Mechanical Analysis Research Articles

Palladium Single Atom‐supported Covalent Organic Frameworks for Aqueous‐phase Hydrogenative Hydrogenolysis of Aromatic Aldehydes via Hydrogen Heterolysis

Developing a method for the tandem hydrogenative hydrogenolysis of bio‐based furfuryl aldehydes to methylfurans is crucial for synthesizing sustainable biofuels and chemicals; however, it poses a challenge due to the easy hydrogenation of the C=C bond and difficult cleavage of the C–O bond. Herein, a palladium (Pd) single‐atom‐supported covalent organic framework was fabricated and showed a unique 2,5‐dimethylfuran yield of up to 98.2% when reacted with 5‐methyl furfuryl aldehyde in an unprecedented water solvent at 30°C. Furthermore, it exhibited excellent catalytic universality while converting various furfuryl‐, benzyl‐, and heterocyclic aldehydes at room temperature. The analysis of the catalytic mechanism confirmed that H2 was heterolytically activated on the Pd–N pair and triggered the keto‐enol tautomerism of the covalent organic frameworks (COFs) host, resulting in H––Pd∙∙∙O–H+ sites. These sites served as novel asymmetric hydrogenation sites for the C=O group and hydrogenolysis sites for the C–OH group through a scarce SN2 mechanism. This study demonstrated remarkable bifunctional catalysis through the H2‐induced keto‐enol tautomerism of COF catalysts for the atypical preparation of methyl aromatics in a water solvent at room temperature.

The Interfacial Reaction Traits of (Al63Cu25Fe12) 99Ce1 Quasicrystal-Enhanced Aluminum Matrix Composites Produced by Means of Hot Pressing

This study fabricated (Al63Cu25Fe12)99Ce1 quasicrystal-enhanced aluminum matrix composites using the hot-pressing method to investigate their interfacial reaction traits. Microstructure analysis revealed that at 490 °C for 30 min of hot-pressing, the interface between the matrix and reinforcement was clear and intact. Chemical diffusion between the I-phase and aluminum matrix during sintering led to the formation of Al7Cu2Fe, AlFe, and AlCu phases, which, with their uniform and fine distribution, significantly enhanced the alloy’s overall properties. Regarding compactness, it first increased and then decreased with different holding times, reaching a maximum of about 98.89% at 490 °C for 30 min. Mechanical property analysis showed that compressive strength initially rose and then fell with increasing sintering temperature. After 30 min at 490 °C, the reinforcement particles and matrix were tightly combined and evenly distributed, with a maximum compressive strength of around 790 MPa. Additionally, the diffusion dynamics of the transition layer were simulated. The reaction rate of the reaction layer increased with hot-pressing temperature and decreased with holding time. Selecting a lower temperature and appropriate holding time can control the reaction layer thickness to obtain composites with excellent properties. This research innovatively contributes to the preparation and property study of such composites, providing a basis for their further application.

Mechanical Properties Test and Failure Analysis of Composite Foam Sandwich Structure in Ramp-Down Zone

Mechanical Properties Test and Failure Analysis of Composite Foam Sandwich Structure in Ramp-Down Zone

PhotoinducedEDA Complex-initiated Synthesis of Fluoroalkylated Isoquinolinonediones.

A visible-light-induced radical tandem difluoroalkylation/cyclization to construct CF2-containing isoquinolinonedione skeletonswith methacryloyl benzamides is developed. Broad substrate scopes are compatible with metal-, oxidant- andphotocatalyst-free conditions under roomtemperature in good-to-excellent yields. Mechanistic analysis revealed that the transformation is initiated by photoinducedelectron donor-acceptor (EDA) complexes formation.

Co@NC Chainmail Nanowires for Thermo- and Electrocatalytic Oxidation of 2,5-Bis(hydroxymethyl)furan to 2,5-Furandicarboxylic Acid.

