, but a reduced deposition rate of 0.29 nm/s. The estimated C sp3 fraction correlated well with the nanoindentation measurements, while internal stress showed a consistent relationship with film adhesion. These findings suggest that a TSD of 10 mm is optimal for balancing hardness, adhesion, deposition rate, and surface roughness, making NDC films a promising candidate for cutting tool applications.

Residual stress depth profiles self-developed in cathodic arc deposited Ti-Al-N coatings prepared at different constant substrate bias values

Ti-Al-N coatings were prepared by cathodic arc deposition on Inconel 718 substrates at different values of constant substrate bias voltage, aiming to produce samples with different self-developed residual stress (RS) depth profiles through the thickness of the coatings. RS profile measurements and structural characterization were performed on a laboratory-scale x-ray diffraction system (x-ray energy of 8 keV) and in a synchrotron x-ray radiation facility (x-ray energy of 15 keV). Mechanical testing to obtain hardness and Young’s modulus values was performed by instrumented nanoindentation. The results indicate higher compressive RS at the film/substrate interface that decays to lower compressive stress or mild tensile stress at the film surface. Surface hardness and the compressive RS value of the coating increase with larger values of the substrate bias voltage. By comparing the stress characterization done on a laboratory scale and at the synchrotron facility, one observes a generally good agreement, indicating that these analyses may be conducted at a smaller scale and with less costly equipment, and still maintain a reliable precision. The work presents and reviews in detail the methodology of the RS depth-profile analysis. The highest hardness of 31.1 GPa and near-substrate compressive RS around −10 GPa were obtained for a bias of −100 V. Transmission electron microscopy results indicate that regions with higher compressive stresses are found to have smaller columns and denser structure, while portions of the same sample with mild compressive or tensile stresses present larger column size and are richer in hexagonal phases. The findings demonstrate the complex interplay between stress, microstructure, and ultimately mechanical properties in industrially produced Ti-Al-N coatings and indicate that any successful strategy to mitigate stress development should consider the inhomogeneous self-developed stress gradients present even in coatings deposited under constant and controlled conditions.

Directed biomechanical compressive forces enhance fusion efficiency in model placental trophoblast cultures.

The syncytiotrophoblast is a multinucleated structure that arises from fusion of mononucleated cytotrophoblasts, to sheath the placental villi and regulate transport across the maternal-fetal interface. Here, we ask whether the dynamic mechanical forces that must arise during villous development might influence fusion, and explore this question using in vitro choriocarcinoma trophoblast models. We demonstrate that mechanical stress patterns arise around sites of localized fusion in cell monolayers, in patterns that match computational predictions of villous morphogenesis. We then externally apply these mechanical stress patterns to cell monolayers and demonstrate that equibiaxial compressive stresses (but not uniaxial or equibiaxial tensile stresses) enhance expression of the syndecan-1 and loss of E-cadherin as markers of fusion. These findings suggest that the mechanical stresses that contribute towards sculpting the placental villi may also impact fusion in the developing tissue. We then extend this concept towards 3D cultures and demonstrate that fusion can be enhanced by applying low isometric compressive stresses to spheroid models, even in the absence of an inducing agent. These results indicate that mechanical stimulation is a potent activator of cellular fusion, suggesting novel avenues to improve experimental reproductive modelling, placental tissue engineering, and understanding disorders of pregnancy development.

Experimental and Numerical Study of Membrane Residual Stress in Q690 High-Strength Steel Welded Box Section Compressed Member.

High-strength steel (HSS) members with welded sections exhibit a notably lower residual compressive stress ratio compared with common mild steel (CMS) members. Despite this difference, current codes often generalize the findings from CMS members to HSS members, and the previous unified residual stress models are generally conservative. This study focuses on the membrane residual stress distribution in Q690 steel welded box sections. By leveraging experimental results, the influence of section sizes and welding parameters on membrane residual stress was delved into. A larger plate size correlates with a decrease in the residual compressive stress across the section, with a more pronounced reduction observed in adjacent plates. Additionally, augmenting the number of welding passes tends to diminish residual stresses across the section. Results showed that membrane residual stress adhered to the section's self-equilibrium, while the self-equilibrium in the plates was not a uniform pattern. A reliable residual stress simulation method for Q690 steel welded box sections was established using a three-dimensional thermal-elastic-plastic finite element model (3DTEFEM) grounded in experimental data. This method served as the cornerstone for parameter analysis in this study and set the stage for subsequent research. As a result, an accurate unified residual stress model for Q690 steel welded box sections was derived.

Hybrid deposition of AlTiN/WN multilayer films with low compressive stress at low temperature

AlTiN/WN multilayer films with low compressive stress were deposited by arc evaporation and DC magnetron sputtering at a low temperature. The phase structure, morphologies, mechanical properties, wear behavior, and cutting performance of the AlTiN/WN multilayer films were evaluated. The results show that all the as-prepared AlTiN/WN multilayer films have fcc structure and exhibit (111) preferred orientation. The lowest value of −1.7 ± 0.3 GPa for compressive stress was obtained under low-temperature deposition. The film hardness increases as the temperature increases. High-temperature deposition provides higher energy to grow a dense film, which improves the film hardness. Increasing the WN layer thickness reduces the adhesion strength of the film. Compared with room temperature, the friction coefficients of the films against stainless steel reduce at high temperatures. This was attributed to lubricative oxides WOx formed on the wear surface at high temperatures. Dry cutting experiments were conducted and the longest service life of the coated tool reaches ∼3730 m. The worn flank surface shows that both adhesion and abrasive wear dominate the failure of the coated tools.

Compressive stress in three types of finishing lines with lithium disilicate crowns in permanent teeth: finite element analysis

In oral rehabilitation, the use of ceramic restorations is widely accepted due to its aesthetic capacity to mimic the naturalness of the dental tissue, provide longevity of the material, and present a greater marginal fit compared to crowns with a metal structure. Termination lines are biological preparations whose function is to minimize the cervical opening of the marginal seal. Consequently, analyzing the behavior of restorative materials under compressive forces decreases the risk of fracture and increases the success of the treatment. To compare the compressive stresses of lithium disilicate crowns with three different finishing lines. In silico study of the simulation of a dental preparation on a lower right first molar with chamfer (0.6 mm), shoulder (0.5 mm) and deep chamfer (0.5 mm) finish lines. Using the SolidWorks®️ version 2017 software, the maximum stresses, minimum stresses, and location of the compressive force were collected on the Megapascal (Mpa) measurement scale. The chamfer type termination line (0.6mm) obtained a lower compressive stress compared to the other two shoulder type termination lines (0.5mm) and deep chamfer (0.5mm). It was shown that the chamfer type finishing line (0.6mm) presented a better force distribution, determining greater reliability in the selection of this finishing line with the use of a lithium disilicate crown in a unitary manner.

Optimization of transparent conductive properties of magnetron sputtered Sb-doped SnO2 films by RF power: Towards application in polymer-dispersed liquid crystal (PDLC) films

Sb-doped SnO2 (ATO) films were prepared with different RF powers (PRF) under two O2 flow rates (FO2) by magnetron sputtering, and then subjected to rapid thermal annealing (RTA) treatment. The effects of PRF, FO2, and RTA on the crystallinity, stress, surface morphology, conductive properties, transmittance in visible-light range (TVis), and energy gap (Eg) of the films were investigated. As the PRF increases, the film crystallinity improves or first improves and then slightly degrades, and the compressive stress decreases. With increasing PRF, the surface changes from textured to granular morphology and from granular to honeycomb-like morphology under two FO2, respectively. Meanwhile, the conductive properties first enhance and then degrade, and the TVis and Eg tend to decrease, especially at higher PRF. Basically, the films prepared with higher FO2 have lower compressive stress, inferior conductive properties, and larger TVis and Eg compared with the films prepared with lower FO2. After RTA, the film crystallinity obviously improves, the compressive stress transforms into tensile stress, and the surface morphology has not undergone significant changes. Meanwhile, the conductive properties significantly enhance and Eg obviously increases. The TVis of the films prepared with lower FO2 can be increased by RTA. The influence mechanisms of the above factors on the structure and optoelectronic properties of the ATO films were explored, and ultimately, the ATO films have the TVis of 76.35–80.86%, sheet resistance of 51.7–91.9 Ω/sq., and quality factor of 1.03–1.67 × 10−3 Ω−1 within the optimized PRF range. Polymer-dispersed liquid crystal (PDLC) films were fabricated using optimized performance ATO films as electrodes, and their on-state transmittance, off-state transmittance, threshold electric field, and saturation electric field were 2.08–4.61%, 61.69–68.56%, 0.656–0.796 V/μm, and 1.68–2.108 V/μm, respectively. The current results indicate the potential application of ATO films in PDLC films as electrode.