2,5-Furandicarboxylic acid (FDCA) has emerged as an important bio-based furanic compound, which has broad application prospects in renewable energy and materials, especially in the preparation of polyethylene 2,5-furandicarboxylate (PEF). While the conventional synthesis of FDCA involves oxidation of 5-hydroxymethylfurfural (HMF) as a substitute, the thermal and chemical instability of HMF due to its aldehyde group poses challenges. A more favorable alternative is the utilization of 2,5-bis(hydroxymethyl)furan (BHMF), a non-aldehyde and more stable precursor. This study pioneeringly reports nitrogen-doped-carbon encapsulated cobalt (Co@NC) chainmail nanowires for the thermal and electrocatalytic oxidation of BHMF to FDCA. The Co@NC/NF achieved a 97.9 % conversion of BHMF with a 93.3 % yield of FDCA at 1.475 V vs. RHE, whereas thermal catalysis only obtained 14.9 % FDCA yield after 10 hours. Kinetic studies indicated that the large electrochemically active surface area and excellent kinetic parameters contribute its superior electrochemical performance. Mechanistic analysis revealed that the migration of inner electrons to the exterior modified the electronic properties of the carbon layer, thereby facilitating the oxidation of BHMF. Furthermore, the in-situ generation of high-valent cobalt species markedly accelerated the BHMF oxidation. This research underscores the potential of carbon-encapsulated metal chainmail catalysts in thermal and electrochemical biomass conversion.

Fabrication and Enhanced Flexibility of Starch-Based Cross-Linked Films.

The development of sustainable materials has driven significant interest in starch as a renewable and biodegradable polymer. However, the inherent brittleness, hydrophilicity, and lack of thermoplasticity of native starch limit its application in material science. This study addresses the limitations of native starch by converting it to dialdehyde starch (DAS) and cross-linking with polyether diamines via imine bonds. The effects of Jeffamine molecular weights (D-2000, D-400, and D-230) and mole ratios on the mechanical, thermal, and structural properties of starch-based films were examined. The cross-linked DAS/Js films exhibited significant enhancements in flexibility and toughness. Specifically, DAS/J2000 at a 0.03 mol ratio achieved a tensile strength of 62.9 MPa. In comparison, DAS/J400 at a 0.5 mol ratio demonstrated 126.2% elongation at break, indicating the balance between cross-linking density and chain mobility. X-ray diffraction (XRD) analysis revealed reduced crystallinity and tighter molecular packing with increased cross-linking. Dynamic mechanical analysis (DMA) indicated a decrease in Tg with an increasing mole ratio, reflecting enhanced molecular mobility. The results underscore the potential of optimized cross-linking conditions to produce starch-based films with properties that contribute to developing sustainable biopolymer materials.

Mechanical properties of basalt/jute fiber composites to improve the phenomenon of drawing delamination

AbstractIn recent years, natural fibers have been commonly used to reinforce various polymers, resulting in composites with excellent mechanical properties. To address the challenge of delamination and significant fiber pull‐out in inter‐laminar hybrid composites during stretching, this study focused on preparing intra‐laminar hybrid textile composites using basalt fibers (BFs) and jute fibers (JFs) as raw materials. Moreover, the mechanical properties of BF/JF intra‐layer blended fabric composites were investigated. The prepared composites underwent tensile, flexural, impact, and dynamic mechanical analysis (DMA). The results indicated that intra‐laminar blended composites demonstrated superior mechanical properties compared to inter‐laminar blended fabric composites. The DMA results revealed that the intra‐laminar blended composites featured a high peak loss factor. Morphological analysis indicated enhanced stress transfer from fiber‐to‐fiber and fiber‐to‐matrix in the intra‐laminar blended composites.Highlights Fiber blending can expand the application areas of natural fibers. Fiber blending can reduce interlayer damage. Intra‐layer blending differs from interlayer hybrid composites. Strong bonding between fibers facilitates effective stress transfer. “Green” composites exhibit exceptional mechanical properties.

Modelling of dislocations pile-ups at crack tip. Application to silicon

ABSTRACT The mechanical analysis of plastic zones at crack tip has progressed very little since the publication of the founding BCS model, 60 years ago. This two-dimensional model, and those that followed, consider the plastic zone as a pile-up of dislocations of one sign only. They assume that the crack absorbs the part of the dislocation loop of the opposite sign. Here the real three-dimensional problem is addressed and we demonstrate that the crack front behaves as an obstacle. This change of paradigm requires the plastic zone to be modelled as a two-sign dislocation pile-up. The model fits well with experimental observations in bulk silicon. In addition, the presence of dislocations of opposite signs completely modifies the amplitude of crack shielding. The closer the dislocation is to the crack front, the more significant the effect. Therefore, the increase in toughness observed experimentally is linked to the part of the loop attached to the crack front, and not to the expanding part of the loop. This conclusion is in direct contradiction to that provided by previous models.