Experimental Study on Seismic Performance of Prefabricated Monolithic Concrete–Polystyrene Panel Composite Wall Panels

A normal composite wall panel is a structural component composed of polystyrene insulation boards and concrete surface layers reinforced with steel wire mesh. It can be entirely prefabricated in a factory or constructed with the concrete surface layers cast on-site. A novel prefabricated monolithic concrete–polystyrene panel composite wall panel (CPC wall panel) is proposed in this study. The CPC panel features a middle part that is prefabricated in the factory while the reinforced concrete regions at its two side ends are cast on-site. To evaluate the seismic performance of the wall panel, 18 CPC specimens were designed, manufactured, and quasi-statically tested, through which the structural behaviors, failure mode, and load-bearing capacity were studied. In addition, the influences of the height-to-width ratio and the vertical compressive stress level on the seismic performance of the CPC panels were also investigated. The test results showed that the connectors spaced at 400 mm × 500 mm could ensure the concrete layers on both sides of the polystyrene board worked collectively under seismic conditions. When subjected to lateral loads, the interface between the newly poured concrete and the existing concrete exhibited good bonding. Moreover, the failure mode of the CPC wall panel was largely correlated to the height-to-width ratio that, for specimens having four steel bars of 12 mm diameter and a height-to-width ratio greater than 1, the flexural failure was initially developed, followed by diagonal shear failure. In specimens with a height-to-width ratio of 1, flexural and diagonal shear failures occurred almost simultaneously. For specimens with a height-to-width ratio of less than 1, the final diagonal shear failure was predominant. The longitudinal reinforcing bars at the two ends of the CPC panels could effectively improve their lateral load-bearing capacity, with the enhancement influenced by the height-to-width ratio, the vertical load applied to the wall panel, and the cross-sectional area of the steel bars. In practice, the lateral load-bearing capacity of the CPC panel can be conservatively evaluated using the calculation method of the reinforced concrete shear walls. Finally, the ductility of the CPC specimens was affected by the height-to-width ratio and the axial compressive stress level, such that the specimens with a larger height-to-width ratio and lower axial compressive stress exhibited better ductility.

Test, modelling and design of a demountable stainless steel bar connection system for precast concrete pavements

To promote the reuse of precast concrete pavement units, an innovative demountable stainless steel bar connection system is proposed in this paper. Monotonic load tests were conducted to investigate the effects of the width of the stainless steel bar connection, the width and the end distance of the stainless steel plate on the mechanical behaviour of the proposed connection system. As localised concrete crushing was observed after tests, the stainless steel bar connection system was updated with an expanded contact area between concrete and steel. Test results revealed that specimens with the updated connection system exhibited high initial stiffness with low concrete compressive stress concentration. Finite element analysis (FEA) was then carried out to further investigate the parameters that affected the structural performance of the updated connection system. According to the deformations of the stainless steel bar connection and high-strength bolts, an analytical approach was developed to predict the design load of the proposed connection system. Design recommendations were finally summarised based on the obtained test and parametric analysis results to guide the demountable connection design.

Residual Stresses in Ribbed Reinforcing Bars.

Ribbed reinforcing bars (rebars) are used for the reinforcement of concrete structures. In service, they are often subjected to cyclic loading. In general, the fatigue performance of rebars may be influenced by residual stresses originating from the manufacturing process. Knowledge about residual stresses in rebars and their origin, however, is sparse. So far, residual stress measurements are limited to individual stress components, viz., to the non-ribbed part of the rebar surface. At critical points of the rebar surface, where most of the fatigue cracks originate, i.e., the foot radius regions of transverse ribs, the residual stress state has not yet been investigated experimentally. To extend the knowledge about residual stresses in rebars within the scope of this work, residual stress measurements were carried out on a rebar specimen with a diameter of 28 mm made out of the rebar steel grade B500B. In addition, numerical simulations of the TempCoreTM process were carried out. The results of the experimental investigations show tensile residual stresses in the core and the transition zone of the examined rebar specimen. Low compressive residual stresses are measured at the non-ribbed part of the rebar surface, while high compressive residual stresses are present at the tip of the transverse ribs. The results of the numerical investigations are in reasonable accordance with the experimental results. Furthermore, the numerical results indicate moderate tensile stresses occurring on the rebar surface in the rib foot radius regions of the transverse ribs. High stress gradients directly beneath the rebar surface, which are reported in the literature and which are most likely related to a thin decarburized surface layer, could be reproduced qualitatively with the numerical model developed.

Atomistic study on the origins of the anisotropic lithiation behaviors of the silicon anode using the reactive force field based molecular dynamics simulations

We employed the Reactive-Force-field (ReaxFF) based molecular dynamics simulations to investigate the lithiation mechanisms and anisotropic lithiation behaviors of the Si-based anode during the lithiation processes. In order to accurately predict the relative lithiation kinetics on different surface facets of c-Si, we have developed new ReaxFF parameters for the Li-Si system based on first-principles calculations. Our results demonstrated that the lithiation kinetics on the Si(110) and (112) surfaces manifestly outperformed those occurred on the Si(100) and (111) surfaces. The lithiation reactions on the Si(110) and (112) surfaces tend to proceed through a ledge mechanism involving the layer-by-layer peeling of the {111} atomic facets. However, the lithiation reaction on the Si(100) surface is more likely to occur via the layer-by-layer etching of the {100} atomic facets. The discrepancy in the lithiation kinetics among the c-Si(100), (110) and (112) substrates was mainly ascribed to the variation in the compressive stresses that developed within the phase boundary upon lithiation. Regarding the Si(111) surface, the significantly slower lithiation kinetics than other surface facets were primarily attributed to the presence of a considerably larger barrier for Li insertion into the subsurface region to initiate the lithiation reaction. Furthermore, the order of the energy barriers for Li insertion into different c-Si surfaces was determined as follows: Si(111)>>(100)>(110)>(112), indicating that Li atoms tend to migrate into c-Si predominantly through the (110) and (112) surfaces upon lithiation. Consequently, lithiation reactions would occur majorly on the (110) and (112) surfaces due to the much lower compressive stresses that developed within the phase boundary and smaller Li insertion barriers than other surface facets, resulting in the observed anisotropic lithiation behaviors of the c-Si nanomaterials.

Smooth diamond-like carbon films prepared by cathodic vacuum arc deposition with large glancing angles

Diamond-like carbon (DLC) films were prepared by cathodic vacuum arc (CVA) deposition with different glancing angles (the angle between the normal reverse direction of the arc target and the normal direction of the substrate surface) in range of 0 to 135°. The effects of the glancing angle on the morphology, carbon structure, mechanical property and tribological behavior of the DLC films were investigated. The results show that the surface quality of the DLC films is significantly improved by increasing the glancing angle. The macroparticles in the surface as well as the surface roughness of the DLC films decrease sharply as the glancing angle increases. The sp3/sp2 of the DLC films decreases at first and then increases as the glancing angle increases. The normal incidence energy of the Cn+ species becomes suitable to the formation of sp3-C when the glancing angle is 45°. The variation in the film hardness and compress stress at different glancing angles are similar in profile to the sp3 bond fractions. However, the compressive stress of the films could be reduced effectively by avoiding the bombardment of the Cn+ species with excessively high energy through increasing glancing angle. The tribological behaviors of the films could be also improved by changing the glancing angle. It is supposed that the CVA with appropriate glancing angle might be one way to prepare the DLC films with smooth surface, high hardness, low compressive stress and good tribological performance.