Research on the Impact of Digital Infrastructure on Urban Breakthrough Green Innovation: A Case Study of the Yangtze River Economic Belt in China

Breakthrough green innovation acts as a critical leverage point and a fundamental driver of the development of new productive forces. This study employs a sample of 108 cities along the Yangtze River Economic Belt from 2011 to 2021 to investigate the impact of digital infrastructure on urban breakthrough green innovation and its underlying mechanisms. The findings are as follows: (1) Digital infrastructure construction facilitates urban breakthrough green innovation, with a notably more substantial impact on strategic breakthrough green innovation. This result is validated through robustness and endogeneity tests. (2) Heterogeneity analysis indicates that the enhancement effect of digital infrastructure on breakthrough green innovation is more prominent in non-resource-based cities, cities with higher levels of marketisation, and those with weaker environmental regulations, with a particularly significant influence on substantive breakthrough green innovation. (3) Mechanism analysis reveals that upgrading industrial structures, optimising market resource allocation, and increasing public environmental awareness are critical mechanisms through which digital infrastructure strengthens urban breakthrough green innovation capacity. Additionally, as improvements occur in industrial structure, market resource allocation efficiency, and public environmental awareness, the impact of digital infrastructure on urban breakthrough green innovation capacity displays a nonlinear effect.

Paper‐based sensors for real‐time cure monitoring in the production of glass fiber‐reinforced phenol‐formaldehyde composites for aerospace interiors

AbstractThe aerospace industries demand for advanced materials necessitates stringent quality control measures, particularly for composite structures to ensure optimal curing and structural integrity. Traditional methods like differential scanning calorimetry (DSC) and dynamic mechanical analysis, while useful, are limited to laboratory settings. This study explores the use of a printed paper‐based sensor for real‐time cure monitoring of glass fiber‐reinforced phenol‐formaldehyde (PF/GF) prepregs. The sensor, composed of a cellulose paper substrate with screen‐printed electrodes, offers flexibility, ease of integration, and cost‐effectiveness compared to commercial polymer‐based dielectric sensors. Real‐time monitoring with the printed paper‐based sensor was conducted at temperatures ranging from 130 to 180°C, both with and without pressure, and validated against DSC and Fourier‐transform infrared (FTIR) spectroscopy. The results showed a strong correlation between real‐time monitoring and the DSC prediction model, as well as FTIR spectroscopy. Notably, the real‐time monitoring revealed a shorter curing cycle on the production line than the predicted cure kinetic model, which is crucial for large‐scale production, such as fabricating honeycomb panels for aircraft interiors. This research underscores the importance of innovative sensor technologies in improving quality control and manufacturing efficiency in aerospace composites.Highlights Cure Monitoring of PF‐based prepregs was carried out using paper‐based sensor. Sensor offered reproducibility and seamless integration in composites. Sensor data showed a strong correlation with DSC and FTIR spectroscopy results. Paper sensors enable online monitoring of composite in aerospace manufacturing.

Study of microstructural evolution during operation of electrically connected components and analysis of failure mechanism

Abstract As a key current-carrying structure of high-voltage bushings, the reliability of electrical connection components is crucial to the safe and stable operation of power equipment. To obtain the microstructural evolution of electrical connection components with different deterioration states, CUD strap contactors were deteriorated in different ways, and electron backscatter diffraction (EBSD) technique was used to test the microstructure of strap contactors with different deterioration states. The results showed that compared to the unused contactors, the contact resistance of the contactors under the combined effect of friction and high temperature increased 203.12 times and was in a failed state. During the process from unused state to wear deterioration, high temperature deterioration, and then to eventual failure of the contactors, the average grain size gradually grows from 8.15 μm to 25 μm, the dislocation density gradually decreases from 2.38×1014 m-2 to 1.04×1014 m-2, and there are a significant proportion of the recrystallized organization. These changes are detrimental to the mechanical properties of the contactors. In addition, the distribution of grain boundaries in the contact area proves the occurrence of over-temperature phenomenon in this area, which will accelerate the deterioration of the contactors and eventually lead to the failure of the component. The relevant conclusions can provide a theoretical basis for the design of electrical connection structure of strap contacts as well as the study of deterioration mechanism.