The Deposition and Properties of Titanium Films Prepared by High Power Pulsed Magnetron Sputtering

Titanium thin films are particularly important as electrode layers, barrier layers, or intermediate buffer layers in the semiconductor industry. In order to improve the quality of Ti thin films and the adhesion and diffraction abilities of irregular parts, this paper used high-power pulsed magnetron sputtering (HPPMS/HiPIMS) to prepare titanium thin films. The effects of different trigger voltages (700 V, 800 V, and 900 V) on plasma properties were studied, and the microstructure, mechanical properties and corrosion resistance of the films were also studied. The results showed that as the voltage increased, the grain size of the thin films gradually increased. The residual stress of the titanium films changed from compressive stress (−333 MPa) to tensile stress (55 MPa) and then to low compressive stress (−178 MPa). The hardness values were 13 GPa, 9.45 GPa and 6.62 GPa, respectively. The wear resistance of the films gradually decreased, while the toughness gradually increased. The corrosion resistance of the films decreased as well.

A Study of the Mechanical Properties of Polyester Fiber Concrete Continuous Rigid Frame Bridge during Construction

This study investigates the mechanical performance of a polyester fiber concrete continuous rigid frame bridge during construction and the spatial stress distribution of the 0# block box girder, with a focus on the backdrop of the bridge in Pipa Zhou, Jiangxi Province. Stress monitoring at critical cross-sections during bridge construction was combined with FE simulations to analyze the stress and alignment deviation variations along the cantilevered construction process of the bridges. Subsequently, after validating the accuracy of the whole bridge model, the actual internal force of the box girder cross-section was extracted to act on the 0# block box girder solid model, and the spatial force of the 0# block box girder under the state of maximal cantilever and the completed bridge was further investigated. The results indicate that during cantilever construction, the top, and bottom plates of the box girder were subjected to compression, with the bottom plates having relatively low compression stress close to the critical values for compression and tension. Attention should be paid to controlling tensile stress application. After reaching a quarter of the bridge’s span in construction, the alignment deviation of the main beam increases, necessitating enhanced monitoring and adjustments of the main beam elevation. Furthermore, FE analysis shows that under maximum cantilever and the completed bridge states, the stress variations of the top and bottom plates of the 0# block box girder remain consistent, with the top plate stress varying by no more than 2.5 MPa and the bottom plate stress varying by approximately 1 MPa. Moreover, the 0# block box girder shrinkage cracks were mainly located in the bottom and web plate, and the number of cracks in the 0# block box girder with polyester fibers was reduced compared to the cracks in the ordinary concrete box girder.

Mechanical, thermal insulation, and ablation behaviors of needle-punched fabric reinforced nanoporous phenolic composites: The role of anisotropic microstructure

Needle-punched fabric reinforced nanoporous phenolic composite (NPC) is a kind of promising ablative thermal protection material for spaceflight. However, in practical applications, typically anisotropic microstructure of NPC may lead to different performances and damage mechanisms under various directional mechanical or thermal loads. Herein, NPC is prepared and cut into specimens along three typical plane directions including XY-plane (0°), Z-plane (90°), and transitional-plane (45°), and their mechanical, thermal insulation, and ablation behaviors are systematically investigated. Benefiting from the woven fabric in XY-plane, NPC in 0°-plane direction exhibits highest tensile strength (169.2 ± 12.6 MPa), and CT image-based simulation further verifies that woven fabrics are primary load-bearing structure. Meanwhile, NPC in 45°-plane direction shows highest compressive strength (443.1 ± 18.2 MPa) but low compressive stress at low strain, demonstrating a weak bonding between two layers of woven fabrics. Moreover, the heat transfer simulation indicates that horizontally stacked woven fabrics effectively protect the internal material from thermal erosion, thus NPC in 0°-plane direction exhibits optimal thermal insulation. The ablation testing and micro-CT observations further demonstrate that the angle between woven fabric and thermal load significantly influences the ablation mechanism. The present work will further promote the structural reliability and optimization of needle-punched composites.