Improvement of superconducting, morphological, and flux pinning ability of YBa2Cu3O7−y matrix with oxygen and Mn2O3 impurity

Abstract In the current work, the influence of oxygen and Mn2O3 impurity levels intervals 0.00 ≤ x ≤ 0.30 on various key properties such as electrical resistivity, superconducting, flux pinning ability, stabilization of ceramic system, and morphological properties of YBa2Cu3O7-y (Y-123) superconductor were examined by electrical resistivity, critical current density, and scanning electron microscopy (SEM), electron dispersive x-ray (EDX) measurements. The EDX test results indicated that all the Y-123 ceramics produced possessed different composition distributions on the sample surface. SEM photomicrographs also confirmed the improvement in the appearance of surface morphology and crystallinity quality of the YBa2Cu3O7-y system. Moreover, the development in the interaction quality between grains, pinning ability and strength quality of 2D coupled vortices was obtained with the oxygen ambient and optimum manganese impurity addition highly dispersing throughout the intra grain and inter-grain boundary couplings due to the increase in the artificial flux pinning nucleation sites in the Y-123 system. Thus, the best sample with the highest Jc value of 98 A/cm2 showed the most resistance to the applied magnetic field and current. Similarly, the same sample exhibited the greatest superconductive offset (98.320 K) and onset (100.504 K) temperatures values based on the development of the Cu-O coordination and stability of the crystal structure. In conclusion, this comprehensive study based on the analysis of oxygen and Mn2O3 impurity addition mechanism through the YBa2Cu3O7-y ceramic matrix may open a new and applicable field for advanced engineering, heavy industry technology and large-scale applications.

A Hybrid Data-Driven Method for Main Circuit Gound Faults Diagnosis in Electrical Traction Drive Systems

A main circuit ground fault (MCGF) is a typical system fault in an electrical traction drive system (ETDS). When two or more MCGFs occur, it will cause serious accidents. Therefore, it is particularly important to detect and handle MCGFs in a timely manner. To improve the efficiency of train operation and ensure driving safety, this paper proposes a hybrid data-driven MCGF diagnosis method. First, the voltage signals related to the fault are selected according to the mechanism analysis of the MCGF, and then the initial feature variables are constructed according to these voltage signals. Secondly, the initial feature variables of different types of MCGF are analyzed in the time and frequency domains by wavelet transform, and four feature indicators are calculated. Finally, the fault feature indicators are trained by random forest to obtain a model for subsequent fault diagnosis. After comparative experiments using various machine learning methods, it was found that the RF used in the proposed method has a better diagnostic effect, and the correct isolation rate exceeds 99%.

Stress level dependent behavior of sand-rubber mixtures

This study investigates the mechanical behavior of sand-rubber mixtures, focusing on the influence of stress levels. Quantitative analysis reveals significant effects of stress levels on void ratio and coordination number, which become more pronounced with increasing rubber content. Small-strain stiffness could be affected by stress level by demonstrating unified relationships between small-strain stiffness and conventional state variables, with the coefficients of determination for fitted relationships increasing from 0.66 to 0.95 as rubber content increases from 0% to 80%. This is attributed to the impact of stress levels on conventional state variables. Alternative state variables that exclude rubber materials more effectively describe the small-strain characteristics of sand-rubber mixtures, suggesting that rubber materials should be excluded when considering these characteristics in practical engineering for conservation purposes. The stress level effect is also evident in the variation of stress ratios with axial strain, particularly when rubber content exceeds 25%, showing that higher stress levels restrict the mobilization of stress ratios for rubber materials. This study highlights the importance of considering stress level effects in the mechanical analysis of sand-rubber mixtures, which exhibit unique characteristics compared to natural sands in both compression and shearing behavior.

Air pollution under formal institutions: The role of distrust environment

Formal trust is an important formal institution that may significantly impact the environment. This study uses regional distrust environment as a reverse proxy variable for formal trust and studies the impact of formal trust on corporate sulfur dioxide emissions. This study finds that the environment of distrust significantly increases the sulfur dioxide emission levels of enterprises, which means that formal trust affects the environmental management strategies of enterprises. This study also finds that some other formal institutional factors, which include marketization, the development of intermediate organizations, the legal system environment, and GDP levels, have moderating effects on the impact of distrust environment on corporate sulfur dioxide emissions. In addition, climatic conditions including temperature, humidity, and precedence, as well as the location of the enterprise, have certain moderation effects. Mechanism analysis indicates that distrust environment affects corporate sulfur dioxide emissions through the increase in coal sulfur content in enterprise production, the decrease in exhaust gas processing capacity, the reduction in financing capacity, and the decline in social and environmental responsibilities. Finally, this study finds through further analysis that the local government appears to have noticed this negative impact, and the regions with a distrust environment tend to increase their environmental regulation intensity.

Investigating the Effects of the Height-to-Diameter Ratio and Loading Rate on the Mechanical Properties and Crack Extension Mechanism of Sandstone-Like Materials

The causes of the size effect (SE) and loading rate effect (LR) for rocks remain unclear. Based on this, a gypsum-mixed material was used to simulate sandstone, where the dosing ratio was 7.5% river sand, 17.5% quartz, 58.3% α-high-strength gypsum, and 16.7% water. The specimens were designed to have a height-to-diameter ratio (HDR) of 0.6~2, and three strain rates (SRs)—static, quasi-dynamic, and dynamic—were used to perform single-factor rotational uniaxial compression experiments. PFC2D was used to numerically simulate the damage pattern of a sandstone-like specimen. The results showed that the physical parameters did not change monotonically, as was previously found. The main reason for this is that the end-face friction effect (EFE) is generated when the dynamic SR or the HDR is 0.6~1, with a damage pattern of “X”. Under mechanical analysis, the power consumed by the EFE was inversely proportional to the HDR and directly proportional to the LR, and it can reduce the actual amount of energy transferred inside the specimen. This paper may provide a foundation for the study of non-linear hazards in coal and rock.

CMC/Gel/GO 3D-printed cardiac patches: GO and CMC improve flexibility and promote H9C2 cell proliferation, while EDC/NHS enhances stability.

In this research, carboxymethyl cellulose (CMC)/gelatin (Gel)/graphene oxide (GO)-based scaffolds were produced by using extrusion-based 3D printing for cardiac tissue regeneration. Rheological studies were conducted to evaluate the printability of CMC/Gel/GO inks, which revealed that CMC increased viscosity and enhanced printability. The 3D-printed cardiac patches were crosslinked with N-(3-dimethylaminopropyl)-n'-ethylcarbodiimide hydrochloride (EDC)/ N-hydroxysuccinimide (NHS) (100:20 mM, 50:10 mM, 25:5 mM) and then characterized by mechanical analysis, electrical conductivity testing, contact angle measurements and degradation studies. Subsequently, cell culture studies were conducted to evaluate the viability of H9C2 cardiomyoblast cells by using the Alamar Blue assay and fluorescence imaging. A high concentration of EDC/NHS (100:20 mM) led to the stability of the patches; however, it drastically reduced the flexibility of the scaffolds. Conversely, a concentration of 25:5 mM resulted in flexible but unstable scaffolds in PBS solution. The suitable EDC/NHS concentration was found to be 50:10 mM, as it produced flexible, stable, and stiff cardiac scaffolds with high ultimate tensile strength (UTS). Mechanical characterization revealed that % the strain at break of C15/G7.5/GO1 exhibited a remarkable increase of 61.03% compared to C15/G7.5 samples. The improvement of flexibility was attributed to the hydrogen bonding between CMC, Gel and GO. The electrical conductivity of 3D printed CMC/Gel/GO cardiac patches was 7.0×10-3 S/cm, demonstrating suitability for mimicking the desired electrical conductivity of human myocardium. The incorporation of 1 wt% of GO and addition of CMC concentration from 7.5 wt % to 15 wt % significantly enhanced relative % cell viability. Overall, although this research is at its infancy, CMC/Gel/GO cardiac patches have potential to improve the physiological function of cardiac tissue.

Mechanical Properties Optimization and Microstructure Analysis of Pure Copper Heterostructured Laminates via Rolling

Heterogeneous metallic structures constitute a novel class of materials with excellent mechanical properties. However, the existing process for obtaining heterostructures from a single material does not meet large-scale industrial requirements. In this study, a pure copper heterostructured laminate (HSL) composed of a surface elongated-grain layer and a central equiaxed-grain layer was fabricated by rolling bonding and annealing. To study the effect of the interface on the mechanical properties of gradient-structured materials, both laminate metal composite (LMC) and non-composite laminate (NCL) were fabricated by cold-rolling pretreatment of the center layer (60% reduction) and cold-rolling bonding of the whole blank (67% reduction). Then, the HSL was obtained by controlling the post-annealing regimes, the microstructure of each layer was optimized, and a larger degree of microstructural heterogeneities, such as grain size, misorientation angle, and grain orientation, was obtained, which resulted in obvious mechanical differences. Tensile tests of the HSL, surface layer, center layer, and NCL specimens revealed that the HSL annealed at 300 °C for 1 h had a significantly higher strength than the center layer and a higher elongation than the surface layer. The HSL had a tensile strength and elongation at fracture of 278.08 MPa and 46.2%, respectively, indicating a good balance of strength and plasticity. The improved properties were primarily attributed to the strengthening or strain hardening due to the inhomogeneous deformation of the heterogeneous layers in the laminate and the mutual constraint acquired by the distinct layers with strong mechanical differences. The HSL had an interfacial bonding strength of 178.5 MPa, which played a vital role in the coordinated deformation of the heterogeneous layers. This study proposes an HSL design method that effectively simplifies the process of obtaining heterostructures in homogeneous materials by controlling the cumulative deformation of the surface and center layers.

Evaluation of the thermomechanical properties of novel epoxy composites reinforced with Geonoma baculifera fibers

Natural lignocellulosic fibers (NLFs) have shown a great potential as reinforcements in composites in recent decades. Among other reasons, environmental concerns and the depletion of oil reserves justify research on natural composites as they offer an environmentally friendly alternative and align with the principles of sustainable development. Among the plethora of NLFs available in nature, the ubim fiber (Geonoma baculifera) has not yet been investigated as a reinforcement for composites in potential engineering applications. Therefore, this study evaluates, for the first time, the mechanical properties of epoxy composites with 10, 20, and 30 vol% of ubim fibers. These properties were assessed through Izod impact, tensile and flexural tests as well as dynamic mechanical analysis (DMA). The data were statistically analyzed using the ANOVA method. Scanning electron microscopy (SEM) analysis indicated a transition from a purely brittle fracture mechanism to a ductile-brittle combination as the fiber volume in the composite increased. Tensile tests of the composites demonstrated an increasing trend in strength and elastic modulus with fiber volume. The results of the flexural tests also displayed a similar trend in strength and elasticity modulus for the composites. The results of DMA tests showed that composite materials with a 30 vol% of ubim fibers exhibited a high glass transition temperature and a low tan δ value, suggesting higher stiffness of this composite compared to others. Overall, the results indicated that the incorporation of 30 vol% ubim fibers into the composites significantly improved their mechanical properties compared to other tested fiber fractions. Additionally, their functional characteristics, such as simplicity in the manufacturing process, low cost, and excellent strength-to-weight ratio, make these composites particularly suitable for applications in sectors such as the automotive industry, construction panels, and packaging. These factors contribute to the development of an efficient, sustainable, recyclable and environmentally friendly composite.

Industrial Robots, Factor Market Distortion, and Productivity

ABSTRACTWe find that robot adoption significantly increases firm‐level TFP, but factor market distortion hinders the promotion effect of robot adoption on firm‐level TFP. Mechanism analysis reveals that the cost‐saving and labor productivity improvements brought about by industrial robot application stimulate market entry by new firms and elevate the exit risk for incumbent enterprises. This dynamic intensifies competition, resulting in an enhanced market environment that contributes to firm‐level TFP. However, factor market distortions impede the survival of the fittest among firms and stifle the competitive effects of market entry and exit. This ultimately leads to sluggish growth in firm‐level TFP.